Chapter 23. Airway Management in the Patient with Burns to the Head, Neck, Upper Torso, and the Airway

The emergency department receives a call from the emergency medical services (EMS) about a burn victim coming to your facility in about 5 minutes. In an attempt to take his own life, a 40-year-old man, while locked inside his vehicle, set himself on fire with gasoline. The patient's arrival at hospital was delayed due to a prolonged extrication and transport time of about 1 hour. He had significant burns to the anterior trunk, thighs, head, and neck. The EMS personnel advise that a difficult airway ought to be anticipated.

Attempts to examine his airway, establish intravenous (IV) access, and oxygenate are foiled by his severely agitated and uncooperative state.

23.2.1 How Can Airway Assessment and Management, Resuscitation, Patient Comfort, and Cooperation Be Achieved?

The evaluation of the airway in a burn victim is crucial to patient management. Difficulties with bag-mask-ventilation (BMV), the use of extraglottic devices, laryngoscopy, and surgical airways may all be present and should be anticipated.

Despite extensive burns, these patients are often awake, alert, and in severe pain. They are likely to require significant fluid resuscitation early in the course of their care. However, unless there are associated injuries, the immediate priorities for burn victims are early airway control, fluid resuscitation, and pain management. Accurate assessment of the airway and the patient's underlying physiological status may be impossible, until control of pain and agitation is achieved. Immediate IV access is desirable to facilitate this. But, access may also be restricted by the location of the burns.

In this case, the patient arrived very agitated, in severe pain, and without IV access. Haldol and morphine were given intramuscularly to achieve cooperation. Due to the location of his burns, access was restricted to his lower extremities and groin, areas which were spared due to his seated position. While nursing staff attempted peripheral IV access in his feet, a right femoral venous catheter was placed under ultrasound guidance.

Limited IV access requires that conditions be used to optimize success. It is recommended that the most experienced practitioners be assigned to provide vascular access using ultrasound guidance through unburned skin. Attention to sterile technique is particularly important in this population as delayed infections represent a serious risk. Intravenous access through an overlying burn is not contraindicated, but is more difficult to locate landmarks, can be challenging to secure, and may become dislodged with subsequent tissue edema. An intraosseous line is an alternative access option in an emergency situation when intravenous access cannot be achieved.

23.2.2 Are There Difficulties with Bag-Mask-Ventilation that Might Be Anticipated in This Patient?

Anatomical features predictive of difficult BMV may be present as well in burn victims, although other barriers to effective ventilation with a bag-mask must be considered. This patient is not obese, not elderly, and there is no facial hair or edentulous state to suggest a poor seal. However, edema associated with the burn may have created anatomic changes affecting airway patency, airway resistance, and compliance. These may affect the ability to deliver adequate ventilation by either BMV or extraglottic devices.

Inspection of the face and neck revealed deep burns in this patient (Figure 23-1). The loss of skin elasticity was severe, restricting the mouth opening to several centimeters and preventing full movement of his jaw and extension of his neck. Further inspection revealed nasal hair singeing, pharyngeal erythema, and soot present in his posterior oropharynx. But, no swelling or stridor was appreciated.

While the indirect sign above strongly suggest the presence of thermal injury, the absence of facial burns, singed hairs, or carbonaceous sputum cannot reliably exclude the presence of supraglottic and laryngeal edema. When managing a significant burn injury which occurred in an enclosed space, even if the external examination is normal, one should assume airway swelling and inhalation injury are present and direct visualization is indicated (or warranted). The obstruction caused by thermal injury is related to progressive swelling and may also be complicated by skin sloughing. Early in the course of this evolving upper airway obstruction, BMV with positive-pressure manual ventilation may be able to overcome it. Bronchospasm and mucosal edema of the lower airways may accompany inhalation injury, further complicating attempts at bag-mask-ventilation. Fourth-degree burns (extend through the skin into underlying tissues) and deep third-degree burns to the chest may cause a significant reduction in chest wall compliance, particularly if the burn is circumferential. Eschar of the neck may prevent appropriate positioning of the patient for airway management. Emergency escharotomies of the chest or neck may be required (see later).

23.2.3 Are There Issues with Laryngoscopy and Intubation that Need to Be Considered in This Patient?

The fundamental principle of airway management in the acute burn victim is early tracheal intubation and airway control, before conditions deteriorate. The intrinsic difficulties related to laryngoscopy uncovered with the LEMON assessment (see Section 1.6.2) remain relevant and need to be assessed. Reduced mouth opening, airway obstruction, and restricted neck mobility are the most common difficulties encountered. Edema caused by thermal injury to the perioral area, oropharynx, and glottis represents the primary difficulty in airway management. Associated swelling may obscure the upper airway and prevent visualization of the vocal cords. Mouth opening may be further reduced by loss of skin elasticity. Neck immobilization may be required if there is associated trauma to the cervical spine, or may be produced by neck eschar. Vocal cord edema is an independent predictor of need for intubation and has been associated with the presence of oral soot, facial burns, and the degree of body burns.1

This patient has a reduced ability to open the mouth. Despite the neck burn, mobility appears reasonable and there are no signs of a cervical fracture. The mechanism of an enclosed space burn, associated with facial burns and carbonaceous sputum, all strongly suggest the presence of thermal injury to the glottis. There is no stridor present. However, this is considered a late finding in an adult. Only 50% of patients with thermal injury to the airway present with hoarseness or respiratory distress, and only 20% will present with stridor.1,2

Despite the potential for difficult laryngoscopy in this patient, airway management should not be delayed and definitive airway control must be achieved urgently. The natural evolution of upper airway burn injury is progressive swelling, airway narrowing for 12 to 24 hours, and resolution in 3 to 5 days. Although significant airway edema may be present in the first 2 hours, visualization sufficient to permit intubation is usually possible at this time, and will only deteriorate with delay. Immediate airway evaluation and consideration of early intubation is strongly recommended. In a study of patients requiring transportation to a burn center, the most common findings were loss of or inability to secure intravenous access and inability to secure an airway.3

23.2.4 Are There Physiologic Issues Which Need Be Considered While Managing the Airway of This Patient?

Other issues to consider in the burn patient are fluid resuscitation, the presence of trauma, and the presence of inhalation injury. Fluid resuscitation requirements in burn patients can be significant. There are a number of suggested formulas to guide volume replacement. But there is no demonstrated superiority in outcome among them and in general, most suggest approximately 4 mL·kg−1·%BSA burn replacement in the first 24 hours. Despite much debate, studies have also failed to demonstrate a significant difference in patient outcome with the use of specific fluid regimens. The most important thing to remember regarding fluid management is the need for early replacement of the volume deficit to support tissue perfusion and to correct the metabolic acidosis.4 The end points for resuscitation are debatable, but hourly urine output is a useful parameter for guiding fluid management. A urine output of 0.5 mL·kg−1·h−1 or approximately 30 to 50 mL·h−1 in most adults and older children is desirable. In small children, the end point should be higher, approximately 1 mL·kg−1·h−1. Conversely, fluid overload is a potential concern in the initial resuscitation as overly aggressive fluid resuscitation can lead to unnecessary edema and pulmonary dysfunction. Too aggressive fluid resuscitation can also increase the need for escharotomies and extend the time required for ventilator support.

In this case, there is no history to suggest associated trauma, however, when the burn is associated with a blast injury, concurrent assessment of traumatic injuries will be necessary. The presence of associated injuries may enhance the need for early intubation, to facilitate therapy or operative intervention. Associated hemorrhagic shock will increase the need for aggressive volume resuscitation and the early consideration of blood replacement.

Inhalation injury may take up to 24 hours to become evident.5,6 Due to the impressive heat exchange capacity of the upper airway, thermal injury is usually most significant above the vocal cords. However, heat-induced injuries may be present in the lower airway. Smoke inhalation can cause significant, progressive toxicity and hypoxemia by three mechanisms: the inhalation of gases causing hypoxia; airway inflammation from direct pulmonary toxins; and tissue hypoxia from systemic toxins such as cyanide and carbon monoxide. Any burn which takes place in an enclosed space, such as in the case of the patient described above, should raise the suspicion for inhalation and smoke injury. Chest radiography at presentation is a poor predictor of inhalation injury, since it is often normal initially. The presence of pulmonary infiltrates on initial evaluation suggests severe injury and a poor prognosis.7

23.2.5 How Can Carbon Monoxide Poisoning Be Identified?

Most pulse oximeters cannot reliably differentiate between oxygenated hemoglobin (HbO2) and carboxyhemoglobin (COHb) and will give a spuriously high measurement of oxygen saturation. Reliance on pulse oximetry or a calculated SpO2 (as may occur with arterial blood gas measurement) rather than hemoglobin oxygen saturation measured by co-oximeter (spectrophtometry) will fail to diagnose carbon monoxide poisoning, and will provide false reassurance that there is adequate issue oxygenation. An arterial blood gas specifying measured rather than calculated oxygen saturation should be obtained early in the course of management, and a COHb determination performed. High-flow oxygen through a non-rebreather mask should be applied immediately, regardless of the pulse oximetry reading. Depending on the level of COHb and patient presentation, other therapies, such as hyperbaric oxygen may be considered. The presence of significant carbon monoxide poisoning is another indication for early intubation to facilitate ventilation with 100% oxygen.8

23.3.1 What Would Be the Best Way to Manage This Airway?

This patient represents potential difficulties to laryngoscopy and intubation, as well as ventilation with a bag-mask. Cricothyrotomy is possible despite the burn but the open technique is preferred. Despite the difficulties discussed earlier, the extent of the burns, the involvement of the face and neck, and the potential for associated inhalation injury mandate definitive airway management. As stated previously, the fundamental principle is early airway intervention. Any existing difficulties will only become worse with delay.

Anticipating these difficulties, there are a few options possible in this patient. Regardless of the strategy employed, there needs to be a bedside rescue device and surgical airway available before proceeding with any airway management technique. With limited mouth opening and restricted neck movement in the patient described earlier, it is advisable to have a device at the bedside that may be inserted blindly. When mouth opening and neck extension is restricted by loss of skin elasticity, or oral swelling is anticipated, video laryngoscopy may be a preferred alternative to traditional laryngoscopy.

Rescue devices such as the lightwand (Trachlight™), the intubating LMA, the Combitube™, or a rigid fiberoptic laryngoscope, such as the Shikani scope or the Bullard laryngoscope, may be used in this setting. One case report describes the successful use of a Combitube™ in a patient with facial burns, reduced oral opening, and known tracheal stenosis.9 Due to the potential for severe delayed facial edema, the placement of an oral tube is preferred over a nasal approach. However, severe oral swelling from local chemical burns (ingestions, Freon "huffing", etc) may prevent an oral approach, and blind nasotracheal or flexible bronchoscope-assisted nasal intubation may be the only nonsurgical option. Regardless of the intubating technique chosen, an open surgical cricothyrotomy kit should be available at the bedside.

Three approaches may be considered in this patient:

1. Inspection with the patient awake following topicalization and sedation using a laryngoscope or video laryngoscope. This technique has been well described in other chapters. If assessment suggests that the cords are likely to be visualized, the practitioner may undertake a rapid-sequence induction (RSI) technique. The urgency of the situation may preclude the use of an antisialagogue as it takes 15 to 20 minutes to be effective in enhancing a topical application of local anesthetic agent. A combination of IV midazolam and ketamine would be reasonable choices in this patient. The analgesic properties of ketamine are desirable and the potential for inhalation-induced bronchospasm favor this agent. Pain associated with this injury and respiratory distress may make it difficult to achieve an adequate level of cooperation unless high doses are used. Inability to gain cooperation without compromising ventilation may require the practitioner to move directly to RSI as outlined in option three, later.

2. Assessment of the airway with a flexible bronchoscope. The technique is similar to that described earlier, including topical anesthesia of the nares. This also requires a level of cooperation that cannot be achieved without sedation and analgesia. Utilizing the flexible bronchoscope, the practitioner may consider intubation over the scope, or proceeding to RSI if assessment suggests this is likely to be successful.

3. Another option is going directly to RSI. This may be considered if:

   1. Difficulty with laryngoscopy and intubation is not anticipated.

   2. The urgency or uncooperative state of the patient prevents the two options described earlier.

   3. Success was felt to be likely after an awake look.

The RSI procedure should not begin until Plan B and C are prepared and available at the bedside. Plan B should incorporate one of the rescue devices discussed earlier. Plan C should include rapid surgical cricothyrotomy. If difficulties are anticipated but urgency requires RSI, a double setup with the neck prepped and the surgical kit open is recommended. Attendance by another practitioner skilled in cricothyrotomy is desirable. An intubating stylet should be part of the initial laryngoscopic attempt, particularly since the glottic opening may be narrowed or difficult to visualize. Failure of laryngoscopy should be recognized early, allowing no more than three attempts. Persistent laryngoscopic attempts are unlikely to be successful and are associated with adverse outcomes. Instead, be prepared to move rapidly to Plan B or C.

23.3.2 If the Airway Appears Normal on Presentation, Should the Trachea Be Intubated Prophylactically?

As described earlier, not all airway injuries manifest immediately. Edema and associated obstruction will continue for at least 24 hours. Significant generalized edema may progress over several days because of the increased microvascular permeability of all tissues and the significant fluid requirements of burn patients. Tracheal intubation and paralysis may be required to facilitate care such as escharotomies, wound management, associated traumatic injuries, and pain control. If patient transport is required, the initial presentation at the scene or hospital may offer the best conditions for airway management and tracheal intubation, and is strongly encouraged before transportation takes place.3 Even if the upper airway is normal, progression of inhalation injury, particularly in the face of an increased work of breathing, may require tracheal intubation and positive-pressure ventilation. In the care of a burn patient, as a general rule, it is always better to intubate the trachea early than late.

23.3.3 Is Cricothyrotomy Contraindicated in a Patient with Burns Involving the Anterior Neck?

No. In fact there are no absolute contraindications to a surgical airway when the patient cannot be oxygenated and the trachea cannot be intubated, since the alternative is death. Many of these patients have a tracheotomy in their course of treatment (see discussion later), even when burns involve the neck. However, endotracheal intubation is the preferred method of primary airway control. In patients with burns to the anterior neck, elective tracheotomy is generally delayed until 5 to 7 days after skin grafting.10

A cricothyrotomy remains the rescue airway of choice should attempts to secure the airway fail and the trachea cannot be ventilated. In this patient, the significant anterior neck burns have created a noncompliant skin and eschar, obscuring landmarks and causing difficulty with neck extension. An open cricothyrotomy technique using an adequate midline vertical incision, as opposed to a percutaneous Seldinger technique, is therefore recommended in this patient. This will serve as an escharotomy to release the contracted tissue and enhance the ability to identify the cricothyroid space by palpation through the wound.

23.4.1 How Does the Presence of an Inhalation Injury Affect Ventilation?

The clinical effects of inhalation injury include upper airway edema from thermal injury, capillary leak of fluids into the airways, bronchospasm from toxins, and small airway occlusion from sloughed mucosal debris and impaired ciliary clearance. This can lead to increased dead space, intrapulmonary shunting, and decreased lung and chest wall compliance. These problems are compounded if pulmonary infection supervenes.5

Bronchospasm may well respond to inhaled β2-agonists. Air trapping can occur and adequate expiratory times should therefore be permitted. Vigorous pulmonary toilet will be required in the days following injury due to endobronchial debris, alveolar fluid, and infection. Positive end-expiratory pressure is often required to maintain small airway patency. Avoidance of excessive inflating pressures may be needed to avoid secondary lung injury. The concept of permissive hypercapnia has been associated with improved pulmonary outcomes in these patients.11 Prophylactic steroids in the burn patient have not been associated with improved outcome and may increase mortality.

23.4.2 Are There Other Concerns Specific to Postintubation Management in the Burn Victim?

Endotracheal tube stabilization in patients with facial burns can be challenging, particularly during debridement and grafting of facial burns. Methods of securing the tube to a nasogastric tube looped around the hard palate or nasal septum have been described.12

The role of tracheotomy in the management of inhalation injury and burns remains controversial.13 Advantages include ease of pulmonary toilet and the avoidance of dislodged orotracheal tubes. A tracheotomy is more likely to be needed in patients with greater than 60% total body surface area burns and has been associated with an increased incidence of pulmonary infections.14 The potential long-term sequelae, such as tracheal stenosis and fistula formation, will be major considerations in the decisions of the health-care team. The two emergency indications for a surgical airway are the failure to achieve tracheal intubation upon initial airway management, and if the endotracheal tube is inadvertently dislodged, the subsequent edema makes replacement impossible. Recognizing that significant airway edema will likely occur, cutting the endotracheal tube short is not advised. Great care should be taken to ensure tube security and prevent accidental extubation. Replacement of a defective endotracheal tube should be attempted only by employing a tube exchanger with rescue devices immediately available.

23.5.1 When Should Escharotomy Be Considered in the Burn Patient?

Severe third-degree and fourth-degree burns cause the collagen in skin to lose its elasticity, shorten, and become rigid. When this occurs in the chest wall, particularly in circumferential burns, significant restrictive pulmonary mechanics can occur with a reduction in pulmonary compliance. Incisional escharotomy may be needed to improve compliance of the lungs and maintain ventilation. The same can be said of circumferential burns of the extremities in which circulation may be compromised.15 Chest wall escharotomies are typically performed by a plastic surgeon, although they are easily performed by any physician if required as a lifesaving intervention. Vertical incisions are made bilaterally in the anterior axillary lines, from below the level of the clavicles to the lower rib margin. The top and bottom of the incisions are then joined to form a square across the chest. A tight neck eschar may draw the neck into flexion and impair ventilation. This may require a vertical incision from the sternal notch to the chin to release the constricting eschar.

Escharotomies do not take precedence over airway management, but in the case of significant circumferential chest burns with persistent ventilatory compromise, immediate escharotomies may be indicated, particularly if transport is contemplated.

23.5.2 Is Succinylcholine Contraindicated in Acute Burns?

The risk of lethal hyperkalemia following succinylcholine administration is well documented in patients with greater than 5% of body surface area (BSA) burned. The greatest risk would appear to be between 18 and 66 days postburn.16,17 However, it should be noted that one author found that the risk of hyperkalemia was present just 9 days postburn.18 It seems reasonable to consider succinylcholine safe if used 4 to 5 days after the burn is sustained and then not used until the burn is fully healed (see also Section 4.4.2.4). Rocuronium is an appropriate alternative. Burn injury has been associated with some resistance to the effects of nondepolarizing muscle relaxants over time, therefore higher doses of rocuronium (1.5 mg·kg−1) have been described as effective in this setting.19

Unless there is associated trauma, the immediate priorities for burn victims are early airway control, fluid resuscitation, and pain management. The acutely burned patient should always be evaluated for thermal airway injury and inhalation injury, particularly if the burn occurred in a confined space, more so if superheated steam is involved. Signs of upper airway obstruction ought to motivate further evaluation of the upper airway to determine if endotracheal intubation is indicated. Ventilatory failure is potentially multifactorial in these patients, being related to heat-induced upper airway obstruction, inhalation injury, and the acute reduction of compliance caused by chest wall eschar. Finally, as in all patients presenting to the ED, one must be vigilant for other associated injuries, such as blunt or penetrating trauma, as well as underlying medical conditions.