Complications of Intubation

Oesophageal Intubation

Unrecognised oesophageal intubation is a preventable but potentially fatal complication that continues to cause avoidable deaths. The Fourth National Audit Project (NAP4) identified nine cases of unrecognised oesophageal intubation in the United Kingdom: three in the operating theatre, four in the intensive care unit (ICU) in the absence of capnography, and two in the emergency department. The outcomes were poor, with six deaths and one case of permanent brain damage – representing 18% of all deaths reported to NAP4. Eighty percent of ICU airway-related deaths in NAP4 were associated with failure to use or correctly interpret the capnogram trace. Oesophageal intubation can occur in any patient, at any age, regardless of the seniority or experience of the airway practitioner, and is primarily a consequence of human error, including anchoring bias, confirmation bias, poor team communication, and distraction during the critical phase of tube placement.

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Clinical signs commonly used to confirm tracheal intubation – including tube misting, chest movement, auscultation of breath sounds, and observation of the tube passing through the vocal cords – are fallible and may lead to dangerous delays or incorrect diagnoses. Waveform capnography, the measurement and display of expired carbon dioxide, is the recognised gold standard for confirming tracheal tube placement. It provides sensitivity and specificity of 100% for tube placement confirmation even in low perfusion states and cardiac arrest. Safe practice requires a two-person verbal check immediately after every intubation, in which two witnesses confirm seven consecutive capnography waveforms of equal or increasing amplitude and verbally state ‘good trace, right place’ before any other activities are permitted to distract from this step.

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Pulmonary Aspiration

Pulmonary aspiration – the introduction of gastric or oropharyngeal material into the lower respiratory tract – is the commonest cause of anaesthesia-related death and brain damage. NAP4 found that aspiration accounted for 50% of anaesthesia-related deaths. The severity of aspiration-related injury is underlined by a large closed claims analysis in the USA, in which death occurred in 57% of 115 aspiration cases and severe permanent injury in 14%. Importantly, the risk of aspiration is not confined to induction: it also exists at extubation, when the anaesthetist must ensure the patient is able to protect their own airway before removing the cuffed tracheal tube. Rapid sequence induction and intubation (RSII) was developed to minimise this risk by reducing the interval between loss of protective airway reflexes and inflation of a cuffed tracheal tube. Significant risk factors for aspiration include unreliable fasting, pregnancy, obesity, upper gastrointestinal pathology, and emergency surgery; notably, 28% of aspiration events in NAP4 occurred in patients who had been appropriately fasted.

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Haemodynamic Complications

The physiological stimulus of laryngoscopy and tracheal intubation provokes a sympathetically mediated cardiovascular response characterised by hypertension, tachycardia, and – in susceptible patients – cardiac arrhythmia. This response is most pronounced in patients with hypertension, cardiac disease, raised intracranial pressure, or aortic disease, and may be attenuated by the use of opioid adjuncts. In critically ill, elderly, or haemodynamically compromised patients, the induction agents required before intubation may instead cause profound hypotension and cardiovascular instability, particularly in those with pre-existing circulatory shock or cardiac impairment. The most significant adverse events associated with rapid sequence induction include hypoxia, hypotension, and pulmonary aspiration. Hypoxaemia may occur even when intubation is performed promptly and successfully, particularly in patients who are critically ill, obese, or in the peripartum period, owing to reduced functional residual capacity and increased oxygen consumption.

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Failed Intubation

Difficulty securing the trachea carries significant risk of hypoxaemia and escalating airway trauma. NAP4 found that failed tracheal intubation occurs in approximately 1 in 2,000 elective cases, rising to 1 in 300 during rapid sequence induction and intubation, and to 1 in 50–100 in the emergency department, ICU, or obstetric setting. The higher failure rates in non-elective and critical care environments reflect the contribution of physiological deterioration, limited preparation time, suboptimal positioning, and reduced assistance. Repeated failed intubation attempts increase the risk of airway bleeding, oedema, and obstruction, potentially precipitating a cannot-intubate, cannot-oxygenate (CICO) scenario in which emergency front-of-neck access becomes necessary.

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Dental and Soft Tissue Trauma

Trauma to the teeth, lips, tongue, and pharyngeal mucosa is among the most common immediate complications of laryngoscopy and intubation. Dental damage is a leading source of medico-legal claims in anaesthesia. Upper incisor teeth are at greatest risk during direct laryngoscopy, particularly if the laryngoscope blade is used as a lever against the dental surfaces. The soft tissues of the oropharynx and larynx are susceptible to pressure injury from both the laryngoscope blade and the tracheal tube itself, producing local erythema and mucosal trauma even after brief intubations. The use of a bougie or nasogastric tube may also contribute to laryngeal injury.

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Laryngeal Complications

Laryngeal injury is common, widely reported, and frequently underestimated. Even after a brief general anaesthetic requiring tracheal intubation, the reported incidence of laryngeal injury is 57–83%, with dysphonia in 76%, pain in 76%, hoarseness in 83%, and dysphagia in 49% of affected patients. Hoarseness is reported in up to one-third of patients after short-duration intubation, although the majority of cases are minor and transient, resulting from erythema or mild mucosal oedema. More significant injuries include vocal cord (VC) ulceration, granuloma formation, and VC palsy or paresis. Anterior arytenoid dislocation may result from direct pressure during intubation, while posterior dislocation is more likely during extubation or with cuff over-inflation.

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The risk and severity of laryngeal injury are directly related to the duration of intubation. The risk of VC paralysis increases two-fold when the trachea is intubated for 3–6 hours and fifteen-fold when intubated for 6 hours or more. Laryngeal stenosis – one of the most serious late complications – occurs in approximately 2% of patients intubated for 3–5 days and in 5% of those intubated for 6–10 days. Prolonged intubation causes progressive pressure-related necrosis of the submucosa, perichondrium, and eventually cartilage, leading to scarring, fibrosis, and chronic glottic or subglottic stenosis. Laryngeal oedema, which increases the risk of respiratory failure and failed extubation, may be screened for pre-extubation using the cuff-leak test, which carries a sensitivity of 88.6% and a specificity of 90% when validated against videolaryngoscopy.

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Post-extubation dysphagia is a clinically important complication that is frequently silent, often missed, and associated with significant morbidity. It is reported in approximately 60% of ICU patients and 50% of cardiac surgery patients after prolonged intubation, may persist beyond hospital discharge in up to one-third of patients, and can lead to aspiration, malnutrition, prolonged hospital stay, and excess mortality. The inability to vocalise or swallow during and after critical illness carries significant psychological consequences, including anxiety, depression, and reduced engagement with recovery and rehabilitation, and necessitates early involvement of speech and language therapy.

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Conclusion

The complications of tracheal intubation span a spectrum from immediately life-threatening events – unrecognised oesophageal intubation, pulmonary aspiration, haemodynamic collapse, and failed intubation – to chronic morbidity from laryngeal injury, dysphagia, and subglottic stenosis. Prevention depends on rigorous adherence to monitoring standards, particularly waveform capnography for every intubation, careful patient preparation, optimal technique, and early multidisciplinary recognition and management of post-extubation laryngeal complications. Awareness of these complications and their risk factors is an essential component of safe anaesthetic practice.