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Dehydration and hypovolemia

Last updated: July 13, 2021

Summarytoggle arrow icon

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 increased 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.

See also “Intravenous fluid therapy” and “Shock.”

Dehydration and hypovolemia often occur together, however, there are significant pathophysiological and clinical differences between the processes that can affect management.

Overview of dehydration and hypovolemia[1][2][3]
Dehydration Hypovolemia (extracellular volume depletion)
Typical causes[1][4]
Fluid loss
  • Hypotonic (i.e., includes free water loss)
  • Occurs from all body fluid compartments
  • Intracellular compartment is most affected
  • Leads to ECF hypertonicity
  • Typically isotonic
  • Occurs primarily from ECF
  • Intracellular compartment mostly unaffected.
  • Typically does not affect ECF tonicity
  • Can progress to shock if severe (see “Hypovolemic shock”)
Compensatory mechanism
  • Activation of thirst center
  • ADH release
  • Creation of additional intracellular osmoles [3][4]
Clinical features

Diagnostics

(See “Laboratory findings in hypovolemia and dehydration for details)

Treatment

References:[5][6][7][8][9]

Common features

  • General symptoms include thirst, headache, weakness, dizziness, and fatigue.
  • Physical findings often include:
  • Hemodynamic instability may be present in severe cases

Estimating severity

Clinical features of dehydration and hypovolemia[1][10]
Clinical features

Mild fluid loss

(3–5% weight loss)

Moderate fluid loss

(6–9% weight loss)

Severe fluid loss, i.e, hypovolemic shock

(≥ 10%weight loss)

Symptoms Behavior and activity level
  • Normal
  • Reduced activity level
  • Children: may also be irritable
  • Lethargic
  • Disoriented
  • Children: may also have marked irritability when touched
Thirst
  • Slightly increased
  • Moderately increased
Physical findings Vitals
  • HR: normal
  • BP: normal
  • Peripheral pulse: strong, easily palpable
  • RR: normal
  • HR: elevated
  • BP: Normal or slightly reduced; orthostatic hypotension may be present.
  • Palpated pulses weaker than normal
  • RR: may be elevated with deep inspirations
Eyes
  • Normal appearance
  • Normal tear production
  • Sunken orbits
  • Decreased tear production
  • Deeply sunken orbits
  • No tear production
Skin
Mucous membranes
  • Tacky
  • Dry
  • Extremely dry
  • Deep longitudinal furrows may be visible on the tongue
Urine output
  • Normal or slightly decreased
  • Moderately decreased
Anterior fontanelle (infants only)
  • Normal
  • Sunken
  • Markedly sunken

Approach

Dehydration and hypovolemia are clinical diagnoses.

Laboratory studies

Laboratory findings in dehydration and hypovolemia [2]
Dehydration Hypovolemia

Plasma

Urine

Replacing body fluid losses typically involves rapid correction of extracellular volume depletion and judicious correction of intracellular dehydration (see also “IV fluid therapy strategies”).

Approach

Stabilization through correction of intravascular volume deficit with fluid resuscitation is the first priority. Manage urgent metabolic abnormalities (e.g., severe symptomatic hyponatremia, acute hypoglycemia) concurrently with fluid resuscitation. Address subacute electrolyte abnormalities after stabilization.

Initial IV fluid therapy[10][12][13]

Avoid hypotonic solutions in IV fluid resuscitation, especially in children, as this can cause hyponatremia and cerebral edema. [11]

Oral rehydration therapy [10][12]

Sample ORS protocols[10][16][21]

Severity

Recommended total ORS volume to administer over the first 4 hours [11][12] Suggested administration schedule
Mild fluid loss
  • 30–50 mL/kg
  • ∼ 2–4 L for an average-sized adult
  • Option 1[10]
    • Determine the recommended 4-hour volume based on the patient's weight and severity of fluid loss.
    • Divide this volume into smaller amounts to be given every 5 minutes.
  • Option 2
    • Start with 1–2 mL/kg (max. 30 mL) every 5 minutes.
    • Increase gradually as tolerated to meet the recommended replacement volume.
Moderate fluid loss
  • 60–90 mL/kg
  • ∼ 4–5.5 L for an average-sized adult

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. [10]

Total ORS volume required in the first 4 hours for adults and children with mild fluid loss or moderate fluid loss can be approximated to 75 mL/kg. [12]

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 [22]
    • Adults: 50–1250 mL/hour [23]
    • 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.

Approach

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:
    • Addition of electrolyte solutions or crystalloid required: Reduce intake of other replacement fluids to avoid fluid creep.
    • Restriction of free water required (rare in dehydrated patients): Reduce ORS accordingly and replace it with isotonic parenteral fluid.
Common metabolic disturbances associated with dehydration and hypovolemia
Metabolic disturbance Etiologies to consider Treatment
Hyponatremia
  • Replacement of isotonic fluid losses with hypotonic solutions
Hypernatremia
Hypokalemia
  • GI fluid loss
Hyperkalemia
Hypoglycemia
Hyperglycemia

Remaining fluid deficit

The remaining fluid deficit includes any isotonic fluid deficit and free water deficit that persists after fluid resuscitation with isotonic solutions.

The free water deficit is a part of the remaining fluid deficit. Do not add the free water deficit to the remaining fluid deficit.

Daily maintenance fluid requirements

See “Maintenance fluid therapy” for further details on maintenance fluid calculations and daily fluid requirements for special patient groups.

  • 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., 5% dextrose in 0.9% NaCl) are the preferred maintenance IV fluids in adults and children. [25][26]

Ongoing GI fluid loss[10]

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 “Replacement of ongoing fluid loss” 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) [16]
    • 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. [12]
  • 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 [16][21][27]
    • Fixed volume [16]
      • Children < 10 kg: 60–120 mL ORS for each episode of vomiting or diarrhea
      • Children ≥ 10 kg: 120–240 mL ORS for each episode of vomiting or diarrhea
      • Adults: 250 mL after every episode of vomiting or diarrhea [28]

Follow local hospital protocols if available and tailor disposition to individual patient needs.

Reasons for hospital admission [11][16]

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.:
    • Young infants
    • Elderly patients
    • Patients with prolonged or excessive fluid loss
    • Patients with underlying health conditions and those who use certain medications, e.g., diuretics
  • Inability to understand or adhere to discharge instructions or attend follow-up appointments

Evaluation for hospital discharge [11][16]

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) [11][16]

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

References:[29][30][31][32]

We list the most important complications. The selection is not exhaustive.

All patients

Severe fluid loss (treat as hypovolemic shock)

Mild or moderate fluid loss

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