Pediatric emergency medicine trisk 489

TABLE 90.7
MANAGEMENT OF HYPOTHERMIA
Initial management
Provide supplemental oxygen
Cardiopulmonary resuscitation for asystole, ventricular fibrillation, or any
nonperfusing rhythm (use Echo to distinguish PEA from perfusing rhythm if
pulses are not palpable)
Laboratory determinations
Arterial blood gas analysis corrected for temperature
Complete blood cell count, platelet count
Prothrombin time, partial thromboplastin time
Electrolytes, blood urea nitrogen, creatinine, glucose
Amylase, Lipase
Urine drug screen
Monitoring
Heart rate, electrocardiogram, respiratory rate, blood pressure
Temperature
Consider central venous pressure
Treatment
Correct hypoxemia, hypercarbia
Correct hypokalemia
Correct hypoglycemia, dextrose 0.5–1 g/kg IV
Tolerate hyperglycemia
Temperature
≥32°C (89.6°F): passive rewarming or simple external rewarming
<32°C (89.6°F) (acute): external or core rewarming
<32°C (89.6°F) (chronic): core rewarming
Fluid replacement
(acute) 5% dextrose in normal saline at maintenance rates
(chronic) normal saline and/or fresh frozen plasma to maintain blood
pressure

All patients should be given supplemental oxygen. Patients with profuse
secretions, respiratory depression, or impaired mental status should be intubated
and mechanically ventilated. Intubation should be performed as gently as possible
to minimize the risk of arrhythmias.
A decreased metabolic rate produces less carbon dioxide, and usual minute
ventilation would produce respiratory alkalosis, increasing the risk of dangerous
arrhythmias. Therefore, ventilation should begin at approximately one-half the
normal minute ventilation.
Assessment of acid–base status and ventilation in the hypothermic patient is
the subject of considerable confusion. Blood gas machines heat the patient’s
blood sample to 37°C (98.6°F) before measuring pH and gas partial pressures
(thus providing theoretical values if the patient were 37°C [98.6°F]). If the
patient’s actual temperature is provided with the sample, the machine can correct
the values according to the nomogram of Kelman and Nunn ( Table 90.6 shows
one set of guidelines for appropriate correction). However, it is important to
understand two concepts. The first is the ectothermic principle, which relies on
the following aspect of physiology: dissociation of ions and partial pressures of
gases are decreased in cooled blood. In hypothermia, therefore, neutral pH is
higher, whereas “normal” PCO 2 is lower than is encountered at 37°C (98.6°F).
For example, hypoventilation of the hypothermic patient with a pH of 7.5 would
actually induce an undesirable respiratory acidosis. A second, more practical
concept is that if the patient’s blood volume is restored and oxygenation
maintained, acidosis will be corrected spontaneously as the patient is warmed.
Heart rate and rhythm should be monitored continuously and the patient
handled gently to avoid precipitation of life-threatening arrhythmias in an irritable
myocardium. Sinus bradycardia, atrial flutter, and atrial fibrillation are common
but rarely of hemodynamic significance. Spontaneous reversion to sinus rhythm
is the rule when temperature is corrected. It may be difficult to detect pulses in

the hypothermic patient; therefore, it is important to provide chest compressions
until pulseless electrical activity has been ruled out by echocardiography or
arterial BP monitoring. Ventricular fibrillation may occur spontaneously or with
trivial stimulation, especially at temperatures less than 28° to 29°C (82.4° to
84.2°F). Electrical defibrillation is warranted but frequently is ineffective until
core temperature rises. Chest compressions should be initiated and maintained
until the temperature is higher than 30°C (86°F), when defibrillation is more
likely to be effective.
Fluid replacement is essential. Relatively little plasma loss occurs in acute
hypothermia but losses may be great in hypothermia of longer duration. Normal


saline or lactated Ringer solution, warmed to about 43°C (109.4°F) in a bloodwarming coil, is appropriate initially. Electrolyte determinations should guide
further replacement. If clotting abnormalities occur, fresh-frozen plasma (10
mL/kg) is a useful choice for volume expansion (see Chapter 93 Hematologic
Emergencies ). As temperature rises and peripheral vasoconstriction diminishes,
hypovolemia is expected. Fluid volume should be sufficient to maintain an
adequate arterial BP.
Hypoglycemia, if present, is treated with glucose (0.5 to 1 g/kg by IV).
Hyperglycemia, which may result from impaired insulin release in the
hypothermic pancreas, should be tolerated to avoid severe hypoglycemia with
rewarming.

FIGURE 90.8 Algorithm for rewarming. (Adapted from Danzl DF, Pozos RS. Accidental
hypothermia. N Engl J Med 1994;331(26):1756–1760.)

A number of rewarming strategies exist ( Fig. 90.8 ). Passive rewarming
implies removal of the patient from a cold environment and use of blankets to
maximize the effect of basal heat production. For patients with mild hypothermia
(temperature higher than 32°C [89.6°F]), this may be adequate. As shown in the

algorithm, the adequacy of perfusion and the degree of hypothermia are the major
factors in the selection of rewarming strategies. For patients with an adequate
pulse, passive rewarming is used as the initial strategy if the temperature is
greater than 32°C and active core rewarming if the temperature is less than 32°C.
Those with poor perfusion require active rewarming with a temperature greater
than 32°C and ECMO, if available, with temperature less than 32°C.
Active rewarming is divided into external and core rewarming techniques.
Electric blankets, hot-water bottles, overhead warmers, and thermal mattresses
are simple, easily available sources of external heat. Immersion in warm-water


baths is also possible but complicates monitoring or response to arrhythmias.
These methods, however, cause early warming of the skin and extremities with
peripheral vasodilation and shunting of cold, acidemic blood to the core. This
causes the well-known phenomenon of “afterdrop” of core temperature. Severe
hypotension may also occur in chronic cases as vasodilation increases the
effective vascular space. External rewarming techniques limited to the head and
trunk may minimize vasodilation and afterdrop. In acute hypothermia, active
external rewarming is appropriate, but there is some evidence that in chronic
cases (more than 24 hours), mortality is higher if active external rewarming is
used instead of simple passive techniques.
Core rewarming techniques are almost certainly more rapid and less likely to
be associated with afterdrop, dangerous arrhythmias, or significant hypotension.
These methods are especially valuable in the setting of severe chronic
hypothermia (temperature less than 32°C [89.6°F]), where fluid shifts are most
likely to occur. A nonshivering model of severe hypothermia indicated that
inhalation rewarming offered no rewarming advantage, whereas forced air
warming (approximately 200 W) allowed a 6- to 10-fold increase in rewarming
rate over controls. At the same time, peritoneal dialysis with dialysate warmed to
43°C (109.4°F) is effective and requires only equipment routinely available in

most hospitals. Gastric or colonic irrigation has also been advocated, but
placement of the intragastric balloon may precipitate dysrhythmias.
Hemodialysis, extracorporeal blood rewarming, and mediastinal irrigation are
effective but require mobilization of sophisticated equipment and personnel. New
endovascular warming catheters, introduced after cannulization of the femoral
vein and advancement to the inferior vena cava, use closed-loop circuitry to
maintain the patient’s temperature.

Indications for Admission and Discharge
In patients with mild temperature depression (greater than 32°C [89.6°F]),
external rewarming techniques and supportive care based on vital signs, ABGs,
and metabolic parameters such as glucose and calcium levels, should result in
prompt recovery. Patients with mild hypothermia due to environmental exposure
who improve with passive rewarming may be discharged after observation in the
ED. However, it should be noted that other causes of hypothermia should be ruled
out prior to discharge.
Children who present with a temperature less than 32°C (89.6°F), and
especially those in whom hypothermia developed over 24 hours or more, require
meticulous attention to continuously changing vital signs and metabolic needs.
More elaborate core rewarming techniques are appropriate.