Postoperative intravenous patient-controlled analgesia using hydromorphone and metamizole (dipyrone). A prospective, randomised study

Most potent opioid analgesics available in Germany have been investigated for use in postoperative patient-controlled analgesia (PCA). To conclude an older comparative series, it was the aim of the present study to define analgesic potency, side effects and patient acceptance of hydromorphone and its interaction with the non-opioid analgesic metamizole. A total of 120 patients recovering from elective abdominal or orthopaedic surgery, performed under standardised general anaesthesia, were randomised into 3 double-blind treatment groups to receive intravenous PCA demand doses of hydromorphone 283 mug (low dose, LD), 566 mug (high dose, HD) or a combination of hydromorphone 283 mug and metamizole 50 mg (low dose hydromorphone + metamizole, LM). Demand-independent low-dose background infusions were added to deliver hydromorphone at 67.9 mug/h in all groups, with additional metamizole at 12 mg/h in group LM. Lockout times were set to 2 min. After an average observation time of 24.5 +/-2.6 h (mean, SD) since start of PCA, cumulative PCA hydromorphone doses in groups LD, HD and LM were 7.8 +/-3.3, 12.1 +/-4.8 and 7.5 +/-2.0 mg, respectively, with the well known large inter-individual variability in all groups. Although hydromorphone consumption was significantly higher in group HD, self-reported pain intensities (VAS, retrospective pain scores) were quite comparable between the groups. Low dose, PCA bolus-linked metamizole did not significantly reduce hydromorphone consumption nor improve patient acceptance. Side-effects were typical for potent postoperative opioids, but never required special treatment; haemodynamic or respiratory complications were not observed in any patient. It can be concluded by comparison with other PCA opioid investigations performed under the same study protocol that hydromorphone is about 3-4 times as potent an analgesic as morphine under the conditions of intravenous postoperative PCA. Due to a favourable patient acceptance, hydromorphone can be recommended as a suitable alternative to other opioids for the treatment of postoperative pain.