Critical care nutrition (Proceedings)


Stress Starvation: lack or absence of calories and protein (absolute or relative) compounded by physiologic stress associated with illness or injury.

Key clinical diagnostic points

Patient assessment:

     • Debilitated patients require aggressive nutritional support.

          o History of weight loss, anorexia, cachexia

          o Dry, course, lusterless coat

          o Hypoalbuminemia, low blood urea nitrogen, lymphopenia, anemia

     • Non-debilitated patients with acute illness must be recognized for the risk for developing malnutrition

          o Animals unwilling or unable to eat within 3 days

          o Severe trauma, burn, sepsis, pancreatitis, head injury

          o Patients managed with an open abdomen

          o Patients that are mechanically ventilated

Starvation: Key Etiologic and Pathophysiologic Points

     • Consequences of Starvation

          o Decreased calories lead to a shift in neuro-humoral mediators to promote catabolism.

          o The body's response to starvation preserves plasma nutrients to maintain vital cell structure and function. This occurs at expense to adipose stores and lean body mass.

Simple Starvation: lack or absence of calories and protein in animals without illness or injury.

     • >48 hours:

          o Induction of ketogenic enzymes

          o Production of ketones from FFA and protein sparing

          o Shift to renal gluconeogenesis using glutamine as a substrate

          o Provision of calories and protein reverses starvation by restoring glycogen and adipose stores and promoting protein anabolism

Stress Starvation: lack or absence of calories and protein (absolute or relative) compounded by physiologic stress associated with illness or injury.

In comparison to simple starvation, protein catabolism is much more pronounced.

     • Inflammatory cytokines and mediators may augment the effects of elevated catecholamines and glucocorticoids in critically ill animals, and diminish the normal humoral signals for body weight control

     • Inadequate nutrition in the critical care patient sets the stage for complications that result in weakness, sepsis, organ dysfunction, immune suppression and poor wound healing.

     • Provision of nutritional support may hasten recovery from critical illness and diminish some of the typical complications of the critically ill.

Key therapeutic points

     • Nutritional Support: Why Bother?

     • Proven benefits in humans include: patients unable to eat (simple starvation), in severely malnourished patients about to undergo major surgery, in patients with major trauma, in bone marrow transplant recipients, and in patients undergoing anticancer therapy.

Patient identification

     • General guidelines for providing nutritional support include:

          o Patients that have lost or are expected to lose 10% of lean body mass

          o Anorectic patients or patients not expected to eat within 3 days

          o Patients with severe trauma, sepsis, or systemic inflammation

          o Patients with increased nutrient losses: draining wounds, burns, vomiting/diarrhea

          o Always consider appropriate feeding tube placement in patients undergoing major surgical procedures.

Caloric requirements

     • Basal Energy requirements (BER)

          o BER (Kcal) = 70 x weight (kg) 0.75

          o Or, BER (Kcal) = [30 x weight (kg)] + 70

     • Injury/Illness severity factor (IER)

          o Previously adopted illness factors from human medicine are no longer utilized

Nutritional support methods

     • Enteral Nutrition is preferred if the gastrointestinal tract is completely or even partially functional

          o Physiologic approach: digestion and absorption by the gut promotes normal gut structural and functional integrity; nutrients delivered to gastrointestinal circulation and liver as in the normal patient

          o May prevent secondary gastrointestinal changes that result in bacterial and toxin translocation, sepsis, and derangements in amino acid metabolism

     • Parenteral Nutrition is indicated only if enteral support is precluded or as a supplement to partial enteral support.

Key prognostic points

     • Patient prognosis mainly depends on diagnosis and treatment of the primary disorder

     • Nutritional support is essential for positive outcome in patients with moderate to severe malnutrition

     • Institution of early nutritional support in patients with acute illness may prevent complications typical of critically ill patients, and promote recovery


     • Provision for adequate protein and calories should be a routine part of the therapeutic plan of most veterinary patients, especially those exhibiting signs of malnutrition or suffering from acute illness.

     • Enteral nutrition is the preferred route of proving nutritional support. The route and method of nutritional support depends on the individual patient and condition. Placement of feeding tubes should always be considered in patients undergoing laparotomy.

Enteral nutrition


     • Nasogastric/Nasoesophageal tubes:

          o Used for short to medium term nutritional support (3-14 days), and relatively inexpensive

          o Tube placement should be verified with radiography

          o Contraindications include protracted vomiting, functional or mechanical GI obstruction, upper airway obstruction, facial trauma, esophageal disease, facial fractures, patients with increased intracranial pressure (induced sneezing may increase ICP), or a decreased level of consciousness

          o Disadvantages and problems include patient discomfort, epistaxis, sinusitis, vomiting, reflux esophagitis, and tube dislodgement, require liquid diet

     • Esophagostomy tubes:

          o Used in patients with normal GI function and in those needing nutritional support for medium to long tern duration

          o Risks include aspiration pneumonia, reflux esophagitis, and vomiting/regurgitation, and tube dislodgement

          o Complications include cellulitis or abscess at -ostomy cite, horners, laryngeal paralysis, hemorrhage

     • Gastrostomy tubes:

          o Indicated for any patients needing medium to long term enteral nutritional support

          o Gastrostomy tubes are well tolerated in anorectic and ill animal patients.

          o G-tubes may be placed surgically, endoscopically, or by a blind, percutaneous technique

          o Contraindications include persistent vomiting or functional/mechanical obstruction

          o G-tubes should be left in place for a minimum of 7-10 days before removal is attempted; malnourished and hypoalbuminemic patients may require longer

          o Disadvantages include the necessity of general anesthesia and the potential for regional infection or cellulitis at the stoma, and dehiscence and peritonitis with tube migration

          o Feeding started 24 hours after placement to allow a fibrin seal b/w stomach & body wall

          o Easy to manage patients in the home environment


     • Several types of liquid enteral nutrition formulations are available for use in humans, only veterinary diets are specifically balanced for canine and feline patients; these should be used whenever possible

     • Formula selection should be based on knowledge of the patient needs, including degree of malnutrition, caloric and protein requirements, and digestive and absorptive capabilities as well as method of enteral access

     • Disease process is also relevant to the type of enteral nutrition provided (e.g., high-quality, low-protein in patients with hepatic or renal disease) Numerous advances have been made to human enteral formulas including addition of omega 3 and 6 fatty acids, supplementation with vitamin C & E


     • After consideration for the diet type based on the disease process and route if enteral feeding, diets should be introduced slowly to provide assessment of gastrointestinal function. Typically ⅓ RER on day 1, ⅔ RER on day 2, full RER on day 3.

     • Isosmolar solutions in frequent small volumes or as a constant rate infusion (CRI) are best for beginning enteral nutritional support. CRI preferred in NE, NG or J tube feedings.

     • In some patients with acute illness and injury, full nutritional support may be instituted within 2 days, whereas a chronically malnourished patient may require a slower introduction

     • Parameters used to assess the appropriate increase in calories include residual fluid volume present in the stomach, and the presence of nausea, bloating, vomiting, or regurgitation/vomiting

     • J-tube feedings needs to be performed frequently and in small volumes; diet should be isosmolar; CliniCare and RenalCare, even though polymeric diets, are well tolerated (elemental diets are not necessary as one would expect)

     • Consider enteral product volume when calculating total fluid input for a patient, especially in patients sensitive to fluid overload

Parenteral nutrition

     • Parenteral nutrition allows for the provision of calories and protein substrate through the intravenous administration of variable mixtures of amino acids, lipids, and dextrose, along with vitamins, minerals and electrolytes

     • Indications for parenteral nutrition include severe vomiting and regurgitation, acute pancreatitis, severe intestinal disease with malabsorptive disorders, or as a supplement to enteral nutrition so that full caloric needs will be met

     • Exclusive use of parenteral formulations for nutritional support should be performed with the understanding of the negative effects on the gastrointestinal barrier function and the development of mucosal atrophy

Partial parenteral nutrition

     • PPN provides approximately 50% of caloric needs

     • Although most parenteral formulations are hyperosmolar, the lowered calorie density of PPN allows administration through a smaller, peripheral vein with little risk of thrombophlebitis

Total parenteral nutrition

     • Total parenteral nutrition strives to administer 100% of needed calories

     • Due to the hyperosmolarity of TPN solutions, it must be delivered through a dedicated central venous catheter

     • TPN must be started and discontinued in a stepwise fashion to prevent abrupt changes in plasma nutrients, allowing for an appropriate period of metabolic adaptation (e.g., 1/2 calories day 1, full calorie support on day 2)

Vascular access

     • Central intravenous catheters should be placed in a sterile fashion (clip, surgical scrub and placed with sterile gloves). Catheter site & bandage should be examined daily.

     • PPN and TPN solutions should be delivered through a dedicated line, with no disconnections, and one bag/IV set & extension set per day.


     • Mechanical/technical: Catheter occlusion, disconnection, thrombophlebitis

     • Metabolpic: Hyperglycemia – Hypoglycemia – Hypokalemia/hypophosphatemia/hypomagnesemia - Lipemia

          o Septic: Potential for bacterial growth within the solution however very uncommon. Patients showing clinical signs of infection and sepsis should be actively examined, and cultures of PN solution or catheters performed if indicated


Daily: pcv/ts/azo/bg, electrolytes, urine glucose, and lipemia assessment of serum.


     • Recipe

          o Typically the patients RER is provided in equal proportions of dextrose and lipid.

          o The ratio can be adjusted as needed: diabetics or hyperglycemic patients can be provided a greater proportion RER from lipid, conversely lipemic patients a greater proportion RER from dextrose.

     • Mixture

          o Sterile technique is important

          o Syringe transfer (least sterile)

          o Closed circuit, 3-lead system

                √ Gravity dependent, +/- 50 ml

                √ Pumps, +/- 1 ml


Recognition of the influence of certain nutrients on the immune and inflammatory response of the critically ill has led to the evolution of more sophisticated nutritional strategies and concepts. Administration of immune enhancing formulas supplemented with a combination of glutamine, arginine, omega-3 fatty acids (u-3 FA), and nucleotides have been shown in most studies to reduce infectious outcomes.


A conditionally essential nutrient in severe illness or injury. Preferred fuel source of enterocyte & absorbed preferentially over glucose in ischemic intestine. Also important in nucleotide synthesis, has antioxidant properties via metabolism to glutathione, and may enhance immune function. Both enteral & parenteral routes reduce infectious complications in critically ill people.


Arginine is a semi essential amino acid obtained both from dietary sources and endogenous synthesis via the urea cycle. The metabolic products of arginine participate in cellular restoration processes and modulate the immune response of the host. Under nonstressed conditions, arginine contributes to adequate wound healing, an enhanced immune response, and stimulation of various anabolic hormones. L-arginine is also a unique substrate for the production of nitric oxide (NO). Two isoforms of arginase exist, arginase I and arginase II. Aginase I is also known as inducible nitric oxide synthase which typically produces excess NO in sepsis contributing to vasodilation and poor perfusion. The host's immune status modulates aginase isoform expression. Research results are mixed, however recommendations are to avoid aginine supplementation in sepsis; while it tends to be beneficial in trauma and other non-inflammatory conditions.

Omega Fatty Acids

Omega-3 fatty acids have demonstrated significant anti-inflammatory properties. There have been three prospective randomized trials of enteral supplementation with u-3 FA in critically ill patients with respiratory distress syndrome (ARDS), and all have shown beneficial effects on respiratory mechanics and survival benefit. Fewer data are available for other patient groups (e.g.- trauma, sepsis).

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