Effects of routine postural repositioning on the distribution of lung ventilation and perfusion in mechanically ventilated patients

Abstract

Objectives: To analyse the effects on respiratory function, lung volume and the regional distribution of ventilation and perfusion of routine postural repositioning in mechanically ventilated critically ill patients.

Methods: Prospective descriptive physiological study. We evaluated gas-exchange, lung mechanics, and Electrical Impedance Tomography (EIT) determined end-expiratory lung impedance and regional ventilation and perfusion distribution in five body positions: supine-baseline (S1); first lateralisation at 30° (L1); second supine position (S2), second contralateral lateralisation (L2) and third final supine position (S3). To evaluate the effects of lateral repositioning we compared S1 with S2 and with the changes during L1 and L2.

Results: We included 32 patients. The lateralisation sequence was well tolerated. When comparing S1 with S3 respiratory system compliance increased by 7 % (p = 0.021), the partial pressure to inspired oxygen fraction ratio (PaO₂/FiO₂) by 16 % (p = 0.06) and dead-space decreased by 5 % (p = 0.09). During lateralisation, haemodynamic parameters and PaO₂/FiO₂ did not change, while dead-space and PaCO₂ presented small non-significant increases. Although with great inter-individual variability, end-expiratory lung impedance increased in the non-dependent 163 ± 123 ml and dependent lung 69 ± 119 ml, both p < 0.009). Regional ventilation decreased in the non-dependent and increased in the dependent lung, while regional perfusion decreased in the dependent lung, especially in dorsal regions.

Conclusions: Postural changes are well tolerated, result in improved lung mechanics and have a positive effect on gas exchange. Lateralisation does not result in a decrease in lung volume in the dependent lung.

Implications for clinical practice: Postural repositioning can be safely performed in ICU patients to foster its known benefits. To the known beneficial effects on the prevention of pressure wounds, postural changes can improve regional end-expiratory lung volume (i.e., the functional volume of the lung). Regional changes vary among patients and extended monitoring options such as EIT can help to individualise this useful therapeutic intervention.

Keywords: Electrical Impedance Tomography; End-expiratory lung volume; Mechanical ventilation; Patient repositioning; Pulmonary gas exchange; Respiratory mechanics; Ventilation-perfusion ratio.