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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
Cardiopulmonary exercise tests could be used as a risk-stratification tool in the preoperative assessment of patients due to undergo some types of major abdominal surgery. This systematic review found that measuring anaerobic threshold during exercise testing was the most helpful predictor of risk for liver, pancreatic and general abdominal surgery, while peak oxygen uptake was best for abdominal aortic aneurysm repair. Identifying patients at risk of poor outcomes could help hospitals plan resources more effectively, for example by booking time in critical care for immediate postoperative care, and may improve collaborative decision making.
More work is needed before it is possible to make definitive recommendations. The range of procedures and outcomes measured was broad, there were various sources of study bias, and the reviewers were unable to pool the results. Higher quality research is needed in several areas, including colorectal and upper gastrointestinal surgery.
Despite these concerns, preoperative testing as a risk assessment tool is increasing in popularity and this review adds to our understanding of its usefulness in abdominal surgery.
Why was this study needed?
Cardiopulmonary exercise testing assesses the performance of the heart and lungs before, during and after exercise, such as on an exercise bike.
Aerobic fitness tends to translate into better surgical outcomes. The fitter the person is then the more able they are to recover from the stresses of major surgery. Patients at risk of a poor outcome - such as death, morbidity (illness) or extended length of hospital stay - may be identified by their response to exercise testing. Test results can help doctors and patients decide whether or not to proceed with the surgery, and where care following surgery is best provided, for example in intensive care or on a general ward.
Exercise testing is already used as a prognostic tool for heart and lung surgery. This study investigated its prognostic usefulness for a range of abdominal operations.
What did this study do?
This was a systematic review of 37 observational studies that assessed the ability of exercise testing to predict postoperative outcome in adults undergoing major abdominal surgery. The review included liver transplant and resection (seven studies), abdominal aortic aneurysm repair (five studies), colorectal (six studies), pancreatic (four studies), kidney transplant (two studies), upper gastrointestinal (four studies) and weight-loss surgery (two studies), as well as general abdominal surgery (12 studies).
Nearly two thirds of the trials were from the UK. All but three used an exercise bike, two used a treadmill and one did not report the exercise type. Fifteen trials included fewer than 100 participants.
Meta-analysis was not performed because the studies were too different from one another in terms of surgery type, outcomes measured and statistical approach. The researchers comment that reporting in the underlying trials was incomplete. For example, only three of the studies reported the type of anaesthetic used. Most studies did not appear to control for confounding factors, such as age or renal function, which might also influence post-operative morbidity. Few quantitative measures of the strength of any associations were reported. The results therefore need to be treated with caution.
What did it find?
- Liver transplant and resection: there was quite consistent evidence that exercise testing predicted overall survival but less evidence that it may predict intensive care unit admission after surgery.
- Abdominal aortic aneurysm repair: there was some evidence that testing predicted overall survival, but more studies are needed to support these findings.
- Pancreatic surgery: exercise testing was not predictive of survival. There was some evidence that it may predict length of hospital stay and morbidity after surgery.
- General abdominal surgery: testing predicted overall survival, length of hospital stay and morbidity.
- The most useful prognostic measure for liver, pancreatic and abdominal surgery was anaerobic threshold—defined as the level of exercise intensity at which lactic acid builds up in the body faster than it can be cleared away. The most useful measure for abdominal aortic aneurysm repair was VO2 max— peak oxygen uptake during exercise.
- There was variation in the “cut-off points” that were predictive of outcome between surgeries and between studies.
What does current guidance say on this issue?
NICE does not currently have guidance on cardiopulmonary exercise testing for risk stratification before abdominal surgery.
In general, the recent 2016 NICE guideline on routine preoperative tests recommends reducing the number of investigations used in healthy patients.
What are the implications?
Given the variety of studies included and inability to pool the results, it is difficult to draw definitive conclusions from this review. The overall direction of results does suggest that cardiopulmonary exercise testing may be a useful risk-stratification tool in the preoperative assessment of liver, pancreatic, abdominal aortic aneurysm repair and general abdominal surgery. There were no clear results for colorectal and upper GI surgery, kidney transplant and weight-loss surgery, and more quality research in these specific areas is needed.
Major abdominal surgery is common, and so improved ability to predict recovery could make a meaningful difference to patient care and outcomes, and ensure optimal use of healthcare resources. As research in this area is still in its infancy, more studies will be necessary before it is possible to describe accurate prognostic cut-off points for each type of surgery.
Citation and Funding
Moran J, Wilson F, Guinan E, et al. Role of cardiopulmonary exercise testing as a risk-assessment method in patients undergoing intra-abdominal surgery: a systematic review. Br J Anaesth. 2016;116(2):177-91.
Trinity College Dublin funded a studentship grant to J. Moran.
Bibliography
Huddart S, Young EL, Smith RL, et al. Preoperative cardiopulmonary exercise testing in England - a national survey. Perioper Med (Lond). 2013;2(1):4.
Levett DZ, Grocott MP. Cardiopulmonary exercise testing, prehabilitation, and Enhanced Recovery After Surgery (ERAS). Can J Anaesth. 2015;62(2):131-42.
NICE. Routine preoperative tests for elective surgery. NG45. London: National Institute for Health and Care Excellence; 2016.
NICE. NICE publishes updated clinical guideline on routine preoperative tests [press release]. 05 April 2016. National Institute for Health and Care Excellence; 2016.
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