Slowing of the heart during hypotension in major abdominal surgery

Heart rate (HR) and mean arterial blood pressure (MBP) were studied during abdomino-perineal resections of the rectum under neurolept anesthesia in order to observe HR deviations due to hypovolemic hypotension. Of the 65 patients followed, 18 developed a systolic BP under 100 mmHg. Their blood loss (37 +/- 9 ml/kg, mean +/- s.e. mean) was higher than that of the normotensive control group (20 +/- 2 ml/kg, P less than 0.01), the urine production lower (8 +/- 1 versus 10 +/- 3 ml/kg, P less than 0.01) and blood transfusions amounted to 40 +/- 8 versus 24 +/- 2 ml/kg (P less than 0.01). In the hypotensive patients a decrease in MBP from 108 +/- 3 to 94 +/- 3 mmHg was accompanied by a simultaneous increase in HR from 81 +/- 3 to 91 +/- 3 beats/min (P less than 0.05). However, during the hypotensive incident where the MBP averaged 69 +/- 4 mmHg, HR decreased temporarily to 75 +/- 3 beats/min (P less than 0.001). After MBP was restored to 94 +/- 3 mmHg using volume repletion, HR increased to 95 +/- 3 beats/min (P less than 0.001). The results demonstrated a temporary slowing of HR in anesthetized, bleeding and hypotensive patients.