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 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, (T20/30); at OL-PEEP, following another recruitment manoeuvre (TOLP).

Results: The ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) increased from T0 to TOLP (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 (T20/30). However, left ventricular end-diastolic area decreased at T20/30 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 TOLP.

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

Figure 1

Recruitment procedure using the Open Lung Tool™. Cdyn = dynamic compliance of the respiratory system; ΔP = driving pressure; PEEP = positive end-expiratory pressure; T₀ = time at baseline; T_20/30 = time when positive end-expiratory pressure at 20 cmH₂O and driving pressure at 30 cmH₂O.

Figure 2

Positive end-expiratory pressure titration using the Open Lung Tool™. Cdyn = dynamic compliance of the respiratory system; OL-PEEP = open lung positive end-expiratory pressure; ΔP = driving pressure; PEEP = positive end-expiratory pressure; T₀ = time at baseline.

Figure 3

Correlation graph of percentage difference of dynamic compliance and percentage change in PaO₂ from T₀ to T_OLP. P < 0.05, r = 0.62. PaO₂ = partial pressure of arterial oxygen; T₀ = time at baseline; T_20/30 = time when positive end-expiratory pressure at 20 cmH₂O and driving pressure at 30 cmH₂O.

Figure 4

End-diastolic area changes of the left and right ventricle from T₀ to T_20/30 to T_OLP. *P < 0.05 compared with T_0; ^†P < 0.05 compared with T_20/30. LVEDA = left ventricular end-diastolic area; RVEDA = right ventricular end-diastolic area; T₀ = time at baseline; T_20/30 = time when positive end-expiratory pressure at 20 cmH₂O and driving pressure at 30 cmH₂O; T_OLP = time at open lung-positive end-expiratory pressure.

Figure 5

(a) End-systolic transgastric midpapillary views obtained at baseline, (b) during the recruitment manoeuvre and (c) during open lung positive end-expiratory pressure. Note the massive dilation of the right ventricle (RV), causing acute leftward shift of the interventricular septum (IVC) and compression of the left ventricle (LV; d-shaped) during the recruitment manoeuvre.