Effects of intramuscular or interpleural administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy

Objective-To evaluate effects of interpleural or IM administration of morphine and interpleural administration of bupivacaine on pulmonary function in dogs that have undergone median sternotomy. Design-Experimental trial. Animals-18 healthy dogs. Procedure-Dogs underwent median sternotomy and were randomly assigned to groups of 6 dogs each. Group-A dogs were given morphine (1.0 mg/kg of body weight) IM; group-B dogs were given 0.5% bupivacaine (1.5 mg/kg) interpleurally; and group-C dogs were given morphine (1.0 mg/kg) interpleurally. Heart rate; systolic. diastolic, and mean arterial pressures; rectal temperature; pain score; and arterial blood gas partial pressures were measured and pulmonary function testing was performed immediately after extubation (time 0) and up to 48 hours later. Serum cortisol and morphine concentrations were measured at time 0 and up to 12 hours after surgery. Results-There was a significant decrease in pH, Pa-o2, mean oxygen saturation of hemoglobin, and dynamic compliance; and a significant increase in Pa-co2, alveolar-arterial difference in partial pressure of oxygen, pulmonary resistance, and work of breathing for dogs in all groups after surgery. Serum cortisol concentrations were significantly increased, compared with preoperative values, in all dogs. Serum cortisol concentrations were significantly higher in group-B dogs between 3 and 5 hours after surgery, compared with group-A dogs. Conclusions-Median sternotomy was associated with significant alterations in pulmonary function. Effects of interpleural administration of bupivacaine and morphine were similar to effects of IM administration of morphine.