Principles of Managing Dehydration 💧

Dehydration is a common but potentially serious clinical condition that reflects a failure of the body to maintain fluid and electrolyte balance — a core example of disrupted homeostasis.

Even small fluid deficits can impair circulation, organ perfusion, and cellular function, particularly in infants, older adults, and unwell patients.

Core principles of dehydration management

✅ Assessment of Severity 

Dehydration is broadly classified as mild, moderate, or severe based on clinical signs such as:

• Thirst and dry mucous membranes
• Tachycardia and reduced urine output
• Delayed capillary refill or hypotension (suggesting circulatory compromise)

This assessment guides how urgently and by what route fluids are replaced.

✅ Routes of rehydration: least invasive first

In clinical practice, fluids are given via the safest and simplest effective route:

1. Oral rehydration – preferred whenever possible
2. Nasogastric (NG) rehydration – if oral intake is inadequate or unsafe (especially in babies)
3. Intravenous (IV) fluids – for severe dehydration or shock
4. Intraosseous (IO) access – emergency access when IV is not rapidly achievable

This hierarchy reflects both physiology and patient safety.

✅Why oral rehydration works (salty + sweet)

Oral rehydration solutions (ORS) are carefully designed mixtures of:

• Sodium (salt)
• Glucose (sugar)
• Water

Glucose and sodium are absorbed together in the small intestine via coupled transport mechanisms.
When sodium is absorbed, water follows, allowing effective rehydration even during ongoing diarrhoea.

This is why plain water alone is often insufficient — and why ORS can be life-saving. You don't have to buy prepared products - they are easy to make. 

✅  Rehydration Therapy

• Mild to moderate dehydration: 

Oral rehydration therapy (ORT) is the preferred approach using oral rehydration solution (ORS) to replace lost fluids and electrolytes.

• Severe dehydration or shock: 

Intravenous isotonic crystalloids (e.g. normal saline or Hartmann’s solution) are required to rapidly restore circulating volume.. Consider IO if life threatening and no access

✅ Correction of Electrolyte Imbalances 

Significant dehydration may be accompanied by abnormalities in:

• Sodium
• Potassium
• Glucose

These are particularly important in patients with vomiting, diarrhoea, renal disease, or prolonged illness.

✅ Treat the cause, not just the fluids

Rehydration alone is not enough. Ongoing losses must be addressed, whether due to:

• Gastroenteritis
• Heat illness or excessive sweating
• Burns
• Endocrine or renal conditions

✅ Monitoring and Reassessment 

Fluid management is dynamic. Clinicians continuously reassess:

• Vital signs
• Urine output
• Clinical appearance and mental state

This ensures recovery while avoiding complications such as fluid overload.

🩺 Think like a doctor

When you see a dehydrated patient, clinicians are always asking two linked questions:

How dehydrated is this patient?

What is the safest and most effective way to rehydrate them right now?

These decisions are based on clinical signs, not just the history — and they guide both urgency and route of treatment.

Clinical vignette 1: “Drinking, but not quite right”

A 4-year-old child presents with a 2-day history of vomiting and diarrhoea.
They are alert but tired, have dry lips, and their parents report fewer wet nappies than usual. Heart rate is mildly elevated. Blood pressure is normal.

Pause and think:

• How severe is the dehydration?
• What is the most appropriate initial management?

Clinical reasoning:
This presentation is most consistent with mild to moderate dehydration.
The child is conscious, perfused, and able to drink.

➡️ Preferred management:
Oral rehydration therapy (ORT) using an oral rehydration solution.

This approach supports physiological absorption of water and electrolytes while avoiding unnecessary invasive treatment.

Dehydration signs in infants

Clinical vignette 2: “Looks unwell”

An 82-year-old woman from a residential aged care facility presents with confusion and lethargy. She has had poor oral intake for several days during a heatwave. On examination she is tachycardic, hypotensive, has delayed capillary refill, and minimal urine output.

Pause and think:

• How severe is the dehydration?
• Is oral rehydration appropriate?

Clinical reasoning:
This presentation suggests severe dehydration with circulatory compromise.
The patient is not safe to manage with oral fluids alone 

➡️ Preferred management:
Intravenous isotonic fluids to rapidly restore circulating volume.

Here, speed and reliability of delivery are critical.

Reduced skin turgor can be significant

Key takeaway for medical students

Fluid management is not about memorising recipes.
It’s about matching:

• Severity of dehydration
• Physiological need
• Safest effective route

As your training progresses, you’ll learn how much, how fast, and which fluid.
For now, focus on recognising the problem and choosing the right approach.