A 30-year-old family physician moves from Florida to a town in the Colorado mountains to establish a medical practice. On the night of arrival, she experiences headache and has difficulty falling asleep. The next day she develops fatigue, nausea, dizziness, and mild dyspnea on exertion. She has no chronic medical conditions. Temperature is 37.2 C (99 F), blood pressure is 116/68 mm Hg, pulse is 90/min, and respirations are 20/min. Pulse oximetry shows 90% on ambient air. Medication with which of the following effects is most appropriate to improve her symptoms?

Question

A 30-year-old family physician moves from Florida to a town in the Colorado mountains to establish a medical practice.  On the night of arrival, she experiences headache and has difficulty falling asleep.  The next day she develops fatigue, nausea, dizziness, and mild dyspnea on exertion.  She has no chronic medical conditions.  Temperature is 37.2 C (99 F), blood pressure is 116/68 mm Hg, pulse is 90/min, and respirations are 20/min.  Pulse oximetry shows 90% on ambient air.  Medication with which of the following effects is most appropriate to improve her symptoms?

Quizplus · Accepted Answer

11ec25c8_d303_a13c_bc81_b1b052640c0c_MD0003_00 This patient is experiencing symptoms of high-altitude illness (HAI), including fatigue, nausea, headache, lightheadedness, and dyspnea. These symptoms most commonly occur within 1-2 days of ascent to an elevation >2,500 m (~8,000 ft) and are driven by the hypoxemia that results from low partial pressure of inspired oxygen (PiO₂) at high altitude. Hyperventilation is the most immediate and important physiologic adjustment to high altitude. Hypoxemia stimulates peripheral chemoreceptors in the aorta and carotid body to increase minute ventilation, which helps increase PaO₂. However, this comes at the expense of increased CO₂ removal and respiratory alkalosis, which create a ceiling for the ventilatory response because central chemoreceptors sense the elevated blood pH and stimulate negative feedback to limit ventilation. The kidneys compensate for the respiratory alkalosis by increasing HCO₃⁻excretion to decrease pH and increase the ventilatory ceiling, but this process requires approximately 72 hours to optimize. ⁻ Acetazolamide, a carbonic anhydrase inhibitor, helps prevent and treat HAI by accelerating the increase in the ventilatory ceiling. The drug blocks sodium bicarbonate (NaHCO₃) reabsorption in the proximal tubule to increase HCO₃⁻excretion and promptly assist with metabolic compensation for respiratory alkalosis. The reduction in pH is accelerated, alleviating central inhibition of the ventilatory response and facilitating the maintenance of adequate PaO₂ to reduce the symptoms of HAI. ⁻ (Choice A) Direct suppression of the respiratory center, as occurs with central respiratory depressants (eg, opioids, benzodiazepines, alcohol), decreases the ventilatory response and worsens HAI. (Choice B) Hydroxyurea increases erythrocyte hemoglobin F levels, which increases overall hemoglobin affinity for O₂ and shifts the hemoglobin dissociation curve to the left. However, one of the initial responses to high altitude is increased production of 2,3-bisphosphoglycerate, which shifts the curve to the right to facilitate O₂ unloading in the tissues. In addition, months are required for hydroxyurea to take effect. hemoglobin dissociation curve (Choice C) Peripheral chemoreceptors are already fully activated at high elevation in response to hypoxemia. Further sensitization is not a potential mechanism for improving HAI. (Choice E) Hypoxemia at high altitude results from low PiO₂ leading to low alveolar partial pressure of oxygen. The alveolar-arterial oxygen gradient is already normal and cannot be further reduced. Educational objective: Acetazolamide helps prevent and treat high altitude illness by increasing renal HCO₃⁻excretion to reduce blood pH and alleviate central chemoreceptor inhibition of the hypoxic ventilatory response. ⁻

A 30-Year-Old Family Physician Moves from Florida to a Town