Makindo Medical Notes

Related Subjects: |Water Physiology |Dehydration Physiology |Sodium Physiology |Potassium Physiology |Aldosterone Physiology |Atrial Natriuretic Peptide (ANP) |Brain Natriuretic Peptide (BNP)

💧 Dehydration occurs when fluid losses exceed intake, creating a fluid deficit that disrupts homeostasis. It affects multiple systems and, if severe, can progress to hypovolaemic shock with multi-organ failure. ⚠️ High-risk groups: frail elderly, children, those with chronic disease.

🌡️ Causes of Dehydration

• Inadequate Intake 🥤: Poor access to fluids, reduced thirst drive (elderly), illness, neglect.
• Excess Losses 💦:
  • GI: Diarrhoea, vomiting, stomas, fistulas.
  • Renal: Polyuria (diabetes, diuretics).
  • Skin: Sweating (fever, heat, exercise, burns).
• Medical Conditions 🩺: Diabetes mellitus/insipidus, adrenal insufficiency, sepsis, cystic fibrosis.

⚙️ Physiological Effects

• Cardiovascular ❤️: ↓ preload → ↓ CO → tachycardia, hypotension → hypovolaemic shock.
• Renal 🧪: Oliguria, concentrated urine, risk of AKI.
• Neurological 🧠: Irritability, headache, confusion, drowsiness → seizures/coma if severe.
• Electrolytes ⚡: Na⁺/K⁺/Cl⁻ derangements → weakness, cramps, arrhythmias.
• GI 🍽️: Constipation, ileus in severe states.

🧾 Regulation of Fluid Balance

• 🔔 Thirst mechanism (hypothalamus senses ↑ plasma osmolality).
• 💧 ADH (posterior pituitary): ↑ water reabsorption in kidneys.
• 🧂 Aldosterone: Na⁺ + water retention.
• 🏃 ANP: counters overload by promoting Na⁺ excretion.

🔎 Clinical Recognition

• Mild: Thirst, dry mouth, dark urine, dizziness.
• Moderate: Tachycardia, reduced skin turgor, delayed capillary refill.
• Severe: Hypotension, oliguria/anuria, confusion, shock.
• Labs: U&E (↑ urea:creatinine ratio), electrolytes, urine osmolality.

🧪 Case Vignette

👵 An 82-year-old woman in a care home is drowsy and has not been eating or drinking for 3 days due to flu-like illness. Exam: dry mucous membranes, tachycardia (110), BP 90/60, urine output minimal. Diagnosis: severe dehydration with hypovolaemic shock. Management: IV fluids (0.9% NaCl), careful monitoring, and infection screen.

💊 Management

• Initial: ABCDE, assess volume status.
• Mild–moderate: Oral fluids or Oral Rehydration Solution (ORS – sodium + glucose).
• Severe: IV crystalloids (0.9% NaCl or Hartmann’s), boluses in shock. Monitor U&E, urine output.
• Treat cause: Stop diuretics, control diabetes, treat sepsis or gastroenteritis.

🧠 Clinical Tips for OSCE

✅ Always ask about fluid intake, vomiting/diarrhoea, polyuria, fevers. ✅ Look for postural hypotension in mild–moderate dehydration. ✅ In elderly: delirium + AKI may be the first signs. ✅ Document fluid balance (input/output chart).

📌 Summary

Dehydration disrupts cardiovascular, renal, neurological, and GI systems. Mild cases → thirst, dark urine, dizziness. Severe cases → hypotension, AKI, shock. 💡 Key learning: identify early, replace fluids appropriately, treat the underlying cause.