Fluid and Electrolytes

HYPERPHOSPHATEMIA  Hyperphosphatemia = Serum phosphate > 4.5 mg/dL (1.45 mmol/L) in adults Severity Serum Phosphate Mild 4.6–6 mg/dL Moderate 6–9 mg/dL Severe >9–10 mg/dL  Life-threatening when associated with: Hypocalcemia Arrhythmias Acute kidney injury Tumor lysis syndrome Normal Phosphate Physiology  Distribution 85% – bone (hydroxyapatite) 14% – intracellular <1% – extracellular (measured serum phosphate) Normal Serum […]

Hypocalcemia Hypocalcemia is a reduction in serum ionized calcium, the biologically active form of calcium.calcium should not be checked daily as an “ICU routine.”Total calcium is useful for screening but is an unreliable indicator of ionized calcium, as ionized calcium is affected by factors such as pH, albumin, sodium, and phosphate concentrations.   Calcium exists

Ringer Lactate (RL) vs Plasma-Lyte Feature Ringer Lactate (RL / Hartmann’s) Plasma-Lyte (Plasma-Lyte A / Plasma-Lyte 148) Type Balanced crystalloid Balanced crystalloid Osmolality ~273–278 mOsm/L (slightly hypotonic) ~294–295 mOsm/L (isotonic) pH ~6.5 ~7.4 Sodium 130 mmol/L 140 mmol/L Chloride 109 mmol/L 98 mmol/L Potassium 4 mmol/L 5 mmol/L Calcium 2.7–3 mmol/L None Magnesium None 1.5

Dextrose containing fluids Feature D25 (25% Dextrose) ½ DNS (D5 + 0.45% NaCl) DNS (D5 + 0.9% NaCl) Composition 25 g dextrose/100 mL 5% dextrose + 0.45% saline 5% dextrose + 0.9% saline Dextrose 250 g/L 50 g/L 50 g/L Sodium 0 77 mEq/L 154 mEq/L Chloride 0 77 mEq/L 154 mEq/L Osmolarity ~1260–1400 mOsm/L

Maintenance Fluid in Critical Care (Adult ICU)  In modern critical care, maintenance fluid is prescribed far less frequently than in the past because: Early enteral nutrition provides water. Many IV medications already deliver substantial fluid. Excess maintenance fluid contributes significantly to fluid overload, prolonged ventilation, AKI, and mortality. Definition Maintenance fluid replaces Insensible water loss

Hyperkalemia  Hyperkalemia is defined as:Serum potassium > 5.0 mEq/L(this value is different in different guidelines i.e >5.2mEq/L,>5.5mEq/L) Severity Classification(even this is not universal) Severity Potassium Level Mild 5.1 – 5.5 mEq/L Moderate 5.6 – 6.4 mEq/L Severe ≥ 6.5 mEq/L or ECG changes Clinical severity correlates more with rate of rise rather than absolute level.

HYPOMAGNESEMIA  Serum magnesium < 1.7 mg/dL/< 0.7 mmol/L/< 1.4 mEq/L Serum magnesium represents <1% of total body magnesium → normal serum levels do not exclude intracellular depletion. Severity Classification Severity Serum Mg Level Mild 1.6–1.8 mg/dL (0.66–0.74 mmol/L) Moderate 1.2–1.5 mg/dL (0.49–0.62 mmol/L) Severe <1.2 mg/dL (<0.49 mmol/L) Normal serum magnesium: 1.8–2.4 mg/dL (0.74–1.0 mmol/L)

Hypokalemia Hypokalemia = Serum potassium (K⁺) <3.5 mEq/L,it is is less dangerous than hyperkalemia. Severity Serum K⁺ Mild 3.0–3.5 mEq/L Moderate 2.5–2.9 mEq/L Severe <2.5 mEq/L 98% intracellular and Only 2% extracellular,Therefore serum potassium may not accurately reflect total body stores. Potassium Homeostasis Mechanism Site/Stimulus Action on Potassium Na⁺/K⁺-ATPase Pump Stimulated by insulin, β₂-agonists, thyroid

HYPONATREMIA   DEFINITION Hyponatremia = Serum Na⁺ < 135 mEq/L Most common electrolyte abnormality in ICU Severity classification Severity Serum Na⁺ Mild 130–134 Moderate 125–129 Severe <125  PATHOPHYSIOLOGY   Hyponatremia is fundamentally a disorder of water balance, NOT sodium deficit Excess ADH (vasopressin) → water retention → dilution of Na⁺ ADH PHYSIOLOGY Released from posterior pituitary Stimuli: