A pediatric nutrition manual will be available to every resident and provides a basic dissertation on the principles of pediatric nutrition. This is to provide an abbreviated form and not to replace the actual manual. The hospital and JCAHO mandates that all patients be screened for nutritional status after three days (ICU patients sooner). You will see these screening notes on the chart and the dietitian may speak to you about their concerns. These must be relayed to the fellow or service attending for discussion. Consultations for nutritional support from the GI service are only obtained upon attending request.
0-1 year 90-120 kcal/kg/day
1-7 years 75-90 kcal/kg/day
7-12 years 60-75 kcal/kg/day
12-18 years 30-60 kcal/kg/day
Of course, physical status (metabolic condition, bedridden, active) will impact on these baseline values.
For infants, the basic principle is that sufficient calories need to be supplied to assure continued growth and development. For chronically hospitalized infants it is important to maintain an accurate growth record in the front of the chart and /or at the bedside.
The expected weight gain is 1% of the infants weight per day. i.e. a 2 week old, 1kg, 34 week gestation infant should gain about 10 g/day.
The problem in very small infants can be that it is difficult to achieve a certain caloric intake without exceeding fluid intake limitations for that reason both ml/kg/d and kcal/kg/d should be calculated daily.
ENTERAL NUTRITION IN THE INFANT
A simple approach to infant formulas: There is a multitude of formulas that all seek to provide nutrients similar in composition to human breast milk.
The primary components of any nutritional product are the 1) protein source, 2) carbohydrate source and 3) fat source. How these are supplied is what constitutes the difference between the various infant formulas and breast milk. The osmolarity of the solution and electrolyte composition have additional and significant effects that must be considered in the enteral nutrition of the premature newborn in particular.
Most formulas can come either premixed or as a powder that gets reconstituted with water which permits changes in the caloric density (and osmolarity). This is just the opposite of what we, as surgeons, do when we dilute feedings to reduce the osmolar load in the initial refeeding mode!
The table below is meant to give a simple stratification of the most commonly used formulas. There are many more very specialized formulas on the market. More complete references can be sought elsewhere.
Lactose based formulas:
Similac, Enfamil and SMA
The protein source is whey and casein and the fat source in primarily coconut and soy oils.
The Protein:Fat:CHO ratios are about the same and the osm for 20kcal formula is 300 mOsm/kg of H2O. These are simply products of different manufacturers!
Lactose free formulas:
Isomil, Prosobee and Nursoy
Sucrose is the CHO source, along with corn syrup solids in the first two formulas. The protein source is soy protein in all three and the fat source is the same as before (coconut and soy oils). Again, the same three companies make lactose free products.
Protein hydrolysate formulas (for infants with absorption problems):
Alimentum, Nutramigen, Pregestimil and Portagen.
These are all casein hydrolysates. Their CHO and fat sources vary (see below). There is significant variability in the osmolarity in these formulas, with Pregestimil closest to normal.
Alimentum, because of its higher osmolarity needs to be used with caution. Nutramigen differs from Pregestimil and Portagen in that the latter two are appropriate for situations in which the long chain fatty acids need to be limited. However, Portagen provides lactose, which may be a problem for some infants.
The Premie formulas:
Enfamil Premature and Similac Special Care:
These formulas are lactose based with other carbohydrate sources, the protein source is whey/casein and the fat source is a combination of MCT/soy and coconut oils. They differ from their regular infant formula counterparts in that they have 1) other sources of CHO, 2) twice-higher amounts of sodium and calcium per 100 ml and 3) slightly more iron.
After the first year of life:
Cows Milk is generally not appropriate until after the first year. At that time the composition of formulas for those children who are dependent on tube feedings or non-solid nutrition, also changes. Typical formulas include Pediasure, Isocal, Osmolite, Sustacal, and Ensure. Again CHO and protein as well as fat sources differ. They have a higher caloric density, usually 30kcal/oz (one kcal/cc) and come in low or high residue varieties.
In writing TPN orders, there are some additional principles to adhere to beyond the simple provision of calories. We can divide this conceptually, much as we did in the section on enteral nutrition, into the provision of carbohydrate, protein and fat intravenously.
The amount of dextrose supplied per day, the caloric density and particularly the rate at which it is administered are critical.
The caloric density of carbohydrates in solution is 3.4 kcal/g glucose. From this one can derive the caloric density of any % dextrose solution.
D10W solution has 10g glucose/100 ml and provides (10gm x 3.4kcal/g)/100ml = 0.34kcal/ml
D20 W solution has twice the caloric density, 0.68kcal/ml. The other solutions density can similarly be calculated, but are provided in the table below.
Peripheral TPN, (rarely used in surgical patients) should not exceed D12.5W and central TPN should not exceed D20W, unless there are severe restraints on fluid intake. D25W - D30W have osmolarities of between 1200 and 1700 mOsm/L. These solutions are useful for patients on ECMO support where not only are the fluids restricted, but also, the large cannula in the atrium allows for prompt dilution of the infusate.
When initiating TPN, the rate of glucose provision should be increased incrementally. In neonates and premature neonates this requires calculation of total grams of glucose provided per day and at an initial rate probably not exceeding 6.5mg/kg/hr. For older infants and children this can be accomplished most easily by starting with D10TPN and progressing to D20TPN over about 3-4 days, while providing it at rates sufficient to support maintenance fluid requirements. Alternatively, in an older child one can start with D20TPN, but infuse it at a rate 25% of the ultimate goal rate and increase by 25%/day. This requires other fluids to be infused concurrently to meet fluid requirements. (This may not be feasible when IV access is limited and you have a line that you want to devote to TPN only). To monitor tolerance of the dextrose infusion, urine should be dipped for glucose and blood dextrostix should be obtained every 6 8 hours until 24 hours at the goal rate have been attained. Then monitoring decreases to once a day.
Fat is used as an energy source and to provide essential fatty acids (linoleic and linolenic acid). With a caloric density of 9 kcal/g, it is a valuable source of calories in parenteral nutrition.
Normally 30-40% of total calories is provided by fat in the form of 20% intralipid solution. It is generally undesirable to exceed 50% of calories. Exogenous fat is handled and metabolized in the same manner as that presented as chylomicrons. Lipid emulsions should therefore be infused cautiously. The enzyme lipoprotein lipase can be saturated by an excessive infusion, which results in lipidemia.
Monitor the effect of infusion by measuring the serum triglyceride level. The goal is <200mg %.
Caution should be used in infusing fat emulsion in premature infants with pulmonary insufficiency, liver failure, jaundice and coagulation disorders. In older children, an allergy to egg whites is a contraindication to use of intralipid.
The amino acid composition of neonatal, childhood and adult TPN differ as there are some amino acids that appear to be conditionally essential during the early phases of life. Further changes occur when there is impairment of either renal or hepatic function.
The calories that could potentially be derived from these solutions are not calculated into the calorie provision. Protein requirements for growth and repair must be met and are generally age dependent. (See table)
The "total calorie" to nitrogen ratio of the TPN formulation has great impact on the optimal utilization of the carbohydrate calories and potentially on the incidence of TPN associated liver disease. Ideally it ranges from 150-180:1. In order to calculate this ratio you must calculate a total number of kilocalories provided by both the dextrose and fat emulsion over one day and divide it by the grams of nitrogen infused with that same volume of TPN. An example follows:
These components of TPN exist in infant and pediatric formulations and are ordered on a per kg basis. There are specific instances when these substances need to be reduced or even withheld. This will be indicated by the fellow or attending monitoring the TPN orders.
An example for calculating goal TPN/Intralipid volumes for an infant or child:
Example: You are asked to start TPN on a 20kg child.
The estimated caloric need is 80 kcal/kg/day
The total fluid rate will be approximately 20% higher than this number, i.e. 80+16=96ml/kg/d
That would be 20kg x 96 = 1920ml/d = 80ml/hr
10% of this rate should be the intralipid rate and the other 90% should be TPN infusion rate.
IL @ 8ml/hr = 192ml/d = 384kcal/day
TPN @ 72ml/hr = 1728ml/d = 1175kcal/day
Total kcal/day = 1559 divide by 20kg= 78kcal/kg/d. If the child is getting close to 3g/kg/d of protein in the TPN, then
the cal:N ratio will be 162:1. Remember that these are the goal concentrations/rates for infusion and not the initial ones! For instance: initiate D10TPN at 72ml/hr and 20 % IL at half the goal rate 4ml/hr. The next day advance to D15TPN at 72ml/hr and increase IL to 6ml/hr, then advance to D20TPN at 72ml/hr and IL at 8ml/hr, if glucose and lipid tolerance are verified. (Dextrostix and triglyceride levels).
Careful monitoring of fluid status and weight gain will allow for subsequent adjustments.
Cycling TPN is a maneuver to further reduce the pathophysiologic consequences of TPN administration. It needs to be achieved gradually and the usual goal is to infuse the necessary volume of TPN and intralipid over a 16 18 hour period. One hour at each end of the infusion time will have the solution running at half the normal rate to allow the pancreas to adjust insulin/glucagon secretion to prevent hypo- or hyperglycemia. To calculate these rates divide the total volume of TPN/day by the number of hours for infusing minus one to obtain the rate of infusion during the main period of infusion. One half that rate is the step-up and step-down rate.
Example: from the previous 20-kg child example.
The 1920cc volume is to be infused over 18 hours.
1920/ (18-1) = 113cc/hr
Start the infusion at 56cc/hr x 1 hr then
Increase to 113cc/hr x 16 hours then
Decrease to 56cc/hr x 1 hr
then stop TPN for 6 hours before resuming the cycle.
Running D10 solution or other fluid should be unnecessary if the patient has been gradually tapered to this regimen from a 24-hour infusion protocol.
Intralipids are not tapered so the rate of the intralipid will be 192/18 = 10.6cc/hr x 18hrs.
This is a lot of calculator time but it is part and parcel of pediatric surgery.