Approach to Hypernatraemia PDF

13 Approach to hypernatraemia 1.Ensure correct blood collection tube sodium citrate anticoagulant > - Blue tube (trisodium citrate, used...

13 Approach to hypernatraemia 1.Ensure correct blood collection tube sodium citrate anticoagulant > - Blue tube (trisodium citrate, used in clotting profile and venesection for polycythaemia) contains additional Na leading to pseudohypernatraemia § Ix: OG –ve (calculated SOsm > measured SOsm) 2. Investigate the cause of hypernatremia and treat accordingly Category Volume status DDx Investigations Treatment Hypervolemic ⑪ Iatrogenic (hypertonic Furosemide 40mg IV + D5 Sodium saline, NaHCO3) gain ②Hyperaldosteronism Impaired thirst ↑Uosm > 300 Calculation of body water deficit^ Impaired No access to water Na < 160: water PO water Na > 160: D5 or half-half solution intake Euvolemic Diabetes insipidus (DI) Polyuria Acute DI: DDAVP 4-8 mcg Q3-4h ↓Uosm < 150 Chronic central DI: DDAVP 10- 40mcg daily intranasally Chronic nephrogenic DI: HCTZ 25mg daily, indapamide 2.5mg Water loss daily or amiloride 5mg daily Hypovolemic Renal loss Polyuria NS 500ml/h till no orthostatic Osmotic diuresis (glucose, ↑Uosm > 300 hypotension, then replace water mannitol, urea*) U[Na] > 40 by calculation of body water Extrarenal loss ↓Uosm < 150 deficit^ Increased insensible loss U[Na] < 20 Na < 160: water PO (fever, sweating) Na > 160: D5 or half-half solution Diarrhoea *↑↑urea in post-obstructive uropathy exceeds the reabsorption maximum in renal tubules, and becomes an effective osmole ^Body water deficit (L) = BW x 0.6 x (measured [Na] -140)/140 Add insensible loss ~ 0.5L/day Replace half of body water deficit over first 24h, then remaining deficit over next 1-2 days Correct Na < 12 mM/24h to avoid cerebral oedema Sea water ingestion Sea water contains 3.5% NaCl (1200 mOsm/kg) Hypertonicity sensed by osmoreceptor: o Trigger thirst centre: drink more sea water à vicious cycle o Trigger ADH: with urine maximally concentrated at 1200mOsm/kg and obligatory osmole load ~600mOsm, urine volume needed to excrete > water taken Drugs associated with dysnatraemia Drug-induced hyponatraemia Drug-induced hypernatraemia Diuretics: thiazides, loop diuretics Na gain: hypertonic saline, NaHCO3 SIADH: SSRI, carbamazepine, morphine Renal water loss: Osmotic diuretics: mannitol, glucose Nephrogenic DI: lithium Central DI: lithium, phenytoin Thirst stimulation: ACEI (rare)