Analgesia in dogs after intercostal thoracotomy. A comparison of morphine, selective intercostal nerve block, and interpleural regional analgesia with bupivacaine.

Three postoperative analgesic protocols were assigned randomly to 24 healthy dogs after thoracotomy at the left fourth intercostal space. Morphine was administered parenterally to eight dogs after tracheal extubation; selective intercostal nerve blocks with bupivacaine hydrochloride and epinephrine were administered to eight dogs before closure of the thorax; and bupivacaine hydrochloride and epinephrine were administered through an interpleural catheter to eight dogs after tracheal extubation. Heart rate, respiratory rate, rectal temperature, hematocrit, plasma protein, blood gas, and pain score evaluations were recorded before surgery and 30 minutes, 1 hour, 2 hours, and 3 hours after extubation. Morphine caused significant decreases in blood pH and blood oxygen tensions, and significant increases in carbon dioxide tensions. Dogs treated with intercostal nerve blocks had no significant changes in these parameters, and dogs treated with interpleural bupivacaine had significant decreases in blood oxygen tension. All dogs had significant decreases in rectal temperature, and hypothermia was prolonged after morphine. Analgesia was initially adequate in most dogs, but some dogs in each treatment group had recurrence of pain and were treated with interpleural bupivacaine. One dog developed pneumothorax. Interpleural administration of bupivacaine produced analgesia equal to that produced by systemic administration of morphine or selective intercostal nerve block with bupivacaine. Bupivacaine was easily readministered through an interpleural catheter. Respiratory compromise was less in dogs treated with bupivacaine than in dogs treated with morphine. After intercostal thoracotomy, interpleural bupivacaine provided prolonged analgesia with fewer blood gas alterations than morphine.