Pharyngeal cooling decreases brain temperature and intracranial pressure during resuscitation in monkeys

Introduction: The development of a technique that enables brain temperature to be immediately and selectively reduced without affecting systemic circulation is needed to perform resuscitative hypothermia in a clinical situation. Since bilateral common carotid arteries exist at about 1 centimeter (C) from the pharynx, cooling the pharyngeal region decreases the carotid arterial temperature first and subsequently decreases brain temperature before lowering cardiac temperature. The present study was designed to evaluate the effects of pharyngeal cooling on brain temperature, systemic temperature, intracranial pressure and extracellular glutamate concentration during resuscitation in monkeys. Methods: Japanese monkeys (7.5+-2.4 kg) were divided into a control group (n=6) and a pharyngeal cooling group (n=3) and were anesthetised with 1% isoflurane. Cardiac arrest (12 minutes) was initiated with electrical stimulation. Changes in intracranial pressure (parietal region) and epidural (parietal region), sub-cortical (parietal region, 3 cm below the cortical surface) and rectal temperatures were monitored during a 30-minute resuscitation period. A micro dialysis probe was inserted into the parietal cortex for the measurement of glutamate concentration. In the pharyngeal cooling group, a pharyngeal cuff was inserted into the pharynx and was perfused with water (5 C degree) at the rate of 500 ml/minute from the onset of resuscitation for 30 minutes. Results: Cortical (33.3+-0.7 C degree) and sub-cortical (35.8+-0.5 C degree) temperatures decreased during cardiac arrest in both groups. In the control group, however, cortical and subcortical temperatures increased with the initiation of resuscitation and reached 35.1+-0.5 C degree and 36.5+-0.2 C degree, respectively, 30 minutes later. In the pharyngeal cooling group, cortical and sub-cortical temperatures decreased and reached 31.1+-1.5 C degree and 32.4+-1.3 C degree, respectively, 30 minutes later. Rectal temperature was unchanged in both groups. During the resuscitation period, the intracranial pressure increased to 30+-16 mmHg (control) and 14+-6 mmHg (pharyngeal cooling) and took 23+-9 minutes (control) and 6+-1 minutes (pharyngeal cooling) to become less than 10 mmHg. Extracellular glutamate concentration was unchanged during cardiac arrest in both groups and increased after the onset of resuscitation. The maximum concentration of extracellular glutamate was decreased in the pharyngeal cooling group (13 micro mol/l) compared to that in the control group (39 micro mol/l). The periods required for recovery of mean arterial blood pressure (>50 mmHg) were the same (4+-1 minutes after onset of resuscitation) in the two groups. Conclusions: Cortical and sub-cortical temperatures were decreased with the initiation of pharyngeal cooling without lowering of rectal temperature during the resuscitation period in monkeys. Intracranial pressure and extracellular concentration of glutamate were lower in the pharyngeal cooling group without affecting time required for recovery of mean arterial blood pressure (>50 mmHg).