Management of Chyle Leaks Following Pancreatic Resection

Component

Concentration

Calories

200 kcal/L

Lipids

5–30 g/L

Protein

20–30 g/L

Lymphocytes

400–6800/mm (28)

Sodium

104–108 mmol/L

Potassium

3.8–5.0 mmol/L

Chloride

85–130 mmol/L

Calcium

3.4–6.0 mmol

Phosphate

0.8–4.2 mmol/L

In addition to the general role of lymphatics for immune function and interstitial fluid balance, the abdominal lymphatic system is necessary for normal fat absorption. The process of fat absorption begins with the breakdown of triglycerides into monoglycerides and fatty acids within the gut. This is mainly through the action of pancreatic lipase and is facilitated by the formation of micelles consisting of bile salts, monoglycerides, and fatty acids. Micelles are absorbed within the intestinal villi where triglycerides are enzymatically reformed. Triglycerides consisting of long-chain fatty acids (> 12 carbons) combine with cholesterol and specific proteins to form chylomicrons. The small intestine has a rich lymphatic network with specialized terminal branches known as lacteals that are necessary for the uptake of chylomicrons. Once within the lymphatic system, this fluid is known as chyle and ultimately enters the systemic circulation through the thoracic duct.

Lymph drainage from all structures below the diaphragm, as well as the left upper extremity and left chest enters the thoracic duct via the cysterna chyli and returns to the circulatory system at the level of the left subclavian vein. This includes the lymphatic system of the gut. Lymphatic drainage of the right chest and upper extremity drains into the right subclavian vein. Lymphatic drainage of the abdominal visceral connects to systemic lymphatic drainage at the level of the cysterna chyli. The cysterna chyli is a roughly 5-cm sack-like dilatation of the lymphatic system located deep within the retroperitoneum at the level of the first and second lumbar vertebrae. The structure is located to the right of the aorta, deep within the interval between the aorta and the inferior vena cava. The function of the cysterna chyli is unclear, but it has been suggested that it functions as a bellows that drives lymph flow via the abdominal pressure changes that occur with normal respiration. The cysterna chyli receives systemic lymphatic drainage from the lower body, lumbar drainage beds, and the visceral drainage beds including the liver. Lymphatic drainage from the intestine and portions of the head of the pancreas course along the superior mesenteric artery through the base of the mesentery and join the cysterna chyli near the junction of the superior mesenteric artery (SMA) with the aorta. The liver, portal, and remainder of the pancreatic lymphatic flow follow the course of the celiac axis distribution retrograde to its junction with the aorta. The exact location of the disruption of the lymphatic system resulting in chyle leak following pancreatic resection is unknown. However, based on this understanding of lymphatic anatomy and chyle flow, one can speculate on the potential areas of disruption of these vessels and the resulting chyle leak. These areas include dissection of the hepatoduodenal ligament, the base of the mesentery at the mid portion of the SMA, the soft tissue surrounding the celiac trunk, and retroperitoneal space in the interval between the inferior vena cava and the right side of the aorta.

The volume of chyle flow ranges from 2 to 4 L/day and varies depending on numerous factors including the composition of the diet [14]. The majority of lymph flow through the thoracic duct is from visceral sources. It is estimated that 25–50 % of all flow from through the thoracic duct originates from the liver. The majority of the remainder comes from the other viscera (chyle) while the minority of lymph through the thoracic duct is from the lower extremities. Approximately 70 % of chyle consists of dietary fat mainly in the form of triglycerides. The concentration of fat varies and ranges from 5 to 30 g/L and has an energy value of approximately 200 kcal/L (Table 29.1). The volume of lymphatic drainage from the abdominal viscera is evident in pathological conditions such as chylous ascites resulting from cirrhosis, pancreatitis, or malignancy in which liters of chyle can be produced each day.

Diagnosis of a Chyle Leak

The diagnosis of a chyle leak is often straightforward and can be determined at the bedside based on the appearance of the drain output in the correct clinical context. The typical presentation of a chyle leak is the transition of clear peritoneal drainage to a milky white color following the institution of a regular diet. Of course, this is often the same time period when the much more common postoperative pancreatic fistula is also diagnosed. Usually, a simple visual inspection of the drain output is able to differentiate between the two types of leaks. Whereas a postoperative pancreatic fistula is often a cloudy tan fluid with fibrinoid debris, a pure chyle leak is most often homogenous and pure white. In order to confirm a chyle leak, the drain fluid should be analyzed for triglycerides and a level of 110 mg/dL is necessary to make the diagnosis. In addition, drain amylase should also be evaluated since, on occasion, a pancreatic fistula may coexist with a chyle leak.

Once the diagnosis of a chyle leak is made, the next determination should be to classify the leak as either a contained leak or as free-flowing ascites. If this is not apparent based on a physical exam demonstrating ascites, an imaging study may be required.

Management of a Chyle Leak

The majority of chyle leaks will resolve spontaneously with conservative treatment which includes management of fluid, electrolytes, nutrition, and chyle drainage. However, a small percentage of chyle leaks will be refractory to this type of treatment and will require a more direct intervention to correct the problem. The general goal in the management of a chyle leak is to control the output and optimize the fluid and nutrition until the leak closes. The best way to accomplish this goal is to tailor management based on further descriptive classification of the leak. First, a determination should be made as to whether or not the patient has a contained chyle leak or chylous ascites. As mentioned previously, this may be evident based on physical exam or may require an imaging study to demonstrate abdominal ascites. Second, the chyle leak should be classified as either high or low output based on the drain volume. Drain volume of less than 200 cc/day constitutes a low-output leak. The determination of these features will be helpful in guiding the route of nutrition, need for fluid and electrolyte repletion and the prognosis. The natural history of a contained chyle leak is very different than that of chylous ascites [2]. A contained chyle leak is easily controlled with drains, has a better chance of closure, and an improved overall outcome compared to chylous ascites. The determination of high-volume leak is also important since this will most often require more intensive nutritional support.

The Contained Chyle Leak

The initial management of a contained chyle leak differs based on whether it is a low- or high-volume leak. A patient with a leak of less than 200 cc/day should simply undergo a change in diet from regular to a “nonfat” or medium chain fatty acid diet. After 12–24 h of this diet, an assessment should be made of the drain output volume and character. Most patients with a low-volume contained leak will have a reduction in output and a change to clear fluid with this maneuver. If there is no change in the drain output over this time, the patient should be made nil per os (NPO) and given intravenous nutritional support. A patient with a chyle leak greater than 200 cc/day should be made NPO placed on total parenteral nutrition (TPN), and be administered octreotide since it is unlikely to seal expeditiously unless the volume is reduced. As with a low-volume leak, the success of the intervention is determined by a drop in the volume of the drain output and a change from milky to clear. In either case, once the drain output clears and the volume drops below 100 cc/day, steps should be taken toward drain removal.

Care must be taken in the process of drain removal so as not to convert a controlled leak into chylous ascites. The best way to avoid this problem is to always restart a regular diet prior to drain removal in order to “test” that the leak is truly sealed. In addition, the proper timing and method of drain removal are important. This is particularly true for drains that have been in place for longer than a week. In this situation, reimaging should be performed to assess the size of the collection and the location of the drain with respect to the fluid cavity. This is best accomplished by a contrast-enhanced computed tomography (CT) scan. A drain sinogram often provides additional useful information about the size of the fluid cavity, length of drain tract, and the relationship of the drain to the collection. Leaks are more likely to close if the cavity is small and the tract is relatively long.

A judgment should be made as to when to give a trial of per os (PO) intake following the initial treatment and reimaging. There are no defined rules but, in general, a trial is warranted if the drain output remains low and non-milky for several days. Once these criteria are met, the patient should be placed on a regular diet. This should have little impact on the drain output if the leak is sealed and the drain can then be removed safely. If the patient fails the challenge, then a nonfat/medium-chain fatty acid diet or TPN should be restarted. If the output modestly increases or turns slightly milky with a regular diet, the drain can still be removed if the tract is long and the collection is small. In this case, the drain is removed by a process called “cracking” in which the drain is pulled out a few centimeters each day until the output abruptly drops or the drain is removed. If at any time the output drops below 10 cc, an imaging study is performed to assess for a clogged drain suggested by an increase in collection size. The drain is removed if no collection is present or flossed if the collection is still present or increased in size.

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