Hyponatremia- Physiology

Hyponatremia: Physiology
Authors: Mannat Dhillon Reviewers: Andrea Kuczynski Kevin McLaughlin* * MD at time of publication
Abnormal Renal H2O Handling (hypo-osmolar serum)
AKI/CKD Heart failure
↓ renal blood flow
↓ glomerular filtration
GFR < 25 mL/min, ↓ urine dilution ↑ H2O retention Note: • Plasma [Na+] is regulated by water intake/excretion, not by changes in [Na+]. • Artifactual hyponatremia can be differentiated by a normal or hyperosmolar serum. Appropriate ADH secretion ↓ EABV Hypovolemia: losses via GI, renal, skin, 3rd spacing, bleeding Hypervolemia: heart failure, cirrhosis ↑ Na+/H2O absorption at PCT ↓ EABV, ↑ H2O retention Urine [Na+] < 20 mmol/L Hereditary: tubular disorders (Bartter, Gitlemann syndromes). Thiazide diuretics Inappropriate: SIADH, hypothyroidism, AI Normal EABV Anti-diuresis Primary polydipsia, eating disorder ↑ H2O or ↓ solute intake ↓ Osmoles Impaired desalination Block NCC ↑ H2O retention ↑ Na+/K+ excretion Hyponatremia Serum [Na+] < 135 mmol/L Urine osmolality > 100 mmol/L
Urine osmolality < 100 mmol/L Cerebral edema, ↑ intracranial pressure, vasoconstriction If hypovolemic: ↓ JVP, ↓ blood pressure Lethargy, altered mental status Abbreviations: AKI: Acute Kidney Injury CKD: Chronic Kidney Disease GFR: Glomerular Filtration Rate H2O: Water PCT: Proximal Convoluted Tubule EABV: Effective Arterial Blood Volume NCC: Na+/Cl- Co-Transporter SIADH: Syndrome of Inappropriate ADH Secretion AI: Adrenal Insufficiency Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published January 11, 2019 on www.thecalgaryguide.com