Approach
Inhalation injury can present as a wide spectrum of symptoms, varying in severity from mild cough to rapid airway compromise causing death. The key to effective treatment is anticipation and early recognition of the myriad of consequences of inhalation exposure. Many of the treatment modalities are supportive, but there are specific therapies for certain complications such as carbon monoxide poisoning.[25] For less severely ill patients, therapy may only involve brief observation and counselling about recurrent exposure avoidance. Others, however, may require supportive critical care services such as intubation, mechanical ventilation, hyperbaric oxygen therapy, intravenous resuscitation, and haemodynamic support.
Upper airway management
Careful evaluation of the patient's ability to maintain a patent airway should be performed as part of the initial assessment and therapy. An airway should be immediately secured with an endotracheal tube (ETT) if the patient has diminished mental status with poor airway reflexes or history and examination is suggestive of injury with threatened patency. Patients with inhalation injury often have difficult airways to secure, and preparations for a surgical airway should be made in anticipation of ETT placement failure. Care should be taken to secure the ETT to prevent unintended extubation. No evidence exists to support early tracheostomy in burn patients once they have been intubated.[26]
If the initial assessment does not lead to intubation, reassessment should occur frequently.
Patients presenting with only inhalation exposure or mild clinical disease should be closely observed and monitored during treatment for evolution or worsening of symptoms, which may be delayed for up to 1 day.[10]
Cellular asphyxiants
Carbon monoxide (CO) poisoning
Should be treated to prevent the associated persistent and delayed neurological sequelae.[27] All patients should receive high-flow supplemental oxygen to decrease hypoxia and facilitate removal of CO. Current guidelines recommend using high flow oxyen therapy for at least 6 hours, or longer if symptoms persist.[26] The use of hyperbaric oxygen has been considered controversial by some.[27][28] While some have recommended its use for pregnant patients or patients with severe disease (coma, seizure, cardiovascular disease, acidosis), the data specific to certain subgroups are unclear.[27] One clinical trial found evidence to suggest that hyperbaric oxygen reduces cognitive sequelae both acutely and at 12 months.[29] One retrospective study found that (after adjusting for age, sex, and underlying comorbidities) patients with carbon monoxide poisoning who were treated with hyperbaric oxygen therapy had a lower mortality rate compared with patients who did not receive hyperbaric oxygen.[30] The reduction in mortality risk was greatest among patients aged younger than 20 years and those with acute respiratory failure.[30]
Cyanide toxicity
While cyanide toxicity is often cited, its true role in inhalation injury is unclear and its treatment is controversial.[21]
If cyanide toxicity is suspected in a patient with inhalation injury, the recommended therapy is intravenous 25% sodium thiosulfate and the direct cyanide binder hydroxocobalamin.[25] Blood cyanide levels of higher than 2.6-3 mg/L are considered fatal.[31]
The commonly available 'antidote kit' of amyl nitrate, sodium nitrite, and sodium thiosulfate should be used very cautiously because nitrates induce methaemoglobin (which binds systemic cyanide). Methaemoglobin, in the presence of significant carboxyhaemoglobin, contributes to critically lowering oxygen delivering capacity. Nitrates are, therefore, contraindicated in the presence of significant carboxyhaemoglobinaemia.
Lower airway injury
Airway cellular injury leading to oedema, sloughing, and bronchoconstriction causes obstruction in patients with inhalation injury. This lower airway injury is treated largely with supportive care. Patients should be clinically monitored for evidence of respiratory muscle fatigue and ventilatory failure. While high levels of inhaled oxygen (hyperoxaemia) may be used therapeutically for carbon monoxide poisoning, once excluded or resolved hyperoxaemia is no longer recommended, and the patient may be supported with a standard fraction of inspired oxygen sufficient to maintain adequate haemoglobin saturation.[32]
Inhaled beta-agonist bronchodilators (e.g., nebulised salbutamol [albuterol]) should be used as needed for bronchoconstriction, and evidence suggests that they may also benefit the patient via anti-inflammatory properties.[33] The role of other therapies, such as heparin, tocopherols, and corticosteroids, is under active investigation.[34][35][36] Airway clearance should be facilitated by humidification of delivered oxygen and aggressive pulmonary toilet.
Parenchymal lung disease
Patients with lung parenchymal injury (which may progress to acute respiratory distress syndrome [ARDS]) should be treated supportively with oxygen and positive pressure ventilation as the clinical situation warrants. It is reasonable to utilise volume-cycled ventilation with low tidal volume ventilation (4-6 cc/kg of ideal body weight) and avoidance of high plateau pressures (>30 cm H₂O), which has proved beneficial in non-selected ARDS.[37] Alternatively, pressure-cycled ventilation may be used to achieve similar physiological goals. While several therapeutic modalities (e.g., vitamin C, heparin, beta-agonists, corticosteroids, antithrombin-III, extracorporeal membrane oxygenation for hypoxaemic failure) are under investigation, none have been proved effective in large clinical trials.[34][35][36][38][39][40]
Other considerations
Comorbid conditions or injuries should be evaluated and treated in patients with inhalation injury. Therapies for individual conditions are often at odds (such as aggressive volume infusion for cutaneous burns and the conservative fluid approach for ARDS), and clinicians must carefully develop a treatment strategy unique to the individual patient. Pain and anxiety are common in these patients and should be treated. Analgesia is often indicated to relieve the discomfort of an endotracheal tube, tissue oedema, coincident trauma, and cutaneous burns. Opioid medications have the additional benefit of relieving dyspnoea.[41] Patients not ventilated through an endotracheal tube should be monitored closely, as respiratory suppression can occur. Continuous intravenous morphine or fentanyl provide excellent analgesia for invasive mechanical ventilation. Sedation and anxiolysis are also indicated for patients receiving invasive mechanical ventilation. Propofol and dexmedetomidine are commonly used agents. In March 2022, the European Medicines Agency (EMA) issued a warning about an increased risk of mortality with dexmedetomidine treatment in critically ill patients aged ≤65 years compared with alternative sedatives. This recommendation follows results from an open-label, randomised trial, comparing dexmedetomidine with usual care (propofol, midazolam, or other sedatives) in critically ill adult patients undergoing mechanical ventilation. The study showed no difference in overall 90-day mortality between treatments. However, dexmedetomidine was associated with an increased risk of mortality in patients ≤65 years old, compared with alternative sedatives.[42] The EMA advises clinicians to weigh these findings against the expected clinical benefit of dexmedetomidine in this age group.[43]
Critically ill patients with burns and inhalation injury are at high risk for complications; preventative measures, including hand hygiene, head-of-bed elevation, catheter care, and deep vein thrombosis prophylaxis, are essential.
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