The effect of subarachnoid lidocaine and combined subarachnoid lidocaine and epidural bupivacaine on electrical sensory thresholds.

Eight patients undergoing abdominal surgery received a combination of spinal anesthesia (catheter at L2-3 level) and epidural anesthesia (catheter at T10-11 level). Sensory thresholds to electrical stimulation were measured at the S1, L1, T10, and T5 levels before injection, after spinal anesthesia, and after the addition of epidural anesthesia. Subarachnoid injections with 5% lidocaine (without dextrose) were given until a T4 sensory level to pinprick was obtained (mean dose, 175 mg lidocaine). The mean sensory thresholds were increased from 2.2 +/- 0.3, 2.4 +/- 0.4, 2.9 +/- 0.4, and 3.8 +/- 0.4 mA to 21.3 +/- 4.3, 13.3 +/- 4.9, 10 +/- 4.4, and 10.6 +/- 4.3 mA, respectively (p less than 0.05 at all levels). The addition of 5 ml 0.5% epidural bupivacaine further increased the mean sensory thresholds to 26.9 +/- 3.1, 21.7 +/- 4.1, 21.3 +/- 4.1, and 17.5 +/- 4.7 mA, respectively (p less than 0.05 at all levels). Combined subarachnoid and epidural local anesthetics provide an enhanced afferent block not obtainable by either technique alone.

Prevention of postoperative pain by balanced analgesia.

Fourteen patients undergoing colorectal surgery received an intraoperative afferent neural block with combined intrathecal and extradural local anaesthetics plus a balanced postoperative low-dose regimen of extradural bupivacaine 10 mg h-1-morphine 0.2 mg h-1 and systemic piroxicam 20 mg/24 h. Postoperative pain, assessed repeatedly during the initial 48 h, was prevented during rest, mobilization from the supine to the sitting position and during walking, in all but one patient; slight pain was observed intermittently during coughing in four patients.

Episodic arterial oxygen desaturation and heart rate variations following major abdominal surgery.

In 20 patients undergoing elective major abdominal surgery, heart rate and arterial oxygen saturation were monitored continuously during the night 2 days before operation and during the first and second nights after operation (23:00 to 07:30). Mean heart rate increased by 16 beat min-1 (P less than 0.0006) and mean oxygen saturation decreased by 3.2% (P less than 0.0002) after operation. Four patients had 21, 27, 120 and 372 episodes of sudden desaturation to a value less than 80% on the second night after operation. The patient with 372 episodes of sudden desaturation had severe cardiac arrhythmias on the morning of the third day after operation. In another patient the episodes of desaturation correlated with increases in heart rate. There was no correlation between administration of opioids and heart rate and saturation disturbances. The mechanism and clinical relevance of episodic desaturation in the late postoperative period remain unknown, but may be important in the pathogenesis of post-operative cardiac, cerebral and wound dysfunction.

Influence of bupivacaine on mepivacaine protein binding.

To elucidate the mechanism of any drug displacement interaction, we examined the protein binding of mixtures of mepivacaine and bupivacaine in serum and solutions of albumin or alpha 1-acid glycoprotein. Protein binding data with mepivacaine alone were best described by a model with one class of binding site and a partitioning constant in serum and by a model with one class of binding site in both isolated protein solutions. Binding affinity of mepivacaine in serum was reduced in the presence of bupivacaine. Displacement of mepivacaine by bupivacaine was observed when an alpha 1-acid glycoprotein solution was studied. Classic competitive inhibition was demonstrated. Bupivacaine reduced mepivacaine binding to albumin, but the degree of displacement was not significant. When administered simultaneously, these two amino-amide local anesthetics interact synergistically to produce a higher than expected free concentration of mepivacaine. This interaction increases the risk of toxicity.