The physiological response to norepinephrine during hypothermia and rewarming

Our purpose was to determine if core hypothermia influences physiological r esponses to norepinephrine (NE); and if rewarming reverses these effects. A nimals were instrumented to measure mean arterial pressure (MAP) and cardia c output (CO). Core temperature was manipulated from 37.5 degrees C (normot hermia), to 30 degrees C (hypothermia) and the back to 37.5 degrees C (rewa rming) using an external arterial-venous femoral shunt. At each of these te mperatures, baseline CO and MAP were measured. Norepinephrine (NE) was infu sed at rates to deliver 0.2, 1.0, or 5 mu g kg(-1) per h. At each dose CO a nd MAP was measured again. Systemic vascular resistance (SVR) was calculate d using the formula (SVR = (MAP/CO) x 80). Eight animals underwent all thre e phases of the protocol. The response to NE during normothermia was a sign ificant increase in MAP to doses of 1 mu g kg(-1) per min (P < 0.01) and 5 mu g kg(-1) per min (P < 0.01) and SVR to doses of 1 mu g kg(-1) per min (P < 0.01) and 5 mu g kg(-1) per min (P < 0.01). The response to NE during hy pothermia was a significant increase in MAP only at doses of 1 mu g kg(-1) per min (P = 0.03) and 5 mu g kg(-1) per min (P = 0.01). The response to NE after rewarming was a significant increase in MAP only at a dose of 5 mu g kg(-1) per min (P = 0.03). This study shows that core hypothermia causes a change in physiological response to NE that rewarming does not reverse. (C ) 1998 Elsevier Science Ireland Ltd. All rights reserved.