Prehospital Trauma Life Support (PHTLS) Practice Test

Which of the following represents adequate spontaneous ventilation in an adult?

1. Tidal volume 100 mL, ventilatory rate 40/minute

2. Tidal volume 500 mL, ventilatory rate 8/minute

3. Tidal volume 300 mL, ventilatory rate 16/minute

4. Tidal volume 600 mL, ventilatory rate 12/minute

The correct answer is: Tidal volume 600 mL, ventilatory rate 12/minute

Adequate spontaneous ventilation in an adult is characterized by a combination of sufficient tidal volume and an appropriate respiratory rate to maintain proper gas exchange and oxygenation. In adults, the normal tidal volume is typically around 500 mL per breath, and a normal respiratory rate ranges from 12 to 20 breaths per minute. In the case of the answer provided, the tidal volume of 600 mL is higher than the average but still within a reasonable range that indicates effective air movement. Coupled with a ventilatory rate of 12 breaths per minute, this gives an adequate minute ventilation, which can effectively meet the body's metabolic demands for oxygen. This combination ensures that the body can adequately exchange oxygen and carbon dioxide. The other choices represent either a low tidal volume or an inappropriate ventilatory rate, which would not be sufficient to maintain adequate ventilation. For instance, a tidal volume of 100 mL, regardless of the high rate, cannot provide the necessary air exchange. Similarly, a tidal volume of 500 mL with a low rate of 8 breaths per minute may not meet the metabolic demands sufficiently, and a tidal volume of 300 mL with a moderate rate may still fall short of what is considered adequate.