Absence of the gag reflex, per se, is not a reliable guide for the need for intubation. The other common indication for intubation only is definite upper airways obstruction. Patients with laryngeal edema, tracheal tumor, macroglossia, and other upper airway problems may initially be seen with stridor. Of course it may be difficult to pass an endotracheal tube, in which case an emergency tracheostomy or cricothyroidotomy may be necessary. Criteria for instituting mechanical ventilation, listed in the box above, can be applied in all cases.
Some examples are in the box below.
Patients undergoing cardiopulmonary resuscitation are intubated and mechanically ventilated to reverse the inevitable hypercapnia and hypoxemia. During general anesthesia patients are routinely ventilated to prevent the hypercapnia and hypoxemia that would otherwise result. Patients are sometimes intubated even though their PaCO 2 is in the normal range. This may be justified if the work of breathing is at the patient's limit and if decompensation is feared. In such cases the goal of mechanical ventilation is to relieve the patient of some or all of the work of breathing and to maintain PaCO 2 at an acceptable level.