A comparative study of three different methods of administering metaraminol during spinal anaesthesia in the elderly

We compared three methods of administering metaraminol during spinal (subarachnoid) anaesthesia. Fifty-two elderly patients with fractured hips were studied. Blood pressure was maintained by either intramuscular (i.m.) metaraminol (0.1 mg x kg(-1)), intravenous (i.v.) boluses (0.01 mg x kg(-1)) or an infusion (0.05 mg x kg(-1) x h(-1)). Non-invasive blood pressure was recorded every one-minute. Spinal anaesthesia initially decreased the systolic arterial pressure by 15 (14) % compared to 35 (15) % for diastolic pressure (P<0.001). I.m. metaraminol restored the systolic arterial pressure back to baseline values (-3%), but there was significant between-subject variability resulting in a very unpredictable effect. I.v. boluses and infusion had a more predictable effect and maintained systolic arterial pressure at about 20% below baseline. Range of effect, measured by inter-quartile range and variance, was greatest in the i.m. group and least in the infusion group (P<0.003). I.m. metaraminol during spinal anaesthesia has a very unpredictable effect. Infusions of metaraminol provided the best blood pressure control. Diastolic blood pressure fell significantly after spinal anaesthesia and this merits further investigation.