Dehydration

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Introduction

Dehydration, or volume depletion, is a major cause of morbidity and mortality worldwide.

The Case of...

a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.

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Causes and Risk Factors

True volume depletion is caused by decreased effective circulating volume and total ECF volume. The most common causes include:

gastrointestinal losses: bleeding, vomiting, diarrhea
renal losses: osmotic or drug-induced diuresis, acute tubular necrosis (recovery phase), diabetes insipidus
skin and respiratory losses: sweat, burns
internal sequestration: peritonitis, pancreatitis, rhabdomyolysis

Volume depletion can also occur with decreased effective circulating volume but increased total extracellular fluid volume. Some causes include:

congestive heart failure
liver disease
sepsis
nephrotic syndrome
pregnancy
anaphylaxis

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Pathophysiology

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Signs and Symptoms

history
physical exam
pediatrics

History

Physical Exam

Clinical manifestations are due to underfilling of the arterial tree and begin with orthostatic hypotension and tachycardia. Recumbent tachycardia soon follows, and urine output diminishes. Severe volume depletion can lead to signs and symptoms of shock, such as mental confusion and cool skin. However, clinical findings may also be absent, such as can occur in people receiving cardiovascular drugs.

Dry mucous membranes, sunken eyes.

Dry axilla is one of the most sensitive (LR 2.8)

Dry mucous membranes not very sensitive, as many people are mouth breathers.

Pediatrics

Mild: <50 ml/kg (5% of infants, 3% of children)

Moderate: 50-90 ml/kg water loss (10% of infants, 6% of children)

Severe: >100 ml/kg water loss (15% of infants, 9% of children)

	mild	moderate	severe
neurologic status	alert, consolable, or irritable	alert, irritable	lethargic or obtunded
pulse	appropriate or increased	slightly increased	increased
mucus membranes	moist	dry	parched
eyes	moist	slightly dry/deep set	dry/sunken
tears	present	present, reduced	absent
urine output	diminished	significantly dec.	oligouric
fontanelle	flat	soft, slightly depressed	sunken
skin	normal	dry	clammy
skin turgor	good	mild tenting	significant tenting, or no turgor
capillary refill	<2 seconds	2-3 seconds	>3 seconds

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Investigations

lab investigations
diagnostic imaging

Lab Investigations

If the cause is extra-renal, urine is highly concentrated, salt poor, and acidic. If the kidneys are involved, urine is inapproporiately dilute but can also be rich in salt.

Diagnostic Imaging

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Treatments

Quantity and rate of fluid replacement depends on severity of depletion.

In children, bolus always 20 cc/kg 0.9% NS, then re-assess, bolus max x3

Hypodermoclysis: infusion of fluid into sc tissue. Appears as effective IV hydration for mild to moderate hydration. Infuse up to 2L per space, often in back, thighs, or abdomen. Harder for people to pull out. Use gravity or pump at 20-125 mL/hr. Over 24hrs, up to 1.5L can be delivered at one site. Caution if bleeding disorder or skin problems.

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