Pneumologie 2015; 69 - P26
DOI: 10.1055/s-0035-1551928

Real-time measurement of transcutaneous PCO2 vs. arterial/venous PCO2 during non-invasive ventilation on the emergency department in subjects with severe respiratory failure – an observational study

C Horvath 1, M Brutsche 1, F Baty 1, J Rüdiger 1
  • 1Pneumology and Sleep Medicine, Kantonsspital St. Gallen, Switzerland

Background: Transcutaneous measurement of carbon dioxide (PtCO2) has been suggested as an alternative to invasively obtained PaCO2 for the monitoring of patients with respiratory failure. Current data show conflicting results in patients on the emergency department (ED).

Methods and Setting: We performed a retrospective comparison of real-time PtCO2 (SenTec Digital Monitor; SenTec AG; Therwil, Switzerland) without drift correction and PaCO2/PvCO2 measurements in patients with severe respiratory failure during non-invasive ventilation (NIV) on the ED. In all patients either an arterial or venous blood gas analysis (a/vBGA) at baseline and after NIV was drawn. Agreement between PtCO2 and PaCO2 was the primary endpoint. For analysis, Bland-Altman plots and linear regression were used.

Results: 121 patients receiving NIV on the ED were identified, 100 with BGA at baseline. Overall PtCO2 was well correlated with PaCO2/PvCO2 (R 2 0. 826; p < 0.001) at baseline and after NIV (R 2 0.872; p < 0.001). The mean difference between PaCO2/PvCO2 and PtCO2 was 0.50 kPa (95% CI: 0.29 – 0.72), and 0.21 kPa (95% CI: 0.05 – 0.36) respectively. The difference was < 1 kPa CO2 in 75%. If restricted to aBGA, the mean difference between PaCO2 and PtCO2 was 0.44 kPa (CI 95%: 0.20 – 0.68) and 0.16 kPa (95% CI: -0.01 – 0.34). A PaCO2 > 8 kPa was associated with a lesser degree of agreement between the levels of PtCO2 and PaCO2 (p < 0.001). The behaviour of changes of PCO2 before and after NIV correlated with PtCO2 changes in 76% of cases overall and in 93% in patients with a ≥1 point kPa-difference in PCO2. In 3 cases technical problems with the probe occurred.

Conclusion: PtCO2 is a reliable and safe alternative to repeated BGA for the monitoring of patients undergoing NIV on the ED. It can be used as real-time guidance for treatment. We recommend an initial BGA to evaluate the respiratory and metabolic state and to rule out a significant discrepancy between the respective values.