Deep hypothermia

Tisherman, S.A., Safar, P., Radovsky, A., Peirzman, A., Marrone, G., Kuboyama, K., Weinrauch, V. (1991). Profound hypothermia (< 10 °C) compared to deep hypothermia (15 °C) improves neurologic outcome in dogs after two hours circulatory arrest induced to enable resuscitative surgery. J. Trauma 31, 1051-1062. 

Weinrauch V., Safar P., Tisherman S., Kuboyama K., and Radovsky A. (1992) Beneficial effect of mild hypothermia and detrimental effect of deep hypothermia after cardiac arrest in dogs. Stroke 23,1454-1462. 

Sutton L. N., Clark B. J., Norwood C. R., Woodford E. J., and Welsh F. A. (1991) Global cerebral ischemia in piglets under conditions of mild and deep hypothermia. Stroke 22,1567-1573. 

M. L. Bias, E. B. Lobato, and T. Martin, Non-Invasive Infrared Spectroscopy as a Monitor of Retrograde Cerebral Perfusion During Deep Hypothermia, J. Cardiothoracic Vase. Anesthesia, 13(2), 244-245 (1999). 

Factors involved in thermal regulation will be considered first for near-neutral environments. Then situations which involve greater thermal stress will be considered. Special life support systems designed to enable man to perform useful work in hostile environments will be discussed. Several examples of using deep hypothermia in surgery will be presented also. The paper will conclude with a discussion of mathematical simulation of the human thermal system. 

Hyperbolic expansion The expansion of a fluid according to the law pV = Hypothalamus The temperature control center at the base of the brain, which regulates body temperature. Hypothermia The physiological state resulting when the deep core body temperature drops below 35 C. It results in vasoconstriction and shivering in an attempt to conserve body heat. 

Patients with ethanol or sedative-hypnotic overdose may be euphoric and rowdy ("drunk") or in a state of stupor or coma ("dead drunk"). Comatose patients often have depressed respiratory drive. Depression of protective airway reflexes may result in aspiration of gastric contents. Hypothermia may be present because of environmental exposure and depressed shivering. Ethanol blood levels greater than 300 mg/dL usually cause deep coma, but regular users are often tolerant to the effects of ethanol and may be ambulatory despite even higher levels. Patients with GHB overdose are often deeply comatose for 3-4 hours and then awaken fully in a matter of minutes. 

Narcosis due lo CO is characterized by mental disturbances which may range from confusion, mania, or drowsiness to deep coma, headache, sweating, muscle twitching, increased intracranial pressure, pounding pulse, low blood pressure, hypothermia, and sometimes papilloedcina. The basic mechanisms by which carbon dioxide induces narcosis is probably through interference with the intracellular enzyme systems, which are all sensitive to pll changes. 

Chlormethiazole is widely used as a sedative in the treatment of alcoholism but tolerance develops rapidly. However patients often stop taking the drug. If, following a bout of heavy (hinking, a large dose of chlormethiazole is tdcen, the patient collapses into deep coma accompanied by respiratory depression, hypotension, and hypothermia. 

Further benefits accrue from combining these techniques the safety of procedures requiring low blood flow techniques is markedly increased, deep levels of hypothermia may be employed without irritation to the myocardium, and adequate oxygenation should allow for an undisturbed rewarming of the body. 

Overdosage with glutethimide (10 to 20 g) produces symptoms that are identical to those produced by barbiturates, which include profound CNS depression, hypothermia, altered deep-tendon reflexes, absence of corneal and papillary reflexes, absence of response to painful... 

Overdose of thioridazine causes CNS depression characterized by deep, unarousable sleep and possible coma, hypotension or hypertension, extrapyramidal symptoms, abnormal involuntary muscle movements, agitation, seizures arrhythmias, ECG changes, hypothermia or hyperthermia, and autonomic nervous system dysfunction. 

B. Hypothermia is common in patients with deep coma, especially if the victim has suffered exposure to a cool environment. Hypotension and bradycardia commonly accompany hypothermia. 

III. Clinical presentation. Overdose with any of these drugs may cause drowsiness, ataxia, nystagmus, stupor, coma, and respiratory arrest. Deep coma may result in absent reflexes, fixed pupils, and depressed or absent electroencephalo-graphic (EEG) activity. Hypothermia is common. Most agents also slow gastric motility and decrease muscle tone. Hypotension with a large overdose is caused primarily by depression of cardiac contractility and, to a lesser extent, loss of venous tone. 

IV. Diagnosis is usually based on a history of ingestion, because clinical manifestations are fairly nonspecific. Hypothermia and deep coma may cause the patient to appear dead thus, careful evaluation should precede the diagnosis of brain death. Chloral hydrate is radiopaque and may be visible on plain abdominal x-rays. 

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