Accidental Hypothermia

A Pilot Study of Mechanical Stimulation and Cardiac Dysrhythmias in a Porcine Model of Induced Hypothermia☆

BACKGROUND

Hypothermia is a frequent complication of cold weather exposure and/or wilderness injuries. Anecdotal reports have postulated that patients suffering from acute hypothermia are at significantly increased risk of developing lethal cardiac dysrhythmias secondary to the physical stimulation from moving and transporting patients.

OBJECTIVE

To develop a model to attempt to determine if rough handling and sudden movement can induce lethal cardiac dysrhythmias in a controlled animal study of mild to severe hypothermia.

METHODS

Ten anesthetized swine had continuous cardiac and invasive blood pressure (BP) monitoring. Core body temperature (CBT) was measured with an esophageal probe. Animals were secured to a backboard in a supine position for the duration of the study and their CBT was serially lowered by external cooling measures. At preset intervals (every 3 degrees C lowered from the baseline CBT of 38 degrees C), the animals were lifted via the backboard and rolled 90 degrees to the left and held for 5 seconds and then rolled to the right and held for 5 seconds. After rolling, the swine were lifted via the backboard 6 inches off the surgical table and dropped back onto the table, and after 15 seconds this was repeated at 12 inches. If no signs of dysrhythmia were noted, external cooling was continued. Data were analyzed by tests of proportion on mortality associated with hypothermia and mechanical stimulation. To determine whether hypothermia and mechanical stimulation were independent effects, a one-sided McNemar's test of matched pairs was employed.

RESULTS

No animal developed a dysrhythmia at a CBT > 25 degrees C with or without stimulation. Fifty percent of the animals developed fatal dysrhythmias (3 ventricular fibrillation, 2 asystole) with no stimulation but at CBT <or= 25 degrees C (average CBT 22.7 degrees C). Twenty percent (2/10) developed fatal dysrhythmias (ventricular fibrillation) during mechanical stimulation. For hypothermia, a binomial test of the observed proportion 0.70 (fatality during hypothermia) against a hypothetical proportion of 0 (no fatality in the absence of hypothermia) yielded P < .001 with power = 1.00. For mechanical stimulation, a binomial test of the observed proportion 0.20 (fatality from mechanical stimulation); against a hypothetical proportion of 0 yielded P < .001 with power = 1.00. The test of matched pairs yielded P < .037, indicating that the variables of mechanical stimulation and hypothermia jointly caused mortality.

CONCLUSION

Profound hypothermia induces fatal dysrhythmias both with and without mechanical stimulation in a swine model.

Hypothermia and localized cold injuries

Hypothermia and localized cold injuries are largely preventable with proper preparation for activities in cold environments. Proficient field management is crucial to the final outcome in terms of function and viability because proper care is vital to preventing exacerbation of the initial exposure and injury. Rapid rewarming is optimal when further cold exposure can be avoided reliably. Repetitive freeze-thaw cycles are associated with increased morbidity and tissue loss caused by progressive microvascular injury and thrombosis. The subsequent care is largely supportive and consists of wound care and physical and hydrotherapy to promote optimal functional recovery.

Environmental injuries

Environmental injuries and illnesses can happen in home, work, or recreational settings. The variety and severity of these injuries might require the clinician to call on skills from internal medicine, emergency medicine, and toxicology. Diseases of thermoregulation are hypothermia and hyperthermia. In each instance, treatment is based on the need to restore the patient's core temperature to normal and on monitoring for complications. The victim of a fire might suffer inhalation injury in addition to burns, and it is more likely that the inhalation injury will be fatal. Oxygen deprivation and inhalation of irritant or asphyxiant chemicals contribute to injury. Toxic plants can be the source of poisoning emergencies, especially in children. Misinformation and myths that surround common plants can create diagnostic problems (i.e., which plants really are toxic and require emergency measures). Venomous marine organisms can cause a wide range of injury, from cutaneous eruption to fatal envenomation. Most are encountered in a recreational setting, such as water sports, but keepers of home aquariums are subject to stings from venomous fish. Lightning injury can present many diagnostic and treatment dilemmas. An important point in this regard is that lightning injury and high-voltage electrical injury are different in pathology and require different approaches for treatment. A discussion of electrical, chemical, and thermal burns makes such differences apparent.

Hypothermia

Hypothermia may present to any department at any time. It may present as a primary or secondary illness and if not detected, and/or managed appropriately, treatment of other concurrent illnesses and patient survival may be severely compromised. This paper will endeavour to assist the nursing and medical staff of Accident and Emergency (A & E) departments to recognise and classify hypothermia. It will discuss the pathophysiology associated with heat loss and heat gain, and the implementation of appropriate management. The survival of the hypothermia patient is greatly dependent on several factors: method of rewarming, severity of hypothermia, duration prior to treatment, degree of hypotension, and severity of underlying disease (this being the most likely determinant of survival).

Noncardiogenic pulmonary edema associated with accidental hypothermia

The pulmonary system may be significantly affected by hypothermia. The association between NCPE and hypothermia is controversial. A 59-year-old man with mild hypothermia presented with NCPE after passive external rewarming following accidental immersion in water. The patient's course was uneventful after 48 h, allowing immediate withdrawal of assisted ventilation and supplemental oxygen.

Internal cardiac massage and mediastinal irrigation in hypothermic cardiac arrest

Two unconscious patients with unknown past medical histories were found to be severely hypothermic, with core temperatures of 80.2 degrees F and 86.7 degrees F, respectively. During the course of active internal rewarming, both patients sustained a cardiac arrest. Emergency thoracotomies were immediately done, and internal cardiac massage with warmed mediastinal irrigation was performed. Spontaneous cardiac activity developed in both patients. Within 24 hours after resuscitation, both patients were responsive and following commands.

Treatment of moderate-to-severe hypothermia in an urban setting

STUDY OBJECTIVES

To study the treatment of moderate-to-severe hypothermia using a combination of core rewarming techniques.

DESIGN

A prospective study.

SETTING

The emergency department of an urban, community hospital. TYPE OF PATIENTS: Sixteen patients who presented with accidental hypothermia with a core temperature of less than 32 C.

INTERVENTIONS

All patients were treated with warmed IV fluids either through central or peripheral IV lines and heated aerosol masks.

MEASUREMENTS AND MAIN RESULTS

The patients had a mean rewarming rate of 1.16 C/hr; all survived. The majority were chronic alcoholic patients who presented with multiple medical conditions that required hospitalization.

CONCLUSION

All patients recovered with this method of core rewarming.

Comparison of gastric lavage and thoracic cavity lavage in the treatment of severe hypothermia in dogs

A study was undertaken to compare warm gastric (Group 1) and closed thoracic cavity (Group 2) lavage for rewarming severely hypothermic dogs. Adult mongrel dogs were monitored by intra-arterial catheter, central venous catheter, and ECG, and by central venous, esophageal, and rectal temperature probes. Animals were externally cooled to an average of 21.2 C using ice bags. Eight Group 1 and eight Group 2 animals underwent continuous warm saline gastric or closed thoracic cavity lavage, respectively, using afferent and efferent nasogastric and thoracostomy tubes. No animal suffered ventricular fibrillation during tube placement. The closed lavage system consisted of a high-efficiency heat exchanger, a roller pump infusion device, and a heat exchange fluid bath. The lavage fluid circulated at a flow rate of 550 mL/min and a temperature of 39 C. Thoracic lavage animals were followed clinically for 24 hours for evidence of complications, then euthanized and autopsied. The mean time required to rewarm the animals 10 C by central venous temperature probe was 210.9 +/- 18.6 minutes for the gastric group and 99.3 +/- 23.0 minutes for the thoracic group (P less than .001). Rectal temperature consistently lagged behind central venous temperature during both the cooling and rewarming phases in both treatment groups. All of the thoracic lavage animals made an uneventful recovery. Continuous warm saline thoracic cavity lavage for core rewarming of severely hypothermic dogs is more effective than gastric lavage, and appears to be safe.(ABSTRACT TRUNCATED AT 250 WORDS)

Multicenter hypothermia survey

A multicenter survey evaluated the clinical presentation, treatment, and outcome of accidental hypothermia. Data were collected from 13 emergency departments, with 401 of the 428 cases presenting during a two-year study period. Core temperatures ranged from 35 C to 15.6 C (mean, 30.57 C +/- 3.53) with 272 cases (63.6%) less than or equal to 32.2 C. There were no significant differences by age in presenting temperature, rewarming strategies, or mortality. The first hour rewarming rate was significantly (P less than .05) faster in the population less than or equal to 59 years (1.08 +/- 1.39 C/hr) than in those greater than or equal to 60 years (0.75 +/- 1.16 C/hr). Male core temperatures averaged 30.27 +/- 3.44 C versus female temperatures of 31.1 +/- 3.61 C. There were no clinically significant differences in male (N = 296) versus female (N = 132) profiles. High ethanol levels (315 to 800 mg%) did not affect outcome. Nine of 27 (33%) patients who received CPR initiated in the field survived, versus six of 14 (43%) with CPR begun in the ED. The profile of the CPR versus non-CPR population differed significantly (P less than .05) in location (outdoors), initial temperature (24.8 +/- 3.77 C vs 30.94 +/- 3.12 C), third-hour rewarming rate (2.28 +/- 1.53 C vs 1.17 +/- 1.18 C/hr), and numerous laboratory parameters. Tracheal intubation was performed without incident in 117 cases, of which 97 were less than or equal to 32.2 C. There were 73 fatalities (17.1%). Of these, 84.9% (N = 62) were less than or equal to 32.2 C. Predisposing conditions in this group included "serious" illness (30), systemic infection (28), trauma (15), immersion (ten), frostbite (seven), and overdose (two). The initial pulse, hemoglobin, and first-hour rewarming rate was lower in the deceased population, while the potassium, urea nitrogen, creatinine, and phosphorus were elevated. Excluding treatment combinations, outcome with exclusive use of a single rewarming strategy was passive external rewarming, 14 deaths below 32.2 C, 13 above; active external rewarming, six deaths below 32.2 C, two above; active core rewarming, 38 deaths below 32.2 C, none above. Refinements of the American Heart Association's CPR standards in hypothermia and a Hypothermia Survival Index are proposed.

Treatment of severe accidental hypothermia using the Clinitron bed

Two cases of severe accidental hypothermia (core temperature less than 28 degrees C) rewarmed employing the Clinitron system are described. The physiological changes during hypothermia and rewarming are discussed and the current concepts of rewarming (active external versus internal) outlined. It is suggested that severely hypothermic patients can be successfully treated by rapid external rewarming using the Clinitron heated fluidised-bead bed. This method combines the advantages of rapid rewarming, minimal physiological disturbance and is non invasive.