Monitoring: Equipment and Computers
Background and Goal of Study: The pulmonary capillary blood flow (PCBF) can be measured by short periods of impairment of the CO2 elimination rate (VCO2), which lead endtidal CO2 partial pressure (PETCO2) to increase (1). We compared two systems for measurement of PCBF that use different degrees of partial CO2 rebreathing.
Materials and Methods: Sixteen adult sheep were anesthetized and mechanically ventilated with the Evita 2 mechanical ventilator (Drägerwerk, Lübeck, Germany). PCBF was estimated noninvasively as VCO2/S. PETCO2 (S = CO2 dissociation curve) with the DAVID Monitor (MedServ, Leipzig, Germany) (PCBFDavid), which has a rebreathing deadspace of 200 ml, and by the Evita 2, which was modified to permit rebreathing maneuvers with a deadspace of 1000 ml and calculate PCBF (PCBFEvita). Measurements were performed at normal and impaired conditions of hemodynamics (variation of cardiac output) and gas exchange (variation of alveolar deadspace and shunt).
Results and Discussions: In total 144 pairs of measurements were obtained. Bias and precision calculations showed a tendency for PCBFEvita to overstimate PCBFDavid (0.3 ± 0.7 ml/min, p < 0.001).
Conclusion(s): The modified Evita 2 tends to overestimate PCBF values as measured by the DAVID Monitor. This is most probably explained by a nonlinear relationship between VCO2 and PETCO2 in the presence of alveolar deadspace, which leads PCBF values estimated by almost total CO2 rebreathing to be higher than by minimal CO2 rebreathing.
Acknowledgements: We acknowledge Drägerwerk AG for financial support.