SUBDURAL INJECTION OF MORPHINE FOR ANALGESIA FOLLOWING CESAREAN-SECTION - A REPORT OF 3 CASES

The subdural area is a potential space between the dura and the arachnoid membranes. It exists in the spinal meninges just as it does in the cranial meninges. In the past 17 yr a number of clinical reports have described the unintentional catheterization of this potential space1-3 and the delayed subdural migration of an epidural catheter.4,5 Recently Miller et al. reported a case of confirmed subdural administration of morphine.6 In that case, a young woman having a cesarean section under presumed epidural anesthesia was given 1.0 mg preservative-free morphine via the lumbar catheter. The patient had good postoperative analgesia, which lasted for 22 h with no side effects. The authors speculated that subdural injection of morphine may result in higher cerebrospinal fluid levels of drug than does epidural injection. In another recently published case, Brown et al. reported an intended epidural placement for long-term management of a patient with cancer pain, but a postoperative epidurogram showed the catheter to be subdural.7 It was left in place and used for pain management. Although the patient had required as much as 1,000 mg oral morphine daily, a dose of morphine usually administered intrathecally was chosen because of the potential for the catheter to migrate into the subarachnoid space. The patient achieved good pain control with an initial dose of 0.75 mg morphine. In both of these cases, the authors noted a markedly reduced dose requirement compared to that usually required by the epidural route, suggesting the potential for respiratory depression in the event of unintentional subdural morphine administration with usual epidural doses. We report three cases of radiographically confirmed subdural catheters that were used for cesarean section anesthesia. All three patients were given subdural morphine for post-cesarean section analgesia. The dose of morphine chosen, more typical of an epidural dose than of a subarachnoid dose, was considerably greater than those reported previously.