Which condition would be least likely to cause hypoxia?

• A. Severe anxiety.
• B. Pleural effusion.
• C. Pulmonary edema.
• D. Narcotic overdose.

Answer: (A)

Hypoxia happens when the body's tissues don’t receive enough oxygen, usually because oxygenation or blood delivery is impaired. Conditions that disrupt lung function or ventilation tend to cause hypoxia by lowering the amount of oxygen that gets into the blood or by worsening gas exchange.

Pleural effusion reduces lung expansion and creates ventilation–perfusion mismatch, leading to lower blood oxygen levels. Pulmonary edema floods the alveoli with fluid, directly impairing gas exchange and causing hypoxemia. Narcotic overdose depresses the respiratory drive, causing hypoventilation and poor oxygen intake, which also leads to hypoxia.

Severe anxiety, on the other hand, typically causes hyperventilation—rapid, shallow breaths that can reduce CO2 but do not usually decrease the amount of oxygen getting into the blood. Oxygen saturation can remain normal, so it is least likely to cause hypoxia.

So the best choice is the one describing severe anxiety.