What have we learned about MAP goals in sepsis?
On April 24, 2014, the New England Journal of Medicine (@NEJM) published an article about MAP (mean arterial pressure) goals in sepsis. Does this paper matter?
*MAP = (cardiac output x systemic vascular resistance) + central venous pressure
(What does that mean? MAP is basically the blood that’s being sent out to the body by the heart.) We simplify the calculation for MAP this way:
*MAP = diastolic blood pressure + 1/3 (systolic blood pressure – diastolic blood pressure)
For a blood pressure of 120/80, the systolic is 120 (the top number) and the diastolic is 80 (the bottom number).
In brief, sepsis means your patient is infected and it’s pretty bad. Sepsis is a spectrum that starts with SIRS (systemic inflammatory response syndrome): fever or hypothermia (low temperature), tachycardia (fast heart beat), tachypnea (fast breathing), and an elevated white blood cell count (a blood marker for infection). SIRS becomes sepsis when there is a source of the infection that’s causing all this badness. Septic shock is when there’s also low blood pressure (hypotension) that accompanies this picture. The last exit before death on this spectrum is multiple organ dysfunction syndrome (MODS), which means that this infection is causing at least 2 organ systems to fail (think: kidneys, liver, heart, brain!). Why does everyone care so much about sepsis? Because patients still die from sepsis despite us blabbing about it all the time. I mean, like 30-50% of patients are dead a month after coming into the hospital depending on which study you read.
In this @NEJM article entitled, “High versus low blood-pressure target in patients with septic shock” the investigators (in France) tested whether aiming for a higher MAP than the standard MAP we strive for in sepsis management improved patients’ outcomes. They tested out a MAP goal of 65-70 (the low group) versus 85-90 (the high group).
What they found was that a) doctors didn’t adhere to the prescribed MAP goals for their group (they aimed for a higher MAP) and b) there was no “significant” difference in death at 28 days, 90 days, length of stay in the hospital, or whether patients needed mechanical ventilation. (“Significant” is statistics jargon but it’s how all medical papers value whether something is real or not.) Lots of people died in both groups, by the way. 36.6% of patients in the high group and 34% of patients in the low group were dead by 28 days. The interesting thing they did find was that people who have chronically elevated blood pressure seemed to do a bit better in the high MAP group. And when I say better, I don’t mean fewer died. I mean that fewer of the ones in the high MAP group needed a machine to work for their kidneys (renal replacement therapy) and fewer had worsening of their kidney function. But this makes sense. When your body is used to a higher pressure of blood (which isn’t good in the long term for you) getting to all of your organs (a.k.a. high blood pressure), it might not like it when you all of a sudden decrease it by a lot.
So, not too much learned from this article. But we doctors believe that even a study that shows no difference between therapies is worth knowing about. Actually, that’s how most of our studies go.
If the MAP and blood pressure stuff went a bit over your head, here’s a good website that I still go back to when I get confused (the site is based on a book “Cardiovascular Physiology Concepts” by Dr. Richard E. Klabunde that I read in med school): Mean Arterial Pressure