A 24-year-old woman is brought to the emergency department after her friend found her unresponsive at home. She was in her usual state of health 12 hours ago. The patient's medical history is significant for generalized anxiety disorder and major depression. On examination, temperature is 36.9 C (98.4 F), blood pressure is 90/56 mm Hg, pulse is 68/min, and respirations are 8/min. There is no response to painful stimuli. Pupils are normal in size. Breath sounds are normal. The patient is given a dose of naloxone but remains unresponsive. Arterial blood gas analysis on room air is as follows: Which of the following most likely explains this patient's arterial blood gas findings?

Question

A 24-year-old woman is brought to the emergency department after her friend found her unresponsive at home.  She was in her usual state of health 12 hours ago.  The patient's medical history is significant for generalized anxiety disorder and major depression.  On examination, temperature is 36.9 C (98.4 F), blood pressure is 90/56 mm Hg, pulse is 68/min, and respirations are 8/min.  There is no response to painful stimuli.  Pupils are normal in size.  Breath sounds are normal.  The patient is given a dose of naloxone but remains unresponsive.  Arterial blood gas analysis on room air is as follows:  Which of the following most likely explains this patient's arterial blood gas findings?

Quizplus · Accepted Answer

11ec25c8_d201_e84b_bc81_2905f4dd95a7_MD0003_00 This patient has respiratory acidosis, as evidenced by decreased pH (<7.35) and increased PaCO₂ (>40 mm Hg; ie, hypercarbia) on arterial blood gas analysis. In addition, she has hypoxia (low PaO₂) and decreased respirations (8/min [normal: 12-18]), consistent with hypoventilation. In this unresponsive patient with an otherwise unremarkable physical examination, this presentation is consistent with decreased central respiratory drive, likely due to an overdose. Her pupils are normal in size, and naloxone, an opioid antagonist, had no effect; this raises suspicion for benzodiazepine toxicity, possibly in combination with alcohol use. respiratory acidosis Central respiratory centers in the brainstem normally regulate respiration based on input from a wide range of central and peripheral sources (eg, chemoreceptors, volitional pathways). Benzodiazepines bind to the GABA A receptor and increase the inhibitory effects of GABA in the CNS; in cases of severe overdose, this can depress central respiratory drive. This effect is potentiated by alcohol, a common coingestant. Management of patients with acute benzodiazepine intoxication should first involve protection of the airway and ventilatory support as needed. Flumazenil, a nonspecific competitive antagonist, is sometimes given as a reversal agent; however, it does not consistently reverse respiratory depression and can potentiate seizures in patients who have developed a tolerance to benzodiazepines. (Choice B) Decreased availability of phosphate (eg, hypophosphatemia) can cause generalized muscle weakness, which may impair the muscles of respiration and lead to respiratory acidosis. However, it is less likely than benzodiazepine intoxication to cause profound alterations in consciousness. (Choice C) Many neuromuscular diseases can impact respiratory neuromuscular function, including amyotrophic lateral sclerosis, myasthenia gravis, and Guillain-Barré syndrome. However, none of these conditions would present with such an acute onset. (Choice D) Increased thoracic cage stiffness can occur due to scoliosis or ankylosing spondylitis and result in respiratory insufficiency. However, these conditions typically progress slowly rather than over a few hours. (Choice E) Excessive cellular carbon dioxide production can be seen in patients with fever or thyrotoxicosis. However, arterial blood gas would show metabolic (ie, low bicarbonate level) rather than respiratory acidosis, and the respiratory rate would be increased rather than decreased (due to respiratory compensation). (Choice F) Increased dead space can be seen when patients take short, shallow breaths or when there is a ventilation-perfusion mismatch (eg, pulmonary embolism). However, this typically results in an increased respiratory rate. Educational objective: Acute benzodiazepine intoxication causes decreased central respiratory drive, leading to hypoventilation and respiratory acidosis.

A 24-Year-Old Woman Is Brought to the Emergency Department After