Cartridge Based & Point-Of-Care Blood Gas Analyser QAP Performances & Quality Management Systems.. Issues AACB QC Workshop 4 Brisbane 16th Sept. 2016 John Calleja
Objectives To discuss Pre-Analytical Issues & the limitations of commonly used Quality Systems. associated with Cartridge Based & Point of Care Blood Gas Devices especially in relation to : RCPA Blood Gas & RCPA POCT Blood Gas.. Programs To highlight optimised procedures to help eliminate / minimise such pre-analytical errors in these programs Generate discussion amongst audience members in how they cope with some of these issues..
1. Why? Eg. 3 Successive QAP POCT BG Program Outlier Summaries. 2 Outliers Po2, Lactate 5 Outliers Ph, Po2, ICA, HCT, HB Very Unsatisfactory! 4 Outliers PCO2, PO2, Lact, HB
QAP POCT Blood Gas 6 Labs using method 4 Labs 4 Labs with-in in group group -- Two Two Labs Labs High High
QAP POCT Blood Gas 5 Labs using method 4 Labs 4 Labs with-in in group group - -Lab Tworeads Labs High High
QAP POCT Blood Gas 4 Labs using method 4 2 Labs in aregroup High 2-Labs Two Labs readshigh Low
QAP POCT Blood Gas 6 Labs using method 4 Labs 4 Labs are in in group group 2- Two LabsLabs outlying High
Content QAP BG / POC BG Programs Sources of Pre-Analytical Errors / Specific Issues Specific Limitations of POCT Device Quality Management Programs.. to demonstrate adequate or deficient ongoing performance. Standardised techniques for pre-analytical error minimisation ABL90 EPOC QAP Outliers Follow-Up / Documentation Pre-Analytical Causes QC Performances on the day & in period Bias investigation & management Imprecision investigation & management
Very Volatile QA Materials Many potential pre-analytical Errors Inability to use Best Practice QC Procedures Wide Int.QC Limits vs.. QAP Limits QAP Method Medians that are not necessarily reliable Peer Group Reference Values
1. Sources of Pre-Analytical Error in.. Blood Gas QAP & POCT Programs
Issues The Importance of QAP Sample Temperature Equilibration Proper QAP Sample Mixing How you Hold the QAP Sample Vial -Effects on Heat Transfer / Vial Temperature Role of Frothing Importance of Prompt QAP Sample Analysis & Correct Handling / vs. The Effects of Time Delays
1.1 Effect of Vial Temperature Equilibration on Gas Solubilities As temperature rises, gasses become less soluble in the aqueous phase. Solubility of CO2 in water = 171 ml CO2 / 100 ml H2O 88 ml CO2 / 100 ml H2O 30 ml CO2 / 100 ml H2O @ 0o C @ 20o C @ 60o C => For a QAP vial with a Low temp - could get False HIGH pco2 gas readings High temp - could get False LOW pco2 gas readings.
1.1 Effect of Temperature on Gas Solubilities Solubility of O2 in water = 0.92 ml O2 / 100 ml H2O 0.61 ml O2 / 100 ml H2O 0.53 ml O2 / 100 ml H2O @ 4o C @ 22o C @ 30o C => For a QAP vial with a Low temp - could get False HIGH po2 gas readings High temp - could get False LOW po2 gas readings.
Excerpt.. From a Blood Gas Analyser Manufacturer s Manual - Showing Temp Corrections for B.Gas QC Ambient Room Temp. taken as 21 23o C If vial 5oC below R.T. PO2: +4 - +9.5 mmhg Higher PCO2: +1.6 mmhg Higher If vial 5oC above RT. PO2: -3.6 - -8.7 mmhg Lower PCO2: -1.5 mmhg Lower
1.1 Effect of Temperature on Gas Solubilities
Action Required: Prior to Analysis - QAP samples should be brought to Room Temperature ~ 22 O c - Remove from fridge 1 hour pre-analysis
1.2 Gas Solubilities & Effects of Mixing At 1 Atmosphere (760 mmhg) and 20 0C Solubility of CO2 & O2 gasses in water is.. CO2 = 88 ml CO2 / 100 ml H2O O2 0.6 ml O2 / 100 ml H2O = O2 CO2 CO2.. is much more soluble in water.. than O2
Sample Mixing Inside the vial:.. Gases (O2, CO2).. are in a state of equilibrium. Distributed between. the air-in-the-vial.. and the aqueous material. Action Required: Samples must be mixed vigorously otherwise.. O2 will tend to stay in gas phase, rather than aqueous phase
1.3 How you Hold the Vial to Mix it! may affect the temperature of the vial which may upset the equilibration of the gases between the aqueous phase & gas phase which may give false results!
In-Correct Handling Holding the vials in either of these manners - results in Heat Transfer!
Correct Handling Action Required: Holding Vial in either of these manners.. Eliminates Heat Transfer to vial from hands!
1.4 Sample Frothing After vigorous mixing.. Froth forms at the Top of the Vial. Get: Froth at top. Liquid at bottom The Froth formed helps to keep the dissolved gases in the aqueous phase!
1.5 Safety - When opening the vial.. Consider Safety Use gauze or tissues to protect fingers. Position the red dot, to face you. Bend both sides downward away from you Snap vial open
1.6 Sampling & Time Delays Post Opening QAP Vials Questions are 1. How much time do we have.. From the time of mixing / opening the vial?.. & 2. How should we Sample the Vials Correctly on Different Analysers to minimise delays..?? & 3. How are results affected by.. Poor Technique &.. Time delays?
Sampling techniques techniques.. l l l l Direct Aspiration (via inst. sample probe). Use of an Adaptor Needle & Syringe Capillary Tube Action Required: lmust be Quick.. lin 10-20 secs. luse a primed 2 ml Syringe / with Blunt Needle. lwith No air bubbles.. into aspirator, syringe or capillary.
The effects of Air Gas Compositions & Delayed Analysis on QAP results. The table below shows The Gas Compositions of Air! 1 Atmosphere = 760 mmhg: Partial Pressures of O2 = 21% x 760 = 159 mmhg Partial Pressures of CO2 = 0.031% x 760 = 0.24 mmhg Implications: Samples with low PO2 may get atmospheric contamination High CO2 may get loss to atmosphere!
2.0 Examples.. Effects on 2.1 P02 2.2 Other Analytes
Effects of Delayed Analysis - QAP sample with Low O2 Sample with Low PO2 (eg) 50 100 mmhg + Delay Contamination of sample with atmospheric O2.. Atmospheric O2 159 mmhg Atmospheric O2 contamination. Outcome Falsely High QAP result.. For O2 Sample w Low O2 ~ 50-100 mmhg
(eg) Lab with Oxygen Contamination Sample with High O2 (Tgt=160mmHg) - is on target (160)! Sample with Low O2 (Tgt=75mmHg) - is High (86)! Investigation showed: - Not in-line with their method group - But Int. QC OK on day & in-period. - Delayed Analysis > Pre-Analytical O2 contamination - giving False High O2!
Same Lab with earlier Oxygen Contamination Results history & duplicate samples show: the lab made the same sampling delay errors later in cycle! see duplicate samples 33-2 & 33-7 But - Non-method related +ve Bias at low concentration...at high concentrations lab performing well!
Delayed Analysis QAP sample with High O2 Sample with High PO2 (eg) 170 200 mmhg + Delay Loss of O2 from sample to atmosphere.. Atmospheric O2 159 mmhg O2 diffuses to atmosphere. Outcome Falsely Low QAP result.. For O2 Sample w High O2 ~ 170-200 mmhg
Balancing Forces for po2 recovery in QAP samples Warm >22oC Cool <22oC false Low false High Poor mixing Good mixing false Low - correct recovery Minimal, < 20s -correct recovery false High Minimal, < 20s -correct recovery Delayed Delayed false Low Need to get temperature, mixing sampling & timing.. RIGHT.. for successful measurement! Temperature Sample Mixing Sampling Delay for samples with PO2 < 160 mmhg Sampling Delay for samples with PO2 >160 mmhg
2.0 Examples.. Effects on 2.1 P02 2.2 Other Analytes
2.3 How analytes are Affected! 1.0 PH: PH is dependant on PCO2 Henderson Hasselback Equation: ph = 6.1 + Log [HCO3-] / (0.031 x PCO2) If PCO2 is falsely High PH will be Falsely LOW If PCO2 is falsely Low PH will be Falsely HIGH 2.0 Haemoglobin - EPOC measures Haematocrit not HB. - No red-cells present in QAP POC material must be microparticles => Correct recovery may be dependant on correct Vial Mixing.
3. Standardised Sampling Techniques to minimise Pre-Analytical Error. 3.1 P.O.C.T (eg) EPOC 3.2 Cartridge Based (eg) ABL90
3.1 EPOC Analyser.
3.1 QAP Sampling EPOC analyser Equilibrate the QAP vial - min. 1 hr @ RT ( Do NOT open yet! ) After QAP Sample Equilibration: Turn on EPOC & allow to initialise Insert an EPOC Test-Card when its ready! EPOC performs Card Integrity Checks & Card Calibration (~ 3 minutes total ) After card is calibrated you have ~ 7 mins to run sample When running QAP samples Important!! run in QA Mode (NOT in Patient Sample mode! ) - This allows a wider response of values & leads to greater analysis success > necessary as QAP samples & Int. QCs are aqueous.. not Whole Blood Prepare a 2ml Syringe + Blunt needle Prime the Syringe plunger (3-4 times).. to get a smooth plunger action. Mix QAP sample vigorously (~ 10-20 secs) Snap-open & Draw QAP sample into syringe Withdraw needle & Expel air from syringe. Invert Syringe & dispel a few drops onto a tissue Apply Sample from Syringe to cartridge.
3.1 QAP Sampling EPOC analyser
3.2 ABL90 Analyser.
3.2 QAP Sampling ABL90 analyser Equilibrate QAP vial - 1 hr @ RT Mix QAP sample vigorously ( ~ 30 secs )
4. Int. QC Management. of P.O.C. & Cartridge Based Blood Gas Analysers
4.1 What does NATA Require?
Acknowledges Cartridge Based Instruments Classifies into 2 types Acknowledges Electronic Checks Requires separate QC/QA of Cartridges
References the AACB POCT Position Statement Adds Wet QC as a Requirement Categorises POCT into: Low & Medium Complexity devices Min. 1 QC / Month Min. 2 QC / Month
Adds conditions for when additional QC checks needed. Comments on ideal QC Matrix States B Gas QC Requirement Daily QC at 2 or more levels Exempts Cartridge Based Instruments from daily req ment
4.2 How do we manage Int. QC for a P.O.C. Blood Gas Analyser? (eg) E.P.O.C. Analyser & What are the Issues?
4.21 P.O.C (EPOC) Analyser Issues Sensor Software Configuration Version Instruments require.. Sensor Software Configuration Version Updates Need to refer to the Alere web-site 2 updates / Year ~ Jan / July 1 month notification by Alere is provided Must be applied before prev. version expires - otherwise can t use analyser! Int. QC Targets & Limits must also be updated at the time. QC Value Assignment Sheets for Software Version
4.22 P.O.C. (EPOC) Analyser Issues QC Ranges Int. QC Targets & Limits updates Specific to.. Sensor Configuration version & Int. QC Lot No QC Value Assignment Sheets for Software Version / QC Lot No. QC Targets & Allowable2sd ranges
4.23 P.O.C (EPOC) Analyser Issues QC Ranges Int. QC Monitoring Spreadsheets QC for a given Sensor Configuration version Int. QC Lot No Test Card Lot No. QC Targets & Allowable2sd ranges.. FROM Value Assignment Sheets
4.24 P.O.C (EPOC) Analyser Issues QC Ranges This is Inappropriate!!! As several Int. QC Lot Nos. noted!.. All being referenced against the same QC Targets & Allowable2sd ranges > Value assignments must be updated for each QC Lot / Sensor Config. versions
4.25 P.O.C (EPOC) Analyser Issues - QC Ranges vs. QAP Allowable Limits EPOC QC Ranges: Int. QC Ranges Expressed as Allowable Range %
RCPA QAP Allowable Limits
4.25 P.O.C (EPOC) Analyser Issues - QC Ranges vs. QAP Allowable Limits Study of the Ratios of.. EPOC Int. QC Ranges / QAP ALE EPOC Ranges! All Should be < 1 Most > 1.. (1.3 4) QAP Ranges! Ratio of.. Int QC 2SD / QAP ALE Ratio = 24.3% / 6% = 4.05
4.25 P.O.C (EPOC) Analyser Issues - QC Ranges vs. QAP Allowable Limits Ratio of.. Int QC 2SD Range / QAP ALE Most Ratios >> 1.. (1.3 4).. All Should be < 1
Other Issues
4.26 P.O.C (EPOC) Analyser - Other Issues : We are unable to apply Traditional Laboratory QC Best Practices.. to assess.. P.O.C (eg. EPOC) analysers.. for ongoing precision & accuracy performances. Reasons being.. Include: We are effectively forced to use manufacturer provided QC Targets & Limits for each lot of QC/Cartridge lot - as.. QC/Cartridge Lots change very frequently. Costs would be prohibitive to establish our own QC ranges ( eg. By running n=20 tests / qc level and.. establish a Mean & SD.. based QC range ) this would be impractical given the frequency with which lots change The QC is run highly infrequently.. per given QC Lot / Cartridge Lot No. (ie) at best.. get.. 4 to 6 results.. per QC level / QC lot THEN cartridge and qc lots change again.. over a 6 month period. This is inadequate to generate meaningful stats ( including Mean recovery, SD & CV ). Hence real bias trends & real imprecision performance trends cannot be meaningfully assessed. [Goto example next page ] -
4.26 P.O.C (EPOC) analyser QC Limit Issues Eg. po2 Imprecision goes unnoticed using P.O.C (EPOC) limits. Bias goes unnoticed using P.O.C (EPOC) limits
4.27 P.O.C (EPOC) Analyser - Summary Even if we eliminate pre-analytical QAP sample handling issues by optimising procedures.. It is still possible to get QAP results outside the allowable limits.. When our Int. QC shows adequate performance. The QAP use Overall Participant & Method- Median Targets So.. if many labs in the peer group do not use optimised procedures and their results are affected by pre-analytical error - the reference medians could be skewed & incorrect. This may give the lab a false impression it is out-of range when it may be acceptable.
4.3 Cartridge Based Blood Gas Analyser Int. QC Management. (eg) ABL90
4.31 ABL90 QC ABL90 QC in AQURE 1. Date Range.. Can Display QC Sequentially.. By Selecting 2. Analyte 3. QC Level 4. Use Movable Focus Bar > Can position over the date you are interested-in. Note - Variable QC Ranges for diff Cartridge Lots 5. Position mouse cursor over data point to show QC Target & QC Range 6. Repeat for next QC Levels
4.32 ABL90 QC ABL90 QC Ranges These are automatically configured by analyser on Change of Cartridge ( lasts 30 days ) Not User Re-Configurable!
4.33 ABL90 QC Comparing ABL90 QC Ranges.. vs. QAP Allowable Limits.. QAP ALEs EPOC Ranges ABL90 QC Ranges Ratio ABL90 Int. QC Range / QAP ALE : Desirable < 1: Most > 1 Comparable for EPOC: Most > 1
4.34 ABL90 QC Saving Grace for ABL90 vs. P.O.C (eg. EPOC ) BGA: - QC Frequency is daily for all QC Levels on the ABL90 - Therefore get a reasonable index of developing Bias & Imprecision - This is similar to traditional best practice QC at one level - On EPOC QC is only analysed monthly. -However QC Limits are fixed & are wider than QAP ALEs... - May get instances of outlying QAP Performances when Int.QC is in-control. - QC lots change monthly so difficult to get a picture of long term accuracy & imprecision
5. AACB VQAG Proposed Survey
5.0 VQAG Proposed Survey VQAG = Victorian AACB Quality Assurance Group Proposal to send a questionnaire to a representative labs.. to investigate: Their Blood Gas Internal QC Management Practices for: Mainstream analysers (eg) ABL800, Siemans vs Cartridge Based (eg) GEM Premier, ABL90 vs. P.O.C.T (eg) istat, EPOC What QC materials are used What QC Limits are applied / Basis. Frequency at which QCs are run. Who is responsible for the analyser. Where instrument is located (eg) Lab, Reg Lab, Hospital Ward Frequency of Outliers on the RCPA Blood Gas & POCT Blood Gas Programs. How they manage follow-up & documentation of their Outliers on the RCPA Programs How they fare with NATA inspections
6. Conclusions
6.0 Conclusions There are many Pre-analytical sources of error at Play.. when analysing QAP Blood Gas & POCT BG samples Po2 is particularly vulnerable to these (pco2, ph are also vulnerable) Pre-Analytical error sources MUST therefore be managed carefully Standardised protocols have been developed & can help POCT QC management is very different to General Lab Best Practice QC Procedures making it difficult to independently & objectively assess the performance of an analyser. Labs are ( in all practical terms) forced to use the manufacturer QC Limits. Assessments have shown that these are often much wider than the RCPA QAP Allowable Limits This extends to cartridge based BG Analysers (eg) ABL90 & GEM Premier. It is either not possible or totally impractical to change these limits This means that QAP Performances may be outside of the allowable limits when Int.QC is in the acceptable Ranges Troubleshooting BG QAP for these devices is complex & a nightmare! Getting a quantitative understanding of how different labs manage the issues as a collective may help us improve our lot.
Thankyou for your attention!
Questions / Comments!