Background and Objectives This study was designed to determine whether subarachnoid clonidine administration alone results in surgical anesthesia for transurethral resection of the prostate.

Methods Blood pressure, heart rate, sedation, and sensory and motor blocks were assessed in 12 patients before and after lumbar subarachnoid injection of increasing doses of clonidine (three patients each received 75, 150, 300, and 450 μg doses). General anesthesia was induced at the request of the patient or surgeon, if conditions were unsatisfactory.

Results Clonidine resulted in marked sedation within a mean of 19 minutes of spinal injection, and no motor block was observed. There was a 25% (range, 0-45%) reduction in mean arterial blood pressure. Although endoscopy was tolerated in all cases, general anesthesia was required when resection began, except in two patients who received 300 and 450 μg of clonidine, respectively. Postoperative analgesic requirements showed wide interindividual variability (mean, 6 hours; range 2-12 hours).

Conclusions Subarachnoid clonidine cannot be reliably used as the sole agent for spinal anesthesia, since general anesthesia is often required or deep sedation occurs. Increasing doses of clonidine do not prolong postoperative analgesia. Thus, clonidine could be used as a spinal analgesic but not as a spinal anesthetic.