Table 1.

Standardized methods of risk assessment

Method of risk assessment	Definition	Advantages	Limitations
Clinical prediction rules	The use of a scoring system based on patient- or procedure-related risk factors to quantify risk	Often cost-neutral	Estimates population risk for patient rather than providing an individualized risk assessment
		Requires no specialist knowledge [34]
ASA-PS	Six-point scale used to grade patient according to comorbidities [35]	Validated in a number of settings [36-38]	Inter-observer variability [39]
			Poor sensitivity and specificity for prediction of morbidity and mortality on an individual patient basis [33,40]
Lee Revised Cardiac Risk Index (RCRI)	Scores patients according to six variables, including whether the surgery is high risk	Discriminates moderately well between patients at low versus high risk for cardiac events after mixed noncardiac surgery [42]	Designed to identify patients at risk of cardiac complications so may miss patients at risk of other complications who may benefit from PACU care
	Assesses cardiac risk [41]	Well validated
POSSUM	A more detailed scoring system with 18 components, 6 operative variables and 12 physiological variables [46]	A revision of POSSUM, the Portsmouth POSSUM [43] has been shown to be a better predictor of outcome in certain surgical settings [33,44,45]	Some variables cannot be ascertained until after surgery, making it of limited use for preoperative identification of patients who may benefit from PACU care
		Variations in the model have been devised for specific patient groups, such as the Cr-POSSUM (colorectal), which has been shown to be a better predictor of outcome in this type of surgery [47]
Cardiopulmonary exercise testing	CPET is an integrative and quantitative measure of a patient’s cardiopulmonary reserve	Good evidence that CPET is useful to help predict perioperative morbidity and mortality and may aid triage to an appropriate level of postoperative care [48-50]	In 2008, 17% of Hospital Trusts in England had a CPET service, and a further 7% were in the process of setting one up [52]
	The assessment requires the patient to exercise (usually on a cycle ergometer) while oxygen consumption, carbon dioxide production, and other cardiorespiratory variables are measured	RCT in progress to further evaluate its use to stratify to appropriate level of postoperative care [51]

ASA-PS, American Society of Anesthesiology Physical Status Score; CPET, cardiopulmonary exercise testing; PACU, postanaesthetic care unit; POSSUM, physiological and operative severity score for the enumeration of mortality and morbidity; RCRI, Lee Revised Cardiac Risk Index; RCT, randomized controlled trial.