To the Editor:-The published description of delayed subarachnoid migration by Jaeger and Madsen is beyond belief. According to their report, the patient was found severely hypopneic approximately 28–32.5 h after commencement of an epidural infusion of 0.125% bupivacaine with 6 mg of hydromorphone per milliliter at 14 ml/h. During that infusion period, the patient would have received a cumulative epidural dose of 392–455 ml fluid, 490–599 mg bupivacaine, and 2,352–2,730 mg of hydromorphone-a dose of hydromorphone large enough to fell a full-grown white rhinoceros.
Assuming an overlooked printing error of “milligrams” instead of micrograms (a fact kindly corroborated by the senior author), the amended cumulative dose of hydromorphone would lie somewhere between 2.35–2.73 mg of epidural hydromorphone. In addition, a hole had been accidentally driven through the dura by a Tuohy needle of unstated caliber, leaving free access to the subarachnoid space. Regardless of the dural puncture, epidural hydromorphone undergoes rostral spread with repeated doses, and sudden respiratory failure has been reported 4.5 h after a single bolus epidural injection of 1 mg hydromorphone. 
Therefore, in the presence of a waterlogged, opioid-rich epidural space and an open highway into the subarachnoid space via the accidental dural puncture hole, the subsequent respiratory collapse becomes highly predictable. There seems no logical reason to invoke some remote deus ex machina to explain the outcome, least of all a highly improbable suspect such as the remarkably soft and pliable Arrow FlexTip Plus epidural catheter.
Philip R. Bromage, M.B.B.S., F.F.A.R.C.S., F.R.C.P.(C)
Montgomery Center, Vermont
(Accepted for publication January 20, 1998.)