How Flow Can You Go
Which statement about the production of compound A during sevoflurane anesthesia is MOST likely true?
a. It is produced by metabolism of sevoflurane in the liver.
b. It results in increased serum creatinine levels.
c. Low fresh gas flow rates (<2 L/min) are associated with increased levels of the compound.
d. Compound A production is unaffected by the type of CO2 absorbent used.
C. Low fresh gas flow rates (<2 L/min) are associated with increased levels of the compound.
Which statement about the Pin Index Safety System is MOST likely true?
a. It prevents turning on two vaporizers at the same time.
b. It prevents interchanging the connections for different gases from the wall outlet to the anesthesia machine.
c. It is designed to prevent administration of an hypoxic gas mixture.
d. It couples the nitrous oxide and oxygen flowmeters.
c. It is designed to prevent administration of a hypoxic gas mixture.
The vapor pressure of a volatile anesthetic depends on
a. temperature only
b. ambient pressure only
c. temperature and ambient pressure
d. pressure and volume of the system
e. none of the above
a. temperature only
This is the Mapleson Circuit most efficient (ie requires lowest fresh gas flow rate) in preventing rebreathing during controlled ventilation.
Mapleson D
A patient whose trachea is intubated develops partial airway obstruction two hours after induction of fentanyl, nitrous oxide, oxygen anesthesia. The anesthesiologist discontinues the nitrous oxide and controls ventilation, and there is gradual improvement during the next hour. No evidence of a respiratory disorder is found at the conclusion of the anesthetic. Which of the following is most likely?
a. The endotracheal tube was in the right mainstem bronchus
b. The patient had an unrecognized air embolism
c. The patient had a nitrous oxide pneumothorax
d. The endotracheal tube cuff narrowed the airway
e. The fentanyl induced chest rigidity
d. The endotracheal tube cuff narrowed the airway
Which gas flowmeter is always positioned furthest to the right, and WHY?
Oxygen
Which statement about the oxygen fail-safe valve is MOST likely true?
a. The valve is controlled by oxygen supply pressure
b. It is present in the gas line supplying the oxygen flowmeter
c. The valve mechanism is standardized for all anesthesia machines.
d. It prevents administration of a hypoxic mixture of gases.
a. The valve is controlled by oxygen supply pressure
This gas has the highest vapor pressure of the modern volatile inhaled anesthetics.
What is Desflurane?
TRUE regarding Descending Bellow ventilators on an anesthesia machine…
a. Descend during inspiratory phase
b. Will continue to move up and down even if circuit disconnects
b. Will reliably activate low airway pressure alarm during circuit disconnect
c. Are safer than ascending bellow ventilators
d. Direction of the bellows movement on expiration determines the classification.
b. Will continue to move up and down even if circuit disconnects
A healthy, 18-year-old, 65-kg woman undergoing diagnostic laparoscopy is being monitored with a properly functioning and calibrated capnograph. The end-tidal carbon dioxide concentration is 6%, and the inspired carbon dioxide concentration is 1%. This may be caused by each of the following EXCEPT
a. malfunction of the expiratory valve in a circle system
b. low gas inflow with a Bain circuit
c. exhausted soda lime within a circle system
d. absorption of carbon dioxide from carbon dioxide laparoscopy
e. carbon dioxide in the fresh gas flow
d. absorption of carbon dioxide from carbon dioxide laparoscopy
What steps can you take to reduce polluting the operating room (and subsequently the atmosphere) with anesthetic gas gas?
-Low flow anesthesia
-Pause gas flow during intubation
-If no 'pause gas flow' button, turn off the total gas flow and NOT the agent
-Turn flows down soon after intubation
-When changing concentration of inhaled agent, turn up percentage of gas rather than total gas flow
-Use less impactful agents (sevoflurane, isoflurane); avoid desflurane (always) and nitrous oxide (mostly)
-BIS/TIVA to minimize inhaled agents
-Etc.
During general anesthesia using a modern anesthesia machine, a patient's spontaneous ventilation is manually assisted with a fresh gas flow of 5 L/min. A sudden malfunction of the pressure-relief (pop-off) valve of the circle absorption system occurs, and the valve cannot be opened. The most appropriate next step is to
a. change to a smaller reservoir bag
b. increase total fresh gas flow
c. open the scavenger valve
d. control ventilation manually
e. switch to mechanical ventilatory mode
e. switch to mechanical ventilatory mode
A sevoflurane vaporizer is filled with isoflurane and the vaporizer dial is set at 1%. What will happen?
Overdose
More than 1% isoflurane will be delivered
A waste-gas scavenger has an active disposal system. Which of the following safety features is necessary to prevent removal of excess gas from the breathing circuit?
a. Positive-pressure relief mechanism
b. Negative-pressure relief mechanism
c. Low-volume scavenging reservoir
d. High-volume scavenging reservoir
e. Maximum vacuum flow rate of 5 L/min
b. Negative-pressure relief mechanism
Your patient has recently had a vitrectomy for retinal detachment repair. Which of the following statements regarding nitrous and recent intraocular surgery is TRUE?
a. It is safe to use nitrous 10 minutes prior to intraocular gas
b. It is safe to use nitrous 7 days after the patient received a filtered room air bubble
c. It is safe to use nitrous 7 days after the patient received a sulfur hexafluoride bubble
d. It is safe to use nitrous 7 days after the patient received a perfluoropropane bubble
b. It is safe to use nitrous 7 days after the patient received a filtered room air bubble
This is approximately the minimum oxygen flow needed for a 70kg male under general endotracheal anesthesia.
5ml/kg/min = 350 mL/min (generally accepted minimal O2 consumption under anesthesia)
-Add ~100ml/min more for leaks, and ~200ml/min for CO2 analyzer, bringing total to around .6-.7L/min of 100% O2 flow
Our modern anesthesia machines use this type of circuit.
What is a semiclosed circle system?
Rank these anesthetics in order of CO production in presence of dry CO2 absorbent, from MOST to Least:
Desflurane, Isoflurane, Sevoflurane
*Include Enflurane and Halothane for double points*
desflurane > enflurane > isoflurane > sevoflurane > halothane
During use of the ventilator on an anesthesia machine, positive pressure is noted on the airway pressure gauge during exhalation. Positive end-expiratory pressure has not been purposefully added to the breathing circuit. Which of the following is the most likely cause?
a. Closure of the pop-off valve in the circle system
b. Excessive tidal volume settings on the ventilator
c. Obstruction of the pressure relief valve on the scavenging system
d. Over inflation of the endotracheal tube balloon
e. Tension pneumothorax
c. Obstruction of the pressure relief valve on the scavenging system
To achieve 1 MAC of Sevoflurane in a hyperbaric chamber, you must dial in this value.
~0.6%
Oxygen 100 ml/min is bubbled through a vaporizer containing an anesthetic with a vapor pressure of 150 mmHg, and this mixture is added to a fresh gas flow of 5 L/min. The delivered anesthetic concentration is
a. 0.25%
b. 0.5%
c. 1%
d. 2.5%
e. 5%
b. 0.5%
SVP/atmP= x/(x + carrier ml)
SVP/atmP=150/760=
=x/(x+100ml), solve for x (which is anes in mL)
=~25ml of gas
25mL/5000mlx100= gas percent of total flow =0.5%
During general anesthesia administered through a circle system, the soda lime absorbent is exhausted. No fresh soda lime is available for use. Which of the following is the most appropriate next step to prevent hypercapnia in this patient?
a. Decreasing the dead space of the circle system
b. Discontinuing nitrous oxide
c. Increasing the fresh gas flow
d. Increasing tidal volume
e. Switching to spontaneous ventilation
c. Increasing the fresh gas flow
Which of the following is the most appropriate action after an anesthetic vaporizer is tipped?
*Extra points to explain why tipping of vaporizer can be bad*
a. Return to the manufacturer for recalibration
b. Flush the vaporizer with oxygen at 5 L/min for 24 hours
c. Store the vaporizer for 24 hours at room temperature
d. Set the vaporizer at low concentration and flush with oxygen at 10 L/min for 30 minutes
d. Set the vaporizer at low concentration and flush with oxygen at 10 L/min for 30 minutes
Tipping may flood the bypass area and lead to dangerously high anesthetic concentrations because liquid anesthetic is much more potent (1ml liquid sevo produces 184ml vapor!)
What is the second gas effect?
Our desflurane usage equates to this many miles driven in one year
(based on CO2 equivalent; data from 2019; OU and TCH)