Correspondence

Accidental Deep Hypothermia

N Engl J Med 1998; 338:1160-1162April 16, 1998

Article

To the Editor:

The report by Walpoth et al. (Nov. 20 issue)1 on survivors of accidental deep hypothermia and circulatory arrest was very interesting. I was impressed by their favorable results. From the published characteristics of the patients it is impossible to determine the length of time during which each patient had documented circulatory arrest with fixed, dilated pupils. This information is known to be important for prognosis and thus should be indicated.

Of the 32 patients in whom rewarming with cardiopulmonary bypass was attempted, 17 were not long-term survivors. It would certainly be of interest to analyze this population for possible prognostic factors.

Georges Offenstadt, M.D.
Hôpital Saint-Antoine, 75571 Paris CEDEX 12, France

1 References

1
Walpoth BH, Walpoth-Aslan BN, Mattle HP, et al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med 1997;337:1500-1505
Full Text | Web of Science | Medline

To the Editor:

Ever since Siebke et al. documented the occurrence of recovery without cerebral sequelae after 40 minutes of submersion in ice-cold water,1 others have pondered the mechanisms influencing survival in such circumstances. In their account of the resuscitation of patients with profound hypothermia with extracorporeal blood warming, Walpoth et al. speculate that the chances of surviving deep hypothermia are better if asphyxia follows cooling of the body (as it does after incarceration in ice, as they describe) than if it precedes it (as, for example, during drowning). They may well be right, but since there is no way of knowing precisely the timing of the cardiac arrest, their observation raises an important question. Should the rescue services recovering victims with hypothermia and cardiac arrest abandon attempts at rewarming but continue cardiopulmonary resuscitation until they reach the hospital in order to keep the victims' brains cool?

Mark Harries, M.D.
British Olympic Medical Centre, Harrow, Middlesex HA1 3UJ, United Kingdom

1 References

1
Siebke H, Rod T, Breivik H, Link B. Survival after 40 minutes' submersion without cerebral sequelae. Lancet 1975;1:1275-1277
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To the Editor:

Walpoth et al. report a beneficial neuropsychological outcome for survivors of accidental deep hypothermia, but the long-term consequences for the peripheral nervous system remain unclear. As stated by the authors and by Dr. Lazar in the accompanying editorial,1 the encouraging outcome is most likely related to the young age and good health of the patients, the type of accidental hypothermia, the clinical experience of the rescue organizations, and the easy availability of cardiopulmonary-bypass techniques. In general, the management and long-term prognosis of accidental (deep) hypothermia also depend on the recognition of its pathophysiology and on the treatment of underlying, predisposing disorders.2 In the management and prevention of accidental hypothermia, it is pivotal to differentiate between hypothermia caused by severe cold stress and other types of hypothermia occurring in less severe environmental conditions, as well as between acute and intermittent or chronic hypothermia.2,3 Serious, recurrent hypothermia can often be prevented by an adequate assessment of its pathophysiology, treatment of predisposing conditions, and improvement of thermoregulatory behavior.

Guidelines for the optimal rewarming strategy in accidental hypothermia that is not caused by severe cooling vary depending on the type and severity of hypothermia and underlying disorders; often, external rewarming techniques are appropriate in patients with stable cardiovascular function. However, unlike active core rewarming, external rewarming after severe cold stress carries the potential risk of a subsequent drop in core temperature, particularly in patients with decreased metabolism.2-4 In patients with thermoregulatory failure, preventive measures are crucial and active rapid rewarming can induce an overshoot in core temperature.

Marius A. MacKenzie, M.D., Ph.D.
University Hospital Nijmegen, 6500 HB Nijmegen, the Netherlands

4 References

1
Lazar HL. The treatment of hypothermia. N Engl J Med 1997;337:1545-1547
Full Text | Web of Science | Medline

2
Reed G. Accidental hypothermia. In: Mackowiak PA, ed. Fever: basic mechanisms and management. 2nd ed. Philadelphia: Lippincott–Raven, 1997:459-65.

3
MacKenzie MA. Poikilothermia in man: pathophysiological and clinical implications. Nijmegen, the Netherlands: University Press Nijmegen, 1996.

4
Lloyd EL. Hypothermia and cold stress. London: Croom Helm, 1986.

Author/Editor Response

The authors reply:

To the Editor: Dr. Offenstadt asks how long each patient had documented circulatory arrest. Six of our 15 patients had cardiorespiratory arrest when they were rescued. Three of them had fallen into a crevasse and one into cold water. They became unresponsive 5, 15, 60, and 135 minutes before their rescue. Two of the six had attempted suicide. Thus, the time at which cardiac function ceased in these six patients is unknown. As noted in the article, nine patients had vital signs at the time of rescue, but cardiopulmonary arrest occurred an average (±SD) of 14.8±18.6 minutes after rescue. The mean interval from the detection of cardiorespiratory arrest to the initiation of rewarming with cardiopulmonary bypass was 141±50 minutes, during which time intubation, ventilation, and cardiac massage (cardiopulmonary resuscitation) were performed.

Dr. Offenstadt's second question relates to the cause of death of the 17 patients who died. Most were avalanche victims who presumably suffered asphyxia before hypothermia developed. This corroborates our assumption, addressed by Dr. Harries, that the chances of surviving deep hypothermia are better if asphyxia follows cooling than if it precedes cooling. Asphyxia did not occur in any of the 15 survivors, whereas it did occur in most of the 17 who died. A Swiss multicenter study that involved 234 patients with mild, moderate, or deep accidental hypothermia analyzed prognostic factors.1 Multiple regression revealed the following: asphyxia was associated with a 30-fold increase in the chance of dying, invasive rewarming with a 20-fold increase, a slow rate of cooling with a 10-fold increase, asystole in cardiac arrest with a 9-fold increase, pulmonary edema or acute respiratory distress syndrome with an 8-fold increase, elevation of serum potassium with a 2-fold increase per millimole per liter, and age with a 1.03-fold increase per year of age. Rapid cooling increased the likelihood of survival 10-fold, ventricular fibrillation in cardiac arrest increased it 9-fold, and ingestion of narcotics or alcohol increased it 5-fold. Surprisingly, core temperature did not influence survival. Similar factors were identified by other authors.2

In answer to Dr. Harries: we believe that attempts at rewarming victims with deep hypothermia outside the hospital should be abandoned. If circumstances permit, such persons should be transported expeditiously to a hospital experienced in the use of rewarming with cardiopulmonary bypass. Hypothermia should be maintained and cardiopulmonary resuscitation continued during transportation.

We and others agree with Dr. MacKenzie that the choice of the appropriate rewarming technique has to be individualized for each patient, 3 depending on the level of hypothermia and the patient's cardiovascular condition. Forced air seems to be an effective external rewarming technique for patients with moderate or even deep hypothermia and stable cardiovascular function.4 However, in patients with cardiopulmonary arrest, we consider core rewarming with extracorporeal bypass to be the method of choice.

Beat H. Walpoth, M.D.
Heinrich P. Mattle, M.D.
Ulrich Althaus, M.D.
Inselspital, 3010 Bern, Switzerland

4 References

1
Locher T, Walpoth B, Pfluger D, Althaus U. Akzidentelle Hypothermie in der Schweiz (1980-1987) -- Kasuistik und prognostische Faktoren. Schweiz Med Wochenschr 1991;121:1020-1028
Medline

2
Schaller MD, Fischer AP, Perret CH. Hyperkalemia: a prognostic factor during acute severe hypothermia. JAMA 1990;264:1842-1845
CrossRef | Web of Science | Medline

3
Larach MG. Accidental hypothermia. Lancet 1995;345:493-498
CrossRef | Web of Science | Medline

4
Steele MT, Nelson MJ, Sessler DI, et al. Forced air speeds rewarming in accidental hypothermia. Ann Emerg Med 1996;27:479-484
CrossRef | Web of Science | Medline

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