A Comparative Study of Three Different Methods of Administering Metaraminol during Spinal Anaesthesia in the Elderly

Abstract

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 (IM) metaraminol (0.1 mg.kg-1), intravenous (IV) boluses (0.01 mg.kg-1) or an infusion (0.05 mg.kg-1.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). IM metaraminol restored the systolic arterial pressure back to baseline values (-3%), but there was significant between-subject variability resulting in a very unpredictable effect. IV 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 IM group and least in the infusion group (P<0.003). IM 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.