Bradycardia during hypotension following release of a tourniquet in orthopaedic surgery.

Heart rate (HR) and mean arterial blood pressure (MBP) were followed in 39 consecutive patients during orthopaedic surgery with the leg exsanguinated by an inflatable tourniquet around the thigh. The circulation was stable in all patients until release of the tourniquet. Following release of the tourniquet MBP decreased from 94 +/- 5 (s.e. mean) to 45 +/- 12 mmHg (12.5 +/- 0.7 to 6.0 +/- 1.6 kPa) (P less than 0.005) in 10 patients, while it remained stable in the others. At the same time the hypotensive group showed a decrease in HR from 83 +/- 6 to 67 +/- 3 beats min-1 (P less than 0.005) while no significant change in HR was seen in the normotensive group. The hypotensive group was older (57 +/- 8 versus 50 +/- 4 years (P less than 0.05)), had a larger blood loss during surgery (2.9 +/- 1.2 versus 0.7 +/- 0.3 ml kg-1 (P less than 0.005)), and the duration of the operation was longer in this group (120 +/- 14 versus 60 +/- 27 min (P less than 0.001). It is suggested that the characteristic deviation of HR in conjunction with hypotension following release of a tourniquet is bradycardia.