Surfactant protein A (SP‐A) is decreased in acute parenchymal lung injury associated with polytrauma*

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Abstract
To further investigate if the pulmonary surfactant system is altered in acute parenchymal lung injury of adults following polytrauma we measured SP‐A level and phospholipid composition in 150 sequentially obtained lung lavage samples from poly‐traumatized patients (n= 19) beginning at the day of trauma and ending 18 days later or when the patient was extubated. Out of the 19 patients studied 10 had severe parenchymal lung injury (ARDS), nine had moderate lung injury. SP‐A was measured using a two‐monoclonal sandwich ELISA‐assay. Phospholipids were separated using high‐performance liquid chromatography and their composition was calculated by comparison with standard phospholipid mixtures. We found immunoreactive SP‐A concentrations ranging from 01 μg ml“‘ to 8–5 μg ml‐1 lung lavage fluid obtained from all patients. The mean SP‐A concentration in patients who had severe parenchymal lung injury (ARDS) was 1–06 ± 0.16 μg ml‐1 lavage fluid, the mean concentration in patients who had only moderate parenchymal lung injury was 1.92 ± 0.18 μg ml‐1 lavage fluid. Both concentrations were lower than in healthy controls (2.74 ± 0.3 μg ml‐1 lavage fluid; n = 12). In patients who had moderate lung injury the SP‐A level normalized, but in patients who had severe lung injury the SP‐A level remained low during the timespan examined. SP‐A alterations did not correlate to changes in phospholipid composition as determined in lung lavage samples of individual patients. We conclude that alveolar SP‐A concentrations decrease in polytraumatized patients who have acute parenchymal lung injury soon after the trauma occurs. In patients who have lung injury of low severity the SP‐A level normalizes with recovery, but with more severe parenchymal lung injury SP‐A levels remain low. We speculate that the metabolic regulation of individual surfactant components might differ during lung injury and repair.

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