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

Transcutaneous carbon-dioxide partial-pressure (T_CPCO₂) can be reliably measured and may be of clinical relevance in COPD. Changes in T_CPCO₂ and exercise-induced hypercapnia (EIH) during six-minute walk test (6MWT) need further investigation. We aimed (1) to define patterns of T_CPCO₂ trends during 6MWT and (2) to study determinants of CO2-retention and EIH.

Sixty-two COPD patients (age: 63±8years, FEV1: 33±10%pred.) were recruited and T_CPCO2 was recorded by SenTec digital-monitoring-system during 6MWT.

Half of patients (50%) exhibited CO₂-retention (T_CPCO₂[Δ]>4mmHg); 26% preserved and 24% reduced T_CPCO₂. Nineteen (31%) patients presented EIH (T_CPCO₂>45mmHg). EIH was associated to higher baseline-P_CCO₂, 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-P_CCO₂ and pre-walk dyspnea better predict EIH.

PCO₂ response to 6MWT is highly heterogeneous; however, very low FEV1 and elevated baseline-P_CCO₂ 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.