Intrathecal ropivacaine for total hip arthroplasty: double-blind comparative study with isobaric 7.5 mg ml(-1) and 10 mg ml(-1) solutions

This study was designed to evaluate the efficacy and safety of two concentr ations of intrathecal ropivacaine, 7.5 and 10 mg ml(-1), in patients underg oing total hip arthroplasty. One hundred and four patients, ASA I-III, were randomized to receive an intrathecal injection of one of two concentration s of isobaric ropivacaine. Group 1 (n=51) received 2.5 ml of 7.5 mg ml(-1) ropivacaine (18.75 mg). Group 2 (n=53) received 2.5 ml of 10 mg ml(-1) ropi vacaine (25 mg). The onset and offset of sensory block at dermatome level T 10, maximum upper and lower spread of sensory block and the onset, intensit y and duration of motor block were recorded, as were safety data. Onset of motor and sensory block was rapid with no significant differences between t he two groups. The median time of onset of sensory block at the T10 dermato me was 2 min (range 1-25 min) in Group 1 and 2 min (range 1-21 min) in Grou p 2. The median duration of sensory block at the T10 dermatome was 3.0 h (r ange 0.5-4.2 h) in Group 1 and 3.4 h (1.1-5.9 h) in Group 2 (P=0.002). The median duration of complete motor block was significantly prolonged (P<0.05 ) in Group 2 compared with Group 1 (1.9 vs 1.2 h, respectively). Anaestheti c conditions were excellent in all but one patient. Intrathecal ropivacaine , in doses of 18.75 and 25 mg, was well tolerated and provided effective an aesthesia for total hip arthroplasty.