Hypovolemia refers to a state of intravascular volume depletion, while dehydration describes a state of reduced total body water volume, mostly affecting the intracellular fluid compartment. In clinical practice, however, these terms are often used interchangeably, as they are often encountered simultaneously. Body fluid loss (dehydration and/or hypovolemia) occurs when fluid excretion exceeds fluid intake, e.g., due to inadequate fluid intake, vomiting, and/or diarrhea. Young children and the elderly are at an increased risk of clinical dehydration because of differences in body water distribution, the potential inability to communicate needs to caregivers, and increased diuretic use in elderly patients. Patients may present with increased thirst, lethargy, prolonged capillary refill, abnormal vital signs, and decreased skin turgor. Patients can also develop hypovolemic shock if hypovolemia is so severe that the body is unable to compensate, resulting in end-organ damage due to hypoperfusion. Hypovolemia and dehydration are clinical diagnoses and laboratory tests are only indicated in patients with suspected associated metabolic disturbances or severe enough fluid loss to cause end-organ damage. The primary goals of treatment are to first address the hypovolemia, if present, in order to quickly restore the circulatory volume, followed by the management of dehydration through the gradual correction of any remaining fluid deficit (including free water deficit), associated electrolyte abnormalities, ongoing fluid losses, and maintenance fluid requirements.
|Overview of dehydration and hypovolemia|
|Dehydration||Hypovolemia (extracellular volume depletion)|
|Typical causes|| || |
|Fluid loss|| |
|Compensatory mechanism|| |
(See “for details)
- Insufficient water intake, particularly in elderly individuals and the critically ill
- Increased free water loss
- See also and .
- General symptoms include thirst, headache, weakness, dizziness, and fatigue.
- Physical findings often include:
- Hemodynamic instability may be present in severe cases
- Dehydration and hypovolemia often coexist in the same patient (see “Overview” for a comparison of clinical features and etiology).
- Estimating overall fluid loss (due to both processes) is helpful to stratify clinical severity upon presentation
- Estimate percent weight loss based on clinical features.
- Severe fluid loss is a cause of hypovolemic shock (see also “ ”).
|Clinical features of dehydration and hypovolemia|
|Clinical features|| |
Mild fluid loss
(3–5% weight loss)
Moderate fluid loss
(6–9% weight loss)
Severe fluid loss, i.e,
(≥ 10%weight loss)
|Symptoms||Behavior and activity level|| || || |
|Thirst|| || || |
|Physical findings||Vitals|| || |
|Eyes|| || || |
|Mucous membranes|| || || |
|Urine output|| || |
|Anterior fontanelle (infants only)|| || || |
- Diagnosing dehydration and/or hypovolemia relies on clinical assessment (see “Clinical features of dehydration and hypovolemia”).
- Laboratory studies can help support the clinical diagnosis but are not routinely required.
- Obtain laboratory studies for:
- Orders: to evaluate severe fluid loss
|Laboratory findings in dehydration and hypovolemia |
: Administer isotonic fluid and choose route and rate based on estimated fluid loss.
- ; (): Begin with aggressive , e.g., 20 mL/kg bolus of isotonic crystalloid.
(hypovolemia without shock)
- Administer enteral OR parenteral fluids to correct extracellular volume deficit. 
- If starting with IV fluids, transition to enteral fluids as soon as possible.
- oral rehydration therapy). : Prioritize enteral replacement of fluids (i.e.,
Supportive care for all patients: Management of these is often begun concurrently with initial fluid administration.
- Treat associated metabolic disturbances: e.g., glucose and electrolyte abnormalities.
- Identify and treat underlying causes (see “Etiology”).
- Address continued fluid needs.
- Monitoring and disposition
Stabilization through correction of intravascular volume deficit with fluid resuscitation is the first priority. Manage urgent metabolic abnormalities (e.g., , acute hypoglycemia) concurrently with fluid resuscitation. Address subacute electrolyte abnormalities after stabilization.
- Fluid administration in the first 2–4 hours of presentation is typically more aggressive, depending on the degree of fluid loss.
- See “Immediate hemodynamic support” for the approach to fluid therapy in patients presenting with undifferentiated shock.
- See “Strategies for parenteral fluid therapy” for further details about IV fluid therapy for all patients.
Initial IV fluid therapy
- Goal: to correct hypovolemia
Approach to fluid administration
- Type of fluid: isotonic cystalloids, i.e., NS or Lactated Ringer's 
- Rate and amount
- Severe fluid loss ( ): Aggressive IV fluid boluses, e.g., 20 mL/kg (∼1000 mL in an average adult)
- Patients with fluid replacement
: Judicious IV
- Consider noninvasive test, e.g.,
- Consider smaller volume 5–10 mL/kg (∼500 mL in an average adult) , e.g.,
- Titrate to individual patient needs (e.g., based on )
- Reevaluate every 15–30 minutes during bolus administration, then hourly.
- Clinical deterioration
- Clinical improvement
Oral rehydration therapy 
- Goal: to correct hypovolemia and dehydration using oral rehydration solutions
- Contraindications include:
Types of oral rehydration solution (ORS)
- Compounded ORS (powdered)
- Commercial ORS (premixed) 
- Rehydration solution for malnourished children (ReSoMal): formulation of ORS specific for children with severe malnutrition 
- Polymer-based ORS: ORS with complex carbohydrates (e.g., from rice, wheat, or corn) instead of glucose 
- ORS alternative (children with mild gastroenteritis): Can consider apple juice diluted to half strength instead of traditional ORS.
Approach to fluid administration 
- Consider a preemptive antiemetic in patients with a history of recent vomiting (see “Overview of antiemetics”).
- Prescribe an initial volume and rate of ORS based on age and severity of fluid loss (see “Sample ORS protocols”)
- Encourage frequent small-volume ingestion to reduce the risk of abdominal discomfort and vomiting.
- Perform regular clinical reassessment (see “Clinical features of dehydration and hypovolemia”)
- Consider serial electrolytes and other in at-risk patients.
|Sample ORS protocols|
|Recommended total ORS volume to administer over the first 4 hours ||Suggested administration schedule|
| || |
- Clinical deterioration
- Clinical improvement
Although common home remedies for rehydration (e.g., sports drinks, teas, soda, juice, and broths) can be used for the prevention of dehydration and hypovolemia in patients with GI illness, they are generally not recommended on their own for treatment, as they may worsen diarrheal symptoms and/or cause severe electrolyte imbalances. 
Total ORS volume required in the first 4 hours for adults and children with or can be approximated to 75 mL/kg. 
Subcutaneous fluid therapy
- Fluids are infused subcutaneously (typically into the upper back between the scapula, abdomen, thigh, or arm) and then slowly absorb into the intravascular compartment.
- Provides a therapeutic alternative in mild fluid loss or moderate fluid loss if the patient:
- Is unable to tolerate enteral fluids (e.g., PO or NG) and IV access is not preferred
- Needs extra fluids to increase the likelihood of successful peripheral IV placement
- Isotonic fluids are recommended 
- Adults: 50–1250 mL/hour 
- Children: 20 mL/kg/hour
Continued fluid needs refer to those that remain after the initial phase of patient stabilization (e.g., after the first 2–4 hours) and are typically administered slowly over the following 24–48 hours.
- Address any urgent continued fluid needs: Begin management concurrently with .
- After stabilization with fluid resuscitation, calculate or estimate:
- Determine the best route to replenish fluids.
Tailor fluid regimen to individual patient needs.
- All fluid and electrolyte requirements can be combined and ordered in one IV solution.
- Isotonic fluids, hypotonic fluids, and free water can also be given separately to allow for individual titration.
- Make adjustments to total fluid rate (or component fluids) based on:
- See also “ .”
Continued fluid needs comprise the remaining fluid deficit (isotonic and free water loss), daily maintenance fluid requirements, ongoing fluid loss, and any fluids required to treat metabolic disturbances.
Management of metabolic disturbances
- Manage acute severe metabolic disturbances immediately, for example:
- Consider monitoring electrolytes and glucose to prevent iatrogenic disturbances:
- Adjust total fluid balance according to the fluid load of each treatment, for example:
|Common metabolic disturbances associated with dehydration and hypovolemia|
|Metabolic disturbance||Etiologies to consider||Treatment|
|Hyponatremia|| || |
|Hypokalemia|| || |
Remaining fluid deficit
Estimate the total fluid deficit (upon initial presentation).
- Estimate the patient's % weight loss clinically, e.g., vs. vs.
- Calculate the estimated total fluid volume loss using estimated % weight loss and their current weight.
- Estimate the patient's well weight: current weight/(1 - % weight loss as a decimal)
- Calculate the weight difference: well weight - current weight
- The estimated total fluid loss in L ≈ calculated weight difference in kg.
Calculate the remaining fluid deficit.
- Remaining fluid deficit = Total fluid loss - total volume resuscitative fluids administered.
- The remaining deficit needs to be administered over the following 24–48 hours.
- For hypernatremic patients:
See “maintenance fluid calculations and .” for further details on
- Maintenance requirements depend on age, weight, and comorbidities.
- Daily fluid requirements can be met via enteral (e.g., PO/NG) and/or parenteral (e.g., IV) routes.
- Isotonic fluids containing dextrose (e.g., IV fluids in adults and children.  ) are the preferred maintenance
Ongoing GI fluid loss
Routinely reassess patients for ongoing fluid loss to prevent recurrence or worsening of fluid deficits. The frequency of monitoring depends on the severity of vomiting and diarrhea. See “ ” for the basic management of patients with other types of ongoing fluid losses (e.g. enteric fistulas, burns).
Inpatient setting: Fluid loss can be replaced via parenteral routes (e.g., IV) and/or enteral routes (e.g., PO/NG).
- Direct measurement: 1:1 replacement of fluid loss (e.g., vomiting and diarrhea) 
- If the volume of an episode of emesis or diarrhea is not measured, weight-based approximations can be used (see “Outpatient setting”).
- Add 10–15 mEq/L of potassium chloride (KCl) to fluid for replacement of GI losses and consider adding bicarbonate (NaHCO3-) for replacement of diarrhea. 
Outpatient setting: ORS
- Calculations to estimate fluid loss
- 10 mL/kg for each episode of diarrhea
- 2–10 mL/kg for each episode of vomiting 
- Fixed volume 
- Calculations to estimate fluid loss
Follow local hospital protocols if available and tailor disposition to individual patient needs.
Reasons for hospital admission 
Hospitalization is typically recommended for patients with any of the following:
- Severe fluid loss
Moderate fluid loss or mild fluid loss requiring parenteral fluids, due to, for example:
- Inability to tolerate oral fluids
- Significant electrolyte abnormalities
- High risk of developing severe dehydration and/or hypovolemia , e.g.:
- Inability to understand or adhere to discharge instructions or attend follow-up appointments
Evaluation for hospital discharge 
For patients requiring inpatient admission, consider discharge home with continued home-based therapy if all of the following are present:
- Electrolyte abnormalities have been corrected.
- Patients are able to meet daily fluid requirements and replace ongoing fluid loss through oral routes.
- Ongoing fluid loss has resolved or is improving.
- No barriers to follow-up exist.
Evaluation for discharge from ambulatory settings after a period of observation (e.g., 4–6 hours) 
For patients seen in the emergency room or clinics, consider discharge home with continued home-based therapy if all of the following are present:
- Mild fluid loss or moderate fluid loss without signs of shock or hemodynamic instability
- Clinical improvement through the observation period
- Ability to tolerate oral fluids: Consider an observed 1-hour oral fluid challenge in patients with a history of vomiting to assess this.
- Counseling provided on:
- Follow-up arranged with primary care provider, urgent care center, or emergency room
- prerenal renal failure →
- Increased risk of infection, particularly of the urinary tract
- Osmotic demyelination syndrome
- Patients with diabetes mellitus: Dehydration can trigger diabetic ketoacidosis.
We list the most important complications. The selection is not exhaustive.
Acute management checklist
- Perform rapid ABCDE survey with an updated set of vital signs.
- Examine for and classify fluid loss into mild, moderate, or severe.
- Provide supportive care (e.g., antiemetics, pain management).
- Identify and treat the underlying cause.
(treat as )
- Obtain IV access.
- Start continuous cardiac monitoring and serial blood pressure monitoring.
- Obtain blood samples including BMP and check POC glucose.
- Provide and .
- Follow fluid resuscitation accordingly. and adjust
- Address urgent metabolic disturbances, e.g., 50% dextrose for acute hypoglycemia, 3% NaCl for severe symptomatic hyponatremia.
- Address after stabilization.
- Admit to hospital.
- Consider serial BMP and glucose monitoring.
Mild or moderate fluid loss
- Consider securing IV access in case IV fluids are needed (e.g., contraindications to ORS, unable to tolerate enteral fluids, or clinical deterioration).
- ORS). : Prioritize enteral fluids (
- : Administer parenteral fluids OR enteral fluids.
- If IV fluids judiciously if used. present, administer
- For enteral fluids, calculate the total 4-hour ORS volume using the rule of thumb: 75 mL/kg.
- Prescribe ORS in 5-minute aliquots by dividing the total 4-hour ORS volume by 48.
- Perform frequent clinical reassessments.
- Address .
- Consider hospital admission vs. discharge from care setting after a period of observation (e.g., 4–6 hours).