A Non Invasive Estimation of Cardiac Output in Mechanically Ventilated Patients

The two gold standard for cardiac output (CO) measurements, i.e., the Fick method and pulmonary artery thermodilution , are both invasive methods, requiring the use of central venous catheter and Swan-Ganz catheter, respectively. With the aim to reduce the risks for the patient, a big research effort has been made to investigate minimally invasive or non-invasive methods. Investigators sought to evaluate the effectiveness of a non invasive method to estimate CO in mechanically ventilated patients.The method is based on prolonged expiration, and relies on measurement of gas concentrations and flow rate. Investigators designed, realized, and characterized a system to induce passive prolonged expirations when connected to the patient circuit. CO is then calculated using an algorithm based a modified version of the Fick equation and the results are compared with the ones obtained by thermodilution. Several advantages can be introduced by the prolonged expiration technique: non-invasive measurement, easy implementation, independency from operator ability among others.