Dehydration is the excessive loss of water from body tissues accompanied by an imbalance in essential electrolytes, such as sodium, potassium, and chloride.
Description
Dehydration occurs when the body loses more fluid than it takes in. Dehydration can be caused by illness, injury, infection, prolonged exposure to sun or high temperatures, inadequate water intake, or overuse of diuretics or other medications that increase urination.
Water is distributed throughout three compartments in the body: inside the cells (intracellular), in the tissue (interstitial), and in the bloodstream (intravascular). Each compartment contains differing amounts of electrolytes that must remain in balance in order for body organs and systems to function correctly. Dehydration upsets this delicate balance. Total body water also varies in relation to age, gender, and amount of body fat. Adult males have approximately 60% water content, adult females have 50%, infants have an estimated 77%, and the elderly have 46% to 52%. An increase in body fat causes a decrease in the percent fluid content because fat does not contain significant amounts of water.
Causes and symptoms
Different types of dehydration have different causes. When managing patients with dehydration, the type of water loss must be determined to ensure appropriate treatment. In addition, water and sodium levels in the body are closely related; if one is abnormal, the other often is too.
Isotonic dehydration is an equal loss of water and sodium. Isotonic means that the number of particles contained on one side of a permeable membrane is the same as on the other side, thus there is no fluid shift in either direction. The amount of intracellular and extracellular water remains in balance. This can be caused by a complete fast, vomiting, and diarrhea.
Hypertonic dehydration occurs when water loss is greater than sodium loss. Blood sodium levels may be >145 mmol/l (normal range=135 to 145 mmol/l). Higher blood sodium levels combined with decreased water in the intravascular space increases the osmotic pressure in the bloodstream, which, in turn, pulls more fluid out of the cells. This type of dehydration is usually caused by extended fever with limited oral rehydration. Mortality is more likely to occur from hypertonic than from isotonic dehydration.
Hypotonic dehydration occurs when sodium loss is greater than water loss. Blood sodium levels may be less than 135 mmol/l; and the osmotic pressure is greater inside the cells, which pulls more fluid out of the intravascular space into the intracellular space. This type of dehydration occurs with overuse of diuretics, which causes excessive sodium and potassium loss. Potassium depletion affects respiration, increases nausea, and, if severe enough, may cause respiratory arrest or central nervous system (CNS) seizures. Potassium depletion may also cause arrhythmias (an alteration in the heartbeat). As a result, patients are told to take diuretics with orange juice or to eat a banana, both of which are high in potassium.
Strenuous activity, excessive sweating, prolonged time in the sun, and extended vomiting or diarrhea cause fluid loss. Elderly people who move to warm, dry climates frequently become dehydrated because of the climate change combined with a tendency to not drink enough water. Large amounts of fluid can also be lost from prolonged fever. Healthy people require about 1 milliliter of water for each calorie their body metabolizes; but during a fever the metabolic rate increases by seven percent for each 1°F rise in body temperature. Fever also increases the respiratory rate, resulting in additional water loss from the lungs. Further causes of fluid loss that may be overlooked include caffeine and alcohol consumption, which increase urination and fluid excretion.
Decreased oral intake of fluids is a common cause of dehydration and often occurs during times of appetite loss from illness or after oral surgery or injury. The elderly are at high risk for decreased intake because their thirst mechanism may no longer function or they may be physically unable to get a drink. Infants, another high-risk group, are more likely to develop dehydration than adults because they have a higher metabolic rate and their immature kidneys have difficulty concentrating urine. Children who do not wet their diapers for three hours or more are dehydrated. Dehydration is also associated with disorders of the adrenal glands, which regulate water-electrolyte balance; diabetes mellitus; eating disorders; renal disease; and chronic lung disease.
Symptoms of dehydration at any age may include some or all of the following: cracked lips, dry or sticky mucous membranes, sunken eyes, lethargy, and/or confusion. Urine output is minimal and the skin loses its elasticity (turgor) and is slow to return to its normal position after being raised off the back of the hand (tenting). The heart rate and respiratory rate may be elevated. A dehydrated infant may not shed tears when crying and may have a depressed fontanel (soft spot on their head), although recent studies have shown that a depressed fontanel is not an accurate indicator of dehydration.
Diagnosis
The general diagnosis of dehydration can be made based on the patient's symptoms and medical history. Physical examination may reveal any of the symptoms mentioned above, along with shock, rapid heart rate, and low blood pressure. Blood tests are required to determine what deficiency exists (or what is elevated) so that therapy for electrolyte replacement can be planned. Blood tests to check electrolyte levels and urine tests such as urine specific gravity are used to evaluate the severity of the fluid loss. Other laboratory tests may be ordered to determine if an underlying condition (e.g., diabetes or an adrenal gland disorder) is the cause.
Treatment
Increased fluid intake and replacement of lost electrolytes are usually sufficient to restore fluid balance in patients who are mildly or moderately dehydrated. For individuals who are mildly dehydrated, just drinking plain water may be all the treatment that is needed. Adults may replace lost electrolytes by drinking sports beverages, such as Gatorade or Recharge. Parents should follow label instructions when giving children Pedialyte or other commercial products recommended for the treatment of dehydration in children. Children who are dehydrated should be given only clear fluids for the first 24 hours.
A child who is vomiting should sip one or two teaspoons of liquid every 10 minutes. A child who is less than a year old and who is not vomiting should be given one tablespoon of liquid every 20 minutes. A child who is more than one year old and who is not vomiting should take two tablespoons of liquid every 30 minutes. A baby who is being breast-fed should be given clear liquids for two consecutive feedings before breastfeeding is resumed. A bottle-fed baby should be given formula diluted with water to half the formula strength for the first 24 hours after symptoms of dehydration are identified.
To calculate fluid loss accurately, weight changes should be charted every day and a record kept of how many times a patient vomits or has diarrhea. A record of fluid output (including sputum or vomit) and of fluid intake or replacement should be kept for at least 24 to 48 hours to see if balance is being accomplished. Parents should note how many times a baby's diaper must be changed. If dehydration continues, emergency department treatment or hospitalization to receive intravenous fluids and electrolytes may be necessary.
Children and adults can gradually return to their normal diet after they have stopped vomiting and no longer have diarrhea. Gelatin is often a welcomed substitute for additional water and does count as fluid replacement. Bland foods should be reintroduced first, with other foods added as the digestive system is able to tolerate them. Milk, ice cream, cheese, and butter should not be eaten until 72 hours after symptoms have disappeared.
When treating dehydration, the underlying cause must be addressed. For example, if dehydration is caused by vomiting or diarrhea, medications should be prescribed to resolve these symptoms. Patients who are dehydrated due to diabetes, kidney disease, or adrenal gland disorders must receive treatment for these conditions as well as for the resulting dehydration. If dehydration is being caused by diuretics. a dose adjustment made by the physician or a change to a different diuretic may be necessary.
Prognosis
Mild dehydration rarely results in complications. If the cause is eliminated and lost fluid is replaced, mild dehydration can usually be resolved in 24 to 48 hours. Vomiting and diarrhea that continue for several days without adequate fluid replacement can be fatal since more is lost than water and sodium. Severe potassium loss may lead to cardiac arrhythmias, respiratory distress or arrest, or convulsions (seizures). The risk of life-threatening complications is greater for young children and the elderly. However, dehydration that is rapidly recognized and treated has a good outcome.
Health care team roles
The nurse and the physician have the greatest responsibility in recognizing and treating dehydration. For hospitalized patients, the physician should order appropriate fluid and electrolyte replacement and the nurse should ensure that the correct fluids are given to the patient. The nurse should monitor the patient for signs that the dehydration (e.g., decrease in fever, increase in blood pressure, reduced heart rate) is resolving and should notify the physician if it is not.
Blood tests used to diagnose dehydration are collected by specially trained nursing assistants or by laboratory technicians. Outpatient samples in a physician's office may be taken by the nurse or a technician. In some institutions, the nurse collects the blood sample. Usually, urine samples are collected by the nurse, and results calculated by the laboratory technician.
Prevention
Patients who are vomiting or who have diarrhea can prevent dehydration by drinking enough fluid to keep their urine the color of pale straw. Infants and young children with diarrhea and vomiting can be given electrolyte solutions such as Pedialyte to help prevent dehydration, as well as suppository medication to stop the vomiting. People who are not ill can maintain proper fluid balance by drinking several glasses of water before going outside on a hot day. It is also a good idea to avoid coffee and tea, which increase body temperature and water loss.
Patients should ask a pharmacist whether or not any medications they are taking may cause dehydration and what to do to prevent it other than adequate fluid intake. Prompt medical attention should be sought to correct any underlying condition that increases the risk of dehydration.
KEY TERMS
Extracellular—Outside the cells.
Hypertonic—One solution having a greater amount of solute (dissolved substance in a solution) than another solution, thus it exerts more osmotic pressure than the second solution and the body will attempt to equalize pressure by passing fluid through the cell membranes.
Hypotonic—One solution having a lesser amount of solute than another solution, thus it exerts less osmotic pressure than the second solution.
Intracellular—Inside the cells.
Isotonic—Two solutions exerting the same amount of osmotic pressure on a cell membrane.
Osmotic pressure—The pressure exerted on a semipermeable membrane that separates two solutions and the particles they contain.
BOOKS
Andreoli, Thomas E., et al., eds. Cecil Essentials of Medicine, 5th ed. Philadelphia, PA: W.B. Saunders Company, 2001.
Porth, C. Pathophysiology: Concepts of Altered Health States. Philadelphia, PA: Lippincott, 1998.
Rakel, Robert E., ed. Conn's Current Therapy 2000. Philadelphia, PA: W.B. Saunders Company, 1999.
Thelan, Lynne, et al. Critical Care Nursing: Diagnosis and Management. St. Louis, MO: Mosby, 1998.
PERIODICALS
Pace, B. "Preventing Dehydration from Diarrhea." JAMA 285, no. 3 (2001): 362.
Sullivan, A. "Hydration for Adults." Nursing Standard 14, no. 8 (1999): 44-46.
