EVALUATION OF PULMONARY-FUNCTION AND ANALGESIA IN DOGS AFTER INTERCOSTAL THORACOTOMY AND USE OF MORPHINE ADMINISTERED INTRAMUSCULARLY OR INTRAPLEURALLY AND BUPIVACAINE ADMINISTERED INTRAPLEURALLY

Eighteen dogs undergoing lateral thoracotomy at the left fifth interco stal space were randomly assigned to 1 of 3 postoperative analgesic tr eatment groups of 6 dogs each as follows: group A, morphine, 1.0 mg/kg of body weight, IM; group B, 0.5% bupivacaine, 1.5 mg/kg given interp leurally; and group C, morphine, 1.0 mg/kg given interpleurally. Heart rate, respiratory rate, arterial blood pressure, arterial blood gas t ensions, alveolar-arterial oxygen differences, rectal temperature, pai n score, and pulmonary mechanics were recorded hourly for the first 8 hours after surgery, and at postoperative hours 12, 24, and 48. These values were compared with preoperative (control) values for each dog. Serum morphine and cortisol concentrations were measured at 10, 20, an d 30 minutes, hours 1 to 8, and 12 hours after treatment administratio n. All dogs had significant decreases in pHa, Pa-O2, and oxygen satura tion of hemoglobin, and significant increases in Pa-CO2 and alveolar-a rterial oxygen differences in the postoperative period, but these chan ges were less severe in group-B dogs. Decreases of 50% in lung complia nce, and increases of 100 to 200% in work of breathing and of 185 to 3 83% in pulmonary resistance were observed in all dogs after surgery. I ncreases in work of breathing were lower, and returned to preoperative values earlier in group-B dogs. The inspiratory time-to-total respira tory time ratio was significantly higher in group-B dogs during postop erative hours 5 to 8, suggesting improved analgesia. Blood pressure wa s significantly lower in group-A dogs for the first postoperative hour . Significant decreases in rectal temperature were observed in all dog s after surgery, and hypothermia was prolonged in dogs of groups A and C. Significant differences in pain score were not observed between tr eatment groups. Cortisol concentration was high in all dogs after anes thesia and surgery, and was significantly increased in group-B dogs at hours 4 and 8. Significant differences in serum morphine concentratio n between groups A and C were only observed 10 minutes after treatment administration. In general, significant differences in physiologic va riables between groups A and C were not observed. Results of the study indicate that anesthesia and thoracotomy are associated with signific ant alterations in pulmonary function and lung mechanics. Interpleural ly administered bupivacaine appears to be associated with fewer blood gas alterations and earlier return to normal of certain pulmonary func tion values. Interpleural administration of morphine does not appear t o provide any advantages, in terms of analgesia or pulmonary function, compared with its IM administration.