Cardiac output estimation using pulmonary mechanics in mechanically ventilated patients

Abstract

The application of positive end expiratory pressure (PEEP) in mechanically ventilated (MV) patients with acute respiratory distress syndrome (ARDS) decreases cardiac output (CO). Accurate measurement of CO is highly invasive and is not ideal for all MV critically ill patients. However, the link between the PEEP used in MV, and CO provides an opportunity to assess CO via MV therapy and other existing measurements, creating a CO measure without further invasiveness.This paper examines combining models of diffusion resistance and lung mechanics, to help predict CO changes due to PEEP. The CO estimator uses an initial measurement of pulmonary shunt, and estimations of shunt changes due to PEEP to predict CO at different levels of PEEP. Inputs to the cardiac model are the PV loops from the ventilator, as well as the oxygen saturation values using known respiratory inspired oxygen content. The outputs are estimates of pulmonary shunt and CO changes due to changes in applied PEEP. Data from two published studies are used to assess and initially validate this model.The model shows the effect on oxygenation due to decreased CO and decreased shunt, resulting from increased PEEP. It concludes that there is a trade off on oxygenation parameters. More clinically importantly, the model also examines how the rate of CO drop with increased PEEP can be used as a method to determine optimal PEEP, which may be used to optimise MV therapy with respect to the gas exchange achieved, as well as accounting for the impact on the cardiovascular system and its management.

Physiological modeling, tight glycemic control, and the ICU clinician: what are models and how can they affect practice?

“…In the critical care arena, the use of in silico physiological models is only emerging. However, there are already model-based or model-derived applications for managing sedation [ 25 , 26 ], cardiovascular diagnosis and therapy [ 27 , 28 ], mechanical ventilation [ 29 , 30 ], and the diagnosis of sepsis [ 31 , 32 ]. Particular to TGC, there are already some attempts at modeling for both understanding and implementing TGC [ 23 , 33 - 42 ], with a review of many in [ 43 ].…”

Investigations concerning the application of the cross-correlation method in cardiac output measurements

“…It should be emphasized that non-invasive methods of CO measurements are recognized as less accurate [2,3,6,8] and minimally invasive methods must be calibrated before examination by means of thermodilution [7,8]. Actually there are a few methods based on other physical principles [9,10], but nowadays they are being developed. The PAC technique by means of the Swan-Ganz catheter allows to obtain or calculate other valuable hemodynamic parameters basing on intracardiac pressures, e.g.…”