A novel approach for selective brain cooling: implications for hypercapnia and seizure activity.

OBJECTIVE: During selective brain cooling (SBC) the brain temperature (TB) is reduced while the core temperature (TC) remains unchanged. This animal study investigated changes in brain temperature induced by a novel approach of cooling the brain from the pharynx (pSBC) and whether these temperature changes are related to commonly encountered clinical situations (i.e., seizure activity and hypercapnia).
DESIGN: Experimental animal study.
SUBJECTS: Male Sprague-Dawley rats.
INTERVENTIONS: pSBC was achieved by a heat exchanger placed in the pharynx; hypercapnia and seizure activity were induced by adding CO2 to the respiratory gases and by intravenous injection of bicuculline, respectively. MEASUREMENTS AND
RESULTS: TB, TC, and pharynx (TP) were measured continuously with thermocouples. During pSBC TB declined significantly from 36.9+/-0.67 degrees C to 33.1+/-1.23 degrees C. There was a trend towards lower TC during pSBC (from 36.9+/-0.70 to 36.4+/-1.2 degrees C). TP during pSBC was 29.1+/-2.19 degrees C. From the lowest achieved pSBC temperature TB rose during CO2 challenge by 1.22+/-0.67 degrees C (vs. 0.85+/-0.34 degrees C in non-SBC controls). From the lowest pSBC temperature during seizure activity TB rose by 2.08+/-0.35 degrees C (vs. 1.15+/-0.55 degrees C in non-SBC controls).
CONCLUSIONS: Significant cooling of the cortex can be achieved by pSBC in a rat rodent model. Marked increases in TB with hypercapnia and with seizure activity were observed. These results may have implications for cooling methods in clinical settings. For example, pSBC may offer distinct advantages over alternative methods such as whole-body cooling and externally implemented SBC.