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Dehydration

What is dehydration?

Dehydration is defined as the loss of water from your body that results in more than 1% loss of your body weight. Dehydration does not appear to affect muscular strength [1].

Causes

  • Insufficient water intake
  • Increased sweating due to warm ambient, physical exercise, fever, anxiety, ecstasy (MDMA) or amphetamine abuse
  • Prolonged exposure to dry air (and hence increased insensible water loss through the skin and breathing) in winter, due to indoor heating, or during flights at high altitudes
  • Prolonged exposure to cold; cold stimulates urination (cold-induced diuresis) [3]
  • Prolonged diarrhea (infections, poisoning, laxatives abuse) or vomiting
  • Excessive urination due to:
    • Untreated diabetes mellitus
    • Diabetes insipidus caused by a brain or kidney disorder [7]
    • Congenital adrenal hyperplasia
    • Pheochromocytoma, a rare tumor of the adrenal gland that produces epinephrine (adrenaline)
    • Water pills (diuretics)
  • Severe bleeding
  • Burns

Chart 1. Dehydration Symptoms and Signs
SEVERITY SYMPTOMS SIGNS
Mild Thirst (not always, often absent in children and old people), dry mouth, constipation 1-3% loss of body weight, slightly decreased amount of clear or light yellow urine
Moderate Fatigue, sleepiness or restlessness by day, insomnia, loss of appetite, decreased attention, nausea, headache, dizzy spells or fainting, especially when raising from sitting to standing (orthostatic hypotension), muscle cram 4-6% loss of body weight, decreased amount of dark yellow urine or no urination for >8 hours, dry lips, pale skin, cool limbs, increased heart and breathing rate. Skin turgor test: skin fold visible [14]
Severe Extreme thirst or no thirst, apathy, inability to stand or walk, chopped lips, small amount of dark yellow or brown urine or no urination for >12 hours, no sweating, wrinkled skin, sunken eyes, possible irregular heartbeat (arrhythmia) [19], seizures or coma. 7% or greater loss of body weight, skin turgor test: skin fold persists >2 seconds after pinch and release. Capillary refill: nail becomes red in >2 seconds after pressing and release.Infants: sunken eyes and fontanels (the soft spots on the top of the head), no tears when crying, loss of 15% or more weight (3.3 lbs or 1.5 kg in a 22 lbs or 10 kg infant) [14]
Heat exhaustion Fever, thirst, fatigue Body temperature: 98.6-104 °F (37-40 °C) [17], profuse sweating, cool, pale skin
Heat stroke Fever, decreased heat tolerance, extreme thirst, irritability, weakness, severe headache [18] Body temperature >106 °F (41.1 °C), hot, dry, flushed skin, possible coma [18]

Chart 1 sources: [1,2,4,8,9,10,11,12,13,14,15,16,17,18,19]

Thirst

The feeling of thirst is usually triggered by an increase of the blood sodium levels, which can result from [32]:

  • Water loss from the body through urination, invisible perspiration, sweating and breathing
  • Intake of salt or other sodium-containing substances with foods, beverages or medications

Excessive thirst [40] can be caused by:

  • Dry mouth due to stress, anxiety, caffeine, smoking, alcohol, hangover, smoking, disorders that affect salivary glands: Sjögren’s syndrome, mumps, systemic lupus erythematosus (SLE), cystic fibrosis, HIV/AIDS
  • Dehydration due to insufficient water intake, diarrhea, repeated vomiting, diabetes mellitus or diabetes insipidus due to by brain or kidney disorders
  • Pregnancy [39]
  • Syndrome of inappropriate antidiuretic hormone secretion (SIADH) due to by brain and lung disorders, cancer or certain drugs [41]
  • Sudden drop of blood pressure [42], severe bleeding [37], severe anemia [36], peritonitis (inflammation of the membrane that covers the abdominal organs) [18]
  • Psychological causes (psychogenic polydipsia) [38]
  • Water pills (diuretics) and other drugs: anticholinergics, antidepressants, antihistamines, cocaine, ecstasy (MDMA) [19,35,37]

What can decrease the sense of thirst?

  • Arriving at high altitude [28]
  • Old age [34]
  • Health conditions with reduced or absent thirst [33]: head injury, stroke, liver cirrhosis, birth defects, vasospastic syndrome (a mild form of Raynaud’s syndrome)

Complications

  • Acute dehydration:
    • Kidney failure (inability to produce urine) [21]
    • Hypovolemic shock [20]
    • Death ─ after 10-15% loss of body weight [22]
  • Chronic dehydration: urinary tract infections (UTI) [5] and kidney stones [6]. In some studies, chronic dehydration was associated with increased risk of gallstones, colorectal and bladder cancer [23] and thrombosis in infants [20] but more research is warranted.

Diagnosis

A doctor can evaluate the severity of dehydration from symptoms and signs and, if necessary, from blood and urine tests.

Chart 2. Tests for Dehydration
TEST Normal values Values in Dehydration
Blood osmolality 280-290 mOsm/L >290 mOsm/L [24]
Urine specific gravity 1,010-1,030 >1,030 [25]
Urine osmolality 50-1,250 mOsm/L Toward higher values [24]
Blood urea nitrogen (BUN) 8-25 mg/dL BUN >25 mg/dL in a person with a normal kidney function speaks for dehydration [26].
Other tests
  • Increased or decreased blood levels of sodium and potassium and decreased levels of bicarbonate
  • Glucose in urine in uncontrolled diabetes mellitus
  • Ketones in the urine in diabetic ketoacidosis
  • Proteins in the urine in certain kidney disorders

Chart 2 sources: [24,25,26]

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Chart 3. Fluids to Treat Dehydration
Age Appropriate Fluids Inappropriate Fluids
Infants and toddlers (1-3 years) Oral rehydration solutions (ORS), which contain water, sodium, potassium and glucose to enable optimal water absorption and retention and to prevent water intoxication. Infants should continue with regular breastfeeding or formula. Plain water, tea, coffee, fruit juice, energy drinks, alcohol beverages
Children >3 years and adults Water (tap, bottled, mineral, carbonated), herbal tea, coconut water; in severe cases oral rehydration solution (ORS); when these are not available, fruit juices, milk (skimmed, if possible), soft drinks, sport drinks, true tea, ice tea, coffee, energy drinks, compotes, soups and, for adults, beer are acceptable. Large amounts (>1 L) of apple, pear and mango juice or cola sweetened with HFCS (high in fructose; can trigger diarrhea); alcohol beverages with >5% alcohol (may worsen dehydration); seawater;
Anyone with severe dehydration or inability to drink Infusion of a fluid into a vein (intravenous infusion) Any oral fluid

Chart 3 sources: [29,30,31]

Chart 4. Treatment Regime for Dehydration
EXERCISE Water, about 1 cup (237 mL) every 20 minutes; sport drinks for exercise lasting >4 hours
DIARRHEA
Infants (0-12 months) ORS*: 1 teaspoon (5 mL) every minute (bottle feeding may trigger vomiting) as long as the infant accepts fluids until his or her body weight is restored to normal and urine becomes clear. If an infant vomits, wait for 15 minutes or so and continue with ORS. If an infant refuses to drink, take him or her to the hospital immediately.
Toddlers (1-3 years) ORS: a gulp or two at the time, up to a cup (237 mL) per hour.
Older children and adults Water, sport drinks, diluted fruit juices or, in severe diarrhea, ORS, as soon as diarrhea starts, drinking to thirst, one cup (237 mL) at the time, up to about one liter of per hour until diarrhea stops, urine becomes clear and your body weight is restored to normal.
HEAT STROKE Move a person to a cool place and call 911 (emergency). Remove his or her clothes and start with cooling with wet cold sheets, cold shower or fan and give him or her water. Avoid alcoholic and caffeinated drinks. If a person is unable to drink, take him or her to the hospital as soon as possible.

Chart 4 source: [27]  * ORS = oral rehydration solution

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  20. Hbibi M et al 2012, Severe hypernatremic dehydration associated with cerebral venous and aortic thrombosis in the neonatal period  PubMed Central
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  36. Overview of anemia  Merck Manuals
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  38. Hutcheon D, 2013, Psychogenic polydipsia (excessive fluid seeking behaviour)  APA Divisions
  39. Lindheimer MD et al, 1989, Osmoregulation of thirst and vasopressin release in pregnancy  PubMed
  40. Thirst  Patient.info
  41. Thomas CP, Syndrome of Inappropriate Antidiuretic Hormone Secretion  Emedicine
  42. Low blood pressure (hypotension) symptoms  Mayo Clinic

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