Multiple single-breath measurements of nitric oxide in the intubated patient

Multiple flow rate measurements of exhaled nitric oxide (NO) have been advocated to fractionate NO from alveolar and bronchial sources. The aim of this study was to develop a method by which multiple single-breath exhalations at various flow rates could be performed in intubated, mechanically ventilated patients. Nine patients without lung disease were studied awake and after intubation, during general anesthesia. A suction ejection system connected to a restrictor valve was used to control the exhalation flow rate. From these measurements the fraction of alveolar NO (Fa(NO)), the fraction of airway wall NO (Faw(NO)), and the airway wall transfer rate (D-NO) were calculated. The fraction of exhaled NO was reduced by 50% after intubation. DNO was also reduced by intubation (from 10 +/- 1.3 to 6.4 +/- 2.1 nl second(-1) ppb(-1) X 10(-3)) whereas neither Faw(NO) nor Fa(NO) was affected. The peak NO concentration after 20 seconds of apnea during general anesthesia was similar to calculated Faw(NO). The vacuum aspiration method used in this study allowed for reproducible multiple single-breath measurements and calculation of alveolar and bronchial NO parameters. Further studies will reveal whether this methodology will improve the value of exhaled NO analysis in intubated, mechanically ventilated patients with pulmonary disease.