Practical parenteral nutrition--when the gut doesn't work (Proceedings)

October 1, 2011

Article

When patients are unable to tolerate enteral feeding, parenteral (intravenous) nutrition should be considered. A veterinary facility with the ability to obtain and maintain aseptic vascular access, to provide attentive 24-hour nursing care, and to perform in-house serum chemistry analysis can provide parenteral nutritional support. Indications for parenteral nutrition include patients with protracted vomiting, severe malabsorption, prolonged ileus, or at high risk of aspiration. Therefore patients with severe pancreatitis, marked protein losing enteropathy, or patients unable to guard their airway exemplify cases in which parenteral nutrition is likely indicated. Parenteral nutrition can be classified as total parenteral nutrition (TPN) or partial parenteral nutrition (PPN).

TPN provides 100% of an animal's resting energy requirements and must be administered through a dedicated central catheter, such as a jugular catheter, because of its hypertonicity (generally >1000 mOsm/L). Typical TPN admixtures provide energy, protein, certain water soluble vitamins and trace minerals, and may contain additional electrolytes such as potassium. PPN can provide approximately 70% of energy requirements and 50-100% of protein requirements and can be administered through a dedicated jugular or peripheral vein catheter. Because PPN does not provide all energy requirements, it is only intended for short-term use (e.g., 3-5 days) in a patient that is not already debilitated or in a patient who will concurrently be receiving a portion of his nutritional needs via the enteral route.

Animals that are already malnourished, those that have high nutritional requirements, or those with on-going protein loss (e.g., patients with large draining wounds, open abdomen, or severe protein losing enteropathy), or those that have been anorectic for a prolonged period should receive TPN instead.

With either form of parenteral nutrition, it is critical to correct any major fluid, electrolyte, or acid-base abnormalities before initiating parenteral nutrition. Prior to initiating parenteral nutrition, it should be established that the patient is fluid tolerant for the volume of PN to be administered. Evaluation of the patient for conditions which may cause specific nutrient intolerances (such as the hepatic or renal failure patient who may require decreased protein) should be considered. Similar to enteral nutrition, simple worksheets for calculating TPN and PPN requirements can be made available in the hospital for easy use.

TPN should be started gradually (ie, 50% of total requirements on day 1, 75-100% of total requirements on day 2). Therefore, it will take 2-3 days to reach the animal's total nutritional requirements. Therefore, TPN is typically utilized in patients in which it is anticipated that intravenous nutritional support will be necessary for at least 3 days. Since PPN is only providing a portion of the animal's energy requirements, it can be started at the full rate. All parenteral nutrition should only be administered through an accurate fluid pump.

Catheter care is critical to successfully using parenteral nutrition. Whether using a jugular vein catheter for TPN or a peripheral catheter for PPN, the patient's catheter is a dedicated line. That means that is should not be used for administering medications, collecting blood samples, or measuring central venous pressure. Either a separate dedicated catheter or a clearly labeled dedicated line of a multilumen catheter can be used. Calculations for parenteral nutrition formulas supply 24 hours worth of parenteral nutrition so the bag will need to be changed at the end of every 24-hour period. In between the bag changes, the line from the bag to the animal's catheter should not be broken for any reason.

When walking dogs, the line should be removed from the pump, the drip rate should be adjusted (slowed so the dog only receives a small amount during the walk but not clamped off completely which could cause the catheter to clot) and the bag should be carefully carried during the walk. When the bag is changed at the end of every 24-hour period, the lines also should be changed. All handling of the lines and catheters should be done with aseptic technique including sterile placement of catheters and utilizing sterile gloves during bag and line changes to minimize the risk of contamination. The catheter should be carefully rewrapped each day so that the catheter site can be inspected for redness, swelling, or discharge. Finally, catheter type is important to reduce the risk of thrombophlebitis. Long catheters composed of silicone, tetrofluoroethylene (Teflon), or polyurethane should be used for all patients receiving parenteral nutrition.

Routine monitoring is essential to identify potential complications of TPN. The clinical situation should dictate the need as some patients will need more and some less monitoring. Each case is an individual but at least the following should be measured daily in all animals receiving PN:

· Heart/respiratory rate ·Hydration status ·Catheter site

· Attitude ·Glucose ·Body weight

· Temperature ·Check all tubes for lipemia

· Electrolytes (i.e., sodium, chloride, potassium, phosphorus, and magnesium; especially in animals with pre-existing abnormalities, severely ill patients, or in those that have been anorectic >1 week)

Complications of parenteral nutrition are not uncommon but are generally minor. More serious complications can be prevented by recognizing high risk patients and with careful monitoring. Possible mechanical complications include catheter occlusion, line disconnection/breakage, and thrombophlebitis/thromboembolism. The risk for mechanical complications can be reduced by using appropriate catheters, good catheter and line care, and monitoring the catheter site on a daily basis. Recognize that certain patients such as those with receiving high doses of corticosteroids or those with protein losing conditions are at higher risk of thromboembolism.

Metabolic complications are one of the most common occurrences but in most studies, these have been relatively minor and do not require discontinuation of the parenteral nutrition. Hyperglycemia is the most common metabolic complication but can be minimized by using conservative formulations for parenteral nutrition, by starting TPN slowly (PPN can be started at 100%), and by careful monitoring. If glucose concentrations are >200 mg/dL, concurrent insulin administration is recommended. Hypoglycemia can occur with abrupt discontinuation of TPN so patients should be weaned off TPN over 4-6 hours; PPN can be discontinued abruptly. Refeeding syndrome (ie, hypokalemia, hypophosphatemia, and hypomagnesemia) also can occur in animals receiving parenteral nutrition . This occurs most commonly in animals that have not eaten for significant periods of time or in animals with certain predisposing conditions such as diabetic ketoacidosis. This condition usually occurs within 2-3 days of initiating feedings.

Therefore, close monitoring and supplementation of additional electrolytes as dictated by the individual patient's electrolyte profile can prevent serious consequences. Another possible metabolic complication is hypertriglyceridemia. In animals with pre-existing hypertriglyceridemia, the amount of lipid included in the TPN or PPN formulation should be reduced. If hypertriglyceridemia develops, reformulation with a lower lipid content (or without any lipid if triglyceride levels are very high) is necessary.

The complication that is most concerning is sepsis. Fortunately, if careful protocols to compound and administer parenteral nutrition are used, the risk for sepsis is low. Nonetheless, sepsis must be considered in every patient on parenteral nutrition that develops a fever. However, other causes of fever/sepsis should also be considered and ruled out before incriminating parenteral nutrition. If sepsis is suspected, the blood, the parenteral nutrition solution, and the catheter should be cultured.

Once the patient is able to eat, it should be offered food regularly to assess its appetite. The type and amount of food consumed should be carefully recorded. If the gut becomes functional but the patient still will not eat, enteral nutrition techniques should be considered. Oral or enteral nutrition should be used as soon as possible so that gut atrophy can be minimized. When the patient is consuming >60% of its resting energy requirements, parenteral nutrition can be discontinued. For TPN, it should be gradually decreased over a period of 4-6 hours; PPN can be discontinued abruptly.

If a hospital uses parenteral nutrition frequently, it may be most economical to train a technician to compound the parenteral nutrition formulas using sterile technique. If it is not used frequently, it usually is more economical to have parenteral nutrition compounded by a local human hospital or by a human home healthcare company.

Total Parenteral Nutrition (TPN) Worksheet

Patient Name_______________________ Case # __________

Date TPN Initiated ________________ Body Condition Score (1-9) __________

Actual Body Weight_________________kg Muscle Condition Score __________

1. Resting energy requirement (RER)

70 (weight in kg).75 = kcal/day

or for animals 3-25 kg, can also use:

30 (weight in kg) + 70 = kcal/day RER = __________kcal/day

2. Protein requirement Canine Feline

*Standard 4 gm/100 kcals 6 gm/100 kcals

*Decreased requirements (hepatic/renal failure) 2-3 gm/100 kcals 3-4 gm/100 kcals

*Increased requirements (protein-losing conditions) 6 gm/100 kcals 6 gm/100 kcals

(RER¸100) x ___________gm/100 kcals = __________gm protein req/day

3. Volumes of nutrient solutions required

a. 8.5% amino acid solution = 0.085 gm protein/ml

________g protein/day/ 0.085 g/ml = ________ml/day of amino acids

b. Non-protein calories:

Calories supplied by protein (4 kcal/gram) are subtracted from the RER to get non-protein calories needed.

_____g protein req/day x 4 kcal/gram = _____kcals provided by protein

_______RER - kcals provided by protein = ____total non-protein kcals needed/day

c. Non-protein calories are usually provided as a 50:50 mixture of lipid and dextrose. However, if the patient has a pre-existing condition (eg, diabetes, hypertriglyceridemia), this ratio may need to be adjusted

*20% lipid solution = 2 kcal/ml

To supply 50% of non-protein calories

________lipid kcal required/ 2 kcal/ml = __________ml of lipid

*50% dextrose solution = 1.7 kcal/ml

To supply 50% of non-protein calories

________dextrose kcal required/ 1.7 kcal/ml= __________ml dextrose

4. Total daily requirements

__________ml 8.5% amino acid solution

__________ml 20% lipid solution

__________ml 50% dextrose solution

__________ml total volume of TPN solution

5. Vitamins: B vitamins can be added to the TPN at the time of compounding using sterile technique. For a B vitamin complex containing 2 mg/ml of riboflavin, the authors use a dose of 0.2 ml/100 kcals.

6. Using standard amino acids (8.5% amino acids which contain electrolytes), TPN made according to this worksheet will provide potassium at higher than maintenance levels (from 25 mEq/L potassium at 3 gm protein/100 kcal to 38 mEq/L potassium at 6 gm protein/100 kcal). Therefore, you may not need to supplement potassium in any other fluids your patient is receiving. If your patient is hypo- or hyperkalemic, adjustment of the TPN formula may be indicated depending upon other fluid being administered (eg, potassium can be supplemented for hypokalemia and amino acids without electrolytes can be used for hyperkalemia).

7. Administration rate

Day 1: __________ml/hr (33-50% of total)

Day 2: __________ml/hr (66-100% of total)

Day 3: __________ml/hr (100% of total)

Be sure to adjust the patient's other fluids accordingly!

The monitoring required will depend upon the individual patient. However, at least the following should be measured daily:

· Heart/respiratory rate

· Attitude

· Temperature

· Catheter site

· Body weight

· Glucose

· Check all tubes for lipemia

· Electrolytes

Partial Parenteral Nutrition (Ppn) Worksheet

Patient Name_______________________ Case # __________

Date PPN Initiated _______________ Body Condition Score (1-9) __________

Actual Body Weight_______________kg Muscle Condition Score __________

1. Resting energy requirement (RER)

70 (weight in kg).75 = kcal/day

or for animals 3-25 kg, can also use:

30 (weight in kg) + 70 = kcal/day RER = __________kcal/day

2. Partial energy requirement (PER)

Plan to supply 70% of the animal's RER with PPN:

PER = RER x 0.70 = ___________kcal/day

3. Nutrient requirements

(Note: For animals £3 kg the volume of fluids will be >maintenance fluid requirements)

a. Cats and Dogs 3-5 kg:

PER x 0.20 =__________kcals/day carbohydrate required

PER x 0.20 =__________kcals/day protein required

PER x 0.60 =__________kcals/day lipid required

b. Cats and Dogs 6-10 kg:

PER x 0.25 =__________kcals/day carbohydrate required

PER x 0.25 =__________kcals/day protein required

PER x 0.50 =__________kcals/day lipid required

c. Dogs 11-30 kg:

PER x 0.33 =___________kcals/day carbohydrate required

PER x 0.33 =___________kcals/day protein required

PER x 0.33 =___________kcals/day lipid required

d. Dogs >30 kg:

PER x 0.50 =___________kcals/day carbohydrate required

PER x 0.25 =___________kcals/day protein required

PER x 0.25 =___________kcals/day lipid required

4. Volumes of nutrient solutions required

a. 5% dextrose solution = 0.17 kcals/ml

______kcals carbohydrate required/day/0.17 kcals/ml = ____ml/day dextrose

b. 8.5% amino acid solution = 0.085 g/ml = 0.34 kcals/ml

____kcals protein required/day/0.34 kcals/ml =__________ml/day amino acid

c. 20% lipid solution = 2 kcal/ml

__________kcals lipid required/day/2 kcals/ml = __________ml/day lipid

5. Total daily requirements

__________ml 5% dextrose solution

__________ml 8.5% amino acid solution

__________ml 20% lipid solution

__________ml total volume of PPN solution

6. Vitamins: B vitamins: B vitamins can be added to the TPN at the time of compounding using sterile technique. For a B vitamin complex containing 2 mg/ml of riboflavin, the authors use a dose of 0.2 ml/100 kcals.

7. The standard amino acids used in PPN contain potassium. For animals <35 kg, the PPN solution made according to this worksheet will provide approximately maintenance levels of potassium. For animals >30 kg, the PPN solution will contain approximately 12 mEq/L of potassium. Therefore, supplementation may be required depending upon other fluid being administered.

8. Administration rate. This formulation provides approximately a maintenance fluid rate. Note that in some cases, the calculated PPN rate may be greater than maintenance fluid requirements or greater than what the animal can tolerate (eg, cardiac disease). Adjustment of the formula will be needed in these cases. __________ml/hour PPN solution