A 28-year-old man is brought to the emergency department due to shortness of breath that has been progressively worsening for the past 12 hours. The patient started a new job working in a warehouse, and he thinks that the dust and heat triggered his symptoms. He has 2 prior hospitalizations for asthma, one of which required intubation. His last exacerbation was over 2 years ago. The patient uses a combination budesonide-formoterol inhaler twice daily and as needed for acute relief. Temperature is 37 C (99 F), blood pressure is 158/90 mm Hg, pulse is 105/min, and respirations are 24/min. Pulse oximetry is 91% on room air. On examination, the patient is alert, speaks in full sentences, and has minimal accessory muscle use. He has prominent bilateral inspiratory and expiratory wheezing and prolonged exhalation. Venous blood pCO2 is 29 mm Hg. Which of the following is the greatest risk factor for severe and life-threatening asthma in this patient?
Fatal asthma: risk factors | |
Patient history |
|
Clinical status (impending respiratory failure) |
|
ABG = arterial blood gas; AMS = altered mental status; ICU = intensive care unit; NIPPV = noninvasive positive pressure ventilation; SaO2 = arterial saturation of oxygen; WOB = work of breathing. | |
This patient has an acute asthma exacerbation. Although most exacerbations can be resolved with bronchodilators with or without glucocorticoids, they can become life-threatening or even fatal in some cases. Risk factors for fatal asthma are based on 2 variables: patient history and present clinical status.
The greatest single risk factor for life-threatening asthma is any previous attack requiring intubation and/or admission to the intensive care unit. Most patients with fatal asthma had a history of a severe exacerbation requiring mechanical ventilation either invasively (intubation) or noninvasively (facemask).
Other historical factors include poorly controlled asthma (eg, nocturnal awakenings, increased reliever use); escalating reliever inhaler use; recent or frequent visits for acute care; multiple courses of systemic corticosteroids; and the presence of major socioeconomic concerns in a patient's life.
In addition to the historical factors above, clinical assessment is focused on detecting impending respiratory failure through vital signs, physical examination, and blood gas analysis. Unstable vital signs include marked tachypnea (respirations >30/min) and/or hypoxemia (oxygen saturation ≤90%) (Choices C and F). Physical examination features include trouble speaking due to respiratory distress, accessory muscle use (eg, neck muscle tensing), and altered mental status.
(Choice A) Age >65 increases the risk of fatal asthma slightly, possibly due to more extensive airway remodeling and medical comorbidities. Conversely, older patients with a long duration of well-controlled asthma are likely at lower risk (surviving the "test of time"). Therefore, any history of respiratory failure (eg, intubation) is a much more powerful predictor than age alone.
(Choice B) Both inspiratory and expiratory wheezing, as seen in this patient, are common during asthma exacerbations. In contrast, the absence of wheezing (ie, "silent chest") due to tight bronchospasm causing diminished air flow is another concerning sign of impending respiratory failure.
(Choice D) Acute asthma usually induces a respiratory alkalosis (↑ pH, ↓ PaCO2) due to increased respiratory drive. Therefore, an elevated or even inappropriately normal PaCO2 is worrisome for impending respiratory failure due to respiratory muscle fatigue. Arterial blood gas measurement remains the gold standard, but venous blood gases are sometimes performed in emergency settings due to ease of sample collection; a low pCO2 on venous blood gas (as in this patient) helps exclude hypercapnia.
Educational objective:
The greatest risk factor for life-threatening asthma is a history of respiratory failure, defined as prior intubation or need for mechanical ventilation. In addition, impending respiratory failure is signaled by unstable vital signs, accessory muscle use, abnormal mental status, and PaCO2 that is elevated or inappropriately normal in the face of increased work of breathing.