Performance of a capnodynamic method estimating cardiac output during respiratory failure - before and after lung...

Respiratory failure may cause hemodynamic instability with strain on the right ventricle. The capnodynamic method continuously calculates cardiac output (CO) based on effective pulmonary blood flow (CO_EPBF) and could provide CO monitoring complementary to mechanical ventilation during surgery and intensive care. The aim of the current study was to evaluate the ability of a revised capnodynamic method, based on short expiratory holds (CO_EPBFexp), to estimate CO during acute respiratory failure (LI) with high shunt fractions before and after compliance-based lung recruitment. Ten pigs were submitted to lung lavage and subsequent ventilator-induced lung injury. CO_EPBFexp, without any shunt correction, was compared to a reference method for CO, an ultrasonic flow probe placed around the pulmonary artery trunk (CO_TS) at (1) baseline in healthy lungs with PEEP 5 cmH₂O (HL_P5), (2) LI with PEEP 5 cmH₂O (LI_P5) and (3) LI after lung recruitment and PEEP adjustment (LI_Padj). CO changes were enforced during LI_P5 and LI_Padj to estimate trending. LI resulted in changes in shunt fraction from 0.1 (0.03) to 0.36 (0.1) and restored to 0.09 (0.04) after recruitment manoeuvre. Bias (levels of agreement) and percentage error between CO_EPBFexp and CO_TS changed from 0.5 (- 0.5 to 1.5) L/min and 30% at HL_P5 to - 0.6 (- 2.3 to 1.1) L/min and 39% during LI_P5 and finally 1.1 (- 0.3 to 2.5) L/min and 38% at LI_Padj. Concordance during CO changes improved from 87 to 100% after lung recruitment and PEEP adjustment. CO_EPBFexp could possibly be used for continuous CO monitoring and trending in hemodynamically unstable patients with increased shunt and after recruitment manoeuvre.