“Weaning” a patient from ventilatory assistance ranges from a simple to an extremely complex process. Certain general factors should be optimized before weaning is initiated. Included would be the correction of anemia, low cardiac output, fluid imbalance, arrhythmias, fever, electrolyte abnormalities, infection, and acid-base disturbances.Specific respiratory physiologic parameters should be evaluated. Tests indicative of adequate mechanical capability to allow weaning include: vital capacity greater than 10–15 ml/kg; forced expiratory volume in one second of greater than 10 ml/kg; peak inspiratory pressure of −20 to −30 cm H2O; spontaneous resting minute ventilation less than 10 L/min (which can be doubled with a maximal voluntary ventilation maneuver). Tests indicative of adequate oxygenation capability include: an AaDo2on 100% oxygen of less than 300–350 torr; a shunt of less than 10–20%; dead space to tidal volume ratio of less than .55 or .6.By following the guidelines reviewed in this discussion of techniques of respirator weaning, the majority of patients can readily be weaned from a respirator without complication.