Page 77 - JSOM Winter 2021

Following the test, it is important to actively reduce this value anesthesia machine manufacturers recommend not using a
for mechanical ventilation. fresh gas flow <20% of the minute volume of the patient or
<1L/min. 6–11 When ventilating patients with increased CO
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Gas measurements should be connected and utilized. 6–11 Un- production (i.e., those with high metabolic demands), we
like many ICU ventilators, gas measurement of most anesthe- recommend a marked increase in the fresh gas flow (e.g., to
sia machines uses SideStream technology (Philips). Therefore, >50% of the minute volume).
the gas measurement values and waveforms often are delayed
by several seconds. Some manufacturers recommend hose systems with water
traps in the inspiratory and expiratory limb; longer hoses are
In the event of oxygen shortages, the use of concentrated oxy- preferred, as is the removal of the inspiratory port filter of the
gen (“O 93”) can be used with some anesthesia machines. 6–11 breathing system as well as the use of a mechanical filter with
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Considerations include ensuring that the fresh gas flow equals a heat and moisture exchange filter (HMEF) at the Y-piece.
at least the minute volume of the patient (to prevent argon Check the following parts for humidity regularly (at least ev-
accumulation) (Table 2). Also, the Fio low-alarm limit must ery 4 hours during prolonged use): water traps in patient hoses
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be set to an appropriate value, considering enough buffer should be drained when condensation is detected; the water
for reaction of the user, because overload of an oxygen con- trap at the gas bench should be drained when >50% is filled
centrator may result in a lower oxygen concentration of the with condensate; the filter should be exchanged if increased
provided supply gas. Some accuracy values required by the condensation is detected; the CO absorber should be ex-
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anesthesia machine console may not be fully achieved—for changed when two thirds of it has changed its color to purple
example, patient flow measurement, fresh gas flow, and fresh to reduce condensation in the breathing system (noting that
gas concentration. consumption of the CO absorber will increase significantly
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when lowering the fresh gas flow). Filters may get clogged and
TABLE 2 Key Considerations when Ventilating Patients Utilizing have to be exchanged earlier; therefore, we recommend setting
Anesthesia Machines close alarm limits for minute volume low and P high limits.
aw
• Alarm settings and volumes must be adjusted and increased to An alarm limit for low Fio should be set with an adequate
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ensure their notice in the nonoperative setting. Alarms must be buffer because the difference between the set fresh gas flow
reviewed at each bedside clinical encounter with the machine to and the Fio will result in delayed recognition. The system will
ensure continued safety of ongoing ventilation. react far slower to modifications of the O setting. We like-
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• Fresh gas flow rates must be increased beyond the delivered wise recommend setting an alarm limit for high inspiratory
minute ventilation. Failure to do so will result in unnoticed
hypoxemia, rebreathing, and respiratory acidosis. CO to an appropriate value (default settings may need to be
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• Anesthesia machine self-tests may need to be performed every changed).
24 hours. Self-testing requires circuit disconnect and the ability
to provide ongoing ventilation to the patient for the duration of
the self-test. Suction Management
• Anesthesia machines fail to compensate for circuit leaks. In Negative pressures by suctioning can harm the lung of the pa-
patients with circuit leak, early transition to Pressure Control tient and impair the function of the anesthesia machine and
mode of ventilation may be lifesaving. may lead to failures of the ventilation system via external re-
• Anesthesia machines fail to accommodate for closed circuit moval of inspiratory gas flows and collapse of the inspiratory
suctioning. High suction levels will lead to atelectasis and
inadequate minute ventilation. Suction should be set at the gas flow reservoirs. Therefore, we recommend reduction of
lowest level tolerable while still maintaining adequate airways the suction provided by the system. If in doubt, and if patients
clearance. can tolerate the derecruitment associated with the circuit, dis-
connect the anesthesia machine for endotracheal suctioning
(consider the loss of PEEP). Alternatively, by disconnecting
Carbon Dioxide Management
the manual breathing bag, one can ensure that the bag won’t
The anesthesia machine should not be operated without a CO collapse because of the suctioning. By this measure, the po-
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absorber, except when changing a used absorber. The perma- tential of negative pressures in the system is reduced. Special
nent use of a CO absorber ensures that the patient does not attention is needed for the fact that, after the suctioning, the
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inhale CO even in the case of error, such as problems with manual breathing bag must be reconnected by the user. 6–11
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the fresh gas supply and/or delivery. For anesthesia machines
with high fresh gas flows of at least 150% of the minute vol-
ume of the patient, there will be only limited rebreathing and, Filter Management
therefore, the absorber will provide long-term functionality. We strongly recommend the use of mechanical filters for long-
Nevertheless, most anesthesia machine manufacturers recom- term ventilation. With electrostatic filters, the filtering perfor-
mend that the absorber be changed every 7 days, regardless of mance is reduced with humidity. The use of mechanical filters
whether the absorption capacity has been spent. 6–11 also ensures that the excess gas—gas leaving the circuit when
the handbag is detached—will not be contaminated. Regard-
Regarding breathing circuit, humidity, and filter management, ing filter use with anesthesia machines, the APSF recommends
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if reduced fresh gas flows are used (e.g., due to shortage of that a HMEF be placed at the endotracheal tube connection
supplied gases or the need for increased humidity of the pa- to the breathing circuit, and a second HMEF or filter placed
tient gas), increased patient rebreathing will take place, and on the expiratory hose at the connection to the anesthesia
condensation may compromise the system functionality (even- machine. Use of an airway HMEF is intended to preserve
tually resulting in system malfunction); the consumption of humidity in the lungs during long-term ventilation. HMEFs
soda lime will increase, and condensation may block filters may contribute to a humidity problem and frequent clogging
in the patient circuit (notably at the inspiratory port). Some because they are inherently designed to hold moisture. Viral

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