CURRENT Essentials of Critical Care.pdf

102 Current Essentials of Critical Care■■■Mechanical Ventilation, Failure to Wean fromEssentials of Diagnosis• Excessive dyspnea or hypercapnia, hypoxemia when ventilatorysupport withdrawn; often imbalance between ventilatory requirementand inadequate capacity• Anticipate if minute ventilation (V E) on ventilator 12 L/min,spontaneous rate/VT (L) 100, spontaneous V E 6 L/min, vitalcapacity 15 mL/kgDifferential Diagnosis• High V E requirement (12 L/min): fever, metabolic acidosis,renal failure, agitation, activity, infection, hyperthyroidism, administrationof excessive calories (especially carbohydrate),lung or heart disease (high dead space/tidal volume ratio).• Low V E capacity (spontaneous V E 6 L/min): neuromuscularweakness (critical illness polyneuropathy or myopathy), malnutrition,hypophosphatemia, hypokalemia, primary muscle disease,diaphragmatic weakness, flail chest, rib fractures, ascites,abdominal distension, pain, high resistance of endotracheal tube(7.0 mm)Treatment• Wean when V E 10–12 L/min; patient afebrile, stable hemodynamically;normal serum potassium and phosphorus, adequatenutritional support, minimal respiratory secretions, little or nobronchospasm, no pulmonary edema, serum bicarbonate 18mmol/L• Relieve severe ascites or abdominal distension, abdominal orchest wall pain (especially if with respiration)• If stable, perform daily spontaneous breathing trial; respiratoryrate/tidal volume (L) 60, predicts successful weaning; 110predicts failure; 60–110, marginal predictive value• Correct electrolytes; consider malnutrition, neuropathy or myopathy,diaphragmatic fatigue or paralysis; avoid excessive sedation• Transient noninvasive positive pressure ventilation helpful afterextubation■ PearlRoutine daily trials of spontaneous breathing in stable patients decreaseslength of stay in ICU and duration of mechanical ventilation.ReferenceMacIntyre NR et al: Evidence-based guidelines for weaning and discontinuingventilatory support. Chest 2001;120(6 Suppl):375S. [PMID: 11742959]