NONINVASIVE CARBON DIOXIDE MONITORING IN A PORCINE MODEL OF ACUTE LUNG INJURY DUE TO SMOKE INHALATION AND BURNS

ABSTRACT In critically ill intubated patients, assessment of adequacy of ventilation relies on measuring partial pressure of arterial carbon dioxide (PaCO2), which requires invasive arterial blood gas analysis. Alternative noninvasive technologies include transcutaneous CO2 (tPCO2) and end-tidal CO2 (EtCO2) monitoring. We evaluated accuracy of tPCO2 and EtCO2 moni-toring in a porcine model of acute lung injury (ALI) due to smoke inhalation and burns. Eight anesthetized Yorkshire pigs underwent mechanical ventilation, wood-bark smoke inhalation injury, and 40 % total body surface area thermal injury. tPCO2 was measured with a SenTec system (SenTec AG, Therwil, Switzerland) and EtCO2 with a Capnostream-20 (Oridion Medical, Jerusalem, Israel). These values were compared with PaCO2 measurements from an arterial blood gas analyzer. Paired measurements of EtCO2-PaCO2 (n 276) and tPCO2-PaCO2 (n 250) were recorded in the PaCO2 range of 25 to 85 mmHg. Overlapping data sets were analyzed based on respiratory and hemodynamic status of animals. Acute lung injury was defined as PaO2/FIO2 e 300 mmHg; hemodynamic instability was defined as mean arterial pressure e 60 mmHg. Before ALI, EtCO2 demonstrated moderate correlation with PaCO2 (R 2 0.45; P G 0.0001), which deteriorated after onset of ALI (R2 0.12; P G 0.0001). Before ALI, tPCO2 demonstrated moderate correlation (R 2 0.51, P G 0.0001), which was sustained after onset of ALI (R2 0.78; P G 0.0001). During hemodynamic stability, EtCO2 demonstrated moderate correlation with PaCO2 (