Unit 12: Miscellaneous Topics Flashcards
Define an ionic bond, covalent bond, and polar covalent bond
Ionic Bond: complete transfer of valence electrons from one atom to another
- leaves one atom w/ a negative charge and the other w/ a positive charge
- metals, acids, and bases tend to form ionic bonds
Covalent Bond: equal sharing of electrons (strongest type of bond)
- single bond is created when 1 pair is shared, double bond = 2 shared
Polar Covalent Bond: an “in-between” type of bond
- atoms share electrons but electrons tend to remain closer to one atom than the other
- one area of the molecule is relatively positive and the other is relatively negative
What are Van der Waals forces?
Very weak intermolecular force that hold molecules of the same type together
-weakest type of molecular attraction
What is Dalton’s Law? List several examples of how it can be used in the OR
Dalton’s Law of Partial Pressures = 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 it:
-calculate partial pressure of an unmeasured gas
-calculate 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 Sevo as 3%. What is the partial pressure of Sevo in the exhaled tidal volume?
Partial Pressure = Volumes % x Total Pressure
0.03 x 760 mmHg = 22.8 mmHg
*application of Dalton’s Law
What is Henry’s Law? List several examples of how it can be used in the OR
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
-the higher the gas pressure, the more of it will dissolve into a liquid (assuming constant temp)
Increased Temp = Decreased Solubility
Decreased Temp = Increased Solubility
Application:
-anesthetic emergence is prolonged in the hypothermic pt
-dissolved O2 in the O2 carrying capacity equation
What is 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 are
Inversely Proportional To:
-membrane thickness
-molecular weight
What are the clinical examples of Fick’s Law of Diffusion?
-Diffusion hypoxia
-Pt w/ COPD has a reduced alveolar surface area and therefore has a slower rate of inhalation induction
-Calculation of CO
-Drug transfer across the placenta
What are Boyle’s, Charles’s, and Gay-Lussac’s Laws?
Boyle’s Law: P1 x V1 = P2 x V2 – inverse relationship
Charles’s Law: V1/T1 = V2/T2 – direct relationship
Gay-Lussac’s Law: P1/T1 = P2/T2 – direct relationship
What are the clinical examples of Boyle’s Law?
Pressure x Volume – (constant = temp)
-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)
What are the clinical examples of Charles’s Law?
Volume / Temperature – (constant = pressure)
-LMA cuff ruptures when placed in an autoclave
What are the clinical examples of Gay-Lussac’s Law?
Pressure / Temperature – (constant = volume)
-Oxygen tank explodes in heated environment
What is the function of the ideal gas law?
Ideal Gas Law unifies all 3 gas laws into a single equation: PV = nrT
P = pressure
V = volume
n = # of moles
r = constant 0.0821 L-atm/K/mole
T = temperature
What is Ohm’s Law?
Current passing through a conductor is directly proportional to the voltage and inversely proportional to the resistance
-can adapt 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 = πR^4ΔP / 8 nL
Q - blood flow
R - radius
ΔP - arteriovenous pressure gradient (Pa - Pv)
n - viscosity
L - length of tube
How do changes in radius affect laminar flow?
Altering radius of the tube exhibits the greatest impact on flow
R = 1^4: 1x1x1x1 = 1
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 of PRBCs?
PRBCs can be delivered faster if we:
-increase the radius w/ a large bore IV
-increase the pressure gradient w/ a pressure bag and/or increase height of IV pole
-decrease viscosity by diluting blood w/ 0.9% NS 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?
Predicts the type of flow (laminar, turbulent, and transitional) 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 2000-4000: transitional flow
Reynolds’ # = Density x Diameter x Velocity / Viscosity
**in status asthmaticus – airway resistance is increased, thus increases turbulent flow and WOB (treat w/ Heliox to improve Reynold’s # by reducing density)
What is Bernoulli’s principal?
Describes the relationship between the pressure and velocity of a moving fluid (or gas)
-if fluid’s velocity is high – pressure exerted on the walls of the tube will be low
-if fluid’s velocity is low – pressure exerted on the walls of the tube will be high
*ex: think of a river:
- wide river = water moves slowly
- narrow river = water moves faster –> slow water exerts more pressure on riverbank than fast narrow river
What is the Venturi effect? Give examples
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 diameter of the constriction allows for control of the pressure drop and the amount of air that is sucked into the tube
Ex: jet ventilator, Venturi, and nebulizer
What is the Coanda effect? Give examples
Describes how a jet flow attaches itself to a nearby surface and continues to flow along that surface even when the surface curves away from the initial jet direction
Ex: 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? How about for a cylinder?
Sphere: Tension = (Pressure x Radius) / 2
-examples: alveolus, cardiac ventricle, saccular aneurysm
Cylinder: Tension = Pressure x Radius
-examples: blood vessels, aortic aneurysm
*Law of Laplace illustrates the relationship between the wall tension, internal pressure, and radius
What is the yearly maximum for radiation exposure? How does this change if someone is pregnant?
Yearly Max Exposure = 5 rem
-eye and thyroid are most susceptible to injury
Pregnant Yearly Max Exposure = 0.5 rem or 0.05 rem/month for the fetus
-fetus is most susceptible to injury
What are 3 ways to protect yourself from radiation exposure?
Distance – minimum safe distance is 6ft
Duration
Shielding
How can we apply the inverse square law to radiation exposure?
The amount of exposure is inversely proportional to the square of the distance of the source
Intensity = 1 / Distance^2
Can quantify the amount of exposure at two different locations with the following equation:
Intensity1 = Distance2^2
Intensity 2 = Distance1^2
What is boiling point, and how is it affected by atmospheric pressure?
The temp at which a liquid’s vapor pressure equals atmospheric pressure
Increased P atm –> Increased boiling point (ex. hyperbaric O2 chamber)
Decreased P atm –> Decreased boiling point (ex. high altitude) –> Increased
What is specific heat?
The amount of heat required to increase the temp of 1g of a substance by 1*C
What is 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 (vapor pressure)
What is latent heat of vaporization? Apply this to an anesthetic vapor inside of a vaporizer
Latent heat of vaporization = # of calories required to convert 1g of liquid vapor w/o a temp change in the liquid
- anesthetic liquid in the vaporizer exerts a vapor pressure inside the vaporization chamber (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 vapor pressure of the liquid (fewer anesthetic molecules that enter the gas phase)
- net result is a decrease in the vaporizer output
*Modern vaporizers compensate for this temp change
What is the Joule-Thompson effect in the context of gas cylinders?
Joule-Thompson Effect: a gas stored at high pressure that is suddenly released escapes from its container into a vacuum – quickly loses speed as well as a significant amount of kinetic energy resulting in a fall in temperature
-explains why an O2 cylinder that is opened quickly feels cool to the touch
What is an adiabatic process?
Describes a process that occurs without gain or loss of energy (heat)
Ex: a very rapid expansion or compression of a gas where there is no transfer of energy
What is critical temperature, and how does this apply to gas cylinders?
Critical Temp = highest temp where a gas can exist as a liquid (the temp above which a gas can’t be liquefied regardless of the pressure applied to it)
-critical temp for N2O = 26.5C – explains why it primarily exists as a liquid inside the cylinder
-critical temp for O2 = -119C – explains why it exists as a gas inside the cylinder
*only N20 and CO2 have critical temps above room temperature
**critical pressure = minimum pressure required to convert a gas to a liquid at its critical temperature
What is the formula to convert Celsius to Kelvin? What about Celsius to Fahrenheit?
Celsius to Kevlin and back:
– C = K - 273.15
– K = C + 273.15
Celsius to Fahrenheit and back:
– C = (F - 32) x 5/9
– F = (C x 1.8) + 32
What are the pressure conversion factors?
- ?? atm = ?? mmHg = ?? bar = ?? kPa = ?? cmH20 = ?? lb/inch^2
- ?? mmHg = ?? cmH20
- ?? cmH20 = ?? mmHg
1 atm = 760 mmHg = 1 bar = 100 kPa = 1033 cmH2O = 14.7 lb/inch^2
1 mmHg = 1.36 cmH2O
1 cmH2O = 0.74 mmHg
What is Avogadro’s number?
Says that 1 mole of any gas is made up of 6.023 x 10^23
-a mole of gas is equal to the molecular weight of that gas in grams
-if a molecule is 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%)
What are the 3 stages of intraoperative heat transfer?
Phase 1: heat redistribution from core to periphery – Hour 1 following induction of anesthesia
Phase 2: heat transfer > heat production – Hours 1-5
Phase 3: heat transfer ~ heat production – Hours 5+
What are the consequences of perioperative hypothermia?
Cardiovascular:
- SNS stimulation –> myocardial ischemia/dysrhythmias
- Shifts oxyhbgb dissociation curve left –> decreased O2 available to tissues
- Vasoconstriction + decreased tissue PO2 –> surgical site infection
- Coagulopathy + platelet dysfunction –> increased blood loss
- Sickling of hgbS –> risk of sickle cell crises
Pharmacologic:
- Slowed drug metabolism –> prolonged effects of anesthetic agents
- Increased solubility of volatile agents –> prolonged emergence
What three drugs can be used to treat postop shivering?
-Meperidine (kappa)
-Clonidine (alpha-2)
-Dexmedetomidine (alpha-2)
*shivering increases O2 consumption up to 400-500% – increases risk of myocardial ischemia and infarction
When is hypothermia a good thing?
-Cerebral ischemia (stroke)
-Cerebral aneurysm clipping
-TBI
-Cardiopulmonary bypass
-Cardiac arrest
-Aortic cross-clamping
-Carotid endarterectomy
based on the fact that O2 consumption is reduced by 5-7% for every 1C
In which region of the esophagus should an esophageal temp probe be placed? How doe misplacement affect the reading?
Should be placed in the distal 1/3 - 1/4 of the esophagus (38-42cm past the incisors)
-falsely high if placed too far (in stomach) due to heat created by liver metabolism
-falsely low if placed too proximal due to cool inspiratory gas
What are the three ingredients required to produce a fire? Give an example of each
Fuel – Oxidizer – Ignition Source
-fuel ex: ETT, drapes, surgical supplies
-oxidizer ex: O2, N2O
-ignition source ex: electrosurgical cautery, laser
What are the steps you 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 airway
5. If fire isn’t extinguished on the 1st attempt, then use a CO2 fire extinguisher
Steps to Take After Fire is Controlled:
1. Re-establish ventilation by mask – avoid supplemental O2 or N2O
2. Check ETT for damage – fragments may remain in the pt’s airway
3. Perform bronchoscopy to inspect for airway injury or retained fragments
*DO NOT squeeze reservoir bag as you extubate the pt – can create a blow torch effect at distal end of ETT or push debris lower into airway
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
What are the four degrees of burns? Which require a skin graft?
1st Degree:
-spontaneous healing
-epidermis only
-stinging, tender, and sore
2nd Degree Superficial:
-spontaneous healing
-epidermis –> upper dermis
-very painful
2nd Degree Deep:
-skin graft
-epidermis –> lower dermis
-very painful
3rd Degree:
-skin graft
-complete destruction of epidermis and dermis
-no sensation (nerve endings are obliterated)
4th Degree:
-skin graft
-extends to muscle and bone
-no sensation (nerve endings are obliterated)
What is the rule of 9’s for burns? How does this apply to the adult?
Total body surface area is divided into areas representing 9% (or multiples of 9%) – due to rounding the numbers don’t add up to 100
-Head = 10%
-Arms = 9% each
-Torso = 18%
-Back = 18%
-Legs = 18% each
*concept is important for calculating fluid requirements
How does the rule of 9’s for burns apply to children?
-Head = 19% (9.5% for front and 9.5% for back)
-Arms = 9.5% each
-Torso = 16%
-Back = 16%
-Legs = 15%
**For every year of age >1 year up to 10 years – decrease head surface area by 1% and increase each leg by 0.5%
What are the consequences of the capillary leak that occurs after a burn?
-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
-Hypovolemia –> hemoconcentration (rising Hgb in first few days suggests inadequate volume resuscitation)
*fluid shifts and edema formation are greatest in the first 12 hours and begins to stabilize by 24 hours – explains why fluid requirements are higher in the first 24 hours following a burn
What is the Parkland formula for resuscitation in burn patients?
First 24 Hours:
-Crystalloid = 4mL LR x %TBSA burned x kg (1/2 in 1st 8hrs then 1/2 in next 16)
-Colloid = None
Second 24 Hours:
-Crystalloid = D5W at normal maintenance rate
-Colloid = 0.5mL x %TBSA burned x kg
What is the Modified Brooke formula for resuscitation in burn patients?
First 24 Hours:
-Crystalloid = 2mL LR x %TBSA burned x kg (1/2 in 1st 8hrs then 1/2 in next 16)
-Colloid = None
Second 24 Hours:
-Crystalloid = D5W at normal maintenance rate
-Colloid = 0.5mL x %TBSA burned x kg
What is an acceptable urine output in a burn patient? Is this different in children or patients who’ve suffered a high voltage electrical injury?
Adult = > 0.5 mL/kg/hr
Child = > 1 mL/kg/hr
High Voltage = > 1-1.5 mL/kg/hr
*myoglobinemia is the result of extensive muscle damage following a high voltage electrical injury
Why is the burn patient at risk for abdominal compartment syndrome? What is the diagnosis and treatment of this complication?
-May result from aggressive fluid resuscitation
-Intra-abdominal HTN is defined at IAP > 20 mmHg or >12 mmHg AND evidence of organ dysfunction
Treatment:
-neuromuscular blockade
-sedation
-diuresis
-abdominal decompression via laparotomy
What are the clinical considerations for the patient with carbon monoxide poisoning?
-Binds to hemoglobin w/ an affinity 200x that of O2
-Shifts oxyhgb dissociation curve to the left (left = love) – impairs offloading of O2 to the tissues
-Oxidative phosphorylation is also impaired
-Inadequate O2 delivery and utilization causes metabolic acidosis
-Blood takes on a cherry red appearance
-Pulse Ox is NOT accurate (unable to distinguish between HgbO2 and HgbCO)
-SpO2 may give a falsely elevated result
-Treatment includes 100% FiO2 or hyperbaric O2
How is the use of neuromuscular blockers different for burn patients?
Up-regulation of extrajunctional receptors begins after 24 hours:
-SUX is safe within the first 24 hours following the burn, but can cause lethal hyperkalemia after 24 hours
-Dose of NDMRs should be increased 2-3 fold (there are more receptors)
What physiologic changes accompany ECT treatment?
Initial Response: Increased PNS activity during tonic phase (lasts ~15 seconds)
- decreased HR/brady-dysrhythmias
- decreased BP
- increased oral/gastric secretions
Secondary Response: Increased SNS activity during clonic phase (lasts several minutes)
- increased HR/tachydysrhythmias
- increased BP
- increased intragastric pressure
- increased cerebral blood flow
- increased intracranial pressure
- increased intraocular pressure
What are the absolute and relative contraindications to ECT?
Absolute Contraindications:
- recent MI (<4-6 months)
- recent intracranial surgery (<3 months)
- recent stroke (<3 months)
- brain tumor
- unstable cervical spine
- pheochromocytoma
Relative Contraindication:
- pregnancy
- pacemaker/ICD
- CHF
- glaucoma
- retinal detachment
- severe pulmonary disease
*related to an increased SNS response or increased ICP
What is neuroleptic malignant syndrome? Compare it to malignant hyperthermia
Neuroleptic Malignant Syndrome (NMS):
-caused by dopamine depletion in the basal ganglia and hypothalamus from dopamine antagonists or withdrawal from dopamine agonists
-treatment: bromocriptine, dantrolene, supportive care, ECT
Compare to MH:
-NMS = no genetic link –> MH = genetic link
-NMS = Does not develop acutely –> MH = develops acutely
-NMS = associated w/ Psychiatric Med –> MH = not associated
-Both have muscle rigidity, hyperthermia, tachycardia, acidosis
-Treat both w/ dantrolene
-NMS = neuromuscular blockers cause paralysis –> MH = they do not cause paralysis (cause of rigidity is beyond the NMJ)
What is the etiology of serotonin syndrome? What drug interactions with SSRIs increase the risk of developing it?
Occurs when there’s excess 5-HT activity in the CNS
Key drug interactions that increase the risk of serotonin syndrome include an SSRI and:
-Meperidine
-Fentanyl
-Methylene blue
What are the determinants of intraocular pressure? What’s the normal value?
Intraocular Perfusion Pressure = MAP - IOP
-the globe is relatively non-compliant –> IOP is determined by the choroidal blood volume, aqueous fluid volume, and extraocular muscle tone
-Normal IOP = 10-20 mmHg
-aqueous humor is produced by the ciliary process (posterior chamber)
-aqueous humor is reabsorbed by the canal of Schlemm (anterior chamber)
What factors increase intraocular pressure?
-hypercarbia
-hypoxemia
-increased CVP
-increased MAP
-laryngoscopy/intubation
-straining/coughing
-SUX
-N2O (if SF6 bubble in place)
-trendelenburg and prone position
-external compression by facemask
What factors decrease intraocular pressure?
-hypocarbia
-decreased CVP
-decreased MAP
-volatile anesthetics
-N2O
-NDMRs
-propofol
-opioids
-benzos
-hypothermia
What is the difference between open and closed angle glaucoma?
Open-Angle: caused by sclerosis of the trabecular meshwork – impairs aqueous humor drainage
Close-Angle: caused by a closure of the anterior chamber – creates a mechanical outflow obstruction
*Glaucoma is caused by a chronically elevated IOP that leads to retinal artery compression
*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?
Decrease Aqueous Humor Production:
- Acetazolamide (inhibits carbonic anhydrase)
- Timolol (non-selective beta antagonist)
Facilitate Aqueous Humor Drainage:
- Echothiophate (irreversible cholinesterase inhibitor) – promotes drainage via the canal of Schlemm
*can prolong the duration of SUX and ester-type local anesthetics
What is strabismus correction? What unique considerations apply to the anesthetic management of these patients?
Corrects the misalignment of the extraocular muscles and re-establish the visual axis
Key Considerations:
-increased risk of PONV
-increased risk of activating the oculo-cardiac reflex (afferent CN 5 + efferent CN 10)
What is a TAP block? Which patient populations benefit from one?
Transverse Abdominal Plane Block (TAP): unilateral peripheral nerve block that targets the nerves of the anterior and lateral abdominal wall
-best suited for abdominal procedures (general, GYN, and URO) that involve the T9-L1 distribution
-bilateral TAP blocks are required for a midline incision or laparoscopic surgery
Explain the “chemo man”
