Non-invasive cardiac output measurement of assisted and spontaneously breathing patients by means of partial CO2 rebreathing.

DOI: 10.36210/BerMedJ/epub27112024

Abstract

: In the partial carbon dioxide rebreathing method, cardiac output (CV) is proportional to the change in CO₂ elimination divided by the change in end-tidal CO₂ as a result of a rebreathing period. This measurement principle has so far made it impossible to specifically determine the HRV in past studies during spontaneous breathing and assisted spontaneous breathing. The advantages of NICO™ compared to invasive methods are the continuous measurement of end-tidal CO₂ concentrations and the resulting possibility of determining dead space ventilation (VD/VT), alveolar ventilation (MValv), the measurement of effective pulmonary blood flow (PCBF) as well as the determination of the pulmonary blood flow. blood flow (PCBF) and the determination of VCO₂ and VO₂. For the study, 45 patients requiring intensive care with existing invasive monitoring (PiCCO, CCO) and assisted ventilation (BIPAP ASB, SIMV) or assisted spontaneous breathing (ASB, CPAP) via a horizontal endotracheal tube were recruited. NICO™ monitoring with NICO CO₂ loop flow sensor, NICO sensor with rebreathing valve and monitor was provided by hesto med Lichtenstein and Respironics® Germany. At the same time, the microcirculation parameters (SO₂, flow, velocity) were measured at a tissue depth of 3 and 7 mm using LEA O2C laser Doppler flow spectrometry. The cardiac output determined by CO2 rebreathing correlates with the invasively determined cardiac output (6.15±1.83 l/min vs. 6.73±1.70 l/min; Pearson=0.66, R²= 0.43; p>0.1). The measured CO₂ output correlates with the end-expiratory tidal volume (268±68.08 ml vs.187.48 ±76.75 ml; Pearson =0.35; R²=0.13) and end-expiratory CO₂ (32.74±5.02 mmHg; Pearson=0.45, R²=0.2) and is dependent on ventilation-perfusion mismatch (VQI =25.93±8.61%) and dead space ventilation (TRV=58.8±49.29 ml). The factors of CO₂ production (VCO₂) have an influence on the subcutaneous oxygen saturation (SO₂P1S; Pearson=0.4) and on the blood flow (Flow P1S) in 3 mm tissue depth (Pearson=0.5) as well as on the blood flow (Flow P1D) in 7 mm tissue depth (Pearson=0.3). The pulmonary capillary blood flow (PCBF) has a negative correlation to the subcutaneous oxygen saturation (SO₂P1S; -0.3) and the blood flow (Flow P1D) in the tissue layer of 7 mm (Flow; -0.4). There is no influence of the determined cardiac output on microperfusion. The NICO CO₂ rebreathing method thus proves to be a suitable instrument for the continuous monitoring of spontaneously or assisted breathing patients. A correlation of the parameters determined in the NICO system and the measured parameters of the microcirculation (O2C) can be found from VCO₂ subcutaneous oxygen saturation and blood flow as well as pulmonary blood flow (PCBF) to subcutaneous oxygen saturation and deep tissue blood flow (FlowP1D).