Evaluation of lung and chest wall mechanics during anaesthesia using the PEEP-step method.

Background: Postoperative pulmonary complications are common. Between patients there are differences in lung and chest wall mechanics. Individualised mechanical ventilation based on measurement of transpulmonary pressures would be a step forward. A previously described method evaluates lung and chest wall mechanics from a change of ΔPEEP and calculation of change in end-expiratory lung volume (ΔEELV). The aim of the present study was to validate this PEEP-step method (PSM) during general anaesthesia by comparing it with the conventional method using oesophageal pressure (PES) measurements.

Methods: In 24 lung healthy subjects (BMI 18.5-32), three different sizes of PEEP steps were performed during general anaesthesia and ΔEELVs were calculated. Transpulmonary driving pressure (ΔPL) for a tidal volume equal to each ΔEELV was measured using PES measurements and compared to ΔPEEP with limits of agreement and intraclass correlation coefficients (ICC). ΔPL calculated with both methods was compared with a Bland-Altman plot.

Results: Mean differences between ΔPEEP and ΔPL were <0.15 cm HO, 95% limits of agreements -2.1 to 2.0 cm HO, ICC 0.6-0.83. Mean differences between ΔPL calculated by both methods were <0.2 cm HO. Ratio of lung elastance and respiratory system elastance was 0.5-0.95.

Conclusions: The large variation in mechanical properties among the lung healthy patients stresses the need for individualised ventilator settings based on measurements of lung and chest wall mechanics. The agreement between ΔPLs measured by the two methods during general anaesthesia suggests the use of the non-invasive PSM in this patient population.

Clinical Trial Registration: NCT 02830516.