- Clinical science
Dehydration
Summary
Dehydration (exsiccosis) is a state of decreased total body water. This decrease in total body water occurs in excess of sodium (also called “free water loss”), resulting in a hypertonic and hypernatremic state. The terms “hypotonic” and “isotonic” are sometimes incorrectly used to describe dehydration, but these terms are only associated with hypovolemia and hypovolemic shock. Dehydration most often affects children and the elderly. Treatment of dehydration involves correcting the free water deficit.
Etiology
- Insufficient water intake, particularly in elderly individuals and the critically ill
-
Increased free water loss
- Renal loss: diuretics, hyperglycemia, polyuric phase of renal failure, diabetes insipidus
- Extrarenal loss: diarrhea , vomiting, burns, increased sweating, fever, inflammation, ascites
- See also hypovolemic hypernatremia and euvolemic hypernatremia.
References:[1][2][3][4][5]
Clinical features
- Thirst
- Dry skin and mucous membranes
- Headache, dizziness, disorientation
- Weakness, fatigue, hemodynamic instability
- Dark circles around the eyes and frequent blinking (reduced tear fluid quantity)
- Children: no tears when crying
- Infants: sunken fontanelle, restlessness/lethargy
| Clinical feature | Mild dehydration | Moderate dehydration | Severe dehydration | |
|---|---|---|---|---|
| Decrease in body weight | < 3% | 3–9% | > 9% | |
| Symptoms | Mental status | Alert | Restless, irritable | Lethargic, confused |
| Thirst | Slightly increased | Thirsty; drinks eagerly | Refuses to drink | |
| Urine output | Normal | ↓ (dark concentrated urine) | ↓↓ | |
| Signs specific to dehydration | Eyes | Normal | Slightly sunken | Significantly sunken |
| Tears (especially children) | Normal | Decreased | Absent | |
| Tongue | Moist | Dry | Parched | |
| Skin turgor | Instant recoil | Recoil within 2 seconds | Recoil after 2 seconds; significant skin tenting | |
| In infants: anterior fontanelle | Normal | Slightly sunken | Significantly sunken | |
| Signs of hypovolemia and hypovolemic shock | Pulse rate | Normal | Mildly tachycardic | Initially tachycardia → later bradycardia |
| Blood pressure | Normal | Normal; postural hypotension may be present | Hypotension | |
| Capillary refill time | Normal (< 2 seconds) | 2–3 seconds | > 3 seconds | |
| Extremities | Warm | Cool | Mottled | |
| Breathing | Normal | Tachypnea | Tachypnea with deep breathing (Kussmaul breathing) | |
References:[3][4][6][7][8]
Diagnostics
- Serum sodium:
- Hypernatremia
- Serum sodium levels can be used to determine the amount of free fluid needed to correct dehydration (see treatment of hypernatremia).
- ↑ Hematocrit
- ↓ Serum bicarbonate levels
- BUN to serum creatinine ratio > 20:1 → renal hypoperfusion due to hypovolemia
-
Urine osmolality: See sodium imbalance for more information.
- < 800 mOmol/L → renal free water loss
- > 800 mOmol/L → extrarenal free water loss
- Blood glucose levels
- Hypoglycemia → decreased fluid intake as a possible cause of dehydration
- Hyperglycemia → osmotic diuresis as a possible cause of dehydration
References:[3][4][7][9][10][11][12]
Treatment
Patient who are hypovolemic as a result of severe dehydration require immediate fluid resuscitation with crystalloid solutions.
-
Fluid resuscitation
- Severe hypovolemia
- Children: rapid infusion of 20 mL/kg of isotonic saline → reassess → repeat as needed
- Adults: rapid infusion of isotonic crystalloid → reassess → repeat as needed
- Moderate hypovolemia
- Children: consider oral hydration therapy or 10 mL/kg of isotonic saline → reassess → repeat as needed
- Severe hypovolemia
- Correction of electrolyte abnormalities
-
Sodium imbalance should only be addressed once the patient is adequately resuscitated.
- Hypernatremia → Once volume resuscitated, free water deficit can be used to determine further management (see correct free water deficit).
- Hyponatremia → Once volume resuscitated, monitor closely, and consider hypotonic fluids to avoid rapid overcorrection (see sodium disorders).
-
Sodium imbalance should only be addressed once the patient is adequately resuscitated.
References:[3][13][14][15]
Complications
- Hypovolemic shock → prerenal renal failure
- Increased risk of infection, particularly of the urinary tract
- Thrombosis
- Osmotic demyelination syndrome
- Patients with diabetes mellitus: Dehydration can trigger diabetic ketoacidosis.
References:[16][17][18][19]
We list the most important complications. The selection is not exhaustive.
