Efficacy of Intraoperative Cooling Methods : Anesthesiology

Background: Patients may require perioperative cooling for a variety of reasons including treatment of a malignant hyperthermia crisis and induction of therapeutic hypothermia for neurosurgery. The authors compared heat transfer and core cooling rates with five cooling methods. Cited Here...: Six healthy volunteers were anesthetized with desflurane and nitrous oxide. The cooling methods were 1) circulating water (5 [degree sign] Celsius, fulllength mattress and cover), 2) forced air (10 [degree sign] Celsius, full-length cover), 3) gastric lavage (500 ml iced water every 10 min), 4) bladder lavage (300 ml iced Ringer's solution every 10 min), and 5) ice-water immersion. Each method was applied for 40 min or until the volunteers' core temperatures approached 34 [degree sign] Celsius. The volunteers were rewarmed to normothermia between treatments. Core cooling rates were evaluated using linear regression. Cited Here...: The first volunteer developed abdominal cramping and diarrhea after gastric lavage. Consequently, the technique was not again attempted. Bladder lavage increased heat loss 10 [nearly =] 10 W and decreased core temperature 0.8 +/0.3 [degree sign] Celsius/h (r2 = 0.99 +/0.002; means +/SD). Forced-air and circulating-water cooling comparably increased heat flux, [nearly =] 170 W. Consequently, core cooling rates were similar during the two treatments at 1.7 +/0.5 [degree sign] Celsius/h (r2 = 0.99 +/0.001) and 1.6 +/1.1 [degree sign] Celsius/h (r2 = 0.98 +/0.02), respectively. Immersion in an ice water slurry increased heat loss [nearly =] 600-800 W and decreased core temperature 9.7 +/4.4 [degree sign] Celsius/h (r sup 2 = 0.98 +/0.01). Immersion cooling was associated with an afterdrop of [nearly =] 2 [degree sign] Celsius. Conclusions: Bladder lavage provided only trivial cooling and gastric lavage provoked complications. Forced-air and circulating-water cooling transferred relatively little heat but are noninvasive and easy to implement. Forced-air or circulating-water cooling, perhaps combined with intravenous administration of refrigerated fluids, may be sufficient in some patients. When noninvasive methods prove insufficient for rapid cooling, ice-water immersion or peritoneal lavage probably should be the next lines of defense. Mild hypothermia (1-3 [degree sign] Celsius below normal temperature) provides substantial protection against cerebral ischemia and hypoxemia in many animal species. [1-3] As might be expected from these data, core temperatures near 32 [degree sign] Celsius improve outcome after traumatic brain injury in patients with Glascow Coma Scores of 5-7. [4] Consequently, many anesthesiologists believe that mild hypothermia is indicated during operations likely to cause cerebral or spinal cord ischemia, such as carotid endarterectomy and neurosurgery. Mild hypothermia also slows triggering of malignant hyperthermia and reduces the severity of the syndrome once triggered in susceptible swine. [5,6] Core temperatures near 34 [degree sign] Celsius also appear to facilitate recovery and reduce the risk of death from septic adult respiratory distress syndrome. [7] Treatment of malignant hyperthermia crises should focus on administration of the specific antidote, dantrolene. [8] However, hyperthermia per se aggravates the syndrome, [5,6] produces coagulapathy, [9,10] and may worsen acidosis and electrolyte imbalances. Consequently, most reviews and book chapters on malignant hyperthermia recommend that patients experiencing a crisis be cooled actively. [11-13] Specific recommendations on how to cool patients, however, tend to be vague and often include statements such as "not only must the patient be cooled externally by water baths, but internal cooling is also necessary. This can be accomplished by intravenous infusions and lavage of the stomach, rectum, and open body cavities with cold solution. Extracorporeal cooling may also be employed." [12] In practice, it is rarely possible to simultaneously implement several independent cooling strategies, and efforts to do so may detract from other important treatments. Furthermore, some cooling methods are mutually exclusive (i.e., circulating water and water immersion), and others have substantial intrinsic dangers. It would thus be helpful to provide clinicians with specific cooling recommendations, based on the relative efficacy of available methods. Therefore, we compared heat transfer and core cooling rates with five different cooling methods: circulating water, forced air, gastric lavage, bladder lavage, and ice-water immersion.