What is our MAP target?
It has been a while since my last post and surprisingly my first one while on the west coast. I landed in San Diego on June 26, 2021 and today is July 5, 2021 — it’s about time I wrote about something.
This is also a very practical question in the critical care world that we all pose: What is our MAP goal?
Before we attempt to answer this question (as there is no good answer), there are a few concepts and guidelines we should review.
MAP = (CO x SVR) + CVP
Also that perfusion pressure (such as CPP and renal perfusion pressure) is dictated by MAP - CVP. Makes sense: total arterial pressure minus the pressure that the heart receives back — this is what perfuses the organs.
The conventional MAP target is usually >65 mmHg. In the 2012 and 2016 Surviving Sepsis Campaign guideline, they offer a strong recommendation/moderate quality of evidence for attaining a initial target MAP ≥65 mmHg. They utilize the SEPSISPAM funded “High versus Low-Blood Pressure Target in Patients with Septic Shock” (Asfar, et al) published in the NEJM in April 2014. This study was a multi-center, open-label randomized trial of 776 patients that questioned 28-day mortality after using MAP goals 65–70 mmHg and 80–85 mmHg. They concluded that 28-day (34% with low MAP and 36.6% with high MAP) and 90-day (42.3% and 43.8%) mortality did not significantly differ in the two groups. I’m glad they did this trial but I never usually attempt to target MAP goals around 80 mmHg. That is so high (maybe use that in the neuro unit or a post-arrest patient). But it’s also nice to know their secondary outcomes. Renal function didn’t seem to change much after looking at urine output, net fluid balance, and doubled plasma Cr. By day-3 it seems that the NE use in the low MAP group decreased significantly — on day-3 NE was 0.02 vs 0.14 (weight based ug/kg/min). What is interesting to note is that rates of AF were higher in the high MAP target (2.8% vs 6.7%). This is nice to note because of my cardiac patient population. Digital ischemia and mesenteric ischemia did not differ between the two groups as well. Enough about this trial though. What I really want to know is if there is a difference between using a MAP of 60 vs 65 mmHg in mortality and morbidity.
I also need to remind you guys and myself that most of these trials are in septic shock patients. But since septic shock is a state of vasodilation I think I can apply this to those patients of mine with mixed cards and vasodilatory shock as well.
The “Effect of Reduced Exposure to Vasopressors on 90-Day Mortality in Older Critically Ill Patients With Vasodilatory Hypotension” by Lamontagne, et al. was published in JAMA in February 12, 2020. This trial is also commonly referred to as “The 65 Trial.” The premise was that in the other trials they noticed that the subgroup of patients older than 65 years old had higher mortality rates at higher MAP target groups. They attributed it to higher vasopressor infusion rates. This trial tested the mortality in patients with lower vasopressor infusion rates by utilizing a lower MAP target of 60 mmHg (permissive hypotension) compared to conventional MAPs of 65 mmHg in patients older than 65 years with vasodilatory hypotension. 2600 patients were randomized. There was no significant difference in 90-day mortality between the two groups (41% vs 43.8%).
There is a RCT called OVATION trial: “The Optimal VAsopressor titraTION” RCT by published in American Journal of Respiratory and Critical Care Medicine in 2015 by Lamontagne, et al. Don’t want to get too into it but it hypothesized that patients with chronic HTN will need higher MAP goals. It was a small trial but concluded that there were no mortality differences between target MAP 60–65 and 75–80 mmHg. They made three subgroup analyses with chronic HTN, congestive heart failure, and those older than 75 years old. They summarize that chronic HTN and CHF were not modifiers to mortality but those with higher MAP goal (75–80) had more cardiac arrhythmias and longer ICU LOS. Important for me.
There is a lot of practical takeaways to this. For me, it would change my clinical practice of now utilizing an evidence-based target of MAPs 60 rather than 65. It seems safe to do so unless other physiologic parameters are not met or there are signs of hypoperfusion. Of course, we need to keep in mind the equation of systemic perfusion pressure = MAP minus CVP. Patients typically with a higher CVP will need a higher MAP goal in order to achieve proper systemic perfusion. This is important for our patient population with heart failure and cardiogenic shock. So if a typical CVP is 0 in “normal” patients, SPP is 60. So maybe utilizing a MAP of 70 for patients with CVP 10 makes more sense.
Cheers.
Dk
