AS11.1-6 | Oxygen Therapy and Airway Management Foundations — Glossary

Alveolar collapse caused by high FiO₂ washing out nitrogen, which normally splints alveoli open; oxygen is absorbed faster than gas enters from the airway.

Direct measurement of PaO₂, PaCO₂, pH, and bicarbonate from an arterial blood sample; essential for monitoring CO₂ retention and acid-base status in patients on oxygen therapy.

A classification system (I–VI, E suffix for emergency) grading the severity of a patient's systemic disease for anaesthetic risk stratification; unrelated to airway anatomy or Mallampati grading.

The articulation between the atlas (C1) and the base of the skull (occiput); extension at this joint is the mechanism by which head-tilt opens the upper airway.

A manual resuscitation device consisting of a self-inflating bag, oxygen reservoir, and face mask, used to deliver assisted or controlled ventilation to apnoeic or inadequately breathing patients.

A fracture at the base of the cranium, suggested by periorbital haematoma (raccoon eyes), mastoid haematoma (Battle's sign), haemotympanum, or CSF from the nose or ear; contraindicates nasopharyngeal airway insertion.

Continuous measurement and waveform display of exhaled CO₂; the gold standard for confirming endotracheal tube placement and the most reliable non-invasive monitor of ventilation adequacy.

Continuous monitoring of exhaled CO₂ concentration via a waveform display; the presence of a CO₂ waveform confirms that the airway is patent and ventilation is occurring.

Haemoglobin bound to carbon monoxide with an affinity ~240 times that of oxygen; impairs oxygen delivery and is misidentified as oxyhaemoglobin by pulse oximetry.

A single-operator bag-valve-mask technique in which the thumb and index finger form a 'C' around the mask connector to maintain seal, while the remaining three fingers form an 'E' under the mandible for jaw lift.

The placement of a cuffed tube through the glottis into the trachea under laryngoscopic vision, providing a definitive, protected airway and enabling mechanical ventilation.

A leaf-shaped cartilage at the base of the tongue attached to the hyoid by the hyoepiglottic ligament; falls over the laryngeal inlet during unconscious muscle relaxation and is lifted by anterior tongue traction.

The proportion of oxygen in the inspired gas mixture, expressed as a decimal (0.21 for room air, up to 1.0 for pure oxygen).

An oxygen delivery device (e.g., Venturi mask) that maintains a constant, prescribed FiO₂ regardless of the patient's respiratory pattern by delivering total gas flow exceeding peak inspiratory demand.

A protective reflex mediated by cranial nerves IX (glossopharyngeal) and X (vagus) triggered by stimulation of the posterior tongue or soft palate; its presence contraindicates OPA use.

The opening between the vocal cords and arytenoids at the top of the larynx; the functional entrance to the trachea that must be kept clear for effective ventilation.

The phenomenon whereby increased oxygenation of haemoglobin causes release of CO₂ from haemoglobin (reduced CO₂ carrying capacity of oxyhaemoglobin), contributing to hypercapnia when high FiO₂ is given to COPD patients.

A manual airway opening manoeuvre in which the head is extended at the atlanto-occipital joint while the chin is lifted upward and forward by pressure on the bony mandible, displacing the tongue anteriorly.

A device delivering heated, humidified oxygen at 20–70 L/min via wide-bore nasal prongs, capable of FiO₂ close to 1.0 and providing modest CPAP effect.

A U-shaped bone at the level of C3 in the anterior neck, suspended between the mandible and thyroid cartilage; anterior displacement (via chin-lift or jaw-thrust) lifts the tongue-hyoid-epiglottis complex to open the airway.

The respiratory drive component stimulated by low PaO₂ via peripheral chemoreceptors (carotid and aortic bodies); the primary respiratory drive in patients with chronic CO₂ retention and blunted central chemosensitivity.

A calculated weight based on height used to set tidal volume, preventing injuriously large volumes in obese patients whose lungs are sized for their IBW, not their actual weight. Male IBW ≈ 50 + 0.91 × (height cm − 152.4) kg.

A manual airway opening manoeuvre in which the mandible is displaced anteriorly by bilateral upward pressure at the angles of the mandible, opening the airway without extending the cervical spine; used when cervical spine injury is suspected.

A four-class grading of the oropharyngeal view (with mouth open and tongue maximally protruded) used to predict ease of laryngoscopy; Class I = best view (all structures visible), Class IV = worst (soft palate not visible).

The total volume of gas exhaled per minute, equal to tidal volume × respiratory rate; determines CO₂ clearance (alveolar ventilation portion minus dead space ventilation).

A low-flow oxygen device with nasal prongs delivering approximately 24–44% FiO₂ at 1–6 L/min, the most comfortable device for mild-moderate hypoxaemia.

A soft flexible tube inserted through the nare along the nasal floor to maintain airway patency in the hypopharynx; tolerated in semi-conscious patients with preserved gag reflex.

A face mask with an attached oxygen reservoir bag and one-way valves that prevents re-breathing of exhaled gas, delivering FiO₂ of 60–90% at 10–15 L/min.

A rigid curved plastic airway adjunct inserted through the mouth and rotated into position to hold the tongue away from the posterior pharyngeal wall; contraindicated when the gag reflex is intact.

Pulmonary and systemic damage caused by prolonged exposure to high FiO₂ (>0.6), mediated by reactive oxygen species; ranges from tracheobronchitis to diffuse alveolar damage.

A pattern of chest and abdominal movement in which the chest wall and abdomen move in opposite directions during breathing; indicates airway obstruction or impaired respiratory mechanics.

The maximum airway pressure recorded during each ventilator breath, reflecting both airway resistance and lung compliance; elevated peak with normal plateau indicates increased resistance, not reduced compliance.

A positive pressure maintained at end-expiration during mechanical ventilation that prevents alveolar collapse, recruits atelectatic alveoli, and improves oxygenation; physiological PEEP 3–5 cmH₂O, therapeutic PEEP 8–15+ cmH₂O in ARDS.

A deliberate strategy in ARDS ventilation of accepting elevated PaCO₂ (50–60+ mmHg, pH ≥7.20) to allow the use of lower, less injurious tidal volumes; the patient's pH, not PaCO₂, is the safety boundary.

The airway pressure measured during an end-inspiratory pause (no flow), reflecting alveolar distending pressure; a surrogate for lung compliance; target ≤30 cmH₂O to prevent barotrauma.

The process of breathing 100% oxygen via a tight-fitting NRM for 3–5 minutes before anaesthetic induction to fill the functional residual capacity (FRC) with oxygen, extending safe apnoea time.

A partially assisted ventilation mode in which the patient triggers each breath and the ventilator provides a set pressure boost; used during weaning from mechanical ventilation.

A ventilation mode in which the ventilator delivers each breath to a set pressure; tidal volume varies with changes in compliance and resistance.

Non-invasive monitoring of arterial haemoglobin oxygen saturation using photoplethysmography; unreliable in carbon monoxide poisoning as carboxyhaemoglobin is misread as oxyhaemoglobin.

An anaesthetic technique for patients at risk of aspiration involving pre-oxygenation, simultaneous administration of an induction agent and rapid-onset muscle relaxant, and immediate intubation without bag-mask ventilation.

Application of firm pressure on the cricoid cartilage (the only complete tracheal ring) during RSI to compress the oesophagus between the cartilage and the cervical vertebra, aiming to prevent passive regurgitation; evidence base is debated.

A variable-performance face mask delivering 40–60% FiO₂ at 5–10 L/min; minimum 5 L/min required to flush exhaled CO₂.

The head position for laryngoscopy — head extended at the atlanto-occipital joint and neck flexed by placing a pillow under the occiput — that aligns the oral, pharyngeal, and laryngeal axes to create a line of sight from mouth to glottis.

Sonorous inspiratory noise caused by partial upper airway obstruction, typically from the tongue partially contacting the posterior pharyngeal wall; indicates the need for airway intervention.

The volume of gas delivered with each breath by the ventilator; in lung-protective ventilation, set at 6–8 mL/kg of ideal body weight (not actual weight) to avoid ventilator-induced lung injury.

The largest muscular organ of the oral cavity, attached to the hyoid bone and mandible; the most common cause of upper airway obstruction in the unconscious patient as muscle tone is lost.

Partial or complete blockage of the airway above the larynx, most commonly caused by the tongue falling posteriorly in the unconscious patient; manifested as snoring (partial) or silence with paradoxical chest movement (complete).

Ventilation-perfusion inequality in which blood flows through poorly ventilated lung regions, reducing arterial oxygenation; worsened by high FiO₂ in COPD when hypoxic pulmonary vasoconstriction is abolished.

An oxygen delivery device (e.g., nasal cannula, simple mask) in which the delivered FiO₂ varies with the patient's minute ventilation because room air is entrained during inspiration.

Lung damage caused by mechanical ventilation, primarily from overdistension of alveoli (volutrauma/barotrauma) from excessive tidal volume or plateau pressure; prevented by lung-protective ventilation strategy.

A fixed-performance oxygen delivery device using the Bernoulli principle to entrain room air in a fixed ratio, producing precise, discrete FiO₂ values (24%, 28%, 35%, 40%, 60%).

A ventilation mode in which the ventilator delivers a set tidal volume with each breath; airway pressure varies depending on lung compliance and resistance.