Question

A 35 year old relatively healthy patient is seen in the emergency department for cough and shortness of breath; the evaluation takes place at sea level. Chest x-rays examination shows a large infiltrate, consistent with the clinical diagnosis or pneumonia, in his left lung. When the patient is breathing ambient air and his flow of oxygen is .21, his arterial pressure of oxygen is 52mmHg , arterial pressure of CO2 is 39mmHg, and pH is 7.42. Minute ventilation is 12L/min. Does this minute ventilation, together with PaCO2 indicate an increase in wasted ventilation? How is an increase in wasted ventilation explained by ventilation/perfusion imbalance?

Answer 1

Minute ventilation and PaCO2 levels can indicate an increase in wasted ventilation. Ventilation/perfusion imbalance can explain the increase in wasted ventilation.

Step-by-step explanation:

The minute ventilation and PaCO2 levels can indicate if there is an increase in wasted ventilation. Minute ventilation is calculated by multiplying the tidal volume (amount of air inhaled or exhaled in one breath) by the respiratory rate. In this case, the minute ventilation is 12 L/min. PaCO2 represents the partial pressure of carbon dioxide in the arterial blood and is measured in mmHg. In this case, the PaCO2 is 39mmHg.

To determine if there is an increase in wasted ventilation, we need to compare the measured minute ventilation with the expected minute ventilation. The expected minute ventilation can be calculated by multiplying the ideal body weight (in kg) by a factor of 100.

If the measured minute ventilation is higher than the expected minute ventilation, then there is an increase in wasted ventilation. This can be caused by a ventilation/perfusion imbalance, where there is an unequal distribution of ventilation and blood flow in the lungs. In this case, the large infiltrate in the left lung may be affecting the ventilation to that area, leading to wasted ventilation.