Disorders of Water Balance PDF

Disorders of water balance Lecture Number 4.2 Status Done Type Lecture 4.2 Disorders of water balance Overview This lecture covers disturbances of water balance, particularly focusing on the conditions of hyponatremia (low plasma sodium concentration) and hyper...

Disorders of water balance Lecture Number 4.2 Status Done Type Lecture 4.2 Disorders of water balance Overview This lecture covers disturbances of water balance, particularly focusing on the conditions of hyponatremia (low plasma sodium concentration) and hypernatremia (high plasma sodium concentration). It explores how sodium and water balance influence extracellular fluid (ECF) osmolality, brain volume alterations, and their role in clinical symptoms. The mechanisms of these imbalances, differential diagnosis, and treatments are discussed in detail, with attention given to their pathophysiological impacts on cellular and organ function. Learning Objectives Objective 1: Define the central role of impaired water regulation in hyponatremia and hypernatremia. Objective 2: Describe the effects of plasma osmolality on brain volume and related symptoms. Objective 3: Explain the mechanisms behind hyponatremia and hypernatremia. Objective 4: Outline differential diagnosis methods and treatment strategies for water balance disorders. Key Concepts and Definitions Plasma Osmolality: Calculated as 2[Na+] + [glucose] + [urea]. Sodium is the main contributor, but glucose and urea can affect the measurement in conditions like diabetes or renal failure. Hypernatremia: Serum sodium concentration > 145 mmol/L, caused by water loss or sodium gain, leading to hyperosmolarity. Hyponatremia: Serum sodium concentration < 135 mmol/L, associated with hypoosmolarity and often found incidentally in hospitalized patients. Clinical Applications Case Study: A 70-year-old patient with chronic renal failure presents with confusion and elevated plasma sodium. Investigations reveal a serum sodium concentration of 150 mmol/L, consistent with hypernatremia secondary to water loss. Diagnostic Approach: Step 1: Assess osmolality (normal, high, or low). Step 2: Assess ECF volume (hypovolemic, euvolemic, or hypervolemic). Step 3: Measure urinary sodium concentration. Treatment Options: Correct underlying cause and fluid balance. In hypovolemic hypernatremia, restore volume with isotonic saline before addressing hypernatremia with hypotonic solutions. Pathophysiology Hyponatremia: Results from excessive water relative to sodium, leading to cellular swelling. Key mechanisms include SIADH (syndrome of inappropriate ADH secretion), heart failure, and liver disease. Hypernatremia: Caused by water loss or sodium gain, leading to cellular dehydration. It is most common in patients with impaired thirst mechanisms. Pharmacology  Demeclocycline: Used to treat SIADH by inhibiting ADH action on the kidney's principal cells. Hypertonic Saline: Administered in acute symptomatic hyponatremia to raise sodium levels and reduce cerebral edema. Differential Diagnosis Hyponatremia: Classified by osmolality and volume status. Hypovolemic hyponatremia is linked to renal or GI sodium loss, while hypervolemic hyponatremia often occurs in heart failure. Hypernatremia: Associated with water loss, especially in patients with impaired thirst, such as the elderly or intubated patients. Investigations Plasma Osmolality: Helps differentiate between hyperosmolar, isosmolar, and hypo-osmolar states. Urinary Sodium : Helps identify the cause of hyponatremia—whether renal or extra-renal. Key Diagrams and Visuals Summary and Key Takeaways Takeaway 1: Hyponatremia is common in hospitalized patients and can have serious neurological consequences if not treated. Takeaway 2: Hypernatremia is less common but presents significant risks, particularly in patients with impaired thirst. Takeaway 3: Treatment must carefully consider volume status and osmolality to avoid complications like cerebral edema or osmotic demyelination. Further Reading/References Resource 1: Brenner & Rector’s The Kidney, 11th edition. Resource 2: Comprehensive Clinical Nephrology, Fig. 8.7. Questions/Clarifications Question 1: How do cerebral adaptations differ in acute vs. chronic hyponatremia? Question 2: What factors should guide the rate of sodium correction in hypernatremia?