Hemodynamic effects of interpleural analgesia in pigs

Evaluation of the hemodynamic effects of interpleural bupivacaine in dogs

The hemodynamic effects of interpleural (IP) bupivacaine were studied in six halothane-anesthetized dogs. On four separate occasions, each dog received IP saline (S), or bupivacaine at a low dosage of 1.5 mg/kg (L), high dosage of 3.0 mg/kg (H), or high dosage of 3.0 mg/kg with epinephrine 5 micrograms/mL (HE). Heart rate, systolic and mean arterial pressures, and base excess were significantly lower in the H dosage group than in the other treatment groups. Cardiac output, expressed as a percentage of change from baseline, was significantly higher in the L group than in the H and S groups. Pulmonary arterial pressure and respiratory rate were significantly higher in the HE group than in the other three groups. Mean plasma concentrations of bupivacaine peaked between 5 and 15 minutes after IP injection. Maximum plasma concentrations in individual dogs were variable; however, mean maximum plasma concentrations in the H and HE groups were not significantly different. Clinically significant hypotension occurred in one dog in the H group and in one dog in the HE group. No pulmonary complications were detected.

[Intrapleural analgesia]

Interpleural analgesia, a recently devised method for postoperative analgesia, consists of the injection of a local anaesthetic into the pleural space. The technique of the catheter insertion is simple and derived from the threadening of an epidural catheter, using the same equipment. An unilateral analgesia is obtained with a rapid onset but not efficient enough for a surgical procedure. The area covered by analgesia includes the thorax and the upper part of the abdomen. No haemodynamic adverse effects occur and ventilatory function is rather improved. The main mechanism of analgesia is probably a retrograde intercostal nerve blockade. Although the exact dose and volume of local anaesthetic is still controversial, 20 to 30 mL of 0.5% bupivacaine is very likely the most convenient. Lidocaine may also be administered at the dose of 2 mg.kg-1 of a 2% solution. Main indications of interpleural analgesia are cholecystectomies and thorax trauma patients. Adverse effects and hazards are uncommon and include mainly pneumothorax and toxic effects of a local anaesthetic overdose.