Standard versus individualised positive end-expiratory pressure (PEEP) compared by electrical impedance tomography in neurocritical care: a pilot prospective single centre study.

Background: Individualised bedside adjustment of mechanical ventilation is a standard strategy in acute coma neurocritical care patients. This involves customising positive end-expiratory pressure (PEEP), which could improve ventilation homogeneity and arterial oxygenation. This study aimed to determine whether PEEP titrated by electrical impedance tomography (EIT) results in different lung ventilation homogeneity when compared to standard PEEP of 5 cmH₂O in mechanically ventilated patients with healthy lungs.

Methods: In this prospective single-centre study, we evaluated 55 acute adult neurocritical care patients starting controlled ventilation with PEEPs close to 5 cmH₂O. Next, the optimal PEEP was identified by EIT-guided decremental PEEP titration, probing PEEP levels between 9 and 2 cmH₂O and finding the minimal amount of collapse and overdistension. EIT-derived parameters of ventilation homogeneity were evaluated before and after the PEEP titration and after the adjustment of PEEP to its optimal value. Non-EIT-based parameters, such as peripheral capillary Hb saturation (SpO₂) and end-tidal pressure of CO₂, were recorded hourly and analysed before PEEP titration and after PEEP adjustment.

Results: The mean PEEP value before titration was 4.75 ± 0.94 cmH₂O (ranging from 3 to max 8 cmH₂O), 4.29 ± 1.24 cmH₂O after titration and before PEEP adjustment, and 4.26 ± 1.5 cmH₂O after PEEP adjustment. No statistically significant differences in ventilation homogeneity were observed due to the adjustment of PEEP found by PEEP titration. We also found non-significant changes in non-EIT-based parameters following the PEEP titration and subsequent PEEP adjustment, except for the mean arterial pressure, which dropped statistically significantly (with a mean difference of 3.2 mmHg, 95% CI 0.45 to 6.0 cmH₂O, p < 0.001).

Conclusion: Adjusting PEEP to values derived from PEEP titration guided by EIT does not provide any significant changes in ventilation homogeneity as assessed by EIT to ventilated patients with healthy lungs, provided the change in PEEP does not exceed three cmH₂O. Thus, a reduction in PEEP determined through PEEP titration that is not greater than 3 cmH₂O from an initial value of 5 cmH₂O is unlikely to affect ventilation homogeneity significantly, which could benefit mechanically ventilated neurocritical care patients.