Thermoregulatory and metabolic responses following cardiac surgery

Abstract

The thermoregulatory responses in 13 haemodynamically stable patients were evaluated over a 7-h period following coronary artery bypass graft surgery. Cutaneous vasoconstriction was defined by a forearm-to-fingertip skin temperature gradient (ΔTskin) ≥ 4°C and muscular hyperactivity was assessed by integrating the electromyographic signals (iEMG). Blood gases and lactate were measured in arterial, mixed venous and femoral venous blood. After arrival in ICU, we observed: (1) mild central hypothermia (Tc = 34.8±0.6°C) and elevated peripheral vascular resistance in all the patients; (2) ΔTskin ≥ 4°C in 11 of 13 patients that persisted until a median Tc of 37.1°C was achieved; (3) a transient increase in iEMG (±18%)was accompanied by an increase in total body O₂ uptake (+28%); (4) elevated muscle O₂ extraction rate(56±18% after 3 h) and lactate release. These data suggest that residual hypothermia in sedated patients safter cardiac surgery elicits appropriate thermoregulatory responses that are associated with transient O₂ supply/uptake mismatch within skeletal muscles.