Mechanical ventilation with positive end-expiratory pressure in critically ill patients: comparison of CW-Doppler ultrasound cardiac output monitoring (USCOM) and thermodilution (PiCCO)

Abstract

Background Aggressive mechanical ventilation can markedly and unpredictably aff ect cardiac function. The fall in cardiac output (CO) is due to a reduction in left ventricular stroke volume (SV). The aim of the present pilot study was to assess the eff ects of diff erent positive end-expiratory pressure (PEEP) levels on circulatory function and to compare them with continuous wave (CW)-Doppler ultrasound cardiac output monitoring (USCOM) and a thermodilution-based haemodynamic monitoring system (PiCCO).Methods Twenty mechanically ventilated (PEEP ≤10 mbar) adult patients (female n = 6, male n = 14, mean age 62 years, mean SAPS II-score 48.5), the majority with pneumonia and septic shock) were followed with USCOM and PiCCO at stepwise increased PEEP-levels from 0-10 mbar (1 mbar steps). The changes in CO/SV were recorded.Results With both methods, an increase of PEEP resulted in a decrease of SV and CO. Although the absolute decrease was consistently higher by USCOM, the changes of the parameters were qualitatively comparable. CO fell from 8.83 L/min (± 2.39) by 0.4 L/min to 8.49 L/min (± 2.48) with PiCCO and from 9.3 L/min (± 3.43) by 1.0 L/min to 8.3 L/min (± 3.2) with USCOM. The median CO/SV fell by 4.5%/5.2% with PiCCO and 10.8%/9% with USCOM, respectively. Correlation of CO values with the two methods by Bland-Altman yielded comparable results (mean percentage error at PEEP 0 mbar 13%, PEEP 10 mbar 18%). An adequate fl ow signal with USCOM was achieved in all patients.Conclusions A signifi cant infl uence of mechanical ventilation with PEEP on haemodynamic parameters was evident both with USCOM and PiCCO. While thermodilution methods like PiCCO are well established but time-consuming and invasive, CW-Doppler based USCOM constitutes an important tool for easy, rapid and reliable diagnosis and haemodynamic monitoring of critically ill patients.