COLD INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 402

ventricular fibrillation, orbaseline artifacts—but theydoreliably indicate thepresence ofa
heartbeat by portraying QRS complexes.)
Attempting to take a blood pressure may not be helpful because hypothermic persons
with a functioning heart commonly have reduced blood pressure, and blood pressure de-
termination may be further hindered by the absence of the Korotkoff sounds used when
measuring pressure.
CPR should be given at one-half the usual rate to severely hypothermic persons, who
have such a slow metabolism that they need limited amounts of oxygen and are producing
little carbon dioxide. A slower rate of ventilation avoids excessive carbon dioxide loss and
respiratory alkalosis, which predisposes hypothermic individuals to ventricular fibrillation.
A slower rate of cardiac compression provides a longer interval for the heart to be filled
with blood by the slow circulation.
CPR should be instituted immediately following a witnessed cardiac arrest or fibrilla-
tion, particularly when transportation to a hospital is expected to require more than a few
minutes. CPR probably should be administered for individuals with unwitnessed cardiac
arrest who appear resuscitatable, but each situation can be expected to be so unique that
moredefinitiverecommendationsarenotpossible.CPRshouldnotbeinitiatedifaseverely
hypothermic individual can be transported to a hospital in minutes.
CPR should not be initiated for fibrillating hypothermic individuals considered unsuit-
ableforresuscitationduetotheirsituationorforfibrillatingindividualswithextremelylow
bodytemperature,associatedsevereillnessorinjuries,anoncompressiblechest,prolonged
cardiac inactivity, or drowning with more than one hour of witnessed submersion.
No clear role for drugs in preventing fibrillation is known.
COLD WATER IMMERSION
Cold water immersion is poorly understood by the general public and even some outdoor
medical experts. A common belief is that immersion in very cold water, even with protect-
ive clothing, results in death from hypothermia within minutes. Although most cold water
immersion fatalities do occur within less than twenty minutes, the deaths occur while the
persons are still normothermic. These incorrect assumptions have serious implications be-
cause believing that death from hypothermia is imminent can result in panic and poor de-
cision making.
Cold water has been defined as water temperature below 68° to 77°F (20° to 25°C). Im-
mersion in cold water has been divided into four phases:
◆ Cold shock response
◆ Cold incapacitation
◆ Hypothermia
◆ Circumrescue collapse