Evaluation of the Argos System to Estimate Cardiac Output in Critically Ill Patients

In patients with acute circulatory failure, hemodynamic monitoring including cardiac index (CI) assessment is recommended for most severe patients. Transpulmonary thermodilution (TPTD) is one of the methods that are recommended for this purpose, in particular because it is considered as reliable in this type of patients. The PiCCO2 system (Pulsion Medical Systems, Getinge, Feldkirchen, Germany) relies on TPTD method and associate two methods to measure CI. On the one hand, TPTD is considered as one of the gold standards for CI evaluation (CITPTD). On the other hand, pulse contour analysis calculates stroke volume from the waveform of the systolic part of the arterial pressure curve (CIpwa). The way this estimation is performed and it is regularly re-evaluated differs among the devices that are available on the market. This estimation of CIpwa is calibrated when TPTD is performed. Thus, it allows a real-time pulse contour derived CI assessment, which is very precise. However, TPTD system are considered invasive, expensive and are not available in all settings.

The Argos monitor (Retia Medical, Valhalla, USA) uses the so-called multi-beat analysis (MBA) to estimate CI after analyzing the arterial pressure waveform over periods of multiple heartbeats (up to 20) and scaling CI estimations to biometric data. The algorithm estimates the theoretical central arterial blood pressure waveform using MBA, minimizing and avoiding the cofounding effect of the wave reflection phenomena. Based on this central arterial blood pressure waveform and biometric patient data, the system estimates cardiac output. The Argos monitor has a second advantage. It simply connects to the analogue output of the blood pressure signal from a compatible multi-parameter monitor and needs no additional specific pressure sensor. During cardiac surgery, the Argos monitor showed reasonable agreement and trending ability compared to the pulmonary artery catheter. However, in patients after cardiac surgery, including those with low cardiac output and arrhythmia, CI estimated by the device was not interchangeable with the continuous thermodilution method via a PAC.

The primary objective of the study is to evaluate the reliability of the Argos system to track changes of CI induced by changes in norepinephrine or fluid administration, compared to CITPTD in critically ill patients.