Purpose: After resetting of a ventilator the adequacy of alveolar ventilation is often judged on the basis of PaCO2. This causes delay, costs and is invasive. CO2 elimination (VCO2, ml/min) reflects in steady state the metabolic rate. A change of alveolar ventilation and/or perfusion leads to a transient change of VCO2. This study explores the usefulness of VCO2 as an indicator of adequacy of gas exchange after ventilator resetting. Methods: VCO2 and end-tidal CO2 were measured with the 930 CO2 Analyzer of the ServoVentilator 900C before and immediately after resetting of the ventilator PaCO2 was measured and dead space fractions analyzed with the single breath test for CO2 before and 20' after resetting of either inspiratory pressure (tidal volume) and/or respiratory rate (RR). In a critical care ward 58 patients with moderate lung function perturbation demanding an inspiratory pressure of >25 cm H2O were studied in an acute phase of disease. Results: The change of VCO2 (in %) after resetting correlated with the change in PaCO2: ΔVCO2=-0.93*ΔPaCO2+0.5 (r=0.79). In each patient the sign of ΔVCO2 was opposite that of ΔPaCO2. Resetting led to complex changes of Vt, airway and alveolar dead space and unforeseeable changes in gas exchange which were adequately reflected by ΔVCO2. End-tidal CO2 or other parameters were not efficient indicators of gas exchange after resetting. Discussion: ΔVCO2 gives immediate information about changes in efficient alveolar ventilation after resetting the ventilator. In critically care, optimal setting of a ventilator may be sought by trial and error. It is then important to get immediate information if a resetting leads toward the goal or not. It appears that ΔVCO2 is a suitable indicator for that purpose.
|Original language||English (US)|
|Issue number||4 SUPPL.|
|State||Published - Oct 1996|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Critical Care and Intensive Care Medicine
- Cardiology and Cardiovascular Medicine