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 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 are the risk factors for PONV? It helps to divide them into pt, surgical, and anesthetic risk factors
Where is the P6 acupressure point, and why is it important?
The P6 acupressure point is a nonpharmacologic method of reducing PONV
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
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
How can you use BMI to classify obesity?
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 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
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
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 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
How do position changes affect respiratory function?
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
Detail the steps involved with responding to a lawsuit.
list the factor for developing substance use disorder
