The Gas Exchanger: Matching Ventilation and Perfusion
Review Questions
DIRECTIONS: Each of the numbered items or incomplete statements in this section is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case.
Q1: Complete the missing elements in the table below that summarizes the factors used to analyze the physiological causes of hypoxia.
PHYSIOLOGICAL CAUSE OF HYPOXIA
A-aDO2 (NORMAL OR INCREASED)
SIGNIFICANT RESPONSE TO SUPPLEMENTAL O2 (Y/N)
RESPONSE AT REST (Y/N)
Decreased PIO2
Alveolar hypoventilation
Ventilation-perfusion mismatch
Shunt
Diffusion abnormality
Explanation: See the completed table below
| PHYSIOLOGICAL CAUSE OF HYPOXIA | A-aDO2 (NORMAL OR INCREASED) | SIGNIFICANT RESPONSE TO SUPPLEMENTAL O2 (Y/N) | RESPONSE AT REST (Y/N) |
|---|---|---|---|
| Decreased PIO2 | Normal | Y | Y |
| Alveolar hypoventilation | Normal | Y | Y |
| Ventilation-perfusion mismatch | Increased | Y | Y |
| Shunt | Increased | N | Y |
| Diffusion abnormality | Increased | Y | N |
Questions 2, 3, 4 are based on the following case.
You are taking care of a patient in the intensive care unit (ICU). She is 40 years old and has only one lung (she underwent a left pneumonectomy several years earlier because of recurrent infections), and that lung is damaged by severe scarring or pulmonary fibrosis. She entered the ICU with respiratory failure caused by severe bronchitis. She is very weak, and you are having trouble getting her to sustain her own breathing without the ventilator. On the ventilator with an FIO2 of 0.35, her arterial blood gas shows PaO2 = 80 mm Hg; PaCO2 = 60 mm Hg; and pH = 7.34 with a respiratory rate of 25 and a tidal volume of 350 mL. When you take her off the ventilator, she immediately increases her respiratory rate to 40 breaths/min with a tidal volume of 250 mL. Assume the patient has an anatomic dead space of 125 mL and an alveolar dead space of 50 mL.