The question asks for the correct arterial blood gas (ABG) findings in acute hypoxemic respiratory failure.

Hypoxemic Failure ABG Findings

Hypoxemic respiratory failure occurs when blood oxygen levels, indicated by the partial pressure of oxygen ($PaO_2$), are abnormally low. This is primarily due to impaired gas exchange in the lungs, meaning the lungs cannot effectively transfer oxygen into the blood.

Arterial Blood Gas (ABG) Interpretation

Key ABG values in this condition are:

• $PaO_2$: Partial pressure of oxygen in arterial blood. This value is characteristically decreased in hypoxemic respiratory failure (typically below 60 mmHg or 8 kPa).
• $PaCO_2$: Partial pressure of carbon dioxide in arterial blood. In response to low oxygen levels (hypoxemia), the body often compensates by increasing the breathing rate (tachypnea). This increased ventilation helps eliminate more carbon dioxide ($CO_2$), typically resulting in a normal or low $PaCO_2$ level.

Analysis of Options

Evaluating the given options based on this understanding:

• Option 1 states $PaO_2$ is decreased and $PaCO_2$ is either normal or low. This matches the expected findings of hypoxemic respiratory failure with compensatory hyperventilation.
• Option 2 states $PaO_2$ is decreased and $PaCO_2$ is high. This describes combined respiratory failure (both hypoxemic and hypercapnic).
• Option 3 states Both $PaO_2$ and $PaCO_2$ levels are markedly reduced. This is physiologically unlikely as the primary presentation.
• Option 4 states $PaO_2$ is normal and $PaCO_2$ is high. This defines hypercapnic respiratory failure, not hypoxemic.

Therefore, the correct ABG profile for acute hypoxemic respiratory failure is a reduced $PaO_2$ with a normal or low $PaCO_2$.