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

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.

A software programme (Open Lung Tool™) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH₂O and increased driving pressures at 20, 25 and 30 cmH₂O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH₂O 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 cmH₂O. 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 (T₀); during the final recruitment step with PEEP at 20 cmH₂O and driving pressure at 30 cmH₂O, (T_20/30); at OL-PEEP, following another recruitment manoeuvre (T_OLP).

The ratio of partial pressure of arterial oxygen (PaO₂) to fraction of inspired oxygen (FiO₂) increased from T₀ to T_OLP (120 ± 59 versus 146 ± 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 ± 5 versus 27 ± 6 ml/cmH₂O, P < 0.005). At constant PEEP (14 ± 3 cmH₂O) and tidal volumes, peak inspiratory pressure decreased (32 ± 3 versus 29 ± 3 cmH₂O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO₂) 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.

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 T₀, although left ventricular function was unchanged, indicating effective lung volume optimisation.