## First-Line Osmotic Agent in Acute Head Injury **Key Point:** Mannitol is the gold-standard osmotic agent for acute reduction of intracranial pressure (ICP) in head injury with mass effect. ### Mechanism of Action Mannitol works by: 1. Creating an osmotic gradient across the blood–brain barrier 2. Drawing fluid from the brain parenchyma into the intravascular space 3. Reducing cerebral edema and ICP within 15–30 minutes 4. Peak effect at 20–60 minutes; duration 4–6 hours ### Dosing & Administration - **Dose:** 0.25–1 g/kg IV bolus - **Typical:** 0.5–1 g/kg in acute head injury - **Repeat:** Every 4–6 hours as needed - **Serum osmolality:** Keep <320 mOsm/L to avoid renal toxicity ### Clinical Advantages - Rapid onset (15–30 min) - Proven efficacy in reducing ICP - Diuretic effect reduces total body fluid - Does not cross intact blood–brain barrier **High-Yield:** Mannitol is preferred in acute head injury with herniation risk or significant midline shift because of its rapid and potent ICP-lowering effect. ### Hypertonic Saline (3%) — Alternative - Equally effective for ICP reduction - May be preferred in hypotensive patients (maintains intravascular volume) - No osmolality ceiling like mannitol - Can be used as first-line or second-line agent - Often combined with mannitol in refractory cases **Clinical Pearl:** In this case, the patient has acute subdural hematoma with 8 mm midline shift — a neurosurgical emergency. Mannitol should be given immediately while arranging urgent neurosurgical consultation and likely craniotomy. ### Why Not the Others? - **Acetazolamide:** Carbonic anhydrase inhibitor; reduces CSF production but onset is slow (hours) and effect is modest — not suitable for acute ICP crisis. - **Furosemide:** Loop diuretic; can reduce ICP but less effective than osmotic agents and causes significant hypovolemia — not first-line in acute head injury.
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