Can arterial minus end-trial carbon dioxide gradient be used for peep titration?

Abstract

Objectives: There is a debate about how to find optimal positive end-expiratory pressure (PEEP) in the current literature. Our aim was to determine whether arterial minus end-tidal carbon dioxide can be used to find optimal PEEP in acute respiratory distress syndrome (ARDS) patients. Setting: Eight beds, postsurgical intensive care unit of a university hospital. Patients: Eight patients with ARDS were included in the study. One patient was excluded due to desaturation in the initial phase of the study. Interventions: The patients were sedated and paralyzed. PEEP levels were applied in random sequence as 5, 10, 15 and 20 cmH2O. Results: PaCO2- PetCO2 gradient was 11.0 (2.8-20.0) at 5 cmH2O of PEEP and decreased to 9.0 (1.2-20) with 10 of PEEP, further decreased to 7.0 (2.0-16.1) with 15 of PEEP and increased to 17.0 (4.6-22.0) with 20 cmH2O PEEP. Qsp/Qt was 0.4 (0.28-0.71) and 0.4 (0.19-0.45) with 5 and 10 cmH2O of PEEP and decreased to 0.31 (0.11-0.71) with 15 cmH2O of PEEP and to 0.30 (0.29-0.32) with 20 cmH2O PEEP. VD/VT decreased to 0.21 (0.2-0.36) and 0.15 (0.6-0.36) with 10 and 15 cmH2O of PEEP from 0.35 (0.05-0.41) at 5 cmH2O of PEEP and increased to 0.31 (0.05-0.47) with 20 cmH2O of PEEP. As we increase PEEP we observed that the intrapulmonary shunt was decreasing although PaCO2-PetCO2 decreased up to 15 cmH2O PEEP and increased at 20 cmH2O PEEP just as VD/VT PaCO2-PetCO2 gradient was minimal when PaO2 was maximal. Conclusion: PaCO2-PetCO2 gradient is a useful and easily available parameter to find optimal PEEP in patients with ARDS.