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The contribution of exercise testing for risk assessment for lung resection is well established and has been embedded in international guidelines from Europe1 and the USA.2 There are many forms of exercise tests (6 min walk, 12 min walk, shuttle walk, stair climbing), but the most established investigation is formal assessment of maximum oxygen consumption during exercise (Vo2 max). British and American (American College of Chest Physicians (ACCP)) guidelines use Vo2 max as the ultimate assessment of operative risk, positioned at or near the end of the functional algorithm,3 whereas European guidelines recommend the use of this test much earlier in patients with a forced expiratory volume in 1 s (FEV1) or carbon monoxide transfer factor (Tlco) <80% predicted.1 2
Numerous cohort studies and a meta-analysis report the association of low Vo2 max and ‘high risk’ lung resection.4–18 However ‘high’ is not quantified and ‘risk’ is not defined, two fundamentally important definitions if guidelines that use these terms are to be applied clinically. Here we focus on validity of the Vo2 max studies and the clinical utility of the available evidence with respect to individual interpretation of risk.
Sample size and precision of risk estimation of death
Arguably, the most important outcome when considering surgery for lung cancer is the ability to survive the procedure. The most apparent limitation of the currently available evidence is the lack of appropriately powered studies to address this. The precision of a risk model is not specifically dependent on sample size, but rather the number of events—that is deaths—an uncommon outcome in thoracic surgery. In the UK, lobectomy, the most common procedure for lung cancer, carried an operative mortality of ∼2% in 2004–2005,19 and in the USA the mortality rate has been reported to range from …