In which of the following situations is volume-controlled ventilation sometimes used?
1. When a precise PaCO2 has to be maintained (some closed-head injuries)
2. When more even distribution of ventilation is required
3. When ventilating patients with severe, refractory hypoxemia
4. When ventilating patients with unstable or changing ventilatory drives
a. 1 and 2 only
b. 3 and 4 only
c. 1, 2, and 3 only
d. 1, 3, and 4 only
ANS: A
Volume-controlled continuous mandatory ventilation is indicated when a precise minute ventila-tion or blood gas parameter, such as PaCO2, is therapeutically essential to the care of patients with normal lung mechanics. Theoretically, volume control (with a constant inspiratory flow) re-sults in a more even distribution of ventilation (compared to pressure control) among lung units with different time constants where the units have equal resistances but unequal compliances (e.g., acute respiratory distress syndrome [ARDS]).
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