Physician Assistant Exam: Low Blood Pressure
The Physician Assistant exams will ask about low blood pressure, along with questions about high blood pressure. Hypotension has many causes, including infection, volume depletion, adrenal insufficiency, anemia, blood pressure medications, and so forth. Because of the depth of this topic, your focus for test purposes should be on the main causes of low blood pressure.
Cardiogenic shock occurs when the systolic function of the heart goes kaput. Often, this occurs as a consequence of a myocardial infarction (MI), especially an ST elevation myocardial infarction (STEMI) affecting the anterior wall. The person in cardiogenic shock usually has some history of underlying coronary artery disease (CAD).
On examination, the person is hypotensive, with significant jugular venous distention (JVD). Rales are present, as is a significant hypoxemia. Edema may be present as well. The person may be intubated because the hypoxemia is so bad as a result of the increased work of breathing.
Here are some key points concerning cardiogenic shock:
Because there are different types of shock, part of the identification depends on using invasive monitoring. In cardiogenic shock, you expect the following hemodynamic pattern: elevated systemic vascular resistance, low cardiac output, elevated pulmonary capillary wedge pressure, elevated central venous pressure, and elevated pulmonary artery diastolic pressure. Simply put, everything is elevated except the cardiac output, which is low because the systolic function of the heart sucks big time.
The mainstay of treatment involves using ionotropes and/or diuretics if the blood pressure allows. Examples of ionotropes are dopamine, dobutamine (Dobutrex), and milrinone (Primacor). Furosemide (Lasix) in high doses is also used.
When the systolic function is really bad, an intra-aortic balloon pump (IABP) can be inserted. Sometimes, especially in the setting of a really bad myocardial infarction, emergent cardiac surgery may be required.
Orthostatic hypotension means that the blood pressure is okay when the patient is in one position, but if he or she stands or sits up, the blood pressure drops. Orthostatic hypotension is established by one of the following criteria:
Systolic change: The person has a drop of 20 mmHg in his or her systolic blood pressure when switching from one position to another, usually when assuming a standing position.
Diastolic change: The person has a drop of 10 mmHg in his or her diastolic blood pressure when switching from one position to another, again usually when assuming a standing position.
Causes of orthostatic hypotension include blood pressure medications, volume depletion, adrenal insufficiency, aortic stenosis, cardiomyopathy, and anemia, among others. Other causes include amyloidosis and autonomic neuropathy that can be associated with variations of Parkinson’s syndrome (also known as multiple-system atrophy). The most common cause of autonomic neuropathy is diabetes mellitus.
Here’s a big testing-taking tip: The difference between orthostatic hypotension due to volume depletion and anemia versus autonomic neuropathy has to do with the pulse. In autonomic neuropathy, the heart rate doesn’t increase when the patient stands up. You’d expect an increase in the heart rate (not necessarily a tachycardia) when the blood pressure drops.
The treatment for orthostatic hypotension depends on what’s causing it — a blood pressure medication, anemia, volume depletion, and so forth. When the hypotension is due to autonomic neuropathy, be aware of a couple of meds used for treatment:
Midodrine (ProAmatine) is an alpha agonist that raises blood pressure. It’s short-acting and can be given 2 to 3 times a day. A major side effect is supine hypertension.
Fludrocortisone (Florinef) is a synthetic aldosterone that raises blood pressure. Side effects can be hypertension, edema, volume overload, and hypokalemia. Fludrocortisone can also be used in the treatment of primary adrenal insufficiency, because it’s a replacement for missing aldosterone.