Anesthesia Student Survival Guide.pdf - Index of

130 ● AnesthesiA student survivAl Guide
they could be misconnected. This is because they are diameter indexed and
cannot be attached to the wrong outlet or inlet. You can inspect the pressure
gauges on the anesthesia machine to ensure that there is adequate pressure
in the lines (indicated by a green band).
How can you tell if you have adequate backup gas supplies should the hospital
supply fail?
All anesthesia machines also have tanks of oxygen and usually nitrous oxide
attached directly to the back of the machine to be used as backup supplies.
You can open the valve on one of the oxygen tanks and inspect the pressure
valve for tank pressure to ensure that you have an adequate supply. It is usually
recommended that you have at least half a tank, which should register
as 1,100 PSI, compared to a full tank at 2,200 PSI. This corresponds to a little
more than 300 L of oxygen, enough for over an hour at 5 L per minute and
much longer at low fresh gas flows.
How can you test to make sure the machine will prevent administration of a
hypoxic gas mixture?
There are several safety mechanisms in the machine to ensure admnistration
of adequate oxygen to prevent hypoxia. You can test the oxygen monitor’s
accuracy by running 100% oxygen through the circuit and ensuring
that it reads 100%, and you can place the sensor outside the circuit exposed
to room air and make sure it reads 21%. This monitor should alarm if the
mixture is hypoxic. There is also an interlock on the gas flow controls that
should prevent you from setting a flow of nitrous oxide that is too high
relative to the oxygen flow. You can turn on both gases and then decrease
the oxygen flow; at some point the nitrous oxide flow should automatically
decrease. Finally, there is a “fail-safe valve” that senses oxygen and nitrous
oxide pressures and should turn off all other gases should oxygen pressure
drop. You can test this valve by disconnecting the wall supply of oxygen
while administering nitrous oxide (and with the oxygen tank turned off).
The nitrous oxide flow should be turned off and an alarm should sound.
Later you are doing the case, which began uneventfully. The patient is intubated
and being mechanically ventilated. You note on the capnograph that
there appears to be inspired CO 2 . Given your understanding of the anesthesia
machine, why might this be occurring (see Fig. 10.2)? Which of the causes
should you have been able to pick up during the machine checkout?