Transcutaneous carbon-dioxide partial pressure trends during six-minute walk test in patients with very severe COPD

Background: Transcutaneous carbon-dioxide partial-pressure (TCPCO2) can be reliably measured and may be of clinical relevance in COPD. Changes in TCPCO2 and exercise-induced hypercapnia (EIH) during six-minute walk test (6MWT) need further investigation. We aimed (1) to define patterns of TCPCO2 trends during 6MWT and (2) to study determinants of CO2-retention and EIH. Methods: Sixty-two COPD patients (age: 63 +/- 8years, FEV1: 33 +/- 10%pred.) were recruited and T(C)PCO2 was recorded by SenTec digital-monitoring-system during 6MWT. Results: Half of patients (50%) exhibited CO2-retention (TCPCO2 [Delta] >4 mmHg); 26% preserved and 24% reduced TCPCO2. Nineteen (31%) patients presented EIH (TCPCO2 >45 mmHg). EIH was associated to higher baseline-PCCO2, worse FEV1, lower inspiratory-pressures, underweight/normal BMI, and pre-walk dyspnea. Stronger determinants of CO2-retention were FEV1 and pre-walk dyspnea, whereas baseline-PCCO2 and pre-walk dyspnea better predict EIH. Conclusions: PCO2 response to 6MWT is highly heterogeneous; however, very low FEV1 and elevated baseline-PCCO2 together with pre-walk dyspnea increase the risk for CO2-retention and EIH. Overweight-BMI seems to carry a protective effect against EIH in very severe COPD.