Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

Abstract

Introduction

To investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.

Methods

A software programme (Open Lung Tool™) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH ₂O and increased driving pressures at 20, 25 and 30 cmH ₂O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH ₂O every two minutes, with tidal volume set at 6 ml/kg). The open lung PEEP (OL-PEEP) was defined as the PEEP level yielding maximum dynamic respiratory compliance plus 2 cmH ₂O. Gas exchange, respiratory mechanics and central haemodynamics using the Pulse Contour Cardiac Output Monitor (PiCCO™), as well as transoesophageal echocardiography were measured at the following steps: at baseline (T ₀); during the final recruitment step with PEEP at 20 cmH ₂O and driving pressure at 30 cmH ₂O, (T _20/30); at OL-PEEP, following another recruitment manoeuvre (T _OLP).

Results

The ratio of partial pressure of arterial oxygen (PaO ₂) to fraction of inspired oxygen (FiO ₂) increased from T ₀ to T _OLP (120 ± 59 versus 146 ± 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 ± 5 versus 27 ± 6 ml/cmH ₂O, P < 0.005). At constant PEEP (14 ± 3 cmH ₂O) and tidal volumes, peak inspiratory pressure decreased (32 ± 3 versus 29 ± 3 cmH ₂O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO ₂) was unchanged (58 ± 22 versus 53 ± 18 mmHg). No significant decrease in mean arterial pressure, stroke volume or cardiac output occurred during the recruitment (T _20/30). However, left ventricular end-diastolic area decreased at T _20/30 due to a decrease in the left ventricular end-diastolic septal-lateral diameter, while right ventricular end-diastolic area increased. Right ventricular function, estimated by the right ventricular Tei-index, deteriorated during the recruitment manoeuvre, but improved at T _OLP.

Conclusions

A standardised open lung strategy increased oxygenation and improved respiratory system compliance. No major haemodynamic compromise was observed, although the increase in right ventricular Tei-index and right ventricular end-diastolic area and the decrease in left ventricular end-diastolic septal-lateral diameter during the recruitment suggested an increased right ventricular stress and strain. Right ventricular function was significantly improved at T _OLP compared with T ₀, although left ventricular function was unchanged, indicating effective lung volume optimisation.