What passive external rewarming method is typically applied to treat mild hypothermia?
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Hypothermia is a core body temperature < 35° C. Symptoms progress from shivering and lethargy to confusion, coma, and death. Mild hypothermia requires a warm environment and insulating blankets (passive rewarming). Severe hypothermia requires active rewarming of the body surface (eg, with forced-air warming systems, radiant sources) and core (eg, inhalation, heated infusion and lavage, extracorporeal blood rewarming). Show
Primary hypothermia causes about 600 deaths each year in the US. Hypothermia also has a significant and underrecognized effect on mortality risk in cardiovascular and neurologic disorders. Hypothermia results when body heat loss exceeds body heat production. Hypothermia is most common during cold weather or immersion in cold water, but it may occur in warm climates when people lie immobile on a cool surface (eg, when they are intoxicated) or after very prolonged immersion in swimming-temperature water (eg, 20 to 24° C). Wet clothing and wind increase risk of hypothermia. Conditions that cause loss of consciousness, immobility, or both (eg, trauma, hypoglycemia, seizure disorders, stroke, drug or alcohol intoxication) are common predisposing factors. Older people and the very young also are at high risk:
Hypothermia slows all physiologic functions, including cardiovascular and respiratory systems, nerve conduction, mental acuity, neuromuscular reaction time, and metabolic rate. Thermoregulation ceases below about 30° C; the body must then depend on an external heat source for rewarming. Renal cell dysfunction and decreased levels of vasopressin (ADH) lead to production of a large volume of dilute urine (cold diuresis). Diuresis plus fluid leakage into the interstitial tissues causes hypovolemia. Vasoconstriction, which occurs with hypothermia, may mask hypovolemia, which then manifests as sudden shock or cardiac arrest during rewarming (rewarming collapse) when peripheral vasculature dilates. Immersion in cold water can trigger the diving reflex, which involves reflex vasoconstriction in visceral muscles; blood is shunted to essential organs (eg, heart, brain). The reflex is most pronounced in small children and may help protect them. Also, hypothermia due to total immersion in near-freezing water may protect the brain from hypoxia by decreasing metabolic demands. The decreased demand probably accounts for the occasional survival after prolonged cardiac arrest due to extreme hypothermia. Symptoms and Signs of HypothermiaIntense shivering occurs initially, but it ceases below about 31° C, allowing body temperature to drop more precipitously. Central nervous system dysfunction progresses as body temperature decreases; people do not sense the cold. Lethargy and clumsiness are followed by confusion, irritability, sometimes hallucinations, and eventually coma. Pupils may become unreactive. Respirations and heartbeat slow and ultimately cease. Initially, sinus bradycardia is followed by slow atrial fibrillation; the terminal rhythm is ventricular fibrillation or asystole.
Diagnosis is by core temperature, not oral temperature. Electronic thermometers are preferred; many standard mercury thermometers have a lower limit of 34° C. Rectal and esophageal probes are most accurate. Laboratory tests include complete blood count, glucose (including bedside measurement), electrolytes, blood urea nitrogen, creatinine, and arterial blood gases (ABGs). ABGs are not corrected for low temperature. An electroencephalogram (EEG) may show J (Osborn) waves (see figure
Abnormal ECG showing J [Osborn] waves [V4]
Abnormal ECG showing J (Osborn) waves (V4) Abnormal ECG showing J (Osborn) waves (V4)The J (Osborn) wave is visible as a hump at the junction of the QRS complex and ST segment. Computer programs cannot reliably differentiate J waveform abnormalities from myocardial injury current.
For a given degree and duration of hypothermia, children are more likely to recover than adults.
The first priority is to prevent further heat loss by removing wet clothing and insulating the patient. Subsequent measures depend on how severe hypothermia is and whether cardiovascular instability or cardiac arrest is present. Returning patients to a normal temperature is less urgent in hypothermia than in severe hyperthermia. For stable patients, elevation of core temperature by 1° C/hour is acceptable. Fluid resuscitation is essential for hypovolemia. Patients are given 1 to 2 L of 0.9% saline solution (20 mL/kg for children) IV; if possible, the solution is heated to 40 to 42° C. More fluid is given as needed to maintain perfusion. In mild hypothermia (temperature 32.2 to 35° C) with intact thermoregulation (indicated by shivering), insulation with heated blankets and warm fluids to drink are adequate. Active rewarming is required if patients have temperature < 32.2° C, cardiovascular instability, hormone insufficiency (such as hypoadrenalism or hypothyroidism), or hypothermia secondary to trauma, toxins, or predisposing disorders. In moderate hypothermia, body temperature is at the warmer end of the range (28 to 32.2° C), and external rewarming with forced hot air enclosures may be used. External heat is best applied to the thorax because warming the extremities may increase metabolic demands on a depressed cardiovascular system. In severe hypothermia, patients with lower temperatures (< 28° C), particularly those with low blood pressure or cardiac arrest, require core rewarming. Core rewarming options include
Inhalation of heated (40 to 45° C), humidified oxygen via mask or endotracheal tube eliminates respiratory heat loss and can add 1 to 2° C/hour to the rewarming rate. IV crystalloids or blood should be heated to 40 to 42° C, especially with massive volume resuscitations. There are 5 types of ECR: hemodialysis, venovenous, continuous arteriovenous, cardiopulmonary bypass, and extracorporeal membrane oxygenation. ECR measures require a prearranged protocol with appropriate specialists. Although they are intuitively attractive and heroic, these measures are not routinely available, and they are not commonly used in most hospitals. Hypotension and bradycardia are expected when core temperature is low and, if due solely to hypothermia, need not be aggressively treated. CPR should be withheld if patients have a perfusing rhythm unless true cardiac arrest is confirmed by absence of cardiac motion on bedside cardiac ultrasonography. Treat with fluids and active rewarming. Chest compressions are not done, because
Advanced life support should be continued until temperature reaches 32° C unless obviously lethal injuries or disorders are present. However, advanced cardiac life-support drugs (eg, antiarrhythmics, vasopressors, inotropes) are usually not given. Low-dose dopamine (1 to 5 mcg/kg/min) or other catecholamine infusions are typically reserved for patients who have disproportionately severe hypotension and who do not respond to fluid resuscitation and rewarming. Severe hyperkalemia (> 10 mEq/L [10 mmol/L]) during resuscitation typically indicates a fatal outcome and can guide resuscitation efforts.
Click here for Patient Education What is passive rewarming of a hypothermic person?Passive external rewarming — Passive external rewarming is used for mild hypothermia. It is also used in patients undergoing aggressive rewarming for moderate to severe hypothermia. After wet clothing is removed, the patient is covered with blankets or other types of insulation.
Which passive warming measure would the nurse use to promote the warmth and comfort of a client experiencing hypothermia select all that apply?Passive external rewarming (PER) is typically used to treat mild hypothermia. It simply involves placing the individual in an appropriately warm environment, covered in insulation, and gradually raising the core body temperature a few degrees every hour.
How do you rewarm a hypothermic patient?The most effective method of active core rewarming is extracorporeal blood warming, accomplished by cardiopulmonary bypass, arteriovenous rewarming, venovenous rewarming, or hemodialysis. These techniques are highly effective and increase core temperature by 1°C to 2°C (3.6°F) every three to five minutes.
Which method is an example of active internal rewarming?Active internal rewarming techniques can be simple or invasive. Simple techniques may be initiated immediately and include the use of warmed intravenous fluids (heated to 43°C by microwave or heat infusion pump)66 and warmed oxygen,67 which together warm at a rate of 1°C–2°C per hour.
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