The median effective dose of intrathecal hyperbaric bupivacaine is larger in the single-shot spinal as compared with the combined spinal-epidural technique

The combined spinal-epidural technique (CSE) has been associated with prolonged motor recovery and more frequent arterial hypotension as compared with a single-shot spinal (SSS) technique. We determined the median effective dose (MED) of intrathecal hyperbaric bupivacaine for CSE and SSS by using the up-down sequential allocation technique. Sixty male patients were randomly allocated to receive intrathecal administration through an SSS or CSE technique. Needle insertion occurred at the L3-4 interspace in all patients. In SSS, 9.5 mg of hyperbaric bupivacaine was administered through a 27-gauge Whitacre spinal needle. In CSE, a 17-gauge Tuohy needle with 4 mL of air was used to locate the epidural space, through which a 27-gauge Whitacre spinal needle was introduced and 7.0 mg of hyperbaric bupivacaine was administered. The dosing adjustment was 0.5 mg. A "successful" outcome was arbitrarily defined as sensory anesthesia at or above the T6 dermatome lasting for 60 min. A "success" resulted in a 0.5-mg decrement, whereas a "failure" resulted in a 0.5-mg increment in the next patient. There were 13 successes in both groups. The MED of bupivacaine was 9.18 mg (95% confidence interval, 8.89-9.47 mg) for CSE as compared with 11.37 mg (95% confidence interval, 10.88-11.86 mg) for SSS (P < 0.001). CSE required 19.3% (95% confidence interval, 14.9%-23.6%) less local anesthetic to achieve the defined clinical target. We found significant discrepancies in the MED of hyperbaric bupivacaine between the two techniques. Under similar clinical conditions, a 20% decrement in the dose of bupivacaine may be warranted whenever CSE is intended in place of SSS.