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Risk Assessment

Questions to Ask Yourself

What does high-risk mean to you?

Is it sufficient to base risk on a subjective assessment?

Should there be a separate pathway for high-risk surgical patients?

Why do we need to understand risk in surgical patients?

Difference Between Risk Scores and Risk Prediction models

Risk scores assign a weighting of factors identified as independent predictors of outcomes.


Risk prediction model looks at an individual's probability of risk (P-POSSUM is the best known risk prediction model)

Types of Risk Assessment

The following risk-assessment tools are the main ones employed in clinical practice:

1. ASA





6. BNP


American Society of Anesthesiologists House of Delegates/Executive Committee (2019)

Bottom line: ASA Score predicts population based mortality not individual risk. Also, it is subjective, without any prediction for an individual patient or operation. 

Use the calculator here.

Copeland GP, Jones D, Walters M. POSSUM: a scoring system for surgical audit. Br J Surg. 1991;78(3):355-360. doi:10.1002/bjs.1800780327

Bottom line: POSSUM assesses morbidity and mortality in patients undergoing general surgery. It can be used for both emergency and elective surgery. POSSUM has 18 components (12 physiological status variables and 6 surgical variables). 

Unfortunately, we need intraoperative variables to complete the score which precludes its ability to be used in the preoperative period.

Use the calculator here.

3. Portsmouth-POSSUM (P-POSSUM)


An Evaluation of the POSSUM Surgical Scoring System

Whiteley MS, Prytherch DR, Higgins B, Weaver PC, Prout WG. An evaluation of the POSSUM surgical scoring system. Br J Surg. 1996;83(6):812-815. doi:10.1002/bjs.1800830628

Bottom line: Portsmouth-POSSUM (P-POSSUM) is a modification of the POSSUM, which uses same variable and grading system, but a different equation to provide better results for predicting in-hospital mortality. Unfortunately, does not have morbidity prediction.

Unfortunately, like the POSSUM, we need intraoperative variables to complete the score which precludes its ability to be used in the preoperative period.

P-POSSUM tends to overestimate risk in low risk patients.

Use the calculator here

Protopapa KL, Simpson JC, Smith NC, Moonesinghe SR. Development and validation of the Surgical Outcome Risk Tool (SORT). Br J Surg. 2014;101(13):1774-1783. doi:10.1002/bjs.9638

Bottom line: The SORT is a pre-operative risk prediction tool for death within 30 days of surgery. It has been developed and validated for use in inpatient non-neurological, non-cardiac surgery in adults (aged 16 or over).

Use the calculator here.

Bottom line: "CPET provides an objective assessment of exercise capacity preoperatively and identifies the causes of exercise limitation. Information gained from CPET can be used to:

  • Estimate the likelihood of perioperative morbidity and

  • Inform the processes of multidisciplinary collaborative decision making and consent

  • Triage patients for perioperative care (ward vs critical care)

  • Direct preoperative interventions and optimization

  • Identify new comorbidities

  • Evaluate the effects of neoadjuvant cancer therapies

  • Guide prehabilitation and rehabilitation

  • Guide intraoperative anaesthetic practice."

Courtesy of POETTS 2018 Guidelines

Duceppe E, Parlow J, MacDonald P, et al. Canadian Cardiovascular Society Guidelines on Perioperative Cardiac Risk Assessment and Management for Patients Who Undergo Noncardiac Surgery [published correction appears in Can J Cardiol. 2017 Dec;33(12 ):1735]. Can J Cardiol. 2017;33(1):17-32. doi:10.1016/j.cjca.2016.09.008

Bottom line: Measuring brain natriuretic peptide (BNP) or N-terminal fragment of proBNP (NT-proBNP) before surgery  enhances perioperative cardiac risk estimation in patients who are 65 years of age or older, are 45-64 years of age with significant cardiovascular disease, or have a Revised Cardiac Risk Index score greater than or equal to 1. 

Daily troponins should be measured for 48 to 72 hours after surgery in patients with an elevated NT-proBNP/BNP measurement before surgery.

Daily troponins should also be measured post-operatively if there is no pre-operative NT-proBNP/BNP measurement, as long as the patient has a Revised Cardiac Risk Index score ≥1, is between 45-64 years with significant cardiovascular disease, or is older than 65 years. 

Bilimoria KY, Liu Y, Paruch JL, et al. Development and evaluation of the universal ACS NSQIP surgical risk calculator: a decision aid and informed consent tool for patients and surgeons. J Am Coll Surg. 2013;217(5):833-42.e423. doi:10.1016/j.jamcollsurg.2013.07.385

Bottom Line: A web-based surgical risk tool was created using data from almost 400 NSQIP hospitals and over 1 million patients.

The tool requires the user to enter 21 pre-operative factors (including demographic factors, comorbidities and procedure-related factors as well as a subjective surgeon adjustment score). The tool then outputs an estimate of risks for most surgical operations.

 Use the calculator here.

Relevant Literature

Moonesinghe SR, Mythen MG, Das P, Rowan KM, Grocott MP. Risk stratification tools for predicting morbidity and mortality in adult patients undergoing major surgery: qualitative systematic review. Anesthesiology. 2013;119(4):959-981. doi:10.1097/ALN.0b013e3182a4e94d

Bottom line: This qualitative review looked at 27 papers to answer the question: "What is the performance of risk stratification tools, validated for morbidity and mortality, in heterogenous cohort of surgical (non-cardiac, non-neurosurgical) patients?".

P-POSSUM and Surgical Risk Scale were found to be the most consistently accurate systems. ASA-PS was surprisingly accurate given its simplicity. NSQIP was not included in the review because it has not been validated in heterogenous patients groups.  

Major Points:

1. P-POSSUM is the most frequently and widely validated tool but given that it requires intra-operative variables, it cannot be used for pre-operative risk prediction. It is also quite complex, requiring 18 variables, both subjective and objective. 

2. Surgical Risk Scale is also accurate and uses entirely pre-operative variables. However, it has only been validated in single-centre studies in the UK.

3. ASA-PS discriminates well for post-operative mortality especially considering its simplicity. 

4. Other models that are worth noting are the Biochemistry and Hematology Outcome Model as well as the Identification of Risk in Surgical Patients tool. A cheap and entirely pre-operative NSQIP would also be a valuable tool.

5. The ideal surgical risk stratification tool should be accurate, cheap and simple to implement all while using entirely pre-operative variables. 

    Wijeysundera DN, Pearse RM, Shulman MA, et al. Assessment of functional capacity before major non-cardiac surgery: an international, prospective cohort study. Lancet. 2018;391(10140):2631-2640. doi:10.1016/S0140-6736(18)31131-0

    Bottom line: This prospective cohort study enrolled ~1400 patients, across 25 hospitals in Canada, UK, Australia and New Zealand, to look at how subjective preoperative assessment, CPET, DASI questionnaire and NT pro-BNP performed in: (a) assessing pre-operative functional capacity, (b) predicting 30-day and 1-year mortality, myocardial infarction and myocardial injury; and (c) predicting post-operative complications. 

    The findings suggest that subjective assessment of functional capacity should not be used in clinical practice. Instead, objective measures such as the DASI questionnaire, or NT pro-BNP levels should be considered for assessing perioperative cardiac risk. CPET may be used but only to predict post-operative complications. 

    Major points:

    1. Preoperative subjective assessment correctly identified only 16% of patients who were found to have METS<4 on CPET testing. There was no association between preoperative subjective assessment and any of the four primary outcomes. These findings suggest that it should not be used to assess patients' risk for major post-operative cardiac complications. 

    2. DASI questionnaire improved prediction of 30-day mortality, myocardial infarction and myocardial injury. It also performed well as a measure of functional capacity. This is inline with current recommendations of using objective scales to assess functional capacity. 

    3. NT pro-BNP improved predictions of 30-day mortality and myocardial injury. It was also predictive of 1-year death rate. 

    4. CPET improved predictions of moderate/severe post-operative complications. It was not predictive of post-operative myocardial injury, myocardial infarction or death at either 30-days or 1-year. This conflicts with current guidelines suggesting that functional capacity should be used for preoperative cardiac risk evaluation. 

    Michael Robinson, MB ChB FRCA, Andrew Davidson, MA MBBS FRCA FFICM, Aspiration under anaesthesia: risk assessment and decision-making, Continuing Education in Anaesthesia Critical Care & Pain, Volume 14, Issue 4, August 2014, Pages 171–175,

    Bottom line: According to NAP-4, life threatening airway complications occurred in approximately 1:20,000 general anesthetics in one year in the UK.  Aspiration was the leading cause of death (50%) over failure to intubate or ventilate.  Identifying high risk patients and adjusting the airway plan perioperatively is key to avoiding the severe morbidity and mortality associated with aspiration. 

    Major points:

    1. Failure to use rapid sequence induction when indicated substantially increased aspiration risk

    2. Incomplete assessment and failure to modify anesthetic management implicated in morbidity/mortality.  93% of pts who aspirated in this study had identifiable risk factors not identified.


    3. Surgical/anesthetic risk factors: surgical position (trendelenberg, lithotomy, laparoscopy, cholecystectomy, upper GI surgery), light anesthesia with a nonsecured airway, supra-glottic airways (1st generation), PPV, >2h surgery length.


    4. Strategies: preop fasting, nasogastric aspiration, prokinetic premedication, alternatives to general anesthetics (regional), reducing pH of gastric contents (antacids/h2 antagonists/PPI), airway protection (intubation/2nd generation LMA>1st generation LMA), ?cricoid pressure, RSI, extubate awake after return of airway reflexes, positioning, consider extubating on side.


    5. If aspiration occurs – trachea should be suctioned ideally prior to PPV to prevent distal displacement, likely to occur in right main stem bronchus, early X-ray will show consolidation in up to 75% of cases and early bronchoscopy may help prevent distal atelectasis if particulate matter aspirated.


    6. Aspiration can lead to chemical pneumonitis, bacterial pneumonia, or ARDS, and mechanical ventilation may be required for longer periods.  Antibiotics should only be used if pneumonia develops.  There is no evidence that steroids reduce mortality/outcome

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