CFRN Physiology and Gas Laws 4

Question 1

A flight nurse is managing a ventilated patient at altitude. Tidal volume has NOT been changed, yet peak airway pressures have increased. The most likely gas law explanation is:

Accepted Answer

Gas in the circuit expanded due to lower cabin pressure, increasing effective delivered volume

Answer

Boyle's Law explains that gas in humidified circuits or bellows can expand at altitude, effectively increasing delivered tidal volume and airway pressures.

Question 2

The concept of 'equivalent oxygen percentage' at altitude means that to maintain a PaO2 equivalent to sea-level room air at 8,000 feet cabin altitude, a patient needs supplemental FiO2 of approximately:

Accepted Answer

30%

Answer

At 8,000 feet (PB ~565 mmHg), an FiO2 of approximately 30% is needed to achieve the same PiO2 as breathing 21% oxygen at sea level (760 mmHg).

Question 3

Which patient condition poses the GREATEST risk of expanding gas complications during aeromedical transport?

Accepted Answer

Recent pneumocephalus following neurosurgical procedure

Answer

Pneumocephalus contains intracranial air that expands at altitude per Boyle's Law, potentially causing increased intracranial pressure and brain herniation.

Question 4

Hypemic hypoxia during aeromedical transport would MOST likely occur in a patient with:

Accepted Answer

Severe anemia with hemoglobin of 5 g/dL

Answer

Hypemic hypoxia results from reduced oxygen-carrying capacity of blood, most commonly from severe anemia, methemoglobinemia, or carboxyhemoglobin binding.

Question 5

A patient on 100% non-rebreather mask at sea level has a PaO2 of 500 mmHg. During transport at 8,000 feet cabin altitude (PB 565 mmHg), the expected PaO2 on the same mask would be approximately:

Accepted Answer

372 mmHg

Answer

PaO2 at altitude scales with barometric pressure; 500 × (565/760) ≈ 372 mmHg, reflecting the proportional decrease in available oxygen partial pressure.

CFRN - Certified Flight Registered Nurse Practice Test

CFRN - Certified Flight Registered Nurse Practice Test

CFRN Physiology and Gas Laws 4