INHALATION OF NITROUS-OXIDE EXPANDS EPIDURAL AIR BUBBLES

Background and Objectives. Epidural air bubbles are known to persist f or more than 24 hours after injection. Nitrous oxide may cause expansi on of these bubbles. Methods. Nine dogs were anesthetized. Ten mL air and 9 mL of iophendylate were injected into the lumbar epidural space. Control animals (n = 3) breathed halothane in 100% oxygen. Experiment al animals (n = 6) breathed halothane in 70/30 nitrous oxide/oxygen. L ateral radiographs were taken before and just after injection, and aga in 3 hems after breathing either 70% nitrous oxide or 100% oxygen, Epi dural space pressure was monitored and recorded during these 3 hours. Results. Ln all experimental animals, an increase in bubble size was o bserved. In the control animals, bubble size either remained the same or decreased. Epidural space pressure did not change in any animal. Co nclusions. Inhalation of nitrous oxide results in expansion of epidura l air bubbles. This may cause displacement of epidural local anestheti cs if large volumes of air are present in the epidural space.