S16 An RER of 1.05 should not be used to determine maximal effort during CPET

Intro A recent ERS statement on standardisation of cardiopulmonary exercise testing (CPET) in chronic lung diseases (Radtke et al 2019) discussed the criteria for determining maximal effort. A CPET with a respiratory exchange ratio (RER) >1.05 is considered maximal using these criteria; V’O2 85% predicted, and HR We hypothesise that using an RER >1.05 as maximal will result in misinterpretation. Methods Retrospective analysis of CPETs performed at Birmingham Heartlands Hospital in 2019. Inclusion criteria: patient limited, RER >1.15 at peak, >6 mins. Exclusion criteria: highly variable RER indicating dysfunctional breathing. V’O2, V’E, and HR were measured at RERs of 1.05, 1.15 and peak, and were compared with Friedman tests. Results CPET was performed in 422 patients. 199 had an RER > 1.15 at peak. 23 patients were excluded due to dysfunctional breathing. The indication for testing was pre-operative assessment in 117 patients and CPET was for diagnostic purposes in 59 patients. Mean (SD) age = 61.4 (16.9) years, BMI = 27.7 (5.4), CPET duration 9.4 (1.8) mins; gender (F:M) 50:126. Of the 59 patients that were investigated for cause of breathlessness, 37% were normal at peak exertion based on the ERS criteria for abnormality. At an RER of 1.05 this was 3.4% and at an RER of 1.15 this was 25.4%. Of the 117 preoperative assessments, 88 had a V’O2peak >15 ml/min/kg and could be considered low risk for surgical intervention. At an RER of 1.05, 70% of these patients would have been considered high risk; 30% would have been considered high risk at RER 1.15. Discussion Using an RER of 1.05 an indicator of maximal effort underestimates some patients’ true exercise capacity. This will have an impact on diagnosis and risk stratification.