Pulmonary surfactant function in patients with acute lung injury/acute respiratory distress syndrome treated by mechanical ventilation

Aim

The evaluation of the quality and surface active properties of surfactant carried out in vitro in setting the bubble, that is pulsating, with the use of a surfactometer (Pulsating Bubble Surfactometer).

Materials and methods

Patients requiring mechanical ventilation were enrolled to the study. All patients met the criteria for acute lung injury (ALI) or acute respiratory distress syndrome, according to the American–European Consensus Conference. Additionally, the Lung Injury Score criteria to determine the severity and the course of lung injury were used. Sixty-five patients were included in the study – 45 with respiratory insufficiency, of the latter 30 with indirect ALI and 15 with direct ALI. Twenty patients were included in the reference group. All patients underwent bronchoscopy and bronchoalveolar lavage. The procedures were carried out during the first 24 hours of mechanical ventilation. Analysis of pulmonary surfactant activity was carried out using Pulsating Bubble Surfactometer (Electronetics Corp., USA). Changes of value of the surface tension in the cycle compression–expansion, minimum value of the surface tension, maximum value surface tension and the hysteresis loop changes of the surface tension measured as their area value changes were measured. The normalized hysteresis area, the stability index and the rate of effectiveness of reducing the surface tension were calculated.

Results

Differences were seen between groups with direct ALI and indirect ALI and the control group, with reference to separate analyses parameters. Minimum value of the surface tension (P < 0.001) and maximum value of the surface tension (P < 0.002) were significantly lower in the control group, whereas the normalized hysteresis area (P < 0.001), the stability index (P < 0.001) and the rate of effectiveness of reducing the surface tension (P < 0.02) were significantly higher.

Comparison of separate groups revealed significantly lower values of the minimum value of the surface tension (P < 0.003), the normalized hysteresis area (P < 0.001), the stability index (P < 0.007) and the rate of effectiveness of reducing the surface tension (P < 0.003) in the group with direct ALI, compared with the group with indirect ALI. There were no differences in relation to maximum values of the surface tension (P = 0.135).

Conclusions

(1) Pulmonary surfactant dysfunction was observed in the early phase ALI. (2) Direct lung injury was associated with higher impairment of surfactant function than indirect lung injury. (3) Correlation exists between the level of the lung injury and dynamic surface active properties of pulmonary surfactant.