Mechanical ventilation is a treatment option for patients who have suffered a critical burn of the upper respiratory tract by inhalation.
Inhalation trauma usually occurs in the context of multi-system burn injuries, carbon monoxide poisoning and cyanide intoxication. Ultimately, it results from inhaling very hot gas and products of incomplete combustion, usually during a fire.
2% of burn patients suffer injuries by inhalation, while burning of a larger body surface is more common. In burned patients, however, damage to the airways is the primary determinant of increased morbidity and mortality.
This type of inhalation injury is also responsible for half of the deaths in burned patients. For many of them, mechanical ventilation is the only way to survive the critical days.
Damage to the respiratory tract and lungs depends on the components of the inhaled smoke, the degree of exposure and the body’s response.
Mechanical ventilation and injuries of the respiratory system
Heat and toxic gas injuries cause swelling of the upper respiratory tract and clinical obstruction. These symptoms become more severe the younger the patient is. They usually appear within the first 12-18 hours after the accident. But in some cases, the onset of symptoms may be delayed up to 72 hours.
Airway damage is the leading cause of immediate death. There are several types of this type of damage:
- Thermal damage. Heat damage is usually limited to the oropharynx and is associated with reflex closure of the glottis and a high potential for heat dissipation by these tissues.
- Inhalation damage by reacting products. The water-soluble gases react with the water of the mucous membranes, releasing strong acids and alkalis, causing bronchospasm and swelling. Conversely, slightly soluble gases cause lesions in the most remote areas. Their main toxic product of combustion is carbon monoxide. Another toxic gas of clinical importance is also hydrogen cyanide.
- Endogenous lung damage. Patients with extensive burns may also develop progressive respiratory failure after the initial stage. This can happen even if the airways are not directly damaged by inhalation.
Issuing a diagnosis
Issuing an accurate diagnosis of an inhalation injury occurs primarily in a clinical setting. It should be suspected when the patient has been unconscious in an enclosed space where there has been a fire or a hot gas leak.
A physical examination looks for signs that give rise to a suspicion of injury. It is checked for burnt nose hair, dark sputum, and burns to the face and nostrils. Coughing, hoarseness, and wheezing may also indicate upper respiratory tract burns.
It is important to examine the oropharynx to evaluate any changes in the mucosa. Complementary diagnostic methods help assess lung and systemic damage. However, none of them are sufficiently detailed or allow a definitive diagnosis to be made.
Most symptoms of lung injury do not appear until several hours of latency. For this reason, it is very important to use mechanical ventilation in the event of any abnormalities found.
However, there is no specific treatment for a patient with critical upper respiratory burn. The therapeutic approach is based primarily on maintaining a patent airway.
In severe cases, intubation and mechanical ventilation are also used. In addition, lung cleaning is performed and antibiotics are given in case of infection.
Intubation and mechanical ventilation
Intubation is necessary in up to 50% of patients with inhalation trauma. Severe cases, as we have seen, require early intubation using a large bore tube which is used to:
- Maintaining the airway patency.
- Avoiding aspirations.
- It allows the elimination of secretions and lumps of mucus.
- It helps with ventilation.
In cases where intubation is late, the patient may experience severe swelling of the airways. Such a situation may make intubation impossible and the only solution may be tracheotomy, i.e. an incision of the trachea.
Depending on the degree of lung damage, conventional ventilation with permissive hypercapnia or inhalation with nitric oxide is used. High frequency ventilation or extracorporeal membrane oxidation can also be used.
For example, prophylactic administration of corticosteroids and antibiotics has shown no utility. In addition, corticosteroid treatment has been associated with increased lung infection and mortality in some studies . On the other hand, the presence of inhalation trauma increases the need for fluid expansion in a critically ill patient.