Direct heat injury caused by the inhalation of air heated to a temperature of 150^O C or higher ordinarily results in burns to the face, oropharynx, and upper airway (above the vocal cords). Even superheated air is rapidly cooled before reaching the lower respiratory tract because of the tremendous heat-exchanging efficiency of the oropharynx and nasopharynx.

Heat produces an immediate injury to the airway mucosa, resulting in edema, erythema, and ulceration. Although these mucosal changes may be anatomically present shortly after the burn, physiologic alterations will not be present until the edema is sufficient to produce clinical evidence of impaired upper airway patency. This may not occur for 12 to 18 hours. The presence of a body burn magnifies the injury to airways in direct proportion to the size and depth of the skin burn. The massive fluid requirements necessary to treat the skin burn are in part responsible, as are mediators released from the burned skin.

Another compounding injury is any face or neck burn that will accentuate the problem by producing marked anatomic distortion and, in the case of the deep neck burn, external compression on the larynx. A particularly dangerous injury is the third degree facial burn in which minimal external edema is present. The lack of external edema is due to the non-elastic third degree burn, which does not allow expansion. Intraoral edema in this case is usually massive but unrecognized unless looked for. A more superficial burn causes massive external edema but may produce much less mucosal edema and airway compromise. The effect of deep face burns on airway maintenance are:

The local edema process usually resolves in 4 to 5 days.

Click to Enlarge the Image

Symptoms of obstruction, namely, stridor, dyspnea, increased work of breathing, and eventually cyanosis, do not develop until a critical narrowing of the airway is present. Upper airway noise indicative of increased turbulent airflow often precedes obstruction. It is difficult to distinguish noise from a narrowed airway from that caused by increased oral and nasal secretions due to smoke irritation. The airway edema and the external burn edema process have a parallel time course so that by the time symptoms of airway edema develop, external and internal anatomic distortion will be extensive.

A history must be obtained regarding the nature of the burn. This information may not always be available from the Emergency Medical Service transport team if the patient has been transferred from another emergency room rather than the scene and if the patient cannot provide the information. Inspection of the oropharynx looking for soot or evidence of a heat injury should be done with every burn victim. A number of techniques have been used to assess further the degree of injury and determine the need for endotracheal intubation. Fiberoptic bronchoscopy or laryngoscopy will determine whether physical evidence of pharyngeal or laryngeal mucosal injury is present, namely, erythema and edema. Laryngoscopy is the most rapid and least complicated diagnostic tool. Unfortunately, unless serial studies are performed, none of these tests can accurately predict the severity of subsequent airway compromise, since the edema is progressive during the first 18 to 24 hours.

Maintaining an adequate airway is essential for successful early management. There are four standard criteria (the four P’s) for the need for endotracheal intubation:

A judgment decision must be made in the initial assessment as to whether the airway can be managed safely without an endotracheal tube. When in doubt, it is safer to intubate. There are many other indications in the burn patient besides airway edema for the need for intubation, which will be discussed.

Three major categories of patients, who are at risk for upper airways compromise, are described.

Heat and smoke Exposure Plus Extensive Face, Neck Burns. A patient with a significant inhalation injury and deep facial burns is managed by early endotracheal intubation. Management without intubation is allowed only if intubation can be safely and rapidly performed when needed. However, increasing anatomic distortion caused by face and neck burns usually makes a later intubation very difficult. Make the decision to intubate in the first 4 to 8 hours based on progression of symptoms, and the clear understanding that the edema process will get worse over the next 12 to 18 hours.

Burn Alone: No inhalation. Patients with very deep second or third degree burns to the face, particularly lips and neck, also frequently require early intubation, especially in the presence of other burns. Neck compression from burn edema and inability to handle secretions make respiratory distress a likely event and make a delayed intubation very difficult. Emergency tracheotomies are difficult, at best, to perform in these patients and lead to airways infection. The resolution of edema will require 4 to 5 days. The intubated patient can now be anesthetized over the next several days if burn excision is needed.

Heat and Smoke Inhalation: No Facial Burns. The criteria for early intubation in this group is based on the findings on initial laryngoscopy or bronchoscopy as well as the respiratory function of the patient.

INITIAL ASSESSMENT OF AIRWAY ( to Intubate or Not to Intubate)