Hyper or hypoventilation may have serious clinical consequences in critically ill patients and should be generally avoided, especially in neurosurgical patients. Therefore, monitoring of carbon dioxide partial pressure by intermittent arterial blood gas analysis (PaCO2) has become standard in intensive care units (ICUs). However, several additional methods are available to determine PCO2 including end-tidal (PETCO2) and transcutaneous (PTCCO2) measurements. The aim of this study was to compare the accuracy and reliability of different methods to determine PCO2 in mechanically ventilated patients on ICU. After approval of the local ethics committee PCO2 was determined in n = 32 ICU consecutive patients requiring mechanical ventilation: (1) arterial PaCO2 blood gas analysis with Radiometer ABL 625 (ABL; gold standard), (2) arterial PaCO2 analysis with Immediate Response Mobile Analyzer (IRMA), (3) end-tidal PETCO2 by a Propaq 106 EL monitor and (4) transcutaneous PTCCO2 determination by a Tina TCM4. Bland-Altman method was used for statistical analysis; p < 0.05 was considered statistically significant. Statistical analysis revealed good correlation between PaCO2 by IRMA and ABL (R2 = 0.766; p < 0.01) as well as between PTCCO2 and ABL (R2 = 0.619; p < 0.01), whereas correlation between PETCO2 and ABL was weaker (R2 = 0.405; p < 0.01). Bland-Altman analysis revealed a bias and precision of 2.0 ± 3.7 mmHg for the IRMA, 2.2 ± 5.7 mmHg for transcutaneous, and -5.5 ± 5.6 mmHg for end-tidal measurement. Arterial CO2 partial pressure by IRMA (PaCO2) and PTCCO2 provided greater accuracy compared to the reference measurement (ABL) than the end-tidal CO2 measurements in critically ill in mechanically ventilated patients patients.
Keywords: Arterial blood gas analysis; Capnography; Capnometry; Point-of-care testing.