Correlation of End-Tidal Carbon Dioxide with Arterial Carbon Dioxide in Mechanically Ventilated Patients

BACKGROUND: Patients undergone mechanical ventilation need rapid and reliable evaluation of their respiratory status. Monitoring of End-tidal carbon dioxide (ETCO(2)) as a surrogate, noninvasive measurement of arterial carbon dioxide (PaCO(2)) is one of the methods used for this purpose in intubated patients. OBJECTIVES: The aim of the present trial was to study the relationship between end-tidal CO(2) tensions with PaCO(2) measurements in mechanically ventilated patients. MATERIALS AND METHODS: End-tidal carbon dioxide levels were recorded at the time of arterial blood gas sampling. Patients who were undergoing one of the mechanical ventilation methods such as: synchronized mandatory mechanical ventilation (SIMV), continuous positive airway pressure (CPAP) and T-Tube were enrolled in this study. The difference between ETCO(2) and PaCO(2) was tested with a paired t-test. The correlation of end-tidal carbon dioxide to (ETCO(2)) CO(2) was obtained in all patients. RESULTS: A total of 219 arterial blood gases were obtained from 87 patients (mean age, 71.7 ± 15.1 years). Statistical analysis demonstrated a good correlation between the mean of ETCO(2) and PaCO(2) in each of the modes of SIMV, CPAP and T-Tube; SIMV (42.5 ± 17.3 and 45.8 ± 17.1; r = 0.893, P < 0.0001), CPAP (37 ± 9.7 and 39.4 ± 10.1; r = 0.841, P < 0.0001) and T-Tube (36.1 ± 9.9 and 39.4 ± 11; r = 0.923, P < 0.0001), respectively. CONCLUSIONS: End-tidal CO(2) measurement provides an accurate estimation of PaCO(2) in mechanically ventilated patients. Its use may reduce the need for invasive monitoring and/or repeated arterial blood gas analyses.