Baroreflex modulation of peripheral vasoconstriction during progressive hypothermia in anesthetized humans

Mild hypothermia is a major concomitant of surgery under general anesthesia . We examined the hypothesis that baroreceptor loading/unloading modifies t hermoregulatory peripheral vasoconstriction and, consequently, body core te mperature in subjects undergoing lower abdominal surgery with general anest hesia. Thirty-six patients were divided into four groups: control group (C) , applied positive end-expiratory pressure (PEEP; 10 cmH(2)O) group (P), ap plied leg-up position group (L), and a group of leg-up position patients wi th PEEP starting 90 min after induction of anesthesia (L + P). The esophage al temperature (T-es) and the forearm-fingertip temperature gradient, as an index of peripheral vasoconstriction, were monitored for 3 h after inducti on of anesthesia. Mean arterial pressure and pulse pressure did not change during the study in any group. The change in right atrial transmural pressu re from the baseline value was 0.3 +/- 0.1 mmHg in C, -3.0 +/- 0.5 mmHg in P, and 2.3 +/- 0.4 mmHg in L (P < 0.01). The change in Tes at the end of th e study was -1.7 +/- 0.1 (35.1 +/- 0.1)degrees C in C, -1.1 +/- 0.1 (35.7 /- 0.1)degrees C in P, and -2.7 +/- 0.1 (34.1 +/- 0.1)degrees C in L, showi ng significant differences (P < 0.01). The Tes threshold for thermal periph eral vasoconstriction was 35.6 +/- 0.1 degrees C in C, 36.2 +/- 0.2 degrees C in P, and 34.8 +/- 0.2 degrees C in L (P, 0.01). Excessive Tes decrease in the leg-up-position operation was attenuated by applying PEEP (L + P gro up; P < 0.05). Our data indicate that baroreceptor loading augments and unl oading prevents perioperative hypothermia in anesthetized and paralyzed sub jects by reducing and increasing the body temperature threshold for periphe ral vasoconstriction, respectively.