There are numerous indications for endotracheal intubation and mechanical ventilation (see Table:Situations Requiring Airway Control), but, in general, mechanical ventilation should be considered when there are clinical or laboratory signs that the patient cannot maintain an airway or adequate oxygenation or ventilation. Concerning findings include respiratory rate > 30/min, inability to maintain arterial O2 saturation  >  90% with fractional inspired O2(Fio2)  > 0.60, and PaCO2  > 50 mm Hg with pH < 7.25. The decision to initiate mechanical ventilation should be based on clinical judgment that considers the entire clinical situation and should not be delayed until the patient is in extremis.