Individual research recommendation details

Recommendation ID

NG154/2

Question

What is the optimal ratio of non-nitrogen energy to nitrogen in parenteral nutrition for preterm and term babies?

Any explanatory notes
(if applicable)

There was limited evidence, and the evidence did not provide sufficient data to inform optimal ratios. The committee used their knowledge and experience to agree ratios, taking into account the available evidence and current practice.

When the amount of parenteral nutrition is changing (for example, when transitioning onto enteral feeding), there is a risk of negative outcomes associated with too low or too high ratios. Too low a ratio (non-nitrogen energy to nitrogen below 20 kcal per gram) could cause oxidation of amino acids and high blood urea. Too high a ratio (non-nitrogen energy to nitrogen above 30 kcal per gram) could result in deposition of excess body fat, which is associated with metabolic ill health in later life (for example, risk of cardiovascular disease, diabetes and obesity-related conditions). Because of these risks, the committee recommended keeping the ratios the same when changing the amount of parenteral nutrition.

The evidence supported the need to give babies enough energy to ensure the nitrogen provided is retained.

Because of the limited evidence, the committee decided to prioritise this topic for further research. This is important because insufficient non-nitrogen energy (carbohydrates and lipids) leads to nitrogen (protein) being used for non-growth purposes so is not available to generate new tissues. An excess of non-nitrogen energy can lead to increased adiposity and may cause hyperglycaemia or hypertriglyceridemia. Having more evidence about the optimal ratio of non-nitrogen energy to nitrogen in parenteral nutrition is therefore needed.

Ratio of carbohydrates to lipids
There was limited evidence, so the committee used their knowledge and experience to agree the ratio, taking into account the available evidence and current practice. One study provided lipids in a range from 18% to 40% (meaning that the other 82% to 60% of non-nitrogen energy was made up of glucose), with better growth associated with 40% lipid intake.

The committee also discussed the recommendations developed for glucose and lipid dosages (recommendations 1.5.1 and 1.5.4). They agreed that it should be clear to those prescribing parenteral nutrition that when calculating the relative amounts of carbohydrate and lipid, the recommended dosages of each of these components should not be exceeded.

The committee decided not to recommend the lower end of the lipid range (18%) that was used in the evidence because that would lead to a high glucose intake, for which the risk of hyperglycaemia was considered to be too high. Therefore, the committee agreed that a lower level of 25% lipid is needed to limit the risk of hyperglycaemia, and to provide sufficient essential fatty acids and fat-soluble vitamins. The committee agreed, based on their knowledge and experience, that there should be an upper limit of 40% fat. Even though there is no evidence available to firmly state the risks of higher lipid provision, the committee agreed 40% would be safe and not risk fatty liver or raised triglyceride levels.

The recommended ranges aim to provide sufficient lipid energy to optimise growth, provide essential fatty acids and fat-soluble vitamins, and minimise the risk of hyperglycaemia. However, it is important not to give too much lipid because this could risk high triglyceride levels, fatty liver and increased fat deposition.

Why the committee did not make a recommendation on ratios of phosphate to amino acids
The evidence on the relative amounts of amino acids and phosphate to be given in parenteral nutrition was limited.

The committee agreed that the phosphate to amino acid ratios derived from following the phosphate and amino acid recommendations (1.5.11, 1.5.2 and 1.5.3) in this guideline are appropriate. However, because the evidence was limited and did not provide enough detail on the exact amount of phosphate needed per gram of amino acid, the committee decided not to make a recommendation on specific relative amounts.

How the recommendations might affect practice
The committee agreed that the recommendations reflect current best practice and should have little impact on practice. They should reduce any variation across units.

Full details of the evidence and the committee's discussion are in:

evidence review D7: ratio of non-nitrogen energy to nitrogen

evidence review D8: ratio of carbohydrates to lipids

evidence review D10: ratio of phosphate to amino acids.

Source guidance details

Comes from guidance

Neonatal parenteral nutrition

Number

NG154

Date issued

February 2020

Other details