Epidemiology

Chylothorax can arise due to congenital malformations, genetic syndromes, trauma, and conditions of high central venous pressure (thrombosis of the superior vena cava or subclavian vein Post-Fontan surgery, right-sided heart failure), among others. ^{Reference Soto-Martinez and Massie9} While the most common cause remains cardiac surgery, the prevalence of chylothorax arising from right heart failure is not low. High venous pressure can increase abdominal lymph production, but the stiffness of the veno-lymphatic junction limits lymphatic flow. The other mechanism is having high pressures in the left subclavian vein that slows down lymphatic drainage. ^{Reference Villena, de Pablo and Martin-Escribano10} In a national study by Haines C et al, 172 children with post-operative chylothorax in the United Kingdom, the most reported cases manifested after the Fontan procedure and the repair of Tetralogy of Fallot. ^{Reference Haines, Walsh and Fletcher11} In another study by Chan EH et al, the incidence of chylothorax post-cardiac surgery was the highest in Fontan procedure and heart transplantation. ^{Reference Chan, Russell and Williams5} The risk factors for chylothorax post-cardiac surgery in children include younger age, lower body weight, presence of genetic syndromes, the complexity of the operation, secondary chest tube closure, vein thrombosis, extended cardiopulmonary bypass time, longer cross-clamp time, and a higher annual hospital volume.

Endogenous glucocorticoids are known to reduce the amount of protein in most tissues by increasing the rate of extrahepatic protein degradation. This helps the liver to manufacture more plasma proteins from free amino acids. More fluid moves directly from the interstitial area into the bloodstream as plasma oncotic pressure rises, leaving less fluid for the lymphatics to empty. This action may be beneficial in reducing lymph flow long enough to restore normal lymph outflow. ^{Reference Mery, Moffett and Khan12,Reference Biewer, Zurn and Arnold13}

Anatomy and pathophysiology

The thoracic duct starts from the abdomen at the cisterna chyli at the second or third lumbar vertebra level. ^{Reference Phang, Bowman and Phillips14} It then ascends on the right side of the vertebral column and ventral to the aorta and azygos vein to reach the posterior mediastinum. ^{Reference Kiyonaga, Mori and Matsumoto15} However, the course may have several anatomical variations. In 40% of the individuals, variations in the upper and lower thoracic duct segments exist in addition to differences in termination points ^{Reference Phang, Bowman and Phillips14} (Fig 2). An injury to the thoracic duct below the fifth-sixth thoracic vertebrae leads to right chylothorax, whereas injury above that level leads to left chylothorax. ^{Reference Valentine and Raffin16} Chylothorax may be caused by thoracic duct injury in which the risk is increased in, increased superior vena cava pressure leading to lymphatic congestion as in patients who undergo the Fontan operation.

Figure 2. Anatomy of the lymphatic duct.

Clinical presentation and diagnosis

Clinically, the milky appearance of the fluid takes time to accumulate. Thus, early in the post-operative phase, the fluid may range between bloody and serous. Initially, the quantity of long-chain triglycerides in the diet is small. This is responsible for the lymphocytic predominance of the fluid. As the diet regimen advances, the fluid may become milky. Similar to pleural effusion, this manifests on a chest X-ray. Computed tomography scans, lymphangiography, and lymphoscintigraphy are some imaging studies that may be used to identify the site of the chyle leak. ^{Reference Sharma, Wendt and Rasmussen17} Patients who are not intubated may be asymptomatic or express respiratory distress symptoms. The severity of the manifestations depends on the amount of fluid present and the rate of accumulation. In rapid conditions, hemodynamic instability may be present. ^{Reference Soto-Martinez and Massie9} Patients with chronic chylothorax may present with signs of immunosuppression and malnutrition such as weight loss and muscle wasting. ^{Reference Faul, Berry and Colby18} To confirm chylothorax, a sample taken by thoracocentesis must be tested by biochemical analysis (Table 1). ^{Reference Buttiker, Fanconi and Burger19–Reference Ahmed23} In post-operative patients with decreased dietary fat content, the fluid may not be milky at the beginning. ^{Reference Mery, Moffett and Khan12} The mainstay of diagnosis is the presence on chylomicrons on Sudan III stain with a higher triglyceride amount than found in the plasma. ^{Reference Ahmed23} This is in addition to a lymphocytic predominance and presence of other products of digestion such as electrolytes and vitamins. ^{Reference Buttiker, Fanconi and Burger19}

Table 1. .Characteristics and biochemistry analysis of chyle.

Management

Management of chylothorax can be divided into two components: non-surgical and surgical. Our institutional strategy is presented in Table 2. ^{Reference Rudrappa and Paul1} The aim is to provide symptomatic relief from the chyle effusion and to decrease or stop chyle accumulation. ^{Reference Sharma, Wendt and Rasmussen17} If the patient is in acute distress, then the initial step is drainage through thoracentesis for confirmation of diagnosis and symptom relief otherwise conservative management can be started immediately if highly suspected (Fig 3).

Figure 3. Institutional approach to chylothorax.

Table 2. .Management of Chylothorax showing the available treatment modalities and steroids added as a new effective treatment option.

Medical

Initially, in the first days after the operation, the patient feeding will be started gradually when the patients conditions allow this. Patients diagnosed with chylothorax are started on zero-fat diet with the exception of medium-chain-triglycerides. ^{Reference Biewer, Zurn and Arnold13} The benefit of using medium-chain-triglycerides in chylothorax is that it is absorbed directly into the portal system bypassing the intestinal lymphatics and thus the thoracic duct. If the patient cannot tolerate oral intake, the chyle output is high or the central venous pressure was >15 mmHg; then a more aggressive approach might be needed. Some patients may be placed on total parenteral nutrition. ^{Reference Biewer, Zurn and Arnold13} Drugs to decrease the central venous pressure such as diuretics, sildenafil, or angiotensin-converting enzyme inhibitors can be used. Additionally, heparin for management of thrombosis or a cardiac catheterisation to treat and relieve the obstruction may be attempted. Endogenous hormones such as somatostatin or octreotide (a long-acting somatostatin analogue) can be used. ^{Reference Roehr, Jung and Proquitte24}

Complications

The severity of the complications is determined by how fast the chylothorax accumulated, its size, and its chronicity. Some early complications of chylothorax loss include dehydration, hypoalbuminemia, respiratory distress, and a longer post-operative course. As chyle carries several nutrients and immunoglobulins, it is expected that complications from chylothorax, especially if long term, includes malnutrition, weight loss, muscle wasting, and immunodeficiency leading to susceptibility to infections. This increases both the risk of morbidity and mortality on the patient. ^{Reference McGrath, Blades and Anderson37} Therefore, optimising the diet of these patients with proteins, electrolytes, and proper nutrients is essential. Additionally, the administration of intravenous immunoglobulin to maintain normal immunoglobulin G levels is important to avoid serious post-operative infections. ^{Reference Orange, Geha and Bonilla38} This emphasises the need to treat chylothorax promptly including the early worthy consideration of steroids for a speedy recovery.