A Non Invasive Estimation of Cardiac Output in Mechanically Ventilated Patients
Condition: Non Invasive Estimation of Cardiac Output
Study type: Interventional

Summary: 
      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.
    

Detailed description: 
      This prospective trial was designed to assess the performance of a non invasive method to
      estimate cardiac output in mechanically ventilated cardiac surgery patients and its outcome
      is compared to the values obtained from the invasive measurement system based on
      thermodilution. The pulmonary blood flow (PBF), which is the volume of blood that actively
      participates in the gas exchange per unit of time, is the directly estimated variable that
      this technique employ to calculate cardiac output. The method investigators studied is
      theoretically based on the application of an algorithm which derives from a modified version
      of the Fick equation in two different phases; the former involves measurements during the
      steady state, whilst the second starts when a sudden perturbation into the carbon dioxide
      (CO2) elimination process is introduced. The algorithms investigated in this work requires
      the analysis of the expired gas content during both normal breathing and prolonged
      expiration, providing a non-invasive estimation of the artero-venous content of CO2, and
      consequently allows the calculation of PBF according to the Fick method. At this purpose, a
      metabolic monitor was used; it sampled gas from the "Y" piece of the mechanical ventilator's
      breathing circuit through a suction pump. In order to obtain the prolonged expiration, a
      pneumatic system, with an ad hoc designed orifice resistance (5 cmH2O•L-1•min),has been made
      and experimentally characterized to adapt the breathing circuit to this application.
      Experimental data of CO2 and O2 concentrations were recorded and processed after the
      measurement session thanks to an ad hoc developed LabView application. This application
      performs the following tasks: it converts the gas fractions into partial pressures, segments
      the trends of partial pressures, executes the data-reduction and, after obtaining the values
      of venous carbon dioxide tension (PvCO2) and arterial carbon dioxide tension (PaCO2)
      obtained, it calculates the CO value using the above mentioned algorithms.

      The values calculated with non invasive method showed good agreement with ones obtained by
      thermodilution and a precision comparable to those of other minimally invasive techniques.
    

Intervention name(s): cardiac output measurement
Intervention type(s): Procedure
Intervention description(s): non invasive cardiac output estimation based on passive induced prolonged expiration in mechanically ventilated patients
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Supportive Care
Keywords: cardiac output; fick method; thermodilution