Out of all the possible complications of burns, the college examiners have been most interested in airway burns, and specifically in the various clinical features which alert you to the presence of such burns. Question 11 from the first paper of 2013, Question 13 from the second paper of 2006 and Question 11 from the second paper of 2000 are virtually identical: they all ask about airway burns, smoke inhalation injury and other forms of thermal damage to the upper respiratory tract. Question 23 from the second paper of 2017 is somewhat unique because it presented the candidates with a patient who has ARDS due to smoke inhalation, and who is ventilated with some profoundly stupid settings.

  • Clinical features of airway burns include soot in the airway, stridor, hoarseness, singed nose hair, and mucosal ulceration
  • Historically, survivors of explosions and fires in enclosed spaces are more likely to have suffered airway burns
  • Consequences of theramal inhalation injury include acute thermal damage to airway  structures, delayed inflammatory damage, and systemic effects of the inhaled substance (eg. carbon monoxide poisoning)

Features of history and examination associated with airway burns

Historical features associated with airway burns

  • Explosions
  • Fires in an enclosed space
  • Exposure to heated steam
  • Fires involving volatile solvents
  • Corrosive ingestion
  • Laryngeal surgery (using a laser)

Clinical features of airway burns

  • Stridor, hoarseness, or cough
  • Burns to face, lips, mouth, pharynx, or nasal mucosa
  • Soot in sputum, nose, or mouth ("carbonaceous material"
  • Singed vibrissae (the zoological term for innervated whisker hairs, misapplied to the coarse nasal hair which grows in human nostrils and has no role in tactile sensing)
  • Bronchocopic findings of tracheal erythema, oedema or or ulceration.
  • Dyspnoea, decreased level of consciousness, or confusion
  • Hypoxaemia (low pulse oximetry saturation or arterial oxygen tension) or increased carbon monoxide levels (>2%)

Pathophysiologic consequences of airway burns

Mechanisms organised by pathophysiological mechanism

Mechanism

Specific factors

Clinical features Management
Thermal
  • Exposure to flames
  • Splash with corrosives
  • Inhalation of superheated smoke or steam
  • Facial burns
  • Burns of the mucosa
  • Soot on lips
  • Carbonised material in the pharynx
  • Carbonised material in sputum
  • Early assessment of airway patency
  • Examination of the upper airway
  • Serial assessments
  • Upright positioning
  • Suctioning of upper airway secretions
  • Early elective intubation
  • Referral to ENT for tracheostomy in case of severe burns, if strictures are anticipated
Inflammatory
  • Thermal damage to mucosa
  • Effects of inhaled particles
  • Mucosal oedema
  • Pharyngeal oedema
  • Vocal cord oedema
  • Tracheal oedema
  • Difficulty swallowing
  • Hoarse voice
  • Cough
  • Stridor
  • Wheeze
  • Increased work of breathing
Inhaled agents
  • Carbon monoxide
  • Cyanide
  • "Cherry red" complexion
  • Hypoxia despite normal SpO2 readings

Mechanisms organised by anatomical location

Mechanisms, Clinical Features and Management of Upper Airway Burns
Anatomical location

Mechanism

Clinical features Management
Face
  • Exposure to flames
  • Splash with corrosives
  • Facial burns
  • Early assessment of airway patency
  • Examination of the upper airway
  • Serial assessments
  • Upright positioning
  • Suctioning of upper airway secretions
  • Early elective intubation
  • Referral to ENT for tracheostomy in case of severe burns, if strictures are anticipated
Oral cavity
  • Exposure to flames
  • Splash with corrosives
  • Soot on lips
  • Burns of the mucosa
  • Mucosal oedema
Pharynx
  • Inhalation of superheated smoke or steam
  • Carbonised material in the pharynx
  • Pharyngeal oedema
  • Difficulty swallowing
Larynx
  • Inhalation of superheated smoke or steam
  • Hoarse voice
  • Cough
  • Vocal cord oedema
  • Stridor
  • Increased work of breathing
Trachea
  • Inhalation of superheated smoke or steam
  • Stridor
  • Wheeze
  • Tracheal oedema
  • Carbonised material in sputum
Lungs
  • Inhalation of superheated smoke or steam
  • Exposure to toxic products of combustion
  • ARDS
  • Lung-protective ventilation
  • Standard ARDS non-ventilatory management

ARDS due to inhaled products of combustion

 Question 23 from the second paper of 2017 offered the candidates a slightly singed miner, pulled out of some sort of underground conflagration. The question does not specifically ask about ARDS - rather, the candidates were asked as to why he might be so hypoxic. One of the main differentials would certainly be "inhalation injury resulting from exposure to pyrolysis and combustion atmospheres". The authors who have published the most helpful articles on this were Kimmel & Still (1999). They write mainly about the smoke inhalation experience of naval personnel, largely because military ships always seem to catch on fire and  "because of the extraordinary difficulties associated with escape and avoidance of ship-board fire atmosphere". In contrastAkgun & Gorguner (2010) report that acute lung injury due to inhalation of flaming gas seems to be epidemiologically more common among miners, because of the combination of inescapable confinement and limited fresh gas supply.

In summary:

  • The inhaled "fire atmosphere" can do damage by:
    • Heat damage
    • Chemical burn (eg. if it is corrosive)
    • Absorption of toxins, eg. asphyxiant agents such carbon monoxide
    • Blast damage, eg. in explosions
    • Asphyxiation, by absorbing all oxygen in an enclosed space
  • The fire atmosphere can consist of:
    • Hot gases
    • Particles, which will cause injury at different points in the respiratory tract dependig on their size.
    • Aerosolised toxins (eg. by explosion)
    • Vacuum (eg. by process of combustion the partial pressure of gases can decrease in an enclosed space)
  • The effect of this is:
    • Pulmonary oedema
    • Delayed pulmonary oedema, as in chlorine inhalation
    • Multiple pulmonary thromboses
    • Blast injury barotrauma
    • Mucus plugging due to sloughed epithelial lining

Question 23 from the second paper of 2017 asks for several differentials for hypoxia in a miner pulled from an underground fire. His ABG result demonstrates a severe metabolic and respiratory acidosis. Specific elements which arouse concern in that setting are:

  • He's a miner, and therefore possibly exposed to exotic substances. Who knows what he was mining in there?
  • He was underground, which as an enclosed space has two major consequences:
    • It amplifies blast waves
    • It concentrates heat
    • It limits the oxygen supply

The differentials therefore are:

  • Inhalational burns injury
  • Corrosive agent inhalation
  • Asphyxiant agent exposure (eg. carbon monoxide or cyanide)
  • "Blast lung" due to primary blast injury.
  • Aspiration due to a decreased level of consciousness
  • Pulmonary oedema due to primary myocardial damage

References

Lund, Tjostolv, et al. "Upper airway sequelae in burn patients requiring endotracheal intubation or tracheostomy." Annals of surgery 201.3 (1985): 374.

Bartlett, Robert H., et al. "Acute management of the upper airway in facial burns and smoke inhalation." Archives of Surgery 111.7 (1976): 744-749.

Gaissert, Henning A., Robert H. Lofgren, and Hermes C. Grillo. "Upper airway compromise after inhalation injury. Complex strictures of the larynx and trachea and their management." Annals of surgery 218.5 (1993): 672.

Bishop, Sophie, and Simon Maguire. "Anaesthesia and intensive care for major burns." Continuing Education in Anaesthesia, Critical Care & Pain 12.3 (2012): 118-122.

McFadden, E. R., et al. "Thermal mapping of the airways in humans." Journal of Applied Physiology 58.2 (1985): 564-570.

Lund, Tjostolv, et al. "Upper airway sequelae in burn patients requiring endotracheal intubation or tracheostomy." Annals of surgery 201.3 (1985): 374.

Tredget, EDWARD E., et al. "The role of inhalation injury in burn trauma. A Canadian experience." Annals of surgery 212.6 (1990): 720.

Kimmel, Edgar C., and Kenneth R. Still. "Acute lung injury, acute respiratory distress syndrome and inhalation injury: an overview." Drug and chemical toxicology 22.1 (1999): 91-128.

Gorguner, Metin, and Metin Akgun. "Acute inhalation injury." The Eurasian journal of medicine 42.1 (2010): 28.