Performance of a revised capnodynamic method for cardiac output monitoring

Abstract

Cardiac output (CO) monitoring is ideal for guiding fluid, vasopressor and inotropic therapy for sufficient oxygen delivery and may improve outcome in high risk surgery. In this context, many minimally-and non-invasive methods have emerged during recent years, however, they appear less reliable when compared to the thermodilution methods during rapid changes in vascular volume and resistance, a common feature during major surgery. The capnodynamic method calculates non-shunted cardiac output, the effective pulmonary blood flow (COEPBF), on the basis of a capnodynamic equation describing the mole balance of CO2 transported to and from the lungs. By prolonging three out of every nine breaths in mechanically ventilated patients, COEPBF is automatically and continuously calculated with each new breath. In previous studies the capnodynamic method with inspiratory holds provided CO mon-itoring, however with unacceptable accuracy and precision during lung injury and elevated positive end-expiratory pressure (PEEP).

In this thesis we evaluated the revised capnodynamic method with expiratory holds in four separate studies. In a large animal model (study I-III), COEPBF was compared to a gold stan-dard flowmeter placed around the pulmonary trunk during different hemodynamic, ventila-tory, respiratory and metabolic challenges. Finally, COEPBF was compared to transpulmonary thermodilution in patients undergoing high risk abdominal cancer surgery. The capnodynamic method showed overall acceptable agreement and good trending abil-ities in a variety of conditions familiar to a perioperative team. The agreement was tempo-rarily disrupted after ischemia-reperfusion, however reestablished within five minutes. The accuracy was marginally affected during lung injury, both at high shunt fractions and after recruitment manoeuvre with PEEP adjustment. However, both precision and trending ability were maintained. In high risk patients, COEPBF showed good accuracy, acceptable precision and good trending ability in various conditions. The performance was especially robust after individualized lung recruitment and PEEP adjustment. COEPBF may provide continuous CO monitoring with short response time, good trending abilities and acceptable agreement to guide hemodynamic treatment during surgery.