Hypotension during subarachnoid anaesthesia: haemodynamic effects of colloid and metaraminol

We have studied 45 patients, aged 60-95 yr, receiving subarachnoid block for neck of femur fractures. Patient received either colloid (polygeline, Haemaccel) 8 ml kg-1 (n = 15), metaraminol 5 micrograms kg-1 and 1.7 micrograms kg-1 min-1 (n = 15) or a combination of both treatments to maintain systolic arterial pressure (SAP) between 75 and 100% of baseline. If necessary, additional colloid 2 x 4 ml kg-1 or metaraminol 3 x 2.5 micrograms kg-1 was given. Arterial pressure was measured by automated oscillotonometry, central venous pressure (CVP) by a manometer and cardiac index (CI), stoke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. Colloid was less effective than metaraminol (P < 0.05). In the colloid group, SAP and SVRI decreased and CVP, CI and SI increased (P < 0.001). In the metaraminol group, initial decreases in SAP, SVRI and CVP were restored after 10-15 min and HR decreased after 12 min (P < 0.001). In the combined group, initial decreases in SAP and SVRI were restored after 4 and 16 min, and CVP, CI, SI and HR increased (P < 0.001). Metaraminol was more effective than colloid because it increased SVRI, whereas colloid increased CVP without significantly increasing CI.