Single-Breath Measurements of Pulmonary Oxygen Uptake and Gas Flow Rates for Ventilator Management in ARDS

Monitoring data in critical care and anesthesiology should be displayed to present a rapid and easily comprehensible definition of the patient's clinical status. A graphic computer display of the analog output of gas flow rates and the O2 and CO2 concentrations of respiratory gases profiles the expired breath for an estimation of pulmonary function and gas exchange. An estimate of pulmonary perfusion, cardiac output, and the general adequacy of cardiovascular circulation is obtained from the computer calculation of O2 uptake and CO2 elimination, dead space, and alveolar ventilation. Adjunctive data from the spirometric measurements of airway pressures, volumes, and compliance, supplemented by hemodynamic monitoring, aids in the diagnosis of physiologic changes. For > 10 years, we have used this system to monitor patients who are anesthetized, sedated, and receiving mechanical ventilation during anesthesia and surgery, and recently have extended the technique to intensive care areas. Our experience has shown good correlation of changes in the computer-assisted expired breath analysis with coinciding clinical events, including upper airway obstruction, bronchospasm, and alveolar volume/pulmonary capillary blood flow impairment. To demonstrate the use of this system, we describe the ventilator management for a patient with severe ARDS. In this patient, changes in ventilator management, including pressure control ventilation, improved pulmonary O2 uptake (mean, 18.7 vs 8.5 mL/breath), CO2 elimination (mean, 17 vs 13 mL/breath), and compliance (mean, 29.7 vs 19.0 mL/cm H2O), were compared with intermittent mandatory ventilation.