The DIRECT trial is a prospective, multi-centre, two arm parallel feasibility pilot randomised controlled trial. The primary aim is to determine the feasibility of using repeat indirect calorimetry measurements to direct energy delivery in critically ill patients with obesity.

The trial will recruit 60 mechanically ventilated patients from 4-6 ICUs in Australia and New Zealand.

Indirect calorimetry is the current reference standard for measuring energy expenditure during critical illness, allowing for personalisation of energy delivery. Use of indirect calorimetry may be important in mitigating under- and overfeeding and associated adverse outcomes. This may be particularly important in patients with obesity, where energy expenditure is difficult to estimate, and limited data is available on the optimal nutritional management of this subgroup.

Although access to indirect calorimetry is gradually improving, it remains an underutilised tool and skills required to complete and interpret measurements are limited which may hinder use and integration into practice. There is a resulting knowledge gap on the impact of indirect calorimetry on outcomes in comparison to standard care predictive equations.

A definitive and pragmatic trial is needed to assess the impact of guiding energy delivery with indirect calorimetry on patient outcomes. Importantly, confirming the feasibility of using indirect calorimetry to guide energy delivery is needed to define optimal measurement protocols prior to completion of a larger trial.

The primary aim of the DIRECT trial is to determine the feasibility of using repeat indirect calorimetry measurements to direct energy delivery in critically ill patients with obesity. The secondary aim is to inform a larger trial by collecting process, nutrition, functional, clinical and safety outcomes.

The investigators will consider the main trial feasible to conduct if 2 of the following 3 feasibility criteria are achieved: (a) recruitment rate is ≥ 1 patient per calendar month; (b) between group separation of ≥20% in energy adequacy during ICU admission is achieved in relation to measured energy expenditure and; (c) the number of indirect calorimetry measurements completed/planned ≥60% during ICU admission.

Inclusion Criteria:

• Adult (≥ 18 years) patients
• Body mass index ≥30 kg/m2
• Between day 3 and 6 of index ICU admission
• Receiving invasive mechanical ventilation
• Receiving enteral or parenteral nutrition

Exclusion Criteria:

• Receiving extracorporeal membrane oxygenation support
• Major burns (≥20% total body surface area)
• Unable to perform indirect calorimetry within 24 hours of randomisation
• Known pregnancy
• Death is imminent
• Treating clinician believes the study is not in the best interest of the patient

Data sharing requests will be considered following publication of the primary trial data on an individual basis by the trial management committee (the data custodians). Data sharing will only be considered for investigator-initiated, independent researchers who provide a written data evaluation proposal that is judged to be methodologically sound. A data sharing agreement will be required to detail conditions under which data is shared and used. Resulting publications should appropriately cite and acknowledge the original data custodians. Requests for data sharing are to be made to anzicrc@monash.edu and the corresponding author, Dr Oana Tatucu; oana.tatucu@monash.edu

Open-label trial. However, clinicians will be blinded to indirect calorimetry measurements in the control arm.