Peri‐operative fitness: a question of stamina?

We read with interest two articles about pre-operative exercise tests. Lee et al. 1 analysed data on six-minute walk tests from a previous study 2. They suggested the test could provide prognostic information. We were also drawn to the eloquent editorial by Carlisle and further re-analysis of the same data 3. So, does the distance a patient can walk in six minutes help the anaesthetist? We would like to raise issues about the original data and question what type of fitness a patient may need for surgery. The original study 2 was designed to examine changes in the six-minute walk test following exercise ‘prehabilitation’. The control group (recommended to walk daily and perform ankle and breathing exercises) outperformed the exercise intervention group. Excluded from this were patients who could not complete the exercise programme or exercise tests; therefore, most (79%) patients included were of ASA physical status 1-2. This same data were then analysed retrospectively by Lee et al. Surely this patient group is not the intended population for a pre-operative fitness test? Lee et al. looked at whether complications following various colorectal procedures for benign disease could be predicted by performance in the walk test done as part of the prehabiliation study. This analysis showed that patients who could walk further had fewer complications and this was the basis of re-analysis by Carlisle. However, the original data also showed that older patients had fewer complications. This could not be explained and is counter-intuitive. Even the elegant statistical re-analysis by Carlisle failed to show that a walk test correlated with outcomes. In such a mixed group this is not a surprise to us. We know that for these types of studies to predict outcomes reliably, large patient numbers are required 4, 5. Both surgical and anaesthetic factors also need to be taken into account, and the analysis should seek to detect an inflexion point or threshold rather than modelling a straight-line process. If patients are fit enough to walk 600 m then they are probably at no higher risk than someone able to walk 800 m in six minutes. A debate about a finite number of heartbeats does not help us decide the role of pre-operative exercise testing or the particular role of a low-tech walk test or full ergonometric assessments. Although all our experience suggests being fit for surgery is vital, exactly why a cardiorespiratory reserve matters is still uncharted. With good anaesthesia, cardiovascular demands can be maintained at near resting levels. So is fitness more a question of stamina and the ability to maintain a moderately raised cardiac output for a period of 48–72 hours to cope with fluid shifts, lower haematocrit and the metabolic sequelae of surgery? If so, which pre-operative test correlates best with stamina? The evidence we have points to the lactate threshold rather than maximal oxygen consumption but other indicators, such as duration and recovery speed, could contribute if the testing is performed according to a standard protocol.