Changes in cardiorespiratory and muscle function associated with the development of postoperative fatigue.

An understanding of the factors which contribute to postoperative fatigue may benefit the rehabilitation of patients after surgery. Subjective feelings of fatigue and fatigue measured objectively in the adductor pollicis muscle after ulnar nerve stimulation have been studied in relation to changes in cardiorespiratory function and muscular efficiency both at rest and when walking on a treadmill at a work rate of 20 and 56 kpm min-1. Twelve patients admitted for elective abdominal surgery were studied before operation and again on the third postoperative day. The postoperative period was characterized by an increased feeling of fatigue. Surgery had no effect upon fatigue in the adductor pollicis muscle suggesting that the genesis of postoperative fatigue is partly central in origin. Muscular efficiency (s.d.) fell from 34(6) per cent before operation to 22(3) per cent (P less than 0.05) on the third postoperative day and was accompanied by a 19 per cent rise in the net energy (s.d.) expenditure (7.3(0.8) to 8.6(0.3) kJ min-1; P less than 0.03) required to perform a given workload. The increased cardiorespiratory effort and reduced muscular efficiency associated with the performance of low-intensity exercise may limit mobilization after surgery and contribute to a greater feeling of fatigue.