Acute effects of sitting out of bed and exercise on lung aeration and oxygenation in critically ill subjects

BACKGROUND: Early mobilization during critical illness is safe and has beneficial effects on functional outcomes. However, its impact on pulmonary function has not been thoroughly explored. We hypothesized that a sitting position out of bed coupled with exercise could result in an improvement in oxygenation and lung aeration. METHODS: The study was conducted on a cohort of adult subjects within a week of their admission to an ICU. Subjects were transferred to a chair and undertook a 15-min session of exercise, either active or passive. Subjects in the control group were only transferred to a chair. Electrical impedance tomography, a reliable bedside technique monitoring regional lung aeration and the distribution of ventilation, was continuously performed, and blood gases were assessed at baseline and 20 min post-exercise. RESULTS: The cohort included 40 sub-jects, 17 of whom were mechanically ventilated and 23 spontaneously breathing. The control group for each modality consisted of 5 mechanically ventilated or 5 spontaneously breathing subjects. Mild hypoxemia was present in 45% of the spontaneously breathing cohort, whereas the mechanically ventilated subjects demonstrated moderate (50%) or severe (12%) hypoxemia. Compared with the control group, early mobilization induced a significant increase in lung aera-tion. In mechanically ventilated subjects, lung aeration increased, especially in the anterior lung regions (mean impedance [95% CI]: T1 (baseline in bed) = 1,265 [691–1,839]; T2 (chair sitting) = 2,003 [1,042–2,963]; T3 (exercise) = 1,619 [810 2,427]; T4 (post exercise in chair) = 2,320 [1,186–3,455]). In spontaneously breathing subjects, lung aeration increased mainly in the poste-rior lung regions (mean impedance [95% CI]: T1 = 380 [124–637]; T2 = 655 [226–1,084]; T3 = 621 [335–906]; T4 = 600 [340–860]). P_aO2 /F_IO2 increased, especially in subjects with lower P_aO2 /F_IO2 at baseline (< 200) (133 ± 31 to 158 ± 48, P = .041). CONCLUSIONS: For critically ill subjects, a sitting position and exercise increased lung aeration and were associated with an improvement in P_aO2 /F_IO2 in the more severely hypoxemic subjects.