Effects of interpleural bupivacaine (0.5%) on canine diaphragmatic function

Several authors have questioned the potential for phrenic nerve paralysis with interpleural analgesia. This study was designed to examine the potential for phrenic nerve paralysis with the use of interpleural bupivacaine in dogs. Seven dogs were anesthetized, tracheally intubated, and allowed to breathe spontaneously with halothane/oxygen while in the supine position. After a midline laparotomy, two wires were inserted into the costal portion of each hemidiaphragm for measurement of electromyographic (EMG) signals. A balloon catheter was placed in the abdominal cavity to measure abdominal pressure. The abdomen was then closed. Airway pressure was measured through a side port in the endotracheal tube. Bilateral interpleural catheters were inserted with the loss-of-resistance technique. Each dog was used for two experiments, one on each side, except for one animal. To assess the contribution of the ipsilateral diaphragm to total respiratory effort, the airway was occluded at functional residual capacity for three consecutive breaths, and EMG, airway pressure, and abdominal pressure were measured. In five of nine experiments with bupivacaine, there was complete loss of EMG activity on the side of the injection. In two dogs, there was partial loss of diaphragmatic function, and in the remaining two, there was no change in EMG. In the normal saline solution group (n = 4), there was no change in the EMG. Two dogs that received bilateral bupivacaine injections developed paradoxical respiration with negative inspiratory intraabdominal pressures. Phrenic nerve paralysis or paresis can occur with interpleural blockade. The factors affecting the occurrence of this complication remain to be elucidated.