OVERVIEW

• outcome measures are important for research and quality control
• clinically meaningful outcomes measure how patients feel, function or survive, e.g. mortality, quality of life
• surrogate outcomes is a substitute that would be expected to be beneficial based on epidemiological, physiological, therapeutic or other scientific grounds
• unless validated surrogate outcomes should not be used to change clinical practice

ICU MORTALITY

Advantages

• simple, single metric
• concrete endpoint which is already available in hospital databases
• death is an important endpoint
• aggregation of a large number of diagnoses with a small number in each increases power to detect variation
• variation over time may reflect institutional and organisational events or characteristics- budget cuts, bed pressure etc. and be able to detect true quality deficiencies
• May be useful when combined as part of an overall quality program

Disadvantages

• Definition of ICU is very hospital specific which can influence mortality (e.g. non-ICU stepdown areas in some hospitals)
• can be ‘gamed’ e.g. transfers out to die in the ward or other units
• Poor correlation between mortality and quality of care in some diagnoses; alternatives available e.g. diagnosis specific risk models such as EuroSCORE for CABG, APACHE SMR, trauma scores
• Can mask problems in low volume diagnostic groups
• Difficult to draw hospital comparisons and or allow league table construction
• False conclusions can be drawn unless robust statistical methods used

HOSPITAL MORTALITY

• Hospital mortality can often be 50% higher than ICU mortality, and is a reasonable surrogate (90%) for 90 days mortality

Advantages

• gets over differences in definition of ICU and ICU discharge thresholds and avoids avoids many problems of censoring at ICU discharge.
• Still a simple and robust endpoint
• easy to obtain from exisiting hospital databases

Disadvantages

• can confound intensive care outcomes with deficiencies in ward or other post ICU care
• Does not address in any way functional outcomes, e.g discharge from hospital to a nursing home in a vegetative state is counted as a positive outcome

90 DAY MORTALITY

Advantages

• simple robust endpoint
•  addresses the issue of ongoing mortality after hospital discharge (though this difference is about 10% relative in recent large trials)
• data may be available by linkage with external registries (e.g. Births, Deaths and Marriages)

Disadvantages

• still an arbitrary time point
• 90 days may still be insufficient to accurately measure the attributable mortality from an episode of critical illness
• Problems with loss to follow up after ICU discharge
• Ethical implications of contacting patients after discharge (especially for research studies)

1 YEAR FUNCTIONAL OUTCOME

Advantages

• a ‘POEM’ (patient oriented endpoint that matters)
• Takes into account disability and true long-term consequences of critical illness

Disadvantages

• no ideal scoring tool available – existing tools all have problems; some measure particular functional domains well; problems with face validity
• All functional outcome measures are time consuming to apply
• Problems with loss to follow up
• Follow up— time consuming, labour intensive, costly face to face vs. phone vs. mail
• Depending on disease may reflect more the natural history of the disease rather than the ICU care per se