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Cardiopulmonary bypass significantly reduces surfactant activity in children
F X McGowan1, M Ikegami, P J del Nido
1Department of Anesthesiology/Critical Care Medicine, University of Pittsburgh School of Medicine, Pa.
Insights
Cardiopulmonary bypass in children alters lung surfactant, shifting it to smaller aggregates with reduced activity. This change is linked to decreased lung function and increased inflammatory cells post-surgery.
Area of Science:
- Pulmonary medicine
- Cardiothoracic surgery
- Biochemistry
Background:
- Lung injury is a significant complication following cardiopulmonary bypass (CPB).
- The role of altered surfactant concentration or activity in post-CPB pulmonary dysfunction is not fully understood.
- Surfactant exists in different aggregate forms (small and large) with varying density, composition, and function, and a shift towards less active small aggregates occurs in experimental lung injury.
Purpose of the Study:
- To investigate changes in surfactant aggregate fractions before and after CPB in pediatric patients.
- To correlate these surfactant changes with pulmonary function tests and inflammatory markers.
Main Methods:
- Pulmonary function testing was performed on 12 pediatric patients (2-12 years) undergoing CPB.
- Bronchoalveolar lavage (BAL) was collected before CPB and approximately 1 hour after its termination.
- Saturated phosphatidylcholine (SPC) pool sizes and protein content in small- and large-aggregate surfactant fractions were quantified.
Main Results:
- The ratio of SPC in small- to large-aggregate fractions increased significantly after CPB (0.19 to 0.37, p < 0.02).
- The ratio of SPC to protein in the small-aggregate fraction also increased post-CPB (0.04 to 0.08, p < 0.05).
- Pulmonary function declined, with reductions in forced vital capacity (-19%), inspiratory capacity (-15%), and small airway flow rates (-32%), accompanied by a fivefold increase in polymorphonuclear leukocytes.
Conclusions:
- CPB in children is associated with surfactant alterations similar to those seen in experimental lung injury, characterized by a shift towards less functional small aggregates.
- These surfactant changes correlate with measurable decreases in lung function and increased pulmonary inflammation after CPB.
Abstract:
Lung injury remains an important problem after cardiopulmonary bypass. The contribution of altered surfactant concentration or activity to pulmonary dysfunction after cardiopulmonary bypass is unclear. Recent evidence indicates that alveolar surfactant exists in specific aggregate forms that differ with respect to density, phospholipid composition, and function. A transition from surface active, higher density, large aggregates of surfactant to lower density, small aggregates that possess reduced surface activity has been demonstrated after experimental lung injury. The purpose of the present study was to examine surfactant aggregate fractions before and after bypass in children. Twelve acyanotic patients, aged 2 to 12 years, underwent intraoperative pulmonary function testing followed by bronchoalveolar lavage before incision and approximately 1 hour after termination of cardiopulmonary bypass. Saturated phosphatidylcholine pool sizes and total protein content of the small- and large-aggregate fractions of bronchoalveolar lavage fluid were determined. One hour after termination of cardiopulmonary bypass, the ratio of saturated phosphatidylcholine in small-aggregate as compared with that in large-aggregate fractions increased (mean +/- standard error) from 0.19 +/- 0.03 to 0.37 +/- 0.07 (p < 0.02), as did the ratio of saturated phosphatidylcholine to protein in the small-aggregate fraction (from 0.04 +/- 0.01 to 0.08 +/- 0.02, p < 0.05). Reductions in forced vital capacity (-19% +/- 5%), inspiratory capacity (-15% +/- 3%), and small airway flow rates (-32% +/- 6%) were also observed after bypass. These changes were accompanied by a fivefold increase in alveolar polymorphonuclear leukocyte content. The present study suggests that cardiopulmonary bypass of moderate duration in relatively healthy children is associated with surfactant changes that are similar in type and magnitude to those observed in experimental lung injury.