Certified Respiratory Therapist Practice Exam

A pulmonary capillary wedge pressure (PCWP) of 18 mm Hg may be caused by all of the following except:

1. Heart failure

2. Overhydration

3. Hypovolemia

4. Pulmonary hypertension

The correct answer is: Hypovolemia

A pulmonary capillary wedge pressure (PCWP) is an important measurement used to assess left atrial pressure and, by extension, left ventricular function. A PCWP reading of 18 mm Hg indicates elevated pressures, often associated with conditions that increase blood volume within the pulmonary circulation or restrict left ventricular filling. Heart failure typically leads to increased pressures in the pulmonary circulation due to a backup of blood, resulting in an elevated PCWP. Overhydration can also lead to increased blood volume and pressure, contributing to elevated readings. Similarly, pulmonary hypertension, which is elevated pressure within the pulmonary arteries, can cause an increase in the pulmonary capillary wedge pressure as the left heart's ability to eject blood is compromised by high resistance in the pulmonary vasculature. Hypovolemia, however, refers to a decreased volume of blood in the body. When the body is low on blood volume, there isn't an excess of fluid backing up into the pulmonary circulation. Instead, the pressure in the pulmonary capillaries would be expected to decrease rather than increase. Therefore, hypovolemia would not contribute to a PCWP reading of 18 mm Hg, making it the correct choice for the scenario presented.