All of the following are stages of hemostasis except:

Choice A reason: Pulmonary emboli are a priority in ARDS, as they can cause or worsen hypoxemia and lung injury. Emboli block pulmonary arteries, leading to ventilation-perfusion mismatch, a common ARDS trigger, making this the correct condition to assess first.

Choice B reason: Pneumonia may contribute to ARDS but is less urgent than pulmonary emboli, which can rapidly cause life-threatening hypoxia. Emboli are a more immediate concern in ARDS, so this is incorrect.

Choice C reason: Acute pulmonary edema is linked to heart failure, not a primary ARDS cause. Pulmonary emboli directly trigger ARDS’s acute lung injury, making this less critical and incorrect for priority assessment.

Choice D reason: Heart failure may cause pulmonary edema but isn’t a primary ARDS trigger. Pulmonary emboli are a more urgent cause of ARDS-related hypoxia, so this is incorrect.

Choice A reason: Hyperventilation causes decreased CO2 levels (respiratory alkalosis) due to rapid breathing from pain, anxiety, or restlessness. This matches the patient’s symptoms and blood gas results, making it the correct cause.

Choice B reason: Nephrolithiasis causes pain but doesn’t typically lead to hyperventilation or low CO2. Respiratory alkalosis from hyperventilation better explains the findings, so this is incorrect for the cause.

Choice C reason: Acute fracture causes pain but not necessarily hyperventilation or low CO2. Anxiety-driven hyperventilation is more likely to cause respiratory alkalosis, so this is incorrect for the primary cause.

Choice D reason: Urinary tract infection may cause discomfort but not low CO2 or hyperventilation. Anxiety and pain causing hyperventilation align with the blood gas, so this is incorrect.