A 72-year-old man comes for evaluation of shortness of breath, headache, and fatigue. He has a history of hypertension, lives alone, and is not compliant with his medications. The patient drinks 1 or 2 glasses of wine daily but does not smoke. Blood pressure is 184/128 mm Hg, pulse is 96/min, and oxygen saturation is 90% by pulse oximetry on room air. He has early papilledema on funduscopic examination. Pulmonary examination shows bibasilar coarse crackles. Cardiac examination shows a grade 2/6 systolic ejection murmur along the left sternal border. There is trace pedal edema. Chest x-ray reveals mild pulmonary edema. An ECG is unchanged from prior tracings. Laboratory studies are normal except for serum creatinine of 2.0 mg/dL. The patient is given oxygen and furosemide and is started on a nitroprusside drip. After 36 hours, his blood pressure is 140/80 mm Hg and he is no longer dyspneic; however, he is confused and disoriented and has diffuse hyperreflexia. There are no other focal neurologic findings. Repeat laboratory results are as follows: Which of the following is the most likely cause of this patient's current symptoms?

Question

A 72-year-old man comes for evaluation of shortness of breath, headache, and fatigue.  He has a history of hypertension, lives alone, and is not compliant with his medications.  The patient drinks 1 or 2 glasses of wine daily but does not smoke.  Blood pressure is 184/128 mm Hg, pulse is 96/min, and oxygen saturation is 90% by pulse oximetry on room air.  He has early papilledema on funduscopic examination.  Pulmonary examination shows bibasilar coarse crackles.  Cardiac examination shows a grade 2/6 systolic ejection murmur along the left sternal border.  There is trace pedal edema.  Chest x-ray reveals mild pulmonary edema.  An ECG is unchanged from prior tracings.  Laboratory studies are normal except for serum creatinine of 2.0 mg/dL.  The patient is given oxygen and furosemide and is started on a nitroprusside drip.  After 36 hours, his blood pressure is 140/80 mm Hg and he is no longer dyspneic; however, he is confused and disoriented and has diffuse hyperreflexia.  There are no other focal neurologic findings.  Repeat laboratory results are as follows:  Which of the following is the most likely cause of this patient's current symptoms?

Quizplus · Accepted Answer

11ec25c8_d203_e41e_bc81_a50c01c7fd8b_MD0003_00 This patient's presentation suggests cyanide toxicity. Common etiologies include combustion of carbon- and nitrogen-containing compounds (eg, wool, silk), industrial exposure (eg, metal extraction in mining), and medications (eg, sodium nitroprusside). Cyanide binds to cytochrome oxidase and inhibits mitochondrial oxidative phosphorylation. Cells then shift to anaerobic metabolism with decreased ATP production and eventual lactic acidosis. Patients can develop symptoms affecting the neurologic (eg, headache, confusion, hyperreflexia due to thiocyanate accumulation), cardiovascular (eg, arrhythmias), respiratory (eg, tachypnea followed by respiratory depression), and gastrointestinal (eg, vomiting) systems, and skin (eg, flushing). Sodium nitroprusside is a potent arterial and venous vasodilator often used for hypertensive emergencies. The drug contains 5 cyanide groups and undergoes rapid conversion to cyanide and eventually thiocyanate, which is eliminated by the kidneys. Prolonged infusion (>24 hours) at high rates (5-10 µg/kg/min) can lead to cyanide toxicity, especially in patients with chronic kidney disease. As a result, low infusion rates (<2 µg/kg/min), short-term use, and close monitoring are recommended. Treatment includes sodium thiosulfate. (Choice A) Alcohol withdrawal can cause agitation, tachycardia, hypertension, and mental status changes. However, withdrawal is more common in patients with heavy alcohol use who stop suddenly. This patient's moderate alcohol use and absence of tachycardia make this less likely. (Choice C) Cerebral vessels may not auto-regulate in chronic hypertension. Significant decreases in blood pressure with failed autoregulation may significantly lower cerebral blood flow and cause ischemia. However, this patient's symptoms after sodium nitroprusside use are more concerning for cyanide toxicity. (Choice D) Lacunar infarcts are small strokes from occluded penetrating arteries, usually located in deep brain structures. Lacunar infarcts usually present with sensory or motor deficits, impaired cognition, or dysarthria. This patient's absence of focal neurological findings makes this less likely. (Choice E) Uremic encephalopathy can present with altered mentation and occasional myoclonus and usually occurs in patients with advanced renal failure. This patient's mild creatinine rise from 2.0 mg/dL to 2.5 mg/dL is unlikely to cause uremic encephalopathy. Educational objective: Prolonged infusion of sodium nitroprusside at high rates can lead to cyanide toxicity, especially in patients with chronic kidney disease. Typical findings include headache, confusion, arrhythmias, flushing, and respiratory depression. References: Sodium nitroprusside in 2014: A clinical concepts review. (http://www.ncbi.nlm.nih.gov/pubmed/25425768)

A 72-Year-Old Man Comes for Evaluation of Shortness of Breath