- Misuse of anesthesia gas delivery equipment
is three times more common than equipment failure in causing equipment-related
adverse outcomes. Lack of familiarity with the equipment and a failure
to check machine function are the most frequent causes. These mishaps
account for only about 2% of cases in the ASA Closed Claims Project
database. The breathing circuit was the most common single source
of injury (39%); nearly all incidents were related to misconnects
- The anesthesia machine receives medical gases from
a gas supply; controls the flow of desired gases reducing their
pressure, when necessary, to a safe level; vaporizes volatile anesthetics
into the final gas mixture; and delivers the gases to a breathing
circuit that is connected to the patient’s airway. A mechanical
ventilator attaches to the breathing circuit but can be excluded
with a switch during spontaneous or manual (bag) ventilation.
- Whereas the oxygen supply can pass directly to its
flow control valve, nitrous oxide, air, and other gases must first
pass through safety devices before reaching their respective flow
control valves. These devices permit the flow of other gases only
if there is sufficient oxygen pressure in the safety device and
help prevent accidental delivery of a hypoxic mixture in the event
of oxygen supply failure.
- Another safety feature of anesthesia machines
is linkage of the nitrous oxide gas flow to the oxygen gas flow;
this arrangement helps ensure a minimum oxygen concentration of
- All modern vaporizers are agent specific, capable of
delivering a constant concentration of agent regardless of temperature
changes or flow through the vaporizer.
- A rise in airway pressure may signal worsening pulmonary
compliance, an increase in tidal volume, or an obstruction in the
breathing circuit, tracheal tube, or the patient’s airway.
A drop in pressure may indicate an improvement in compliance, a
decrease in tidal volume, or a leak in the circuit.
- Traditionally ventilators on anesthesia machines have
a double circuit system design and are pneumatically powered and
electronically controlled. Newer machines also incorporate microprocessor
control, which relies on sophisticated pressure and flow sensors.
Some models offer anesthesia machines with ventilators that use
a single circuit piston design.
- The major advantage of a piston ventilator is
its ability to deliver accurate tidal volumes to patients with very
poor lung compliance and to very small patients.
- Whenever a ventilator is used, “disconnect
alarms” must be passively activated. Anesthesia workstations should
have at least three disconnect alarms: low pressure, low exhaled
tidal volume, and low exhaled carbon dioxide.
- Because the ventilator’s spill valve
is closed during inspiration, fresh gas flow from the machine’s
common gas outlet normally contributes to the tidal volume delivered
to the patient.
- Use of the oxygen flush valve during the inspiratory
cycle of a ventilator must be avoided because the ventilator spill
valve will be closed and the adjustable pressure-limiting (APL)
valve is excluded; the surge of oxygen (600–1200 mL/s)
and circuit pressure will be transferred to the patient’s
- Large discrepancies between the set and actual ...
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