American Board of Internal Medicine (ABIM) Certification Practice Exam

What FVC percentage suggests the need for ventilatory assistance?

1. Less than 50% of predicted

2. Less than 60% of predicted

3. Less than 40% of predicted

4. Less than 70% of predicted

The correct answer is: Less than 50% of predicted

A forced vital capacity (FVC) percentage of less than 50% of predicted indicates a significant reduction in lung capacity, which suggests that the individual may have severe respiratory impairment. This level of impairment can be insufficient for adequate ventilation, leading to inadequate oxygenation and carbon dioxide elimination. When FVC falls below this threshold, it often signals that the patient cannot maintain effective respiratory mechanics, making ventilatory assistance necessary to support effective breathing and avoid respiratory failure. In clinical practice, FVC values serve as an important guide for determining the need for interventions such as non-invasive ventilation or invasive mechanical ventilation. Lower thresholds, such as those below 40%, may further indicate a more critical situation, but the threshold of 50% is often the point at which the need for intervention becomes more pronounced and urgent. Understanding these values helps in making decisions about respiratory support in patients with potential respiratory failure.