[Low isobaric 0.5% bupivacaine doses for unilateral spinal anesthesia.]

Unilateral spinal anesthesia may be advantageous, especially in the outpatient setting. Low local anesthetic doses, slow spinal injection rate and the lateral position have been related to the easiness of inducing unilateral spinal anesthesia. This study aimed at investigating the possibility of inducing unilateral spinal anesthesia with isobaric 0.5% bupivacaine.

Spinal anesthesia with 1 mL isobaric 0.5% bupivacaine (5 mg) was induced through 27G Quincke needle in 25 physical status ASA I and II patients undergoing orthopedic procedures. Dural puncture was performed with patients in lateral decubitus with the limb to be operated facing upwards. One mililiter of isobaric bupivacaine was injected in 30 seconds. Sensory and motor blocks were compared between the operated and the contralateral side.

Motor and sensory blocks on operated and contralateral sides were significantly different in all studied moments. All patients presented surgical anesthesia in the operated limb. At 20 minutes, nine patients presented sensory block in the contralateral side; at 40 minutes they were 18 and at 60 minutes they were 17 patients. So, unilateral block was present in seven patients (28%) and bilateral block was present in the remaining 18 patients (72%). No patient developed post-dural puncture headache.

Isobaric bupivacaine (5 mg) provides predominant unilateral block after 20 minutes in the lateral position. Isobaric bupivacaine moves in the CSF after 20 minutes resulting in just 28% unilateral blocks. Major advantages of unilateral spinal anesthesia are hemodynamic stability and short duration and it might be a new alternative for outpatient procedures.