Miscellaneous Topics Flashcards
Describe the architecture of an atom.
The atom is the basic building block that makes up all matter. It consists of 3 components:
* Protons (+ charge)
* Neutrons (no charge)
* Electrons (- charge)
the protons and neutrons reside at the center of the atom, and together they form the nucleus. The number of protons in the nucleus determines the atom’s atomic number.
The electrons orbit the nucleus in the electron cloud. Because electrons have a negative charge, they are attracted to the positive charge of the nucleus. This keeps the electrons from flying away.
how do you know if an atom carries a charge? what is a charged atom called?
an atom will have a:
* Neutral charge if (# electrons = # protons
* Protons charge if: # electrons < # Protons
* Negative charge if: # electrons > # protons
An ion is an atom that carries a positive or negative charge
* An atom with a positive charge ( it has lost electrons) is called a cation
* An atom with a negative charge (it has gained electrons) is called an anion
What is an ionic bond?
An ionic bond involves the complete transfer of valence electron(s) from one atom to another. This leaves one atom with a negative charge and the other with a positive charge. Metals tend to form ionic bonds.
Ionic bonds are common with metals as well as acids and bases
What is a covalent bond?
A covalent bond involves the equal sharing of electrons. This is the strongest type of bond.
- A single bond is created when 1 pair of electrons is shared
- A double bond is created when 2 pairs of electrons are shared
- A triple bond is created when 3 pairs of electrons are shared
what is polar covalent bond?
polar covalent bonds are an “in-between” type of bond
Atoms share electrons, but the electrons tend to remain closer to one atom than the other. This creates a polar molecule, where one area of the molecule is relatively positive, and the other is relatively negative
What are Van der Waals forces?
Van der Waals’ forces describe a very weak intermolecular force that holds molecules of the same type together.
Electrons (an their negative charges) orbiting a molecule are in constant motion. This creates temporary partial (+) and (-) charges at different parts of the molecule at any given time. The net result is that electron-rich areas of one molecule will be attracted to electron-poor areas of another molecule.
This is the weakest type of molecular attraction
Define Dalton’s law. List several examples of how it can be used in the operating room.
Dalton’s law of partial pressures says that the total pressure is equal to the sum of the partial pressures exerted by each gas in the mixture.
P total= P1+P2+P3
Ways to apply Dalton’s law of partial pressures:
* Calculate the partial pressure of an unmeasured gas
* Calculate the total pressure
* Convert partial pressure to volumes percent
* Convert volumes percent to a partial pressure
At sea level, the agent monitor measures the end-tidal sevoflurane as 3%. What is the partial pressure of sevoflurane in the exhaled tidal volume?
This is an application question about Dalton’s law of partial pressures.
Partial pressure= volumes percent x total pressure
- Partial pressure = 0.03 x 760 mmHg
- Answer= 22.8 mmHg
Define Henry’s law. List several examples of how it can be used in the operating room.
At a constant temperature, the amount of gas that dissolves in a solution is directly proportional to the partial pressure of that gas over the solution. Said another way, the higher the gas pressure, the more of it will dissolve into a liquid (assuming a constant temperature).
* Increase temp= decreased solubility
* Decreased temp= increase solubility
How can we apply Henry’s law:
* Anesthetic emergence is prolonged in the hypothermic patient
* Dissolved oxygen in the oxygen-carrying capacity equation (CaO2)
Describe Fick’s law of diffusion.
Fick’s law of diffusion describes the transfer rate of gas through a tissue medium
Rate of transfer is directly proportional to:
* Partial pressure difference (driving force)
* Diffusion coefficient (solubility)
* Membrane surface area
Rate of Transfer is inversely Proportional to:
* Membrane thickness
* Molecular weight
list clinical examples of Fick’s law of diffusion
- Diffusion hypoxia
- A patient with COPD has a reduced alveolar surface area and therefore has a slower rate of inhalation induction
- Calculation of cardiac output
- drug transfer across the placenta
Compare and contrast Boyle’s, Charle’s, and gay-lussac’s law.
Boyle’s law has inverse relationship
* as one variable gets larger, the other gets smaller
* As one variable gets smaller, the other gets larger
P1 x V1= P2 x V2
Charle’s law and Gay-lussac’s law have direct relationships:
* As one variable gets larger, the other gets larger.
* As one variable gets smaller, the other gets smaller
Charles: V1/T1= V2/T2
Gay-lussac’s: P1/T1=P2/T2
List several examples of how Boyle’s law can be applied in the operating room.
Boyle’s law (P x V):
* Diaphragm contraction increases tidal volume
* Pneumatic bellows
* Squeezing an Ambu bag
* Using the bourdon pressure gauge to calculate how much O2 is left in a cylinder (assumes a given flow rate)
List an example of how Charle’s law can be applied in the operating room.
Charle’s law (V/T):
* LMA cuff ruptures when placed in an ambulance
List an example of how Gay-Lussac’s law can be applied in the OR.
Gay-Lussac’s law (P/T)
* Oxygen tank explodes in a heated environment
what is the function of the ideal gas law?
the ideal gas law unifies all 3 gas laws into a single equation, where: PV=nrT
* P= pressure
* V= volume
* n= number of moles
* r= constant 0.821 liter-atm/K/mole
* T= temperature
Define Ohm’s law
Ohm’s law says that the current passing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. We can adapt Ohm’s law to understand fluid flow.
Current= voltage difference/ resistance
or
Flow= Pressure gradient/ resistance
How is Poiseuille’s law related to Ohm’s law?
Poiseuille’s law is a modification of Ohm’s law that incorporates vessel diameter, viscosity, and tube length
- Q blood flow
- R Radius
- change in P Arteriovenous pressure gradient (Pa-Pv)
- n Viscosity
- L Length of the tube
How do changes in radius affect laminar flow (x2, x3, x4, and x5)
Altering the radius of the tube exhibits the greatest impact on flow.
* R= 1^4: 1x1x1x1= 4
* R= 2^4: 2x2x2x2= 16
* R= 3^4: 3x3x3x3= 81
* R= 4^4: 4x4x4x4= 256
How can we apply Poiseuille’s law to the administration of a unit packed red blood cells?
We can deliver red blood cells faster if we:
* Increase the radius with a large-bore IV
* INcrease the pressure gradient with a pressure bag and/or increase the height of the IV pole.
* Decrease the viscosity by diluting the blood with 0.9 NaCl and/or running it through a fluid warmer
* Decrease the length by not using longer tubing than you really need
what does Reynold’s number tell you?
There are 3 types of flow: Laminar, turbulent, and transitional.
Reynold’s number allows us to predict the type of flow that will occur in a given situation
* RE < 2000: laminar flow is dependent on gas viscosity (Poiseuille’s law)
* Re> 4000: turbulent flow is dependent on gas density (Graham’s law)
* Re 2,000 - 4,000: transitional flow
Reynold’s number= (Density x Diameter x Velocity)/ Viscosity
grahams: rate of effusion of gas is inversely proportional to the square root of the molar mass of its particles
Explain how understanding Reynold’s number helps you treat status asthmaticus
The pt with status asthmaticus suffers from an increased airway resistance, and this increases flow turbulence and the work of breathing.
* because turbulent flow is primarily dependent on gas density, we can improve flow by having the patient inhale a lower density gas
* An oxygen/helium mixture (Heliox) improves Reynold’s number by reducing density
* The key here is that we are converting turbulent flow to laminar flow. Helium does NOT improve flow if its is already laminar
Explain Bernoulli’s principal, and discuss it in the context of a river.
Bernoulli’s principle describes the relationship between the pressure and velocity
* If the fluid’s velocity is high, then the pressure exerted on the walls of the tube will be low.
* If the fluid’s velocity is low, then the pressure exerted on the walls of the tube will be high
Example: Think of a river. When the river is wide, the water moves slowly, but when it becomes narrow, the water moves much faster. This is because the same volume of water is moving through the wide and now parts of the river at any given time. When the water is moving slowly, the pressure exerted on the riverbank is higher, and when the river narrows, the velocity of the water increases, so it exerts less pressure on the riverbank
Explain the Venturi effect, and give some examples.
The venturi effect is an application of the Bernoulli principle. As airflow in a tube moves past the point of constriction, the pressure at the constriction decreases (Bernoulli principle), and if the pressure inside the tube falls below atmospheric pressure, then air is entrained into the tube (venturi effect)
Adjusting the diameter of the constriction allows for control of the pressure drop and the amount of air that is sucked into the tube. The key here is air entrainment!
Examples: Jet ventilator, Venturi, and nebulizer
Explain the Coanda effect, and give some examples
The Coanda effect describes how a jet flow attaches itself to a nearby surface and continues to flow along that surface even when the surface curves from the initial jet direction
Examples: Wall-hugging jet of mitral regurgitation and water that follows the curve of a glass
How do you calculate the law of Laplace for a sphere? for a cylinder?
in spheres and cylinders, the law of Laplace illustrates the relationship between the wall tension, internal pressure, and radius.
* Pressure is a pushing force. It pushes the walls of the object apart.
* Tension is a pulling force. It holds the walls of the object together
Surface tension of a sphere:
* Tension= (pressure x radius) / 2
* Examples: alveolus, cardiac ventricle, saccular aneurysm
Surface tension of a cylinder:
* Tension= (pressure x radius)
* Examples: blood vessels, aortic aneurysm
What is the yearly maximum for radiation exposure? How does this change if someone is pregnant?
Non-pregnant person:
* The yearly maximum radiation exposure is 5 rem
* The eye and thyroid are most susceptible to injury
Pregnant person:
* The yearly maximum exposure for the fetus of a pregnant worker is 0.5 rem or 0.05 rem/month
* the fetus is most susceptible to injury
list 3 ways to protect yourself from radiation exposure.
- distance
- Duration
- shielding
How can we apply the inverse square law to radiation exposure?
Distance is an easy way to protect yourself from ionizing radiation. The minimum safe distance from the radiation source is 6 ft
Radiation exposure obeys the inverse square law. It states that the amount of exposure is inversely proportional to the square of the distance of the source
Intensity = 1/distance^2
We can quantify the amount of exposure at two different locations with the following equation:
Intensity1= distance2^2
Intensity2= distance1^2
What is boiling point, and how is it affected by atmospheric pressure?
The boiling point is the temperature at which a liquid’s vapor pressure equals atmospheric pressure
* Increase P atm -> increase boiling point (example: hyperbaric oxygen chamber)
* Decreased P atm -> decrease boiling point (example: high altitude)
Define specific heat
specific heat is the amount of heat required to increase the temperature of 1 gram of a substance by 1 degree C
define vapor pressure.
In a closed container, molecules from a volatile liquid escape the liquid phase and enter the gas phase. The molecules in the gas phase exert pressure on the walls of the container. This is vapor pressure.
Define vaporization.
Vaporization is the process by which a liquid is converted to a gas. This requires energy (heat)
Define heat of vaporization.
Heat of vaporization is the number of calories required to vaporize 1 mL of liquid
explain latent heat of vaporization, and apply this anesthetic vapor inside of a vaporizer.
latent heat of vaporization is the number of calories required to convert 1 gram of liquid to vapor WITHOUT a temperature change in the liquid. Let’s apply this to what happens inside the vaporizer:
* Anesthetic liquid in the vaporizer exerts a vapor pressure inside the vaporization chamber. This means some of the agent exists as a liquid, and some exists as a gas
* Fresh gas flows over the anesthetic liquid, carrying away some of the agent that exists in the gas phase.
* This cools the remaining liquid, which reduces the vapor pressure of that liquid. Therefore, there are fewer anesthetic molecules that enter the gas phase
* The net result is a decrease in the vaporizer output
* modern vaporizers compensate for this temperature change
Explain the Joule-Thompson effect in the context of gas cylinders.
The joule-thompson effect says that a gas stored at high pressure that is suddenly released escapes from its container into a vacuum. It quickly loses speed as well as a significant amount of kinetic energy, resulting in a fall in temperature. This explains why an oxygen cylinder that is opened quickly feels cool to the touch. Conversely, rapid compression of a gas intensifies its kinetic energy, causing the temperature to rise
Remember: Joule is cool
What is an adiabatic process?
Adiabatic process describes the process that occurs without gain or loss of energy (heat). For example, a very rapid expansion or compression of a gas where there is no transfer of energy is an example of an adiabatic process
What is critical temperature, and how does this apply to gas cylinders?
critical temperature is the highest temperature where a gas can exist as a liquid. Said another way, it is the temperature above which a gas cannot be liquified regardless of the pressure applied to it.
The critical temp for nitrous oxide is 36.5C, which explains why it primarily exists as a liquid inside the cylinder (room temperature is abou 20 C). Conversely, the critical temperature of oxygen is -119 c, so it exists as a gas inside the cylinder.
Of the gases used in the OR, only N2O and CO2 have critical temperatures above room temperature
What is the critical pressure?
Critical pressure is the minimum pressure required to convert a gas to a liquid at its critical temperature.
Know the temperature conversion formulas.
Cesius to Kelvin and back:
* Celsius= K-273.15
* Kelvin= C+ 273.15
Cesius to Fahrenheit and back:
* Cesius = (F-32) x 5/9
* Fahrenheit = (cx1.8) + 32
Define Pressure.
Pressure= Force/Area
* Increased area -> decreased pressure
* Decreased area -> increased pressure
Know the pressure conversion factors.
You should be able to convert between the common units of pressure. All of the following are equal:
- 1atm= 760 mmHg = 760 torr = 1 bar = 100kPa = 1033 cm H2O = 14.7 lb/inch^2
- 1mmHg = 1.36 cm H2O
- 1 cmH2O = 0.74 mmHg
What is Avogadro’s number?
Avogadro’s number says that 1 mole of any gas is made up of 6.023 x 10^23 atoms
* A mole of a gas is equal to the molecular weight of that gas in grams
* if a molecule is a diatomic (O2), you must account for both atoms
What are the 4 mechanisms of heat transfer? Rank them from most to least important
Radiation - infrared (60%)
convection- air (15-30%)
Evaporation - water loss (20%)
Conduction - contact (<5%)
explain the 3 stages of intraoperative heat transfer
when no attempts are made to maintain normothermia, heat transfer follows a triphasic curve
Phase 1: heat redistribution from core to periphery: 0-1 hours
phase 2: heat transfer > heat production: 1-5 hours
Phase 3: heat transfer is same as heat production: 5-7 hours
what are the consequences of perioperative hypothermia?
Cardiovascular:
* SNS stimulation
* Shifts oxyhemoglobin dissociation curve to the left
* vasoconstriction + decreased tissue PO2
* Coagulopathy + platelet dysfunction
* Sickling of hemoglobin S
Pharmacologic
* slowed drug metabolism
* increased solubility of volatile agents
Clinical relevance
* Myocardial ischemia and dysrhythmias
* Decreased O2 available to tissue
*Surgical site infection
* increased blood loss
* Risk of sickle cell crises
* prolonged effects of anesthetic agents
* prolonged emergence
Name 3 drugs that can be used to treat postoperative shivering
shivering increases oxygen consumption up to 400-500%. This increases the risk of myocardial ischemia and infarction
Pharmacologic modalities used to treat postoperative shivering include:
* Meperidine (kappa)
* Clonidine (alpha 2)
* dexmedomidine (alpha-2)
when is hypothermia a good thing?
Although there are many reasons why perioperative hypothermia contributes to poor outcomes, there are several circumstances where it can improve outcomes. All of these are based on the fact that oxygen consumption is reduced by 5-7% for every 1 degree reduction of body temp. Induced hypothermia is useful during:
* Cerebral ischemia (stroke)
* Cerebral aneurysm clipping
* Traumatic brain injury
* Cardiopulmonary bypass
* cardiac arrest
* Aortic cross-clamping
* carotid endarterectomy
in which region of the esophagus should be an esophageal temperature probe be placed? How does misplacement affect the reading?
It should be placed in the distal 1/3rd - 1/4th of the esophagus (38-42cm pas the incisors)
* increased is placed in the stomach due to heat created by liver metabolism
* Decreased is placed in the proximal esophagus due to cool inspiratory gas
compare and contrast various sites of temperature measurement
what are the three ingredients required to produce a fire? Give examples of each
Fuel: ETT, drapes, surgical supplies
Oxidizer- oxygen, nitrous oxide
Ignition source: electrosurgical cautery, laser
Detail the steps you would take during an airway fire.
Steps to take when fire is present:
1. Stop ventilation and remove ETT
2. stop the flow of all airway gases
3. remove other flammable material from the airway
4. pour water or saline into the airway
5. if the fire isn’t extinguished on the first attempt, then use a CO2 fire extinguisher
Steps to take after fire is controlled
1. Re-establish ventilation by mask. Avoid supplemental O2 or Nitrous oxide
2. Check ETT for damage- fragments may remain in the patient’s airway
3. Perform bronchoscopy to inspect for airway injury or retained fragments
Do NOT squeeze the resevoir bag as you extubate the pt. This can create a blow torch effect at the distal end of the ETT and/or push debris into the lower airway
What does “laser” stand for? How is it different from ordinary light?
Laser: Light Amplification by Stimulated Emission of Radiation. Laser light differs from ordinary light because it is:
* Monochromatic (the light is a single wavelength)
* Coherent (the light oscillates in the same phase)
* Collimated (the light exists as a narrow parallel beam)
What is the difference between a long and short wavelength laser? What are the clinical consequences of this?
Long wavelength lasers:
* Absorb more water and do NOT penetrate deep into tissue
* The cornea is at risk
Short wavelength lasers:
* Absorb less water and penetrate deeper into tissue
* The retina is at risk
CO2 = used in Oropharyngeal and vocal cord surgeries, can damage corneas, wavelength: 10,600
Nd:Yag: used for tumor debulking, and tracheal surgeries, can damage the retina, wavelength: 1,064
Ruby: used for retinal surgeries, can damage the retina, wavelength 694nm
Argon: used for vascular lesion, can damage retina, wavelength: 515nm
What color goggles must be worn for each type of laser: CO2, ND:YAG, Ruby, and Argon?
- CO2= Clear
- Ruby= red
- Argon= Amber
- nd: YAG= Green
Discuss the flammability of ETT in the context of laser surgery on the airway.
Things to know about airway surgery that require a laser:
* Most ETT are flammable (PVC, Red rubber, silicone)
* Laser reflective tape is no longer advised. It’s smarter to use a laser resistant ETT
* Laser resistant ETTs are NOT laser proof!
*The cuff is the most vulnerable component of the ETT
* Fill the cuff with saline (dye is optional). This helps absorb the thermal energy produced by the laser, which makes the balloon less likely to ignite
* Many laser resistant ETTs have 2 cuffs. The proximal cuff is filled with saline or dye. If it becomes perforated by the laser, then the distal cuff will hopefully remain intact and permit continued PPV.
* Laser resistant ETTs do not reduce the risk of fire when electrosurgical cautery is used
Describe the 4 degrees of burns. Which require a skin graft?
Describe the rule of 9’s. How does this apply to the adult?
Burn severity is a function of the depth of the burn as well as the fraction of the total body surface area (TBSA) consumed by the burn.
* The TBSA is divided into areas representing 9% (or multiples of 9%)
* Due to rounding, the numbers do not add to 100
* this concept is important for calculating fluid requirements
How is the rule of 9’s different for children?
The child’s head is 19% of the TBSA (9.5% front and 9.5% back)
* As a general rule: for every year of age> 1 year up to 10 years, you can decrease the head surface area by 1% and increase each leg by 0.5%
Describe the consequences of the capillary leak that occurs after a burn.
Immediately after a burn, microvascular permeability increases, and this creates a capillary leak. The magnitude of the leak becomes greater in the presence of a major burn, inhalation injury, or a delay in resuscitative efforts
Consequences of the capillary leak:
* Increased vascular permeability -> edema formation
* Loss of protein-rich fluid to the interstitial space -> decreased plasma oncotic pressure -> edema formation
* Loss of intravascular volume -> hypovolemia & shock
Fluid shifts and edema formation are greatest in the first 12 hours and begin to stabilize by 24hrs. This explains why fluid requirements are higher in the first 24hrs following a burn
*Albumin should be avoided during the first 24 hours because it is lost to the interstitial space
* Hemolysis is common during the initial stage, however, profound hypovolemia promotes hemoconcentration
* Rising Hgb in the first few days suggests inadequate volume resuscitation
* Consider transfusion if Hct < 20 (healthy pt) or Hct < 30 (preexisting cardiovascular dx)
Describe the Parkland formula for resuscitation in burn pts.
First 24 hrs:
* Crystalloid= 4mL LR x %TBSA burned x kg (1/2 in 1st 8 hours then 1/2 in the next 16hrs)
* Colloid= none
Second 24hrs:
* Crystalloid = D5W at a normal maintenance rate
* Colloid= 0.5mL x %TBSA burned x kg
Describe the modified Brooke formula for resuscitation in burn pts.
First 24hr:
* Crystalloid= 2mL LR x %TBSA burned x kg (1/2 in 1st 8 hr then 1/2 next 16 hrs)
* Colloid= none
Second 24hrs
* Crystalloid = D5W maintenance rate
* Colloid= 0.5mL x % TBSA burned x kg
What is an acceptable urine output in a burned pt? is this different in children or pts who’ve suffered a high voltage electrical injury?
Urine output goals:
* Adult: > 0.5mL/kg/hr
* Child= >1mL/kg/hr
* High voltage electrical injury = 1- 1.5mL/kg/hr
- Myoglobinemia is the result of extensive muscle damage following a high voltage electrical injury. Remember that myoglobin is nephrotoxic and needs to be flushed out of the body.
Why is the burn pt at risk for abdominal compartment syndrome? what is the diagnosis and treatment of this complication?
Abdominal compartment syndrome:
* May result from aggressive fluid resuscitation
* Intra-abdominal HTN is define at IAP > 20mmHg or >12mmHg AND evidence of organ dysfunction (hemodynamic instability, oliguria, increased PIP)
* Treatment: Neuromuscular blockade, sedation, diuresis, and abdominal decompression via laparotomy
discuss the clinical considerations for the pt with carbon monoxide poisoning.
Carbon Monoxide Poisoning
* CO binds to Hgb with an affinity 200x that of O2
* CO shifts the oxyhemoglobin dissociation curve to the left , which impairs offloading of oxygen to the tissues
* Oxidative phosphorylation is also impaired
* Inadequate oxygen delivery and utilization cause metabolic acidosis
* blood takes on a cherry red apearance
* The pulse oximeter is NOT accurate in the pt with CO poisoning because it is unable to distinguish between HgbO2 and HgbCO
* The SpO2 may give falsely elevated result
* treatment includes 100% FiO2 or hyperbaric oxygen
Discuss the use of neuromuscular blockers in a burn pt
Up-regulation of extrajunctional receptors begins after 24hrs
* Succ’s is safe within the first 24hrs following the burn, but its use can cause lethal hyperkalemia after 24 hrs
* the dose of non-depolarizing NMBs should be increased 2-3 fold (there are more receptors)
Describe the physiologic changes that accompany electroconvulsive therapy
the seizure caused by ECT results in profound physiologic changes.
* Initial response: Increased PNS activity during the tonic phase (last approx 15 seconds)
* Secondary response: increased SNS activity during the clonic phase (lasts several minutes)
Discuss the absolute and relative contraindications to ECT
Contraindications are typically related to an increased SNS response or increased ICP
The most common causes of death are myocardial infarction and cardiac dysrhythmias. Having said this, pts with co-existing cardiovascular dx can safely undergo ECT provided that hemodynamics are well managed
Compare and contrast neuroleptic malignant syndrome with malignant hyperthermia
NMS is caused by dopamine depletion in the basal ganglia and hypothalamus
* Causes: Dopamine antagonists or withdrawal from dopamine agonists
* tx: Bromocriptine, dantrolene, supportive care, ECT
What is the etiology ad tx of serotonin syndrome?
Serotonin syndrome occurs when there’s excess 5-HT activity in the CNS and PNS. Key drug interactions that increase the risk of serotonin syndrome include:
SSRI (citalopram, dapoxetine, fluoxetine (prozac), sertraline) and:
* meperidine
* Fentanyl
* Methylene blue
What are the determinants of intraocular pressure? what’s the normal value?
Intraocular perfusion pressure = MAP - ICP
the globe is a relatively non-compliant compartment. Therefore, IOP is determined by the choroidal blood volume, aqueous fluid volume, and extraocular muscle tone
- Normal IOP = 10 - 20mmHg
- Aqueous humor is produced by the ciliary process (posterior chamber)
- Aqueous humor is reabsorbed by the canal of Schlemm (anterior chamber)
what factors reduce IOP? which increase it?
Increase IOP:
* Hypercarbia
* Hypoxemia
* increase CVP
* increased MAP
* Laryngoscopy/intubation
* Straining/ coughing
* succ’s
* Nitrous oxide (if SF6 bubble in place)
* Trendelenburg position
* Prone position
* External compression by facemask
Decreased IOP
* Hypocarbia
* Decreased CVP
* Decreased MAP
* Volatile anesthetics
* Nitrous oxide
* Nondepolarizing NMB
* Propofol
* Opioids
* Benzos
* Hypothermia
LMA placement and/or removal has a minimal effect on IOP
* Ketamine may or may not increase IOP, but it does cause rotary nystagmus and blepharospasm. For this reasons it should be avoided during eye surgery
What is the difference between open and closed angle glaucoma?
Glaucoma is caused by a chronically elevated IOP that leads to retinal artery compression
* Open-angle glaucoma is caused by sclerosis of the trabecular meshwork. This impairs aqueous humor drainage
* Closed-angle glaucoma is caused by a closure of the anterior chamber. This creates a mechanical outflow obstruction
IOP is reduced by drugs that reduce aqueous humor production or facilitate aqueous humor drainage (causes miosis)
which drugs reduce aqueous humor production? which increase aqueous humor drainage?
Aqueous humor is produced by the ciliary process (posterior chamber), and it is reabsorbed by the canal of Schlemm (anterior chamber)
Drugs that decrease aqueous humor production:
* Acetazolamide inhibits carbonic anhydrase and decreases aqueous humor production
* Timolol is a non-selective beta antagonist that decreases aqueous humor production
Drugs that facilitate aqueous humor drainage:
* Echothiophate is an irreversible cholinesterase inhibitor that promotes aqueous humor drainage via the canal of Schlemm
* It can prolong the duration of succinylcholine and ester-type local anesthetics
what is strabismus correction? What unique considerations apply to the anesthetic management of these patients?
Strabismus surgery corrects the misalignment of the extraocular muscles and re-establish the visual axis. There are 3 key considerations in this population:
* Increased risk of PONV
* Increased risk of activating the oculocardiac reflex (afferent CN 5 + Efferent CN 10)
Which patient populations benefit from a TAP block?
The transverse abdominal plane block (TAP) is a unilateral peripheral nerve block that targets the nerves of the anterior and lateral abdominal wall.
- It’s best suited for abdominal procedures (general, GYN, and urologic) that involve the T9 to L1 distribution
- Bilateral TAP blocks are required for a midline incision or laparoscopic surgery
Describe the anatomy and landmarks required to perform a TAP block
Abdominal wall structures organized from superficial to deep:
Subcutaneous tissue -> external oblique muscle -> Internal oblique->Transverse abdominis muscle -> peritoneum
Define allodynia and give an example
Allodynia is pain due to a stimulus that does not normally produce pain
Ex fibromyalgia
Define dysesthesia and give an example
Dysesthesia is an abnormal and unpleasant sense of touch
Ex. Burning sensation from diabetic neuropathy
Define neuralgia and give an example
Neuralgia is pain localized to a dermatome
Ex: Herpes Zoster (shingles)
What is the defining characteristic between Type I and type II complex regional pain syndrome?
There are 2 types of CRPS:
* Type 1 (reflex sympathetic dystrophy)
* Type 2 (causalgia)
Complex regional pain syndrome is characterized by neuropathic pain with autonomic involvement. The key distinction is that type 2 CRPS is always preceded by nerve injury (type 1 is not)
Discuss the use of a thoracic paravertebral block
- Local anesthetic injected into the paravertebral space (a potential space) targets the ventral ramus of the spinal nerve as it exits the vertebral foramen
- This creates a unilateral sensory and sympathetic block along that specific dermatome
- You can think of the paravertebral block to a single shot, unilateral epidural block
- You’ll have to perform one block at each dermatome to be anesthetized
- The thoracic paravertebral block provides analgesia for breast surgery, thoracotomy, and rib fractures
what structures are anesthetized by a celiac plexus block? How about a superior hypogastric block?
Celiac Plexus Block:
* The celiac plexus block innervates the upper abdominal viscera (except the left side of the colon)
* It does NOT innervate the pelvic organs
* therefore, it is useful for pain from the upper abdominal organs, but not the pelvic organs (useful in cancer pts) liver, pancreas, gallbladder, kidneys, intestines, adrenal glands and blood vessels
Superior hypogastric plexus block
* The superior hypogastric plexus innervates the pelvic organs
* Blockade of the superior hypogastric plexus is useful in patients with pain involving the pelvic organs (useful in cancer pts) colon, bladder, lower intestines, uterus, ovaries, prostate
Aside from an epidural blood patch, which regional technique is used to release post-dural puncture headache?
Sphenopalatine block (through the nose)
What is post-retrobulbar block apnea syndrome?
The optic nerve is unique because it is the only cranial nerve that is part of the central nervous system (it is enveloped by the meningeal sheath and bathed in CSF). Because of this, a local anesthetic injected into the optic sheath is permitted direct entry to the brain. It’s likely giving a subarachnoid block in the optic sheath!
Discuss the use of cephalosporins in the PCN allergic pt
also what antibiotic are grouped together and what are their side effects
Previous literature suggested a high rate of cross-reactivity between PCN and cephalosporins (up to 10%). These numbers are grossly overstated (due to contamination during the manufacturing process)
If a pt reports an allergy to PCN, then s/he may receive a cephalosporin if the reaction:
* Was NOT IgE mediated (anaphylaxis, bronchospasm, urticaria)
* Did NOT produce exfoliative dermatitis (stevens-johnson syndrome)
if the pt experienced any of these complications, then vancomycin or clindamycin are acceptable alternatives
Cephalosporins : cefaclor, cehpalexin, Ceftriaxone, cefazolin, cefoxitin, cefuroxime
What is the antibiotic of choice to treat MRSA? What are the special considerations for the administration of this antibiotic?
Vancomycin is the drug of choice for patients with active MRSA
To reduce histamine release and HoTN, vanco should be administered at a rate of 10-15 mg/kg over 1 hour
The histamine response to vanco can be minimized by diphenhydramine 1mg/kg + cimetidine 4mg/kg 1 hour before anesthesia
Discuss the different levels of infection control precautions. Give examples with specific pathogens
what is the rate of seroconversion following exposure to HIV infected blood
The most common cause of occupational exposure to HIV is needle-stick with a hollow-bore needle.
Seroconversion rates after exposure to HIV-infected blood:
- Percutaneous injury (needle-stick) = 0.3%
- Mucous membrane exposure = 0.09%
What are the functions of the 5 types of white blood cells?
white blood cells can be divided into granulocytes (neutrophils, basophils, and eosinophils) and agranulocytes (monocytes and lymphocytes):
Neutrophils:
* Fight bacterial and fungal infection
* Make up 60% of all WBC’s (most abundant WBC type)
Basophils:
* Are the essential component of hypersensitivity reactions
* Release histamine, serotonin, heparin, and bradykinin (mast cells do the same thing)
* Epinephrine prevents degranulation (release of intracellular contents) by binding to beta-2 receptors on the cell membrane
Eosinophils:
* Defend against parasites
Monocytes
* phagocytosis
*release cytokines
* present pieces of pathogens to T-lymphocytes
Describe the presentation of anaphylaxis
what hypersensitivity reactions stimulate the H1 and H2 receptors and what are their effects?
Describe the pathophysiology of the 4 types of hypersensitivity reactions. List examples of each.
Type 1: Immediate hypersensitivity:
* IgE- Antigen + antibody interaction in a pt who has been previously sensitized to the antigen
* Examples: anaphylaxis, extrinsic asthma
Type 2: Antibody-mediated:
* IgG and IgM antibodies bind to cell surfaces or extracellular regions
* Examples: ABO-incompatibility, heparin-induced thrombocytopenia
Type 3: Immune complex-mediated
* An immune complex is formed and deposited into the pt’s tissue (normally, these complexes are cleared from the body)
* Examples: Snake venom reaction, protamine induced vasoconstriction
Type 4: Delayed
* Allergic reaction is delayed at least 12 hours following exposure.
* Examples: contact dermatitis, graft-vs-host reaction, tissue rejection
what is the tx for intraoperative anaphylaxis?
Tx of intraop anaphylaxis:
* Discontinue the offending agent
* Airway support: increased FiO2 and provide airway support
* Epinephrine: start with 5 - 10mcg IV for hypotension and 0.1-1mg IV for cardiac collapse
* Liberal IV hydration: Crystalloid 10-25 mL/kg or colloid 10mL/kg (repeat if necessary)
* H1-receptor antagonist: Diphenhydramine 0.5-1 mg/kg IV
* H2-receptor antagonist: Ranitidine 50mg IV or famotidine 20mg IV
* Hydrocortisone 250mg IV (prevents delayed release of inflammatory compounds - does not produce an immediate effect)
* Albuterol for bronchospasm
* Vasopressin for refractory HoTN,. Start at 0.01 unit/min
What are the 3 most common causes of intraoperative anaphylaxis?
1 neuromuscular blockers (succinylcholine is most common)
#2 latex
#3 antibiotics
Which pts are at the highest risk of latex allergy?
high-risk groups:
* Spina bifida/myelomeningocele
* Atopy (heightened immune response- asthma, allergic rhinitis)
* Health care workers
* Food allergy to banana, kiwi, mango, papaya, pineapple, tomato
If you had to explain the “chemo man” to a friend, could you do it? practice it
C- Cisplatin (alkylating agent)- acoustic nerve injury + nephrotoxicity
V- Vincristine and vinblastine (tubulin-binding drug= peripheral neuropathy
B- Bleomycin (antitumor antibiotic)= pulmonary fibrosis (keep FiO2 <30%)
D- Doxorubicin (antitumor antibiotic)= cardiotoxic
5- 5 fluorouracil (antimetabolite)= Bone marrow suppression
M- Methotrexate (antimetabolite= Bone marrow suppression
What are the 5 most important GI hormones? What is the key function of each?
Gastrin- when food enters the stomach, gastrin increases stomach acid and stimulates chief cells to secrete pepsinogen. In the presence of stomach acid, pepsinogen is converted to pepsin (aids in protein digestion)
Secretin: Tells the pancreas to secrete bicarbonate and the liver to secrete bile
Cholecystokinin: tells the pancreas to release digestive enzymes and the gallbladder to contract
Gastric inhibitory peptide: Slows gastric emptying and stimulates pancreatic insulin release
Somatostatin: the universal “off” switch for digestion
What is gastric barrier pressure? why is it important?
the likelihood of gastroesophageal reflux is determined by barrier pressure. The higher the barrier pressure, the lower the likelihood of reflex
Barrier pressure= LES pressure - intragastric pressure
what are the 3 most important inputs to the vomiting center? what receptors are involved in each one?
The vomiting center resides in the nucleus tractus solitarius (medulla). Sensory input to the vomiting center arises from the chemoreceptor trigger zone, GI tract, and vestibular system
what is the MOA of NK-1 antagonists? give an example of a drug in the class
Neurokinin-1 antagonists block substance P in the chemoreceptor trigger zone
Ex: aprepitant
What are the risk factors for PONV? It helps to divide them into pt, surgical, and anesthetic risk factors
Name 2 antiemetics that prolong the QT interval
Droperidol and ondansetron
List 2 contraindications for metoclopramide
As a dopamine antagonist, metoclopramide is contraindicated in the pt with Parkinson’s dx
As a prokinetic agent, metoclopramide is contraindicated in the pt with a bowel obstruction
Where is the P6 acupressure point, and why is it important?
The P6 acupressure point is a nonpharmacologic method of reducing PONV
How long must the tourniquet remain inflated after a bier block? why?
When used for a bier block, the tourniquet must remain inflated for at least 20 min after the local anesthetic is injected. Premature release increases the risk of seizure and/or cardiac arrest.
- Bier block upper extremity: 250mmHg or 100mmHg over SBP (whichever is higher)
- Bier block lower extremity: 350-400 mmHg or 2x over SBP (whichever is higher)
what physiologic changes accompany tourniquet deflation?
Tourniquet release stresses the body in 2 ways:
* restoring blood flow to the extremity produces a relative decrease in the circulating blood volume
* the products of cellular hypoxia enter the systemic circulation
Releasing the tourniquet produces transient changes that include:
* increase EtCO2
* Decreased core body temperature
* Decreased blood pressure
* decreased SvO2 (SaO2 is usually normal)
* Metabolic acidosis
Discuss the role of the cyclooxygenase enzyme in the arachidonic acid cascade
COX-1 is always present
It maintains normal physiologic function
Inhibition of the COX-1 enzyme impairs platelet function, causes gastric irritation, and reduces renal blood flow
COX-2 is not always present
It is expressed during inflammation
Inhibition of the COX-2 enzyme produces analgesic, anti-inflammatory, and antipyretic effects. Unlike opioids, there is a ceiling effect to analgesia
*understanding this image will help you predict the side effects of COX inhibitors
Compare the equianalgesic dose of ketorolac and morphine
ketorolac 30mg IV- morphine 10 mg IV
what is Samter’s triad? why is it important?
Aspirin exacerbated respiratory disease (Samter’s triad) refers to the combination of asthma, allergic rhinitis, and nasal polyps. These patients can develop life-threatening bronchospasm following aspirin administration
List 4 herbal supplements that increase bleeding risk
garlic
ginger
gingko biloba
saw palmetto
list 2 herbal supplements that reduce MAC
Kava Kava
Valerian
Chronic ingestion of which herbal medication can mimic Conn’s syndrome?
licorice
Describe the modified aldrete
the modified aldrete scoring system is used to assess readiness for PACU discharge. A score of 0 - 2 is awarded in 5 areas, where a score of 9 or more is generally accepted as discharge ready
Compare and contrast android and gynecoid obesity
Android obesity (apple shape)
* More common in men
* characterized by central or abdominal visceral fat accumulation
* increased risk of ischemic heart disease, hypertension, dyslipidemia, insulin resistance, and death
Gynecoid obesity (pear shape):
* more common in women
* Characterized by gluteal and femoral fat accumulation
* Unlike abdominal fat that is metabolically active, gynecoid fat is metabolically inactive and is primarily used for energy storage
* increased risk of joint disease and varicose veins
* This type of fat is associated with a reduced incidence of non-insulin-dependent diabetes
What are the diagnostic indicators for metabolic syndrome?
MEtabolic syndrome (syndrome X) incorporates a number of disease states that coincide with obesity. Cardiovascular risk of 50-60% greater than the general population. In order to be diagnosed with metabolic syndrome, one must have at least 3 of the following signs:
- Large waist circumference (men> 40 inches & women >35)
- Triglycerides >150mg/dL
- high density lipoprotein (HDL) < 40mg/dL for men and <50mg/dL for women
- BP >135/85
- fasting glucose >110 mg/dL
How can you use BMI to classify obesity?
How can you classify obesity in children?
Child body weight 2- 18 yr weight percentile
Overweight 85th-94th
obese 95th-98th
severely obese 99th
what is the formula for BMI
BMI= weight (kg)/Height (m^2)
(be careful with the units!)
how can you calculate IBW for a man? for a woman?
Ideal body weight describes the BMI associated with the lowest risk of body weight- related comorbidities. We can estimate the IBW with the following formulas:
- Men (kg)= height (cm)- 100
- Women (kg)= Height (cm)- 105
Describe how obesity creates a restrictive ventilatory defect.
Lung inflation is inhibited due to the following:
* Chest fat compresses the rib cage and hinders its outward expansion
* Abdominal fat shifts the diaphragm cephalad and compresses the lungs
* Kyphosis and lordosis develop over time and alter the geometry of the ribcage
The extra weight on the chest increases the work of breathing. A rapid and shallow breathing pattern provides the most energy-efficient way to achieve this goal
How does obesity affect respiratory gas tensions?
Fat is a metabolically active organ, so these patients have an increased oxygen consumption and carbon dioxide production. Minute ventilation must be increased to maintain normal blood gas tensions.
While the obese patient may experience hypoxemia, PaCO2 is usually normal. This is explained by the high diffusing capacity of CO2 and the favorable characteristics of the CO2 dissociation curve. An elevated PaCO2 signals impending respiratory failure.
How does obesity affect FRC? how about the other lung volumes and capacities?
FRC is inversely proportional to BMI.
* the reduction in FRC (due to decrease in ERV) below closing capacity creates a situation where distal airway collapse occurs during tidal breathing
* this leads to V/Q mismatch, shunt, and hypoxemia. Premature airway closure also increases dead space.
* General anesthesia causes FRC to fall by 50% (non-obese around 20%)
* A higher oxygen consumption coupled with a smaller FRC predisposes this population to rapid desaturation during apnea
How can you reduce atelectasis in the morbidly obese patient who is mechanically ventilated?
Keep FiO2 < 80% during anesthetic maintenance to prevent absorption atelectasis.
To recruit collapsed alveoli, you must do 2 things:
* Re-open collapsed alveoli with a recruitment maneuver (valsalva). Give a breath to about 40cm H2O and hold for 10 seconds. This may temporarily reduce venous return, blood pressure, and heart rate
* hold open the re-expanded alveoli with PEEP or CPAP 5-10 cm H2O. This improves FRC, V/Q matching, and arterial oxygenation. It may reduce venous return and cause HoTN.
what is the optimal tidal volume for a morbidly obese pt who is mechanically ventilated?
Use a tidal volume of 6-8 mL of Ideal Body Weight. Higher tidal volumes only minimally increase PaO2 and may cause sheer stress to the lungs
Try to control PaCO2 by adjusting the respiratory rate, not by increasing tidal volume.
Does a morbidly obese pt require a rapid sequence induction? why or why not?
Obesity alone does not mandate a rapid sequence intubation
There is conflicting evidence regarding the effects of obesity on gastric pH, residual gastric volume, and gastric emptying time. Despite these conflicts, there is no data that illustrate an increased incidence of pulmonary aspiration on the basis of BMI alone and that the decision for a RSI should be made on a case-by-case basis.
Patients with other risk factors, such as GERD or diabetes, should be considered candidates for aspiration prophylaxis and RSI.
How does obesity impact the cardiovascular system?
The expansion of intravascular blood volume and a high cardiac output state are the key changes that lead to cardiovascular complications of obesity.
The proliferation of adipocytes requires that the vasculature grows in order to support their growth. This requires an increased blood volume and cardiac output.
An increase stroke volume is responsible for the increased cardiac output (HR is usually normal)
A larger vascular network, blood volume, and oxygen consumption place a higher workload on the myocardium. Venous return must match cardiac output, so the heart dilates to accept the larger incoming volume. Additionally, it becomes thicker to compensates for the increased wall stress. This reduces ventricular compliance and causes diastolic dysfunction. Eventually, the heart dilates beyond its ability to increase wall thickness. At this point, the pt will experience systolic dysfunction and ultimately biventricular heart failure.
HTN is the result of hyperinsulinemia, SNS and RAAS activation, as well as an elevated cytokine Concentration in the plasma
Describe the EKG changes that can accompany obesity
Low voltage EKG: Increased distance between heart and leads
left axis deviation: the stomach pushes the heart up and to the left. Also, there is LVH secondary to volume overload and HTN
Right axis deviation: Right ventricular hypertrophy from OSA and volume overload
QT prolongation: Increases the risk of sudden death
Ischemia: Oxygen supply and demand mismatch
Dysrhythmias: Caused by fatty infiltration of the conduction system, myocardial hypertrophy, hypoxemia, hypercarbia, obesity hypoventilation syndrome, and ischemic heart dx
What valvular defect is highly suggestive of pulmonary HTN in the obese pt?
The presence of tricuspid regurgitation on TEE may be the most useful confirmation of pulmonary HTN
what factors affect volume of distribution in the obese population?
the volume of distribution of a drug in the obese pt is altered by:
* increased blood volume- requires a higher dose to achieve a given plasma concentraiton
* increased cardiac output- faster drug delivery to the vessel righ group
* altered plasma protein binding- altered free fractions available
* lipid solubility of the drug- large fat mass greatly increased Vd for lipophilic drugs
Increased body weight comes with an increased volume of distribution for both hydrophilic and lipophilic drugs. Remember that fat mass AND muscle mass increase. This means that the Vd for water-soluble drugs will increase some because the plasma volume is larger, but the Vd for fat-soluble will increase a whole lot more because of the large fat mass: Vd lipophilic»_space;> Vd hydrophilic drugs *but both increase!
how does obesity impact your selection of inhaled anesthetic agents?
Inhalation agents in the obese population
* MAC is not changed by obesity
* Volatile anesthetics are lipophilic, so agents with the lowest blood:gas coefficients should be used
* Sevoflurane or des provide a faster emergence than isoflurane or propofol
* Nitrous oxide is generally avoided, because it restricts FiO2 that can be delivered
how does obesity affect the dosing of propofol?
the loading dose of propofol is based on Lean body weight. This is because its offset is caused by redistribution and not clearance (which would depend on Vd)
* induction: LBW
* Maintenance: TBW
How does obesity affect the dosing of succ’s?
even though succ’s is a water-soluble drug, the dose for intubation is calculated with TBW. This is a clear exception to the rule for water-soluble drugs. SHortly stated, the combination of an increased blood volume (increased Vd) and increased pseudocholinesterase activity (increased clearance) necessitates a TBW dose to be given to ensure adequate paralysis
* induction: TBW
How does obesity affect the dosing of nondepolarizing neuromuscular blockers?
Rocuronium and vecuronium are distributed throughout body water and are dosed on LBW. Loading doses of cisatracurium and atracurium should probably be dosed on TBW. However, the recommendations for maintenance dosing are far from consistent.
Roc/vec
* induction: LBW
Maintenance: LBW
cis/atracurium
Induction: TBW
Maintenance: TBW or LBW
How does obesity affect the dosing of opioids
Because of their fat solubility and large Vd, the initial dose of fentanyl and sufentanil are based according to TBW. Maintenance dosing is based on LBW. An increased Vd correlates with a prolonged elimination half-life.
Remifentanil is the exception. Since it is rapidly cleared by plasma esterases, it does not behave like a high Vd drug, so remi is always based on LBW.
Fent/sufent:
* loading: TBW
* Maintenance: LBW
Remi:
* Loading: LBW
* Maintenance: LBW
how does obesity affect the dosing of an epidural?
Engorgement of the epidural veins and an increased epidural fat content will cause a greater spread of local anesthetic in the epidural space. For this reason, the dose should be reduced to 75% of the normal dose
Name the key muscles that control the diameter of the upper airway, and describe their functions
You can think of the pharynx as a collapsible tube. Airway patency is maintained by the balance between pharyngeal muscles that dilate that airway and the negative pressure of inspiration that collapses it
Define Hypopnea.
Hypopnea is defined as a 50% reduction in airflow for 10 seconds, 15 or more times per hour, and is linked to snoring and decreased oxygen saturation
Discuss the pathophysiology of OSA
OSA is defined as the cessation of airflow for at least 10 seconds (apnea) with 5 or more unsuccessful efforts to breathe (obstruction) and a greater than 4% reduction in SaO2
What is the definitive test for OSA? What does it measure? how do you interpret the findings?
Polysomnography is the definitive test for OSA. The results of this test allow for the calculation of the apnea-hypopnea index (AHI), which is used to quantify the severity of OSA.
AHI= number of episodes of apnea and hypopnea/hours of sleep
The American academy of sleep medicine defines OSA as:
* mild= 5-15 episodes/hr
* Moderate= 15-30 episodes/hr
* severe= >30 episodes/hr
Pts with severe sleep apnea are at higher risk of difficult mask ventilation and difficult intubation
What is the bedside test to identify undiagnosed OSA? How do you interpret the findings?
Most pts with OSA haven’t had a sleep study, don’t even realize they have OSA! the STOP-BANG scoring system is a bedside tool that allows you to predict the likelihood that a pt has undiagnosed OSA.
- high risk= >3 questions answered yes
- low risk = < 3 questions answered yes
What is obesity hypoventilation syndrome? How do you identify a pt with this condition?
Obesity hypoventilation syndrome is a long-term consequence of untreated OSA. Over time, the respiratory center in the medulla fails to respond to hypercarbia appropriately. The classic presentation of OHS includes episodes of apnea during sleep WITHOUT any respiratory effort. Pickwickian syndrome is the old school name for OHS.
Diagnostic criteria:
* BMI > 30 kg/m^2
* Awake PaCO2 >45 mmHg
* Dysfunctional breathing during sleep
Signs:
* Obesity
* hypersomnolence during the day
* Hypoxemia
* hypercarbia
* respiratory acidosis
* compensatory metabolic alkalosis
* polycythemia
* pulmonary HTN
What are the most common signs of an anastomotic leak following gastric bypass?
Gastric bypass is associated with a 2% incidence of anastomotic leak. Unexplained tachycardia is the most sensitive sign of an anastomotic leak. An unexplained HR > 120bpm should send up a red flag, even if the pt shows no other signs
The most common S/sx include:
* Tachycardia (72%)
* Fever (63%)
* abdominal pain (54%)
Ketorolac probably increases the incidence of this complication, so it should be avoided in the perioperative period
what is Ma huang? What are the complications of its use?
Ma huang is a natural source of ephedrine, an indirect-acting adrenergic agonist and thermogenic agent.
Any drug interactions that would occur with ephedrine will apply here as well. Complications of adrenergic overstimulation including HTN, CVAs, seizures, and death, have occurred with the use of Ma huang containing drugs.
What is Orlistat? what are the complications of its use?
Orlistat is a lipase inhibitor that reversibly binds to lipase and hinders the absorption and digestion of consumed fats.
Since fat and the vitamins it contains (A, E, D, K) are not absorbed by the gut, they must be supplemented orally. Insufficient quantities of vitamin K will impair the synthesis of clotting factors 2, 7, 9, 10 and may cause coagulopathy.
How does the Trendelenburg position affect the distribution of blood volume, MAP, and venous pressure?
Blood shifts towards the central circulation:
* Increase venous return -> increase position on the Frank-Starling curve
* caution with heart failure
MAP stays the same or increases:
* Although venous return initially increases, this is followed by vasodilation and a slower heart rate
venous pressure increases:
* Hydrostatic pressure -> edema of the face, eye, and airway
* Intracranial HTN
How do position changes affect respiratory function?
How do position changes affect the position of the ETT?
Securing the ETT after intubation fixes its location. For the rest of the procedure, the position of the carina in the chest.
Neck position
* Neck flexion pushes the ett toward the carina. This increases the risk of endobronchial intubation
* Neck extension pulls the ett tip towards the vocal cords. This increases the risk of inadvertent extubation.
* Remember, “the tube goes where the nose goes”
Carina position
* in the trendelenburg position, the abdominal contents shift cephalad. This pushes the diaphragm towards the ett, increasing the risk of endobronchial intubation
Which positions increase the risk of post-operative airway edema, and how can you assess the severity of this complication?
Edema of the face, tongue, pharynx can affect airway patency.
*prone and trendelenburg: increased hydrostatic pressure -> edema formation
* Sitting: Neck flexion impairs venous drainage from the head -> edema formation
If you have a concern about the patency of the airway prior to extubation, you can:
* perform a leak test to assess for air movement around the ETT while the pt is spontaneously ventilating
* Visually inspect the larynx with direct laryngoscopy
Discuss how the brachial plexus is susceptible to stretch and compression injury
Stretch injury:
* Stretch injury occurs because the brachial plexus is anatomically fixed at two locations: the cervical vertebrae and the axillary fascia
* As a general rule, the risk of stretch injury is highest when the arms are abducted >90 degrees and/or the head is rotated to one side
Compression injury
* Compression injury usually occurs when the brachial plexus is compressed as it passes between the clavicle and first rib or by an external force (shoulder brace or bean bag)
Should shoulder braces be used for the pt in the Trendelenburg position? why or why not?
Although shoulder braces were developed to prevent the pt from sliding on the OR table, they cause more harm than good!
- the best answer is never use shoulder braces. A non-sliding mattress is a safer option
- if shoulder braces are used, they should be placed at the distal end of each clavicle (over the acromion)
- Shoulder braces applied near the base of the neck or midway along the clavicle increase the risk of a compression injury
How do you assess a pt for thoracic outlet syndrome? which surgical position increase the likelihood of this complication?
Thoracic outlet syndrome is more likely to occur in any position where the arms are placed over the head (prone).
During the preoperative interview, ask the pt to clasp her hands behind her head. If she complains of pain, this may suggest an increased risk of thoracic outlet syndrome. It may be prudent to tuck the arms while in the prone position.
Thoracic outlet syndrome occurs from compressed vessels or nerves causing pain, in the shoulder and neck and numbness, weakness, and coldness in the fingers
Where should an axillary roll be placed for the pt in the lateral decubitus position?
An axillary roll is placed distal to the axilla
A roll placed inside the axilla can cause neurovascular compression. A poor SpO2 signal in the dependent arm is a good monitor for this.
describe the anatomy of the cubital tunnel.
Boundaries of the cubital tunnel:
* medial epicondyle of the humerus
* Olecranon process of the ulna
* cubital tunnel retinaculum (creates the roof of the cubital tunnel)
The ulna n. emerges from the cubital tunnel between the humeral and ulnar heads of the flexor carpi ulnaris
Who is at risk for ulnar nerve injury?
The ulnar nerve is the most commonly injured peripheral nerve.
Ulnar neuropathy isn’t always caused by intraoperative positioning. Other risk factors include:
- Male gender (especially if >50 yrs old)
- Preexisting ulnar neuropathy
- Extremes of body habitus (very thin or obese)
- Prolonged hospital stay/bedrest
Describe the presentation of ulnar nerve injury
- impaired sensation of the 4th and 5th digits
- Inability to ABduct or oppose the pinky finger
- Chronic injury presents with claw hand (muscular atrophy)
Which nerve injury provides a greater risk for long term injury (sensory or motor)?
Sensory deficits are more common, less serious, and tend to resolve on their own (usually 5 days or less).
Motor deficits are less common and more serious
What are the causes of median nerve injury?
Etiology:
* IV placed in the antecubital space
* Carpel tunnel syndrome- the median nerve is the only nerve that passes through the carpal tunnel
* Elbow hyperextension
* Forced elbow extension during positioning after a neuromuscular blocker has been administered
Describe the presentation of median nerve injury
- Reduced sensation over palmar surface of the thumb, index finger, and lateral aspect of the ring finger.
- Unable to oppose the thumb (chronic injury can lead to the ape hand deformity)
What are the causes of radial nerve injury?
The radial nerve passes along the spiral groove at the lateral aspect of the humerus (about 3 fingerbreadths above the lateral epicondyle)
Etiology:
* External compression by an IV pole
* excessive cycling of the NIBP cuff
* Upper extremity tourniquet
* Sheets that are too tight (if the arms are tucked)
Describe the presentation of radial nerve injury
Presentation= wrist drop
* inability to extend the hand at the wrist
Discuss the etiology, presentation, and prevention of obturator nerve injury.
Etiology:
* Excessive flexion of the thigh towards the groin
* Excessive traction during lower abdominal surgery
* Forceps delivery
Presentation:
* Inability to ADDuct the leg
* reduced sensation over the medial aspect of the thigh
Prevention:
* Minimize hip flexion
Discuss the etiology, presentation, and prevention of femoral nerve injury
Etiology
* Excessive traction during lower abdominal surgery
Presentation:
* Impaired knee extension and hip flexion
* Reduced sensation over the anterior thigh and anteromedial aspect of the leg
Prevention:
* Avoid excessive traction during lower abdominal surgery
Discuss the etiology, presentation, and prevention of Saphenous nerve injury
Etiology:
* Medial aspect of the leg leans against the supporting cradle in the lithotomy position (the saphenous n. resides near the tibia)
Prevention:
* Place padding between leg and stirrup
Discuss the etiology, presentation, and prevention of common peroneal nerve injury
Etiology:
* The common peroneal nerve is highly susceptible to injury when the patient is placed in stirrups. This nerve wraps around the fibular head, and it can be compressed when the lateral aspect of the leg leans against the stirrup bar.
Presentation
* Foot drop
* Inability to evert the foot
* Inability to extend the toes dorsally
TIPPED
Tibial Inversion Plantar flexion, Peroneal Eversion Dorsiflexion
peroneal = foot drop
tibial= can’t stand on (tip) toes
Prevention:
* Place padding between the leg and stirrup
* Pad under the fibular head
* Knees should be flexed with minimal rotation
Discuss the etiology, presentation, and prevention of sciatic nerve injury
Etiology:
* lithotomy- extreme hip flexion and/or external rotation of the legs
* Sitting- straight legs
Prevention:
* Ample padding under buttocks
* Avoid excessive external rotation of the hips
* Flex table at the knees
Presentation:
* foot drop
which position is most likely to cause compartment syndrome?
Compartment syndrome is most common in the lithotomy position.
* the lithotomy position is associated with increased leg compartment pressure, and raising the legs above the heart reduces lower extremity perfusion pressure.
* Taken together, these changes set the stage for leg ischemia -> edema -> more ischemia -> more edema…
* this can progress to rhabdomyolysis and/or reperfusion injury
compartment syndrome is treated with fasciotomy
which position is most likely to cause venous air embolism?
Sitting
Although the sitting position is most commonly associated with venous air entrainment, this complication can occur in any position that produces a pressure gradient between the atmosphere and the veins at the surgical site.
Venous air embolism -> right heart-> pulmonary vasculature -> increased dead space & increased RV workload
Paradoxical air embolism -> right heart -> patent foramen ovale -> left heart -> systemic circulation -> stroke
which position is most likely to cause midcervical tetraplegia?
Midcervical tetraplegia is associated with hyperflexion of the neck (chin to chest). Ischemia occurs as a result of stretching and/or compression of the midcervical spinal cord (usually C5)
- this complication is most common in the sitting position
- You should be able to place at least 2 fingers in-between the chin and the chest
what is the purpose of a positioning device for a pt in the prone position?
in the prone position, a positioning device (chest rolls, wilson frame, or Jackson table) and padding distribute the patient’s weight to the thoracic cage and the boney pelvis. This allows the abdomen to hang freely, which promotes normal diaphragmatic excursion throughout the respiratory cycle.
- if the abdomen is compressed, intraabdominal pressure increases, which reduces pulmonary compliance and increases intrathoracic pressure
- venous pressure is also increased, and this can cause back bleeding via the epidural veins during spinal surgery.
the jackson table is better than the wilson frame or chest rolls
which position provides the most optimal V/Q matching in the patient with ARDS?
The prone position optimal V/Q matching, which explains why we use the prone position for patient with ARDS
List 3 factors that worsen tracheobronchial compression in the patient with an anterior mediastinal mass.
Supine position
induction of general anesthesia
positive pressure ventilation
What is the best induction technique for a patient with an anterior mediastinal mass?
Spontaneous ventilation preserves the normal airway distending pressure gradient, but this gradient is often abolished during positive pressure ventilation. The sitting position and maintenance of spontaneous ventilation will minimize, but not always prevent, compression of the vital chest structures.
what are your options if you lose the airway during induction in the patient with an anterior mediastinal mass?
If the mass compresses the tracheobronchial tree before the airway is secured, it may be impossible to advance the ETT beyond the tumor. It is also possible for the tumor to compress the tracheobronchial tree past the distal tip of the ETT, causing complete obstruction of the airway.
Should airway collapse occur, repositioning the pt laterally or prone may restore patency to the airway. A rigid bronchoscope should be available. Emergent femoral-femoral cardiopulmonary bypass may be required if ventilation via the lungs becomes impossible
What is the AANA Code Of Ethics?
Dictates the principles of conduct and professional integrity that guide the decision-making and behavior of nurse anesthetists. The document speaks to the anesthetist’s responsibilities as a professional, which holds the individual CRNA accountable for his or her own actions and judgements, regardless of institutional policy or physician orders
what are practice guidelines?
Practice guidelines are systematically developed statements to assist providers in clinical decision-making that are commonly accepted within the anesthesia community
Guidelines “should” be adhered to
what are practice standards?
Practice standards are authoritative statements that describe minimum rules and responsibilities for which anesthetists are held accountable.
Standards “must” be adhered to
what are position statements?
Position statements express the AANA official positions or beliefs on practice-related topics; they may also define that knowledge, skills, and abilities considered necessary for a nurse anesthetist.
Define autonomy.
Autonomy refers to the patient’s ability to choose without controlling interference by others and without limitations that prevent meaningful choices
Define nonmaleficence
Nonmaleficence asserts that a provider has an obligation not to inflict hurt or harm-in other words, the Hippocratic oath primum non ocere (first do no harm)
Define beneficence
Beneficence is the principle that providers should take action for the benefit of others. This includes both preventing harm and actively helping their patients. Beneficence underpins the fundamental guiding principle of evidence-based interventions- the benefits of the treatment should be demonstrable and must clearly outweigh the risks.
List the 6 elements of informed consent
- Competence
- Decision-making capacity
- disclosure of information
- Understanding of disclosed information
- voluntary consent
- documentation
What is informed refusal? list one example of this concept in a specific patient population
A pt has a right to refuse medical tx or therapy
A common example is the refusal of blood or blood products by a Jehovah’s witness. When a recommended therapy is refused, it places an even higher burden on the health care provider to disclose the risks and benefits of both the recommended and any alternative care.
what is an advanced directive?
An advanced directive is a legally binding document that delineates the patient’s wishes regarding healthcare interventions in the case of incapacity and/or delegates the authority to make healthcare decisions to another party
Advance directives often include specific provisions that modify aspects of anesthesia management, including intubation, use of antibiotics, blood transfusion, and/or the use of CPR and advanced life support measures. Because many of these measures, when used in conjunction with a procedure/surgery, are temporary, it is recommended that advance directives be reconsidered before anesthesia is administered
list the 4 things that must be proven in a lawsuit asserting malpractice.
Duty
Breach of duty
causation
damages
What is res ipsa loquitur
res ipsa loquitur (“the thing speaks for itself”) can shift the burden of proof from the paintiff to the defendant. This can occur if 4 conditions can be established:
- if the injury would not have occurred in the absence of negligence
- the injury was caused by something under the complete control of the defendant (provider)
- The patient did not contribute in any way to the injury
- The evidence for the explanation of events is solely under the control of the provider
what is the difference between libel and slander?
libel is defamation in the written form
Slander is defamation in the verbal form
what is the difference between assault and battery?
Assault is the attempt to touch another person
battery is touching a person without either expressed or implied consent
what is the vicarious liability? what’s another name for this concept?
One person (or entity) may be liable for the actions of another person. For instance, a physician might be held liable for the actions of a PA. This concept typically does not apply to CRNAs working under a physician.
Respondea superior is often used interchangeably with vicarious liability
What is the Patient Care and Affordable Care Act?
the ACA mandated that all individuals carry health insurance, established standards and requirements for health insurance policies, and launched health care clearinghouses or exchanges to assist people in finding medical insurance. In addition, insurers are no longer permitted to charge more for pre-existing conditions
What is Emergency in Medical Treatment and Active Labor Act
Over 30 years ago, Congress enacted the Emergency Medical Treatment & Labor Act (EMTALA) to ensure public access to emergency services regardless of their ability to pay. This is also known as the “Anti-Patient Dumping” act.
This act imposes specific obligations on Medicare-participating hospitals that offer emergency services to provide a medical screening examination when a request is made for examination or treatment for an emergency medical condition (EMC) regardless of an individual’s ability to pay
What is Health Insurance Portability and Accountability Act?
Most health care providers are aware of HIPAA, the federal law that prohibits the disclosure of individually identifiable health information (AKA personal health information, PHI). PHI includes past and present health conditions, treatments, and payments for health care.
Disclosure can occur in any form, including orally, written, or electronically.
Even if you think you’re keeping the patient anonymous, there’s always a risk of HIPPA violation when you post any patient-related stories, data, etc., on social media
What is the controlled substances act?
We all know that the federal government regulates the manufacture, importation, possession, and distribution of drugs deemed “controlled substances.” The government defines what is controlled and what level of restriction various controlled substances are subject to.
What schedule I drugs are used to provide anesthesia?
By its very definition, a schedule I drug has NO currently accepted medical use. Therefore, we don’t use any schedule I drugs in anesthesiology.
As an aside, the legalization of marijuana at the state level challenges its schedule I designation at the federal level.
What is a schedule II drug? List some examples.
A schedule II drug has a high potential for abuse potentially leading to dependence.
Examples:
*Opioid agonists (fentanyl, morphine, *hydromorphone, etc.)
* Cocaine
* methamphetamine
* phencyclidine (ketamine)
what is the Health Information Technology for Economic and Clinical Health Act (HITECH)?
This act was intended to create a healthcare information technology infrastructure in order to improve care quality and coordination between providers, i.e., to promote the “meaningful use” of such information
HITECH is essentially an amendment to HIPAA and applies to the same covered entities, including providers, health plans, and healthcare clearinghouses. HITECH precipitated a massive expansion in the exchange of electronic PHI and widened the scope of privacy and security protections available under HIPAA.
Detail the steps involved with responding to a lawsuit.
what is an emancipated minor?
Emancipated minors are patients younger than 18 years of age who are legally given the rights of an adult by a state court. Although variable by state law, criteria for emancipating a minor may include the fact that they are:
- married
- A parent or is currently pregnant
- IN the military
- Economically independent
Discuss the ethical dilemma of surgery for a child of Jehovah’s Witness?
Families should be informed that, despite all reasonable efforts to eliminate the need for transfusion, if an emergency occurs, a court order for transfusion will be sought
When the likelihood for transfusion is high, a court order should be sought prior to surgery. In a lfe-threatening crisis, emergency transfusion should be given prior to obtaining a court order.
As these children approach maturity, they should be involved in the decision-making regarding the use of blood and blood products.
What is anesthesia crisis resource management?
In an anesthetic crisis, effective response and management are dependent upon non-technical skills. Crisis resource management (CRM) uses a simple model in which effective communication is the “glue” that holds all the other components together.
Resources available in a crisis include all the personnel involved and their inherent knowledge, skills, and abilities (and limitations). Resources also include available supplies, pharmaceuticals, technology, and information. The same skill set is required to prevent and intervene when threats to patient safety occur. CRM training is detailed and extensive and is often accompanied with high fidelity simulation training.
List 5 complications of fatigue.
- Diminished reaction time
- Impaired decision-making
- decreased situational awareness
- Impaired concentration or memory
- periods of microsleep
What is microsleep?
Microsleep is an actual sleep episode that lasts seconds to minutes; it is insidious in a fatigued provider and cannot be predicted. Performance between microsleep episodes is impaired, and errors of omission increase when microsleep occurs.
what is the relationship between 24-hrs of wakefulness and alcohol consumption?
Research has also shown that 24-hr of wakefulness is equivalent to a blood alcohol content of 0.1% (legal impairment for driving is 0.08%). Thus, scheduling or working a 24-hr shift, or working multiple long shifts with short sleep time intervals, puts both the provider and the pt at risk.
when is sleep-related behavior most common?
after 16 or more continuous hours of work
During the night shift
List 6 countermeasures for fatigue
- Napping
- Caffeine
- exercise
- Consistent sleep-wake pattern
- Medications
- Recovery between shifts
What is the OSHA limit for occupational exposure to ionizing radiation?
Annual = 5 rem
Lifetime= (N-18) x 5 rem
* N= age in years
what are the physiologic effects of MRI exposure?
Lower frequency electromagnetic fields from MRI can cause transient symptoms of nausea, dizziness, vertigo, or light flashes. There are no published regulations limiting occupational exposure to MRI fields
What are the OSHA limits for noise exposure?
The OSHA limit for an 8-hour span is 90dB, and single noise levels should not exceed 115 dB
Who is the “second victim”?
One of the most significant acute stressors for an anesthesia provider is being involved in a case with a bad outcome (death or significant morbidity). The effects of perioperative catastrophe on the provider are just beginning to be studied
Current thinking conceptualizes the provider as a “second victim” and the provider’s subsequent patients as possible “third victims”
Define addiction
a need (psychological or compulsive) for a substance. There is often a loss of self-control, where the user continues using a drug despite the desire to stop drug use. This represents a severe stage of chronic substance abuse disorder
Define impairment
the inability to safely participate in life (or professional) activities
Define tolerance
More drug is needed to achieve a given effect (intoxication) - or - a lesser effect is produced by a given dose of a drug
Define withdrawal
a characteristic syndrome that is the direct result of stopping or reducing the use of a drug
list the factor for developing substance use disorder
What are some typical behaviors of the impaired provider?
- Frequent and unexplained tardiness, absences, or illnesses often with elaborate excuses
- Poor performance with errors, accidents, or injuries that are inadequately explained
- Confusion, memory loss, difficulty concentrating or recalling details
- Severe mood swings, changes in personality
- Visibly intoxicated
- Refuses drug testing
- Track marks, bloodshot eyes, significant weight loss or gain
What are the key issues regarding re-entry to clinical practice following a substance abuse disorder
Safe return to work is determined on an individual basis- not all providers will be able to return to practice safely
Readiness for re-entry is a collaborative decision of the monitoring program, certified drug and alcohol counselor, and employer. One full year in recovery is recommended prior to returning to anesthesia practice
Due to the high risk of relapse, abstinence-based recovery and refraining from substitute treatments is also recommended
Of the ten criteria that should be met prior to considering re-entry, the most salient point is participation in a monitoring program at least 5 years in length with random drug testing
What should you do if you suspect a fellow anesthesia provider is impaired?
- Do not let the person out of your site, and do not let them drive
- have a bed in a treatment facility available
- Do not let the impaired person decide their treatment. (they are sick, and an intervention can make them suicidal)
- Only when all else fails, threaten to call the police.
what are the 6 elements of high-quality care?
- patient-centered
- safe
- effective
- timely
- efficient
- equitable
Discuss the cultural competence in the context of anesthesia delivery
Cultural competence is emphasized as a strategy to reduce health care disparities and improve equity.
What does this mean? you should be providing the same level of care and consideration to a homeless drug user that you would to the hospital’s CEO! the ethnicity, race, religion, sexual orientation, cultural background, or status in the community simply may not play into your interactions, communication, and planning process with the patient and family. Thus, cultural competence requires the anesthesia provider to:
* Know and apply current standards of care
* Offer and use evidence-based interventions
* Have a keen awareness of their own biases and assumptions
* Be sensitive to the presence of health disparities and discrimination
At sea level, the agent monitor measures the end-tidal sevo as 16mmHg. Convert this to volumes percent.
2.1% sevo
* Volumes % = (partial pressure/total pressure) x 100
what effect does a fever have on blood flow?
It decreases viscosity which reduces resistance to blood flow
why is ionized radiation so dangerous to healthcare workers?
it can remove electrons from atoms, which produces free radicals. This wreaks havoc at the cellular level. Risks include tissue injury, chromosomal damage and malignancy
what is an adiabatic process?
A process that occurs without gain or loss of energy (heat).
what is the boiling point of water in Fahrenheit?
212F
convert 120 mmHg to cm H2O
1 mmHg= 1.36 cm H2O
163cm H2O
Convert 40cmH2O to mmHg
1 cm H2O = 0.74mmHg
29.6mmHg
hypothermia is defined as a core body temperature less than:
36 degrees C
list two perioperative medications that can lead to anticholinergic poisoning.
atropine scopolamine
what are 3 clinical features of anticholinergic poisoning?
- red, dry, hot skin
- Delirium
- Mydriasis
what is the MOA of neuroleptic malignant syndrome?
Dopamine depletion in the basal ganglia and hypothalamus
what three key drug interactions increase the risk of serotonin syndrome?
- SSRI (fluoxetine, citalopram) combined with : Meperidine and fentanyl
- MAOI(Selegiline, phenelzine, isocarboxazid) combined with: Meperidine and ephedrine
- Methylene blue combined with: Other serotonergic drugs
when should N2O be discontinued before placement before placement of an SF6 bubble in the eye? and how long should N20 be avoided for gas bubble used?
15 minutes
how many days to avoid N20
silicone oil= 0 days
air bubble= 5 days
SF6= 7-10 days
Perfluoropropane (c3F8)= 30 days
what causes open-angle glaucoma?
It’s caused by sclerosis of the trabecular meshwork. This impairs aqueous humor drainage
what is the most common side effect of antibiotic prophylaxis?
Pseudomembranous colitis
what is the antibiotic of choice for an active MRSA infection?
Vancomycin
What is the first line treatment for Tuberculosis?
Isoniazid
list 3 things that reduce gastric barrier pressure
anticholinergics, pregnancy, cricoid pressure
when should ondansetron be administered in surgical cases?
30 min prior to emergence
what is the best class of antiemetics for patients undergoing mastoidectomy?
anticholinergics
list 2 early signs of BCIS (bone cement implantation syndrome) in an awake pt
dyspnea, and altered LOC
what 3 symptoms are most commonly seen with fat embolism syndrome?
- Respiratory insufficiency (hypoxemia, bilateral infiltrates on CXR, ARDS)
- Neurologic involvement (confusion to coma)
- Petechial rash (skin of neck and axilla, oral mucosa, conjunctiva)
what is the tx for fat embolism
supportive, but some texts say corticosteroids help outcomes
