Physiology and Gas Laws Flashcards

A flight crew is transporting a patient with a pneumothorax from a rural facility at sea level to a trauma center. As the aircraft ascends to cruising altitude, the patient develops increasing respiratory distress, hypotension, and tachycardia. Which gas law best explains this clinical deterioration?

Answer: Boyle's Law

Boyle's Law states that the volume of a gas is inversely proportional to the pressure exerted upon it, assuming a constant temperature. As the aircraft ascends, the atmospheric pressure decreases, causing the trapped air within the patient's pleural space (pneumothorax) to expand in volume. This expansion can convert a simple pneumothorax into a tension pneumothorax, leading to the observed signs of cardiorespiratory compromise.

A patient with a history of COPD has a baseline oxygen saturation of 92% on room air at sea level. During helicopter transport at 8,000 feet, the flight nurse notes the patient's saturation has dropped to 85% despite being on the same FiO2. This physiological change is primarily explained by:

Answer: A decrease in the partial pressure of oxygen.

Dalton's Law states that the total pressure of a gas mixture is the sum of the partial pressures of its individual components. While the percentage of oxygen in the atmosphere remains constant at approximately 21% regardless of altitude, the total atmospheric pressure decreases with ascent. This decrease in total pressure leads to a proportional decrease in the partial pressure of oxygen (PO2), reducing the driving pressure for oxygen to diffuse from the alveoli into the blood and causing hypoxemia.

A flight nurse is caring for a patient who was rescued after a prolonged deep-sea diving incident. The patient is now complaining of severe joint pain, dizziness, and has a mottled skin rash. These symptoms are most consistent with a condition explained by which gas law?

Answer: Henry's Law

Henry's Law describes how the amount of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. During a deep-sea dive, increased ambient pressure causes more nitrogen to dissolve into the diver's blood and tissues. If the diver ascends too quickly, the rapid decrease in pressure allows the dissolved nitrogen to come out of solution and form bubbles, leading to decompression sickness ('the bends'), which manifests with the described symptoms.

During a winter transport in a rotor-wing aircraft, the flight nurse notices that the pressure reading on a portable oxygen cylinder has decreased significantly since the pre-flight check, even though no oxygen has been administered. Which of the following gas laws provides the best explanation for this observation?

Answer: Charles's Law

Charles's Law states that for a fixed mass of gas at a constant volume, the pressure is directly proportional to the absolute temperature. As the aircraft ascends into colder temperatures, the temperature of the gas inside the oxygen cylinder decreases. This reduction in temperature causes the gas molecules to move more slowly, resulting in a decrease in the pressure exerted on the cylinder walls.

Which of the following is the MOST critical initial intervention for a patient experiencing hypoxic hypoxia due to an unexpected loss of cabin pressure at high altitude?

Answer: Applying 100% supplemental oxygen

Hypoxic hypoxia at altitude is caused by a decreased partial pressure of inspired oxygen (Dalton's Law). The most critical and immediate intervention is to increase the fraction of inspired oxygen (FiO2) to the maximum possible level, which is 100%. This helps to maximize the alveolar oxygen partial pressure, improving the pressure gradient for oxygen diffusion into the blood and correcting the hypoxemia. Descent to a lower altitude is also a primary goal.

A patient with a bowel obstruction is being transported by a fixed-wing aircraft pressurized to a cabin altitude of 8,000 feet. The flight nurse should anticipate and monitor for which potential complication related to gas expansion?

Answer: Increased pain and abdominal distention

According to Boyle's Law, as the aircraft ascends and cabin pressure decreases, the volume of trapped gas within the patient's bowel will expand. In a patient with a bowel obstruction, this expansion can lead to increased abdominal distention, worsening pain, and potentially compromise of the bowel wall or respiratory function due to pressure on the diaphragm.