Parenteral Nutrition
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6. Parenteral Nutrition
Principal indications for parenteral nutrition include uncontrollable vomiting, regurgitation, acute pancreatitis, intestinal obstruction, severe malabsorption, prolonged ileus, and inability to guard the airway. Parenteral nutrition can be delivered through a central vein (central PN or CPN) or a peripheral vein (partial PN or PPN). CPN is the provision of all of the animal’s calorie and protein requirements. PPN only supplies part of the animal’s energy and nutrient requirements (Chan & Freeman, 2006; Delaney et al., 2006).
CPN is often the preferred modality for a cat requiring parenteral nutrition. A disadvantage of CPN includes the requirement for central venous access (jugular or femoral venous catheter), it is slightly more expensive, and it may be associated with more metabolic complications. CPN requires central venous access as the solution is hyperosmolar. The higher the osmolality of the solution, the higher the incidence of thrombophlebitis (Chandler et al., 2000). Relatively few reports are available regarding the use of parenteral nutrition in cats (Lippert et al., 1993; Chan et al., 2002; Pyle et al., 2004; Crabb et al., 2006). The major indication of parenteral nutrition in cats appears to be pancreatitis (Chan et al., 2002; Pyle et al., 2004; Crabb et al., 2006).
Components
Both CPN and PPN are a combination of a dextrose solution, an amino acid solution, and a lipid solution. The most commonly used amino acid solutions contain most essential amino acids for cats, except taurine. However, because parenteral nutrition is typically not used beyond 10 days, taurine deficiency is not a clinical complication in most circumstances. Amino acids solutions are available with and without electrolytes. Cats that have normal serum electrolytes typically receive amino acid solutions with electrolytes, whereas patients who have electrolytes disturbances may benefit from amino acid solutions without electrolytes so that the electrolyte disturbances can be individually corrected (Chan & Freeman, 2006; Freeman & Chan, 2006). The osmolality of the amino acid solutions with and without electrolytes is also significantly different. Consequently, PPN, which requires the osmolality of the final solution to be less than 600 mmOsm/L, is typically formulated using an amino acid solution without electrolytes.
Lipid emulsions are the calorically dense component of parenteral nutrition and a source of essential fatty acids. The ratio of dextrose to lipid should be selected to reflect the hormonal milieu and metabolic condition of the liver. Lipid emulsions are isotonic. Typical lipid emulsions consist of soybean and safflower oil and provide predominantly long-chain polyunsaturated fatty acids, including linoleic, oleic, palmitic, and stearic acids. These solutions are emulsified with egg yolk phospholipids and their tonicity is adjusted with glycerol. The emulsified fat particles are comparable in size to chylomicrons and are removed from the circulation through the action of peripheral lipoprotein lipase. Infusions of lipid have not been shown to increase pancreatic secretion or worsen pancreatitis, excepted in cases where serum triglycerides are elevated, indicating a failure of triglyceride clearance. Although specific data on the maximal safe level of lipid administration in veterinary patients are not available, maintaining normal serum triglycerides levels in cats receiving parenteral nutrition seems prudent (Chan & Freeman, 2006; Freeman & Chan, 2006).
The parenteral solution should be formulated to contain 40 mEq/L of potassium to compensate for the insulin mediated transcellular potassium shift associated with refeeding. Similarly, the parenteral solution should be formulated to contain a minimum 5 - 10 mM/L of phosphorus. Water soluble vitamins can be provided by the addition of a multivitamin B complex preparation. These preparations typically do not include folic acid due to incompatibility with riboflavin in solution. Fat soluble vitamins, trace elements, and calcium are not generally included in the parenteral nutrition solution if the duration of treatment is expected to be less than 1 - 2 weeks. The addition of calcium is not routine because of the risk of precipitation of the parenteral solution, and calcium deficiency appears to be well tolerated in the short term. The dose of trace minerals to include in the parenteral nutrition is uncertain. Vitamin K should not be added to the parenteral nutrient solution, but should be administered subcutaneously once weekly.
Compounding and Prescription
Parenteral nutrition requires specific compounding practices to maintain sterility and to prevent precipitation of the components. The macronutrients should be combined in the following order: glucose then amino acids then lipids. For logistical and economical reasons, more than one day’s supply of PN usually is typically compounded at one time, however, no more than a 3-day supply of parenteral nutrition should be compounded and stored (refrigerated) at a time. Parenteral admixtures should never be frozen or heated, and any unused portions should be discarded (Campbell et al., 2006; Freeman & Chan, 2006).
The worksheets presented in Table 13 and Table 14 are designed to provide an admixture that is intended to last 24 hours when administered at a constant-rate infusion. Bags of parenteral nutrition should not be at room temperature for more than 24 hours.
Table 13. Worksheet for Calculating Partial Parenteral Nutrition for Cats |
1. Caculate the resting energy requirement (RER) 70 x (current body weight in kilograms)0.73 = ...... kcal / day |
2. Calculate the partial energy requirement (PER) PER = RER x 0.70 = ...... kcal/day |
3. Determine the nutrient composition For animals under 3 kg, the formulation will provide a fluid rate higher than maintenance fluid requirements. Be sure that the animal can tolerate this volume of fluids a. Cats weighing 3 - 5 kg PER x 0.20 = ...... kcal/day from dextrose PER x 0.20 = ...... kcal/day from protein PER x 0.60 = ...... kcal/day from lipid b. Cats weighing 6 - 10 kg PER x 0.25 = ...... kcal/day from dextrose PER x 0.25 = ...... kcal/day from protein PER x 0.50 = ...... kcal/day from lipid |
4. Calculate the volume of nutrient solutions required each day a. 5% dextrose solution = 0.17 kcal/mL and 253 mOsm/L ...... kcal from dextrose ÷ 0.17 kcal/mL = ...... mL dextrose/day b. 8.5% amino acid solution without electrolytes= 0.085 g protein/mL = 0.34 kcal/mL and 890 mOsm/L ...... kcal from protein ÷ 0.34 kcal/mL = ...... mL amino acids/day c. 20% lipid solution = 2 kcal/mL and 260 mOsm/L ...... kcal from lipid ÷ 2 kcal/mL = ...... mL lipid/day |
5. Calculate the total daily volume of parenteral solution ...... mL total volume of PPN solution = ...... mL 5% dextrose solution + ...... mL 8.5% amino acid solution + ...... mL 20% lipid solution |
6. Calculate the osmolality mOsm/L should be less than 600 mOsm/L for peripheral administration ...... mL 5% dextrose solution * 0.253 mOsm/mL = ...... mOsm ...... mL 8.5% amino acid solution * 0.890 mOsm/mL = ...... mOsm ...... mL 20% lipid solution * 0.26 mOsm/mL = ...... mOsm ...... mL total volume of PPN solution ...... mOsm of PPN solution ...... mOsm/L of PPN solution = 1000*( ...... mOsm of PPN solution ÷ ...... mL total volume of PPN solution) |
7. Calculate the administration rate This formulation provides approximately a maintenance fluid rate. ...... mL/hour PPN solution = ...... mL total volume of PPN solution/24 hrs |
Foot notes Calories supplied by proteins: 4 kcal/g Calories supplied by carbohydrates: 4 kcal/g Calories supplied by lipids: 9 kcal/g |
Table 14. Worksheet for Calculating Central Total Parental Nutrition for Cats |
1. Calculate the resting energy requirement (RER) 70 x (current body weight in kilograms)0.73 = ...... kcal / day |
2. Calculate the protein requirements Standard 6 g / 100 kcal Decreased requirements (hepatic, renal failure) 3 - 4 g / 100 kcal RER ÷ 100 x ...... g / 100 kcal = ...... g protein / day |
3. Calculate the volumes of nutrient solutions required each day 8.5% amino acid solution with electrolytes = 0.085 g protein/mL = 0.34 kcal/mL ...... g protein required / day ÷ 0.085 g/mL = ...... mL of amino acids / day Non-protein calories The calories supplied by proteins are subtracted from the RER to get total non-protein calories needed ...... g protein required / day x 4 kcal/g = ...... kcal provided by protein RER - kcal provided by protein = ...... nonprotein kcal needed / day Non-protein calories are usually provided as a 50/50 mixture of lipid and dextrose. However, if the patient has been preexisting condition (diabetes, hypertriglyceridemia), this ratio may need to be adjusted. To supply 50% of nonprotein kcal with lipid Volume of lipid required = ( ...... nonprotein kcal needed / day * 0.5) ÷ 2 kcal/mL = ...... mL of 20% lipid To supply 50% of nonprotein kcal with dextrose Volume of dextrose required ( ...... nonprotein kcal needed / day * 0.5) ÷ 1.7 kcal = ...... mL of 50% dextrose |
4. Total volume of the solution Total volume of TPN solution = ...... mL 8.5% amino acid solution with electrolytes + ...... mL 20% lipid solution + ...... mL 50% dextrose solution = ...... mL |
5. Calculate the amount of potassium and phosphorus to add to the solution The desired potassium concentration = ...... mEq/L. 8.5% amino acid solution with electrolytes contains 60 mEq/L potassium. Calculate the amount of potassium provided by the amino acid solution: = ( ...... mL of amino acids *60 mEq/L) ÷ 1000 = ...... mEq in ...... mL Total volume of TPN solution = ...... mEq /L. The volume of potassium to add to the parenteral solution to achieve the desired potassium concentration = (desired potassium concentration ...... mEq/L – actual potassium concentration ...... mEq /L) * ...... mL Total volume of TPN solution =vmEq K to add. The desired phosphorus concentration = ...... mM/L. 8.5% amino acid solution with electrolytes contains 30 mM/L phosphorus. Calculate the amount of phosphorus provided by the amino acid solution: = ( ...... mL of amino acids *30 mM/L) ÷ 1000 = ...... mM. Calculate the amount of phosphorus provided by the lipid solution: = ( ...... mL of amino acids *15 mM/L) ÷ 1000 = ...... mM. The amount of phosphorus provided by the parenteral solution = ...... mM/L from amino acid solution + ...... mM/L from lipid solution in ...... mL Total volume of TPN solution = ...... mM /L. The volume of phosphorus to add to the parenteral solution to achieve the desired phosphorus concentration = (desired phosphorus concentration ...... mM/L – actual phosphorus concentration ...... mM /L) * ...... mL Total volume of TPN solution = ...... mM phosphorus to add. |
6. Consider vitamin B supplementation |
7. Administration rate Day 1: ...... mL/hour Day 2: ...... mL/hour Day 3: ...... mL/hour |
Administration
Parenteral nutrition requires a dedicated catheter (central or peripheral) placed aseptically (Table 15). Strict asepsis and regular catheter care should minimize the risk of bacterial colonization and a catheter-related infection. The choice of catheter type may vary depending on the desired formulation (osmolarity and composition), the bleeding propensity of the cat and the available venous access. Triple lumen central IV catheters are often used for CPN. These catheters allow the first port to be used for blood sampling and intermittent drug administration, the second port to be used for continuous medications and fluid adminstration and the third port to be soley dedicated to CPN (Campbell et al., 2006; Delaney et al., 2006). CPN solutions should be administered through a 1.2 μm in-line filter, and as continuous rate infusions utilizing infusion pumps (Chan & Freeman, 2006).
Table 15. Central and Peripheral Intravenous Catheters Recommended For Parenteral Administration in Cats | ||||
Catheter Use | Material | Lumens | Size | Length |
Central jugular for CPN | Polyurethane | 2 - 3 | 4 - 5.5 Fr. | 8 - 13 cm |
Peripheral lateral saphenous for CPN | Polyurethane | 3 | 5.5 - 7 Fr | 30 cm |
Peripheral for PPN | Any | 1 | - | Any |
CPN: central parenteral nutrition - PPN: partial parenteral nutrition | ||||
Hydration status, electrolyte abnormalities and acid-base disturbances should be corrected prior starting parenteral nutrition administration, as provision of nutritional support can cause alterations that may initially worsen these changes. CPN should be instituted gradually over 24 to 48 hours. If there are no complications, the rate of administration can be increased every 4 hours, until the goal rate is achieved (Campbell et al., 2006). Most cats tolerate receiving 50% of total requirements on the first day and 100% on the second day. Cats that have been without food for long periods may require slower introduction (33% on the first day, 66% on the second day, and 100% on the third day). PPN does not require gradual introduction and can be initiated at 100% on the first day. It is important to adjust the cat’s intravenous fluids when initiating parenteral nutrition to avoid fluid volume overload (Campbell et al. 2006, Delaney et al. 2006; Freeman & Chan 2006).
Routine physical examinations including body temperature, heart rate, respiratory rate, twice daily weight measurements, assessment of hydration status, and attitude should be performed on all critically ill patients receiving parenteral nutritional support. To monitor for complications associated with the parenteral nutrition therapy, the packed cell volume, total protein, blood urea nitrogen, serum electrolytes (sodium, potassium, chloride, ionized calcium), venous blood gas and blood glucose concentrations should be monitored every 4 to 6 hours (Table 16). Urine can be checked daily for glucosuria. Serum triglycerides and ammonia concentrations should be determined daily.
Table 16. Potential Complications of Parental Nutrition | ||
| Type of Complication | Methods to Reduce the Risk |
Mechanical | Line breakage Chewed line Disconnected line Perivascular infiltration Catheter occlusion Phlebitis Thrombosis | Aseptic placement of catheter Aseptic handling of catheter and lines Use Elizabethan collars Change bandage and check catheter site daily for swelling, erythema, malpositioning of catheter |
Metabolic | Hyperglycemia Hypoglycemia (when discontinuing parenteral nutrition) Hyper/hyopkalemia Hyper/hypochloremia Hyper/hyponatremia Hyper/hypophosphatemia Hyper/hypomagnesemia Hyperbilirubinemia Hypertriglyceridemia Hypercholesterolemia Refeeding syndrome | Use a conservative approach (RER) for the calculation of caloric requirements Initiate and discontinue parenteral nutrition gradually Monitor glucose and electrolytes daily |
Septique | Clinical signs of sepsis in conjunction with a positive catheter tip or blood culture | Maintain a dedicated catheter Catheter composed of materials of low thrombogenicity Place and handle catheters and lines with aseptic technique Changing catheters at prescribed time Monitor body temperature, catheter site, general attitude If sepsis is suspected, parenteral solution and catheter tip should be cultured |
Complications
Metabolic, mechanical and septic complications can occur in cats receiving parenteral nutrition.
Studies report the rates of metabolic complications in critically ill cats receiving parenteral nutrition to range from 28 - 320% (Table 16). The rates of metabolic complications appear lower when less than full calculated energy requirements are provided (Crabb et al., 2006). The most common metabolic complications described in cats are hyperglycemia, glucosuria, lipemia, hypernatremia, hypokalemia, azotemia, hypocalcemia, hyperchloremia, hypertriglyceridemia, hypophosphatemia, refeeding syndrome and throbocytopenia (Lippert et al., 1993; Chan et al., 2002; Pyle et al., 2004; Campbell et al., 2006; Crabb et al., 2006). These may necessitate adjusting the nutrient ratios, slowing the rate of infusion, or administering insulin, potassium or phosphate supplements. Hyperglycemia appears to be the most common metabolic complication (Crabb et al., 2006). Congestive heart failure can occur secondary to fluid shifts (Freeman & Chan, 2006).
The rate of mechanical complications in critically ill cats receiving parenteral nutrition have been reported to be between 9 - 56% (Lippert et al., 1993; Chan et al., 2002; Pyle et al., 2004; Crabb et al., 2006). Reported mechanical complications include catheter dysfunction or dislodgements, thrombophlebitis, damaged or leaking administration lines, accidental breaking or occlusion of the administration line, and equipment failure. These mechanical complications were rapidly rectified when recognized and usually had little effect on the cat’s outcome (Campbell et al., 2006).
The rate of septic complications has been reported between 3 and 16% (Lippert et al., 1993; Chan et al., 2002; Pyle et al., 2004). Intestinal atrophy that occurs with long-term parenteral nutrition may explain the increased occurrence of bacterial translocation from the gut and sepsis in animals receiving only parenteral nutrition (Campbell et al., 2006). Bacterial infections of the administration line and sepsis can be minimized with sterile placements techniques, sterile parenteral nutrition compounding and regular line care by staff trained specifically in these tasks (Campbell et al., 2006). Rapid removal of any catheter believed to be contributing to localized or systemic infection is advised. The range of potential septic complications includes positive blood cultures, infected catheter sites in febrile animals, positive culture of the catheter tip or the parenteral solution in febrile animals and/or an abnormally high neutrophil concentration (Campbell et al., 2006).
Overall mortality rates in feline patients receiving parenteral nutrition have been reported to be between 19 - 52%, but this is likely influenced by the animal’s underlying medical condition(s) (Lippert et al., 1993; Chan et al., 2002; Pyle et al., 2004; Campbell et al., 2006). Chan et al. (2002) found no differences in metabolic, mechanical or septic complications in cats administered parenteral nutrition centrally versus peripherally. In parallel, this study showed that concurrent enteral nutrition during PN administration was associated with improved survival.
Discontinuing Parenteral Nutrition
Transitioning to oral intake or enteral nutrition should occur as soon as possible to avoid the problem of gut atrophy. In veterinary medicine, parenteral nutrition is typically administered for less than one week. It is important to ensure that the patient is tolerating oral intake or enteral nutrition and is ingesting sufficient amounts (at least 75% of RER) before discontinuing parenteral nutrition. Once the patient is able to eat, it should be offered food regularly to assess its appetite, or a feeding tube should be placed if the animal is anorectic. It is suggested to gradually reduce the rate of administration of CPN over a period of 12 to 24 hours, to allow time for appropriate endocrine equilibration in order to prevent hypoglycemia. PPN can be discontinued abruptly without this gradual decrease (Campbell et al., 2006; Freeman & Chan, 2006).
The use of parenteral nutrition as part of the supportive care plan can be an invaluable addition in select animals. Given cats’ unique nutritional requirements and metabolic particularities, future additional studies aimed at more closely examining PN formulations may lead to the development of a formulation more suitable for cats with a lower overall rate of complications.
Conclusion
Critical care nutrition is a rapidly evolving field. It is clear, and fortunate that the paradigm has changed from waiting until a cat decides to eat on it’s own (and suffers severe body mass loss in the process) to proactively implementing nutritional support as soon as the patient’s life threatening conditions are stabilized.
The consequences of critical illness culminate in significant changes that clearly alter not only nutrient metabolism, but also increase the risk of morbidity and mortality to the patient. Critical steps in management include early recognition of the need to feed the patient, adapting the caloric and nutrient intake to match the metabolic environment and continual monitoring to optimize the prescription and minimize the risk of complications. Aggressive nutritional management will not only increase the survival chances of the critically ill patient, but also aid rapid recovery and return to the home environment.
1. Armitage-Chan EA, O’Toole T, Chan DL. Management of prolonged food deprivation hypothermia, and refeeding syndrome in a cat. J Vet Emerg Crit Care 2006; 16: S34-35.
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Affiliation of the authors at the time of publication
1Ecole Nationale Vétérinaire de Lyon, Marcy l'Etoile, France. 2Royal Canin USA, St Charles, MO, USA.
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