Philip R Judge BVSc MVS PG Cert Vet Stud MACVSc (Veterinary Emergency and Critical Care; Medicine of Dogs)
What is Microenteral Nutrition?
Term microenteral nutrition was developed in 1991 to define the delivery of small amounts of water, electrolytes, and readily absorbed nutrients – including glucose, amino acids, and small peptides – directly to the gastrointestinal tract1,2.
What is the rationale for microenteral nutrition?
Provision of enteral nutrients has been shown to have the following effects:
- Decreases intestinal permeability2-5
- Decreases adherence of bacteria to the microvilli2-5
- Decreases risk of gastric ulcer development6-7
- Increases mucosal blood flow8
- Increases gastric pH8
- Increases intestinal neuro-hormonal activity8
- Increases gastric mucous production9
- Maintains intestinal secretory IgA secretion9
Indications for provision of microenteral nutrition9
Microenteral nutrition should be used in patients who meet any of the following criteria
- As an aid to transition to enteral feeding of more complex enteral diets in patients with reduced oral nutrition intake
- In patients who are not able to receive full enteral nutritional support
- In patients with critical illness
- In patients following gastrointestinal surgery
- In patients receiving parenteral nutrition
- In patients in the immediate post-surgical period (0-3 days)
- In patients following traumatic injury until full enteral nutrition is tolerated
- Acute kidney injury
- Acute liver injury
- In patients suffering from acute gastroenteritis
Microenteral nutrition formulations
Microenteral nutrition solutions are generally combinations of isotonic, or near-isotonic glucose and electrolytes, supplemented with amino acids and other nutrients that potentially improve gastric health9.
Glucose concentrations typically range from 2.5% and 20%, with some references suggest that glucose concentrations in microenteral nutrition solutions between 5 and 20% offer increasing benefit in protection of the gastric mucosal barrier7-9.
Most commercially produced solutions contain glycine at 0.3%. Oral supplementation of glycine has been shown to have the following characteristics in both human and animal studies9-11:
- Hastens resolution of diarrhoea
- Improves intestinal mucosa characteristics in animals with diarrhoea
- Increases intestinal uptake of glucose
- Reduces intestinal inflammation
- Potentiates antioxidant properties of enterocytes by preserving glutathione concentrations
- Stimulates enterocyte protein synthesis
- Potentiates repair of intestinal tight junctions following intestinal injury
Amino acids may also be added to microenteral nutrition solutions. The use of 3% amino acids solutions has been shown to reduce the extent of protein malnutrition in critically ill humans9. In addition, specific amino acids, including leucine, glutamine and arginine can have a beneficial outcome in critically ill patients, through stimulation of anabolic activity and immune function in the intestine12-14. It is important to note that many intravenous amino acid solutions do not contain glutamine, so it may be necessary to supplement these solutions with glutamine if using them for microenteral nutrition9. Glutamine is the preferred energy source of rapidly dividing cells (e.g. gastrointestinal cells, lymphocytes, and fibroblasts). Glutamine also plays a role in the maintenance of the integrity of the GI mucosal barrier and preventing bacterial translocation.
Isotonic commercial solutions such as Lectade (Jurox) or Vytrate (Jurox), have the following composition when reconstituted15,16:
- Glucose: 2.2%
- Sodium chloride 0.45%
- Glycine 0.3%
- Potassium phosphate 0.2%
A microenteral solution can be formulated in-clinic using the following formula:
- 500 ml 2.5% glucose/0.45% NaCl solution used for parenteral fluids
- Add glycine 1.6g to the 500 ml solution
- Add potassium phosphate 1 grams to the 500 ml solution
A 3% amino acid solution may be added to the commercial or clinic-formulated microenteral nutrition solutions, in addition to glutamine supplementation.
If the patient tolerates initial feeding, the glucose concentration may be increased to between 5-20% if desired.
Protocol for administering microenteral nutrition
Microenteral nutrition should be commenced within 6 hours of patient stabilisation in any patient with an indication for nutritional support presents to the clinician.
The normal stomach has a basal rate of fluid distension from saliva and gastric secretions of approximately 1.5 ml/kg/hr. The rate of administration of microenteral nutrition represents a minor increase over these basal volumes.
Microenteral nutrition is initially commenced at a rate of 0.2 ml/kg/hr, either given by small bolus administration or by continuous infusion delivered by a fluid pump, delivered by nasogastric or oesophagostomy tube.
The rate of administration may be increased to a total of 1-2 ml/kg/hr over a 24-48 hour period, based on patient tolerance9.
Begin feeding a commercial liquid diet if microenteral nutrition solution is being tolerated after 12-18 hours
Complications of microenteral nutrition
Microenteral nutrition is very well tolerated in most patients9.
Patients with persistent vomiting may benefit from placement of a nasogastric tube to facilitate gastric residual volume suctioning immediately prior to administration of microenteral nutrition. Additionally, blood glucose should be measured periodically following commencement of microenteral nutrition to monitor for hyperglycaemia, which can occur in insulin-resistant patients. If hyperglycaemia is detected, regular insulin should be administered at 0.09 unit/kg/hr (dog); 0.05 unit/kg/hr (cat) to achieve glucose concentration between 4-9 mmol/L9.
- Crowe Jr DT. Ways to administer fluids. Practical parenteral and enteral techniques. Tijdschrift voor diergeneeskunde. 1992 Apr 1; 117:19-22.
- Chandler M. Nutritional support for the hospitalised small animal patient. In practice. 2008 Sep;30(8):442-8.
- Marik PE, Zaloga GP. Immunonutrition in critically ill patients: a systematic review and analysis of the literature. Intensive care medicine. 2008 Nov;34(11):1980-90.
- Marik PE, Zaloga GP. Immunonutrition in high‐risk surgical patients: a systematic review and analysis of the literature. Journal of Parenteral and Enteral Nutrition. 2010 Jul;34(4):378-86.
- Li J, Langkamp‐Henken B, Suzuki K, Stahlgren LH. Glutamine prevents parenteral nutrition‐induced increases in intestinal permeability. Journal of Parenteral and Enteral Nutrition. 1994 Jul;18(4):303-7.
- Ephgrave KS, Horton JW. Gastric mucosal protection during confinement stress: The role of intragastric glucose. Current surgery. 1985;42(5):375-8.
- Pingleton SK, Hadzima SK. Enteral alimentation and gastrointestinal bleeding in mechanically ventilated patients. Critical care medicine. 1983 Jan 1;11(1):13-6.
- Ephgrave KS, Kleiman-Wexler RL, Adair CG. Enteral nutrients prevent stress ulceration and increase intragastric volume. Critical care medicine. 1990 Jun 1;18(6):621-4.
- Devey JJ, Crowe DT. Microenteral Nutrition in Kirk’s Current Veterinary Therapy XIII (2000) P 136-140.
- Naylor JM, Leibel T, Middleton DM. Effect of glutamine or glycine containing oral electrolyte solutions on mucosal morphology, clinical and biochemical findings, in calves with viral induced diarrhea. Canadian journal of veterinary research. 1997 Jan;61(1):43.
- Razak MA, Begum PS, Viswanath B, Rajagopal S. Multifarious beneficial effect of nonessential amino acid, glycine: a review. Oxidative medicine and cellular longevity. 2017 Jan 1;2017.
- Burrin DG, Davis TA. Proteins and amino acids in enteral nutrition. Current Opinion in Clinical Nutrition & Metabolic Care. 2004 Jan 1;7(1):79-87.
- Ruth MR, Field CJ. The immune modifying effects of amino acids on gut-associated lymphoid tissue. Journal of animal science and biotechnology. 2013 Dec;4(1):1-0.
- Wang WW, Qiao SY, Li DF. Amino acids and gut function. Amino acids. 2009 May 1;37(1):105-10.