004795 – Calibration of Pressure Transducers

Caboolture Hospital Intensive Care Unit

Guideline 

Effective from: January 2020

Review date: January 2023

Calibration of Pressure Transducers – 004795

 

Invasive haemodynamic measurements are utilised in clinical management decision making for critically ill patients. Identifying the phlebostatic axis, zeroing, levelling and dynamic response testing of haemodynamic waveforms are essential components of assuring the quality and accuracy of measurements. Maintaining the transducer at the phlebostatic axis will help ensure a proper reading. If the transducer is positioned below the phlebostatic axis, the readings will be erroneously high; if above the phlebostatic axis, the readings will be erroneously low. Either error can lead to mismanagement of patients and their care.

Purpose and intent

This guideline outlines the process for assessing dynamic response and calibrating invasive monitoring transducers to ensure accuracy of data.  This includes intra-arterial blood pressure and central venous pressure.

Scope and target audience

This guideline applies to all Caboolture ICU medical and nursing clinical staff (permanent, temporary and casual) and all organisations and individuals acting as its agents (including Visiting Medical Officers and other partners), involved in providing care and management of patients admitted to the Intensive Care Unit.

Competency and education

All clinicians involved in the calibration of pressure transducers must ensure that this is within their scope of clinical practice, determined by the individual’s credentials, education, training, competence and maintenance of performance at an expected level of safety and quality. Education is provided to nursing and medical staff through their unit induction process and formal education programs such as in-service and ICU Transition to Nursing Practice program, this includes supervised practice and/or simulation.

Procedure / process

The core principles of calibrating pressure transducers follows Aseptic Non-Touch Technique (ANTT) and the Queensland Health I-CARE guidelines. Personal protective equipment (PPE) including eye-protection must be worn for all procedures with risk of exposure to bodily fluids. Observe the five moments of hand hygiene throughout all clinical patient contact. Pay attention to the micro critical aseptic fields and observing strict ANTT when handling caps, bungs, and covers attached to pressure transducers. 

Responsibilities

It is the responsibility of the registered nurse to:

  • Have an adequate knowledge base regarding the technical aspects of haemodynamic monitoring.
  • Report any significant changes in haemodynamic values to medical staff.
  • Advise medical staff of inaccurate haemodynamic waveforms.

Arterial waveform

The arterial waveform corresponds with the cardiac cycle: 

  • Ventricular systole corresponds with a steep upstroke followed by a downward turn at the end of systole as the pressure falls in the aorta.
  • A diacrotic notch is visible on the downward stroke which represents the closure of the aortic valve.
  • The remainder of the downward stroke represents late systole and diastole, blood flow slows, the slope of the waveform begins to decline as pressure decreases.

Retrieved February 28, 2017. From: https://seattleclouds.com/myapplications/dukeg/ican/ArtLine.html

Central venous pressure waveform

The central venous pressure waveform corresponds with the cardiac cycle:

  • ‘a wave’ represents atrial contraction and is seen after the P wave on the electrocardiograph (ECG).
  • ‘c wave’ represents tricuspid valve elevation into the right atrium and is seen after the QRS complex on the ECG.
  • ‘x descent’ represents right ventricular contraction.
  • ‘v wave’ represents filling of the right atrium and is seen after the T wave on the ECG.
  • ‘y descent’ represents opening of the tricuspid valve in early ventricular diastole.

Retrieved November 25th, 2019 from https://derangedphysiology.com/main/core-topics-intensive-care/haemodynamic-monitoring/Chapter%202.1.3/interpretation-central-venous-pressure-waveform

Waveform damping

Refers to the reduction in amplitude of the waveform:

  • Under-dampened waveforms have increases in oscillations
  • This can be a result of increase tubing length
  • Under-dampened waveforms overestimate blood pressure
  • Over-dampened waveforms have reduced oscillations and are more smooth in appearance
  • This can be a result of clots, air bubbles and loose connections
  • Over-dampened waveforms underestimate the blood pressure

 

Square wave test

The square wave test is used to assess the accuracy of the waveform.  It tests the ability of the tubing catheter system to accurately send a waveform from the blood vessel to the transducer.

Test method:

The square wave test should be performed as part of the nursing assessment at the beginning of each shift or if there is doubt about the accuracy of the waveform

  1. Ensure that the pressure bag is inflated to 300mmHg and that there is adequate fluid in the bag
  2. Pull the pigtail on the transducer system while watching the monitor, then release
  3. The monitor should show a waveform that rises suddenly and sharply, tops off, then declines sharply
  4. As you release, one or two oscillations appear above and below the baseline indicating optimal dynamic resistance

A. Optimal damping in which rapid flushing produces less than three beats of oscillations.

B. Overdamped system in which no oscillations are seen.

C. Underdamped system in which there are excessive oscillations.

Transducer levelling and zeroing

To ensure consistency and accuracy of invasive pressure monitoring the transducer must be positioned and calibrated regularly to an anatomical consistent site. This site is called the phlebostatic axis.

Transducer levelling

  • The phlebostatic axis is the anatomical reference point that is used for consistent transducer height placement.
  • The site of the phlebostatic axis is at the intersection of the fourth intercostal space and mid axillary line as this point approximates the level of the atria.
  • The purpose is to line up the air-fluid interface with the left atrium to correct for changes in hydrostatic pressure in blood vessels above and below the level of the heart.

Levelling procedure:

  1. ensure pressure bag is inflated to 300 mm Hg, to maintain patency of the line
  2. preform a square wave test before obtaining a reading
  3. ensure the bed is level and position patient supine
  4. the reading may be reliably measured with the head of bed positions from 0 (flat) to 600
  5. identify the phlebostatic axis
  6. using a spirit level, align the phlebostatic axis with the stopcock of the transducer
  7. adjust the mounted transducer bracket so the two are in horizontal alignment

 

Transducer Zeroing

  • Eliminates the effects of atmospheric pressure (760 mmHg at sea level) and hydrostatic pressure (the weight of the fluid in the tubing) from the measured pressure readings.
  • Zeroing of transducers is to be done as soon as possible every shift as part of comprehensive patient assessment and as required, such as changing patient position.

Zeroing procedure:

  1. turn the stopcock on the transducer so that it is off to the patient
  2. remove dead-end bung observing strict ANTT
  3. select appropriate menu on the monitor (e.g. ART, CVP)
  4. select ‘zero’ key and wait for reading to stabilise
  5. ensure monitor indicates ‘zero complete’ and zero appears on the screen
  6. replace dead-end bung (using strict ANTT) and reopen stopcock to neutral (open to patient and monitoring) position

Trouble shooting

ACTION

POSSIBLE SOLUTION

No Waveform

  • Check the pressure scale setting on monitor is appropriate to the measurement
  • Check for loose connection in pressure monitoring line
  • Check for loose connection between transducer/cable/monitor
  • Check that taps are ‘open’ to patient
  • Check for kinks/compression of tubing
  • Port may be occluded – attempt to aspirate port
  • DO NOT ATTEMPT TO FLUSH PORT AS A CLOT MAY BE DISLODGED
  • If successful, discard blood filled syringe and flush line
  • If unsuccessful, notify medical staff

Dampened Waveform

  • Check pressure scale setting
  • Check for loose connections/kinks/air bubbles
  • Check that there is enough fluid in the flush bag
  • Check the pressure bag is inflated to 300 mmHg
  • Port may be partially occluded – attempt to aspirate port
  • DO NOT ATTEMPT TO FLUSH PORT AS CLOT MAY BE DISLODGED
  • If successful, discard blood filled syringe and flush line
  • If unsuccessful, notify medical staff

Unable to flush line with continuous flush system

  • Check that all stopcocks are open to the patient
  • Check that there is enough fluid in the flush bag
  • Check the pressure bag is inflated to 300mm Hg
  • Port may be partially occluded – attempt to aspirate port.
  • DO NOT ATTEMPT TO FLUSH PORT AS CLOT MAY BE DISLODGED
  • If successful, discard blood filled syringe and flush line
  • If unsuccessful, notify medical staff

Excessive artefact

  • Check for electrical interference (from bed, pumps etc.)
  • Check for patient movement
  • Check connections in pressure monitoring system and in the and in the monitor/cable/transducer system
  • Faulty cable

Reading too high/ too low

  • Re-level and zero transducer
  • Check tubing for kinks/bubbles/loose connections
  • Check that all stopcocks are open to the patient
  • Check the patient
  • Check non-invasive measurement

Partnering with consumers

The Patient and their carer/next of kinare to be encouraged and given the opportunity to ask questions, clarify information and identify goals of care during communication processes.  Staff are responsible for providing information in a way that is understandable and that meets patient’s needs and are to use perception checking techniques to ensure patient and family’s understanding of discussions. 

Aboriginal and Torres Strait Islander considerations

Specific cultural implications exist for the provision of healthcare for Aboriginal and Torres Strait Islander patients and their families.

  • As a matter of best practice to provide culturally capable patient care, seek cultural guidance from the local Aboriginal and Torres Strait Islander Hospital Liaison Officer, the Aboriginal and Torres Strait Islander Cultural Practice Coordinator, Health Worker, the family group or the wider community.
  • Refer to the Metro North Hospital and Health Service Intranet page on Cultural Resources and Queensland Health Publication: “Aboriginal and Torres Strait Islander:  Patient Care Guidelines Published by the State of Queensland (Queensland Health), May 2014.

Legislation and other authority

  • Health Act 1937
  • Health Practitioner Regulation National Law Act 2009
  • Health Legislation Amendment (Midwives and Nurse Practitioners) Act 2010

References

Arterial blood pressure wave. From: Google Images. Retrieved February 28, 2017. From: https://seattleclouds.com/myapplications/dukeg/ican/ArtLine.html

Central venous pressure waveform. Retrieved November 25, 2019. From: https://derangedphysiology.com/main/core-topics-intensive-care/haemodynamic-monitoring/Chapter%202.1.3/interpretation-central-venous-pressure-waveform

Elliott, D, Aitkin, L & Chaboyer, W (2014) ACCCN’s Critical Care Nursing (2nd ed). Elsevier: Chatswood

Liverpool Hospital Intensive Care Unit (2014) Arterial lines monitoring and management.

Sydney Local Health District (2015) Arterial line management using the Safeset.

Urden, D., Stacey, K & Lough, M. (2014) Thelan’s Critical Care Nursing (7th ed). Mosby: St Louis.

Related documents

  • 003818 Arterial line management and blood gas sampling in ICU
  • 005334 Central Venous Access Device (CVAD) – Insertion, Management and Removal


Document history

Author

Clinical Nurse Consultant, Caboolture Hospital ICU

Custodian

Clinical Nurse Consultant, Caboolture Hospital ICU

Compliance evaluation
and audit 

Adverse events relating to pressure monitoring will be documented in the patient’s medical record. All clinical incidents, near-miss events and procedural noncompliance of pressure monitoring are to be recorded via RiskMan and addressed by the Caboolture ICU Safety and Quality Committee. This information will be used to review practice and identify areas for future quality improvement initiatives as per MNHHS Quality Improvement Procedure (PROC089). In the absence of clinical incidents, proactive annual audit from CIS data of pressure monitoring documentation will be conducted and presented within the schedule of Caboolture ICU Safety and Quality Committee. 

Replaces Document/s

CRICU V4_2017/WUG Calibration of Pressure Transducers

Consultation

Key stakeholders

Clinical Nurse Consultant, Caboolture ICU

Director, Caboolture ICU

Staff Specialist Intensivists, Caboolture Hospital

Members of Caboolture ICU Safety and Quality Committee

Broad Consultation

CN ICU Portfolio Holder, Standard 6: Communicating for Safety

Marketing Strategy

Dissemination via email cascade to key staff groups and stakeholders; online publishing on QHEPS; ICU staff notification as per clinical in-service/meetings

Key words

Arterial line; central venous pressure; transducer calibration; IAL; CVP; 004795

 

 

 

Custodian Signature

Date

Clinical Nurse Consultant, Caboolture Intensive Care Unit, Metro North Hospital and Health Service

AUTHORISATION

 

 

 

Authorising Officer Signature

Date

Director, Intensive Care, Caboolture Hospital, Metro North Hospital and Health Service 

 

The original signed version is kept in file at Service Improvement Unit, Caboolture Hospital, Metro North.