Australasian MARS – Multicentre Aspiration Risk Study

What is MARS?

MARS is an Australasian multicentre observational cohort study looking at rates of pulmonary aspiration under anaesthesia.

The study aims to assess whether permitting clear fluid drinks until the start of anaesthesia (“Sip Til Send”) is non-inferior compared to advising patients to stop drinking 1 or 2 hours before anaesthesia (restrictive fluid fasting).

Why do we need MARS?

Despite national guidelines advising patients to consume clear fluids until 1 to 2 hours before an anaesthetic, in practice patients often go without fluids for much longer – commonly averaging 7 to 13 hours [Markman 2024]. This can cause thirst, dehydration, heightened anxiety, nausea, and issues with blood sugar management.

Sip Til Send fasting has become an effective and popular strategy to shorten fluid fasting duration before anaesthesia, improving the patient experience and avoiding the problems related to dehydration. Between 2023 and 2025, approximately 50 Australasian hospitals changed their preoperative fasting policies to routinely offer their patients Sip Til Send [Markman 2024].

Pulmonary aspiration under anaesthesia is rare and in most cases the consequences are mild, but it remains an important cause of severe complications during anaesthesia. Studies to date have suggested that Sip Til Send is equally as safe as restrictive fasting with regard to aspiration [Andersson, Marsman, EUROFAST], but we need to study larger populations to be sure of these results.

The MARS project is designed to provide the best evidence yet on the safety of Sip Til Send.

Study design

The MARS project will collect aspiration data from 250,000 adults and children undergoing anaesthesia for elective or emergency procedures in participating hospitals across Australia and New Zealand.

Registered hospitals

As of May 2025, there are 40 hospitals registered for the MARS project, spanning all parts of Australia and New Zealand

Register your hospital for MARS

All hospitals in Australia and New Zealand are eligible to join MARS, provided the following pre-requisites are met:

• Your hospital has an actively-promoted aspiration audit that is considered to have a low risk of under-reporting (see below)
• The principal investigator at each hospital must be able to identify the patients involved in reported aspirations, to enable the manual diagnosis verification and the collection of additional data. Therefore, aspiration reporting systems that irreversibly anonymise the cases are unsuitable.

Features of an aspiration reporting system that may minimise the risk of under-reporting:

• Users aware the audit is running, how to enter a case and why it is important that the audit generates accurate data.
• Data capture process is “low friction”, quick and efficient for the user, and does not require delaying the entry of the case until ALL the outcomes are known.
• Clear definition of the measured outcome, with the diagnostic criteria built into the questionnaire. Secondary diagnosis verification.

Study progress

April 2025

Multicentre ethics approval has been granted by the respective authorities in Australia and New Zealand, and recognised by all hospitals in their respective countries.

40 participating hospitals are listed in these ethics approvals.

Funding has been secured to facilitate the study’s design and implementation.

May 2025

Commencement of local governance approval application process for participating sites.

Study co-ordination

Lead Investigators:

Dr Phuong Markman, Staff specialist anaesthetist, Cairns Hospital, Australia

Dr Ruth Blank, Staff specialist anaesthetist, Cairns Hospital, Australia


Central Coordinating Centre:


Department of Anaesthesia and Perioperative Medicine – Cairns and Hinterland Hospital and Health Service, Queensland, Australia

New Zealand Coordinator:

Dr Alec Beresford, Specialist Anaesthetist – Health NZ Waitaha Canterbury – Christchurch hospital, New Zealand