Nutrition for hospitalized patients can present a challenge, for a variety of reasons.

Clinical signs such as nausea and emesis can suppress appetite and complicate ingestion and absorption of nutrients. Trauma to the jaw or dentition can make prehension and mastication of solid food impossible. Food aversions are frequently a problem in patients with conditions such as renal failure or pancreatitis and can complicate recovery. Voluntary feeding for many hospitalized patients may be inadequate to meet the daily energy requirement, and assistance becomes necessary. Providing nutrition to critical care patients requires constant reassessment and may involve a combination of assisted feeding methods throughout the hospitalization period. In this article, we aim to cover how to identify the patients that need assistance and the feeding options available.

Healthy vs diseased: response to starvation

Being in a diseased state affects the metabolic response to a period of inappetence when compared to a healthy animal [1, 2]. A healthy animal and an animal with concurrent disease will preferentially utilize different sources of energy. Starvation in a healthy animal will result first in the use of stored glycogen in the liver and the muscle via glycogenolysis which can provide an energy source for up to 36 hours, driven by the secretion of the hormone glucagon [3]. Adipose stores and fatty acids are then catabolised for energy via the beta-oxidation process supplying ketone bodies as an alternative to glucose; the preservation of protein stores and lean muscle is prioritized [4]. Fatty acid metabolism occurs in the mitochondria of the cell, so can be utilized in almost all cells, with the exception of red blood cells and brain matter [3]. The conversion of free fatty acids into Acetyl CoA requires l-carnitine for transportation into the cells, so increased demand for this non-essential amino acid can be noted [3].

In a healthy animal in acute starvation, resting energy requirements will also be decreased due to thyroid action lowering the metabolic rate [1]. In this way the animal can utilize all stored energy sources and effectively lower demand for that energy metabolically.

For cats in particular

Even in the healthy cat, we do observe a greater reliance on protein intake as a source of glucose via gluconeogenesis, and cats have very limited ability to adjust this even if their protein intake is reduced [3]. Amino acids can enter the citric acid cycle following removal of the amino group and subsequent breakdown of the carbon skeleton- hepatocytes are the major site for this breakdown [3].

Following a period of anorexia, even in healthy patients, an amino acid deficit is even more of a risk for our feline patients.

Water soluble B vitamins including thiamine (B1), niacin (B3) and pyridoxine (B6) are required in a higher demand in cats than other species and are frequently depleted in a starvation state [3].

In an animal with ‘stress starvation’, or concurrent illness associated with the anorexia, the response to malnutrition is complicated by an increased sympathetic drive and release of catecholamines (norepinephrine and epinephrine) and inflammatory mediators in response to the disease process [3]. Diseased patients are often noted to be insulin-resistant and have decreased glucose utilization because of this neuroendocrine response [3-5]. In both human and feline critical care cases, a circulating hyperglycaemia can be noted.

Increased production of inflammatory proteins increases consumption of amino acids [3]. The focus falls on lipid and protein metabolism, resulting in catabolism of muscle stores to meet demand [1].

Cardiac output increases along with an increased metabolic rate and protein catabolism. The result of this altered response is increased muscle loss and if prolonged, this affects cardiac and intercostal muscle, representing an increased risk of mortality by cardiac or respiratory failure [1]. Cats are at greater risk of this protein-energy malnutrition due to their higher protein requirement compared with dogs [3, 5].

Because of these alterations in metabolism, diets designed for use in critical care patients have a high-fat and protein to low-carbohydrate ratio [1, 4] as seen in the Emeraid and Royal Canin Recovery ranges.

During a prolonged anorexic period, the patient can become both calorie- and nutrient-deficient. Both are associated with greater morbidity and mortality [1]. The importance of adequate and balanced nutrition in these patients cannot be overstated. Malnutrition is associated with decreased immunocompetence and tissue synthesis and repair; these patients are also likely to have greater repair demands compared to a healthy pet [1].  Decreased immunocompetence will put hospitalized patients at risk of nosocomial infections and increase the odds of infections and risk of sepsis at catheter access sites, for example.

When to assist with nutrition?

To manage this risk, it is imperative to assess patients for signs of malnutrition. The aim is to prevent malnutrition where possible and identify and correct rapidly when prevention is not possible.

An assessment including history, body condition score and interpretation of laboratory results is a good start.

Change in body weight in a critically ill patient is more relevant than the actual body weight and condition score during hospitalization [6]. Drastic weight loss in an overweight patient is considered a risk factor for malnutrition, even if their weight now falls within the healthy range. This would also be of greater relevance in the feline species, as the risk of hepatic lipidosis is increased with significant weight loss. These patients would be recommended for immediate nutritional support.

Serum markers of malnutrition include albumin, blood urea nitrogen (BUN), total protein, potassium, and creatinine. Serum potassium and BUN will fluctuate on a daily basis, but albumin and total protein will reflect the nutritional status of a patient over a longer term (weeks to months)[6]. Low albumin levels have been linked to mortality rates in both humans and companion animals in critical care with various conditions including pancreatitis [5].

Hyperglycaemia has also been noted in feline patients with critical illness, through an altered carbohydrate mechanism- with increased gluconeogenesis, hyperlactataemia and peripheral insulin resistance documented [7]. In human patients, hyperglycaemia in cases of critical illness have been identified as a negative prognostic indicator [5, 7]. The degree of hyperglycaemia has been found to be proportional to the severity of the illness in human patients and we need to recognize the possible implications in our companion animal patients [5, 7]. In human cases, exogenous insulin can be used to lower the serum glucose.

The Nutrition Plan

Having determined the patient needs assistance, the next question is Parenteral vs Enteral feeding?

• Parenteral nutrition (PN) is the process of supplying essential nutrients straight into the vein and by-passing the gastrointestinal system entirely [2, 8].
• Enteral nutrition (EN) involves using the gastrointestinal system for digestion and evidence has shown this is the preferred method of assisted feeding in humans as well as veterinary medicine [9].

Physiological changes in the intestines associated with lack of ingestion have been documented- such as villous atrophy, decrease in gut motility and alterations in mucosal permeability [4, 5]. The risk of bacterial translocation and sepsis is greater with PN than when the gastrointestinal tract is utilized [9].  PN will result in a complete absence of nutrients in the gastrointestinal tract and several, such as glutamine, are conditionally essential for good gut health- providing nutrition to enterocytes [1].

PN may be the only option for animals with severe gastrointestinal disease or decreased mentation. In addition, if anaesthesia to place a feeding tube is considered too risky, then parenteral feeding may be the best choice [6]. This form of nutrition can be given to cover all the patients’ daily nutrient requirements (Total Parenteral Nutrition or TPN), or it can be used in combination with enteral feeding (Partial Parenteral Nutrition or PPN). Metabolic imbalances including hyperglycaemia, hypophosphataemia and lipaemia may be noted after PN [2] so careful monitoring must be available. Adjustment of the infusion rate may be adequate to reverse any disturbances [5].

Parenteral feeding can be given by central or peripheral venous access- peripheral access has a greater risk of thrombophlebitis and sepsis, and more limitations on suitable products for use [4]. Given general practitioners are often more comfortable with peripheral venous access, it is possible that using shorter administration times and use of lipid-containing mixtures can reduce these risks [6]. Solutions used in PN must be prepared aseptically and it may be difficult to impossible for clinics in certain regions to access.

EN is the provision of nutrition via the gastrointestinal tract and is used in a clinic setting normally with reference to tube feeding. Multiple options and techniques exist for placement of the tube, and often the cause of trauma or illness will determine the best site.

Nasogastric feeding tubes– can be used easily in patients without trauma or disease to the nasal or oral cavity. They are more suited to shorter term placement- from 3-5 days up to several weeks in some cases and can be placed conscious [4]. This may also be a short-term solution in a patient who is not stable enough to undergo an anaesthetic. [1] 

Oesophagostomy and gastrostomy feeding tubes will need to be placed surgically under anaesthesia. These feeding tubes can be used for months if required and patients may be treated as outpatients with these systems indwelling [10]. Complications associated with use of oesophagostomy tubes include patient displacement of the tube, obstruction during usage, peristomal inflammation or infection and vomiting of the tube [10]. Most of these complications can be easily managed, but infections around the stoma are associated with a worsened prognosis and some complications may lead to euthanasia [10].

Jejunostomy feeding tubes are placed into the small intestine via a transabdominal incision. Jejunostomy tubes need to be fitted under anaesthetic and require specialist equipment and training- cost is subsequently greater than other options. The placement is caudal to the duodenal opening of the pancreatic duct and so require a highly specialized diet [4]. Maintenance of these feeding systems will require the patient to remain in the hospital for the duration of use [4].

Feeding options and amounts for a critical care patient

The provision of nutrition to these patients is extremely important- but the priority is to preserve body mass and support organ function and recovery. The restoration of body condition and weight is reserved for the recovery phase [4]. Current recommendations on amount fed are to aim for RER using the formula 70 x (BW)^0.75. Previous advice included using an ‘ilness’ factor of this formula, however research on re-feeding syndrome has determined over-feeding to be detrimental [4, 11].

Re-feeding syndrome is a term used to describe the electrolyte imbalances that can be seen in an anorexic patient when feeding is reintroduced. It is a rare syndrome but can be life-threatening if not noted and addressed quickly.

Recommendations for nutrition in these patients also include volume and frequency advice as the stomach capacity will often decrease during a period of anorexia, and the patient will need time to adjust [4]. It is recommended to split the feeds into 4-6 smaller meals. Initial feeding rates should never exceed the RER and often the RER is reached only after 48-72 hours of incremental increases.

Nutrient requirements for enteral feeding:

• Protein- to provide enough to avoid catabolism of lean muscle and correct the nitrogen deficit. Protein needs to be balanced in terms of amino acid content as well as quantitiative- certain amino acids being in higher demand in critical care patients; glutamine, taurine, arginine, leucine and valine supplementation has been documented to improve protein metabolism, intestinal repair and immune function [4]. L-carnitine is also supplemented to support fat metabolism and energy production.  
• Fat- to use for energy, providing more energy per gram than the other macronutrients and to spare protein [4].
• A low starch content should assist in management of hyperglycaemia and insulin resistance.
• The use of fermentable fibre or prebiotics will help with colonic health and try to prevent/manage a dysbiosis.
• Adequate amounts of sodium, potassium and phosphorus to avoid re-feeding syndrome.
• Vitamins- cobalamin and antioxidants such as Vitamin E may help with metabolism and may be in increased demand in certain disease states.

Options for diets for tube feeding include commercial preparations that can be blended with water for a more liquid consistency. Royal Canin Recovery falls into this category- and the advantages associated include no need to change the diet rapidly if the patient starts to eat again voluntarily. Always bear in mind that the high protein and fat content may not be appropriate in cases of renal or hepatic disease, or certain gastrointestinal conditions- some pancreatitis cases or lymphangiectasia.

Liquid diet preparations may be more appropriate in smaller patients with smaller diameter tubes- or any patient with a nasogastric tube. Royal Canin liquid diets include Recovery and Renal. These diets are hydrolyzed or ‘pre-digested’ which makes them a sensible choice if using a jejunostomy tube, which will bypass the bile and pancreatic secretions [4].

Potential risks with assisted feeding

Assisted feeding in some cases may result in vomiting, diarrhoea and potentially abdominal pain associated with the decreased stomach capacity of these patients and volume overload [11]. Metabolic complications include electrolyte disturbances such as hyperglycaemia, hypophosphataemia and hypokalaemia. These disturbances are known as Re-feeding syndrome. In cases of prolonged anorexia, often the patient will have low intracellular electrolyte levels but may appear within the normal range on serology. Once feeding is introduced, intracellular uptake of electrolytes will exhaust supply if the diet is not adequately supplemented. It is recommended to monitor the electrolyte profile of the patient if possible once daily, and feed a diet with adequate potassium, phosphate and magnesium [1].

Initial feeding rates should never exceed the RER and the RER is reached after 48-72 hours of incremental increases (Day 1- 30% of RER, Day 2 60% and Day 3 100% of RER as an example).

• Warm the fluid to room temperature.
• Flush the feeding tube prior to and after feeding with 10mls of warm water.
• In case of obstruction in the tube- use pancreatic enzymes mixed with warm water (1 tablespoon with 5mls of warm water), coca cola or pineapple juice to break down the blockage [11]. Repeated aspiration and then pressure with a syringe will assist.

The Royal Canin Recovery and Renal liquids for cats and dogs are an energy-rich formulation for critical care and convalescence. Recovery liquid can be used for enteral tube feeding and has a high protein content to assist with recovery and maintenance of lean muscle mass. It is the ideal product to provide the variety of options needed for the recovering patient. With tube feeding, Recovery delivers calories in a low volume manner with the appropriate electrolyte content to avoid re-feeding syndrome and support healing.

Renal liquid is the ideal liquid food for cases of temporary or chronic renal insufficiency. With moderate protein and reduced phosphate, Renal liquid will be able to support and replenish nutrients while optimising renal recovery.

EmerAid Sustain HDN Canine and Feline are semi-elemental therapeutic diets developed by veterinarians and nutritionists. The diets are designed to support animals who are underweight, recovering from critical illness or cachexia and can be used for complete enteral feeding as well as supplemental. EmerAid Sustain HDN meets or exceeds requirements for all life stages, meaning it can be used in puppies through to geriatric patients under supervision of the clinician.

At home, following discharge, EmerAid can also be used to supplement a maintenance diet and can be used regularly in patients with sarcopenia or cachexia related to terminal illness.

References

1. Remillard, R.L., Nutritional support in critical care patients. The Veterinary clinics of North America. Small animal practice, 2002. 32(5): p. 1145.
2. Chan, D.L., et al., Retrospective Evaluation of Partial Parenteral Nutrition in Dogs and Cats. Journal of Veterinary Internal Medicine, 2002. 16(4): p. 440-445.
3. Pibot, P., V. Biourge, and D. Wlliott, Encyclopedia of Feline Clinical Nutrition. Vol. 1. 2010, Aimargues, France: Direction Publication Royal Canin Group  
4. Norris, J.D., S.D. Kilborn, DVSc, Diplomate ACVIM, and M.D. Evason, Diplomate ACVIM, Feeding Patients Requiring Nutritional Support. 2014, Royal Canin.
5. Jensen, K.B. and D.L. Chan, Nutritional management of acute pancreatitis in dogs and cats. Journal of veterinary emergency and critical care, 2014. 24(3): p. 240-250.
6. Perea, S.C., Critical Care Nutrition for Feline Patients. Topics in Companion Animal Medicine, 2008. 23(4): p. 207-215.
7. Chan, D.L., et al., Alterations in carbohydrate metabolism in critically ill cats. Journal of Veterinary Emergency and Critical Care, 2006. 16(s1): p. S7.
8. Crabb, S.E., et al., Retrospective evaluation of total parenteral nutrition in cats: 40 cases (1991-2003). Journal of Veterinary Emergency and Critical Care, 2006. 16(s1): p. S21.
9. Qin, H.L., et al., Effect of early intrajejunal nutrition on pancreatic pathological features and gut barrier function in dogs with acute pancreatitis. Clinical Nutrition, 2002. 21(6): p. 469-473.
10. Olivia, N., et al., Esophagostomy tube complications in dogs and cats: Retrospective review of 225 cases. Journal of Veterinary Internal Medicine, 2019. 33(5): p. 2014-2019.
11. Wara, A.D. Enteral Feeding:Tube Feeding. Clinician’s Brief, 2014. https://www.cliniciansbrief.com/article/enteral-nutrition-step-step.

Written on January 16, 2024.