Nutrition - Pharmacology

Nutrition is a three-step process that gives the body materials needed to make the body grow and function. The process begins when food is ingested. Chemical reactions in the body then break down food into molecules that enter the blood stream and are distributed to different parts of the body where they are used to sustain life.

Some nutrients are used for cell growth and cellular functions. Other nutrients become involved in enzyme activities and carbohydrate-fat-protein synthesis. Nutrients are used to contract muscles and help wounds to heal. They also play a critical role in the integrity of the GI tract and in the immune system.

Think of nutrients as fuel for your car. Fuel is used as you drive your car. The same is true about your body. Your body uses nutrients to go about daily activities. And just like your car, your body can continue to operate without a full complement of nutrients that is, without a full tank of gas. A healthy, well-nourished person has a nutritional level to last 14 days before they begin to show signs of malnutrition. That is, your full tank of gas will last 14 days.

However, there comes a point when your performance sputters.the level of nutrients fall below the level needed to sustain your daily activity. You simply run out of fuel and become fatigued, irritable, and exhibit an abnormal appearance.

This is referred to as a nutritional deficit. A nutritional deficit can occur from a number of situations. The most obvious is not eating a balanced, nutritional diet. However, there are less apparent reasons that cause a nutritional deficit. These are surgery, trauma, malignancy, and other illnesses that break down (catabolize) the body.

The effect of a nutritional deficit can be dramatic. The body needs nutrients to recover from trauma and disease. A nutritional deficit prolongs healing and severe cases can prevent total recovery. Critically ill patients have sufficient nutrients to sustain them for a few days to a week before they begin to show signs of nutritional deficit.

Healthcare professionals provide nutritional support therapy for patients who are at risk for nutritional deficit. Nutritional support therapy replaces nutrients that the patient has lost and there by provide the patient with the fuel needed for a full recovery.

A nutritional deficit is called a negative nitrogen balance, which means that the patient lacks sufficient nitrogen to fight infectious disease. Healthcare professionals treat patients who are at risk for negative nitrogen balance by providing the patient with nutrients before the imbalance occurs. The patient is then able to fight infectious diseases.

A common misnomer is that dextrose 5% in water (D5W), normal saline, and lactated Ringer’s solution provide nutrients to the patient. However, these intravenous fluids are not forms of nutrients. These are electrolytes and fluids.


Nutrients are given to a patient via an enteral or parenteral route. Using the enteral route, food is administered by mouth or by a feeding tube that is directly inserted into the GI tract usually into the stomach or small intestine. A feeding tube is used whenever the patient cannot swallow.

The parenteral route is the use of high caloric nutrients administered through large veins such as the subclavian vein in a process called total parenteral nutrition (TPN) or hyperalimentation. The parenteral route is the least preferred because the process is three times more expensive than enteral with out a significantly improved benefit.

Furthermore, the parenteral route has a high rate of infection and does not promote GI function, liver function, or weight gain.

Enteral nutrition

Enteral feeding is the preferred method of providing nutritional support to a patient. However, the patient must have adequate GI tract function to enable food to be digested, absorbed, and waste eliminated.

It is important to determine if the patient has GI motility and small bowel function. Otherwise, the patient may experience uncontrolled vomiting and become at high risk for aspiration should the intestine be obstructed. Decreased bowel sounds are common in critically ill patients. They may also have a decrease or absence of gastric emptying.

There are several methods used for enteral feeding. These are:

  • Oral. This is ingesting food naturally.
  • Nasogastric tube. This is the most common method. It consists of a tube
    passed through the nose and down the esophagus ending shortly below the
    xiphoid process. This is used for short-term therapy.
  • Gastrostomy. A feeding tube placed in a hole in the abdomen leading to the stomach. This is used for long-term therapy.
  • Nasoduodenal. A tube is passed through the nose and down the esophagus ending in the duodenum.
  • Nasojejunal. A tube is passed through the nose and down the esophagus ending in the small intestine.
  • Jejunostomy. A feeding tube is placed in a hole in the abdomen leading to the small intestine.

There are various mixtures that are given to patients who are receiving nutri¬tional support therapy based on the nutrient, caloric values, and osmolality that the patient requires.

These mixtures belong to one of the following groups:

  • Blenderized. This consists of liquids that are individually prepared based on the nutritional needs of the patient and can include baby food with added liquid.
  • Polymeric. This is divided into two subgroups:
    1. Milk-based. Powder mixed with milk or water is given in large amounts to provide complete nutritional requirements and can be used as a nutritional supplement in smaller amounts.
    2. Lactose-free. Liquid is used for replacement feedings and consists of 50% carbohydrates, 15% protein, 15% fat, and 20% other nutrients in an isotonic solution (300 to 340 mOsm/kg H2O). This provides 1 calorie per milliliter of feeding. This includes Ensure, Isocal, and Osmolite.
  • Elemental. Also know as monomeric, this is the more expensive enteral solution. It is useful for partial GI tract dysfunction and is available in both liquid and powder. Elemental nutrients are rapidly absorbed in the small intestines.

Regardless of the group, these solutions consists of

  • Carbohydrates in the form of dextrose, sucrose, and lactose. These are simple sugars that are absorbed quickly. Starch and dextrin are also carbohydrates that the solution may contain.
  • Protein in the form of intact proteins, hydrolyzed proteins, or free amino acids.
  • Fat in the form of corn oil, soybean oil, or safflower oil.

Enteral feedings are administered as:

  • Bolus, 250–400 mL 4 to 6 times each day. Each bolus may take about 10 minutes to administer. The patient may experience nausea, vomiting, aspicration, abdominal cramping, and diarrhea if he or she cannot tolerate the large amount of solution given in a short timeframe. This method is if the patient is ambulatory and relatively healthy.
  • Intermittent drip or infusion, 300-400 mL given 3 to 6 hours over 30-60 minutes by gravity drip or infusion pump.
  • Continuous drip or cyclic infusion, 50-125 mL infused per hour at a slow rate over a 24-hour period using an infusion pump such as a Kangaroo set. This method is used for treating critically ill patients and for patients who have a feeding tube in their small intestine or in the stomach.

Enteral feedings expose the patient to complications. These are:

  • Dehydration. An insufficient amount of water is given to the patient or a hyperosmolar solution is given, which draws water from the cells to maintain serum iso-omolality.
  • Aspiration. The patient is fed while in a supine position or is unresponsive. Prevent this by raising the head of the bed 30° and check for gastric residuals by gently aspirating the stomach contents before the next feeding.
  • Diarrhea. A major complication due to rapid administration of feeding, the high caloric solution, malnutrition, GI bacteria (Colstridiumdifficile), and medications such as antibiotics and magnesium containing drugs such as antacids and sorbitol. Sorbitol is a used as a filler for certain drugs. Drugs in the form of oral liquids are hypersomolar and pull water from the cells and into the GI tract resulting in diarrhea. Decreasing the infusion rate, diluting the solution, changing the solution, discontinuing the medication, or increasing daily water intake helps to manage diarrhea.

Table 11-1 contains commonly used preparations for enteral feeding.

contains commonly used preparations for enteral feeding

Administering medications through the NG tube is discussed in Route of Administration.the drug must be in liquid form or dissolved into a liquid and must be properly diluted—it is usually given as a bolus and followed by water liquid medications should be diluted with water to reduce the osmolality to 500 mOsm/kg H2O (mildly hypertonic) to decrease GI intolerance

Calculation for dilution of enteral medications:

  1. Calculate the drug order to determine the volume of the drug:
    drug order to determine the volume of the drug
  2. Determine the osmolality of the drug (drug literature or pharmacist) and liquid dilution. Use 500 mOsm as a constant for the desired osmolality: knownmOsm×volume of drug = total volume of liquid desired mOsm
  3. Determine the volume of water for dilution:
    total volume of liquid - volume of drug = volume of water for dilution
    Example: acetaminophen 650 mg, q6h, PRN for pain
    Have (on hand): Acetaminophen elixir 65 mg/mL. Average mOsm/kg = 5400


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