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Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
Venous and arterial blood gas analysis in the ED: What we know and what we don't
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Venous and arterial blood gas analysis in the ED: What we know and what we don't

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This presentation delivered at the International Conference on Emergency Medicine in Dublin summarises agreement between venous and arterial blood gas parameters and utility of venous blood gas …

This presentation delivered at the International Conference on Emergency Medicine in Dublin summarises agreement between venous and arterial blood gas parameters and utility of venous blood gas analysis in emergency department clinical practice. It also highlights important gaps in our knowledge on this topic.

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  • Going to report statistical agreement, but we are probably more interested in agreement within clinically acceptable limits
  • Single study; small numbers; needs further research
  • Going to report statistical agreement, but we are probably more interested in agreement within clinically acceptable limits
  • Transcript

    • 1. VENOUS AND ARTERIAL BLOOD GASANALYSIS IN EMERGENCYDEPARTMENTS:WHAT WE KNOW AND WHAT WE DON’T!Anne-Maree KellyProfessor and DirectorJoseph Epstein Centre for Emergency MedicineResearch @Western Health
    • 2. Permissions This presentation can be used in part or whole foreducational purposes on the condition that the followingappears on each slide used:‘Re-produced with permission of Professor Anne-MareeKelly, Joseph Epstein Centre for Emergency MedicineResearch, Melbourne, Australia’@kellyam_jec
    • 3. Conflicts of interest I received financial support for travel and accommodation from Radiometer Pty Ltdto present a similar presentation at 4thInternational Symposium on Blood Gas andCritical Care in France in 2008. I am undertaking some research with A/Prof Rees into calculated values which maybe commercialised. I have no pecuniary interest in this program. I have not received industry funding for any of my blood gas research projects.
    • 4. Objectives After this presentation, participants will: Understand the agreement performance of variables on arterial andvenous blood gas analysis, in particular pH pCO2 Bicarbonate Base excess Be aware of the unanswered questions Be aware of new approaches being taken to improve accuracy ofprediction of arterial values from venous blood gas samples
    • 5. Caveats Discussion will be limited to comparisons betweenarterial and peripheral venous samples Data is up-to-date as of publications to May 2012 Includes some of data only ‘published’ as abstract in2012
    • 6. Blood gases in emergency medicine Establishing acid-base status Mainly pH; but also bicarbonate Measuring respiratory function/ ventilation Mainly pCO2; but also pH ‘Quick check’ potassium, haematocrit, someelectrolytes Not addressed in this presentation
    • 7. Why venous rather than arterial? Less pain for patients Fewer complications, especially vascular andinfection Fewer needle-stick injuries Easier blood draw Minimal training requirement
    • 8. Setting the context JANE 26 year old, insulindependent diabetic 2 days of vomiting anddiarrhoea. Pulse 120 bpm, BP100/-, BSL ‘Hi’ TRAN 74 year old COAD Acute respiratory distress. Pulse 110, BP 140/-,SpO2 (air) 88%
    • 9. The clinical questions Can we Exclude / diagnose Monitor progress of Base therapeutic decisions for (eg use and settings ofNIV)Metabolic acidosis or acute respiratory failureusing venous blood gas analysis rather thanarterial?
    • 10. Statistical considerations Outcome of interest is howclosely venous and arterialvalues agree, not how well theycorrelate Weighted mean difference givesan estimate of the accuracybetween the methods 95% limits of agreement giveinformation about precisionArterial valueVenous value95% LoA
    • 11. Clinical considerations There is limited data about the toleranceclinicians have with respect to agreementbetween arterial and venous values of blood gasparameters Depending on this tolerance, the degree ofagreement may be acceptable or unacceptable There is known variation between clinicians re this
    • 12. Issues with the evidence Patient cohorts highly varied Patient groups of interest are those at high riskof acidosis or hypercarbia Reporting does not always report this detail Data may to be dominated by patients with normal pH,pCO2 and blood pressure Need for research focussed on high risk patient groups
    • 13. pH 13 studies Range from 44 to 346 patients Various conditions DKA (3), COAD (4), trauma (1) 2009 patients Weighted mean difference of 0.033 pH units 95% limits of agreement (7 studies) generally within +/-0.1 pH units
    • 14. pH in illness subgroups DKA 3 studies (265patients) Weighted meandifference = 0.02 pHunits 95% limits ofagreement = -0.009 to0.02 pH units (1 study) COAD 5 studies (643 patients) Weighted meandifference= 0.034 pHunits 95% limits of agreementgenerally +/- 0.1 (3studies)
    • 15. pH- Other One ICU-based study suggests that ashypotension increases, AV pH agreementdeteriorates Very small patient numbers Finding not yet validated
    • 16. What we know & evidence gaps We know: Generally close AV agreement in both respiratory andmetabolic disease Evidence gaps: AV agreement in various levels and types of shock AV difference in toxicology scenarios (1 small study inTCA OD only) AV difference in mixed acid-base disease
    • 17. Bicarbonate 8 studies 1211 patients Various conditions (COAD 2) Weighted mean difference = -1.3mmol/l 95% limits of agreement : up to +/- 5mmol/l (3studies)
    • 18. Bicarbonate in illness subgroups DKA 1 study (21 patients) Weighted meandifference = -1.88mmol/l 95% limits ofagreement = -2.8 to0.9 mmol/l COAD 2 studies (643 patients) Weighted meandifference= -1.34 mmol/l 95% limits ofagreement: nonereported
    • 19. What we know and evidence gaps We know: Limited data suggests good agreement Very little data re limits of agreement ? +/- 5mmol/L Evidence gaps: AV agreement in specific disease states AV agreement in various levels and types of shock AV difference in toxicology scenarios AV difference in mixed acid-base disease
    • 20. pCO2 8 studies 965 patients Various conditions (COAD 4) Weighted mean difference = 6.2 mmHg 95% limits of agreement: up to -17.4 to +23.9mmHg 5/7 studies reporting LoA report LoA band >20mmHg
    • 21. pCO2 in COAD 4 studies 452 patients Weighted man difference = 7.26 mmHg 95% limits of agreement: up to -14 to +26 All 3 studies that reported LoA report LoA band>20mmHg
    • 22. Venous pCO2: A screening test for hypercarbia?Author, year No. Screeningcut-offSens. Spec. NPV %ABGavoidedKelly, 2002 196 45 100 57 100 43Kelly, 2005 107 45 100 47 100 29Ak, 2006 132 45 100 * 100 33McCanny,201194 45 100 34 100 23POOLEDDATA52945 100(95% CI97-100)53(95%CI 57-58)100(95% CI97-100)35%(95% CI32-41)Data limited to studies in cohorts with respiratory disease
    • 23. Using venous pH and CO2 to track progress? Preliminary data presented at this meeting as aposter 41 comparisons in 29 patients Arteriovenous difference for change in pH =0.004 (95%LoA -0.09 to 0.1) Arteriovenous difference for change in pCO2 = 0.55mmHg(95% LoA -16.6 to 17.6mmHg)
    • 24. What we know & evidence gaps We know: AV agreement is NOT good enough for clinical inter-changeability Wide limits of agreement Venous pCO2 has potential as a screening test for hypercarbia Excellent NPV AV agreement in change in pCO2 is NOT good enough for clinicalinter-changeability (pilot data only) Wide limits of agreement Evidence gaps: Whether trend in venous pCO2 and pH can safely drive a care pathwayfor COAD Subject of current international research project
    • 25. Base excess Two studies only In a sample of 103 patients (various conditions), theyreport: mean difference of 0.089mmol/L 95% limits of agreement -0.974 to +0.552 mmol/L In 326 trauma patients mean difference -0.3 BE units 95% limits of agreement -4.4 to +3.9 BE units 20% did not fall within pre-defined clinical equivalence thresholdCurrent view: LOA too wide. If accuracy needed in critically ill,need ABG
    • 26. Clinical application JANE DKA AV agreement isacceptable; at leastin non-shockedpatients Can use venous pHto diagnose/monitor TRAN Acute respiratorydistress pH agreement good butpCO2 has considerableimprecision Can use venous pCO2as a screening test forhypercarbia
    • 27. Another approach Team from Center for Model Based Medical Decision SupportSystems, Dept of Health Science and Technology, AalborgUniversity, Denmark (A/Prof Steven Rees) Developed venous to arterial conversion method using venousblood gas variables and pulse oximetry Designed to be incorporated into blood gas analysers
    • 28. The model The method calculatesarterial values usingmathematical models Assumes: Constant value of therespiratory quotient of 0.82 Change in base excess fromarterial to venous blood is 0mmol/lRees SE, Toftegaard M, Andreassen S. A method for calculation of arterial acid–base and blood gas status from measurements in the peripheralvenous blood. Comp Methods Programs Biomed. 2006, Vol 81, 18-25.
    • 29. Validations Respiratorypatients N=40 (55% acuteadmissions) Arterial-calculated pHdifference = -0.001pHunits (95% LoA -0.026 to+0.026) Arterial-calculated pCO2difference = -0.68mmHg(95% LoA -4.81 to +3.45mmHg) Respiratory/ ICU N=103 Arterial-calculated pHdifference = -0.002pHunits (95% LoA -0.029 to+0.025) Arterial-calculated pCO2difference = 0.3mmHg(95% LoA -3.58 to +4.18mmHg)Toftegaard et al. Emergency Medicine Journal. 2009;26:268-72Rees et al. Eur Respir J. 2009;33:1141-7.
    • 30. Validations Emergency dept patients N=148 patients (47 clinical needfor ABG, 101 without) pH can be calculated to within0.02 pH units (95% LoA) pCO2 can be calculated to within4mmHg (0.5kPa)Tygesen et al. Eur J Emerg Med. 2011 Nov 11. [Epub ahead of print]
    • 31. Monitoring over time: ExampleRed=measured arterialBlack dots =calculated arterialBlue dashes=measured venouspH pCO2Courtesy of SE Rees (unpublished)
    • 32. Comments Hard to know how many patients were acidotic orhypercarbic No validation in patients undergoing respiratory supporte.g. NIV Model undergoing commercialisation Add on licence to blood gas machine No app planned at this stage (personal communication)
    • 33. Take home messages pH and bicarbonate probably close enough agreement for clinicalpurposes in DKA, acute respiratory failure, isolatedmetabolic acidosis More work needed in toxicology, shock, mixeddisease
    • 34. Take home messages pCO2 NOT enough agreement for clinical purposes, either asone-off or to monitor change Data suggests venous pCO2 is useful as a screening test Base excess Probably not enough agreement for clinical purposes
    • 35. Take home messages Mathematical modelling approaches might be moreaccurate especially for pCO2 For broad applicability an app/ similar would be morefeasible than integration into blood gas machines More work needed to prove accuracy and precision in highrisk groups
    • 36. Questions?Questions?Questions?@kellyam_jec

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