Dehydration

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Early Symptoms of Dehydration

Symptoms and signs of dehydration can be minor, such as increased thirst, or severe and life-threatening, depending on the extent of the dehydration.

The early symptoms of dehydration are

  • thirst, and
  • reduced urine output and darkening of the urine.

As dehydration progresses, other symptoms develop, including

  • dry mouth,
  • lightheadedness,
  • muscle cramps, and
  • palpitations.

Quick GuideDehydration: Causes, Symptoms and Tips to Stay Hydrated

Dehydration: Causes, Symptoms and Tips to Stay Hydrated

Dehydration facts

  • The body needs water to function.
  • Dehydration occurs when water intake is less than water loss.
  • Symptoms range from mild to life-threatening.
  • The young and the elderly are especially susceptible to dehydration.

What is dehydration?

Water is a critical element of the body, and keeping the body adequately hydrated is a must to allow the body to function. Up to 75% of the body's weight is made up of water. Most of the water is found within the cells of the body (intracellular space). The rest is found in the extracellular space, which consists of the blood vessels (intravascular space) and the spaces between cells (interstitial space).

Dehydration occurs when the amount of water leaving the body is greater than the amount being taken in. The body is very dynamic and always changing. This is especially true with water in the body. We lose water routinely when we:

  • breathe and humidified air leaves the body (this can be seen on a cold day when you can see your breath in the air, which is just water that has been exhaled);
  • sweat to cool the body; and
  • eliminate waste by urinating or having a bowel movement.

In a normal day, a person has to drink a significant amount of water to replace this routine loss.

The formula for daily fluid requirements depends upon an individual's weight. Normally, fluid and weight are calculated using the metric system; however, below is the approximation in imperial (American) units.

Body weightDaily fluid requirements (approximate)
10 pounds15 ounces
20 pounds30 ounces
30 pounds40 ounces
40 pounds45 ounces
50 pounds50 ounces
75 pounds55 ounces
100 pounds50 ounces
150 pounds65 ounces
200 pounds70 ounces

If you would like to calculate your body weight and daily fluid requirements using the metric system, please use this formula.

  • For the first 10kg (kilogram) of body weight the daily fluid intake required is 100cc (or mL) per kg.
  • For the next 10kg of body weight, the fluid required is an additional 50 cc/kg.
  • For every additional kg of body weight, an additional 10cc/kg is required

This is the basic body requirement. More fluid would be needed to replace excess sweating from exercise or fever, fluid loss from vomiting, and diarrhea or increased urine production.

Medically Reviewed by a Doctor on 6/30/2015

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