Respiratory management

Airway management

(a) Endotracheal intubation

Respiratory therapy begins with ensuring that the burn patient has a protected and stable airway. Failure to recognize the potential for airway obstruction, or impending airway obstruction may result in lethal consequences for the burn patient. Classically, airway obstruction in burn victims rapidly progresses from mild pharyngeal edema to complete upper airway obstruction [1]. Endotracheal intubation of a burn-injured patient is generally indicated in the following situations:

Physical evidence of upper airway injury. This necessitates careful direct observation of the lips, tongue, oropharynx, and (if possible) laryngeal structures. Fiberoptic nasal-laryngoscopy under topical anesthesia is particularly helpful in some cases. Evidence of swelling, erythema, heavy carbonaceous deposits, hoarseness or voice changes, and stridor should be considered indicative of possible upper airway injury and should prompt prophylactic intubation.

Large surface area burns. The large anticipated fluid resuscitation volumes delivered in these cases can result in massive generalized edema, including airway edema, even in the absence of a direct airway injury or smoke inhalation. While there is no exact burn size above which intubation is mandatory, in general, as the burn size

Marc G. Jeschke et al. (eds.), Handbook of Burns

exceeds 35% to 40% of the body surface area, intubation is advisable. An additional benefit of this approach is that the practitioner can be more liberal with provision of analgesics and anxiolytics with the airway protected.

Suspected smoke inhalation. While intubation is not necessary for every case of smoke exposure [2] it is frequently difficult to predict which patients have sustained a serious smoke inhalation injury and who will progress to an upper airway obstruction or develop early aggressive respiratory failure. Ideally the decision to intubate should be made based on awake fibreoptic assessment of the airways [3, 4]. However, this is often neither feasible nor practical in many emergency departments and a decision to intubate must be made based on clinical assessment of the patient. Strong indications would include a clear history of prolonged exposure to smoke or asphyxiants, any depression of mental status, or any evidence of edema, erythema or heavy carbonaceous deposits in the upper airway.

Extensive facial and/or neck burns. The local edema associated with these wounds may cause extrinsic obstruction of the airway. It is mandatory to recognize this situation early, before edema develops because intubation may subsequently become impossible.

High risk of heat transfer to the lower airways. Heat is infrequently transferred to the lower air-

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ways. However, this can occur in a few unique scenarios which include steam inhalation, close proximity to a forceful explosion, and aspiration of hot liquids. The clinician should consider early prophylactic intubation in these situations.

Significant carbon monoxide (CO) poisoning. Ventilation with 100% oxygen is the mainstay of treatment for CO poisoning. While mask ventilation using a reservoir bag and non-rebreather valve is effective in many cases, when carboxyhemoglobin levels rise above 25–30%, CNS depression will develop and a preferred approach is to deliver 100% oxygen by endotracheal intubation and mechanical ventilation.

Depressed level of consciousness. This can accompany burn injury and may be related to any number of causes including inhalation of asphyxiants (e. g. CO or hydrogen cyanide), associated injuries, or

impared oxygenation or ventilation.

Once the decision to intubate is made, it is preferable to have the most experienced health care provider available perform the procedure. The airway of a burn patient should always be viewed as potentially difficult. Paralyzing or long-acting sedating agents should be avoided because if intubation turns out to be difficult a rapidly deteriorating scenario of being unable to intubate and unable to ventilate may en-

Fig. 1. Danger associated with prior shortening an endotracheal tube. Massive edema of the soft tissues of the lip and mouth leads to a precarious connection of the endotracheal tube with the ventilator circuit (arrow). The endotracheal tube cannot be safely exchanged at this point

sue. Small doses of parenteral fentanyl, midazolam, and propofol combined with topical anesthetic agents, while attempting to intubate with the patient as awake as possible is the preferred approach. At the very least, an attempt at visualization of the airway with the patient awake should be considered. The fibreoptic bronchoscope or glidescope may be useful adjunctive devices. The endotracheal tube should not be shortened because if there is significant facial and lip edema, the connection between the tube and the circuit may become buried within the mouth (Fig. 1). The endotracheal; tube should always be secured with circumferential cotton ties around the face and neck. Adhesive tape should not be used.

(b) Elective tracheostomy

For patients who do not appear extubatable by 14 days, elective tracheostomy is usually indicated to avoid the long term complications of more prolonged endotracheal intubation, namely laryngeal and tracheal damage [5, 6]. However, controversy continues to surround both the indications for, and the timing of earlier elective tracheostomy in burn patients, prior to this somewhat arbitrary 14 day cutoff point. Earlier tracheostomy potentially offers the benefits of improved patient comfort with the resulting need for less sedation, greater airway security especially in children, easier suctioning with improved pulmonary toilet, and easier weaning from the ventilator, compared with use of an endotracheal tube.

Retrospective studies from the 1970’s and 1980’s focused on the potential morbidity of tracheostomy in the burn patient. Enthusiasm for tracheostomy was curbed by reports in these studies of tracheobronchial contamination from the burn wound leading to pulmonary infection, tracheal injuries including tracheal erosion, tracheo-innominate artery or tracheo-esophageal fistulas, and mortality directly linked to the tracheostomy [7–10]. Subsequent to these early reports, further retrospective studies identified that that burn patients who had tracheostomies were at no higher risk of pulmonary sepsis or increased mortality than those managed with intubation [11]. Gaissert et al. [12] reviewed patients with tracheal strictures after inhalation injury and found that the inhalation injury itself and the method

of airway support were likely equally contributory. Lund et al. found that the duration of intubation was probably the most important variable in predicting complications from tracheostomy [13]. Thus, retrospective studies prior to 1990 provide only conflicting conclusions on the safety of tracheostomy in burn patients, and do not answer questions on the efficacy or timing of early elective trachesotomy.

In 1997, Sellers et al. from the Intermountain Burn Center in Utah [14], used logistic regression analysis to derive, from a development set of 110 patients, a predictive equation for determining the likelihood of prolonged ventilator dependence (PVD). Variables in their formula that correlated with PVD were the full thickness burn size, patient age, presence of inhalation injury, and the PaO2/FiO2 ratio on day three post burn. When the equation was applied prospectively to a test set of 29 patients, it had a sensitivity of 90%, a specificity of 100%, and a positive predictive value of 100% in predicting PVD. This study is particularly relevant because any meaningful investigation of early tracheostomy efficacy and timing must select patients who would be at high risk of PVD. With this in mind, two relatively recent studies addressing the tracheostomy question should be examined (Table 1):

Saffle et al. [15] randomized 44 adult burn patients who were predicted to have prolonged ventilator dependence based on the predictive formula just described, to either early tracheostomy (ET), which occurred at a mean of 4 days post burn, or to conven-

tional treatment (CON) with an endotracheal tube and tracheostomy after 14 days of mechanical ventilation if extubation was not possible. There were no significant differences between the groups in the development of pneumonia, length of stay, duration of mechanical ventilation, or mortality. The ET group had superior improvements in PaO2/FiO2 ratio from post burn day 2 to 5, compared to CON, and this was attributed to better secretion clearance in the patients with a tracheostomy. However, there were a significantly higher number of intubated patients in the CON group who were extubated and liberated from mechanical ventilation support before day 14, than in the ET group. It was hypothesized that more aggressive weaning and earlier removal of the endotracheal tube in the CON group was prompted by the higher degree of patient discomfort and perceived need to extubate these patients, whereas in the ET group, the patients were more comfortable and tolerated the tracheostomy more easily, which did not prompt the same degree of aggressiveness in corking and discontinuation of ventilatory support. In summary, no particular advantage of early tracheostomy was identified, but importantly, the authors stated that there did not appear to be any particular downside either.

Palmieri et al. [16] retrospectively reviewed 38 severely burned children who underwent tracheostomy at a mean of 3.9 days post burn centre admission. There was no comparison group of patients with endotracheal tubes. The decision to perform