Ropivacaine for Unilateral Spinal Anesthesia; Hyperbaric or Hypobaric?

Background and objectives: The aim of this study was to compare the unilaterality of subarachnoid block achieved with hyperbaric and hypobaric ropivacaine. Methods: The prospective, randomized trial was conducted in an orthopedics surgical suite. In all, 60 ASA I-Ill patients scheduled for elective total knee arthroplasty were included in the study. Group Hypo (n = 30) received 11.25 mg of ropivacaine (7.5 mg.mL(-1)) + 2 mL of distilled water (density at room temperature was 0.997) and group Hyper (n = 30) received 11.25 mg of ropivacaine (7.5 mg.mL(-1)) + 2 mL (5 mg.mL(-1)) of dextrose (density at room temperature was 1,015). Patients in the hyperbaric group were positioned with the operated side down and in the 15 degrees Fowler position, versus those in the hypobaric group with the operated side facing up and in the 15 degrees Trendelenburg position. Combined spinal epidural anesthesia was performed midline at the L3-4 lumbar interspace. Hemodynamic and spinal block parameters, regression time, success of unilateral spinal anesthesia, patient comfort, surgical comfort, surgeon comfort, first analgesic requirement time, and adverse effects were assessed. Results: Time to reach the T10 dermatome level on the operated side was shorter in group Hyper (612.00 +/- 163.29 s) than in group Hypo (763.63 +/- 208.35 s) (p < 0.05). Time to 2-segment regression of the sensory block level on both the operated and non-operated sides was shorter in group Hypo than in group Hyper. Conclusion: Both hyperbaric and hypobaric ropivacaine (11.25 mg) provided adequate and dependable anesthesia for total knee replacement surgery, with a high level of patient and surgeon comfort. Hypobaric local anesthetic solutions provide a high level of unilateral anesthesia, with rapid recovery of both sensory and motor block, and therefore may be preferable in outpatient settings.