AACN ECCO Pulmonary Practice Exam

To confirm the diagnosis of acute hypoxemic respiratory failure, a key finding is a significantly low arterial oxygen partial pressure (PaO2). In this scenario, a PaO2 level of 55 mmHg is indicative of severe hypoxemia, which is a hallmark of acute hypoxemic respiratory failure.

While tachypnea and tachycardia can also be present in patients experiencing acute respiratory issues, they are nonspecific and can occur in a variety of conditions, not exclusively those associated with respiratory failure. Tachypnea, which refers to an increased respiratory rate, often occurs as a compensatory mechanism in response to low oxygen levels, while tachycardia may be a response to hypoxemia or stress but does not specifically confirm a diagnosis of respiratory failure.

Therefore, the presence of a PaO2 of 55 mmHg is critical in confirming the diagnosis of acute hypoxemic respiratory failure, as it directly reflects the severity of hypoxemia. Hence, although tachypnea and tachycardia support the clinical picture, it is the significantly low PaO2 that definitively helps in confirming the diagnosis.