What is the map needed to perfuse kidneys?

From the Guidelines

The mean arterial pressure (MAP) needed to perfuse the kidneys is typically around 60-65 mmHg, as evidenced by a recent study published in 2024 1. This is the minimum pressure required to maintain adequate blood flow to the kidneys and ensure proper filtration and urine production. When MAP falls below this threshold, autoregulation mechanisms begin to fail, and kidney function becomes compromised. The kidneys require this specific pressure because they filter blood through a complex system of glomeruli, which depend on adequate hydrostatic pressure to force fluid across the filtration membrane. If MAP drops too low, glomerular filtration rate decreases, potentially leading to acute kidney injury.

Key Considerations

• In critically ill patients, maintaining MAP above 65 mmHg is often a treatment goal, achieved through fluid resuscitation or vasopressor medications like norepinephrine, phenylephrine, or vasopressin if needed, as suggested by the Surviving Sepsis Campaign Guidelines 1.
• Individual patient factors such as chronic hypertension may necessitate higher MAP targets, as chronically hypertensive patients often have shifted autoregulation curves requiring higher perfusion pressures to maintain kidney function.
• The optimal approach is to use an individualized MAP target based on frequent assessment of end-organ perfusion, including mental status, capillary refill, urine output, extremity perfusion, lactate, central venous oxygen saturation, and end-organ function, as recommended by a study published in 2024 1.

Additional Factors

• A retrospective observational study of 273 critically ill patients with cirrhosis reported that ICU mortality increased below a threshold of 65 mm Hg and suggested maintaining an MAP of > 65 mm Hg as an early goal in critically ill patients with cirrhosis 1.
• A large RCT of general critical care patients with vasodilatory shock demonstrated that reducing vasopressors with permissive hypotension (MAP target 60–65 mm Hg) was associated with no difference in 90-day mortality, highlighting the importance of individualized care 1.

From the FDA Drug Label

When appropriate, increase blood volume with whole blood or plasma until central venous pressure is 10 to 15 cm H2O or pulmonary wedge pressure is 14 to 18 mm Hg. Begin infusion of dopamine hydrochloride solution at doses of 2 to 5 mcg/kg/min in adult or pediatric patients who are likely to respond to modest increments of heart force and renal perfusion In more seriously ill patients, begin infusion of dopamine hydrochloride at doses of 5 mcg/kg/min and increase gradually, using 5 to 10 mcg/kg/min increments, up to a rate of 20 to 50 mcg/kg/min as needed.

The map needed to per fuse kidneys is not explicitly stated, but the recommended dosage of dopamine to improve renal perfusion is:

• 2 to 5 mcg/kg/min for adult or pediatric patients
• 5 mcg/kg/min with gradual increases up to 20 to 50 mcg/kg/min for more seriously ill patients 2 It is also important to increase blood volume with whole blood or plasma until central venous pressure is 10 to 15 cm H2O or pulmonary wedge pressure is 14 to 18 mm Hg before starting dopamine infusion 2.

From the Research

Optimal Mean Arterial Pressure (MAP) for Renal Perfusion

• The optimal mean arterial pressure (MAP) needed for preservation of renal function is most likely a MAP of 60-80 mmHg 3.
• Attention should be paid to renal outflow pressure, typically central venous pressure, in addition to MAP 3.

Importance of Blood Pressure Regulation

• Maintaining a high MAP during cardiopulmonary bypass may have a significant impact in protecting the brain and abdominal organs, particularly in the subset of patients at high risk for embolization and end-organ dysfunction 4.
• Higher perfusion pressure during cardiopulmonary bypass affects regional blood flow to the kidneys and visceral organs 4.

Role of Dopamine in Renal Function

• There is no direct evidence in the provided studies to suggest a specific role of dopamine in maintaining optimal MAP for renal perfusion.
• Dopamine is a neurotransmitter involved in various physiological processes, including motor control, motivation, and cognitive function, but its role in renal function is not explicitly discussed in the provided studies 5, 6.

Fluid Management and Renal Function

• Correction of intravascular hypovolemia is a key component of the prevention and management of acute kidney injury (AKI), but excessive fluid administration is associated with poor outcomes 7.
• Fluid administration should be individualized and take into account patient characteristics, nature of the acute illness, and risks and benefits of fluids 7.