Certified Respiratory Therapist Practice Exam

A patient weighs 150 lbs and has a tidal volume of 550 mL. What is their estimated alveolar ventilation per minute?

1. 6.00 L/min

2. 7.00 L/min

3. 8.00 L/min

4. 9.00 L/min

The correct answer is: 8.00 L/min

To determine the estimated alveolar ventilation per minute, first, it is important to calculate the total ventilation and then consider the factors that affect alveolar ventilation. Total ventilation, also known as minute ventilation, can be calculated using the formula: \[ \text{Minute Ventilation} = \text{Tidal Volume} \times \text{Respiratory Rate} \] However, in this question, the respiratory rate isn't provided, so instead, we can find the estimated alveolar ventilation using an approximation based on typical respiratory rates. A normal respiratory rate for adults is typically between 12 to 20 breaths per minute. Using an average value, we'll use 15 breaths per minute for this calculation. First, calculate the total minute ventilation: \[ \text{Minute Ventilation} = 550 \, \text{mL} \times 15 = 8250 \, \text{mL/min} \, = 8.25 \, \text{L/min} \] Next, to find the estimated alveolar ventilation, we need to account for the proportion of tidal volume that reaches the alveoli. Generally, not all the tidal volume contributes to alveolar ventilation due to dead space in the lungs.