THE CLINICAL CHALLENGE
There are a number of confounders that make airway management of the patient with asthma or chronic obstructive pulmonary disease (COPD) challenging. These patients are often hypoxic, desaturate quickly, and can be hemodynamically unstable. Unlike many other clinical conditions, intubation itself does not resolve the primary problem, which is obstruction of the small, distal airways. The actual intubation may be the easiest part of the resuscitative sequence, because postintubation ventilation may be extremely difficult with persistent or worsening respiratory acidosis, barotrauma, or hypotension caused by high intrathoracic pressures with diminished venous return. Thus, the decision to intubate must be made carefully, and the appropriate technique must be chosen to facilitate the best possible outcome.
Severe asthma often presents one of the most difficult airway management cases encountered in the emergency department. Diaphoresis is a particularly ominous sign, and the diaphoretic asthmatic patient who cannot speak full sentences, appears anxious, or is sitting upright and leaning forward to augment the inspiratory effort must not be left unattended until stabilized.
Standard initial management of acute severe asthma exacerbation includes reversal of dynamic bronchospasm using continuous β2-agonist nebulization therapy (Albuterol 10 to 15 mg per hour) and anticholinergic nebulization therapy (ipratropium bromide 0.5 mg every 20 minutes for three doses). Although the benefit is not immediate, oral or intravenous (IV) steroids are indicated for the treatment of the inflammatory component. If the patient is severely bronchospastic and cannot comply with a nebulized treatment, intramuscular epinephrine or terbutaline 0.25 to 0.5 mg is beneficial. For severe, refractory asthma, administration of IV magnesium sulfate 2 g in adults and 25 to 75 mg per kg (up to a maximum of 2 g) in children may be of benefit, although evidence supporting this is mixed. The addition of inhaled or IV anticholinergic agents (atropine or glycopyrrolate), titrated doses of IV ketamine, or inhalational helium/oxygen mixture is controversial but also may be considered in severe cases (Fig. 35-1).
In COPD, much of the obstruction is fixed, comorbidity (especially cardiovascular disease) plays a greater role, and the prognosis (even with short-term mechanical ventilation) is worse. In the patient with COPD, anticholinergic therapy may be as important as β2-agonist therapy. Steroids are again important to attenuate underlying inflammation. As is the case for many asthma patients, it is progression of fatigue, not worsening bronchospasm, that leads to respiratory failure and arrest. The intubated COPD patient may have a prolonged, difficult course, and weaning from the ventilator is not assured. Therefore, unless the patient’s condition forces early or immediate intubation, a trial of noninvasive ventilation is recommended. Noninvasive ventilation (bilevel positive airway pressure [BL-PAP] is of proven value in certain COPD patients and may help avoid intubation (see Chapter 6). As for the asthmatic patient, mechanical ventilation after intubation in COPD is notoriously difficult to manage. Ventilation pressures often are high, and breath stacking (automatic positive end-expiratory pressure [auto-PEEP]) is common, even with excellent ventilator management. Increased intrathoracic pressures induced by mechanical ventilation, combined with volume depletion from the patient’s work of breathing before intubation, coexisting cardiovascular disease, and hemodynamic changes related to decreased sympathetic tone after intubation makes the peri-intubation period highly dynamic and unstable. Ventilator management is discussed in the following section.
• FIGURE 35-1. Approach to the patient with severe asthma exacerbation. (Adapted from National Heart, Lung, and Blood Institute, National Institutes of Health, National Asthma Education and Prevention Program. Expert Panel Report 3 (EPR-3): Guidelines for the Diagnosis and Management of Asthma—Summary Report 2007.
APPROACH TO THE AIRWAY
Despite this vast array of noninvasive medical treatment modalities, 1% to 3% of acute severe asthma exacerbations will require intubation. These patients are usually fatigued and have reduced functional residual capacity; so it may be challenging to preoxygenate them optimally, and rapid desaturation must be anticipated. Because most of these patients have been struggling to breathe against severe resistance, usually for hours, they have little if any residual physical reserve, and mechanical ventilation will be required. In fact, the need for mechanical ventilation is the indication for tracheal intubation; the airway itself is almost invariably patent and protected. This fact argues strongly for rapid sequence intubation (RSI), which often is the preferred method even if a difficult airway is identified on preintubation assessment (the “forced to act” scenario; see Chapters 2 and 3). If the patient has a difficult airway, the operator might plan intubation even earlier than for the nondifficult patient, in an attempt to have the best conditions and greatest amount of time possible for an awake technique.
Technique
The single most important tenet in managing the status asthmaticus patient who requires intubation is to take total control of the airway as expeditiously as possible. Patients typically adopt an upright posture as their respiratory status worsens; this position should be maintained as much as possible during the preintubation period. Preoxygenation should be achieved to the greatest extent possible (see Chapters 5 and 20). Noninvasive ventilation may be considered as a means of increasing FIO2 during this phase while decreasing work of breathing. The RSI drugs chosen should be administered with the patient in their position of comfort, often sitting upright. As the patient loses consciousness, the patient should be placed supine, the head and neck should be positioned, and laryngoscopy and intubation should be performed, preferably with an 8.0- to 9.0-mm endotracheal tube (ETT) to decrease ventilator resistance and facilitate pulmonary toilette.
Drug Dosing and Administration
Ketamine is the induction agent of choice in the asthmatic patient because it stimulates the release of catecholamines and also has a direct bronchial smooth muscle relaxing effect that may be important in this clinical setting. Ketamine 1.5 mg per kg IV is given immediately before the administration of 1.5 mg per kg of succinylcholine or 1.0 to 1.2 mg per kg of rocuronium. If ketamine is not available, etomidate may be used. Other induction agents (such as propofol or midazolam) are options but may predispose these patients to hypotension in the setting of hypovolemia and increased intrathoracic pressure changes. In COPD patients with concomitant cardiovascular disease, etomidate may be preferred to avoid the catecholamine stimulation of ketamine.
POSTINTUBATION MANAGEMENT
After the patient is successfully intubated and proper tube position has been confirmed, sedation and analgesia are titrated according to a sedation scale (see Chapter 20). Neuromuscular blockade may be required during the first few hours of mechanical ventilation to prevent asynchronous respirations, promote total relaxation of fatigued respiratory muscles, decrease the production of carbon dioxide, and allow optimal ventilator settings. Often, however, these same goals are achieved using a proper balance of sedation and analgesia. Prolonged neuromuscular blockade is not required and may worsen the patient’s overall course of management. Intravenous epinephrine drips can be initiated in the most severe cases. Meticulous ventilator management is critical in achieving the best patient outcome. Additional ketamine, as well as continuous in-line albuterol and other pharmacologic adjuncts, may also be given.
Mechanical Ventilation
All asthmatic patients have obstructed small airways and dynamic alveolar hyperinflation with varying amounts of end-expiratory intra-alveolar gas and pressure (auto-PEEP or intrinsic PEEP). Elevations in auto-PEEP increase the risk for baro/volutrauma. Reversal of airflow obstruction and decompression of end-expiratory filled alveoli are the primary goals of early mechanical ventilation in the asthmatic patient. The former requires prompt administration of IV steroids and continuous in-line nebulization with β2-agonists until reversal is objectively measured (decrease in peak and plateau airway pressures) or unacceptable side effects are produced. Safe, uncomplicated alveolar
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