How to Calculate Cerebral Perfusion Pressure

The cerebral perfusion pressure (CPP) is an essential measure of how well a patient is doing in many situations, such as when undergoing surgery or recovering from a brain injury. A CPP of 70 mm Hg or higher is acceptable for patients recovering from a brain injury; if the CPP gets too low, then the brain is not getting enough oxygen and the patient can suffer hypoxic brain injury.

Things You'll Need

• Manometer or transducer
• Sphygmomanometer
• Pen and paper

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Instructions

• 1

  Measure the patient's blood pressure (BP). Place the sphygmomanometer cuff around the patient's upper arm and place a stethoscope in the crook of the patient's elbow. Pump up the sphygmomanometer until the gauge reads 180 mm HG. Gradually release the pressure on the cuff until you hear "heartbeat" sounds in the stethoscope; when you start to hear the sounds, the reading on the gauge is the systolic BP. Continue to loosen the cuff pressure. When you stop hearing the sounds, the reading on the cuff is the diastolic BP.

• 2

  Multiply the diastolic blood pressure by 2. For example, if the blood pressure is 120/80, then 80 * 2 = 160.

• 3

  Add the systolic blood pressure to the total from step 2. For example, if the blood pressure is 120/80, then 120 + 160 = 280.

• 4

  Divide the total from step 3 by 3. For example, if the blood pressure is 120/80, then 280 ÷ 3 = 93. This is the mean arterial pressure (MAP).

• 5

  Measure the patient's central venous pressure (CVP) using a manometer or a transducer. With local anesthetic, the physician will make a small incision above a vein (typically one of the subclavian, internal jugular or femoral veins) and insert a catheter. She will then thread the catheter in until it reaches the point where the superior and interior vena cava meet, just before entering the right atrium of the heart. After verifying placement with a chest x-ray, the physician will stitch the line in place and cover the incision with a sterile dressing. You will hook this line up to a transducer or manometer to obtain the CVP reading. The units will be millimeters of water (mm H2O).

• 6

  Subtract the CVP from the MAP to get the cerebral perfusion pressure. For example, a patient with a CVP of 7 mm H2O and a blood pressure of 120/80 will have a CPP of 93 -- 7 = 86.