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Background Cardiopulmonary bypass has been used to rewarm victims of accidental deep hypothermia. Unlike other rewarming techniques, it restores organ perfusion immediately in patients with inadequate circulation. This study evaluated the long-term outcome of survivors of accidental deep hypothermia with circulatory arrest who had been rewarmed with cardiopulmonary bypass.
Methods Deep hypothermia (core temperature, <28°C) with circulatory arrest was found in 46 of 234 patients with accidental hypothermia. In 32 of the 46 patients, rewarming with cardiopulmonary bypass was attempted, resulting in 15 long-term survivors. In most of these patients, deep hypothermia developed after mountaineering accidents or suicide attempts. After an average (±SD) of 6.7±4.0 years of follow-up, we obtained the patients' medical histories and performed neurologic and neuropsychological examinations, neurovascular ultrasound studies, electroencephalography, and magnetic resonance imaging of the brain.
Results The average age of the patients was 25.2±9.9 years; seven were female and eight were male. The mean interval from discovery of the patient to rewarming with cardiopulmonary bypass was 141±50 minutes (range, 30 to 240). At follow-up there were no hypothermia-related sequelae that impaired quality of life. Neurologic and neuropsychological deficits observed in the early period after rewarming had fully or almost completely disappeared. One patient had cerebellar atrophy on magnetic resonance imaging with mild clinical signs, a condition that may have been caused by hypothermia. Other clinical abnormalities were either preexisting or due to injuries not related to hypothermia.
Conclusions This clinical experience demonstrates that young, otherwise healthy people can survive accidental deep hypothermia with no or minimal cerebral impairment, even with prolonged circulatory arrest. Cardiopulmonary bypass appears to be an efficacious rewarming technique.
In a retrospective multicenter study, 234 patients with accidental hypothermia of various degrees were identified. Forty-six of these had deep hypothermia with circulatory arrest.11 Rewarming with cardiopulmonary bypass was attempted in 32 at three hospitals. The 15 long-term survivors, who were treated between 1977 and 1993, were healthy young people who had suffered deep hypothermia in most cases after mountaineering accidents or suicide attempts. The aim of this study was to assess the late outcome of these patients after rewarming with cardiopulmonary bypass.
Methods
Characteristics of the Patients
We studied 15 young patients without cardiovascular disease (7 female and 8 male; mean [±SD] age, 25.2±9.9 years; range, 9 to 43) who had suffered accidental deep hypothermia with circulatory arrest after mountaineering accidents, a boating accident, or murder or suicide attempts (Table 1). At rescue all patients were comatose. Nine initially had vital signs such as respiration, a pulse, or regular electric cardiac activity. The other six patients had neither respiration nor a pulse. In all nine patients who initially had vital signs, cardiopulmonary arrest occurred a mean of 14.8±18.6 minutes after the rescue operation was begun. All patients were intubated and ventilated and received ongoing cardiac massage during transportation to the hospital. At the time of admission, all 15 patients had documented circulatory arrest (ventricular fibrillation in 10 and asystole in 5) and fixed, dilated pupils. The mean interval from discovery of the patient to rewarming with cardiopulmonary bypass was 141±50 minutes (range, 30 to 240).
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The main problems at discharge were pulmonary in 11 patients, neurologic in 9, neuropsychological in 10, cardiac in 4, and renal in 5. Four patients had fractures, one had a burn caused by an inadequate rewarming attempt, one had pancreatitis, and one had deep venous thrombosis (cardiopulmonary-bypass cannulation site). Five patients were sent home directly from the hospital after 7.8±2.2 days (range, 5 to 10). Ten patients were transferred to other hospitals after 22.7±19.5 days (range, 2 to 55) for further treatment or rehabilitation, where they stayed for 40.2±58.9 days (range, 7 to 228).
Assessment
All patients or their parents were contacted and gave informed consent for the study. All agreed to a follow-up examination. This was performed at the hospital in Bern 6.7±4.0 years (range, 5 days to 179 months) after the accident.
At follow-up, physical and neurologic examinations and special tests described below were performed. The results were categorized as normal, borderline (abnormal without clinical relevance), or pathologic (abnormal with clinical relevance).
Neurovascular Ultrasound Studies
A duplex system for color coding (Acuson XP10, Mountain View, Calif.) was used to visualize the extracranial vessels (internal, external, and common carotid and vertebral arteries on both sides), and a 2-MHz pulsed Doppler system (TC2-64B or TC2-2000, Eden Medical Electronics, Ueberlingen, Germany) was used for flow-velocity measurements of the intracranial vessels (anterior, middle, and posterior cerebral arteries on both sides and basilar artery). These examinations were performed to rule out an extracranial or intracranial macroangiopathy, which could influence the results of other neuropsychological and neurophysiologic studies. Flow velocities were compared with those in a control group of healthy subjects matched for age and sex.
Electroencephalography and Neuropsychological Tests
Electroencephalography was performed on all patients. Standard electrode positions were used according to the 10–20 method. Adult patients underwent comprehensive neuropsychological testing with a standardized battery of clinical tests.16 Patient 6 underwent an equivalent test battery for children on the fifth day after the accident. Functioning in all patients was assessed on the basis of each patient's ability to provide personal information, orientation, mental control, attention span, memory, higher cognitive functions, spatial performance, and language abilities. A score of 0 was assigned if there was no impairment, a score of 1 in the case of slight impairment, a score of 2 in the case of moderate impairment, and a score of 3 in the case of severe impairment. The results were compared with existing values in age-matched controls.16 The patients' overall neuropsychological performance was scored with the same scale.
Magnetic Resonance Imaging of the Brain
Magnetic resonance imaging of the brain was carried out on a 1.5-T system with a circularly polarized head coil (Signa, General Electric, Milwaukee). T1-weighted sagittal and axial multislice scans (single spin–echo) and T2-weighted axial (double spin–echo) sequences covering the entire brain were obtained. Two neuroradiologists independently assessed the images with respect to global or focal atrophy and the presence of lesions. They were told the patients' age and sex but not clinical details.
Statistical Analysis
Descriptive statistics were generated when appropriate. Unless otherwise stated, values are expressed as means (±SD) and ranges. When the results were compared with those in age-matched control subjects, the differences were calculated by the nonparametric Wilcoxon signed-rank test.
Results
History and Physical Examination
Fourteen patients reported complete recovery and one patient (Patient 10) satisfactory recovery from the accident. Despite persistent deficits due to accident-related injuries but not to the hypothermia, none of the patients felt handicapped. They all resumed their former lifestyles. Only one patient (Patient 4) required medical treatment for preexisting psychiatric problems. The general physical examination showed normal findings in all patients.
Neurologic Findings
Three patients had borderline abnormalities that were probably related to circulatory arrest during hypothermia (Table 1). Other abnormalities were preexisting or caused by injuries incurred during the accident but were not related to hypoxia or hypothermia. Patient 6 had mildly impaired coordination of his left arm and hand, which interfered minimally with function. Patient 7 had an impaired ability to make rapid alternating movements of his left hand (dysdiadochokinesia) at follow-up that did not affect his overall performance. He had resumed his profession as an engineer and his sports activities such as mountaineering and climbing. This patient showed the most remarkable recovery, since it took six months for him to be able to walk unaided and about one year for him to be able to read and write normally. Patient 9 had dysesthesia of his left foot.
Neurovascular Ultrasound Studies
All patients had normal carotid and vertebral arteries in the neck on duplex scanning. Flow velocities of the extracranial and intracranial vessels were within the normal range.
Electroencephalography
On visual assessment five patients had borderline results and one had pathologic results (Table 1). The borderline alterations consisted of focal abnormalities (slow waves and epileptiform discharges) in three patients and slowed background activity in two. Patient 12, who had the lowest core temperature at rescue, had an electroencephalogram with slowed background activity and sharp and theta waves in the right temporoparietal region. However, he had no history of seizures and did not require antiepileptic medication. All documented electroencephalographic changes were probably related to hypothermia.
Neuropsychological Findings
Thirteen of the 15 patients completed neuropsychological testing. Patient 4 refused to complete testing, but interview data did not indicate partial or global cognitive impairment. Patient 13 was interviewed in her native language of Swedish and did not show any neuropsychological impairment; however, neither test material nor norms were available in her native language.
Patient 6, who could not be tested at follow-up, made a good recovery and resumed attending school. Patient 7, who had very severe neuropsychological deficits on discharge from the hospital, including aphasia, apraxia, and emotional problems, recovered completely. Patient 10 had slightly impaired orientation and memory and a moderately impaired attention span, corresponding to the traumatic brain damage seen on imaging. Despite severe brain injury, which required rehabilitation for seven months, he attended a regular school and did not require special tutoring. Overall, no patient had any hypothermia-related impairment.
Magnetic Resonance Imaging of the Brain
Findings on magnetic resonance imaging were normal in 13 patients and pathologic in 2 patients. Patient 7 had a global cerebellar atrophy, symmetrically involving both cerebellar hemispheres and the vermis. In addition, T2-weighted images showed a low signal intensity of the basal ganglia due to bilateral calcifications. The calcifications, but not the cerebellar atrophy, were already apparent on a computed tomographic scan obtained 10 days after the accident. Therefore, the cerebellar atrophy was most likely related to the hypothermia, and the calcifications were not. Magnetic resonance imaging of Patient 10 showed cortical and subcortical defects of the right frontal and temporal lobes as a result of a sustained head injury, which was not related to the hypothermia. Twelve of the 15 magnetic resonance scans showed subtle enlargements of basal perivascular spaces, which were considered within the limits of normal.
Discussion
Survival after accidental deep hypothermia (core temperature, <28°C) and prolonged cardiac arrest is rare.7,9,12 Although there have been isolated case reports, the long-term outcome of such patients has not been described. The results of our study are encouraging. At follow-up all 15 patients who survived rewarming with cardiopulmonary bypass had resumed their former activities and lifestyles. There were either no hypothermia-related neurologic or neuropsychological deficits or only mild ones. Abnormal findings on examination were due to injuries sustained during the accident or rescue. Both the high survival rate (47 percent; 15 of 32 patients) and the long-term outcome of our patients are remarkable considering the severe neurologic problems in the early period after rewarming (prolonged coma, amnesia, aphasia, ataxia, or spasticity). Some patients needed long-term rehabilitation. Severe deficits soon after rewarming have also been documented in other studies.6,12,17 The favorable outcome in our study is in contrast to resuscitation results in patients with normothermia and cardiac arrest, who have a poor outcome. Only 8 to 14 percent of patients with out-of-hospital or in-hospital cardiac arrest survive resuscitation and leave the hospital.18,19 In other reports, 33 to 48 percent of survivors had persistent moderate-to-severe neurologic and neuropsychological impairment.20,21
Five main reasons may account for the relatively good survival rate and favorable long-term outcome in our patients with hypothermia. First, hypothermia was deep. Hypothermia increases the tolerance of the brain to ischemia. It slows metabolic processes and reduces oxygen consumption.22,23 The protective effect of moderate hypothermia has been applied successfully in the treatment of traumatic brain injury.24 In cardiac surgery deep hypothermia is routinely used for cerebral protection when circulatory arrest is required.25,26,27,28 At a core temperature of 20°C cardiac arrest is tolerated for up to 30 minutes without clinically significant neurologic or neuropsychological deficits.27,28 Second, none of our patients had asphyxia or hypoxic brain damage before hypothermia developed, problems that often occur in avalanche or drowning victims.3,12,29,30,31 Asphyxia that precedes cooling of the body increases the risk of death.11 Third, our surviving patients were young, were in good general health, and had no vascular risk factors. Unlike patients in other referral centers our patients were not homeless people, who are often malnourished and have other medical problems.32 Fourth, the infrastructure and experience of rescue organizations in Switzerland may have influenced the outcome favorably.33,34 Thirteen patients were rescued by helicopter with a professional team that included a physician. During transportation and at the hospital, hypothermia was maintained and the patients were rewarmed only after cardiopulmonary bypass was initiated.6,11,35
The fifth and potentially crucial factor responsible for the good outcome in this series may have been the rewarming technique.6,35,36 Early rewarming with cardiopulmonary bypass has theoretical advantages as compared with other rewarming methods: it is the fastest method of rewarming; it provides adequate and immediate circulatory support; it may improve tissue perfusion by hemodilution; metabolic and toxic derangements can be corrected rapidly; and the heart is rewarmed before the rest of the body, thus preventing shock due to peripheral vasodilatation.35 In the absence of such contraindications as asphyxia, severe traumatic injury, and extremely elevated serum potassium levels (exceeding 10 mmol per liter), cardiopulmonary bypass appears to be the rewarming method of choice for accidental deep hypothermia with circulatory arrest.6,10,11,35 However, the value of this technique is doubtful for a patient with circulatory arrest but only moderate hypothermia.13,29 The upper and lower limits of the core temperature at which rewarming attempts justify the use of extracorporeal circulation remain unclear.12,13,17,29,34
In patients with preserved circulation and a less severe hypothermia, other rewarming techniques can be used and may be preferable.12,13,32,37,38 For instance, rewarming with warm air is noninvasive and technically easy to perform.39 In addition, the availability of rewarming with cardiopulmonary bypass is limited to large medical centers. Another important goal is to establish predictors of poor outcome in deep accidental hypothermia.8,11,13,17,29,40
In conclusion, our study demonstrates that the long-term outcome of survivors of accidental deep hypothermia with prolonged circulatory arrest and rewarming with cardiopulmonary bypass is favorable. Severe hypothermia-related neurologic deficits observed in the early post-rewarming period had disappeared at follow-up. Permanent neurologic deficits of clinical relevance were either preexisting or due to injuries sustained during the accident or rescue. The long-term survival rate of 47 percent is higher than previously reported9,12,29 and may be explained by the severity of hypothermia, the rewarming technique used, the rescue teams used, the patients' characteristics, and the absence of asphyxia before exposure to the cold.
We are indebted to the emergency physicians at the primary care centers involved in the rescue and referral of patients to the university hospitals; to the Swiss rescue teams (REGA, Air Zermatt, and Air Glacier); and to the personnel of Inselspital for carrying out specialized tests: the personnel of the electroencephalography section, especially Mr. M. Kollar, for performing electroencephalography; Dr. C. Bassetti for helpful comments (the Department of Neurology); Mrs. C. Herrmann of the cerebrovascular laboratory for performing the ultrasound examinations (Departments of Neurology and Neurosurgery); Mr. G. di Stefano, M.A., and Mrs. A. Schnidrig, M.A., for their help in performing neuropsychological tests on some of the patients (the Department of Psychiatry); and the staff of the magnetic resonance imaging unit, especially Dr. E. Tuncdogan and Mr. T. Gbedegbegnon, chief technician, for expert assistance (the Department of Neuroradiology).
Source Information
From the Departments of Thoracic and Cardiovascular Surgery (B.H.W., B.N.W.-A., U.A.), Neurology (H.P.M., L.S.), Psychiatry (B.P.R.), and Neuroradiology (G.S.), University of Bern, Inselspital, Bern; the Department of Cardiovascular Surgery, University Hospital of Lausanne, Lausanne (A.P.F., L.v.S.); and the Department of Cardiovascular Surgery, University Hospital of Zurich, Zurich (L.v.S.) — all in Switzerland.
Address reprint requests to Dr. Walpoth at the Department of Thoracic and Cardiovascular Surgery, University of Bern, Inselspital, 3010 Bern, Switzerland.
References
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Related Letters:
Accidental Deep Hypothermia
Offenstadt G., Harries M., MacKenzie M. A., Walpoth B. H., Mattle H. P., Althaus U.
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Full Text
N Engl J Med 1998;
338:1160-1162, Apr 16, 1998.
Correspondence
This article has been cited by other articles:
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