Answers

Short answers

1 Basic life support should continue until core temperature is greater than 30°C. Cardioactive drugs and further defibrillation should be withheld until this temperature is reached.

2 Invasive rewarming methods should be used, such as airway warming; warm bladder, pleural, peritoneal, or nasogastric lavage; and, if available, partial cardiopulmonary bypass.

3 Resuscitation should continue until core temperature is more than 30°C or be discontinued if the patient has obvious lethal injuries.

Long answers
1 Steps for resuscitation
This patient is hypothermic. Hypothermia is defined as a core temperature of less than 36°C.¹ The drop in temperature can be rapid or slow, with the elderly and children being particularly susceptible.² The risk of hypothermia is increased by drugs, alcohol, and illness.^{3 4} The cause of hypothermia is often environmental in younger patients, whereas in the elderly the cause can be multifactorial (for example, poverty, poor housing, immobility).⁵ Hypothermia can be either primary (for example, immersion in cold water) or secondary (for example, reduced metabolic or vasomotor responses to a cold environment). The symptoms and signs of hypothermia are shown in box 1.

Box 1 Symptoms and signs of hypothermia3 Slow speech Amnesia Ataxia Confusion Cyanosis Coma Reduced ventilation, typical breathing pattern

Initial management should follow the airway, breathing, circulation (ABC) approach. Intravenous access should be obtained and appropriate rewarming techniques instigated. Cardiac monitoring should be started and any electrocardiogram changes observed (box 2).

Box 2 Electrocardiogram changes in hypothermia6 Arrhythmias Broad QRS complex Osborn (J) waves (delayed repolarisation) ST-T wave abnormalities

A core temperature reading should be obtained, and the same method of measurement should be used to measure core temperature throughout resuscitation. Bladder or oesophageal measurements correlate best with pulmonary artery core temperatures, but their use can be limited by what equipment is available. Rectal temperature is easier to measure, but might lag behind any core temperature rises.^{1 7} Arrhythmias can occur spontaneously, with a classic progression through sinus bradycardia, atrial fibrillation, ventricular fibrillation, and, ultimately, asystole.⁸ These arrhythmias can be precipitated by small movements—such as suctioning the airway or moving the patient—and typically occur when core temperature is less than 33ºC.⁹ Spontaneous resolution of arrhythmias can occur following rewarming.

The European Resuscitation Council has published guidelines for the management of cardiac arrest in patients with hypothermia.¹⁰ Initially, standard advanced life support protocols should be followed; however, hypothermic patients with ventricular fibrillation might not respond to defibrillation if their core temperature is less than 30°C. If there is no response to three cycles of shocks, then basic life support should be continued until core temperature is more than 30°C.¹⁰ Defibrillation, external pacing, and cardioactive drugs might not be effective below this temperature. Drug metabolism is reduced at low body temperatures, as is efficacy at site of action; hence, further drug treatment should be withheld until temperature rises to more than 30°C.¹¹ There is no evidence to support the routine use of antibiotics, steroids, or barbiturates in patients with hypothermia.^{12 13} Resuscitation should be continued until a temperature of 30°C is reached, and then a pulse check should be performed. Hypothermia has a protective effect on vital organs; therefore, prolonged resuscitation might still be successful in some patients with severe hypothermia.¹⁴

2 Low temperature and rewarming
General measures should be instigated first to prevent further heat loss. These include passive warming techniques such as cutting off wet clothing, drying the skin, covering the patient with blankets, and keeping them out of the wind.¹⁰ In patients with a perfusing cardiac output (that is, those in whom a pulse is present and are conscious), active rewarming should take place using forced air warming systems with full body blankets, which comprise a warming device and disposable laminate blankets that allow warm air to flow directly onto the patient’s skin.^{15 16} Treatment of patients with more severe hypothermia and no perfusing cardiac output requires invasive rewarming.

An observational study has shown that the administration of warm intravenous fluids (42-44°C) is an effective form of rewarming.¹⁷ Patients treated this way might, however, require large volumes of intravenous fluids because vasodilatation during rewarming increases the vascular space. Other warming techniques include the use of warm humidified oxygen; pleural, nasogastric, peritoneal, or bladder lavage with warm fluid; and extracorporeal blood warming via partial cardiopulmonary bypass.¹⁸ Currently no clinical trial has determined which method of rewarming is most successful. Research does, however, support the use of cardiopulmonary bypass as a method of invasive rewarming for patients with cardiac arrest and severe hypothermia because this strategy also provides circulation, oxygenation, and ventilation while core body temperature is increased.^{19 20} If cardiopulmonary bypass facilities are not available, a combination of rewarming techniques will be needed.²¹ Once spontaneous circulation has returned, passive or active rewarming methods can be used.

The rate of rewarming is determined by whether or not a perfusing cardiac output is present. If a perfusing cardiac output is present, a target of 1-2ºC per hour is appropriate; if not, then a faster rate of >2ºC per hour should be used.²² See figure for an algorithm for selecting an appropriate rewarming strategy.

View larger version (44K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Hospital management of hypothermia. Adapted from J R Army Med Corps 2006;152:223-33

 
Hyperthermia should be avoided because it has been associated with reperfusion injury owing to free radical release and an inflammatory response in cells reperfused with blood.^{23 24} Electrolyte disturbances—in particular hypocalcaemia and hypomagnesaemia—can occur during rewarming. Hypercalcaemia at presentation is a poor prognostic sign and can indicate muscle death. Respiratory depression and lactic acid production can cause a mixed metabolic and respiratory acidosis. Acidosis is invariably present in hypothermic patients with hypothermia, but will only resolve once core temperature is more than 32°C.²³

Rewarming is associated with a number of complications; for example, a phenomenon known as "afterdrop" can occur.¹⁸ Afterdrop is defined as a further fall in core temperature after removal of the patient from the cold environment or after initiation of rewarming methods. This phenomenon can be caused by the reperfusion of cool peripheries, which can lead to "dilution" of the heat.²² Rewarming can also cause neutropaenia, thrombocytopaenia, hypercalcaemia, delayed wound healing, cardiac arrhythmias, gastrointestinal haemorrhage, and infection.²⁵

3 Stopping resuscitation
The decision to cease resuscitation can be difficult, as prolonged resuscitation can be successful in patients with very low temperatures.^{26 27} Hypothermia protects the vital organs and slows metabolism, so dilated pupils and cardiac arrest cannot accurately predict death in this situation. Cold alone can produce an irregular small volume pulse; thus, blood pressure is unrecordable in many cases of hypothermia. Doppler ultrasound can help to detect a cardiac output.

In terms of prognosis, a distinction needs to be made between primary and secondary hypothermia. Primary hypothermia without anoxic brain injury is associated with the best outcomes.^{28 29 30} When treating patients with hypothermia, death must not be called until either the patient has been rewarmed and rewarming methods have failed, or the patient has obvious injuries incompatible with life. Remember, the patient is not dead until they are warm and dead.

Outcome
The patient was invasively rewarmed while cardiopulmonary resuscitation continued. Further defibrillation was successful in restoring sinus rhythm. He was transferred to the intensive care unit and made a full recovery.

Cite this as: BMJ 2009;338:b2085