Blood Pressure Artifact Simulator

• Click the ‘Sign In’ tab above to login with your UF credentials OR to create a free account.
• Read the "Simulation and Context" information below.
• Click the ‘Launch Content’ button below to open the simulation.
• Access the scenario instructions by clicking the arrow in the "Scenarios" section below.
• When you are finished with the course content, click the button to take the Post-Test.

Why Blood Pressure Measurement Matters: The Clinical Role of Accurate Blood Pressure Data in the OR or ICU

Blood pressure is the single most frequently obtained vital sign in every healthcare setting. It informs core clinical decision making across settings. Outpatient clinics, intraoperative management, titration of vasoactive drips in the ICU, and adjustment of blood pressure regimens all depend on real-time, trustworthy numbers. When the measurement is artificially high or low, therapy can be off target.

The Physics That Underlie the Impact of Where Blood Pressure is Measured: Hydrostatic Blood Pressure Artifacts

When blood pressure is sampled above the level of the heart, the measured pressure is less than the actual pressure at the heart level by the effect of the vertical height difference. Conversely, placing the BP sampling location below the heart adds to the blood pressure proportional to that height difference. This may seem complicated as per the hydrostatic pressure equation:

These scenarios each present a problem, ask you to identify the artifact, and then work through the correction process.

NOTE: The online simulator can be used alongside each case to visualize the effect of tilting the bed, moving the invasive BP (IBP) transducer or reading the values at different cuff locations, and adjusting the “Blood Pressure at Heart” slider. Practicing with the simulator consolidates the mental arithmetic required for bedside correction.

Scenario 1: the icu patient

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Patient Profile: 55-year-old patient

Setup:

• Default settings on the simulator with the patient supine 

• Blood pressure reads MAP of 93 mm Hg with the patient supine and the transducer next to the patient’s head

• The patient is then tilted Trendelenburg 10°

Observed reading at Trendelenburg 10°:  MAP = 99 mm Hg

Question 1 – Estimate the Elevation Difference

Estimate the difference in elevation in inches between the brain and the phlebostatic axis for a 5’ 6” person in 10° Trendelenburg.

Question 2 – Estimate the size of the BP artifact based on your estimate of the difference in elevation. 

Is the displayed MAP an over or under estimate of the MAP at the heart level?

Solution:

Click and drag the white dot to the head and read the elevation difference in inches between the red line (phlebostatic axis) and the white line. How does that number compare to your estimate? 

Read the MAP measured by the transducer at the head. How does that number compare to your estimate?

Is the displayed brain blood pressure an overestimate or an underestimate of the heart level MAP?

Answer:

• The Trendelenburg tilt lowers the brain relative to the heart. The measured pressure there will read higher because the blood pressure transducer is below the heart when the transducer is at the level of the head and the patient is in a head-lowered position. Thus, it reads 99 instead of 93.

• Adjust the tilt to different angles, including reverse Trendelenburg and observe the effect of the elevation difference and the size of the BP artifact

  











 

   

Scenario 2: the emergency department (ED) patient with a limb injury

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Patient Profile: 31-year-old patient
Setup:
• Restart the simulator

• The only accessible blood pressure cuff site is at the left ankle.

• The cuff is placed at the ankle. The patient lies supine with a reverse Trendelenburg of 7o; the ankle is about 5.5” below the heart.
Non-Invasive (cuff at ankle) BP displayed: 131/91 mm Hg (MAP 104)
Task: Recognize the Artifact and Adjust
• 5.5in ? 5.5 in × 2 mm Hg ˜ 11 mm Hg

• Because the cuff is below heart level, the reading overestimated the blood pressure at the heart level
Learning point: When the upper arm is unavailable, alternative sites (ankle, forearm, wrist) can be used. A calculable hydrostatic correction is then taken into consideration to avoid misclassifying hemodynamic status

Scenario 3: invasive bp

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Patient Profile: 65-year-old with a femoral arterial catheter

Setup:

• Restart the simulator

• Patient is supine. No Trendelenburg

• The transducer is at the groin and zeroed there. Move the white disc representing the invasive BP sampling location to the general area of the groin while ensuring that the center of the white disc is on the red line representing the extension of the phlebostatic axis (IBP MAP should read 93 mm Hg)

Invasive BP displayed when zeroed to the phlebostatic axis is the same as the BP would be measured at the heart level: 120/80 mm Hg (MAP 93)

• Place the patient into a 15o Trendelenburg position

Invasive BP displayed 15o Trendelenburg: 109/69 mm Hg (MAP 82)

Learning point:
Changing the elevation of an invasive blood pressure transducer relative to the phlebostatic axis after it has been zeroed to the phlebostatic axis reintroduces the hydrostatic blood pressure artifact. Zero the invasive blood pressure transducer to the phlebostatic axis after the patient's position has been established and re-zero after each change in the location of the invasive blood pressure transducer relative to the heart

• Always aim to place the cuff (or transducer) at the level of the heart. If not feasible, estimate the vertical offset and apply the 1-inch ≈ 2 mm Hg rule.
• Rezero invasive lines at the phlebostatic axis (midsternum, fourth intercostal space).
• Document the patient’s posture and bed tilt when a measurement is taken; this information becomes valuable when reviewing trends.
• Use the online simulator (available in the training portal) to develop a mental model of how tilting the bed, the blood pressure cuff location, moving the invasive blood pressure transducer location, and the patient height all can affect the measured pressure in comparison to the actual heart blood pressure.
• Teach the correction process to the entire care team—nurses, residents, and allied health professionals—so that consistency is built into daily workflow.