Intensive Care Outcomes

Reviewed and revised 26 August 2015

OVERVIEW

Appropriate outcome measures is vitally important in ICU research

Types of outcomes

• ICU mortality
• hospital mortality
• 90 day mortality
• 1 year functional outcome

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 organizational 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 step-down areas in some hospitals)
• As a consequence 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 e.g. 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

Compared to ICU mortality, avoids many problems of censoring at ICU discharge.  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.
• Still a simple and robust endpoint which is easy to obtain from existing 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 [so discharge from hospital to a nursing home in a vegetative state is counted as a positive outcome]

90 DAY MORTALITY

Simple robust endpoint which addresses the issue of ongoing mortality after hospital discharge (though this difference is about 10% relative in recent large trials).

Advantages

• simple robust endpoint
• data may be available by linkage with external registries (e.g. Births, Deaths and Marriages)

Disadvantages

• still an arbitrary time point [while 28 days is clearly inadequate, 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).

ONE 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
• Time consuming, labour intensive, costly face to face vs. phone vs. mail follow up
• Depending on disease may reflect more the natural history of the disease rather than the ICU care per se