How high is too high?

Let's talk catecholamines. Epinephrine, dopamine, and norepinephrine are catecholamines that are made in the adrenal gland and regulate heart rate and blood pressure in the body. These chemicals are regulated in the body by the autonomic nervous system. Norepinephrine is the primary neurotransmitter of the sympathetic nervous system, also known as the "flight or fight" system. As medical professionals we all know the role of epinephrine and dopamine in the body, and have often given these as drugs to assist in a patient's hemodynamic stability. But most people are less familiar with norepinephrine. In critical care we may know it better as the drug Levophed. It causes systemic vasoconstriction and increases HR and BP. In patients with the hyperadrenergic form of postural orthostatic tachycardia syndrome (POTS), all catecholamines may be elevated, but more so the norepinephrine. It is the very high levels of norepi that are caused by inappropriate sympathetic response to any and all stimuli. This means that whereas the normal person may have a slight rise in HR when they are standing, or when they are cold, or hungry, the person with H-POTS gets a wildy inappropiate spike in HR, and often, BP. So how high is high? Well, the normal person has a norepi less than 400, even when stressed. The diagnostic criteria for H-POTS is a norepi of greater than 600 when upright. The last time mine was tested it was 984. It can go even higher for some patients, but when it gets over 2000 it is time to consider an adrenal tumor such as a pheocromocytoma. So there is the answer...