Parenteral Feeding
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6. Parenteral Feeding
Parenteral feeding is expensive and technically demanding. It is reserved for cases in which the digestive tract must be rested for medical or surgical reasons or in recumbent patients.
Practical Aspects
Preparation
All the elements are mixed carefully in a sterile bag, in the following order: glucose then amino acids then lipids. The introduction of lipids at the end avoids the risk of emulsion destabilization. The bag is refrigerated and the contents used in less than 48 hours by connection to the intravenous infusion system.
Catheter Placement Sites
The dog is anesthetized or simply tranquilized if it is already weak. The injection site is surgically prepared (Figure 11).
Figure 11. Placement of a central jugular catheter. (© UCD VMTH ICU Service).
Due to their high glucose and amino acid content the solutions for parenteral feeding are often very hypertonic. Their administration must therefore be accomplished with a central catheter placed in the cranial (jugular approach - Figure 12) or caudal vena cava (saphenous approach). The major blood flow of these veins permits rapid dilution of the mixture.
Figure 12. The high flow of the cranial vena cava permits rapid dilution of the parenteral solution. (© UCD VMTH ICU Service).
Rate of Administration
The rate of administration of parenteral solutions is limited by three main factors - fluid volume, osmolarity and the creation of metabolic disturbances. Software is available that can adjust the infusion flow based on the characteristics of the animal.
Fluid Volume
Fluid volume is rarely a major concern except in patients that are fluid overloaded or oliguric/anuric, for example, patients with congestive heart failure, acute renal disease or terminal chronic renal disease. When fluid volume is a concern, an effort should be made to increase the energy density of the solution by increasing the lipid emulsion content when possible.
Figure 13. Adjusting the infusion (for crystalloid solutions only). (© La Semaine Vétérinaire and JY. Deschamps).
Electrolyte Composition
The electrolyte composition of the parenteral solution can also be adjusted along with the amount of free water to allow for its use as a maintenance fluid and decrease overall administered fluid volume. Use of a solution with a high osmolarity can increase the risk of thrombophlebitis (Roongpisuthipong et al., 1994). For example, a solution with an osmolarity of 650 mOsmol/L delivered through a peripheral catheter at maintenance fluid rates is well-tolerated (Chan et al., 2002; Chandler et al., 2000a). However, the same solution delivered at twice the maintenance rate will not be as well-tolerated based on human studies (Kuwahara et al., 1998). On the other hand, a solution with an osmolarity of 1300 mOsmol/L may theoretically be tolerated if delivered at one half of the normal maintenance rate.
Metabolic Complications
Common metabolic complications associated with parenteral nutrition include:
- Hyperglycemia
- Hyperlipidemia
- Refeeding Syndrome.
Hyperglycemia can be associated with the rapid administration of dextrose containing solutions that exceed the ability of the pancreas to respond to the hyperglycemia and to secrete appropriate concentrations of insulin. Avoidance of hyperglycemia is frequently achieved by reducing the rate of infusion and/or the administration of exogenous insulin.
Table 2. Protocol to Regulate Blood Glucose (BG) Concentrations | |
Protocol Blood Glucose Initially start the infusion at 1/4 to 1/3 of goal rate and wean on per guidelines below increasing the rate in 1/3 to 1/4 of goal rate increments. The same recommendations in reverse apply to discontinuing the infusion. Recommend checking the administration rate every 4hr until 100% of goal rate is achieved. | |
Blood Glucose(mg/dL) | Action |
< 70 mg/dL or 4 mmol/L | Possible problem with the measurement, administration, formula and/or patient. Check to ensure that the correct solution is being administered and that the patient does not have an underlying reason to become hypoglycemic. Consider increasing the administration rate and/or concentration of dextrose in the formula. |
< 250 mg/dL or 14 mmol/L | Increase the infusion rate towards 100% of the goal rate if weaning on. Continue at the present rate if already at 100% of goal rate. |
250 - 300 mg/dL or 14 - 17 mmol/L | Hold the present infusion rate during the weaning on period. Continue the infusion at the present rate if already at 100% of goal rate. Decrease the administration rate if the glucose level continues to be elevated over three to four measurements obtained at 4hr intervals or if the urine glucose is over 1+ on a urine dipstick test. |
> 300 mg/dL or 17 mmol/L | Decrease the infusion rate. If the goal rate cannot be reached without >300 mg/dL glucose levels consider: 1. Accepting the highest infusion rate that the animal will tolerate; 2. Adding regular insulin to the nutrient solution (1 unit/10 g dextrose) 3. Decreasing the dextrose content of the solution. |
Similarly a state of hyperlipidemia may develop when the patient's ability to metabolize the delivered fat is exceeded.
The Refeeding Syndrome refers mainly to electrolyte shifts associated with glucose transport into cells following the reintroduction of food after prolonged anorexia. To minimize most of these complications careful monitoring and a weaning protocol should be utilized. Should electrolyte abnormalities occur with refeeding, the authors recommend reducing and/or gradually discontinuing the rate of solution administration, while simultaneously correcting any electrolyte abnormalities. Once the electrolyte abnormalities have resolved, then administration can be resumed or increased to meet energy requirements.
Covering Nutritional Requirements
Table 3. Canine Parenteral Nutrition Worksheet
Table 3-1. Determine if the Solution Is to Be Administered Peripherally or Centrally |
If peripheral, use a 5% dextrose solution. If central (i.e. for a dog with a jugular catheter), use a 50% dextrose solution. |
Table 3-2. Select the Desired Caloric Distribution on a Percent of Metabolizable Energy (%ME)* | |||
| Protein (%ME) | Fat (%ME) | Carbohydrate (%ME) |
Low | 8 - 10 | 20 | 0 - 18 |
Normal | 16 - 18 | 30 - 58 | 20 - 50 |
High | 20 - 22 | 60 - 80 | Contraindicated |
* Only one macronutrient can be low or high at one time. Thus, the other two macronutrients must be in the normal range if the third is low or high. The exception to this rule is when creating a high fat solution. | |||
Selected % ME protein | ... % | ||
Selected % ME fat | ... % | ||
Selected % ME carbohydrate (CHO) | ... % | ||
TOTAL (MUST = 100%) | ... % | ||
Table 3-3. Calculate Daily Caloric Requirement of the Hospitalized Patient | |
If to be delivered peripherally (not using a high fat solution) | 1/2 RER = 35 x (... body weight in kg)0.75 = ... kcal/day |
If to be delivered peripherally (using a high fat solution) or centrally | RER = 70 x (... body weight in kg)0.75 = ... kcal/day |
Table 3-4. Calculate the Daily Volume of each Macronutrient | ||
... % of ME protein | x ... kcal/day = ... ÷ ... kcal/mL for amino acid solution | = ... mL |
... % of ME fat | x ... kcal/day = ... ÷ ... kcal/mL for lipid emulsion solution | = ... mL |
... % of ME CHO | x ... kcal/day = ... ÷ ... kcal/mL for dextrose solution | = ... mL |
TOTAL ml = ... mL | ||
Table 3-5. Check the Osmolarity | ||
... mL of amino acid solution | x ... mOsmol/mL of amino acid solution | = ... mOsmol |
... mL of lipid emulsion solution | x ... mOsmol/mL of lipid emulsion solution | = ... mOsmol |
... mL of dextrose solution | x ... mOsmol/mL of dextrose solution | = ... mOsmol |
TOTAL mOsmol = ... mOsmol | ||
(... Total mOsmol ÷ ... Total mL) x 1000 = ... mOsmol/L) if mOsmol/L > 750 mOsmol/L & the solution is to be delivered peripherally, increase the %ME fat if mOsmol/L > 1400 mOsmol/L & the solution is to be delivered centrally, increase the %ME fat 6 | ||
Table 3-6. Calculate Energy Density of the Solution | ||
... mL of amino acid solution | x ... kcal/mL of amino acid solution | = ... kcal |
... mL of lipid emulsion solution | x ... kcal/mL of lipid emulsion solution | = ... kcal |
... mL of dextrose solution | x ... kcal/mL of dextrose solution | = ... kcal |
TOTAL kcal = ... kcal | ||
(... Total kcal ÷ ... Total mL) x 1000 = ... kcal/L) if the kcal/mL < 0.4 kcal/mL and the solution is to be delivered peripherally (not using a high fat solution), increase the %ME fat and/or check the calculations if the kcal/mL < 0.7 kcal/mL and the solution is to be delivered peripherally (using a high fat solution), increase the % ME fat and/or the % ME protein and/or check the calculations if the kcal/mL < 0.9 kcal/mL & the solution is to be delivered centrally, increase the %ME fat and/or check calculations. | ||
Table 3-8. Calculate the Amount of Vitamin B Complex to Add to the Solution | |||
a. There is a wide variation in the concentrations of B vitamins in commercially available products. Provide enough B Vitamins to meet the following requirements: | |||
Thiamine | 0.29 mg/1000 kcal solution | ||
Riboflavin | 0.63 mg/1000 kcal solution | ||
Pantothenic acid | 2.9 mg/1000 kcal solution | ||
Niacin | 3.3 mg/1000 kcal solution | ||
Pyridoxine | 0.29 mg/1000 kcal solution | ||
Vitamin B12 | 0.006 mg/1000 kcal solution | ||
Supplementation with fat soluble vitamins or trace minerals does not appear to be essential. Unless a specific deficiency is evident, the likelihood of developing a clinically significant deficiency in two to three weeks is highly unlikely. | |||
b. Recommended concentrations and characteristics of macronutrients | |||
| mOsmol/mL | kcal/mL | g protein/mL |
8.5% amino acid solution without electrolytes | 0.78 - 0.88 | 0.34 | 0.085 |
20% lipid emulsion solution | 0.27 | 2.0 |
|
5% dextrose solution | 0.25 | 0.17 |
|
50% dextrose solution | 2.52 | 1.7 |
|
NOTE: There is debate regarding the amount of amino acids available for protein synthesis if the patient’s resting energy requirement (RER) is not met. Therefore, some clinicians will provide the patient with their RER exclusively from fat and carbohydrate and calculate the protein requirement separately. The authors have included the energy contribution of protein in their parenteral solution calculations to provide consistency with accepted methods of evaluating oral/enteral diets. To determine the grams of protein per 100 kcal calories the following calculation can be performed: | |||
c. Standard canine recommendations on a g protein/100 kcal basis | |||
Low | < 4.0 g/100 kcal | ||
Normal | 4.0 - 8.0 g/100 kcal | ||
High | > 8.0 g/100 kcal | ||
Dextrose
It is common for clinicians to "spike" crystalloids used for fluid therapy with dextrose in an attempt to provide some nutritional support. Since chronic infusion of greater than 5% is not performed due to the concern of thrombophlebitis from a hyperosmolar solution, patients only receive approximately a third of their RER when this solution is administered at maintenance fluid rates. There is debate regarding the protein-sparing effect that 5% dextrose provides, but limited research has shown that it is not enough to prevent a negative nitrogen balance (Chandler et al., 2000b).
Case study: A 20-kg dog whose resting energy requirement equals 70 x (20)0.75 = 660 kcal/day.
A liter of 5% dextrose solution provides 200 kcal. 3.3 L will therefore be necessary to cover the dogs daily RER, which is much greater than the volume needed to guarantee the dog’s hydration status and would most likely result in thrombophlebitis.
Amino Acids
A study did find that infusion of a 5% amino acid solution resulted in a mean positive nitrogen balance in three, healthy dogs (Chandler et al., 2000b). However, the success of this therapeutic approach in a larger population of dogs in a catabolic state needs to be determined before this form of nutritional support can be endorsed.
Fats
The ideal solution for parenteral administration would be an energy dense solution with a low osmolarity. Some view lipid emulsions as such an ideal solution. For example, a 20% lipid emulsion can provide 2 kcal/mL with an osmolarity of 268 mOsmol/L. Although the kcal to osmolarity ratio of this solution is ideal, concern exists regarding excessive fat administration. Intravascular fat accumulation has been reported in premature infants with liver dysfunction receiving lipid emulsions (Levene et al., 1980; Puntis & Rushton, 1991; Toce & Keenan, 1995).
In the limited number of cases where this approach has been used, patients have tolerated solutions providing up to 80% of RER from fat. The safety and efficacy of administering 100% of a patient's RER from fat requires further investigation and cannot be recommended at this time.
Monitoring Protocols for Parenteral Feeding Must Include the Following Daily Evaluations:
- Body weight
- Temperature
- Pulse
- Breathing and heart rate
- Thoracic auscultation
- Catheter position and integrity
- Blood glucose concentration and/or urine glucose every 4 hours during the weaning on period
- Hematocrit and evaluation of serum for lipemia or jaundice.
- Potassium and phosphate in the 12 - 24 hours following initial administration
- BUN and albumin concentration in the 24 hours following initial administration, and thereafter every 2 - 3 days.
It is also recommended to measure ionized magnesium concentrations (where possible) in the 24 hours following initial administration, and perform a complete blood count and biochemical panel every 2 - 3 days. Depending on the case, thoracic radiographs and serum triglyceride analyses may be of value.
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Affiliation of the authors at the time of publication
1School of Veterinary Medicine, University of California, CA, USA.2Department of Molecular Biosciences, University of California, CA, USA. 3Royal Canin, St Charles, MO, USA.
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