Nitric oxide and Nitrogen dioxide Concentrations During In Vitro High Frequency Oscillatory Ventilation † 1970

Introduction: Various factors influence nitric oxide (NO) and nitrogen dioxide (NO₂) concentrations in the ventilator circuits. Alveolar concentrations of NO and NO₂ during high frequency oscillatory ventilation (HFOV) have not been systematically studied. We measured variations in NO and NO₂ concentrations in the ventilator circuit and the test lung's bellows during HFOV with various frequencies and amplitudes.Methods: A test lung (Biotech; model VT-2A) with pediatric configuration (compliance 0.01L/cmH₂O and resistance 20 cmH₂O/L/min) and an endotracheal tube (5.5 Fr cuffed was connected to a HFOV (Sensor Medics 3100A). The experiment was done with dry 100% oxygen. Bias flow of the ventilator and NO flow were blended before delivery into the proximal part of the inspiratory limb. NO and NO₂ concentrations were measured at four ports with an electrochemical analyzer (Pulmonox II). Port-1 was placed at the proximal part of the inspiratory limb, port-2 near patient-Y in the inspiratory limb, port-3 at the carina, and port-4 at the bellows of the test lung. Mean airway pressure (20 cm H₂O) and bias flow (20.5 L/min) were not altered during the experiment. Measurements were repeated at a frequency of 3 to 9 Hz and an amplitude (ΔP) of 35 to 50 cmH₂O. Descriptive statistics and repeated measures ANOVA followed by Tukey-Kramer multiple comparison test were used to analyze the data. Results are reported as mean±SEM.Results: A significant decrease in NO and increase in NO₂ concentration was found in the bellows of the test lung compared with the other three sites. The sum of NO + NO₂ concentration was similar in the proximal and distal ports. NO₂ concentration at the test lung bellows increased with increasing inspired NO, frequency, and amplitude.Conclusions: Gas sampling from the ventilator circuit during HFOV may not reflect their true alveolar concentrations of NO and NO₂. Clinical implications of the present data in the test lung need to be confirmed in vivo. Table

Table 1 Table: Nitric oxide and nitrogen dioxide concentrations at various ports.