Calculate the Alveolar ventilation per minute of a patient with respiratory rate 14/min, tidal volume of 500 ml with a vital capacity 7000 ml
**Core Concept**
Alveolar ventilation is the volume of air that reaches the alveoli per minute, which is crucial for gas exchange. It is calculated by subtracting the dead space volume from the tidal volume and then multiplying by the respiratory rate.
**Why the Correct Answer is Right**
To calculate alveolar ventilation, we first need to determine the dead space volume, which is typically 150 ml. The tidal volume is given as 500 ml. We then subtract the dead space volume from the tidal volume to get the effective tidal volume (ETV) used for alveolar ventilation. ETV = 500 ml - 150 ml = 350 ml. We then multiply the ETV by the respiratory rate (RR) to get the alveolar ventilation per minute (VA). VA = ETV x RR = 350 ml x 14/min = 4900 ml/min.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the dead space volume, which is a significant portion of the tidal volume and affects alveolar ventilation.
**Option B:** This option is incorrect because it uses the vital capacity, which is the maximum volume of air that can be exhaled after maximum inhalation, and does not account for the actual tidal volume used for breathing.
**Option C:** This option is incorrect because it does not provide a calculation for alveolar ventilation and simply states the tidal volume.
**Option D:** This option is incorrect because it does not provide a calculation for alveolar ventilation and simply states the respiratory rate.
**Clinical Pearl / High-Yield Fact**
Remember that alveolar ventilation is affected by both the tidal volume and the respiratory rate, but the dead space volume must be subtracted from the tidal volume to get the effective tidal volume used for alveolar ventilation.
**Correct Answer:** B. 4900 ml/min