Water intoxication syndrome

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Water intoxication, also known as water poisoning or dilutional hyponatremia, is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside safe limits by over-hydration.

Water Intoxication

• Under normal circumstances, accidentally consuming too much water is exceptionally rare. Nearly all deaths related to water intoxication in normal individuals have resulted either from water drinking contests in which individuals attempt to consume large amounts of water, or from long bouts of exercise during which excessive amounts of fluid were consumed. Moreover, water cure, a method of torture in which the victim is forced to consume excessive amounts of water, can cause water intoxication.
• Water, just like any other substance, can be considered a poison when over-consumed in a specific period of time. Water intoxication mostly occurs when water is being consumed in a high quantity without giving the body the proper nutrients it needs to be healthy.
• Excess of body water may also be a result of a medical condition or improper treatment; see "hyponatremia" for some examples. Water is considered the least toxic chemical compound, with an LD₅₀ of 90 ml/kg or more in rats.

Risk Factors

Low Body Mass (infants)

It can be very easy for children under one year old to absorb too much water, especially if the child is under nine months old. Because of their small body mass, it is easy to take in a large amount of water relative to body mass and total body sodium stores.

Endurance Sports

Marathon runners are susceptible to water intoxication if they drink too much while running. This is caused when sodium levels drop below 135 mmol/L when athletes consume large amounts of fluid. This has been noted to be the result of the encouragement of excessive fluid replacement by various guidelines. This has largely been identified in marathon runners as a dilutional hyponatremia. A study conducted on participants of the 2002 Boston marathon found that thirteen percent finished the race with hyponatremia. The study concluded that the strongest predictor of hyponatremia was weight gain while racing (over-hydration), and hyponatremia was just as likely to occur in runners who chose sports drinks as those who chose water. Medical personnel at marathon events are trained to suspect water intoxication immediately when runners collapse or show signs of confusion.

Overexertion and Heat Stress

Any activity or situation that promotes heavy sweating can lead to water intoxication when water is consumed to replace lost fluids. Persons working in extreme heat and/or humidity for long periods must take care to drink and eat in ways that help to maintain electrolyte balance. People using drugs such as MDMA (often referred to colloquially as "Ecstasy") may overexert themselves, perspire heavily, and then drink large amounts of water to rehydrate, leading to electrolyte imbalance and water intoxication – this is compounded by MDMA use increasing the levels of antidiuretic hormone (ADH), decreasing the amount of water lost through urination. Even people who are resting quietly in extreme heat or humidity may run the risk of water intoxication if they drink large amounts of water over short periods for rehydration.

Competitive Eating Training

Competitive eaters often train for their sport by drinking large amounts of water in a short period of time in an attempt to stretch their stomach to increase their food intake capacity.

Psychiatric Conditions

Psychogenic polydipsia is the psychiatric condition in which patients feel compelled to drink large quantities of water, thus putting them at risk of water intoxication. This condition can be especially dangerous if the patient also exhibits other psychiatric indications (as is often the case), as the care-takers might misinterpret the hyponatremic symptoms. It is called as Self-induced water intoxication and schizophrenic disorders syndrome

Iatrogenic

When an unconscious person is being fed intravenously (for example, total parenteral nutrition) or via a nasogastric tube the fluids given must be carefully balanced in composition to match fluids and electrolytes lost. These fluids are typically hypertonic, and so water is often co-administered. If the electrolytes are not monitored (even in an ambulatory patient) either hypernatremia or hyponatremia may result.

Some neurological/psychiatric medications (Oxcarbazepine, Desmopressin) have been found to cause hyponatremia in some patients.

Pathophysiology

At the onset of this condition, fluid outside the cells has an excessively low amount of solutes (such as sodium (hyponatremia) and other electrolytes) in comparison to that inside the cells causing the fluid to shift through (via osmosis) into the cells to balance its concentration. This causes the cells to swell. In the brain, this swelling increases intracranial pressure (ICP). It is this increase in pressure which leads to the first observable symptoms of water intoxication: headache, personality changes, changes in behavior, confusion, irritability, and drowsiness. These are sometimes followed by difficulty breathing during exertion, muscle weakness & pain, twitching, or cramping, nausea, vomiting, thirst, and a dulled ability to perceive and interpret sensory information. As the condition persists, papillary and vital signs may result including bradycardia and widened pulse pressure. The cells in the brain may swell to the point where blood flow is interrupted resulting in cerebral edema. Swollen brain cells may also apply pressure to the brain stem causing central nervous system dysfunction. Both cerebral edema and interference with the central nervous system are dangerous and could result in seizures, brain damage, coma or death.

Prevention

Water intoxication can be prevented if a person's intake of water does not grossly exceed his or her losses. Healthy kidneys are able to excrete approximately 0.8 to 1 litre of fluid water (0.21 - 0.26 gallons) per hour.

Treatment

Mild intoxication may remain asymptomatic and require only fluid restriction. In more severe cases, treatment consists of:

• Diuretics to increase urination, which are most effective for excess blood volume.
• Vasopressin receptor antagonists