Protein-energy malnutrition secondary

Aminoacidurias may be primary or secondary. Primary disease is due to an inherited enzyme defect, also called an inborn error of metabolism. The defect is located either in the pathway by which a specific amino acid is metabolized or in the specific renal tubular transport system by which the amino acid is reabsorbed. Secondary aminoaciduria is due to disease of an organ, such as the liver, which is an active site of amino acid metabolism, or to generalized renal tubular dysfunction, or to protein-energy malnutrition. Specific inborn errors of metabohsm are discussed in more detail in Chapter 55. 

Retinol is nearly always present in the food in the form of esters which are hydrolysed in the lumen of the intestine. The retinol released is quite readily absorbed into the mucosal cells where it is re-esterified, chiefly with palmitic acid. The retinyl esters are then transported via the lymphatic system into the portal circulation from which they are removed and stored in the liver. Release of the vitamin from the liver depends on the production by the liver of a special retinolbinding protein (RBP). Production of the retinol-binding protein may be disturbed in diseases of the liver or kidneys or in protein/energy malnutrition. In such circumstances retinol cannot be mobilized from the stores and a secondary deficiency may result. Thus it can be seen that the level of retinol in the general circulation is normally highly regulated and is more or less independent of the body s reserves. 

Signs of vitamin A deficiency also occur in protein-energy malnutrition (section 8.2), regardless of whether or not the intake of vitamin A is adequate. This is due to impairment of the synthesis of RBP. Hence, functional vitamin A deficiency can occur secondary to protein-energy malnutrition. In this case, there is severely impaired immunity to infection, as a result of both the functional vitamin A deficiency and also the impairment of immune responses associated with undernutrition. 

Patients with severe sepsis are susceptible to progressive malnutrition secondary to the hypermetabolism associated with severe illness and injury. Hence early enteral nutrition is recommended in patients with severe sepsis and septic shock to meet the increased energy and protein requirements. Protein requirements are increased to 1.5 to 2.5 g/kg per day, and increased amounts of branched-chain amino acids may be beneficial in septic patients. Nonprotein caloric requirements range from 25 to 40 kcal/kg per day, and overfeeding of carbohydrates should be avoided to reduce the ventilatory requirements of the patient. The use of increased amounts of lipid to meet nonprotein caloric needs while reducing carbohydrate administration may be useful in this setting. 

PEM arises due to a negative energy balance, that is, a combined intake of proteins and calories less than that required for body expenditure. Inadequate food intake in PEM may have multiple causes, ranging from secondary malnutrition to sociopolitical problems (Fig. 24-2). 

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