Neuraxial Pethidine After Lumbar Surgery Trial

Rationale Lumbar laminectomy is commonly performed to alleviate local or nerve root pain in the lower back and legs. Post-operative pain relief may consist of oral or parenteral medication, with an increasing body of research focussing on the use of epidural analgesics and anaesthetics (see references). It is the current practice of surgeons at this hospital to use an epidural infusion of pethidine in some patients.

Epidural medication has sometimes been administered at the conclusion of an operation as a single dose, in the form of a spray1 2 3, paste 4, or been sponged onto the exposed epidural space.5 Agents used in this manner have included morphine, tramadol, buprenorphine and methylprednisolone. In one such study Bourke6 found that a single dose of epidural morphine 3 mg reduced pain scores and analgesic requirements for 24 hours when compared to the same dose given intramuscularly, suggesting that direct epidural administration is superior to parenteral administration.

As an alternative, analgesics have been infused post-operatively via and epidural catheter placed at the end of surgery under direct vision. Cohen7 compared an epidural infusion of morphine and bupivacaine to PCA morphine in 54 patients and found no difference in outcome between groups. Other studies which have been uncontrolled or unblinded have demonstrated the efficacy of epidural narcotic administration (morphine, fentanyl and hydromorphone) following lumbar laminectomy surgery.8 9 10 11 12 Thus there is some evidence supporting the use of this form of analgesia, despite a report of an incidence of technical failure in surgically-positioned epidural catheters. 13

To date, no published study has investigated the use of epidural pethidine following lumbar laminectomy. Pethidine has some theoretical advantage over other agents used.14 As an opioid with intermediate lipid solubility, it is less likely to leave the epidural space than fentanyl. The low lipid solubility of morphine increases its likelihood of causing central respiratory depression as it crosses the dura to the site of action at a slower rate than pethidine.14 Pethidine also has an intrinsic local anaesthetic activity.

An early study showed that patients receiving a single dose of epidural pethidine at the end of major surgery had a longer period before further analgesics were required than patients receiving equipotent doses of morphine or pethidine. Blake15 compared patient-controlled epidural pethidine (PCEA) with intravenous patient-controlled analgesia (PCA) pethidine following abdominal aortic surgery, where all patients also received epidural bupivicaine. The PCEA group had lower pain scores, despite having lower plasma pethidine concentrations, confirming the central action of epidural pethidine. In a similar study, Chen16 compared epidural and PCA pethidine in 37 patients following gastrectomy. Pain and satisfaction scores were similar, but the epidural group had lower plasma concentrations of pethidine and norpethidine.