Understanding Anesthesiology - The Global Regional Anesthesia ...

and common peroneal nerves are at risk of either
stretch or compression injuries when the lithotomy position
is used.
Other organ systems may be vulnerable in the prone
position. Pressure on the orbit of the eye can lead to retinal
ischemia by either arterial compression or obstruction
of venous flow. The eye socket itself provides a
natural protection and specially designed head rests
are helpful. Constant vigilance must be maintained as
patient position may shift during anesthesia. The male
patient’s genitalia must be free of pressure. Finally, pressure
over skin surfaces (e.g. the forehead) must be minimized
as skin sloughing can result after prolonged surgery
in the prone position.
Hypothermia
Hypothermia has deleterious effects on the cardiovascular,
respiratory, central nervous, hematologic and renal
systems. As well, it decreases the rate of recovery
from the effects of muscle relaxants.
Heat is lost through four mechanisms:
• convection (e.g. exposure to drafts of cool air)
• conduction (e.g. contact with cold operating room table)
• evaporation (e.g. airway mucosa, prep solution,
sweat)
• radiation (e.g. temperature gradient between patient
and operating room environment)
Furthermore, the normal responses to hypothermia
(shivering, vasoconstriction) are abolished under anesthesia.
Procedures which are prolonged, involve large
abdominal incisions or require administration of large
volumes of intravenous fluids can be associated with
particularly severe hypothermia.
Heat loss can be minimized by keeping the operating
room temperature as high as tolerable (>21 C, preferably).
Gas humidifiers or the use of low gas flow minimizes
the heat lost through airway evaporation. Fluid
warmers should be used whenever blood products or
large volumes of intravenous fluids are being given. A
forced air warming system should be used routinely
except for those cases which are very short in duration.
If significant hypothermia (