CFRN Physiology and Gas Laws 5

Question 1

A patient with COPD relying on hypoxic drive is being transported at altitude. The flight nurse should be MOST concerned about administering high-flow oxygen because:

Accepted Answer

Eliminating the hypoxic drive may cause apnea or severe hypoventilation

Answer

In COPD patients dependent on hypoxic drive, high-flow oxygen can remove the primary stimulus to breathe, causing dangerous hypoventilation or apnea.

Question 2

The flight nurse calculates oxygen cylinder duration using the formula: Duration = (Cylinder pressure × Cylinder factor) / Flow rate. For a D cylinder (factor 0.16) at 1,800 psi with a flow rate of 4 L/min, the duration is:

Accepted Answer

72 minutes

Answer

Duration = (1,800 × 0.16) / 4 = 288 / 4 = 72 minutes; always plan for at least 30 minutes extra beyond transport time.

Question 3

Third-spacing of fluids at altitude most commonly occurs because of:

Accepted Answer

Reduced oncotic pressure relative to increased hydrostatic pressure from hypoxia-induced pulmonary vasoconstriction

Answer

Altitude-induced hypoxia causes pulmonary vasoconstriction and increased hydrostatic pressure, promoting fluid movement from capillaries to interstitial spaces.

Question 4

Which of the following BEST explains why a patient breathing spontaneously at altitude will have a lower PaCO2 than at sea level?

Accepted Answer

Hypoxia stimulates hyperventilation causing CO2 to be blown off

Answer

Hypoxia at altitude stimulates the carotid body chemoreceptors, increasing respiratory rate and depth, which blows off CO2 and causes hypocapnia.

Question 5

A patient with a pneumothorax that was 15% on chest X-ray at sea level will be approximately what size at a cabin altitude of 8,000 feet (PB ~565 mmHg)?

Accepted Answer

Approximately 20%

Answer

Using Boyle's Law: V2 = V1 × (P1/P2) = 15% × (760/565) ≈ 20%; small pneumothoraces can expand significantly and should be drained before flight.

CFRN - Certified Flight Registered Nurse Practice Test

CFRN - Certified Flight Registered Nurse Practice Test

CFRN Physiology and Gas Laws 5