Hypothermia is defined as a core body temperature below 35 °C.
The normal physiologic thermoregulatory responses start to fail
once the core body temperature reaches this level, leading to the
body’s inability to generate enough heat to maintain bodily
functions. Hypothermia can be subdivided into primary and secondary
hypothermia.1 Primary accidental hypothermia occurs when
a previously normal individual is subjected to an environmental
stress. Secondary accidental hypothermia occurs when a predisposing
factor leads to disruption of temperature homeostasis and increases
the individual’s susceptibility to lesser environmental
stresses (e.g., drug intoxication, trauma, and endocrine disorders).
Drug intoxication and trauma are acquired conditions that are highly
associated with the development of hypothermia.1–6
Hypothermia can progress after arrival
in the Emergency Department. Studies in the trauma population
have reported a significant percentage of patients to have a decrease
in their core body temperature during their stay in the Emergency
Department.2 This recognition has led to the development
of multidisciplinary approaches to maintaining normothermia as the
patient moves through the hospital.3The
importance of continuity and communication in dealing with this
problem cannot be overstated.
Hypothermia can be characterized as mild, moderate, and severe.
Mild hypothermia is defined as a core temperature of 32.2 to 35
°C or 90 to 95 °F. Moderate hypothermia is defined as a core temperature
of 28 to 32 °C or 82.4 to 90 °F. Severe hypothermia is defined as
a core temperature of less than 28 °C or 82.4 °F. The scale can
be amended in the trauma patient to 34 to 36 °C or 93.2 to
96.8 °F for mild hypothermia, 32 to 34 °C or 89.6 to 93.2
°F for moderate hypothermia, and < 32
°C or < 89.6 °F for severe hypothermia.1
Mild hypothermia causes the body to increase heat production
by shivering and increasing its metabolic rate. The heart rate increases
and the patient may become tachypneic. Peripheral vasoconstriction
may result in acrocyanosis. Neurologic symptoms may include confusion,
dysarthria, and impaired judgment.
Moderate hypothermia is associated with a further decrease in
the mental status. This includes lethargy, hallucinations, and loss
of the pupillary reflex. The heart rate changes from tachycardia to
bradycardia.4 The cardiac rhythm commonly converts from
normal sinus to atrial fibrillation.4 The respiratory pattern
becomes depressed, with a decreasing respiratory rate and tidal
volume. The patient stops complaining of “feeling cold” and
The patient is usually comatose by the time severe hypothermia
is present, often with evidence of cardiorespiratory collapse. Ventricular
irritability becomes evident. Ventricular fibrillation becomes refractory
to conversion below 28 °C. Asystole occurs at 20 °C. The characteristic
electrocardiographic (ECG) finding of an Osborne J wave occurs at
approximately 32 °C (Figure 169-1). This is a positive deflection
between the QRS and the ST segment.4–6 It is
often best seen in ECG leads aVL, aVF, and the
left chest leads.4–6
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