AIRWAY CONSIDERATIONS IN THE TRAUMA PATIENT

Several circumstances make management of the trauma patient’s airway unique. These include the frequent need for emergent intubation, the presence of complicating injuries, fixation in neck collars, and the risk of tracheopulmonary aspiration. There is no standard definition for a difficult airway, but it is often defined in the literature as an airway that requires more than two or three attempts for successful intubation. In the emergency department, difficult intubation conditions have been reported in at least 3% of cases. During the last few decades, we have seen a marked reduction in severe airway complications related to anesthesia for surgery in the operating room (OR). This, however, is not the case for airway management outside the OR. Management of the trauma airway is considered a task for the experienced physician.

Airway and breathing are the first two components of the ABCs (airway, breathing, and circulation) of initial evaluation of trauma patients. All seriously injured patients should receive supplemental oxygen, and many require intubation. Trauma victims are frequently either unconscious or combative as a result of head trauma or intoxication. The airway is vulnerable to mechanical obstruction from loss of muscle tone and airway reflexes. In addition, the airway is frequently contaminated with debris, blood, and secretions. Direct airway trauma and facial trauma may make the situation even more complex. The fully conscious, talking patient who maintains his/her own airway may not need airway intervention initially, but it must be kept in mind that the patient’s status may change quickly. Continuous monitoring and frequent reevaluation of the airway is mandatory. Inhalation of oropharyngeal and gastric contents is always a risk in these individuals, but the actual frequency of aspiration is unknown. All trauma patients are presumed to have a full stomach and should be treated accordingly, using a technique to secure the airway that minimizes the risk of pulmonary aspiration.

The cervical spine is considered “unstable” in the trauma victim until proven otherwise. The evaluation of the spine and ruling out or diagnosing injury may be a prolonged procedure, especially in the patient with a decreased consciousness level. In the United States, 1.5%–3% of trauma victims suffer from spinal cord injury, and 55% of these injuries are located in the cervical spine. Complete spinal cord injury with loss of motor and sensory function distal to the lesion occurs in 43%–46% of cases. All trauma patients receive a rigid cervical collar to prevent secondary spine injury. However, this fixation usually makes an intubation more difficult and unpredictable.

There is an increased risk for awareness among trauma patients during airway manipulation and surgery. The incidence of awareness in the general adult patient population undergoing anesthesia is 0.1%–0.2%. Approximately 50% of these patients will have some psychological impact from their experience, and the most severe reaction is full-blown post-traumatic stress syndrome. The incidence of awareness is reported to be higher among trauma patients. These patients often have such hemodynamic instability that they tolerate only very light levels of anesthesia. It is, therefore, good practice to always consider giving amnesia-inducing drugs when neuromuscular blocking agents are used. To be paralyzed and unable to communicate is an extremely traumatic experience.

EVALUATION OF AIRWAY AND RESPIRATORY FUNCTION

Assessment of the airway as well as of the ventilatory and respiratory functions has the highest priority when a new trauma patient is encountered. Start by observing the patient’s ventilatory pattern; and then auscultate the lungs. If time permits, obtain a chest film, and evaluate for the presence of hemothorax and/or pneumothorax. If there is an emergent need for airway intervention, the time for physical examination will be limited. The vital functions of a trauma patient can deteriorate rapidly, and constant monitoring with frequent reevaluation of the airway is crucial. The goal of the evaluation is to get as clear a picture as possible of the airway anatomy and the patient’s ventilatory and respiratory functions, so that an appropriate plan for securing the airway can be established. The objective of the plan should always be a patient who is well oxygenated and ventilated and an airway that is protected after the intervention. The sophistication of the evaluation and the final plan are largely affected by the urgency of the needed intervention. It is not surprising that the incidence of difficult intubation is four to seven times higher in the emergency department than in the OR, largely due to challenging conditions in the trauma patient such as direct injury to the face and neck areas, fractures, hematomas, burns with edema, and secondary distortion of the airway.

In recent years, the development of classification systems to predict difficult intubations has reduced the incidence of airway complications in patients undergoing elective surgery. The Mallampati classification of the airway (see page 59) is commonly used and is based on assessment of tongue size in relation to other pharyngeal structures. The I to IV scoring scale predicts difficulty of intubation. The atlanto-occipital joint extension test measures the ability to extend the neck and, consequently, the ability to align pharyngeal and laryngeal axes to accommodate intubation. Measurements of the thyro-mental distance, sterno-mental distance, mandibulo-hyoid distance and inter-incisor distance are also helpful in evaluating the airway.

To provide high specificity and sensitivity for successful intubation and to assess the level of difficulty of an endotracheal intubation, several tests must be performed. These tests are usually correlated to the visualization of laryngeal structures and vocal cords. The gold standard for classifying the degree of exposure to the larynx entrance is the description by Cormac and Lehane (Figure 1). Grades III and IV are associated with difficult intubation. The dilemma is that all these tests are difficult to utilize in the trauma patient for many reasons, including an immobilized neck. Thus, alternative scoring systems such as the LEMON method have been proposed.

Figure 1 Cormack-Lehane original grading system compared with a modifi ed Cormack-Lehane system (MCLS). E, Epiglottis; LI, laryngeal inlet.

(From Yentis SM, Lee DJH: Evaluation of an improved scoring system for the grading of direct laryngoscopy. Anesthesia 82:1197-1204, 1998.)

The LEMON method was developed by the U.S. National Emergency Airway Management Course and has a maximum score of 10 points, calculated by assigning 1 point for each criterion (Table 1). It has been demonstrated that an airway assessment score based on the LEMON criteria is helpful in predicting difficult intubation in the ER. The LEMON test is designed to be a quick and easy-to-use assessment tool. A poor laryngoscopic view is more common, for example, among patients with large incisors, a reduced inter-incisor distance, and a reduced thyroid-to-floor-of-mouth distance.

Table 1 LEMON Criteria

Another important component in an emergency evaluation is assessment of conditions that may compromise mask ventilation. Mask ventilation is usually used as an intermittent bridge until final airway control is established. Difficult mask ventilation is correlated to obesity, beards, facial trauma, upper airway obstruction, and absence of teeth and is reported in up to 5% of the normal adult population. It is a useful rule to make sure that mask ventilation is possible before paralytic drugs are administered to a patient. In the emergency situation, however, there are exceptions to this rule, and the pros and cons of using muscle blockade must be assessed in each case. Furthermore, the possibility of a “can’t ventilate, can’t intubate” situation is something that should be anticipated; therefore, it is essential that equipment and competence for creating a surgical airway are immediately available. In this circumstance, the team approach and communication among team members becomes crucial in establishing the final management plan, including rescue alternatives.

Planning an approach is the final step of the assessment (Figure 2). The team should then proceed with the airway management plan. When the patient can maintain adequate oxygenation and ventilation, and time permits, it may be beneficial to transport the patient to the OR which normally has better equipment and resources than the ER. In other situations, the right decision may be to immediately establish a surgical airway with the patient breathing spontaneously.

Figure 2 Airway management algorithm.

When reviewing the literature about airway management, it is remarkable how often the quality of professional competence/experience is mentioned. This is something that is very difficult to measure but is obviously critical to a successful outcome. All efforts should be made to have that experience accessible on short notice in a trauma organization that strives for excellence in airway management.

INDICATIONS FOR INTUBATION AND CONTROLLED VENTILATION

There are many indications for intubation and controlled ventilation in trauma patients. The decision to intubate is not always easy, but for the severely injured patient, the threshold should be low. The decision to intubate the trauma patient is usually made after a rapid assessment of injuries and identification of an indication to control the airway. Indications for intubation are: