Master Physiologic Dead Space (VD) with Picmonic for Medicine

The physiologic dead space represents the amount of air that is inspired but does not take part in gas exchange. Two areas of the lung contribute to the physiologic dead space: one is the space in the conductive airway, also called anatomic dead space, and the other is the alveoli that are not well perfused, such as the apex of the lung, also called functional dead space. Physiologic dead space can quickly provide insight into how patients' gas exchange in the lungs is functioning. Causes of an increase in physiologic dead space include shunt or diseases that damage the alveoli. Physiologic dead space can be calculated by multiplying the tidal volume (TV) with the difference between the arterial partial pressure of CO2 (PaCO2) and the partial pressure of CO2 in the expired air (PECO2) and divided by the arterial partial pressure of CO2 (PaCO2). In other words, it is the volume of air that is proportional to the percentage of CO2 that entered the lungs but did not get exchanged.