A 65-year-old man comes to the emergency department due to 3 days of progressive cough and shortness of breath. Medical problems include chronic obstructive pulmonary disease, hypertension, and chronic back pain. Evaluation in the emergency department reveals moderate respiratory distress with tachypnea and use of accessory muscles of respiration. Lung auscultation reveals diffuse wheezing. Heart sounds are normal and there is no extremity edema. Chest x-ray shows hyperinflated lungs with no infiltrate or consolidation. Noninvasive ventilation is begun, as are inhaled bronchodilators, systemic glucocorticoids, and empiric antibiotics. Respiratory status significantly improves over the next several hours, and noninvasive ventilation is stopped. The next morning, the patient is lethargic. Temperature is 37 C (98.6 F), blood pressure is 132/86 mm Hg, pulse is 92/min, and respirations are 16/min. Oxygen saturation is 96% on 2 L/min of oxygen via nasal cannula. The patient moves all extremities to painful stimuli but does not follow instructions. Lung auscultation reveals mild bilateral wheezing. Which of the following is the most appropriate next step in evaluation of this patient's altered mentation?

Question

A 65-year-old man comes to the emergency department due to 3 days of progressive cough and shortness of breath.  Medical problems include chronic obstructive pulmonary disease, hypertension, and chronic back pain.  Evaluation in the emergency department reveals moderate respiratory distress with tachypnea and use of accessory muscles of respiration.  Lung auscultation reveals diffuse wheezing.  Heart sounds are normal and there is no extremity edema.  Chest x-ray shows hyperinflated lungs with no infiltrate or consolidation.  Noninvasive ventilation is begun, as are inhaled bronchodilators, systemic glucocorticoids, and empiric antibiotics.  Respiratory status significantly improves over the next several hours, and noninvasive ventilation is stopped.  The next morning, the patient is lethargic.  Temperature is 37 C (98.6 F), blood pressure is 132/86 mm Hg, pulse is 92/min, and respirations are 16/min.  Oxygen saturation is 96% on 2 L/min of oxygen via nasal cannula.  The patient moves all extremities to painful stimuli but does not follow instructions.  Lung auscultation reveals mild bilateral wheezing.  Which of the following is the most appropriate next step in evaluation of this patient's altered mentation?

Quizplus · Accepted Answer

Altered mental status in the setting of an acute exacerbation of chronic obstructive pulmonary disease (COPD) raises suspicion for symptomatic hypercapnia and should be promptly investigated with arterial blood gas analysis. Despite tachypnea, some patients with COPD retain CO₂ during an exacerbation due to shallow breathing and high levels of ventilation-perfusion mismatch; this patient's noninvasive ventilatory support was likely discontinued too early, leading to acute hypercapnic respiratory failure overnight. The recognition of symptomatic hypercapnia requires high clinical suspicion as it can occur without significant hypoxemia. In fact, supplemental O₂ may encourage hypercapnia in some COPD patients due to worsening of ventilation-perfusion mismatch and depression of respiratory drive. The clinical manifestations of symptomatic hypercapnia are predominantly neurologic. Patients with mild to moderate degrees of hypercapnia may have headaches or hypersomnolence, whereas higher blood CO₂ levels (eg, >75-80 mm Hg) may cause delirium, confusion, lethargy, and eventually coma (CO₂ narcosis) or seizures. (Choice A) Additional history regarding alcohol use is important in patients with suspected alcohol withdrawal; however, alcohol withdrawal presents with signs and symptoms of neurologic overstimulation (eg, tachycardia, tachypnea, agitation, hypervigilance) rather than neurologic depression. (Choice C) CT angiography of the chest is useful in diagnosing acute pulmonary embolism. Patients can develop obstructive shock with confusion due to reduced cerebral perfusion; however, severe hypotension would be expected. (Choice D) Noncontrast CT scan of the head is indicated to evaluate for acute stroke, which is a potential cause of lethargy, somnolence, and confusion. However, stroke is less likely in this patient who is moving all extremities, and hypercapnia should be first evaluated in the setting of an acute COPD exacerbation. (Choice E) Acute intoxication from opioids or benzodiazepines can lead to altered mental status, and urine drug screening can be helpful in the diagnosis. However, opioid or benzodiazepine intoxication is less likely in this patient who was alert on presentation and subsequently developed lethargy and somnolence. Educational objective: Patients with an acute exacerbation of chronic obstructive pulmonary disease are at risk for symptomatic hypercapnia. Clinical manifestations are predominantly neurologic and include headache and hypersomnolence with mild to moderate hypercapnia; higher levels of hypercapnia (eg, PaCO₂ >75-80 mm Hg) can cause delirium, confusion, lethargy, and eventually coma (CO₂ narcosis) or seizures. References: Pattern of breathing and carbon dioxide retention in chronic obstructive lung disease. (http://www.ncbi.nlm.nih.gov/pubmed/6789677)

A 65-Year-Old Man Comes to the Emergency Department Due to 3