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Adequate nutritional support of a child with critical disease is of paramount importance because it can decrease morbidity and mortality (see Chapter 77 ). It is essential to try to meet the caloric and mineral requirements of these patients. The nutritional requirements for healthy children have been defined, but the requirements of critically ill children are less well understood; measurements of oxygen consumption and nitrogen balance are not easy bedside maneuvers.
Even when caloric needs can be ascertained, it may be difficult to deliver adequate amounts because of extenuating circumstances such as bowel compromise, severe fluid restriction for either renal or CNS disease, and glucose intolerance. Therefore, all avenues of nutrition (enteral and parenteral) must be explored, and nutritional intervention must be implemented early, before a catabolic state ensues.
Use of the GI tract for alimentation is usually the safest and most efficient approach. Numerous commercial formulas with variable sources and quantities of protein, fat, and carbohydrate are available. Protein requirements can be met by using whole protein, protein hydrolysates, or individual amino acids. Whole protein, which has the least osmotic effect, allows for greater nutrient density. However, it can be used only in children with normal pancreatic function and no allergy. Children with protein allergy, pancreatic deficiency, or severe intestinal mucosal disease may benefit from a protein hydrolysate. However, these formulas have high osmolarity. Free amino acid formulas are also available and are used in chemically defined diets restricted by specific requirements or intolerances.
The high caloric density of fat makes it an important component in nutritional support. A long-chain triglyceride (LCT) yields approximately 9 kcal/g, whereas a medium-chain triglyceride (MCT) yields 8.3 kcal/g. Though of greater caloric density, LCTs are less readily absorbed. MCTs are hydrolyzed more rapidly and are converted almost exclusively into free fatty acids and glycerol. MCTs are absorbed even in the absence of lipase because of their relative water solubility and emulsification properties. However, there are drawbacks. For example, MCTs may cause osmotic diarrhea, and they contain no essential fatty acids, so linoleic acid must be added to the diet separately.[292]
Secondary disaccharidase deficiency is a common carbohydrate absorption problem in a critically ill child. Lactase function is easily impaired by hypoxia and ischemia, as well as by infection and malnutrition.[293] In these situations, lactose should be avoided and replaced with sucrose or Polycose, which have the least osmotic effect. Enteral feedings can be delivered orally, through a nasogastric tube, or through a gastrostomy tube. Children with an ETT in place can be safely fed through a nasogastric tube; the risk of aspiration is minimized by using a continuous infusion of formula rather than bolus feedings and by placing the child in an upright semisitting position. Opioid analgesics and muscle relaxants hinder enteral feeding; if possible, these groups of drugs should be avoided.
Parenteral nutrition is used in children who cannot tolerate enteral feedings. It is used as supportive therapy in critically ill children with acute respiratory or GI disease and as primary treatment in those with chronic short-bowel syndrome, Crohn's disease, and renal failure.
When intravenous alimentation is considered, 10% dextrose in water (D10 W) is administered at 1 to 1.5 maintenance levels for 24 hours. The patient is closely monitored for glycosuria, hyperglycemia, and edema. If a glucose load is tolerated, a D10 W solution with amino acids (PN-10) can then be initiated. Administration of D10 W with or without amino acids can be done safely through either a central or peripheral catheter. Any more concentrated formula causes sclerosis of peripheral veins and must therefore be given through a centrally placed line. If a central line has been placed and the patient is tolerating the relatively high glucose loads of 1.5 maintenance with PN-10 or D10 W, one may switch to PN-20 and simultaneously decrease the fluid rate to maintenance levels to permit accommodation to the higher glucose load. PN-20 is then advanced over a period of 2 days to the 1.5 maintenance rate. The patient should gain relatively little weight until 1.5 maintenance with PN-20 is achieved.[294] In general, if a patient is malnourished (<0.80 weight for height), fluid rates must be adjusted downward to roughly 80% of those for children of the same weight. After 1 week of nutritional rehabilitation, regular maintenance fluids may be used ( Table 76-15 ).
Frequently, the physician has determined a different maintenance fluid rate for a particular patient on the basis of previous intake/output data. If such is the case, the patient should start taking D10 W at the low side of
| Regular Maintenance Weight | Malnourished Body (mL/kg/day) | Maintenance (mL/kg) |
|---|---|---|
| 1st 10 kg | 100 | 80–90 |
| 2nd 10 kg | 50 | 40 |
| Wt > 20 kg | 20 | 20 |
With central intravenous alimentation, lipid is necessary only to prevent essential fatty acid deficiency and should be given as 5% to 10% of the total calories.[296] The following fluid rate permits rough determination of the lipid rate necessary to prevent essential fatty acid deficiency during central intravenous alimentation: 5 to 10 mL/kg for the first 10 kg, 2.5 to 5 mL/kg for the second 10 kg, and 1.25 to 2.5 mL/kg for weight greater than 20 kg. Lipids are usually introduced a number of days after parenteral nutrition has been started. There are multiple reasons for withholding lipid during the initiation of intravenous alimentation. First, tolerance of lipid products is improved if the patient has been primed by a period of adequate caloric intake. Second, fatty acids may impair the patient's tolerance of the large dextrose load. With increasing dextrose administration, the simultaneous introduction of fat products may confuse the interpretation and treatment of glycosuria. Lipemia checks should be performed whenever lipid is used.
With peripheral intravenous alimentation (10% concentration), the lipid product must constitute a major component of the caloric intake because it is the only isomolar product of sufficient caloric density to provide significant caloric intake by peripheral vein. Thus, once a patient receiving peripheral alimentation has reached a maximum rate of PN-10, Intralipid may be added at a rate of 10 mL/kg/day and advanced by 10 mL/kg/day to a maximum of 40 mL/kg/day. However, lipid calories must not exceed 60% of the total calories.[297] Lipid clearance may be facilitated by administering lipid continuously over a 24-hour period. Serum lipemia is monitored daily during lipid administration. For calculations, the caloric densities shown in Table 76-16 may be used.
| Lipid Product | Caloric Density |
|---|---|
| Amino acids | 3.33 cal/g |
| 10% dextrose | 0.34 cal/mL |
| 20% dextrose | 0.68 cal/mL |
| PN-10 | 0.39 cal/mL |
| PN-20 | 0.73 cal/mL |
| Lipid 10% | 1.1 cal/mL |
| Lipid 20% | 2.0 cal/mL |
Peripheral intravenous alimentation is a stopgap measure that rarely permits caloric intake in excess of maintenance requirements. Therefore, there are few extra calories available for growth and repletion. Peripheral intravenous alimentation should be limited to 2 weeks' duration. By contrast, central alimentation can provide caloric and nitrogen requirements for both growth and maintenance. However, an increased risk of infection is associated with the prolonged use of indwelling catheters.[298]
Caloric requirements represent the energy intake necessary for maintenance, growth, and activity. Whatever net energy is left after allowance for maintenance and activity is available for growth. The caloric cost of growth is at least 5 cal/g weight. Normal growth is approximately 25 to 30 g/day for the first 6 months of life, 10 to 15 g/day for the next 6 months, and roughly 7 to 10 g/day thereafter. Representative maintenance energy requirements for the nonstressed state are listed in Table 76-17 . By using these data, intravenous alimentation can be adjusted to produce normal or moderate catch-up growth rates. Weight gain in the face of inadequate caloric intake (less than maintenance) inevitably means edema. If the goal of nutritional therapy is merely supportive over a period of 1 to 2 weeks, growth may not be necessary, and peripheral alimentation may therefore be adequate. If significant catch-up growth or long-term support is required, the child's growth and activity requirements should be met.[295]
Intake, output, and body weight should be assessed carefully on
a daily basis. The site of alimentation, either
| Age (yr) | Maintenance Energy (kcal/kg/day) |
|---|---|
| <2 | 75–80 |
| 2–5 | 70–75 |
| 5–10 | 55–70 |
| 10–17 | 40–55 |
| Adult | 40 |
A child's survival obviously depends on adequate nutritional intake. It has been shown that an infant with a nonfunctioning GI tract can survive on total parenteral nutrition for years, but this is clearly a stopgap measure.[299] The risk of complications from central venous cannulation increases with time, and vascular access in the child becomes increasingly limited as sites are used. Attention to alimentation has improved outcome in the ICU. Though difficult to quantify, it is my impression that children with any critical illness benefit from improved nutritional intake with faster recovery and decreased morbidity.
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