The impact of fluid optimisation before induction of anaesthesia on hypotension after induction.

Abstract

Intra-operative hypotension is a known predictor of adverse events and poor outcomes following major surgery. Hypotension often occurs on induction of anaesthesia, typically attributed to hypovolaemia and the haemodynamic effects of anaesthetic agents. We assessed the efficacy of fluid optimisation for reducing the incidence of hypotension on induction of anaesthesia. This prospective trial enrolled 283 patients undergoing radical cystectomy and randomly allocated them to goal-directed fluid therapy (n=142) or standard fluid therapy (n=141). Goal-directed fluid therapy patients received fluid optimisation based on stroke volume response to passive leg raise before induction; those with positive passive leg raise received intravenous crystalloid fluid boluses until stroke volume was optimised. Baseline mean arterial pressure was measured on the morning of surgery and on arriving in the operating theatre. This post-hoc analysis defined haemodynamic instability as either a >30% relative drop in mean arterial pressure compared with baseline or absolute mean arterial pressure <55mmHg, within 15min of induction. Forty-two (30%) goal-directed fluid therapy patients underwent fluid optimisation after finding an intravascular fluid deficit via passive leg raise testing; 106 (75%) goal-directed fluid therapy and 112 (79%) standard fluid therapy patients met criteria for haemodynamic instability. There was no significant difference in the incidence of haemodynamic instability between the goal-directed fluid therapy and standard fluid therapy groups using absolute mean arterial pressure drop below 55mmHg (p=0.58) or using pre-surgical testing or pre-surgical mean arterial pressure values as baseline (p=0.21, p=0.89, respectively); however, the difference in the incidence of haemodynamic instability was significant using the operating theatre baseline mean arterial pressure (p=0.004). We conclude that fluid optimisation before induction of general anaesthesia did not significantly impact haemodynamic instability.