National Registry of Certified Medical Examiners (NRCME) DOT Practice Exam

At what altitude should a driver not be certified if an ABG shows a PaO2 of less than 65?

1. 2,000 feet

2. 3,000 feet

3. 5,000 feet

4. 7,000 feet

The correct answer is: 5,000 feet

The correct answer is based on the relationship between altitude and oxygen levels in the arterial blood. When a driver has an arterial blood gas (ABG) analysis showing a partial pressure of oxygen (PaO2) of less than 65 mmHg, this indicates inadequate oxygenation, which can significantly impact their ability to operate a vehicle safely, especially at higher altitudes. Altitude affects atmospheric pressure and, consequently, the availability of oxygen. As altitude increases, the partial pressure of oxygen decreases, which can exacerbate any preexisting conditions that compromise oxygen levels in the blood. At an altitude of 5,000 feet, the ambient pressure is significantly lower than at sea level, leading to further reductions in PaO2 for individuals with existing low levels. Hence, drivers with a PaO2 of less than 65 mmHg should not be certified to drive at this altitude because the risk of hypoxemia (insufficient oxygen in the blood) increases, which can impair cognitive and motor functions crucial for safe driving. In contrast, at lower altitudes like 2,000, 3,000, or even 7,000 feet, while the risks associated with a low PaO2 still exist, the specific threshold for certification is often