Question

A young man suffered third-degree burns over much of his body and is hospitalized in a severe catabolic state. An individual in this state requires about \(40 \mathrm{kcal}\) kg per day and \(2 \mathrm{g}\) protein kg per day to be in positive caloric and nitrogen balance. This young man weighs \(140 \mathrm{lb}\) \((64 \mathrm{kg}) .\) Total Parenteral Nutrition (TPN) is started with a solution containing \(20 \%\) glucose and \(4.25 \%\) amino acids (the form in which protein is supplied). Sometimes a lipid solution is also infused in a paticnt on TPN. In the case of this young man, the purpose of the lipid solution would be to A. supply additional calories to meet caloric needs. B. supply essential fatty acids. C. improve the palatability of the mixture. D. provide fiber. E. assure an adequate supply of cholesterol for membrane building.

Short answer

Short Answer: The primary purpose of the lipid solution infused in a patient on TPN is to supply additional calories to meet caloric needs (Option A) and to supply essential fatty acids (Option B).

Step-by-step solution

Evaluate Option A

A lipid solution would supply additional calories to meet caloric needs. Let's analyze the calories supplied by glucose and amino acids in TPN. Glucose provides \(4 \mathrm{kcal}\)/g and amino acids provide \(4 \mathrm{kcal}\)/g as well. In the TPN solution, \(20 \%\) glucose means \(20\) g of glucose per \(100\) ml of the solution, so the calories from glucose are \(20 \times 4 = 80 \mathrm{kcal}\). Similarly, the \(4.25 \%\) amino acids mean \(4.25\) g of amino acids per \(100\) mL, so the calories from amino acids are \(4.25 \times 4 = 17 \mathrm{kcal}\). The total calories from the TPN solution per \(100\) mL are \(80 + 17 = 97 \mathrm{kcal}\). The young man weighs \(64 \mathrm{kg}\), so he requires \(40 \times 64 = 2560 \mathrm{kcal}\) per day. Since the lipid solution gives additional source of calories, it could help to increase the total calories intake to match the daily needs of the patient. This makes Option A a possible answer.

Evaluate Option B

Lipids supply essential fatty acids which are important for several bodily functions, including cell membrane structure maintenance, creating hormones and energy storage. TPN solution doesn't provide essential fatty acids by itself. Considering that this solution is used when other sources of nutrients aren't allowed, adding lipids to TPN would ensure the patient receives the necessary essential fatty acids his body can't produce. This makes Option B a possible answer.

Evaluate Option C

The TPN solution is injected directly into the veins; therefore, the palatability of the mixture is irrelevant since the patient doesn't taste it. This makes Option C an incorrect answer.

Evaluate Option D

Fibers are important for maintaining the health of the digestive system and bowel regularity. However, since TPN is directly infused into the bloodstream, bypassing the digestive system, the fibers won't have any effect on the digestive process. Thus, Option D is an incorrect answer.

Evaluate Option E

Cholesterol is indeed crucial for membrane building and other body functions. However, the body can synthesize its own cholesterol and doesn't solely rely on dietary sources. Therefore, Option E is not a primary reason for including lipids in TPN.

Conclusion

Evaluating all the options, the primary purpose of the lipid solution in this case is to supply additional calories to meet caloric needs (Option A) and to supply essential fatty acids (Option B).

Key concepts

TPN Caloric Requirements

Total Parenteral Nutrition (TPN) is a form of nutritional support used when the gastrointestinal tract is nonfunctional or has to be bypassed. When administering TPN, the caloric requirements are a critical consideration to ensure that the patient receives the necessary energy for recovery and maintenance of bodily functions. This involves calculating the individual's daily caloric needs based on factors such as age, weight, activity level, and clinical condition.

For patients who are in a catabolic state, similar to the young man with third-degree burns in the given exercise, the body's metabolism is significantly higher. As a result, they have increased caloric needs to support tissue repair and recovery. The exercise emphasized that this patient requires approximately 40 kcal/kg per day, equating to 2560 kcal/day for a 64 kg individual. This high demand often necessitates the inclusion of an additional calorie source, such as a lipid solution, to meet the heightened energy requirements without overly increasing the volume of the TPN solution, which can end up being physically burdensome and potentially lead to fluid overload.

TPN Amino Acids

Amino acids in TPN are pivotal as they provide the building blocks for protein synthesis. In patients receiving TPN, amino acids help sustain muscle mass, boost the immune response, and promote wound healing, especially in hypercatabolic states like severe burns or major surgeries. Unlike fats and carbohydrates, which the body can store for later use, there's no storage for amino acids; they need to be replenished daily to meet ongoing physiological demands.

In the exercise case, the TPN solution contains 4.25% amino acids. Each gram of amino acids provides 4 kcal of energy, which plays a role in the total energy provided by the TPN solution and supports the aim of ensuring the patient remains in positive nitrogen balance. It is essential, especially in a stressed state, as negative nitrogen balance can lead to muscle wasting and delayed recovery. Properly balancing amino acids in TPN is crucial, as both deficiency and excess can have detrimental effects on patient health.

TPN Lipid Solutions

Lipids serve several significant purposes in TPN. They are an efficient, high-calorie source that can help meet the increased energy demands of patients without significantly increasing fluid volume. Lipids also provide essential fatty acids, which are vital for cellular functions, like maintaining the integrity of cell membranes and producing eicosanoids, which are important signaling molecules. TPN solutions without lipids can lead to essential fatty acid deficiency, which may cause skin problems and an impaired immune response.

Given that every gram of lipid provides approximately 9 kcal, it is clear why including a lipid solution in TPN, as considered for the burn patient in the exercise, would substantially contribute to fulfilling the recommended caloric intake, addressing point (A) from the exercise. Furthermore, as discussed in step 2 of the solution, essential fatty acids cannot be synthesized by the body and must be obtained from the diet(or in this case, the TPN lipid emulsion), making point (B) also valid. Thus, incorporating lipid solutions into TPN addresses the need for calories and essential nutrients, contributing to a holistic approach to patient care during critical illness or compromised oral intake.