Book Review

Therapeutic Hypothermia

N Engl J Med 2005; 352:2562June 16, 2005

Article

Therapeutic Hypothermia
Edited by Stephan A. Mayer and Daniel I. Sessler. 629 pp., illustrated. New York, Marcel Dekker, 2005. $149.95. ISBN: 0-8247-5478-6

The recognition that modest changes in temperature may modulate the outcome after global or focal cerebral ischemia, or both, has led to the use of mild-to-moderate hypothermia to reduce reperfusion injury in diverse clinical settings — for example, after cardiac arrest or head trauma and in neonates after intrapartum hypoxia–ischemia. This book provides a clear overview of this type of intervention and integrates many of the complex issues associated with its implementation in clinical practice.

Although the title is Therapeutic Hypothermia, a substantial portion of the book deals with the adverse consequences of hyperthermia in the progression of brain injury — an effect that may be as important as the potential neuroprotective effects of cooling the brain. This influence of changing temperature extends to the period of rewarming after hypothermia and has been associated with rebound cerebral edema, elevation of intracranial pressure, and increased rates of pneumonia.

Although seemingly simple to implement, the lowering and maintenance of core temperature is complex and triggers very active thermoregulatory processes. Several chapters in this book are devoted to the basic practical management of temperature. For example, the optimal site from which to monitor brain temperature varies and appears to be related to the degree of hypothermia. Thus, the nasopharynx and tympanic membrane are the best sites during profound hypothermia, whereas standard core sites provide a reasonable approximation during modest hypothermia. The method of determining arterial blood-gas values is important, because when body temperature is reduced, the blood becomes more viscous and the solubility of the gases in the blood increases, thereby affecting the pH level. Correcting the blood gases for temperature may result in an increase in carbon dioxide with a resultant increase in cerebral blood flow, whereas if the blood gases are not corrected for temperature, this may result in the opposite effect. Changes in cerebral blood flow may exacerbate ongoing brain injury.

Some of the chapters are devoted to potential systemic complications. Notably, the lowering of body temperature interferes with the clearance rates of anesthetics and sedatives, with the potential for prolonged sedation during the recovery phase, which may interfere with the neurologic assessment of the hypothermic patient. The chapter on new methods to induce hypothermia, such as endovascular cooling, points out that these methods are potentially more advantageous than the currently used surface-cooling methods in that the desired core temperature can be achieved more rapidly and with more precision.

Several chapters discuss the clinical application of hypothermia in adults. A criticism of the book is that the two studies that have shown a benefit with the use of modest hypothermia — namely, in patients who remain comatose after out-of-hospital cardiac arrest as a consequence of ventricular fibrillation — are very briefly reviewed, and the significance of the findings may be missed by the casual reader. Conversely, it remains unclear why modest hypothermia has had a limited effect in patients with traumatic brain injury or ischemic stroke, although in both chapters the authors provide an excellent review of the complex issues that may contribute to this observation. Finally, there is the exciting possibility that hypothermia may reduce the extent of myocardial infarct size, although the most effective method of cooling the heart requires further delineation.

Mayer and Sessler are to be commended for producing an excellent textbook that should serve as both a resource for a wide variety of disciplines dedicated to neuroprotection and a spark for future research efforts.

Jeffrey Perlman, M.B., Ch.B.
Weill–Cornell Medical Center, New York, NY 10021