Effect of lateral positioning on ventilation in patients with blunt thoracic injury during pressure support...

In patients with blunt thoracic injury requiring mechanical ventilation lateral positioning is routinely performed. Whether it modifies ventilation distribution and aeration is unclear.

Patients receiving pressure support ventilation (PSV) were positioned 30 degrees on each side for 30 min. Electrical impedance tomography (EIT) was used to quantify the percentage of right and left ventilation. Secondary outcomes included right and left tidal volume and the modified lung ultrasound score. At baseline, patients were categorized according to ventilation distribution: symmetrical (right lung receiving 50-55% of total ventilation) or asymmetrical.

Twenty-four patients were included (mean age 51 ± 20 years, 79% male) under median PSV 5 cmH₂O [25-75% IQR: 5-8] and PEEP 8 [5-8] cmH₂O. Trauma mechanisms included motor vehicle collision (50%) and fall (29%); 54% had bilateral rib fractures and 8% a flail chest. The duration of ventilation and ICU stay were 9 [5-19] and 13 [8-21] days, respectively. Regional right-lung ventilation increased slightly when the lung was dependent [53% (44-58%)], decreased when non-dependent [47% (44-53%)], compared to supine [50% (45-54%)] (p = 0.022). These effects were observed in patients with symmetrical baseline ventilation (n = 8, p = 0.011), but not in those with asymmetrical ventilation (n = 16, p = 0.391), nor in patients with low respiratory system compliance (< 50 ml/cmH₂O, n = 9, p = 0.539). In patients with symmetrical distribution, the right-lung and right-basal ultrasound score increased when dependent (p < 0.05), whereas no changes were observed in the left lung. There were no differences in respiratory mechanics or global ventilation from the beginning to the end of the session once patients were returned to supine.

In blunt thoracic injury, lateral positioning during PSV is associated with a modest increase in regional ventilation of the dependent lung, but this effect is limited to patients with symmetrical ventilation distribution and normal compliance. In others, longer duration or higher degree of lateralization may be required.