Dose-effect relationship of hypobaric ropivacaine in spinal anesthesia in the elderly undergoing hip replacement

Objective To investigate the dose-effect relationship of hypobaric ropivacaine in spinal anesthesia in the elderly undergoing hip replacement.Methods Seventy-five patients,aged 70 to 98 years and scheduled for hip replacement,were randomly allocated to three groups with 25 cases each.A 24-gauge Spinocath catheter was advanced 2.0-2.5cm into subarachnoid space at L3-4 interspace.The patients in group Ⅰ,Ⅱ and Ⅲ were given 1.0-1.2ml of 0.3%,0.4% or 0.5% hypobaric(1.001-1.002,20℃) ropivacaine solution,respectively.Motor and sensory blockade was evaluated,and adverse effects were recorded.Results There was no significant difference in sensory block including onset time and maximum cephalad spread level among three groups.The complete sensory block appeared in most patients except for 2 cases in group I.The onset time and duration of motor blockage in group III were shorter than those in group I(P0.05).The maximum Bromage's score,duration of anesthesia,sensory or motor regressive time in group II were more than those in group I,but less than those in group III(P0.05 or P0.01).The blockade of single leg occurred in all patients.Conclusion Continuous spinal anesthesia with 0.4% hypobaric ropivacaine 4.0-4.8mg is safe and effective for hip replacement surgery in eldly patients.