Five male patients undergoing haemorrhoidectomy received intrathecal meperidine 1 mg.kg I as the sole anaesthetic agent. Plasma concentration-time profiles were investigated. The peak plasma concentration of meperidine was lntrathecal opioid administration has received less clinical investigation than the epidural route. The intrathecal route has been used to provide analgesia after surgery and for the control of pain in labour and myocardial infarction, i-6 We recently reported the use of intrathecal meperidine as the sole agent for spinal anaesthesia. 7 Since there is no quantitative information available for intrathecal meperidine in doses used for spinal anaesthesia, we performed a study of the kinetics of intrathecal meperidine when used in a dose of I mg.kg -l for spinal anaesthesia.
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MethodsFive male patients of ASA physical status I or II presenting for haemorrhoidectomy were studied. The mean age was 38 ---15 years, and the mean weight was 61.6 ---6.5kg (---SD). The protocol was approved by the hospital review committee and informed consent was obtained from the patients. No premedication was given.The protocol described in the original report by Famewo and Naguib 7 was employed in this study. In summary, subarachnoid puncture was performed with the patient in the sitting position, using a 22-gauge spinal needle at the lumbar vertebral level of L3/4 or L4/5. Preservative-free meperidine in a dose of 1 mg'kg -J was injected intrathecally using the undiluted concentration of 50 mg.ln1-1, lntraoperative monitoring included ECG, blond pressure, tidal volume, end-tidal CO2 and arterial blood gases.The onset and duration of sensory block as determined by the pinprick method were noted. The onset and duration of motor weakness of the lower extremities were also noted.Postoperatively, patients were monitored closely. Blood pressure, heart rate, and respiratory rate were recorded at hourly intervals, while arterial blood gases were determined at four hourly intervals for the first 24 hours after the end of surgery. One of the authors was always available for immediate assessment of patients should there by any complaint or problem, and any side effects were noted.