While estimating alveolar minute ventilation for a patient, the therapist identifies a dead space of 150 mL. What is the reported alveolar minute ventilation if the exhaled VT is 450 mL?

To determine the reported alveolar minute ventilation, first, you need to calculate the effective tidal volume (VT) that contributes to alveolar ventilation. This involves subtracting the dead space from the total tidal volume.

In this scenario, the total exhaled tidal volume is 450 mL, and the dead space is 150 mL. You can calculate the effective tidal volume that participates in gas exchange as follows:

Effective VT = Total VT - Dead Space

Effective VT = 450 mL - 150 mL = 300 mL

Next, to find the alveolar minute ventilation (VA), you need to multiply the effective tidal volume by the respiratory rate (RR). However, since the question does not provide a specific respiratory rate, it's implied or commonly assumed that you would estimate an average rate for a typical adult at rest, which is approximately 12 breaths per minute.

Now, using the effective tidal volume of 300 mL:

VA = Effective VT x RR

VA = 300 mL x 12 breaths/min = 3600 mL/min or 3.6 L/min

Thus, the reported alveolar minute ventilation is indeed 3.6 L/min, making it the correct answer. This calculation