An 18-month-old boy is admitted to the pediatric intensive care unit after undergoing cardiac surgery. At age 16 months, his parents brought him to a pediatrician due to intermittent episodes of cyanosis when he became upset. At that time, a cardiac murmur was noted, and echocardiogram revealed tetralogy of Fallot with moderate pulmonary stenosis. The patient's initial postoperative period is unremarkable, but on postoperative day 4 he develops tachypnea with an increasing oxygen requirement. Chest x-ray reveals significant pleural fluid in the right hemithorax. Analyses of serum and pleural fluid obtained by thoracentesis are as follows: Which of the following is the most likely mechanism causing this patient's pleural effusion?

Question

An 18-month-old boy is admitted to the pediatric intensive care unit after undergoing cardiac surgery.  At age 16 months, his parents brought him to a pediatrician due to intermittent episodes of cyanosis when he became upset.  At that time, a cardiac murmur was noted, and echocardiogram revealed tetralogy of Fallot with moderate pulmonary stenosis.  The patient's initial postoperative period is unremarkable, but on postoperative day 4 he develops tachypnea with an increasing oxygen requirement.  Chest x-ray reveals significant pleural fluid in the right hemithorax.  Analyses of serum and pleural fluid obtained by thoracentesis are as follows:  Which of the following is the most likely mechanism causing this patient's pleural effusion?

Quizplus · Accepted Answer

11ec25c8_d94d_2072_bc81_1d1690cfb72f_MD0003_00 The serum and pleural fluid analyses in this patient are consistent with an exudative effusion. Exudates occur when fluid moves into the pleural space due to increased permeability of the pleural or capillary membranes or disruption of thoracic lymphatic drainage. Due to direct leakage of fluid, exudates are characterized by high levels of pleural protein and lactate dehydrogenase. This patient has a chylothorax, which occurs when lymphatic flow through the thoracic duct is disrupted, leading to direct leakage of chyle (ie, lymphatic fluid) into the pleural cavity. Presenting signs and symptoms depend on the size of effusion but include increased work of breathing, tachypnea, hypoxia, and dullness to percussion. Chyle is composed of T cell lymphocytes, immunoglobulins, and lipid-transporting chylomicrons that contain triglycerides. Pleural fluid analysis therefore demonstrates characteristic milky-white fluid with lymphocyte predominance and increased triglycerides. In addition to traumatic causes (eg, cardiothoracic surgery) of chylothoraces, other etiologies include congenital malformations, specific syndromes (eg, Down syndrome, Noonan syndrome), and malignancy. Management includes drainage via thoracentesis or chest tube placement, limitation of dietary fat, and possible thoracic duct ligation. (Choice A) Empyemas are exudative effusions resulting from bacterial infection of the pleural space. Pleural fluid analysis in empyemas shows low glucose, low pH, neutrophil predominance with elevated cell count, and positive Gram stain and bacterial culture. (Choice B) Hemothorax occurs due to bleeding into the pleural cavity after trauma. Thoracentesis reveals frankly bloody pleural fluid with a hematocrit >50% of the peripheral blood. (Choices C, E, and F) Transudative effusions result from oncotic or hydrostatic pressure differentials. Protein loss (eg, nephrotic syndrome), for example, results in decreased plasma oncotic pressures while increased pulmonary vascular pressures (eg, cardiac failure, pulmonary embolism) cause increased hydrostatic forces, both resulting in pleural effusions. Hepatic hydrothorax can also lead to transudative effusions when ascitic fluid flows from below the diaphragm (higher pressure) into the pleural cavity (lower pressure). Educational objective: Chylothorax is an exudative effusion due to disruption of lymphatic flow within the thoracic duct. Pleural fluid analysis demonstrates milky-white fluid with elevated triglycerides. References: Chylothorax after surgery for congenital heart disease. (http://www.ncbi.nlm.nih.gov/pubmed/22498675) Pleural fluid characteristics of chylothorax. (http://www.ncbi.nlm.nih.gov/pubmed/19181646)

An 18-Month-Old Boy Is Admitted to the Pediatric Intensive Care