How to Set Up a Direct Pressure Monitoring Transducer with Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia)

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January 2025

In this VETgirl online veterinary continuing education video, Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia) demonstrates how to set up an electronic transducer for direct blood pressure (aka – invasive blood pressure or IBP) monitoring. Included in this category are the central venous pressure which measures pressure in the cranial vena cava and acts as an indirect measurement of right atrial pressure, and the arterial blood pressure which is the more commonly measured systemic blood pressure. Equipment for this setup includes the transducer, non-compliant (rigid) IV tubing, a bag of saline and a pressure sleeve (also commonly called a ‘pressure’ or ‘slam’ bag). In this video, heparinized saline (1 unit/mL) is attached to the transducer and when under pressure from the pressure sleeves provides a continuous fluid drip system to maintain catheter patency and to prevent back flow of blood towards to the transducer; alternatively you can use non-heparinized saline. The transducer is the box that measures the pressure gradient and transmits this information up to the multiparameter monitor.

Follow the steps below to assemble the setup:

Step 1: Gather supplies including sterile 0.9% NaCl bag, +/- heparin, label, electronic pressure transducer kit*, and pressure sleeve.

*If you elect to reuse a transducer and need to create the tubing assembly, ensure use of non-compliant tubing between the transducer and patient catheter. Transducers should be appropriately sterilized between patients. Manufacturer recommendations are to use the transducer in single-use fashion.

Step 2: If desired, add heparin to the sterile 0.9% NaCl fluid bag to a final concentration of 1 unit/mL. Label bag appropriately with additive, date, and time created. Studies have failed to demonstrate improved arterial catheter patency with the use of heparinized saline in transducer setups however, it is this author’s preference to use heparinized saline.(1,2) 

Step 3: Attach the fluid bag line to the electronic pressure transducer.

Step 4: Place the pressure sleeve over the (+/- heparinized) saline fluid bag and inflate to a pressure of 250 mmHg. Most importantly, the pressure on the fluid bag needs to be greater than the patient’s systolic pressure to prevent back flow of blood up the IV line towards the transducer. At 250 mmHg, a pressurized bag will deliver ~3 mL/h of fluid through the transducer.(3)

Step 5: Prime the transducer box and IV lines with the pressurized (+/- heparinized) saline to remove all air from the system.

Step 6: Connect the electronic transducer cable to the respective port on the multiparameter patient monitor. Monitors may identify invasive blood pressure (IBP) as ‘ART’ for arterial, ‘A-line’ for arterial line, or ‘IBP’ in their factory settings.

Step 7: Zero the transducer to atmospheric pressure. Turn the three-way stopcock ‘off’ to the patient (i.e., non-compliant tubing connecting the transducer to the patient’s arterial or central venous catheter). This allows the transducer to be ‘open’ to the atmospheric pressure – commonly referred to as ‘open to room air’. On the patient monitor screen, navigate to the respective window to ‘zero’ the transducer to atmospheric pressure which you will know is complete when the pressure reading on the monitor shows as ‘0 mmHg’.

Step 8: Once zeroed, return the three-way stopcock ‘off’ to room air and ‘open’ to the patient.

Step 9: After the non-compliant tubing is connected to the patient’s arterial catheter or central line, your monitor should begin displaying both a pressure waveform and numeric pressure values. The transducer needs to be placed level with the patient’s heart (the phlebostatic axis). If the transducer is below the patient’s heart, values will be falsely elevated. If the transducer is above the patient’s heart, values will be falsely decreased. The transducer doesn’t need to rest flat on a surface. Some will secure the transducer to a fluid pole enabling them to more easily raise or lower the IV pole to match transducer height to the level of the patient’s heart after the patient has been moved into final position.

References:
1. Whitta RK, Hall KF, Bennetts TM, et al. Comparison of normal or heparinised saline flushing on function of arterial lines. Critical Care and Resuscitation. 2006;8(3):205-8.
2. Robertson‐Malt S, Malt GN, Farquhar V, et al. Heparin versus normal saline for patency of arterial lines. Cochrane Database of Systematic Reviews. 2014(5).
3. Hug MI, Buettiker V, Cornelius A, et al. Variability in infusion pressure and continuous flow rate delivered from pressurized bag pump flush systems. Anaesthesia and Intensive Care. 2002;30(3):341-7.

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