Low volume and high concentration of local anesthetic is more efficacious than high volume and low concentration in Labat's sciatic nerve block: a prospective, randomized comparison.

BACKGROUND: Various factors markedly affect the onset time and success rate, of peripheral nerve blockade. This prospective, randomized, double-blind study, compared a dose of mepivacaine 300 mg, in a 20 or 30 mL injection volume for sciatic nerve blockade using Labat's posterior approach. METHODS: A total of 90 patients undergoing foot surgery were randomly allocated to receive sciatic nerve block with 20 mL of 1.5% mepivacaine (n = 45) or 30 mL of 1% mepivacaine (n = 45). All blocks were performed with the use of a nerve stimulator (stimulation frequency 2 Hz; intensity 1.5-0.5 mA). In the two groups, appropriate nerve stimulation was elicited at <0.5 mA and the targeted evoked motor response was plantar flexion of the foot. Time required for onset of sensory and motor block in the distribution of the tibial and common peroneal nerves were recorded. A successful block was defined as a complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot. RESULTS: A greater success rate was observed with 20 mL of 1.5% mepivacaine (96.6%) than with 30 mL of 1% mepivacaine (68.9%; P < 0.05). Time to onset of complete sensory and motor block was shorter after injection of 20 mL of 1.5% mepivacaine (11 +/- 6 min and 13 +/- 7 min, respectively) than after 30 mL of 1% mepivacaine (17 +/- 8 min and 19 +/- 8 min, respectively, P < 0.05). CONCLUSION: In Labat's sciatic nerve blockade, administering a low volume and a high concentration of local anesthetic (1.5% mepivacaine) is associated with a higher success rate and a shorter onset time than a high volume and a low concentration of solution (1% mepivacaine).

Needle-induced paresthesiae during single-shot spinal anesthesia: a comparison of sitting versus lateral decubitus position.

BACKGROUND AND OBJECTIVES: Paresthesiae occasionally occur during spinal puncture or injection of local anesthetic for spinal anesthesia. No information is currently available regarding the effects of the patient's position on the incidence of needle-induced paresthesiae. The purpose of this prospective, observational study was to compare the occurrence of needle-induced paresthesiae in patients who received single-shot spinal anesthesia in the sitting position or in the lateral decubitus position. METHODS: A total of 620 patients operated on under spinal anesthesia were included. Spinal anesthesia was performed in the sitting position in 142 patients and in the lateral decubitus position in 478 patients. All blocks were performed with a 25-gauge, 90-mm, Sprotte needle, at the L3-L4 or L4-L5 level. Patients' demographics, patients' position (lateral decubitus or sitting), number of skin punctures, incidence of paresthesiae, and success of the anesthesia were recorded. RESULTS: The overall incidence of paresthesiae was higher in the lateral decubitus position (16.95%) compared with the sitting position (9.15%) (P = 0.0230). The number of punctures and the success rate were similar in both positions. Studying the incidence of paresthesiae for each position, when performing 1 or more punctures, there was no position-related difference noted if a single-needle puncture was sufficient to perform the block (8.0% in the lateral decubitus group versus 5.1% in the sitting group) (P = 0.3305). This difference between positions was significant when more than a single-needle puncture was required (34.1% in the lateral decubitus group versus 18.6% in the sitting group) (P = 0.0497). CONCLUSIONS: Patient's position may influence the occurrence of needle-induced paresthesiae during spinal anesthesia. Lateral decubitus position resulted in a higher incidence of paresthesiae than the sitting position. However, there is no position-related difference noted if a single-needle puncture is sufficient to perform the block.