Surfactant and Lung Function Following Cardiac Surgery

Introduction: Cardio-pulmonary bypass (CPB) is associated with prolonged mechanical ventilation (PMV) in the intensive care unit (ICU), and an increase in morbidity and mortality. Surfactant dysfunction could result in atelectasis and contribute to PMV. However, it is unclear whether cessation of mechanical ventilation, with resultant atelectasis, and the use of a foreign bypass circuit during CPB, would affect the concentration of surfactant constituents and whether this, in turn, is associated with PMV. Pulmonary surfactant, which increases lung compliance and opposes atelectasis by reducing alveolar surface tension, is produced in the lung by alveolar type II cells. It is comprised of 10% protein, predominantly the surfactant proteins A, B, C & D, and 90% phospholipid, which can be separated into large surfactant aggregates (LA) and small surfactant aggregates (SA). LA, the metabolic precursors to SA, are the greatest contributors to reduction of surface tension.

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Results: Of the total 22 patients included in this retrospective analysis, 15 patients received CPB and 7 received off-pump surgery. The median EuroSCORE II and proportion of patients with NYHA III was not significantly different between groups. Clinically diagnosed heart failure was identified at admission in 9 patients in the CPB group (60%) and only 2 patients in the off-pump group (29%). This resulted in greater left atrial area, left ventricular end diastolic diameter and mitral valve inflow E-wave velocity: mitral valve inflow A-wave velocity in the CPB group.  There was no difference in BAL small aggregate concentration between the two groups. A significant difference in BAL large aggregate concentration per mL ELF between the off-pump and CPB groups may have contributed to a trend toward an increase in the small to large aggregate ratio in the CPB group ( p = 0.051).  The duration of CPB was 73.7 ± 20.53 min (mean ± SD). Intra-operative fluid balance was higher and length of mechanical ventilation longer in the CPB group. However, this was not associated with an increase in ICU or hospital total length of stay. No other clinical parameters were significantly different between the groups, including duration of surgery (median of 235 (192–285) min for the CPB group and 220 (210–315) min for the off-pump group; p = 0.91).

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Conclusions: In this retrospective exploratory study, there was a difference in pulmonary surfactant LA concentration following cardiac surgery in patients who underwent CPB compared to those treated without the use of CPB (off-pump). This is a novel finding in adult patients undergoing CPB. This difference in the more surface-active component of surfactant in the CPB group may be associated with the longer length of mechanical ventilation in the ICU in CPB patients found in this study. This observation warrants confirmation with larger cohorts. Future studies should include examining the effect of PEEP and lung recruitment versus lung deflation on surfactant concentrations for patients receiving CPB, and whether this reduces the length of mechanical ventilation.