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Table 2 Estimand for the primary outcome (DAOH-90). “Intercurrent event” denotes a post-randomisation event which may affect the interpretation or occurrence of outcome data (e.g. failure to receive treatment as intended, using a different treatment to the one assigned, etc.). Principal stratum and treatment policy are strategies to handle intercurrent events in the estimand definition. Here, the principal stratum strategy denotes that interest lies in the subpopulation of patients who would undergo emergency surgery regardless of their treatment allocation, and the treatment policy strategy denotes that the intercurrent event (e.g. failure to initiate cardiac output monitoring, the intervention algorithm not being followed) is considered part of the treatment strategy and interest lies in evaluating the treatment regardless of the occurrence of such events

From: Fluid Optimisation in Emergency Laparotomy (FLO-ELA) Trial: study protocol for a multi-centre randomised trial of cardiac output-guided fluid therapy compared to usual care in patients undergoing major emergency gastrointestinal surgery

Aspect

Definition

Target population

Patients ≥ 50 years old who undergo emergency bowel surgery

Endpoint

Days alive and out of hospital within 90 days of randomisation (DAOH-90 = count of days alive and out of hospital within 90 days of randomisation where DAOH-90 = 0 if patient dies within 90 days and DAOH-90 = 90 − (days in hospital within 90 days of randomisation) if patient alive 90 days after randomisation)

Treatment conditions

Intervention group—Protocolised cardiac output-guided haemodynamic therapy during surgery, and for 6 h after, regardless of whether the haemodynamic protocol has been followed correctly

Usual care group—Intravenous fluid administration without the use of cardiac output monitoring or protocol

Summary measure

Ratio of means (Intervention vs. usual care group)

Intercurrent events

Strategy

Surgery not received (applies to both treatment arms)

Principal stratum (of participants who would undergo surgery regardless of treatment allocation)

Procedure modified after surgery begins such that no longer eligible for NELA (applies to both treatment arms)

Treatment policy

Receipt of cardiac output monitoring (control arm only)

Treatment policy

Failure to initiate cardiac output monitoring during/after surgery (intervention arm only)

Treatment policy

Cardiac output monitoring initiated but intervention algorithm not followed

Treatment policy