How is Mean Arterial Pressure (MAP) measured in the Intensive Care Unit (ICU)?

From the Guidelines

Mean Arterial Pressure (MAP) in the ICU is typically measured using an arterial line (arterial catheter), which provides continuous, real-time blood pressure monitoring. The arterial line is inserted into a peripheral artery, most commonly the radial artery, though the femoral or brachial arteries may also be used 1. The catheter is connected to a pressure transducer system that converts the pressure waves into an electrical signal displayed on a bedside monitor. MAP is calculated by the monitoring system using the formula: MAP = (1/3 × Systolic BP) + (2/3 × Diastolic BP), or alternatively as MAP = Diastolic BP + (1/3 × Pulse Pressure). Some key points to consider when measuring MAP in the ICU include:

• The importance of accurate and reliable blood pressure monitoring in critically ill patients
• The use of invasive arterial monitoring as soon as practical, as suggested by the Surviving Sepsis Campaign Guidelines 1
• The need for frequent assessment of end-organ perfusion, including mental status, capillary refill, urine output, extremity perfusion, lactate, central venous oxygen saturation, and end-organ function 1 For accurate measurements, the transducer should be zeroed and positioned at the level of the patient's right atrium (phlebostatic axis). Non-invasive methods using automated blood pressure cuffs can also estimate MAP but are less accurate in critically ill patients with hemodynamic instability. Arterial line monitoring is preferred in the ICU because it provides beat-to-beat pressure measurements, allows for blood sampling without repeated needle sticks, and is more reliable in patients with shock, on vasopressors, or requiring frequent blood gas analysis.

From the Research

Measurement of Mean Arterial Pressure (MAP) in the ICU

• MAP can be measured invasively using an arterial catheter, which provides a continuous blood pressure waveform and derived values such as MAP, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) 2.
• Non-invasive methods for measuring MAP in the ICU include radial artery applanation tonometry and the T-Line TL-200 system, which provide a real-time blood pressure waveform and beat-to-beat values of SAP, MAP, and DAP 3, 4, 5.
• The T-Line TL-200 system has been shown to have a low bias for MAP compared to invasive measurements using a femoral arterial catheter, with a mean difference of +0.47 mmHg and 95% limits of agreement of -16.53 to +17.46 mmHg 3.
• Radial artery applanation tonometry has also been shown to provide clinically acceptable agreement with invasive AP determination, with a bias of +2 mmHg and 95% limits of agreement of -11 to +15 mmHg for MAP 4.
• Non-invasive continuous arterial pressure measurement based on radial artery tonometry using the T-Line TL-200pro device has been shown to be feasible in medical ICU patients, with a bias of +0.72 mmHg and 95% limits of agreement of -9.37 to +10.82 mmHg for MAP 5.

Comparison of Invasive and Non-Invasive Methods

• Invasive arterial blood pressure monitoring using an arterial catheter is considered the gold standard for measuring MAP in the ICU, but it is associated with major complications such as infection, bleeding, and thrombosis 2.
• Non-invasive methods for measuring MAP, such as radial artery applanation tonometry and the T-Line TL-200 system, offer a safer alternative to invasive monitoring, but may have lower accuracy and precision compared to invasive measurements 3, 4, 5.
• The choice of method for measuring MAP in the ICU depends on the individual patient's needs and the availability of resources, with invasive monitoring typically reserved for high-risk patients or those requiring close hemodynamic monitoring 2, 6.