A 65-year-old man with chronic obstructive pulmonary disease, atrial fibrillation, hypertension, and type II diabetes mellitus comes to the emergency department due to shortness of breath for 3 days. The patient's condition began with a runny nose, itchy eyes, and sore throat. His symptoms progressed to productive cough, wheezing, and dyspnea. On examination, blood pressure is 150/90 mm Hg and pulse is 110/min and irregular. Oxygen saturation is 91% on room air. Examination shows a mildly overweight man in moderate respiratory distress. Lung sounds are decreased throughout, with prolonged expiration and bilateral wheezes. The patient is started on inhaled bronchodilators, systemic corticosteroids, high-flow facial mask oxygen, and intravenous lorazepam for agitation. Thirty minutes later, he is lethargic and confused. Shortly thereafter, he experiences a generalized tonic-clonic seizure. Which of the following most likely contributed to this patient's neurologic symptoms?

Question

A 65-year-old man with chronic obstructive pulmonary disease, atrial fibrillation, hypertension, and type II diabetes mellitus comes to the emergency department due to shortness of breath for 3 days.  The patient's condition began with a runny nose, itchy eyes, and sore throat.  His symptoms progressed to productive cough, wheezing, and dyspnea.  On examination, blood pressure is 150/90 mm Hg and pulse is 110/min and irregular.  Oxygen saturation is 91% on room air.  Examination shows a mildly overweight man in moderate respiratory distress.  Lung sounds are decreased throughout, with prolonged expiration and bilateral wheezes.  The patient is started on inhaled bronchodilators, systemic corticosteroids, high-flow facial mask oxygen, and intravenous lorazepam for agitation.  Thirty minutes later, he is lethargic and confused.  Shortly thereafter, he experiences a generalized tonic-clonic seizure.  Which of the following most likely contributed to this patient's neurologic symptoms?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d1f5_8c27_bc81_0fff1396b8bb_MD0003_00 In advanced chronic obstructive pulmonary disease (COPD), destruction of the terminal bronchioles and alveoli causes areas of physiologic dead space to develop. The affected regions have limited surface area available for gas exchange, which leads to ventilation/perfusion (V/Q) mismatch causing local hypoxia and hypercapnia. Hypoxia induces selective vasoconstriction in these areas of the lung and redirects blood flow to better ventilated alveoli, reducing V/Q mismatch. Supplemental oxygen improves hypoxia but can cause CO₂ retention by the following mechanisms: ₂ Loss of compensatory vasoconstriction in areas of ineffective gas exchange worsens V/Q mismatch Increase in oxyhemoglobin reduces the uptake of CO₂ from the tissues by the Haldane effect Decreased respiratory drive and slowing of the respiratory rate causes reduced minute ventilation The acidosis caused by an acute increase in CO₂ increases brain gamma-amino butyric acid and glutamine and decreases brain glutamate and aspartate, causing a change in level of consciousness. Hypercapnia also causes reflex cerebral vasodilation and may induce seizures, as seen in this patient (Choice B). Oxygen should be used cautiously with a goal SaO₂ of 90%-93% or PaO₂ 60-70 mm Hg. Patients who develop significant acidosis or have severely reduced level of consciousness require mechanical ventilation. ₂ cerebral vasodilation ₂ ₂ (Choice C) Although hypocalcemia can cause seizures, this patient has no risk factors for developing hypocalcemia. (Choice D) CO₂ retention causes respiratory acidosis with compensatory metabolic alkalosis (not metabolic acidosis). ₂ (Choice E) Atrial fibrillation predisposes this patient to a thromboembolic stroke. However, a stroke is more likely to cause sudden-onset, focal, neurologic abnormalities than gradual onset of global symptoms (eg, lethargy, somnolence). (Choice F) The majority of subarachnoid hemorrhages are caused by a ruptured aneurysm or bleeding from intracranial vascular malformations. Patients typically present with sudden onset of severe headache, nausea, and vomiting. Educational objective: Supplemental oxygen in patients with advanced chronic obstructive pulmonary disease can worsen hypercapnia due to a combination of increased dead space perfusion causing ventilation-perfusion mismatch, decreased affinity of oxyhemoglobin for CO₂, and reduced alveolar ventilation. The goal oxyhemoglobin saturation in these patients is 90%-93%. ₂ References: Preventing acute hypercapnic respiratory failure in COPD patients. (http://www.ncbi.nlm.nih.gov/pubmed/23987974)

A 65-Year-Old Man with Chronic Obstructive Pulmonary Disease, Atrial Fibrillation