Unilateral Spinal Anesthesia in Hip Arthroplasty: Can the Perfusion Index Differentiate Between Hypobaric and Hyperbaric Bupivacaine?

Abstract Purpose To compare unilateral spinal anesthesia (USA) performed with hyperbaric and hypobaric bupivacaine in terms of perfusion index (PI), sensory-motor block characteristics, hemodynamics, and postoperative analgesia in patients undergoing partial hip arthroplasty. Methods Patients aged 18–65 years with ASA physical status I–II were randomized to receive 10 mg hyperbaric bupivacaine (Group I) or hypobaric bupivacaine (Group II) for unilateral spinal anesthesia. Hemodynamic parameters, perfusion index (PI), sensory and motor block characteristics, postoperative visual analog scale (VAS) scores, and time to first analgesic requirement were recorded. Changes in PI (ΔPI) were calculated as percentage differences from baseline values. Results Baseline hemodynamic parameters were comparable between groups. Group I demonstrated a faster onset of sensory block, higher PI values at 5–30 min, lower early postoperative VAS scores, and a longer time to first analgesic requirement. Group II showed a broader dermatomal sensory block distribution and earlier block regression, accompanied by an earlier decline in PI values. Heart rate and mean arterial pressure were significantly lower in Group I at 15 and 120 min, and ephedrine use was more frequent. Both groups achieved ΔPI values exceeding 200%, indicating successful unilateral spinal anesthesia. Differences in PI and hemodynamic responses appeared to be associated with baricity-dependent distribution and the extent of sympathetic blockade. Conclusion Hyperbaric bupivacaine in unilateral spinal anesthesia provides a faster and more predictable block onset, whereas hypobaric bupivacaine is associated with a broader sensory distribution and earlier block regression. Baricity plays an important role in shaping block characteristics, hemodynamic responses, and recovery profiles in unilateral spinal anesthesia for hip arthroplasty. Clinical Trials number: NCT06417203 – 11.05.2024.