Oxygenation and ventilation are not the same physiologic process.
Oxygenation involves the addition of O
2
from the environment to
the blood, while ventilation and CO
2
elimination is the movement of
air into and out of the lungs. The human body actually needs to
move only small amounts of air in order to be able to saturate the
blood with oxygen. However, that movement may not be sufficient
to eliminate proper amounts of CO
2
. That's why pulse oximetry and
capnography are both needed to monitor the safe administration of
sedation and general anesthesia.
When patients are sedated, drugs that affect the central nervous sys-
tem and depress airway reflexes can compromise ventilation. In addi-
tion, the relaxed muscles of a sedated patient could lead to partial or
complete airway obstruction. LMAs or endotracheal tubes manage the
airways of patients under general anesthesia, but sedated patients,
who do not have such devices placed, are at higher risk of airway
compromise. That's why capnography is arguably more important dur-
ing such cases.
There are a few features to consider when assessing your monitor
options. Are the controls intuitive? Are the surfaces easy to wipe down
between cases? Can you adjust the alarm settings? For example,
providers can set ETCO2 parameters on a capnography monitor to a
range that's appropriate for the patient being sedated. When they're
monitoring a frail, elderly patient, they can set the apnea alarm to
sound in 20 seconds, instead of the typical 30 to 40 seconds, if respira-
tory rate readings fall below the safe range. Certainly, providers should
notice changes in the capnograph long before the apnea alarm sounds,
but the adjustable built-in safety feature is a nice failsafe to have.
Always watching
I use the trends of pulse oximetry and capnography to avoid deteriora-
3 6 • O U T PA T I E N T S U R G E R Y M A G A Z I N E • J U L Y 2 0 1 8
