Fluid and electrolyte management

Fluid and electrolyte management

Fluid and electrolyte management

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Maintenance Fluids - The Daily Drip

  • Calculating Rate: Use the Holliday-Segar ($4/2/1$) rule for hourly rate.
    • $4$ mL/kg/hr for first 10 kg
    • $2$ mL/kg/hr for next 10 kg
    • $1$ mL/kg/hr for remaining weight
  • Daily Needs:
    • 📌 Think 100 Na+, 50 K+, 100 Cl- (mEq) and 100g sugar.
    • Typical maintenance fluid: D5 1/2 NS + 20 mEq KCl/L.
    • Monitor urine output: goal 0.5-1.0 mL/kg/hr.

⭐ Dextrose (as D5) in maintenance fluids is not for calories but to prevent muscle catabolism and starvation ketosis.

Holliday-Segar 4-2-1 Rule for Fluid Calculation

IV Fluid Types - Saline & Friends

  • Crystalloids: Solutions with small molecules (e.g., electrolytes, dextrose) that pass easily from the bloodstream to tissues. Used for resuscitation and maintenance.
    • Isotonic: 0.9% Normal Saline (NS), Lactated Ringer's (LR).
    • Hypotonic: D5W (isotonic in the bag, but physiologically hypotonic as dextrose is metabolized).
    • Hypertonic: 3% NaCl.
  • Colloids: Solutions with larger molecules (e.g., Albumin) that stay in the vascular space longer.
FluidNa⁺ (mEq/L)Cl⁻ (mEq/L)K⁺ (mEq/L)BufferpH
0.9% NS1541540None~5.5
LR1301094Lactate~6.5

Fluid Status Assessment - Reading the Signs

FeatureHypovolemia (Dehydration)Hypervolemia (Fluid Overload)
VitalsTachycardia, Orthostasis↑ JVD, Hypertension
ExamDry mucous membranes, ↓ skin turgorPitting edema, Pulmonary rales
LabsBUN:Cr > 20:1, ↑ Hct, Urine Na+ < 20 mEq/L↓ Hct (dilutional)
Urine↓ Output (Oliguria)↑ Output (Polyuria)

⭐ Tachycardia is often the earliest sign of hypovolemia in a post-operative patient.

Electrolyte Mayhem - The Usual Suspects

  • Hyponatremia (↓Na+)

    • Causes: SIADH, excess hypotonic fluids, adrenal insufficiency.
    • ⚠️ Max correction 8-10 mEq/L/24h to prevent Osmotic Demyelination Syndrome (ODS).
  • Hypernatremia (↑Na+)

    • Causes: Diabetes Insipidus (DI), dehydration, insensible losses.
  • Hypokalemia (↓K+)

    • Causes: Diuretics (furosemide), GI losses (diarrhea, vomiting).
    • 📌 EKG: Flat T waves, prominent U waves.
    • Max infusion: 10 mEq/hr (peripheral), 20 mEq/hr (central).
  • Hyperkalemia (↑K+)

    • Causes: Renal failure, tissue damage (rhabdomyolysis), ACE inhibitors.

⭐ Never add potassium to an IV bag for a patient who is anuric or has severe renal failure without confirming their potassium level first.

High-Yield Points - ⚡ Biggest Takeaways

  • The post-op stress response (↑ADH, ↑aldosterone) causes sodium and water retention.
  • Calculate maintenance fluids with the 4/2/1 rule; a common choice is D5 ½NS + 20mEq KCl.
  • Post-op hyponatremia is often iatrogenic from excess free water (hypotonic fluids).
  • Third spacing causes intravascular depletion; replete with isotonic crystalloids (LR or NS).
  • Lactated Ringer's is preferred over Normal Saline to avoid hyperchloremic metabolic acidosis.
  • Target urine output of >0.5 mL/kg/hr to ensure adequate end-organ perfusion.

Practice Questions: Fluid and electrolyte management

Test your understanding with these related questions

A 55-year-old man with a history of IV drug abuse presents to the emergency department with an altered mental status. He was found unconscious in the park by police. His temperature is 100.0°F (37.8°C), blood pressure is 87/48 mmHg, pulse is 150/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for multiple scars and abscesses in the antecubital fossa. His laboratory studies are ordered as seen below. Serum: Na+: 139 mEq/L Cl-: 105 mEq/L K+: 4.3 mEq/L HCO3-: 19 mEq/L BUN: 20 mg/dL Glucose: 95 mg/dL Creatinine: 1.5 mg/dL Ca2+: 10.2 mg/dL Which of the following is the most appropriate treatment for this patient’s blood pressure and acid-base status?

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Flashcards: Fluid and electrolyte management

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Short bowel syndrome is most commonly seen in patients who have had _____

TAP TO REVEAL ANSWER

Short bowel syndrome is most commonly seen in patients who have had _____

small intestine resection

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