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Background and Aims Fast-track programs for hip- and knee arthroplasty require enhanced perioperative care; however, limited research exists on duration of spinal anesthesia with ropivacaine. This observational study aims to evaluate the duration and sufficiency of spinal anesthesia with ropivacaine 15 mg and observe associated postoperative complications.

Methods Initial inclusion of 129 patients undergoing elective hip- and knee arthroplasty received spinal anesthesia with ropivacaine 15 mg. Based on preliminary results, a supplemental group of 27 hip arthroplasty patients receiving a lower dose of 12.5 mg was included. Primary outcomes were duration of the spinal anesthesia measured as time from injection to remission of sensory and motor function. Sensory function was assessed by pinprick test. Motor function was assessed by voluntary movement of ankle-, knee- and hip joints. Secondary outcomes were incidence and timing of associated postoperative complications.

Results Administration of 15 mg ropivacaine resulted in a median duration of 116 minutes [91-135] until remission of sensory function compared to 90 minutes [75-110] with 12.5 mg ropivacaine (p=0.01). Remission of motor function was 177 minutes [152-222] with 15 mg ropivacaine compared to 146 minutes [115-201] with 12.5 mg ropivacaine (p<0.01). Postoperative complications showed a trend towards increased cerebral- and cardiovascular events among hip-patients.

Conclusions Spinal anesthesia with 15 mg ropivacaine was sufficient for hip- and knee arthroplasty, and administration of 12.5 mg ropivacaine also seems to be sufficient. Remarkably, remissions were significantly delayed in the operated legs compared to the non-operated legs which is not previously described.