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Enteral and Parenteral Nutrition

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Category: Schede
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  • Disciplina: Medicina d'urgenza
  • Specie: Cane e Gatto

Insufficient or inadequate nutrition is responsible for many pathophysiological changes. One of the most serious consequences is cellular and humoural immunoparesis from reduced neutrophil activity. Immune deficiency increases the risk of bacterial and viral infections with possible fatal consequences.1 The reduced availability of oxygen, which is commonly found in critically ill and malnourished patients, can hinder oxidative phosphorylation in the mitochondria, altering the cycle of carbohydrates and leading to a reduction in the production of ATP. The lack of oxygen inside the cells, responsible for anaerobic metabolism, causes a reduction in ATP synthesis from 36 to 2 molecules per mole of glucose. The energy deficit resulting from the anaerobic metabolism and the reduced availability of nutrients alters all cellular activities that require energy; the consequences are a decreased sensory response, reduction in the volume of visceral organs, skeletal muscles, and ventilation efficiency (predisposition to the onset of pneumonia), and a reduced response to hypoxia and hypercapnia. The energy deficit may also impair hepatic and renal perfusion, resulting in reduced concentration and excretion of urine and predisposition to metabolic acidosis.2 For the above reasons, the feeding of haemodynamically-stable critically ill patients should be started as early as possible. Early nutrition has a beneficial effect on recovery times.3

 

PATIENT SELECTION AND EVALUATION

The most common causes requiring forced-feeding are:

  • anorexia
  • surgery, pain
  • trauma
  • vomiting, diarrhoea
  • gastritis
  • respiratory distress
  • systemic tumours
  • SIRS (Systemic Inflammatory Response Syndrome)
  • sepsis, MODS (Multi Organ Dysfunction Syndrome)
  • diabetic ketoacidosis.

Just 24 hours after commencing fasting, glycogen stores are depleted; after 3-5 days of fasting, the patient is deemed to be malnourished. In the cat, after 3 days of fasting, hepatic lipidosis can occur. For this reason, in the cat it is recommended to commence forced-feeding not beyond this time limit. In critically ill patients, prolonged fasting generally causes a reduction in immune system defences, muscular weakness, a decreased myocardial contractile capacity and a reduction in the effectiveness of the accessory muscles of respiration and of the smooth muscles of the intestine. In critically ill patients, immunoparesis predisposes the onset of infections and leads to an increase in mortality.4 A good clinical history must be collected before commencing forced-feeding, with information regarding the type of food normally eaten, any loss of weight, the presence of vomiting and diarrhoea, the presence of polyuria/polydipsia and any treatment underway. After the clinical examination, it is necessary to weigh the patient, to evaluate the nutritional status, to estimate weight loss and to conduct some laboratory tests. The clinical examination should include an evaluation of the neurological function, in order to exclude pathologies that might hinder the intake of food. The laboratory tests needed in the planning of a diet suited for the requirements of each patient must include at least the following parameters: blood glucose, proteinaemia, albuminaemia, electrolytes (Na, K, Cl, Ca, P and possibly Mg during hypokalaemia), azotaemia, creatinaemia, full blood count (important for diagnosing anaemia and leukopaenia) and complete urinalysis.

 

ENTERAL OR PARENTERAL NUTRITION?

In human medicine, up to 20 years ago, the most common forced-feeding technique was the parenteral method (using a central catheter). The complications and costs connected to this nutritional technique led health operators to reconsider this approach and, where possible, to favour the enteral method, as it was more effective, associated with lower risks and less expensive.5 The gastrointestinal tract, apart from being the natural site for the absorption of nutrients, is also an environment whose integrity should be preserved to avoid the migration of microorganisms (barrier function). Malnutrition alters the intestinal canal, reducing its absorption capacities and defence. The physical presence of food in the intestinal tract works towards maintaining the integrity of the mucosa, stimulating the growth and proliferation of intestinal cells, increasing their absorption capacity, encouraging the synthesis of DNA and proteins and maintaining peristalsis. It is exactly for these reasons that it is said: “if the gastrointestinal system works, use it!”

With parenteral nutrition, the cells lining the gastrointestinal mucosa do not receive nourishment, with consequent functional impairment and atrophy. In order to nourish the gastrointestinal epithelium and to preserve the integrity of the mucosal barrier, also in patients with vomiting and diarrhoea, an enteral micro-nutrition is possible, administering food at the rate of 0.25-2 ml/kg/hour in continuous infusion. For enteral micro-nutrition, it is also possible to use intravenous solutions containing amino acids and glucose: 70 ml glucose 50% + 430 ml amino acids solution 8.5%. Enteral micro-nutrition may also be used when enteral nutrition is contraindicated, for example in the presence of: gastrointestinal dysfunctions (e.g. dynamic ileus), loss of consciousness, oesophageal dysfunction (e.g. megaesophagus).

Although enteral nutrition is safer than parenteral nutrition,6 it is not without complications; the most dangerous is the inhalation of regurgitated food, as this can cause aspiration pneumonia and the death of the patient. Diarrhoea is another very common side effect, which can be controlled by adjusting the rate of administration and the osmolarity of the food. The obstruction of the tube is the most common complication, but this can be prevented by infusing drinking water (10 ml) before and after each administration of food. In the case of an obstruction that is non-responsive to the infusion of water, it may be useful to attempt to wash the probe with a drink rich in carbon dioxide (e.g. Coca Cola). After infusion, it should be left for a few minutes to take effect, and then  water is to be infused again under pressure; should this method also be ineffective, pancreatic enzymes may be administered in order to encourage dissolution of the food blockage (to be left in situ to take effect for a few minutes). Stylets or metallic wires should not be inserted in an attempt to unblock the tube, as this may cause injury to the patient and perforate the tube.

 

CALCULATION OF ENERGY REQUIREMENT

The calculation of energy requirement is similar for both enteral nutrition and parenteral nutrition; for parenteral nutrition, there is a tendency to provide 50% of the energy requirement in order to reduce complications from excessive feeding. The daily resting energy requirement (RER) is calculated by the following formula:

(30 x kg) + 70                                                                            

The amount of daily protein for enteral nutrition in the dog and cat varies from 4-9 g/100 kcal of  RER, while for parenteral nutrition it is 2-6 g/100 Kcal. In the case of renal failure in anorexic patients, for which parenteral nutrition is chosen, a lower amount of protein (0.5-1 g/100 Kcal) should be provided; in the presence of a protein-losing enteropathy, when enteral nutrition is used greater amounts of proteins are provided: 4-9 g/100/Kcal. The calories resulting from the protein (P) contribution must be subtracted from the RER calculated calories; the calories thus obtained (CL) must be subdivided into carbohydrates and lipids as indicated by the following formula:

RER - calories from protein (P) = calories to be subdivided into carbohydrates and lipids (CL)       

With parenteral nutrition the calorie share deriving from carbohydrates and lipids (CL) may be divided at 50% between the two components; solutions are thereby obtained with an osmolarity that is compatible with peripheral intravenous administration.

 

ENTERAL NUTRITION

Method of Administration
Two types of diets are used for enteral feeding: polymeric diets, whose nutritional principles must be digested, and monomeric diets which, conversely, should not be digested as they are composed of nutritional principles reduced into amino acids and monosaccharides. Monomeric diets, although more easily digestible, are not without drawbacks. The most common side effects are: vomiting or diarrhoea, collapses of systemic blood pressure and hypovolaemic shock. For these reasons, in veterinary medicine, it is more common to use polymeric diets diluted with water. Commercial products for veterinary use are found on the market, created specifically for this purpose, including, for example, Recovery Diet (Royal Canin), Prescription diet a/d (Hill’s) and High Calorie (Eukanuba). In some special cases, when specific diets are required, for example in the case of renal failure, foods specific for the pathology in question may be used; however, these must be diluted in water 50%, blended and sieved. The non morselisation of the diet may cause obstruction of the tube. The administration of food should be preceded by aspiration; in the presence of a significant amount of fluid in the stomach or in the oesophagus, this must be aspirated, and feeding is to be delayed until the problem is solved. In general, on the first day ⅓ of the energy requirement is administered, subdivided into 6 administrations per day; on the second day ⅔ of the energy requirement is administered in 4-6 administrations and from day 3 the total dose is administered subdivided into at least 4 administrations. In unconscious patients the administration of food in continuous infusion can be useful, and in human medicine the following benefits have been observed: accuracy in administration, less pronounced gastric stasis, less use of personnel, lower incidence of diarrhoea, better absorption and less frequency of inhalation of food material.7 In veterinary medicine, these benefits have not been confirmed,8,9 therefore the preferred enteral feeding method is by bolus. Diarrhoea seems to be more common in the dog than in cat.8 The main disadvantages of continuous infusion are: increase in gastric pH values and consequent bacterial proliferation which, in the presence of gastro-oesophageal reflux and/or microinhalation, can lead to aspiration pneumonia.

Selection and placement of the feeding tube
Tubes for enteral nutrition may be constructed in transparent polyvinyl chloride, they can be flexible and with a rounded end, in silicone or radiopaque polyurethane. Polyurethane tubes are the common red or yellow tubes, some equipped with a stylet; all should have a rounded end. The Salem-type tubes have a small tube within the wall, which during suction prevents the adhesion of the tube to the walls of the organ that is housing it.

The diameter of the tube should be chosen based upon the weight of the patient, as identified below:

  • 0.5-2 kg: 6-10 French
  • 2-15 kg: 11-13 French
  • > 15 kg: 14-18 French
  • > 30 kg: 30 French

The placement of the tube is dependent on the type of pathology present, attempting, however, to use the longest possible gastro-intestinal tract. The most common placements are: naso-oesophageal, nasogastric, esophagostomy, gastrostomy andjejunostomy.

Nasoesophageal and nasogastric tube
Before proceeding with the placement, it is first necessary to measure the length of the tube, which should extend from the tip of the nose to the 5/6th intercostal space, for the naso-oesophageal tube, or from the tip of the nose to the thirteenth rib for the nasogastric placement. The chosen length should be marked on the tube using a permanent marker or, better still, with a plaster tape, which can also be helpful for fixing the tube to the skin. The patient should be held by an assistant with the head in its natural position (semi-flexion), to allow the patient to swallow. A pharmacological containment may be necessary in particularly responsive patients and in cats, to be performed with opiates combined with benzodiazepines. A few drops of  lidocaine 2% are instilled into the nostril into which the tube will be introduced, with the head in semi-extension in order to facilitate the diffusion of the drug along the route taken by the tube. The head is then released, allowing the patient to reposition it and keep the neck flexed. The end of the probe is lubricated with anaesthetic gel and is placed into the nasal cavity, directing it ventrally, medially and caudally up to the plaster mark; the nose of the patient should be pointed downwards so as to facilitate the entry of the tube into the oesophagus through spontaneous swallowing (Fig. 1]). The most difficult part of the placement is the insertion of the tube along the airways; once past this first section, the tube may be easily inserted until the measured mark.

Following the insertion, in order to confirm the correct placement of the tube it is necessary to inspect the larynx (with the aid of a laryngoscope) and to check that the probe is not inserted into the airways but proceeds into the oesophagus. An alternative is to introduce 40-50 ml of air while simultaneously auscultating the abdominal wall (only for tubes which terminate in the gastric cavity) for the presence of borborygmi (bubbling noises), which confirms the correct placement of the tube. An additional method may be to introduce a sterile saline solution into the tube and to auscultate its passage into the stomach using a phonendoscope placed on the abdominal wall. Should doubts still remain about the correct placement it may be necessary to perform an X-ray. The tube should be anchored to the patient with a number of cutaneous sutures: the first should be on the skin near the alar cartilage of the nose, the second on the lateral side of the head (so that the tube is not placed within the patient’s visual field) or on the forehead, and the final one in the region of the nape of the neck. Once the tube is in place, an Elizabethan collar should be applied in order to reduce the risk of tube removal by intolerant patients.

Oesophagostomy tube
The oesophagostomy tube is used in particular when the patient must be fed for a number of weeks or months. It is a very well-tolerated tube, especially in the cat, when the two previous tubes are not accepted. Pharmacological containment of the patient is required for this type of tube placement, by means of sedation with opiates and benzodiazepines or using a short duration general anaesthesia. Once sedation has been achieved, a curved haemostatic clamp forceps is introduced into the oral cavity, pushing it delicately dorsally and caudally to the larynx until reaching the oesophagus in its portion corresponding to about half the length of the neck.

The tip of the forceps is then moved laterally against the wall so as to visualise its position through the skin; the prongs of the clamp are opened and in the cavity thus formed a small incision is made into the skin, subcutaneous tissue and the oesophagus, until the tips of the clamp are exteriorised. The end of the tube is grasped with the prongs of the forceps and it is pulled in a retrograde direction until it is outside of the oral cavity. The end of the tube is subsequently reintroduced into the oesophagus with the aid of the clamp itself. Then, with the fingers, the probe is grasped from the outside, retracted slowly until unwinding of its torsion and then reinserted into the oesophagus in an aboral direction until the pre-measured length (Fig. 2). The size of the tube should be a 14-18 French in the cat and a 20-30 French in the dog. Once inserted until the pre-measured length, the tube should be fixed with a Roman sandal suture to the skin. The tube should stay in situ for at least 7-10 days before its possible removal. The skin and oesophageal incision does not require any suturing; it should be left to heal by second intention.

 

 

Gastrostomy tube
This tube, which is generally used for weeks, months or years, should be placed during a celiotomy, using an endoscope or a curved metal tube. During the celiotomy, an incision is made into the left gastric wall and a tube – size 15-21 French in the cat and 18-30 French in the dog - is inserted, fitted at the end with a balloon-shaped or mushroom-shaped device; the tube is then anchored to the organ with a tobacco-pouch suture. Subsequently, a circular suture - polypropylene 3-0 - is affixed between the serous and muscular portion of the organ and the abdominal wall. The stoma should be protected with an external medication containing antibiotic cream. The tube is removed after at least 10 days, by simply cutting the tube close to the skin and allowing the distal end to fall inside the stomach; the distal end will be ejected with the faeces or removed endoscopically.

When applied with the aid of the endoscope, the tube is inserted percutaneously: once the gastric cavity has been reached with the endoscope, the light source is directed towards the abdominal wall, in correspondence of which a small abdominal and gastric wall incision is made, so as to allow the tube to enter inside the cavity. Once the distal end of the probe (with mushroom device) is inserted into the organ, it is retracted from the outside until it adheres to the gastric wall; the external tube is then anchored to the skin with a Roman sandal suture (Fig. 3). The placement may be made easier by the use of an introducer, which facilitates the insertion of the end of the tube inside the stomach.

When using a curved metal tube for the placement of the gastric tube, the device should be inserted into the oral cavity and pushed gently to the gastric lumen, where it is moved laterally in order to highlight its distal end through the skin of the right abdominal wall. An incision is made into the skin and into the gastric wall near the cavity present at the end of the device;  a guide wire is inserted and pushed inside the tube until it comes out from the cranial end of the tube. At this point, the tube is removed, leaving the guide wire inside the patient. An introducer is threaded onto the oral end of the guide wire, which should be sutured to the end of the tube. The guide wire is retracted from outside the abdominal wall, dragging the tube inside the oesophagus until the gastric cavity; then, by continuing to retract the guide wire, the end of the probe is exteriorised, above the skin layers, until the mushroom pushes the gastric wall against the abdominal wall (Fig. 4). Once the tube is thus positioned, it is anchored to the skin of the abdominal wall with a Roman sandal suture. This latter method is used predominantly in the cat and and in small-sized dogs. Special attention must be paid during insertion of the curved tube inside the oesophagus in order to avoid lacerations. The probe should be left in situ for at least 10 days before its removal.

 

 

 

Jejunostomy tube

The placement of a jejunostomy tube is indicated in the presence of: pancreatitis, vomiting, gastroparesis and in diseases that render the  proximal part of the digestive tract unusable. The tube is usually inserted during abdominal surgery. A small incision is made into the proximal portion of the jejunum where the tube is inserted and pushed forwards for approximately 10-15 cm. It is then fixed to the intestinal loop with a tobacco-pouch suture (Fig. 5). The intestine is then fixed to the abdominal wall with a continuous suture made with an absorbable monofilament suture material. Before removing the tube it is necessary to wait for at least 10 days until a good cicatrisation has occurred. Other techniques exist for the placement of  jejunal tubes using the endoscope; these tubes must necessarily cross the oesophagus, the stomach and then reach the desired position. Other jejunal tubes may be placed, with the aid of the endoscope, through the stomach from the abdominal wall.

 

PARENTERAL NUTRITION

Parenteral nutrition (PN) is necessary in all those diseases characterised by a total or partial lack of absorption of nutritional principles by the gastrointestinal system, such as: parvovirus gastroenteritis, pancreatitis, intestinal lymphoma, systemic tumours, lesions in the facial region (e.g. fracture of the mandible), loss of consciousness or loss of motility of the gastrointestinal system. PN can also be used to complement enteral nutrition when this is not able to ensure a nutrient supply that is sufficient for the needs of the patient.

PN can be divided into TPN (total parenteral nutrition) and PPN (partial parenteral nutrition). With TPN the total resting energy requirement (RER) of the patient is administered by way of a central venous access,10 such as the jugular vein or the caudal vena cava.11 With PPN, 50-60% of the kilocalories of RER are administered; the administration may also be performed by way of a peripheral vein (e.g. forearm cephalic vein). Due to the particular type of venous access and the costs and complications relating to TPN, PPN is increasingly used, combining carbohydrates, proteins and lipids or only lipids. The vascular access should be changed after 3 days or when signs of local inflammation appear. The vascular access should be prepared according to the rules of antisepsis, as for an operating field. The catheter should be protected with a semi-occlusive dressing, which should be inspected at least twice a day for risks of sepsis and phlebitis.

Via the intravenous route (peripheral and central) it is possible to simultaneously administer water, electrolytes, carbohydrates, lipids and proteins. Commercial solutions are found on the market containing lipids with percentages ranging from 10 to 30%; if administered as a sole source of energy, they can provide up to 90% of RER. The administration of lipids as a sole source of energy should be done slowly, in order to accustom the body to the new source of energy; the maximum rate should not exceed 0.5 ml/kg/hr. Lipid solutions may alter laboratory tests, due to hyperlipidaemia. The solutions containing carbohydrates that are most commonly used have a 50% concentration, while protein solutions have a concentration in amino acids which varies between 3.5 and 15%. During parenteral nutrition, the blood concentration of potassium, phosphorus, sodium, chlorine and calcium should be assessed on a daily basis. When 50% of the RER is administered via PPN, formula no. 1 is used; below is an illustration of how to implement a PPN with a non-protein caloric distribution divided on a 50% basis between carbohydrates and lipids.

  1. (30 x kg) + 70 = RER (daily Kcalories); RER/2 = Kcal/day for PPN
  2. calculation of protein requirement: 1 ÷ 6 g/100kcal (RER/100 x 1÷6 = g/prot/day);  volume of amino acids solution: grams of protein per day/0.085% = ml of amino acids solution at 8.5%
  3. Kcal for PPN - Kcal from amino acids = Kcal to be distributed on a 50% basis between carbohydrates and lipids

The 50% glucose solution has a caloric concentration of 1.7 kcal/ml; the solution of 8.5% amino acids 0.34 kcal/ml; and the 20% lipid solution 2 kcal/ml. To perform the calculation quickly, an electronic spreadsheet is suggested. During preparation of the PPN, due to problems of physical incompatibility, the preparation sequence should be the following: firstly, glucose should be inserted into a sterile container, then the amino acids and lastly the lipids. The infusion speed, expressed in ml/hr, is obtained by dividing the total ml obtained with the calculation of PPN by 24. The most common complications to occur with PN include vasculitis, infections, an increase in hepatorenal activity to dispose of nitrogenous or lipid residues, along with limb oedemas, necrosis and skin ulcers, an increase in blood osmolarity and thromboembolism. PN should not be used in the presence of sepsis or skin infections.

 

References

1)  Feldmann BF, Thomson DB. Fibronectin: its diagnostic and therapeutic implications. J. Am. Anim. Hosp. Asso. 1983; pp1027-1030.
1)  Viganò F. Nutrizione enterale e parenterale, In: Viganò F. ed. Medicina d’urgenza e terapia intensiva del cane e del gatto. Milano: Masson/E.V.; 2004, pp. 287-299.
2)  Brunetto MA, Gomes MO, Andre MR, et al. Effects of nutritional support on hospital outcome in dogs and cat. J Vet Emerg Crit Care 2010; 20(2):224-231.
3)  Remillard RL. Parenteral Nutrition, In Di Bartola S. ed. Fluid therapy in small animal practice, 2nd eds.  Philadelphia: W.B. Sounders; 2000, pp. 465-482.
4)  PyleSC, Marks SL, Kass PH. Evaluation of complication and prognostic factor associated with administration of total parenteral nutrition in cats: 75 cases (1994-2001). J Am Vet Med Assoc 2004; 225(2):242-250.
5)  Perea SC. Critical care nutrition for feline patient. Top Companion Anim Vet 2009; 23(4):207-215.
6)  Romano E, Auci E. Denutrizione e ipermetabolismo, In Romano E ed. Il malato critico principi e pratica della terapia intensiva, 1st ed. Torino: Utet; 2000, pp.1-23.
7)  Campbell JA, Jutkowitz LA, Santoro KA, et al. Continuous versus intermittent delivery of nutrition via nasoenteric feeding tubes in hospitalized canine and feline patients: 91 patients (2002-2007). J Vet Emerg Crit Care 2010; 20(2):232-236.
8)  Holaham M, Abood S, Haumptan J., et al. Intermitted and countinuous enteral nutrition in critically ill dogs: a prospective randomized trial. J Vet Intern Med 2010; 24(3):520-526.
9)   Portillo E, Mackin A, Hendrix PK, et al. Comparison of the modified Seldinger and through-the-needle jugular placement techniques in the dog. J Vet Emerg Crit Care 2006;16(2):88-95.
10)  Radinskly MA, Koening A. Central venous access to the cranial vena cava via the omobrachial vein in the dog. J Vet Emerg Crti Care 2008;18(6):659-662.