Impairment in physical function is a significant problem for survivors of critical illness. There is a growing urgency to develop a core set of outcome measures, which can be adopted in clinical and research practice to evaluate efficacy in response to interventions such as rehabilitation.

Phase 1: Development of a new outcome measure. This study aims to examine the development of a single outcome measure which may be able to be utilised across the continuum of recovery of critical illness in the evaluation of physical function. The study will involve examination of two common physical function measures - the Physical Function in intensive care test scored (PFIT-s) and De Morton Mobility Index (DEMMI) and the development of a new measure based on rasch principles which may be able to capture physical functioning changes in individuals with critical illness. Aims: (1) To determine the clinical utility of two physical function measures (DEMMI and PFIT-s) when used in isolation across the hospital admission; and (2) To transform the (15-item) DEMMI and (4-item) PFIT-s into a single measure to evaluate function in intensive care survivors using Rasch analytical principles.

Phase 2: Measurement properties of the PACIFIC physical function outcome measure in an independent validation sample.

Consecutive eligible patients will be recruited into the study.

Phase 1: Two outcome measures - PFIT-s and DEMMI will be performed within 24 hour period. Order of testing will be randomised to minimise testing bias. Time-points of assessment are: awakening, ICU discharge and hospital discharge. Weekly measures will also be performed if required in ICU and/or ward settings for up to a maximum of 30 days in each setting. The measurement properties of the individual tools PFIT-s and DEMMI will be examined (e.g. validity, responsiveness).

Phase 2: Based on the findings in Phase 1 a new single outcome measure will be developed. In the second phase examination of the measurement properties of the tool will be undertaken including (reliability, validity, responsiveness).

Inclusion Criteria:

• Adults > 18 years of age
• Mechanically ventilated > 48 hours
• Premorbid able to ambulate at least 10m independently prior to ICU admission (+/- gait aid)

Exclusion Criteria:

• Premorbid physical or cognitive impairment which would prevent ability to perform functional measures
• New neurological impairment such as stroke or spinal cord injury
• Trauma or orthopaedic injury requiring period of immobilization or non weight bearing status
• Traumatic brain injury with focal neurology

Multi-centre study conducted in four acute hospitals: Royal Melbourne Hospital, Melbourne, Australia; Flinders Medical Centre, Adelaide, Australia; Escola Superior da Saude, Brasilia, Brazil; and National University Hospital, Singapore.