Chylothorax

shona scott Cardiothoracic dietitian, royal Brompton & harefield nhs Foundation trust

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Shona Scott works as a Cardiothoracic dietitian at the royal brompton & harefield nhS foundation trust. in her job she treats patients with a variety of cardiac conditions and chronic lung conditions such as Chronic obstructive Pulmonary disease. She regularly sees patients with chylothorax following cardiac surgery.

nutritionAl mAnAgement of ChylothorAx PAtientS

chyle passes from the intestinal lymphatics to the cisterna chili and then through the thoracic duct from which it will ultimately enter the venous system1 . chylothorax results in accumulation of lymphatic fluid or chyle in the pleural space following leakage from the thoracic duct.

Its aetiology can be traumatic or non-traumatic. Traumatic causes, which are most common, include cardiothoracic surgery, head and neck surgery and radiation, while non-traumatic causes can be cardiac failure, sarcoidosis, benign tumours, amyloidosis and congenital duct abnormalities2. The incidence of a chyle leak after surgery is approximately 1.0-4.0%3 and 0.2-1.0% specifically following cardiothoracic surgery4 .

There is scope for large amounts of fluid to rapidly accumulate in the pleural cavity as approximately 2.4L of chyle is transported through the lymphatic system every day2. Chyle is an odourless, alkaline fluid, 70% of which is absorbed dietary fat, mainly triglycerides4. In the fasting state, chyle will normally be clear but will have a milky appearance after a fatty meal. Equally, a person’s overall intake of fat, intestinal absorption and degree of physical activity5 will affect the fat content of chyle, but it generally ranges from 5.0-30g/litre4 or, in relation to body weight, will be between 10

table 14: a detailed biochemical breakdown of chyle.

Calories 200kcal/l lipids 5-30g/l protein 20-30g/l lymphocytes 400-6800/mm erythrocytes 50-600/mm sodium 104-108mmol/l potassium 3.8-5.0mmol/l Chloride 85-130mmol/l Calcium 3.4-6.0mmol/l phosphate 0.8-4.2mmol/l and >100ml/kg. Chyle has 200kcal/L and a protein content of 20-30g/L6, although some studies state that this can be as high as 60g/L5. In addition, chyle contains lymphocytes, the majority of which are t-lymphocytes, fat-soluble vitamins, electrolytes and enzymes. Table 1 shows a more detailed biochemical breakdown of chyle.

presentation Generally, chylothorax is asymptomatic until large volumes of fluid accumulate and the severity of the symptoms will be related to the rate at which the fluid accumulates and the amount of fluid in the pleural cavity1. Traumatic chylothorax normally develops within two to 10 days post injury1. The symptoms are typical of those seen with a pleural effusion and include dyspnea, coughing, chest discomfort and tachycardia7 .

More serious consequences of chylothorax and the most pertinent for this article are malnutrition due to the loss of protein, fats and fat-soluble vitamins4 and dehydration, hyponatraemia and hypocalcaemia due to the loss of electrolytes2. The loss of lymphocytes can lead to immunosuppression and increase the risk of infection, while the loss of large volumes of fluid can also cause hypovolaemia5 .

diagnosis Chylothorax is usually diagnosed by analysing the composition of the pleural fluid or chest drain. A triglyceride level of >110mg/dl is diagnostic of a chyle leak1, 2 and a level <50mg/dl rules out a diagnosis of chylothorax unless the patient has been fasting or is malnourished, in which case lipoprotein lipase analysis can be used4 .

A chylothorax may exist even if the fluid is not milky and the fluid may be bloody in appearance. In nontraumatic cases, a CT abdomen and thorax should be performed to rule out malignancy2 .

treatment Consensus guidelines for the treatment of chylothorax are lacking 4, 7, but treatment can be conservative or surgical. Varying criteria are given as indications for surgery with some citing a chyle output >1000ml/day4 and others citing drain volumes that are >1.5l/24hrs or >1.0l/day over five days2, 5, or if there is persistent leakage of chyle for >two weeks2 . Nutritional and metabolic complications arising from a chyle leak are also indications for surgery4. A more detailed treatment pathway can be seen below2 .

Conservative management includes placing the patient on a diet low in long-chain triglycerides (LCTs), whether orally or enterally, or placing the patient on a Nil by Mouth regime and using parenteral nutrition. Somatostatin is also used in some circumstances and has been used successfully in neonates4 . It inhibits gastric, pancreatic and intestinal secretions, which helps to reduce chyle production1 .

The key aims of nutritional management are to reduce the volume of the chyle leak (a chest drain will be in place to monitor these amounts) and to allow closure of it, to prevent malnutrition, and to replenish fluids and electrolytes that are lost4. As LCTs comprise almost 70% of chyle4, chest drain volumes can be reduced by minimising the amount of LCT in the diet. This can be done orally or enterally using a specialised enteral feed. Generally, if this is not successful in reducing the volume of chyle leak, then the patient will be commenced on total parenteral nutrition (TPN)4, 5. A review carried out by Smoke and Delegge3 did not find adequate evidence to suggest one nutritional approach was better than another, but of course it is beneficial if more invasive, risky forms of nutrition such as TPN can be avoided. Initiation of a low LCT diet and the use of MCT fat in its place resolves 50% of congenital and traumatic chylothoraces8. This variable success is attributable to the fact that any oral or enteral feeding will contribute to chyle flow and because LCTs derived from the intestine come from endogenous and exogenous sources1 .

Prior to starting nutritional management of a chylothorax, it is important to note the patient’s baseline

Figure 1: recommended treatment pathway for chylothorax

weight and biochemistry (serum electrolytes, lymphocyte count, albumin and total protein)2 so that their nutritional status can be monitored during therapy. Those following an oral low LCT diet will have to eat larger volumes of food to meet their energy and protein requirements; consequently, those who are already nutritionally compromised and struggling to eat may be better off using enteral feeds rather than trying to follow the diet orally. Another approach is to supplement an oral diet with juice-based oral nutritional supplements, which provide valuable calories, protein and vitamins without any fat. Other fat-free or low-fat sources of protein include fat-free yoghurt and cottage cheese, fat-free or skimmed milk, egg whites and protein powders4. Some patients may require their diet to be supplemented with fat-soluble vitamins or a multivitamin and mineral supplement4 . When calculating protein requirements of these patients, one should account for protein losses through the chyle leak as it contains 20-30g/L.

loW lCt diet Although there are no consensus guidelines, in practise, patients following a low LCT diet with no more than 10g of LCT daily for six weeks, will see reductions in chyle output. A previous review by McCray and Parrish9 found that dietary management is being carried out for periods ranging from one week to 24. Talwar and Lee report that two weeks is often the limit for resolution by conservative management1 .

A major obstacle in the success of this diet is patient confusion about what foods can be eaten and in what amounts. Therefore, patients should be given detailed diet sheets so that they are aware of hidden sources of LCT, the amounts of LCT in average portions of commonly consumed foods (fat exchange list) and foods that are free of LCT. Recipe ideas are also a useful way of improving adherence to the diet as patients can easily become bored due to the lack of palatability of lower fat foods. The Tables below show the foods that can be eaten freely on a low LCT diet, plus a typical day on a low LCT diet.

It is virtually impossible to remove all fat from the diet, even vegetables such as broccoli contain 0.8g of LCT in 100g; however, patients are unlikely to be eating these foods in such large volumes that they will exceed the 10g/day threshold. It is more important that patients are made aware that they need to avoid foods that are rich in fat such as full-fat dairy products, red and processed meats, oily fish, most biscuits, cakes, puddings creamy sauces and cereals such as muesli and nut containing breads.

As fat is such an important contributor of energy in the diet, these patients will need to substitute LCT with medium-chain triglycerides (MCTs). As MCTs are directly absorbed into the portal system bypassing the intestinal lymphatic system, they will provide crucial calories without contributing to chyle volumes. MCT is available as oils or in oral or enteral supplements and provides 8.3kcal/g4. MCT oil is not palatable for most patients but can work well if used in cooking or in baking. It should not be heated to a very high temperature as it has a low flash point so can burn easily. Generally, doses of 50-100mls or 385-765kcal worth of MCT oil across the day are well tolerated, but some patients will complain of abdominal pain, bloating or diarrhoea if given more4. There are several commercial MCT oils available, but they can be expensive and not all patients will be prescribed it by their GP if following the diet in the community.

enteral Feeds Specialised enteral formulas can work well to resolve a chylothorax if a patient is unable to eat sufficient amounts orally or is not adhering well to a low LCT oral diet. In addition to being MCT based, some of these formulas are also elemental. It is important to be aware that these formulas will contain varying amounts of LCT; therefore, the total intake should be calculated when planning a regimen. When deciding on an enteral nutrition regimen McCray and Parrish4 suggest that: • enteral nutrition may be useful if chyle output is <1000ml/day; • a low-fat semi-elemental formula may be effective if output is less than 500ml/day; • an elemental formula may be required if output is greater than 500ml/day. These recommendations are based on the literature and clinical experience4 .

parenteral nutrition In unresponsive cases of chylothorax, or when nutrients are being lost rapidly into the pleural space, TPN is indicated5. Reports find that patients with a drain output of >1000ml while NBM will likely require TPN4. As lipids containing TPN do not enter the lymphatic system they will not contribute to chyle production and can be used safely.

table 3: example of day’s menu on 10g lCt diet Breakfast:

all fruits including fresh, tinned, or frozen (excluding olives and avocado) all vegetables including those pickled in vinegar Sugar, honey, golden syrup, treacle, jam Jelly, boiled sweets, mints (not butter mints) Fruit sorbets, water ices, ice lollies, very low-fat frozen yoghurts meringue, egg white, egg replacer spices and essences, salt, pepper, vinegar, herbs, tomato ketchup, chutneys, marmite, oxo, Bovril Fruit juices, fruit squash, fizzy drinks and milkshakes made with skimmed milk and Crusha syrup or Nesquik

1 glass of fortified (CHO powder) orange juice toast x 2 with 100g of baked beans and omelette (1 egg white cooked with mCt oil) lunch: 200mls fat-free soup Cooked pasta (90g raw) with 150g tinned tuna in brine, vegetable and tomato sauce (cooked with mCt oil as required) High-energy jelly (fortified with CHO powder) 1 fat-free yoghurt Dinner: Fish cakes (60g of white fish, 60g boiled potatoes, 20mls skimmed milk to bind, use egg white and 1 slice of white bread for breadcrumbs) fried in mCt oil mashed potatoes (with skimmed milk) and boiled vegetables strawberry milkshake with 200mls of skimmed milk with flavoured powder Fruit salad Offer 3 x 200ml bottles of juice-based oral nutritional supplements throughout the day

essential Fatty aCids Patients who follow an oral low LCT diet for more than three or four weeks will require supplementation with essential fatty acids (EFA)4 . Linoleic acid is the required fatty acid as the body is unable to produce it. Linolenic acid and arachidonic acid can be made from the body if it has a sufficient source of linoleic acids. Daily requirements of EFA will be met by providing 2.0 to 4.0% of calories as linoleic acid4. This can be done using a range of easily available oils (walnut, wheat germ, sunflower), which can be used as salad dressings or added to foods such as pasta after cooking. If using walnut oil, 1.4tsps would provide four percent of energy for every 1000kcal4. Most enteral formulas will meet EFA requirements if used in specific volumes, as will lipid-containing parenteral nutrition formulations. The sedative propofol will also provide a source of EFA, a 150ml infusion would meet the EFA needs of a person who requires 2000kcal per day4 .

summary Despite the fact that dietary manipulation is such an integral part of the conservative management of chylothoraces, there is a distinct lack of evidence-based guidelines. The literature on the use of enteral or parenteral nutrition for its management is largely based on small observational trials, small retrospective trials and case reports7. It is important to do a full nutritional assessment of the patient prior to choosing the appropriate regimen, be it oral, enteral or parenteral or a mix of these. Barriers to adherence to an oral low-fat diet should be alleviated by giving detailed oral and written guidance to patients about those foods that can be eaten freely, the fat content of foods and recipe ideas. Each patient’s need for additional supplementation with EFA and a multivitamin and mineral supplement should be considered. A patient’s nutritional plan should be regularly monitored to ensure that it is effective in reducing chyle output and that nutritional status is not being compromised.