In physiology and medicine, dehydration (hypohydration) is the excessive loss of body water,[1] with an accompanying disruption of metabolic processes. The term dehydration may be used loosely to refer to any condition where fluid volume is reduced; most commonly, it refers to hypernatremia (loss of free water and the attendant excess concentration of salt), but is also used to refer to hypovolemia (loss of blood volume, particularly plasma).

What electrolyte imbalances would you expect to find with dehydration?may show hypernatremia, isonatremia, or hyponatremia; enteral losses: associated with hypokalemia and low bicarbonate level; crush injuries and burns: may be associated with hyperkalemia. Urine Osmolality usually>450 mOsm/kg. The urine specific gravity of normally functioning kidneys: >1.025; abnormally functioningkidneys: normal or inappropriately lowWhat assessment findings are consistent with dehydration?Mental status, activity level assessment: this provides critical diagnostic information. Infants and smallchildren who are inconsolable or listless, or do not seem to resist invasive or uncomfortable proceduresshould be assumed to have serious illness.Mucous membranes: dry or tacky mucous membranes are seen with hypovolemia; pallid mucous membranessuggest chronic blood loss.Capillary refill: classically, volume depletion is associated with a prolonged capillary refill time (>3 seconds).This is most likely to be true in the setting of gradual volume depletion, as is seen in gastroenteritis. A meta-analysis concluded that the 3 most useful clinical findings in a child with volume depletion and dehydrationwere prolonged capillary refill time, decreased skin turgor, and abnormal respiratory pattern. However, in burns, anaphylaxis, and sepsis, capillary refill time may not be prolonged (<3 seconds). Therefore,determining capillary refill time is not a reliable clinical test in all cases.Skin turgor can be notably affected in severe cases of volume depletion, particularly those associated withhypernatremia or hyperosmolarity. A doughy consistency is reported in hyponatremic states. Becausechildren have more skin elasticity than adults, this is often a relatively late sign in the progression of volumedepletion. Assessing skin turgor by pinching a small fold of skin on the abdomen adjacent to the umbilicusand observing recoil is recommended

HEAT EXHAUSTIon
Prolonged exposure to heat over hours or days leads to heat exhaustion, a clinical syndrome characterized byfatigue, light-headedness, nausea, vomiting, diarrhea, and feelings of impending doom.
Tachypnea, hypotension, tachycardia, elevated body temperature, dilated pupils, mild confusion,ashen color, and profuse diaphoresis are also present.
Hypotension and mild to severe temperature elevation (99.6º to 104º F [37.5º to 40º C]) are due todehydration. Treatment begins with placement of the patient in a cool area and removal of constrictive clothing.

Oral fluid and electrolyte replacement is initiated unless the patient is nauseated; a 0.9% normal saline IVsolution is initiated when oral solutions are not tolerated. A moist sheet placed over the patient decreases core temperature
HEATSTR OK
EHeatstroke
results from failure of the hypothalamic thermoregulatory processes.Increased sweating, vasodilatation, and increased respiratory rate deplete fluids and electrolytes, specificallysodium.
Eventually, sweat glands stop functioning, and core temperature increases (>104º F (40º C).
Altered mentation, absence of perspiration, and circulatory collapse can follow.
Cerebral edema and hemorrhage may occur as a result of direct thermal injury to the brain.Treatment focuses on stabilizing the patient¶s ABCs and rapidly reducing the temperature.Various cooling methods include removal of clothing, covering with wet sheets, and placing the patient infront of a large fan; immersion in an ice water bath; and administering cool fluids or lavaging with coolfluids. Shivering increases core temperature, complicating cooling efforts, and is treated with IVchlorpromazine. Aggressive temperature reduction should continue until core temperature reaches 102º F(38.9º C

What are methods of cooling a patient?
External coolingExternal methods include immersion and evaporative cooling.Immersion coolingImmersion in an ice bath, or cooling blankets used in conjunction with ice packs to the axilla, groin, neck,and head, may be the most rapid methods of cooling.Patients cooled in an ice bath frequently suffer afterdrop, so that their core temperature continues to declineeven after they are removed from the bath. To prevent iatrogenic hypothermia, patients are typically removedfrom the ice bath once their core temperature reaches 100°F (37.8°C).Immersion may be a preferable technique when treating patients for whom exposure of the skin is culturallyforbidden.However, immersion can produce difficulties of access in case of a cardiac arrest, and bradycardia due to thediving reflex is not uncommon. In these cases, evaporative methods may be preferable.Evaporative coolingThe patient's skin is exposed to warm air at 113°F (45°C) passing over the body while a mist of cool water at59°F (15°C) speeds heat dissipation. Cooling rates with this technique have been measured at 0.5°F/minute(0.31°C/minute
Internal coolingInternal cooling methods are effective in rapidly decreasing temperature. Gastric, bladder, and rectal coldwater lavage can all be readily performed. Peritoneal and thoracic lavage may also be used, but are moreinvasive and so are used only in extreme cases. Although rarely required, cardiopulmonary bypass is alsoeffective as a cooling method in this setting. No data exist to help practitioners determine when internalcooling methods might be superior to external ones. As such, internal cooling methods should be regarded asan approach for use when external cooling may not be feasible or is ineffective
Fluids can be replaced with oral rehydration therapy (drinking), intravenous therapy, rectally such as with a Murphy drip, or by hypodermoclysis, the direct injection of fluid into the subcutaneous tissue. Fluids administered by the oral and hypodermic routes are absorbed more slowly than those given intravenously.
When there is some dehydration the deficit of water is between 50 and 100 ml for each kg of body weight. If the child's weight is known, the amount of ORS solution required for rehydration can be estimated, using 75ml/kg as the approximate deficit. If the child's weight is not known, the estimated deficit can be determined using the child's age, although this approach is less precise. Both methods are shown in the chart in Figure 5.1, which indicates the range of fluid volumes that is appropriate for a child of a given weight or age. Alternatively, the approximate ORS volume (in ml) can be calculated by multiplying the weight (in grams) times 0.075. Thus, a child weighing 8000 grams would require about (8000 x 0.075) 600 ml of ORS solution.

It should be emphasized that the range of fluid volumes shown in the chart is an estimate of what is needed and should be used only as a guide. The actual amount given should be determined by how thirsty the patient is and by monitoring the signs of dehydration, bearing in mind that larger volumes will be required by larger patients, those with more advanced signs of dehydration, and those who continue to pass watery stools during rehydration. The general rule is that patients should be given as much ORS solution as they will drink, and the signs of dehydration should be monitored to confirm that they are improving.
Heat stroke can be prevented by drinking lots of fluid before, during, and after the sports.
Physicians should encourage their patients to protect themselves by maintaining adequate hydration, avoiding heat exposure, wearing loose, light clothing, and monitoring their exertion level.9 Athletes should be advised to acclimatize for at least three to four days before exerting in the heat. Because a heat injury releases an inflammatory cascade that may increase risk on subsequent days, patients should be protected from exposure to heat for 24 to 48 hours following a mild injury.