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Transducer System Setup and Zeroing

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Jan.25.2024

Transducer System Setup and Zeroing - CE/NCPD

ALERT

The transducer system must be leveled and zeroed to provide accurate hemodynamic values.

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OVERVIEW

Transducer systems provide a catheter-to-monitor interface so intravascular and intracardiac pressure can be measured. The transducer detects a biophysical event and converts it to an electronic signal.

Fluid-filled pressure monitoring systems used for bedside hemodynamic pressure monitoring are based on the principle that a change in pressure at any point in an unobstructed system results in similar pressure changes at all other points in the system.

Intravascular and intracardiac pressure transducers detect the pressure generated in various areas of the cardiovascular system and convert that pressure wave into an electrical signal, which is transmitted to the monitoring equipment for representation as a waveform on the oscilloscope. Invasive measurement of intravascular pressure requires insertion of a catheter into a central vein or an artery. Invasive measurement of intracardiac (right atrial [RA] and pulmonary artery [PA]) pressure requires insertion of a catheter into the PA.

A single-pressure transducer system is used to measure pressure from a single catheter (e.g., arterial or central venous) (Figure 1). A double-pressure transducer system is used to measure pressure from two catheters (e.g., arterial and central venous) or two ports (e.g., PA and RA) from a single catheter (e.g., PA catheter) (Figure 2). A triple-pressure transducer system is commonly used to measure pressure from the arterial and PA catheters (Figure 3). With this system, arterial pressure, PA pressure, and RA pressure can be obtained. All hemodynamic values (PA, RA, and arterial) are referenced to the level of the atria. The external reference point of the atria is the phlebostatic axis.

Labeling the tubing reduces the chance of misconnection, especially in circumstances where multiple IV lines or devices are in use.³

SUPPLIES

See Supplies tab at the top of the page.

EDUCATION

Provide developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, and overall neurologic and psychosocial state.
Provide the patient and family with an explanation of the equipment and the procedure.
Encourage questions and answer them as they arise.

ASSESSMENT AND PREPARATION

Assessment

Perform hand hygiene before patient contact. Don appropriate personal protective equipment (PPE) based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
Introduce yourself to the patient.
Verify the correct patient using two identifiers.
Assess the patient for conditions that may warrant the use of a hemodynamic monitoring system, including hypotension, hypertension, cardiac failure, shock, hemorrhage, respiratory failure, fluid imbalances, and sepsis.

Preparation

Place the patient in the supine position with the head of the bed flat or elevated up to 60 degrees.¹

PROCEDURE

Perform hand hygiene. Don appropriate PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
Verify the correct patient using two identifiers.
Explain the procedure and ensure that the patient agrees to treatment.

Disposable Pressure Transducer System Setup

Follow the organization’s practice regarding the use of a 0.9% sodium chloride solution or a heparinized 0.9% sodium chloride solution in the flush solution for the pressure monitoring system. Consider using an arterial blood conservation system with the arterial pressure line.
Rationale: The decision to use heparin should be based on the clinical risk of occlusion and patient factors, such as heparin sensitivities.²

Although heparin may prevent thrombosis, it has been associated with thrombocytopenia and other hematologic complications. A heparinized 0.9% sodium chloride solution for the flush bag comes as a premixed solution. Ensure that the solution contains the correct strength of heparin before hanging it.
Label the flush bag with the date and time the solution was hung and the nurse’s initials.
Rationale: The label indicates when the flush bag needs to be changed.
Open the prepackaged pressure transducer kits, using aseptic technique.
1. A single-pressure tubing kit can be used for RA or arterial monitoring (Figure 1).
2. A double-pressure tubing kit can be used for PA and RA monitoring (Figure 2).
3. A triple-pressure tubing kit can be used for arterial, PA, and RA monitoring (Figure 3).
Assemble the pressure transducers, pressure tubing, and stopcocks, if not preassembled by the manufacturer. Use the minimum number of stopcocks and the shortest tubing length possible to avoid overdamped and underdamped waveforms.
Tighten all connections.
Remove the air from the flush bag.
1. Invert the flush bag.
2. Spike the outlet port of the flush bag with the pressure tubing, keeping the drip chamber upright.
3. Keeping the flush bag inverted, use one hand to squeeze the air out of the flush bag while activating the fast-flush device with the other hand, until all air is evacuated from the flush bag and the drip chamber is filled to the desired level, usually halfway.⁵
  Rationale: Evacuating air from the flush bag prevents air from being flushed to the patient if the bag runs out of 0.9% sodium chloride solution. Filling the drip chamber halfway prevents air bubbles from entering the tubing and allows the nurse to see that the solution is flowing during a manual flush of the invasive line.
Insert the flush bag into the pressure bag or device and hang it on the IV pole. Do not inflate the pressure bag.
Rationale: Priming the tubing under pressure increases turbulence and may cause air bubbles to enter the tubing.

Never allow air in a hemodynamic system. Air microemboli or macroemboli can migrate to major organs and present a potentially life-threatening complication.
Flush the entire system, including the transducer, stopcock, and pressure tubing, with the flush solution.
Rationale: Flushing eliminates air from the system.
1. Using the flush device, flush the solution from the flush bag through to the tip of the pressure tubing.
2. Turn the stopcock off to the patient’s end of the tubing (Figure 4).
3. Using the fast-flush device, flush the solution from the flush bag through the stopcock.
4. Replace the vented cap on the stopcock with a nonvented cap.
  Rationale: The manufacturer places vented caps to permit sterilization of the entire system. Replacing the vented cap with a nonvented cap prevents bacteria and air from entering the system.
5. Open the stopcock to the transducer (Figure 5).
If using a double-pressure or triple-pressure tubing kit, repeat the system flush and replace the vented cap in each of the pressure transducer systems.
Inflate the pressure bag or device to 300 mm Hg.⁵
Rationale: Inflating the pressure bag to 300 mm Hg allows 3 ml/hr of flush solution to be delivered through the catheter, thus maintaining catheter patency and minimizing clot formation.⁵
If using a pole mount, insert the transducers into the pole mount holder (Figure 6).
Trace tubing or catheter from the patient to the point of origin.⁴
Connect the end of each transducer tube to the appropriate catheter port (e.g., PA, RA, arterial), maintaining the sterility of the end of the tube and the catheter port.
Label the pressure tubing, indicating the date of initiation or the date of change.³
When there are multiple access sites or multiple solutions connected to a central vascular access device (CVAD), label the tubing with the route and medication or solutions at the connection sites closest to the patient and at the container.³

Monitor Setup

Turn on the bedside monitor.
Plug the pressure cables into the appropriate pressure modules or jacks in the bedside monitor (Figure 3). Some monitors are preprogrammed to display the waveform that corresponds to the module or jack (e.g., first position, arterial; second position, PA; third position, RA).
Select the appropriate waveform label (e.g., PA, RA, arterial) in the hemodynamic monitoring system.
Following the manufacturer’s instructions, set the appropriate scales for viewing of the complete waveform and accurate readings.
Rationale: Waveforms vary in amplitude depending on the pressure in the system and the pressure wave being monitored. Scales may vary based on monitoring equipment and may be adjusted based on the patient’s pressure levels.
Check individual alarm signals for accurate settings, proper operation, and detectability.

Leveling the Transducer

Position the patient supine with the head of bed between 0 and 60 degrees.¹ If the patient cannot tolerate the supine position, use the lateral position with the head of the bed at 20, 30, or 90 degrees (Figure 7). The patient may also be positioned prone.¹
Locate the phlebostatic axis for the supine position (Figure 8).
1. Draw an imaginary line along the fourth intercostal space (ICS) laterally along the chest wall.
2. Draw a second imaginary line from the axilla downward, midway between the anterior and posterior chest walls. The point where these two lines cross is the level of the phlebostatic axis (Figure 8).
3. Mark the point of the phlebostatic axis with an indelible marker.
Level the air-fluid interface of the transducer to the phlebostatic axis.¹
Verify the correct angle reference using a laser light or carpenter’s level.
1. Pole mount: low-intensity laser
  1. Place the low-intensity laser leveling device next to the air-fluid interface of the transducer (zeroing stopcock).
  2. Point the laser light at the phlebostatic axis.
  3. Move the pole mount holder up or down until the interface is level with the phlebostatic axis (Figure 9).
2. Pole mount: carpenter’s level
  1. Place one end of the carpenter’s level next to the air-fluid interface (zeroing stopcocks).
  2. Place the other end of the carpenter’s level at the phlebostatic axis.
  3. Move the pole mount holder up or down until the interface is level with the phlebostatic axis (Figure 9).
3. Patient mount
  1. Place the air-fluid interface (zeroing stopcock) at the phlebostatic axis (Figure 9).
  2. Place a 4 × 4-inch gauze or hydrocolloid gel pad between the transducer(s) and the patient’s skin.
  3. Secure the transducer(s) in place with tape.
Wait for the patient’s hemodynamic status to stabilize for 5 to 15 minutes after repositioning the patient to obtain readings from the monitor.¹

Zeroing the Transducer

Turn the stopcock off to the patient’s end of the tubing (Figure 4).
Remove the nonvented cap from the stopcock, opening the stopcock to air.
Rationale: Removing the cap allows the monitor to use atmospheric pressure as a reference for zero.
Push and release the zeroing button on the bedside monitor. Observe the digital reading until it displays a value of zero. Some monitors require that the zero knob be turned and adjusted manually. Some systems also may require calibration. Refer to the manufacturer’s guidelines for specific information.
Rationale: Zeroing negates the effects of atmospheric pressure.
Place a new, sterile, nonvented cap on the stopcock.
Turn the stopcock so it is open to the transducer (Figure 5).
Rationale: Turning the stopcock permits pressure monitoring and maintains catheter patency.
Ensure that the hemodynamic pressure monitoring alarms are active.

Fast-flush Square Wave Test

Briefly activate the fast-flush device.
Rationale: The fast-flush square wave test helps determine whether the transducer system is accurately reproducing the hemodynamic pressure and waveforms.
Observe for changes in the waveform on the monitor oscilloscope. When the fast-flush device is activated, a rapid increase in pressure and a square waveform should be evident. Before the pressure waveform returns, a sharp downstroke with one or two oscillations should appear when the fast-flush device is released.
1. If the system is overdamped, the fast-flush waveform will display a square wave with an angled upstroke and downstroke and no oscillations (Figure 10). An overdamped wave form underestimates the systolic pressure; the diastolic pressure may not be affected.⁵
2. If the system is underdamped, the square waveform will display multiple large oscillations (Figure 10). An underdamped waveform overestimates systolic pressure, and diastolic pressure may be underestimated.⁵

Completing the Procedure

Discard supplies, remove PPE, and perform hand hygiene.
Document the procedure in the patient’s record.

MONITORING AND CARE

Check the level of the solution in the flush bag and replace solution as needed.
Rationale: Checking the solution level helps ensure catheter patency.
Check that the pressure bag or device is maintained at 300 mm Hg⁵ at regular intervals and as needed.
Rationale: A pressure level of 300 mm Hg maintains catheter patency.
For arterial, RA, and PA lines, change the flush bag and hemodynamic monitoring system (pressure tubing, transducer, and stopcocks) every 96 hours, upon suspected contamination, or when the integrity of the pressure monitoring system has been compromised.³ Minimize access to the system to prevent infection. The flush bag may need to be changed more frequently if empty.
Zero the hemodynamic monitoring system during initial setup, before insertion, after insertion, when disconnection occurs between the transducer and the monitoring cable, when disconnection occurs between the monitoring cable and the monitor, and when the values obtained do not fit the clinical picture.
Check the hemodynamic monitoring system at regular intervals and as needed. Ascertain that all connections are tightly secured and that there are no cracks in the system. Ensure that the system is closed, nonvented caps are on all stopcocks, and the system is free of air bubbles.
Rationale: Checking the system ensures system integrity, safety, and accuracy. A crack or loss of integrity in the transducer can result in inaccurate hemodynamic readings.
Perform the fast-flush square wave test at least once per shift, after opening the catheter system for zeroing or drawing blood, and whenever the waveform appears to be distorted.¹

EXPECTED OUTCOMES

The pressure monitoring system is prepared aseptically.
The hemodynamic monitoring system remains intact with secure connections.
The phlebostatic axis is accurately identified.
The air-fluid interface of the transducer is leveled to the phlebostatic axis.
The pressure monitoring system is zeroed.

UNEXPECTED OUTCOMES

Loose connections within the hemodynamic monitoring system
Stopcocks left open to air without nonvented caps
Air bubbles in the system
Pressure bag inflated to less than 300 mm Hg⁵
Air fast flushed to the patient (if the IV flush bag did not have all the air removed before using)

DOCUMENTATION

Education
Patient’s response to the procedure
Date and time of hemodynamic monitoring system preparation
Hemodynamic monitoring system leveling and zeroing
Type of flush solution
Unexpected outcomes and related interventions

REFERENCES

American Association of Critical Care Nurses. (2020). AACN practice alert: Pulmonary artery/central venous pressure monitoring in adults. AACN Advanced Critical Care, 31(1), 41-48. doi:10.4037/aacnacc2020328 (Level A)
Infusion Nurses Society (INS). (2021). Infusion therapy standards of practice. Standard 41: Flushing and locking. Journal of Infusion Nursing, 44(Suppl. 1), S113-S118. (Level A)
Infusion Nurses Society (INS). (2021). Infusion therapy standards of practice. Standard 43: Administration set management. Journal of Infusion Nursing, 44(Suppl. 1), S123-S125. (Level A)
Infusion Nurses Society (INS). (2021). Infusion therapy standards of practice. Standard 59: Infusion medication and solution administration. Journal of Infusion Nursing, 44(Suppl. 1), S180-S183. (Level A)
McGee, W.T., Young, C., Frazier, J.A. (Eds.). (2018). Edwards clinical education: Quick guide to cardiopulmonary care (4th ed.). Retrieved November 16, 2023, from https://assets-us-01.kc-usercontent.com/6239a81e-8f0f-0040-a1df-b4932a10f6ae/24f7979b-51cd-4c38-aef8-2055d40a5fdd/quick-guide-to-pulmonary-care-4th-edition.pdf (Level M)

Adapted from Johnson, K.L. (Ed.). (2024). AACN procedure manual for progressive and critical care (8th ed.). St. Louis: Elsevier.

AACN Levels of Evidence

Level A - Meta-analysis of quantitative studies or metasynthesis of qualitative studies with results that consistently support a specific action, intervention, or treatment
Level B - Well-designed, controlled studies, with results that consistently support a specific action, intervention, or treatment
Level C - Qualitative studies, descriptive or correlational studies, integrative reviews, systematic reviews, or randomized controlled trials with inconsistent results
Level D - Peer-reviewed professional organizational standards with clinical studies to support recommendations
Level E - Multiple case reports, theory-based evidence from expert opinions, or peer-reviewed professional organizational standards without clinical studies to support recommendations
Level M - Manufacturer’s recommendations only

Clinical Review: Joyce Foresman-Capuzzi, DNP, RN, CCNS, CEN, CPEN, CTRN, TCRN, CPN, CCRN, AFN-BC, SANE-A, GERO-BC, NPD-BC, EBP-C, NHDP-BC, EMT-P, FAEN

Published: January 2024