Finding the way into the burnt airway!

The American Society of Anesthesiologists (ASA) defines difficult airway as “A clinical situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, difficulty in tracheal intubation, or both”.[1] In addition to providing guidelines to recognize/anticipate difficult airway, application of the ASA algorithm has saved many lives since its introduction. A significant development for improved outcomes was the addition of laryngeal mask airway (LMA) and Videolaryngoscopes into the algorithm. Prior to that time, in failed intubation the rescue choice was resorting to bag-mask ventilation. Patients with acute/chronic burns frequently have a clearly recognizable difficult airway, but resorting to above rescues may not be practical. The situation becomes even more complicated in patients with acute burns where associated respiratory distress will add an urgency of securing the airway. Burn patients with associated lung injury or pediatric patients with burns poses numerous limitations to the potential savior “awake fiberoptic intubation”.

Unlike most other airway, related problems recognition of the difficult airway in burns may not be hard, but eventually it is the management of it that places challenges where conventional measures are either impossible or severely limited. In the case of acute burns, the altered physiology and cardiopulmonary insult adds to immediate patient morbidity. Patients without immediate postburn signs of airway related injury may rapidly develop airway edema causing severe respiratory distress. Hence even if evidence of direct injury is absent in acute situations presence of soot in sputum, hoarseness of voice, singed nasal hairs or even minimal stridor must prompt an early prophylactic endotracheal intubation.[2] The mouth, pharynx, and larynx should be examined by laryngoscopy to assess edema and identify charred mucosa and presence of soot. Video laryngoscopy can be an asset for such an airway assessment without much stimulation in an awake patient.

In case of patients presenting 5-8 h after burns with airway trauma any delay in securing the airway can lead to a “cannot intubate, cannot ventilate” situation necessitating resort to surgical airway, which must be evaluated with a low threshold to their use.[3] Recent insights into pathophysiology show that although lower airways (below the vocal cords) are often prevented from direct heat-related injury due to vocal cord spasm during the burn. However, nitric oxide pathway-related increased pulmonary perfusion as a response to bronchial irritation abolishes hypoxic pulmonary vasoconstriction and additionally contributes to the development of pulmonary edema. Thus, one may find poor lung/chest compliance in a patient with burns, a seemingly spared airway.[4]

Patients with past history of facial/airway burns with scarring have their own set of unique airway related problems [Figure 1]. Improvization and innovation can help to improve the mask ventilation,[5] but intubation still remains a major challenge. Scarring not only distorts the external anatomy, but can have an associated internal airway deformation as well.[6] Flexion deformities or limited neck extension obviously prevents the visualization of the larynx via a conventional laryngoscope. This may pose a challenge in the visualization of glottis opening despite aligning the oral-pharyngeal-laryngeal axis due to lateral displacement of the larynx by scar tissue. One of the key tools that can be used in such patients with limited neck movement (with adequate mouth opening) are video laryngoscopes. It must however be borne in mind that although visualization of larynx may become easier but difference between visual axis (camera of video laryngoscope) and force for insertion of tube (long axis of endotracheal tube) may have considerable misalignment in a flexed neck.[7] Successful use of intubating LMA for securing the airway in patients with limited neck movements has been reported on many instances.[89] Patients not associated with difficult mask ventilation can be intubated using a flexible fiberoptic bronchoscope (FOB). In addition, patients may have perioral contractures limiting the mouth opening. Fortunately the nares (or choanal opening) are usually spared from burns and can be used for nasal fiberoptic intubation. Patients with difficult mask ventilation requiring awake FOB are the real challenge. To obtund airway reflexes nerve blocks in distorted-scarred skin are challenging and nebulization with 4% lidocaine can be effective.[10]

Figure 1

Patient with past history of burns — difficult mask ventilation and difficult intubation

In uncooperative or pediatric patients (or even in a limited resources situation) with difficult mask ventilation and difficult intubation, airway management can be a difficult. In such cases infiltration of local anesthetics (similar to intumescent anesthesia) into the scar tissue in the neck to partly release the contracture allowing extension for intubation, followed by general anesthesia can be tried. Ketamine (or dexmetedomidine, if available) sedation (to maintain spontaneous breathing) is a useful alternative in such situations. It is advisable to improvise using individual patient and available resources based approach towards each case. Securing the airway by pacing an endotracheal tube does not really end all the troubles for anesthesiologist handling the airway. Fixing the tube poses another unique challenge, in acute burns skin macerates on use of an adhesive tape and “tying” is frequently slippery. It is advisable to use sutures (noncutting) for securing the endotracheal tube.

Patients with airway-related burns can have associated nerve damage, and thereby impaired airway protective reflexes. Thus, caution must be used to avoid or decrease the risk of aspiration. In elective procedures, adequate fasting and antiaspiration prophylaxis are important. Needless to say, that the conservative approach must be adopted, while planning extubation of the trachea in these patients. In the immediate postoperative period surgery skin grafts, surgery related swelling, and tight dressings can turn the already “difficult” airway into an “impossible” airway.