Six-minute walk test in pre-operative evaluation of patients for upper abdominal surgery.

Editor, Pre-operative anaesthetic evaluation aims to assess the functional status1 to estimate the risk of major complications including death (identification of high-risk patients) and to design an optimal peri-operative strategy.2 Evaluation of exercise or functional capacity is traditionally estimated through patient-reported activity (Duke Activity Status Index questionnaire)3 which is then converted to metabolic equivalents of task (MET). For instance, the ability to climb a flight of stairs without dyspnoea is approximately equivalent to four METs; four METs is considered as a cut-off value that grossly discriminates low risk (≥4 METs) from high-risk patients (<4 METs). The cardiopulmonary exercise test (CPET) may be a more reliable assessment method than METs to estimate functional capacity and to predict peri-operative risk, but evidence for this assumption is limited. Sinclair et al.4 observed that the inexpensive six-minute walk test (6MWT) is able to screen patients when the CPET is unavailable. During this test patients walk continuously for 6 min; the longer the performed distance, the better the functional capacity of patients. Different cut-offs for normal or increased functional capacity were described. The current study's aim was to verify whether the 6MWT was able to predict cardiopulmonary complications in a population of patients scheduled for major upper abdominal surgery. The protocol was approved by the Ethics Committee of the ‘Antonio Cardarelli’ Hospital of Naples (protocol number 755, September 2013). Patients aged between 18 and 80 years, scheduled for liver, biliary, pancreatic and gastric surgery were included in this pilot prediction study. The pre-operative anaesthetic assessment was performed within 30 days before the surgery; the 6MWT was performed according to international guidelines.5 The 6MWTs were carried out during the pre-operative assessment in a previously identified corridor of 30 m, in the presence of an anaesthetist. Before and at the end of the test, the following parameters were recorded: SBP and DBP, heart rate, respiratory rate, oxygen saturation by a pulse oximeter, and perceived fatigue according to the Borg Scale.6 The development of one of the following was considered a postoperative pulmonary complication (detailed definitions are available via the first author): respiratory failure, respiratory dysfunction, hypoxaemia, pneumonia, suspected pulmonary infection, hydrostatic pulmonary oedema, atelectasis, pleural effusion, pneumothorax, acute respiratory distress syndrome. The development of one of the following was considered to be a cardiac complication: unstable angina, acute myocardial infarction, acute cardiogenic pulmonary oedema, sudden cardiac death. Postoperative cardiopulmonary complications were investigated at 28 postoperative days by physical examinations, the consultation of medical records of each single day of hospital staying, and through phone interviews. Study population was grouped in patients with cardiopulmonary complications (Group CP+) or without cardiopulmonary complications (Group CP−). Forty-two tested patients completed the follow-up (median age was 64.5 years, interquartile range [IQR] 58 to 68; female 47%; median ASA was 2.5 [2 to 3]; the rate of cardiopulmonary complications was 28.6% [12 out of 42 patients; all complications were pulmonary complications, four combined with cardiac complications (atrial fibrillation)]. The mortality rate was 7.1% (three out of 42 patients); main cause of failure-to-rescue was respiratory failure. Mean (SD) 6MWT of all patients was 494.6 ± 83 m. Group CP+ performed less during the 6MWT (451.7 ± 52.7 m; Group CP− 511.8 ± 87.4 m, P = 0.03); prediction scores were different between this two groups except the revised cardiac risk index (Table 1). A cut-off value of 489 m had a sensitivity of 83.3% and a specificity of 60% to predict a cardiopulmonary complication. Area under the receiver operating characteristics curve was 0.718 (95% CI, P = 0.029) which can be considered as a moderate prediction performance.Table 1: Prediction scores and performed distance during the six-minute walk test (mean ± SD)In a multivariate regression analysis with the outcome cardiopulmonary complications three independent risk factors were identified: age, sex and distance of the pre-operative 6MWT. The current preliminary study has limitations. The sample size was too small for robust estimation of the performance of 6MWT as a predictor of cardiopulmonary complications and therefore, bias is not excluded. Systematic postoperative cardiac troponins were not available, therefore cardiac complications may be underestimated.7 No comparative prediction model (CPET or MET adjusted for similar risk factors) was performed for criterion validity. We conclude based on these preliminary results that the 6MWT may be able to stratify the risk of cardiopulmonary complications after major upper abdominal surgery. In a larger study prediction should be tested with a cut-off distance of 489 m; furthermore, pre-operative and postoperative cardiac biomarkers should be included. Acknowledgements relating to this article Assistance with the letter: the authors thank Dr S. Caiazzo and G. De Benedictis for their contribution in data collecting. Financial support and sponsorship: none. Conflicts of interest: none.