M3The obstetric airway, oxygenation and capnography

Clinical overview

The obstetric airway is a high-consequence airway. Upper-airway mucosal oedema, breast enlargement, weight gain, reduced functional residual capacity, increased oxygen consumption and aspiration risk combine to shorten safe apnoea time and reduce rescue margin. Pre-eclampsia, prolonged labour, fluid loading, infection and repeated airway manipulation may worsen oedema. The best airway rescue is therefore preparation before the first attempt: recognise deterioration early, call the most experienced available operator, optimise position and oxygenation, prepare alternative devices and agree what happens if tracheal intubation fails.

Airway management is not synonymous with intubation. The immediate goals are airway patency, oxygen delivery, adequate ventilation and protection from aspiration. A patient who is oxygenating and ventilating with basic manoeuvres or a supraglottic device may be safer while the team reorganises than after repeated traumatic laryngoscopy. Conversely, a patient with exhaustion, reduced consciousness, severe hypoxaemia, progressive hypercapnia, uncontrolled seizures or impending transport may need a controlled advanced airway before reserve disappears.

This module teaches decision-making and team preparation. Rapid-sequence induction, videolaryngoscopy, front-of-neck access and extubation of a difficult airway require trained anaesthetic or critical-care operators, local equipment familiarity and rehearsal.

Core knowledge

Why pregnancy changes the airway

Pregnancy increases airway vascularity and soft-tissue oedema. The nasal passages and oropharynx may bleed with instrumentation; the laryngeal view can worsen during labour and after fluid administration. A smaller tracheal tube may be required. Enlarged breasts and body habitus can obstruct laryngoscope movement unless the patient is ramped and equipment is positioned deliberately.

The lungs have less resting oxygen reservoir because functional residual capacity falls, while maternal and uteroplacental oxygen demand rises. Apnoea therefore causes faster desaturation. Preoxygenation, a tight mask seal, head-up/ramped position and ongoing oxygen delivery during attempts are central safety measures. Severe shunt physiology may prevent a high end-tidal oxygen concentration despite good technique; this is a warning of limited reserve, not a reason for repeated delay.

Lower oesophageal sphincter tone, increased intra-abdominal pressure, emergency surgery and labour increase regurgitation risk. Treat the critically ill obstetric patient as high aspiration risk unless there is a compelling reason not to. Suction must be working and immediately reachable.

Tap to enlarge

Figure M3.1 — Pregnancy-related airway oedema, reduced functional residual capacity, increased oxygen demand and aspiration risk converge to shorten safe apnoea time; safety begins with ramping, preoxygenation and rescue preparation.

Oxygenation, ventilation and airway protection are separate questions

Ask three questions:

1. Can oxygen enter the blood? Assess saturation, inspired oxygen, work of breathing, lung pathology and PaO₂.
2. Can carbon dioxide leave? Assess rate, tidal breathing, fatigue, mental state, capnography and PaCO₂.
3. Can the patient protect the airway? Assess consciousness, cough, secretions, vomiting, seizure and bulbar function.

A patient may have adequate saturation on supplemental oxygen while ventilation fails and PaCO₂ rises. A patient with severe metabolic acidosis may have normal saturation but require enormous minute ventilation; intubation that removes her compensatory ventilation can precipitate arrest unless the team anticipates the required ventilation. A postictal patient may improve quickly, whereas recurrent eclampsia or intracranial disease may require airway protection.

Oxygen therapy

Give oxygen for hypoxaemia or during immediate resuscitation, not automatically to every unwell patient. During cardiac arrest use maximal inspired oxygen. After return of spontaneous circulation and once measurement is reliable, titrate to avoid both hypoxaemia and unnecessary hyperoxia. In a viable pregnancy, sustained maternal hypoxaemia threatens the fetus, but this does not justify ignoring oxygen toxicity or delaying treatment of the lung or circulation.