A 45 year old man with severe pancreatitis is receiving Total Parenteral Nutrition. Discuss the role of intravenous lipids in his regimen.
Enteral nutrition would be preferable. The question assumes that it is not feasible. Intravenous lipid infusion in TPN is important to prevent essential fatty acid deficiency and as an alternative calorie source. In an acute inflammatory disease or sepsis the standard approach would be to provide at least 50% of the non-protein calories of TPN as lipids, but acute pancreatitis may be associated with familial hyperlipidaemia and the hyperlipidaemia of alcoholism. Lipid infusion has been rarely associated with pancreatitis eg paediatric Crohn’s Disease. Lipid infusion in critically ill patients may cause deterioration in A-aDO2, haemagglutination and immune dysfunction via reticuloendothelial blockade.
It is therefore important to check the serum lipids of this patient and to understand the aetiology of the pancreatitis in this case. If there is no contraindication to lipid infusion, then infusion of 20 mls per hour of commercially available soybean emulsion, eg 20% Intralipid will provide 1000 kcal/day to balance the protein and carbohydrate. Clearing of the lipid can be checked by allowing 10mls of blood to settle and observing for a milky serum or by measuring serum lipid 1 hour after infusion is stopped.
This is a frighteningly specific question. It requires the candidate to have a detailed knowledge of TPN constituents and metabolic pathways influenced by parenteral nutrition. Furthermore, it requires one to consider the use of intravenous lipids in a condition known to be exacerbated by hyperlipidaemia.
In general, one requires about 0.7-1.5g/kg/day of lipid emulsion via TPN. This talk of providing at least 50% of non-protein calories as lipid is surely madness. These days only about 30% of caloric needs is supplied as lipid.
Certainly, the evidence does not support the assertion that intravenous lipids contribute to mortality in pancreatitis. In a cohort of 18 patients, Van Gossum et al did not find any difference in infused lipid concentration between suvivors and non-survivors. The dead, however, did demonstrate elevated serum lipid profiles and increased insulin requirements, suggesting that pancreatitis patient at risk of death will be very inefficient at using nonprotein energy substrates.
Yes, perhaps IV lipids are bad, and can cause reticuloendothelial dysfunction, hypoxia, thrombophilia and hepatosteatosis. They are also essential nutrients. Without question, the pancreatitis patient should receive lipids as a part of their TPN.
Van Gossum, A., et al. "Lipid-associated total parenteral nutrition in patients with severe acute pancreatitis." Journal of Parenteral and Enteral Nutrition 12.3 (1988): 250-255.
Patel, Krutika S., Pawan Noel, and Vijay P. Singh. "Potential Influence of Intravenous Lipids on the Outcomes of Acute Pancreatitis." Nutrition in Clinical Practice 29.3 (2014): 291-294.