Postoperative patient-controlled thoracic epidural analgesia: importance of dose compared to volume or concentration.

This randomised and blinded study evaluated the quality of analgesia and the incidence of side-effects of two concentrations of levobupivacaine (0.15% and 0.5%) given as an equal mg-bolus-dose (5 mg) via patient-controlled epidural analgesia after lower abdominal surgery. The patients were randomly assigned into two groups to receive either 0.15% levobupivacaine as a 3.3 ml bolus on demand, with a lockout interval of 30 minutes (n=30), or 0.5% levobupivacaine as a 1 ml bolus on demand, with a similar lockout interval (n=30). For both groups we combined the bolus on demand with a background infusion of 5 mg/hour levobupivacaine, i.e. 3.3 ml/hour 0.15% or 1 ml/hour 0.5% of levobupivacaine. The epidural catheters were inserted in a lower thoracic intervertebral space before induction of general anaesthesia. The following variables were registered in the 48 hours after surgery: upper and lower sensory block, pain scores at rest and after coughing, rescue morphine consumption, motor blockade, haemodynamic (arterial blood pressure and heart rate), nausea and vomiting, and patient satisfaction ratings. The two groups had similar sensory block, quality of analgesia, rescue morphine consumption requirement, motor blockade and side-effects, and both had a high satisfaction rate. These findings indicate that administering the same dose of levobupivacaine in either a low or high concentration via the patient-controlled epidural analgesia mode, combined with a background infusion, provides an equal quality of analgesia for low thoracic level epidurals with no difference in the incidence of side-effects.