Respiratory depression after intrathecal narcotics

Three out of six patients who had received 1 mg of morphine and 0.22 ml plain bupivacaine 0.5%/segment as a subarachnoid spinal anaesthetic developed serious and delayed respiratory depression on several occasions. This was reversed by intravenous naloxone. It is postulated that the morphine had diffused to the level of the cisterna magnum and thence through brain tissue around the fourth ventricle. Naloxone did not reverse the analgesia.