Certified Hyperbaric Technologist Practice Test

What is the PO2 in mmHg in a patient's mask while breathing O2 at 66 FSW?

1. 1520 mmHg

2. 2280 mmHg

3. 1000 mmHg

4. 300 mmHg

The correct answer is: 2280 mmHg

To determine the partial pressure of oxygen (PO2) in a patient's mask while breathing oxygen at 66 feet of seawater (FSW), we need to understand how pressure changes with depth in a hyperbaric environment. At sea level, the atmospheric pressure is approximately 760 mmHg. As you go underwater, the pressure increases due to the weight of the water above you. For every 33 feet of seawater, the pressure increases by about 1 atmosphere (ATM). Therefore, at 66 FSW, which is two atmospheres (since 66 divided by 33 equals 2), the total pressure would be: Total Pressure = Atmospheric Pressure + Pressure from Water Depth Total Pressure = 760 mmHg + (2 x 760 mmHg) = 2280 mmHg When a patient breathes pure oxygen in this environment, the partial pressure of oxygen can be calculated by multiplying the total pressure by the fraction of oxygen in the breathing gas. Since the patient is breathing 100% oxygen, the PO2 is equal to the total pressure itself: PO2 = Total Pressure PO2 = 2280 mmHg Thus, breathing oxygen at this depth results in a PO2 of 2280 mm