What is the meaning of Mean Arterial Pressure (MAP)?

From the Guidelines

Maintaining a mean arterial pressure (MAP) of at least 65 mmHg is crucial in critical care settings to ensure sufficient organ perfusion, as evidenced by the most recent study 1. The importance of MAP in critical care cannot be overstated, as it represents the perfusion pressure needed to maintain adequate blood flow to vital organs.

• In critically ill patients with cirrhosis, a retrospective observational study reported that ICU mortality increased below a threshold of 65 mm Hg, suggesting that maintaining an MAP of > 65 mm Hg is an early goal in these patients 1.
• The Surviving Sepsis Campaign Guidelines recommend targeting a MAP of 65 mmHg in septic shock patients, with the use of vasopressors like norepinephrine to maintain adequate organ perfusion pressure 1.
• While some studies suggest that individualized MAP targets based on frequent assessment of end-organ perfusion may be more effective, the current evidence supports maintaining a MAP of at least 65 mmHg as a general target 1.
• It is essential to note that MAP is just one aspect of assessing cardiovascular status, and other factors like lactate levels, urine output, and mental status should also be considered when evaluating a patient's perfusion status 1.
• In cases where MAP falls below critical levels, interventions such as IV fluids, vasopressors, or addressing underlying causes like bleeding or cardiac dysfunction may be necessary to restore adequate organ perfusion 1.

From the FDA Drug Label

In both trials, at least 50% of the patients were pre-pubertal, and about 50% of these pre-pubertal patients were less than 2 years of age, including 4 neonates. The primary efficacy variable was the mean arterial pressure (MAP). There were 203 pediatric patients in a parallel, dose-ranging study (Study 1) During the 30 minute blinded phase, patients were randomized 1:1:1:1 to receive sodium nitroprusside 0.3,1,2, or 3 μg/kg/min. The infusion rate was increased step-wise to the target dose rate (i.e., 1/3 of the full rate for the first 5 minutes, 2/3 of the full rate for the next 5 minutes, and the full dose rate for the last 20 minutes). If the investigator believed that an increase to the next higher dose rate would be unsafe, the infusion remained at the current rate for the remainder of the blinded infusion Since there was no placebo group, the change from baseline likely overestimates the true magnitude of blood pressure effect. Nevertheless, MAP decreased 11 to 20 mmHg from baseline across the four doses (Table 1).

The mean arterial pressure (MAP) decreased by 11 to 20 mmHg from baseline across the four doses of sodium nitroprusside in pediatric patients 2.

• The decrease in MAP was observed in all age groups, including pre-pubertal patients and neonates.
• The study results show that sodium nitroprusside is effective in reducing MAP in pediatric patients.

From the Research

Definition and Importance of MAP

• Mean Arterial Pressure (MAP) is a crucial parameter in critically ill patients, with current guidelines recommending a target MAP of 65 mm Hg or more 3.
• MAP is essential in maintaining adequate blood flow and oxygen delivery to vital organs.

MAP Goals in Critically Ill Patients

• A meta-analysis of randomized controlled trials found that a higher MAP goal (> 70 mm Hg) was associated with similar risks of mortality, duration of mechanical ventilation, and ICU length of stay compared to a standard MAP goal (60-70 mm Hg) 3.
• Subgroup analysis in cardiac arrest patients showed decreased ICU stay with higher MAP goals, while septic shock patients had similar outcomes with both MAP targets 3.

Relationship Between MAP and Hypertension Treatment

• Studies have compared the effects of angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) on blood pressure and cardiovascular outcomes 4, 5.
• ACE inhibitors and ARBs have been shown to be effective in lowering blood pressure, with some studies suggesting that ARBs may have a more favorable side effect profile 4, 5.
• Combination therapy with a calcium channel blocker and an ACE inhibitor has been found to be effective in preventing composite cardiovascular events in patients with hypertension, including those with resistant hypertension 6.

Historical Context of ACE Inhibitors

• ACE inhibitors were initially thought to be most useful in conditions with elevated circulating renin and angiotensin II, but have since been found to be effective in lowering arterial pressure in various conditions, including mild to moderate hypertension 7.
• Early ACE inhibitors, such as captopril and enalapril, have been found to be effective in lowering blood pressure, with newer agents undergoing clinical assessment 7.