Preoperative assessment is a key component in major surgery. Assessing the functional capacity of a patient helps in preventing and managing predictable complications perioperatively. Historically there have been numerous objective and subjective methods used, e.g. 6-min walk test, stress echocardiogram or V-POSSUM (Vascular-Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity) in vascular surgery. We must now move beyond these traditional methods
Cardiopulmonary exercise testing (CPET) is known to provide a measure of functional reserve that is objective, validated and safe in high-risk patients.
Prentis et al.  have investigated an established utility of CPET as a prognostic test for postoperative complications and hospital length of stay in a cohort of elderly patients undergoing major urological surgery viz. radical cystectomy and ileal conduit formation for TCC of the bladder. Whilst CPET has been used as a prognostic tool in major cardiorespiratory and abdominal surgeries before there are some interesting and relevant perspectives that this study offers.
CPET provides an integrative overall assessment of the pulmonary, cardiovascular, haematopoietic, neurophysiological and skeletal system to a ramped increase in exercise stimulus. Amongst the parameters that can be derived are peak oxygen uptake (VO2 peak), which is effort dependent; and oxygen uptake at anaerobic threshold (AT), which is independent of effort. The American Thoracic Society/American College of Chest Physicians in their 2003 statement on CPET  enumerated indications like evaluation of exercise tolerance, evaluation of undiagnosed exercise intolerance and specific clinical evaluations, which included preoperative assessment for major cardiorespiratory surgery and other major surgery in an elderly population. These recommendations were to assess cardiovascular reserve and predict risk. Unlike cardiac and respiratory surgery where the cardiorespiratory function is expected to improve or stay the same postoperatively, major non-cardiothoracic surgery can lead to increased demands from a compromised cardiorespiratory system. It is precisely this factor, which vindicates the need for a system that can be used to stratify risk and optimise reserves in a patient.
Prentis et al.  have used a validated system (Clavien Classification) to stratify postoperative complications into ‘none’, ‘minor’ and ‘major’. Using this system as a primary outcome measure they found impaired AT to be an independent predictor for major complications. This corroborates the findings of Smith et al.  of CPET as a risk assessment tool in non-cardiopulmonary surgery. Using a scoring system to identify the patients at high risk may help pre-empt major complications by electively booking postoperative intensive care admission. Older et al.  showed the relevance of such a step where patients were triaged to the Intensive Therapy Unit (ITU)/High Dependency Unit (HDU) or ward based on AT levels, which led to no mortalities in patients transferred to the ward. The urosurgical patients included by Prentis et al.  are by default managed postoperatively in the ward. Preoperative CPET could potentially be used as distinction criteria for ITU/HDU admission.
One of the challenges in the application of this test involves the clinical correlation of the derived variables. An AT of <12 mL/min/kg as a predictor for increased length of stay and postoperative cardiorespiratory fitness in this article emphasises this point. Forshaw et al.  suggested the commonly used value for AT of 10–11 mL/min/kg may not be well validated. In fact, in the review of CPET for non-cardiopulmonary surgery, Smith et al.  suggest variability in AT may be due to different surgeries having different sensitivities for CPET predictors.
Steins Bisschop et al.  highlighted the role of CPET in determining cardiopulmonary fitness levels to tailor physical exercise programmes for patients with cancer. Numerous factors, e.g. anaemia, drug-related arrhythmias or cardiomyopathy have been listed as potential reasons for reduced CPET variables. This further shows the relevance of assessing individual fitness levels to achieve optimum results. There have been studies, which show improved VO2 peak levels in the pre-surgical period by implementing a regular physical exercise programme, although it is yet to be ascertained if improved VO2 levels translate into reduced postoperative complications. Prentis et al.  state that their cohort of patients with TCC of the bladder showed comparable short-term results for oncological therapy and open surgery. This leads to a potentially interesting application of using CPET to assess fitness levels and then initiating a physical exercise regime for those patients at high risk, whilst offering them oncological intervention. On achieving an acceptable level deemed ‘fit for surgery’, they could then have surgery. Of course this would require thorough assessment before considering a potential trial, although the benefits would seem to be clear. Perhaps patients will be more motivated to prepare for their forthcoming surgery using these parameters to stimulate their preparation.
In conclusion we can state that whilst there is need for further studies before deeming CPET a ‘gold standard’ test for preoperative optimization and postoperative risk stratification; studies like these are another step in the right direction.