Anesthesia Student Survival Guide.pdf - Index of

126 ● AnesthesiA student survivAl Guide
Electronically controlled vaporizers are most commonly used for desflurane
(because its low boiling point of 23.5°C (or 73.4°F) is very close to room temperature).
They work by heating desflurane to a temperature of 39°C in order
to create a constant vapor pressure. This particular vaporizer does not have fresh
gas flow through it. Instead the vaporizer simply releases the amount desired
and then mixes it with fresh gas.
All modern vaporizers (except for desflurane vaporizers) compensate for
temperature and ambient pressure changes. This ensures that the same amount
of agent will be delivered to the patient at all times. Note that these vaporizers
do not compensate for changes in elevation or atmospheric pressure.
Because vaporizers are agent specific, it is critically important to fill up the
vaporizer with the correct agent – or else an unanticipated concentration of agent
may be delivered. In order to prevent misfilling, vaporizers are color-coded and
have agent-specific keyed filling ports that only accept the correct key or straw.
Gas Outlet
The gas outlet transports fresh gas carrying volatile agent to the breathing circuit.
In all anesthesia machines, there is an oxygen flush valve that provides a high
flow of oxygen (40–55 L/min) and bypasses both the flowmeters and vaporizers.
This high flow of oxygen “flushes” or fills the circuit with fresh oxygen that is
free of volatile agent. Due to the fact that this valve bypasses all the machine’s
regulatory systems, it has the potential to reach the patient with inappropriately
high pressure. It is important to remember this, since if used improperly it can
cause significant patient barotrauma (lung injury).
Alarms
Anesthesia machines include a number of alarms. Each will have a low pressure
alarm that goes off when a set airway pressure is not reached in the circuit
during positive pressure ventilation. It is the first alarm to go off when a disconnection
occurs in the circuit.
The oxygen fail-safe monitor checks for the presence of low oxygen pressure
within the system. If the pressure drops below a certain limit, the monitor
sounds an alarm and shuts off the inflow of other gases – until the oxygen
pressure is reestablished.
The oxygen sensor in the inspiratory limb of the breathing circuit checks
the concentration of oxygen delivered to the patient and will alarm if the delivered
FiO 2 drops below a set threshold. This is probably one of the most important
monitors in the entire machine.