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
