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A Study to Determine the Optimum Dose of Metaraminol Required to Increase Blood Pressure by 25% during Subarachnoid Anaesthesia

We studied dosage optimization for metaraminol when managing hypotension during subarachnoid anaesthesia. Twenty patients aged 53 to 84 years, were recruited. Non-invasive blood pressure (BP) and heart rate were recorded one-minutely. A series of four IV metaraminol boluses (0.25 to 1.0 mg per 50 kg adult) were administered. From individual patient time plots of BP, predicted dosages for a 25% elevation in BP were estimated. Dose-related elevations in systolic BP [mean (SD)] occurred following dosages of 0.5 mg [25 (11)%] and 1.0 mg [50 (23)%]. Similar elevations occurred in mean and diastolic BP. Overall estimated dosage (median) to produce a 25% elevation in systolic BP was 0.5 mg (per 50 kg adult). However, individual patient responses varied (10–90th centiles=0.23 to 0.80 mg). Thus, we now recommend a starting dose of 0.25 mg, increasing to 0.5 mg if necessary, to treat hypotension (25% decrease in systolic BP) during subarachnoid anaesthesia.