Efficacy of different cooling technologies for therapeutic temperature management: A prospective intervention study.

BACKGROUND: Mild therapeutic hypothermia (32-36 °C) is associated with improved outcomes in patients with brain injury after cardiac arrest (CA). Various devices are available to induce and maintain hypothermia, but few studies have compared the performance of these devices. We performed a prospective study to compare four frequently used cooling systems in inducing and maintaining hypothermia followed by controlled rewarming. METHODS: We performed a prospective multi-centered study in ten ICU's in three hospitals within the UPMC health system. Four different cooling technologies (seven cooling methods in total) were studied: two external water-circulating cooling blankets (Meditherm® and Blanketrol®), gel-coated adhesive cooling pads (Arctic Sun®), and endovascular cooling catheters with balloons circulating ice-cold saline (Thermogard®). For the latter system we studied three different types of catheter with two, three or four water-circulating balloons, respectively. In contrast to previous studies, we not only studied the cooling rate (i.e., time to target temperature) in the induction phase, but also the percentage of the time during the maintenance phase that temperature was on target ±0.5 °C, and the efficacy of devices to control rewarming. We believe that these are more important indicators of device performance than induction speed alone. RESULTS: 129 consecutive patients admitted after CA and treated with hypothermia were screened, and 120 were enrolled in the study. Two researchers dedicated fulltime to this study monitored TH treatment in all patients, including antishivering measures, additional cooling measures used (e.g. icepacks and cold fluid infusion), and all other issues related to temperature management. Baseline characteristics were similar for all groups. Cooling rates were 2.06 ±â€¯1.12 °C/h for endovascular cooling, 1.49 ±â€¯0.82 for Arctic sun, 0.61 ±â€¯0.36 for Meditherm and 1.22 ±â€¯1.12 for Blanketrol. Time within target range ±0.5 °C was 97.3 ±â€¯6.0% for Thermogard, 81.8 ±â€¯25.2% for Arctic Sun, 57.4 ±â€¯29.3% for Meditherm, and 64.5 ±â€¯20.1% for Blanketrol. The following differences were significant: Thermogard vs. Meditherm (p < 0.01), Thermogard vs. Blanketrol (p < 0.01), and Arctic Sun vs. Meditherm (p < 0.02). No major complications occurred with any device. CONCLUSIONS: Endovascular cooling and gel-adhesive pads provide more rapid hypothermia induction and more effective temperature maintenance compared to water-circulating cooling blankets. This applied to induction speed, but (more importantly) also to time within target range during maintenance.

Determinants of heat generation in patients treated with therapeutic hypothermia following cardiac arrest.

BACKGROUND: Therapeutic hypothermia (TH) is recommended to reduce ischemic brain injury after cardiac arrest. The variables that predict heat generation by patients receiving TH are uncertain, as is how this heat generation relates to neurologic outcome. We hypothesized that patient characteristics, medication use, inflammation, and organ injury would be associated with heat generation. We further hypothesized that neurologic outcome would be most strongly associated with heat generation. METHODS AND RESULTS: Surface and intravascular cooling devices were used to provide TH in 57 consecutive cardiac arrest patients. Device water temperatures during the maintenance (33°C) phase were collected. Patient heat generation was quantified as the "heat index" (HI), which was the inverse average water temperature over a minimum of 2 hours of maintenance hypothermia. Variables measuring reduced ischemic injury and improved baseline health were significantly associated with HI. After controlling for presenting rhythm, a higher HI was independently associated with favorable disposition (OR=2.2; 95% CI 1.2 to 4.1; P=0.014) and favorable Cerebral Performance Category (OR=1.8; 95% CI 1.0 to 3.1; P=0.035). Higher HI predicted favorable disposition (receiver-operator area under the curve 0.71, P=0.029). HI was linearly correlated with arteriovenous CO2 (r=0.69; P=0.041) but not O2 (r=0.13; P=0.741) gradients. CONCLUSIONS: In cardiac arrest patients receiving TH, greater heat generation is associated with better baseline health, reduced ischemic injury, and improved neurologic function, which results in higher metabolism. HI can control for confounding effects of patient heat generation in future clinical trials of rapid TH and offers early prognostic information.