A 34-year-old man is brought to the emergency department with increasing shortness of breath and cough. The patient has a 10-year history of asthma and a hospitalization for exacerbation. His home medications include inhaled fluticasone and as-needed albuterol. The attack started 10 hours ago and did not respond to numerous albuterol inhalations at home. He does not use tobacco or illicit drugs. His temperature is 37 C (98.6 F), blood pressure is 120/70 mm Hg, pulse is 110/min, and respirations are 28/min. Pulse oximetry shows 88% on room air. The patient is using accessory muscles of respiration and speaks with difficulty. Lung auscultation indicates decreased breath sounds, prolonged expiration, and bilateral diffuse wheezing. Cardiac examination shows normal heart sounds and no murmurs. Arterial blood gas results on room air are as follows: The chest x-ray reveals hyperinflated lungs. Which of the following findings is most concerning and indicates that the patient is getting worse?

Question

A 34-year-old man is brought to the emergency department with increasing shortness of breath and cough.  The patient has a 10-year history of asthma and a hospitalization for exacerbation.  His home medications include inhaled fluticasone and as-needed albuterol.  The attack started 10 hours ago and did not respond to numerous albuterol inhalations at home.  He does not use tobacco or illicit drugs.  His temperature is 37 C (98.6 F), blood pressure is 120/70 mm Hg, pulse is 110/min, and respirations are 28/min.  Pulse oximetry shows 88% on room air.  The patient is using accessory muscles of respiration and speaks with difficulty.  Lung auscultation indicates decreased breath sounds, prolonged expiration, and bilateral diffuse wheezing.  Cardiac examination shows normal heart sounds and no murmurs.  Arterial blood gas results on room air are as follows:  The chest x-ray reveals hyperinflated lungs.  Which of the following findings is most concerning and indicates that the patient is getting worse?

Quizplus · Accepted Answer

This patient with underlying asthma presents with dyspnea, cough, accessory muscle use, and difficulty speaking consistent with a severe acute asthma exacerbation. The initial physiologic response to an acute pulmonary insult such as an asthma exacerbation is an increase in respiratory drive and resultant hyperventilation. This response may be caused by a combination of hypoxemia, anxiety due to a sensation of dyspnea, and signals from thoracic neural receptors influenced by change in lung volume and presence of inflammatory chemicals (eg, prostaglandins, histamines). Hyperventilation results in a decrease in the PaCO₂ and a primary respiratory alkalosis, which is the typical presentation in an acute asthma exacerbation. This patient's arterial blood gas results demonstrate an essentially normal pH and PaCO₂, which in the setting of ongoing increased work of breathing indicates an inability to maintain adequate ventilation. This inability to meet the demands of increased respiratory drive is caused by respiratory muscle fatigue or severe air trapping and suggests impending respiratory collapse. (Choice A) Severe hypoxemia (eg, PaO₂ <60 mm Hg on room air) is relatively rare in an acute asthma exacerbation and suggests a very severe exacerbation or the presence of comorbid pathology (eg, pneumonia). This patient's PaO₂ of 65 mm Hg indicates an expected level of hypoxemia and is not as concerning as the normal PaCO₂. (Choice B) Lung hyperinflation on chest x-ray is an expected finding in an asthma exacerbation and is not an indicator of severity. (Choices D and E) Severe tachycardia and tachypnea can be indicators of a severe asthma exacerbation. However, moderate tachycardia and tachypnea (as seen in this patient) are expected findings and are not as concerning as the normal PaCO₂. Educational objective: Patients with an acute asthma exacerbation usually have respiratory alkalosis with a low PaCO₂ due to hyperventilation. A normal or elevated PaCO₂ is an alarming and extremely important finding that suggests impending respiratory failure.

A 34-Year-Old Man Is Brought to the Emergency Department with Increasing