Acetazolamide Facilitates Ventilator Weaning

Inclusion Criteria: * Patients on mechanical ventilation for at least 24 hours with an assisted mode and passed acute resuscitation and considered for weaning. (Definition of Weaning point: 1. Oxygenation * FiO2 ≤ 0.4 \& PaO2 ≥ 60 mmHg * O2 index (PaO2/FiO2) ≥ 150 * SaO2 \> 90% * PEEP ≤ 5 cmH2O * MN ≤ 15 L/min 2. Vital sign * Stable BP: MAP ≥ 60 mmHg ((i.e., no epinephrine or norepinephrine \<0.2μg/kg/min, or equivalent dose vasopressin or phenylephrine) * HR ≤ 140bpm * 35 ≤ BT ≤ 38 ℃ * RR ≤ 35/min 3. Clinical status * resolution of acute disease process * no newly developed pulmonary infiltration * Ramsay sedation score 2\~4 * Hb \> 7, pH \> 7.30, normal electrolyte * no active bleeding, no IICP, no bronchospasm, no CAD * no rescure or specific treatment (NO, prone, OP plan) * ABGA : pH ≥ 7.43 and HCO3- ≥ 26mEq/L Exclusion Criteria: * Permanent ventilator dependency due to brainstem disease, diffuse cerebral disease, severe respiratory or neuromuscular disease * Active bleeding, IICP, unstable coronary artery disease, bronchospasm, and rescue treatment (inhaled NO, prone), pre-op condition * Contraindication to acetazolamide: renal insufficiency (creatinine clearance \<20 ml/min and/or renal replacement therapy), intolerance or allergy to acetazolamide or sulfonamides, hyperchloremic metabolic acidosis, hyponatremia (Na\<130), hypokalemia (K\<3.5), adrenal insufficiency. * Diaphragm dysfunction : as diagnosed by fluoroscopy, nerve conduction velocity, USG, or overt paradoxical motion of the abdomen