Evaluating a software-based model for improving management of the circulation of adult patients undergoing major surgery.

The intervention group is the 'pressure field group'. Anaesthetists in the pressure field group will receive clinical education on the pressure field method for managing perfusion. The pressure field method consists of defining a patient's baseline haemodynamic zone and defending this distinct haemodynamic zone during surgery. The education consists of two 1-hour clinical education sessions, using the pressure field software to monitor three patients undergoing surgery, and completing an online questionnaire. The content includes the physiological basis for the haemodynamic zone, the process for determining a patient’s baseline haemodynamic zone, and strategies for maintaining parameters within the zone. The zone is defined in terms of mean perfusion pressure (MPP), stroke volume (SV), and systemic elastance (Esys). The goal of intraoperative care is to maintain MPP within ±15% of the patient’s MPP baseline values without tolerating any MPP below 60 mmHg, and to maintain SV and Esys within ±15% of the patient’s baseline values. Anaesthetists will use the EV1000 or Hemosphere haemodynamic monitor, and the pressure field software, to support the management of patients. No fluids, blood products, inotropes, or vasoactive drugs are to be administered prior to commencement of FloTrac monitoring. Roller clamps on fluid lines are to be closed except where fluid is actively being used to optimise the circulation. A vasopressor infusion is to be connected to the patient prior to induction (so that it can be promptly commenced as needed). Choice and titration of fluids, blood products, inotropes, and vasopressors is otherwise at the discretion of the attending anaesthetist. Implementation scientists will measure the acceptability of the pressure field method by surveying participating anaesthetists at baseline, 6 months post-baseline, and 12 months post-baseline; assess the fidelity of intervention delivery by reviewing protocol deviations at 1, 6, and 12 months post-baseline (by auditing case report forms); and conduct semi-structured interviews with participating anaesthetists based on the Theoretical Domains Framework to identify and understand implementation barriers at 12 months post-baseline. If acceptability or intervention fidelity delivery is below 80%, enhancement strategies will be applied. Enhancement strategies may include additional clinical education or additional clinical research coordinator support in completing case report forms. Anaesthetist participants will use the pressure field method until recruitment of the target number of patient participants in the pressure field group is complete.