A 32-year-old woman is evaluated for cough and shortness of breath while mountain climbing. She has no chronic medical problems and takes no medication. The patient does not use tobacco, alcohol, or illicit drugs. On examination, temperature is 36.5 C (97.7 F), blood pressure is 134/84 mm Hg, pulse is 110/min, and respirations are 20/min. BMI is 25 kg/m². Oxygen saturation is 84% on ambient air. Perioral cyanosis is present. She is in moderate respiratory distress. Pulmonary examination reveals bilateral inspiratory crackles. Chest x-ray reveals normal heart size and bilateral patchy lung infiltrates. Therapy for this patient would most likely focus on which of the following?

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Explanation: 11ec25c8_d1fd_0642_bc81_6f7dbcf12d1a_MD0003_00 This patient with respiratory distress, hypoxemia, and pulmonary crackles while mountaineering likely has high-altitude pulmonary edema (HAPE). The normal response to local alveolar hypoxia is hypoxic pulmonary vasoconstriction (HPV), which diverts blood flow from poorly- to better-aerated alveoli, preserving ventilation-perfusion matching. Low ambient partial pressure of inspired oxygen (PiO₂) at high altitude causes global HPV throughout the lungs, leading to increased pulmonary arterial pressure. ₂ Some genetically predisposed persons experience uneven hypoxic vasoconstriction; as a result, capillary beds in relatively less vasoconstricted areas are hyperperfused, resulting in fluid transudation across the vascular barrier, giving rise to patchy bilateral pulmonary edema. bilateral pulmonary edema Diffuse pulmonary edema (eg, due to decompensated left ventricular failure) causes widespread intrapulmonary shunt effect, and is therefore difficult to overcome with supplemental oxygen alone. However, HAPE is unique. Because HAPE is driven by high perfusion pressure through the lungs, interventions that reduce pulmonary arterial pressure improve the edema. Non-pharmacologic interventions are most effective: Unloading the victim (eg, removing heavy backpacks) reduces peripheral oxygen consumption to prevent further hypoxemia; it also lowers cardiac output and afterload to decrease edema formation. Supplemental oxygen and descent to lower altitude alleviate hypoxic vasoconstriction in accessible alveoli, reducing pulmonary arterial pressure to improve the edema. (Choice A) Increased coronary blood flow (eg, coronary stenting) can alleviate ischemic angina. Persons with underlying coronary artery disease are more likely to experience angina (eg, exertional chest pain) at high altitude. However, myocardial ischemia does not play a role in HAPE. (Choice B) High altitude stimulates the hypoxic ventilatory response to increase minute ventilation, maintaining adequate PAO₂ by lowering PACO₂. Acetazolamide can prevent HAPE by facilitating a metabolic acidosis to help sustain the ventilatory response; however, it is not an effective treatment for HAPE once symptoms develop. ₂ ₂ ventilatory response (Choice C) Sympathetic activity is increased at high altitude, resulting in increased systemic vascular resistance. A further increase (eg, with phenylephrine) is not beneficial for HAPE. (Choice D) Elevated left ventricular (LV) end-diastolic pressure causes cardiogenic pulmonary edema. HAPE is a form of noncardiogenic pulmonary edema, occurring with normal LV function and end-diastolic pressure. (Choice E) Pericardiocentesis can lower pericardial pressure to relieve tamponade; however, hypotension and clear lungs are expected with tamponade. Educational objective: High-altitude pulmonary edema is driven by uneven hypoxic pulmonary vasoconstriction leading to patchy pulmonary capillary hyperperfusion with disruption of the vascular barrier. Treatment involves urgent reduction of pulmonary arterial pressure, typically by unloading the victim, providing supplemental oxygen, and prompt descent to lower altitude. References: Update on high-altitude pulmonary edema: pathogenesis, prevention, and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/19099331)

A 32-Year-Old Woman Is Evaluated for Cough and Shortness of Breath