The effect of epidural anesthesia on respiratory distress induced by airway occlusion in isoflurane-anesthetized cats

The role of afferent information from the chest wall in the genesis of dysp nea is not fully elucidated. We have developed an animal model for the stud y of airway occlusion (AO) and proposed new concepts of minimum alveolar an esthetic concentration for AO (MACAOR) and the duration from the start of A O to the onset of the positive motor response (DOCCL) to evaluate respirato ry distress quantitatively. We examined the effects of thoracic epidural an esthesia on respiratory distress by using our animal model. Adult cats (n = 24) were anesthetized with isoflurane, and an epidural catheter was placed after T9 laminectomy. After determination of MACAOR, DOCCL was measured. A nimals were then randomly assigned into three groups: the EPD Group (n = 12 ) received epidural 1% lidocaine (0.4 mL/kg), IM saline (0.4 mL/kg), and sa line infusion. The IM Group (n = 6) received epidural saline (0.4 mL/kg), I M 1% lidocaine (1 mL/kg), and saline infusion. The PHE Group (n = 6) receiv ed epidural 1% lidocaine (0.4 mL/ kg) and IV phenylephrine (0.5-1 mug . kg( -1) . min(-1)) to maintain a stable arterial blood pressure. DOCCL and MACA OR were measured in each animal at 15 min after the administration of drugs . Plasma lidocaine concentrations were measured before and after epidural o r IM injection. DOCCL was significantly longer after epidural injection in all groups than before the injection. Although there was no significant dif ference in the values of MACAOR between before and after the epidural injec tion in the EPD Group, the IM administration of lidocaine in the IM Group s ignificantly reduced MACAOR. Plasma concentrations of lidocaine were simila r in all groups at all measurement points. Our data indicate that thoracic epidural anesthesia using 1% lidocaine significantly reduced respiratory di stress induced by AO. This effect is most likely caused by a systemic effec t of lidocaine rather than by reduced afferent information from the chest w all.