CFRN Physiology and Gas Laws 2 — Questions and Answers
Question 1: According to Dalton's Law, if the total atmospheric pressure at sea level is 760 mmHg and oxygen comprises 21% of air, what is the partial pressure of oxygen (PaO2) at sea level?
- 159.6 mmHg (Correct answer)
- 100 mmHg
- 713 mmHg
- 21 mmHg
Correct answer: 159.6 mmHg
Dalton's Law states that the partial pressure of a gas equals its fractional concentration multiplied by total pressure (0.21 × 760 = 159.6 mmHg).
Question 2: A flight nurse is caring for a patient at 8,000 feet cabin altitude. Compared to sea level, which physiological change is expected in a healthy individual?
- Increased respiratory rate to compensate for lower PaO2 (Correct answer)
- Decreased heart rate due to reduced metabolic demand
- Increased arterial CO2 due to hypoventilation
- Decreased 2,3-DPG levels shifting the oxyhemoglobin curve left
Correct answer: Increased respiratory rate to compensate for lower PaO2
At altitude, lower PaO2 stimulates peripheral chemoreceptors causing compensatory hyperventilation and increased respiratory rate.
Question 3: Which gas law explains why a pneumothorax can expand during flight as the aircraft ascends to altitude?
- Boyle's Law (Correct answer)
- Charles' Law
- Henry's Law
- Fick's Law
Correct answer: Boyle's Law
Boyle's Law states that at constant temperature, gas volume varies inversely with pressure; as cabin pressure decreases at altitude, trapped gas expands.
Question 4: The oxyhemoglobin dissociation curve shifts to the RIGHT in which of the following conditions encountered during flight?
- Acidosis, hyperthermia, and increased 2,3-DPG (Correct answer)
- Alkalosis, hypothermia, and decreased CO2
- Hypocarbia and decreased body temperature
- Increased pH and decreased 2,3-DPG
Correct answer: Acidosis, hyperthermia, and increased 2,3-DPG
Acidosis, hyperthermia, hypercarbia, and increased 2,3-DPG shift the curve right, reducing hemoglobin's oxygen affinity and facilitating tissue oxygen release.
Question 5: Henry's Law is most clinically relevant for the flight nurse when managing a patient with:
- Decompression sickness after SCUBA diving (Correct answer)
- Tension pneumothorax
- Pulmonary edema
- Carbon monoxide poisoning
Correct answer: Decompression sickness after SCUBA diving
Henry's Law states that the amount of gas dissolved in liquid is proportional to its partial pressure; decompression sickness results from nitrogen bubbling out of solution as pressure decreases.
Question 6: At a cruising altitude with a cabin pressure equivalent to 8,000 feet, the inspired partial pressure of oxygen (PiO2) is approximately:
- 109 mmHg (Correct answer)
- 159 mmHg
- 60 mmHg
- 40 mmHg
Correct answer: 109 mmHg
At 8,000 feet, barometric pressure is approximately 565 mmHg; PiO2 = 0.21 × (565 - 47) = approximately 109 mmHg after subtracting water vapor pressure.
Question 7: Which statement correctly describes the Fick Principle as it applies to oxygen delivery during aeromedical transport?
- Oxygen consumption equals cardiac output multiplied by the arteriovenous oxygen content difference (Correct answer)
- Oxygen delivery equals hemoglobin concentration divided by cardiac output
- Tissue oxygen consumption is independent of cardiac output changes
- Oxygen delivery is primarily determined by dissolved oxygen alone
Correct answer: Oxygen consumption equals cardiac output multiplied by the arteriovenous oxygen content difference
The Fick Principle states VO2 = CO × (CaO2 - CvO2), making cardiac output and hemoglobin critical determinants of tissue oxygen delivery.
CFRN Physiology and Gas Laws 2
According to Dalton's Law, if the total atmospheric pressure at sea level is 760 mmHg and oxygen comprises 21% of air, what is the partial pressure of oxygen (PaO2) at sea level?