Flashcards in Monitors Deck (52)
What are the best places to measure core temperature?
Nasopharynx, tympanic membrane, distal portion of esophagus, or pulmonary artery (via PA catheter)
What is the body's natural core temperature and what range does it regulate itself?
37 C; it regulates within +/- 0.1 C
At what temperature does shivering occur?
A full degree Celsius lower than the vasoconstrictive threshold (which is 36.9 C)
What is true about shivering and the elderly?
They rarely shiver because of their reduced ability for thermoregulatory control
What is the first phase of intraoperative hypothermia?
Redistribution of heat from core to the periphery
What contributes most to the loss of heat in a patient during an operation?
Radiation (transfer of heat from one surface to another via photons - not dependent on temperature differences)
~60% of heat loss
If you have a transection at C7, which of the following would you expect if it has been 1 hour since the accident: risk of hyperkalemia with succinylcholine, risk of autonomic hyperreflexia with foley insertion, need for FOI, increased risk of hypothermia, all of the above
Increase risk of hypothermia below the level of the injury because they lack thermoregulation there
Hyperkalemia after 24 hours
Too fast for autonomic hyperreflexia
How does MAP and SBP differ in the aorta vs. radial artery?
Aorta will have a higher MAP and lower SBP; MAP decreases as pressure wave travels distally (slightly), SBP increases
What factors in an A-line setup can cause overdampening?
Increased length of tubing, decreased stiffness of tubing, multiple cockstops, clots, kinks, and air bubbles (all of which decrease the natural frequency of the system)
What is a good way to prevent an arterial artery thrombosis: propylene catheters, shorter catheter, Allen's test before, larger-gauged catheter, leaving the catheter in for a longer period of time
Larger-gauged (smaller) catheter
How do you adjust for blood pressure if the cuff is above the heart?
For every 1 cm above the heart, increase 0.7 mmHg
When should you be careful about using a PA catheter?
Patients with LBBB since PA catheters can cause RBBB -> complete heart block
What do you suspect if the SaO2 is 92% and the blood looks cherry red?
Carbon monoxide poisoning
Does the Bispectral index scale reduce the incidence of awareness under GA?
What is the neural path for SSEPs?
Peripheral nerve -> dorsal columns of the spinal cord -> sensory cortex
How does etomidate affect SSEPs?
Increases latencies and increases amplitudes
How does propofol affect SSEPs?
Increases latency and minimal effect on amplitudes
To prevent phase I hypothermia during GA, which is more effective: pre-warming the patient with forced air convection or infusing 1L of warmed saline?
Pre-warming the patient with forced air convection
How should you measure core temperature in a patient undergoing a CABG?
Tympanic membrane (esophageal temp is affected by ice in the thorax and pulmonary artery temp will have no flow while on pump)
What situations could you have a falsely low estimation of SpO2?
Severe TR, IABP, or high pressure ventilation (anything that can cause venous pulsations which get mistaken for arterial pulsation by the pulse ox)
How does ambient light affect pulse ox readings?
Falsely increases them
How would the ToF reading compare after non-depolarizing NMB in a patient who is paraplegic?
They have an exaggerated response compared to a normal person; possibly from an increase in extrajunctional ACh receptors and resistance to non-depolarizing NBM
What nerve stimulation pattern best estimates complete reversal of neuromuscular blockade?
Absence of fade on tetanic stimulation at 100 Hz for 5 seconds (66% effective)
What percentage of nicotinic receptors are occupied if a single twitch height is reduced?
What percentage of nicotinic receptors are occupied if the 4th twitch of a ToF is missing?
What do you see on capnography with an incompetent inspiratory valve? Expiratory valve?
Inspiratory: prolonged inspiration given the leak in the valve
Expiratory: Failure of expiration to return to 0 (rebreathing)
What is the normal gradient between PaCO2 and ETCO2 and why does it occur?
Alveolar dead space (ventilated but not perfused)
What would decreased pulmonary blood flow do to the gradient between PaCO2 and EtCO2? Increased CO?
1. Increases the gradient (more V/Q mismatch)
2. Decreases gradient (decreased alveolar dead space and thus V/Q mismatch)
What limbs does lead I display? Lead II? Lead III?
I: Left arm and right arm
II: Left arm and left leg
III: Right arm and left leg
What pressure does a full tank of N2O read? How much N2O is a full tank?
What safety measure is in place to prevent inappropriate wall attachments to the machine?
DISS (diameter index safety system)
Which of the following would least likely cause rebreathing of CO2: channeling, TV slightly larger than volume of air between CO2 absorbent granules, malfunction of inspiratory valve, malfunction of expiratory valve, inspiratory limb leak
Inspiratory limb leak
Channeling is when gas makes it through the CO2 absorbent granules without being touched
At what minimum gas flow rate would a CO2 absorbent be unnecessary to prevent rebreathing of CO2?
At what point does total dead space begin in the circuit?
At the Y-piece; proximal to the Y-piece, the fresh gas flow is continually cycles so it is not part of the volume rebreathed
What safety features prevent delivery of a hypoxic mixture of gas?
1. Diameter index safety system (DISS)
2. O2 supply failure alarm (if O2 pressures fall)
3. Fail-safe mechanism (doesn't allow N2O to be delivered if O2 pressure is low)
4. O2 is the most downstream channel
5. Flowmeter proportioning system (mechanism set that delivers N2O and O2 in a ratio)
6. Oxygen monitor and alarm
What is the difference between a Clark electrode oxygen analyzer vs. a paramagnetic oxygen analyzer?
1. Clark has electrodes in gel so it needs to be changed over time
2. Moisture hastens Clark electrode consumption
3. Paramagnetics are more expensive but have a faster response time and is self-calibrating
What is ventilator-fresh gas flow coupling?
When you get slightly higher TV on the ventilator (compared to what is set) due to high fresh gas flows
What is a microshock?
When 10-100 micro-amps is directly applied to the heart to cause V. Fib
Where should the dispersion pads be placed when using a Bovie?
Furthest away from the heart
What happens in the anesthetic machine if the ambient temperature increases?
More of the volatile anesthetic is in the vapor phase -> the machine decreases the amount of flow to the vaporizing chamber and more flow to the bypass chamber (by decreasing resistance to the bypass chamber - automatic variable bypass system) -> allows for the same amount of gas to be delivered
Why does desflurane require a special vaporizer?
1. High vapor pressure (669 mmHg) -> requires a pressurized vaporizer (to 2 atm)
2. Boils at just above room temp (22.8C)
3. High MAC with comparable latent heat of vaporization (heat required to form a vapor from liquid) -> will cool quickly so requires a heated vaporizer
What happens to the partial pressure of desflurane at higher altitudes?
It decreases since the vaporizer that it is in is set to 2 atm due to its high vapor pressure (669 mmHg) -> elevation decreases the ambient pressure causing a decrease in the partial pressure (different from the other volatile anesthetics because they have different vaporizers that respond to ambient pressures -> will increase partial pressure)
What is the time constant for an anesthesia circuit?
Time constant = volume of circuit / fresh gas flow
How many time constants need to pass before 95% concentration change?
3 time constants
What gas is present in a grey e-cylinder? Brown?
How much NO2 is left when you have a drop in pressure shown on the E-cylinder?
20% (so approximately 20% of 1600 L = 320 L)
What law explains why the pressure in an O2 cylinder is proportional to the volume of gas in the cylinder?
How do pressure regulators work in the anesthetic machines?
Primary pipeline pressure from hospital @ 55 psi -> first-stage regulator -> 45 psi -> second stage regulator -> 14 psi for O2 and 26 psi for N2O
What happens to the amount of volatile anesthetic delivered with changing temperatures in modern variable bypass vaporizers?
The temp-sensing element adjusts gas inflow into the vaporizer chamber as temperature of the liquid anesthetic changes (warmer = more in bypass chamber, less in vaporizer chamber and vice versa)
What happens to desflurane vaporizer outputs when N2O is introduced?
Decreases output because N2O has lower viscosity than O2 (desflurane is calibrated with 100% O2 carrier gas)
Order the following based on how much they are affected by volatile anesthetics: SSEP, MEPs, VEP (visual evoked potentials), BAEP (brainstem auditory evoked potentials)
Least affected -> BAEP, SSEP, MEP, VEP