[Spinal anesthesia with meperidine in general and vascular surgery]

Transient neurological symptoms after subarachnoid meperidine

IMPLICATIONS

The syndrome of transient neurological symptoms (TNS) after subarachnoid use of local anesthetics, particularly lidocaine, has been well described. This syndrome has not been reported with the subarachnoid use of opioids. This case report describes TNS that occurred after administration of subarachnoid meperidine, an opioid with local anesthetic properties.

Clinical and pharmacokinetic aspects of the combination of meperidine and prilocaine for spinal anaesthesia

The aim of this study was to determine whether the addition of a small dose of prilocaine could augment the spinal block induced by meperidine and affect intrathecal meperidine pharmacokinetic behaviour. Spinal anaesthesia was performed in 60 men scheduled for endoscopic resection of a prostatic adenoma or bladder tumour under spinal anaesthesia. They were allocated randomly to receive either 1 mg.kg-1 meperidine (Group 1, n = 30), or 1 mg.kg-1 meperidine plus 0.5 mg.kg-1 prilocaine (Group 2, n = 30). Blood samples were collected prior to and for 24 hr after spinal injection in 24 patients (12 in each group). Plasma meperidine levels were assayed by gas chromatography. Complete motor block was achieved in all Group 2 patients, but was incomplete in seven of Group 1 (P less than 0.05). The onset of both motor and sensory blocks was shorter (P less than 0.01) in Group 2 and the duration was longer (P less than 0.05). Coadministration of prilocaine modifies meperidine pharmacokinetic behaviour. The area under curve was 48% greater (P less than 0.01) and Cmax was higher in Group 2 than in Group 1, 145.8 +/- 42.2 vs 107 +/- 20.5 ng.ml-1 (P less than 0.001). No evidence of respiratory depression was noted in any of the patients. Despite the increase in plasma meperidine concentrations, no side effects were observed. The plasma concentrations remained at one third to one sixth the levels reported to induce a respiratory depression. It is concluded that the addition of prilocaine to meperidine improves motor and sensory block during surgery and alters meperidine kinetics without producing major side effects.

[Pharmacokinetics of pethidine after spinal anesthesia. Clinical implications]

Eleven male patients undergoing endoscopic resection for prostatic adenoma and bladder tumours under spinal anaesthesia received intrathecal pethidine 1 mg X kg-1. Plasma concentration and its evolution with time were assessed; pethidine plasma concentrations were determined by high performance liquid chromatography. Pethidine was rapidly and extensively absorbed. The peak plasma concentration of pethidine was 176 +/- 66 ng X ml-1 (range: 84-208) and the time to peak concentration was 2.3 +/- 1.4 h (range: 0.5-6 h). The terminal elimination half-life was 7.2 +/- 2.2 h (range: 4-11.5 h). The plasma concentrations of pethidine remained below 500-700 ng X ml-1, the minimum concentration necessary to obtain a systemic analgesic effect. Two patients required noramidopyrine as a complement at the 8th and 12th h respectively. No respiratory depression was observed. Intrathecal pethidine (1 mg X kg-1) was an effective agent for spinal anaesthesia: the prolonged postoperative analgesia was due to the drug acting on opioid receptors in the spinal cord. This led to the necessity of postoperative monitoring during 24 h after intrathecal pethidine administration.