Wound instillation for postoperative pain relief: a comparison between bupivacaine and saline in patients undergoing aortic surgery.

In a double blind trial 72 patients having elective aortic surgery were randomized to receive either 40 ml of 0.25% bupivacaine or 40 ml of saline through one or two indwelling wound irrigation catheters every four hours over a total of 48 hours. In transverse incisions the two catheters were randomly placed either subcutaneously or in the rectus sheath; in vertical incisions one catheter was placed subcutaneously. Analgesia was assessed by visual analogue score on Postoperative Days 1 and 2 and the number of doses of intramuscular morphine given during the instillation period. Pulmonary function was monitored by forced expiratory volume and peak flow on Postoperative Days 1 to 5; arterial blood gases were monitored preoperatively and Postoperative Day 2. In all parameters evaluated there was no statistically significant difference between the saline (n = 33) or the bupivacaine (n = 37) groups. Site of the catheter in the transverse groups made no difference. Comparing vertical (n = 21) and transverse (n = 49) incisions, the mean visual analogue scores on the first postoperative day were 40 and 29, respectively (p less than 0.05). Wound instillation with bupivacaine neither improves pulmonary function nor reduces morphine requirements when compared to saline. Transverse incisions may be less painful than vertical ones.