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Primary respiratory depression, caused by the provision of anesthesia itself, refers to a deficit in ventilation or oxygenation or both. Respiratory depression may take the form of mechanical obstruction, caused by collapse of the oropharyngeal soft tissues or occlusion of the airway by the tongue or secretions. Central respiratory depression, characterized by hypopnea or apnea, can also occur either separately or concurrently.

Typically, mechanical obstruction occurs more frequently and at lower anesthetic doses than central apnea does, and it occurs to some extent in susceptible persons. Obese patients, those with short thick necks, those with mandibular retrognathia, and patients with OSA are among the most susceptible groups. In severe cases, this may render these patients unsuitable for ambulatory anesthetic procedures. In most other cases, patient positioning can play a role in airway obstruction. Respiratory obstruction due to mechanical airway obstruction can be managed by careful suctioning, repositioning of the tongue in a forward position, and either a chin lift or jaw thrust maneuver. If necessary, the level of anesthesia may be lessened, as increasing levels of sedation contribute to the degree of airway impediment. Rarely, an oral or nasal airway may be needed to overcome the obstruction in the posterior pharynx and stent the airway open. Supplemental oxygen can be helpful to decrease any oxygen desaturation associated with mild to moderate obstruction, although oxygen by itself does not alleviate the mechanics of obstruction.

Respiratory depression may also be “central,” characterized by a decreased respiratory rate or periods of apnea. Narcotic drugs are most often implicated because of their effects on the medullary respiratory center of the brainstem that results in decreased respiratory drive and decreased response to hypercapnia. At moderate levels of narcotic effect, the decreased respiratory rate is accompanied by a compensatory increase in tidal volume that prevents oxygen desaturation. At higher levels of narcotic sedation, respiratory depression can progress to apnea and respiratory arrest. A brief period of respiratory support in the form of supplemental oxygen via a face mask with cessation of anesthetic drug administration may be all that is necessary in terms of management – particularly with short‐acting drugs in a patient with good respiratory reserve. Whenever there is desaturation in a setting of frank apnea, however, the patient's ventilation should be assisted by a positive pressure face mask until spontaneous respiration resumes.

Occasionally, mask ventilation with or without the placement of an oral or nasal airway will not be sufficient to overcome airway obstruction and provide oxygenation. In these cases, other means of establishing an airway and achieving effective ventilation should be employed. These include laryngeal mask airway (LMA) insertion or endotracheal intubation for administration of positive pressure ventilation with high oxygen flow. Because endotracheal intubation is a technically complex procedure and requires specialized equipment, it is subject to high rates of failure, especially in emergency situations. Intubation should only be considered in a patient who is hypoxemic and cannot be effectively mask ventilated. An LMA can be successfully used for the support of ventilation as an alternative to endotracheal intubation and has several advantages over the traditional endotracheal tube (ET). LMAs are quickly and easily inserted without the need for specialized equipment. Use of an LMA poses no risk of inadvertent intubation of the esophagus or mainstem bronchus or injury to the vocal cords. Airway stimulation is minimal and removal of the LMA can be easily accomplished once spontaneous respirations return. Regardless of the method used to establish an advanced airway, early recognition of the potential need, familiarity with the available equipment, and skill in their effective use are critical.

In addition to respiratory depression or arrest caused by anesthetic drugs, other causes of respiratory complications include stroke or myocardial infarction (MI). The signs and symptoms of stroke or acute coronary syndrome can be significantly masked in a patient undergoing ambulatory anesthesia, and respiratory depression or arrest may initially be diagnosed as a case of oversedation. Any respiratory complication that does not respond to moderate interventions or progresses to a need for airway establishment and support of ventilation should be investigated for additional contributing factors or underlying conditions.