Dose response relationships for isobaric spinal mepivacaine using the combined spinal epidural technique

Mepivacaine, a local anesthetic with similar physiochemical properties to those of lidocaine, is an adequate alternative for patients undergoing ambulatory procedures, and is associated with a lower incidence of transient neurologic symptoms (TNS) than lidocaine. We studied the dose-response characteristics of isobaric intrathecal mepivacaine using the combined spinal epidural technique for patients undergoing ambulatory arthroscopic surgery of the knee. Seventy-five patients were randomized prospectively to receive one of three doses of isobaric mepivacaine for spinal anesthesia: 30 mg (2 mL 1.5%), 45 mg (3 mL 1.5%), or 60 mg (4 mL 1.5%). An observer, blinded to the dose, recorded sensory level to pinprick and motor response until resolution of the block. In addition, the incidence of TNS was determined. An initial intrathecal dose of 30 mg of isobaric mepivacaine 1.5% produced satisfactory anesthesia in 72% of ambulatory surgical patients undergoing unilateral knee arthroscopy with a significantly shorter duration of sensory (158 +/- 32 min) and motor blockade (116 +/- 38 min) than doses of 45 and 60 mg. An intrathecal dose of 45 mg produced satisfactory anesthesia in all patients with a shorter duration of sensory (182 +/-38 min) and motor blockade (142 +/- 37 min) than 60 mg of mepivacaine 1.5% (203 +/- 36 min and 168 +/- 36 min, respectively). The incidence of TNS was 7.4% overall (1.2%-13.6% confidence intervals), less than the rates previously reported after spinal anesthesia with lidocaine in ambulatory surgical patients undergoing knee arthroscopy. We conclude that mepivacaine can be used as an adequate alternative to lidocaine for ambulatory procedures. This study evaluated the postoperative duration of spinal anesthesia after varying doses of isobaric mepivacaine and the incidence of transient radiating back and leg pain. We found that 45 mg of mepivacaine provided adequate anesthesia, a timely discharge, and a lower incidence of back pain than that previously reported after lidocaine spinals.