Physics, Monitoring, & Equipment Flashcards
Which Mapleson system requires a fresh gas flow equal to minor ventilation to prevent rebreathing during spontaneous ventilation?
Mapleson A system
What does the flow proportioning system on an anesthesia machine do?
It maintains a minimum ratio of oxygen to nitrous oxide in fresh gas flow
In which Mapleson system is carbon dioxide removed effectively during controlled ventilation vs. during spontaneous ventilation?
For controlled ventilation: Mapleson D
(“Dog Bites Can Ache” is the pneumonic for controlled breathing)
For spontaneous breathing: Mapleson A
(“All Dogs Can Bite” is the pneumonic for spontaneous breathing)
How does dead space differ in a circle system vs. non-rebreathing systems?
There is no difference
Why must oxygen be administered to anyone in the scanner room during a quench of an MRI machine?
Liquid cryogens that cool the magnet coils boil off quickly, which results in helium escaping very rapidly from the cryogen bath. Therefore, anyone in the MRI suite is at risk for asphyxial injury.
What pathologies will lead to an elevated peak inspiratory pressure (PIP), but an unchanged plateau pressure (PP)?
This signals an increase in airway resistance or inspiratory gas flow rate seen in:
Bronchospasm Kinked endotracheal tube Foreign body aspiration Airway compression Endotracheal tube cuff herniation
What pathologies will lead to an increase in both peak inspiratory pressure (PIP) and plateau pressure (PP)?
This implies an increase in tidal volume (TV) or a decrease in pulmonary compliance seen in:
Pulmonary edema Pleural effusion Ascites Peritoneal gas insufflation Tension pneumothorax Endobronchial intubation ARDS
What pathology would lead to an underestimation of the LVEDP by a PA catheter?
Decreased left ventricular compliance
What is the Venturi effect?
It creates a vacuum (when a gas passes quickly through a narrow space and lowers pressure nearby), which helps deliver more oxygen with each puff of the jet ventilator
A size “E” nitrous oxide (N2O) cylinder contains what volume when the pressure starts dropping below 750 psi?
The pressure in the cylinder drops when there is no liquid left or there are 400 liters of nitrous oxide gas left (the cylinder is 1/4 full at this point).
Full tank is 1600 L
What circuit is the Pethick test used to test the integrity of?
The Bain circuit
The unique hazard of this circuit is occult disconnection or kinking of the inner, fresh gas delivery hose. If this occurs, the entire corrugated limb becomes dead space.
The Pethick text is done by occluding the patient’s end of the circuit (at the elbow) and closing the APL valve. The circuit is then filled using the oxygen flush valve. The occlusion is released and the flush pressed. Venturi effect flattens the reservoir bag if the inner tube is patent.
Pacemaker Position Functions (1-5)
Position 1: Paced Position 2: Sensed Position 3: Response to sensing Position 4: Programmability Position 5: Multisite Pacing
Pacers should not have intrinsic rates below 50 and generally indicate pacer malfunction
What are the major disadvantages of Mapleson breathing circuits in comparison to circle systems?
Mapleson circutis do NOT control anesthetic depth as well due to the high fresh gas flows they employ.
They also waste anesthetic agent due to their inability to scavenge effectively and pollute the OR environment.
Loss of patient heat and humidity
Boyle’s Law
For a fixed mass of gas at constant temperature, the product of pressure and volume is constant.
Used to calculate the volume of gas remaining in a cylinder by measuring the pressure
Relative contraindications for placing pulmonary artery catheters?
LBBB Wolf Parkinson White (WPW) syndrome Ebstein's malformation Sepsis Coagulation disorders
Describe the waves and downward descents of a central venous tracing and how they correspond to ECG waveforms
- a wave: atrial contraction (absent in afib); occurs right after the p wave on ECG
- c wave: tricuspid valve elevation during EARLY VENTRICULAR CONTRACTION; occurs right after the QRS complex on the ECG
- x descent: downward displacement of the tricuspid valve during systole (atrial relaxation) as the pulmonic valve opens; occurs during the t-wave on the ECG
- v wave: VENOUS RETURN against a closed tricuspid valve; occurs directly after the t-wave on the ECG
- y descent: TRICUSPID VALVE OPENING during diastole; occurs before the p-wave but not right after the t-wave on the ECG
How to determine the amount of time a vaporizer (filled with a volatile anesthetic) would be able to deliver a set % of volatile anesthetic at a certain rate (L/min)
Need to know vapor pressures (liquid at 20 degrees Celsius) of volatile anesthetics: Desflurane: 669 Halothane: 243 Isoflurane: 238 Enflurane: 172 Sevoflurane: 157
[Each mL of most volatiles will yield 200 mL vapor at 20 degrees Celsius. Therefore 100 mL of liquid yields 20,000 mL of gas.]
If delivering 2% of isoflurane with a rate of 4 L/min…
In one minute, 2/100 of 4,000 ml is used = 80 mL of gas delivered per minute…
20,000 mL / (80 mL/min) = 250 mins = 4.2 hrs.
What does the color purple on the carbon dioxide colorimetric device indicate?
A color of purple indicates that the end-tidal carbon dioxide % is LESS than 0.4%, and most possibly the tube is NOT in situ or that CPR is not successful
What does the tan color on the carbon dioxide colorimetric device indicate?
A tan color indicates that the percentage of CO2 is 0.4% to 2% and that the tube IS in situ BUT that the cardiac output is low or that the CPR is inadequate.
What does the color yellow on the carbon dioxide colorimetric device indicate?
A color change of yellow would indicate that the tube IS in situ and that there is adequate lung perfusion/adequate CPR.
What is the protocol for managing a Drager vaporizer that was tipped over?
It is recommended to flush the vaporizer at high flows with the vaporizer set at a low concentration until the output shows no excessive agent (this usually takes 20-30 minutes.)
What check system prevents cross-flow from pipelines to cylinders?
The Check Valve
What is the “square root sign” on a CVP waveform, indicative of?
a.k.a. “the dip and plateau sign”
Rapid early ventricular filling followed by a abrupt plateau or slowing of the filling due to the restrictive effect posed by the pericardium
There is a sharp Y descent followed by a plateau
Indicative of Constrictive Pericarditis
How to calculate how much time you have left before your E-cylinder O2 tank is empty
1) Current Gas Volume = Full Volume (625 L) x [Current Tank Pressure / Full Tank Pressure (2000 psi)]
OR
V2 = V1 x [P2/P1]
2) Time Left =
Current Gas Volume / Flow Rate
Dependency of Laminar flow vs. Turbulent air flow
Laminar Air Flow is dependent on gas viscosity (inversely proportional to r4)
vs.
Turbulent Air Flow, which is dependent on gas density (inversely proportional to r5)
What component is found in ALL CO2 absorbents?
Ca(OH)2
Very high fresh gas flow rates will have what effect on vaporizer output of inhaled anesthetics? vs. Very low FGF? Why?
The output will decrease for both very high and very low FGF.
For high flows, the output decreases due to incomplete mixing
For low flows, the output decreases due to insufficient upward mobilization of the vapor molecules
How does the use of N2O in fresh gas flow affect vaporizer output?
N2O DECREASES vapor output (because some of the gas that goes into the vaporizer, becomes soluble in the volatile liquid gas)
At high altitudes, what is the most appropriate management when trying to achieve 1 MAC of isoflurane vs. 1 MAC of desflurane anesthesia? Why?
With Desflurane (Tec 6 vaporizer), the concentration dial should be set higher than 1 MAC (the system is closed to the atmosphere)
However, with variable bypass vaporizers such as isoflurane is contained, you DO NOT have to change the settings.
What method is most commonly used to detect CO2 in the OR?
Infrared absorption (used to detect CO2, N2O, and potent inhaled anesthetic agents; NOT O2).
Based on the Beer-Lambert Law
What method of gas measurement can measure ALL types of gas?
Raman scattering
- photons generated by a high-intensity argon laser collide with gas molecules
“Cannon a waves” on a CVP tracing are indicative of?
AV dissociation or Tricuspid Stenosis
What abnormalities would you see on a CVP tracing in a patient with Tricuspid regurgitation?
Tall C-V wave and NO X descent
What conditions will yield a CVP tracing with “tall A and V waves with a M or W configuration?
RV ischemia or Pericarditis
How is wall thickness proportional to afterload?
Wall thickness is inversely proportional to after load
(The thicker the LV wall thickness, the easier it is to push out the flow (lower afterload).
What is the equation for pulmonary vascular resistance (PVR)?
Pressure divided by flow (CO)
80 x [(PAP - PCWP)/ CO]
Compared to central venous catheters, peripherally inserted arterial catheters have what rate of bacterial colonization?
Equal rate
Which mechanism of heat transfer MOST accounts for heat loss perioperatively?
Radiation
Describe the mechanisms of heat loss
1) Conduction: the transfer of heat from one solid object to another solid object that is in direct contact with it
2) Convection: transfer of heat from a solid object to the atmosphere or a gas
3) Evaporation: turning from a liquid or solid state to a vapor; to give off moisture
4) Radiation: energy emitted as particles/waves/photons
How does phenylephrine effect the P-V loop?
Phenylephrine will increase the pressure and volume slightly (NO decrease in volume)
How does nitroglycerin effect the P-V loop?
Nitroglycerin will veno-dialate and cause a decrease in pressure and volume (decreases preload)
Which type of shock requires less energy? Monophasic or biphasic
Biphasic shock requires less energy than monphasic
On a TOF stimulation, what percentage of receptors are occupied (amount of paralysis) with 1, 2, and 3 twitches present?
1 twitch = 90% paralysis
2 twitches = 80 % paralysis
3 twitches = 75% paralysis
What is the TOF ratio required for safe extubation?
A TOF ratio of 0.9 to 1
What measurement of recovery from neuromuscular block are equivalent to a train of four (TOF) ratio of ~ 0.6?
- A head lift sustained for more than 5 seconds
- A DBS showing no fade
- A spontaneous tidal volume > 3-5 mL/kg
What is a great stimulation test to check recovery from neuromuscular blockade?
No fade on 100 Hz tetanus testing
- the probability of detecting adequate reversal with a DBS test showing no fade is 11%, but is 66% with a 100 Hz tetanus test showing no fade
MAC is greater at what age group?
MAC is greatest at 6 months of age (and drops off by 6% per decade of life, flattening out at about 50% in the elderly
Describe pH-stat vs. alpha-stat ABG assessment
During hypothermia, the solubility of CO2 in blood increases and for a given concentration of carbon dioxide in blood, PCO2 decreases and the blood becomes alkalotic
In pH-stat management: to compensate for increased CO2 solubility, CO2 is ADDED to the gas mixture in the oxygenator to maintain the hypothermic pH at 7.4 and the PCO2 at 40 mmHg
*patient’s are at a greater risk for post-op cognitive dysfunction when CPB duration is > 90 mins
In alpha-stat management: the patient’s pH is maintained at a constant level by managing pH at the patient’s temperature.
- this method allows blood pH to increase during cooling
- the patient’s temperature is neither corrected nor reported to the lab
What are the advantages vs. disadvantages of the closed-circuit?
Advantages:
- conserves heat and humidity
- reduces pollution by decreasing the amount of waste
- lowers the cost of volatile anesthetic since flow rates are used
Disadvantages:
- requires a high level of vigilance to maintain proper anesthetic dose and to avoid hypoxia and hypercapnia
- special equipment may also be required as some ventilators have safety features that do not allow delivery of low gas flows.
- does NOT allow for quick adjustment of anesthetic concentration
What twitch monitoring setting is best for determining adequate reversal of NM blockade?
100 Hz Tetanus showing no fade
over DBS test with no fade
What is a possible complication of using a CPB roller pump?
Flow is predictable and depends on the revolutions per minute of the pump.
*retrograde flow is NOT possible
If there is outflow occlusion to the pump, excessive pressure can build, causing the tubing to rupture or the tubing connections to separate.
In which type of CPB pump is retrograde flow possible?
It is possible with the Centrifugal pump
Using the Stewart approach to acid-base, what are the only 3 mathematically independent variable on which pH depends?
1) the strong ion difference (SID) (sum of sodium, potassium, magnesium, calcium, chloride, and lactate)
2) the total weak acid concentration (phosphate and albumin)
3) pCO2
(Does NOT include HCO3-)
