Water intoxication occurs when the serum osmolarity drops below 240 mOsm/kg; in other words, the blood gets diluted with too much water. This can occur for four reasons: too much water intake, too little water output, too little salt intake or too much salt output.
The symptoms of water intoxication include mental status changes, lethargy, confusion, nausea, convulsions, coma and death. The severity of the symptoms depends both on the degree of intoxication and on the speed with which the serum osmolarity dropped. If the serum osmolarity drops fast, symptoms occur earlier and are more severe than if it drops gradually.
Treatment of water intoxication primarily consists of identifying the cause and remedying it. Sodium and potassium supplements, cessation of thiazide diuretic therapy, cessation of excessive water intake, and screening for adrenal insufficiency, if indicated, should prevent further problems. Potassium-sparing diuretics may be used to eliminate some of the excess fluid, but the patient should be monitored carefully for further problems.
Many of the symptoms of water intoxication are similar to those of heat exhaustion, so sometimes it may be difficult to tell the difference. My husband was in the Army doing a roadmarch. He began to feel bad, so he forced himself to drink canteen after canteen of water, since that is what they had been taught. We estimated that he drank about five gallons of water in the course of 10 hours. He felt worse and worse, but he was urinating frequently, so he didn't think he was dehydrated. Finally, he collapsed, began vomiting and convulsing, and was medevaced to the hospital by helicopter. The medics hung a bag of lactated ringer's solution, since the assumption was that he was dehydrated and suffering from heat exhaustion; that was also the diagnosis that the emergency room finally released him with. When he told me what had happened, I realized that they had gotten it the wrong way round - a day of good American salty food set him right.. unfortunately, I don't think they drew any bloodwork - I would have loved to chat with the doctor who treated him...