PATIENT-CONTROLLED ALFENTANIL - TARGET-CONTROLLED INFUSION FOR POSTOPERATIVE ANALGESIA

We have compared the opioid effects of a patient-demand, target-contro lled infusion of alfentanil (n = 10), with patient-controlled bolus ad ministration of morphine (n = 10) following major spinal surgery in Ch inese patients aged from 11 to 67 years. The same general anaesthesia regimen was used in all patients. One group of patients were given int ra-operative morphine analgesia followed by postoperative intravenous morphine patient-controlled analgesia, while the other group received an intra-operative target-controlled infusion of alfentanil. Following surgery, the alfentanil group were given control of a handset and wer e able to increase the target alfentanil plasma level in 5 ng.ml(-1) i ncrements with a 2-min lockout interval. If analgesia was not demanded within a 15-min period, the computer reduced the target concentration by 5 ng.ml(-1). All patients had continuous pulse oximetry monitoring and hourly recording of pain, sedation, nausea scores and respiratory rate. Patients receiving alfentanil had the target concentration note d hourly and four blood samples taken during the first 24 h for measur ement of plasma alfentanil concentrations by high performance liquid c hromatography. The alfentanil infusion system was equally effective as an analgesic technique when compared with morphine patient-controlled analgesia. There were no hypoxaemic episodes (oxygen saturation <94%) , no difference in sedation scores and the incidence of nausea (30%) w as the same in both groups. There was a significantly (p<0.001) lower respiratory rate in the alfentanil group compared with patients receiv ing morphine at, clinically assessed, equianalgesia. The predicted pla sma alfentanil concentrations increased rapidly from about 30 ng.ml(-1 ) during the first 4 h to around 100 ng.ml(-1) at the end of the 24-h study period. The precision of the target-controlled infusion system w as 75.4% and the mean prediction error (bias) 58.1%, suggesting an und erestimation of the measured alfentanil concentrations by the alfentan il infusion system in these Chinese patients.