[Thoracic paravertebral blockade: postoperative analgesic effectiveness and plasma concentrations of bupivacaine]

To compare the analgesic efficacy of thoracic paravertebral blockade with that of endovenous morphine to measure the plasma levels of bupivacaine and to study the complications derived from both techniques in patients undergoing thoracic or abdominal surgery with unilateral incision.

Twenty ASA I-II patients allocated to two groups (A and B) of ten patients each were studied. Group A (5 cholecystectomies and 5 thoracotomies) received morphine 0.075 mg/kg i.v. every 3 hours after operation. Group B (5 cholecystectomies and 5 thoracotomies) received thoracic paravertebral blockade 15 ml of 0.37-5% bupivacaine with 1:200.000 adrenaline following tracheal extubation. Analgesia was evaluated according to the visual analogic scale (VAS) with laterality and extension of the blockade being assessed. The plasma levels of bupivacaine were measured by liquid chromatography in 5 patients. Blood pressure, heart rate and respiratory frequency were assessed in both groups. In group B the appearance of pneumothorax or other local complications were noted. The results were statistically analyzed using to the Student's test.

The patients in group A presented significantly more pain than those of group B. In these patients analgesia was unilateral. Plasma levels ranged between 0.56 mg/l at 5 minutes of administration and 0.17 mg/l at 240 minutes with a peak of 0.70 mg/l at 10 minutes with all these values being considerably lower those a determined as toxic (2-4 mg/l). No significant differences were found between the values of blood pressure, and cardiac and respiratory frequency of both groups. There were no complications derived from the technique.

Thoracic paravertebral blockade is a very effective postoperative analgesic technique and is superior to that of i.v. morphine in patients undergoing thoracic or unilateral abdominal surgery. Peak plasma levels were much lower than those considered as toxic complications of interest were observed. Therefore, this technique may be considered as an alternative to other blockades such as extradural, interpleural or intercostal.