Nasopharyngeal cooling selectively and rapidly decreases brain temperature and attenuates neuronal damage, even if initiated at the onset of cardiopulmonary resuscitation in rats

Objective: To determine the effectiveness of nasopharyngeal cooling for selective brain cooling and neuroprotection from ischemia. Design: Prospective animal study. Setting: Experimental laboratory in a university hospital. Subjects: Male Wistar rats (n = 28). Interventions: In study 1, hippocampal temperature was decreased to 31°C under spontaneous circulation. In the nasopharyngeal cooling group, physiologic saline (5°C) was infused to the bilateral nasal cavities at the rate of 100 mL·min ^-1·kg weight^-1. In the whole body cooling group, a fan and a water blanket (5°C) were used. In study 2, ischemia and resuscitation were performed in normothermic and nasopharyngeal cooling (initiated with resuscitation after 5 mins of ischemia and continued for 20 mins) groups. Measurements and Main Results: The hippocampal temperature was decreased to 31°C in 7 ± 2 mins without any change in the rectal temperature in the nasopharyngeal cooling group, whereas a decrease in hippocampal temperature to 31°C took 33 ± 1 mins in the whole body cooling group. Although skull base region was cooled by nasopharyngeal cooling, the epidural temperature of the parietal region was lower than the hippocampal temperature, indicating that brain temperature was hematogeneously lowered. There was no difference between changes in cerebral blood flow or between the ratios of oxygen extraction from arterial blood in the head region in the nasopharyngeal cooling and whole body cooling groups. In the second study, all animals were successfully resuscitated, and the times required for recovery of mean arterial blood pressure (60 mm Hg) after resuscitation in the nasopharyngeal cooling and normothermic groups were the same. The histologic damage was significantly attenuated in the nasopharyngeal cooling group (33 ± 21% cell death in the hippocampus) compared with that in the normothermic group (73 ± 11%). Conclusions: Nasopharyngeal cooling enables rapid and selective reductions in cortical and subcortical temperatures without disturbing the recovery of systemic circulation after resuscitation.