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Errors that Affect Arterial Blood Gas Results

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Errors that Affect Arterial Blood Gas Results

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  1. Errors that Affect Arterial Blood Gas Results Carl Mottram, RRT RPFT FAARC Director - Pulmonary Function Labs & Rehabilitation Associate Professor of Medicine - Mayo Clinic College of Medicine

  2. Arterial Blood Gases (ABG’s) • Reflect oxygenation • Adequacy of gas exchange in the lungs • Acid - base balance CO2 pH O2

  3. Garbage in, Garbage out!

  4. ABG Laboratory Standards and Guidelines • Clinical and Laboratory Standards Institute (CLSI) • C46-A2 Blood Gas and pH Analysis and Related Measurements (2009) • H11-A4 Procedures for the Collection of Arterial Blood Specimens (2004)

  5. ABG Laboratory Standards • AARC Clinical Practice Guidelines • In-Vitro pH and Blood Gas Analysis and Hemoximetry (1999); currently in review • Sampling for Arterial Blood Gas Analysis (1999) • ATS Pulmonary Function Management and Procedure Manual (2005)

  6. ABG Laboratory Standards

  7. CLSI’s Path of Workflow

  8. CLSI’s - Path of Workflow • What processes have the highest rate of error? • Pre-analytical errors still account for nearly 60%-70% of all problems occurring in laboratory diagnostics • Nine steps – G. Lundberg • “the brain to brain cycle”

  9. Clinical Chemistry 53:7 1338–1342 2007

  10. Pre-analytical Errors • Personnel • Patient identification and preparation • Sample collection, container, and procedure • Sample handling, transport, and storage

  11. Pre-analytical - Personnel • Job qualifications • Job descriptions • Orientation • Training • Competency assessment • Continuing education • Performance appraisal

  12. Pre-analytical - Patient and sample identification • Two identifiers or electronic barcode • Sample label • Name and medical number (birth date or personal identification number) • Date

  13. Pre-analytical – Patient Variables • Patient’s full name • Identification number • Birth date/age • Location of the patient • Date and clock time of sampling

  14. Pre-analytical – Patient Variables • Body temperature • Clinical indication • Respiratory rate • Name or initials of person who obtained the specimen • Name of physician requesting the test.

  15. Pre-analytical – Patient Variables • Ventilatory status (e.g. spontaneously breathing or mechanically supported) • Mode of ventilation (i.e., pressure support) or delivery device (i.e., cannula or mask) • Site and manner of sampling • arterial puncture, capillary puncture, or indwelling catheter • Position and/or activity • Upright/supine; rest/exercise

  16. Pre-analytical - - Sample collection, container, and procedure • Common • Radial artery • Dosrsalis pedis • Brachial • Femoral • Uncommon • anterior peroneal, axillary and superficial temporal

  17. Pre-analytical - ABG Sample collection • Preferred site - Radial • Superficial and provides rich collateral circulation • Collateral can be evaluated by the modified Allen’s test E.V. Allen, Thromboangiitis obliterans: methods of diagnosis of chronic occlusive arterial lesions distal to the wrist with illustrative cases. Am J Med Sci (1929), pp. 237-244.

  18. Pre-analytical - ABG Sample Collection • Syringe • Dry lithium heparin • Engineered sharps protection (one-handed) • 20-25 gauge short-bevel needles (radial)

  19. Pre-analytical – Sample • Sample error • Failure to observe and record • Contamination of sample • Room air (bubbles) • Venous blood mixing • Flush solution if drawn from an arterial line • Heparin, if using liquid • Delay in analysis • ICU audit showed that 40% of the samples had air or froth and that 4% of sample had a delay in analysis Woolley A. et al Journal of Critical Care. 18(1):31-7, 2003 Mar.

  20. Pre-analytical – Sample • Sample error: Failure to observe and record • Environmental Factors • Suctioning • Recent ventilator changes without crisis • Activity and positioning • Failure to record appropriate information • FIO2, mode of delivery, ventilator management, patient activity • Woolley A. et al Journal of Critical Care. 18(1):31-7, 2003 Mar.

  21. Pre-analytical – Sample • Sample Error: Contamination by room air • Partial pressures of both PaO2 and PaCO2 will migrate towards room air: • PaO2 greater than ~100 torr will decrease • PaO2 less than ~100 torr will increase • PaCO2 greater than 40 will decrease • PaCO2 less than 40 will increase • pH will follow PaCO2 change • Woolley A. et al Journal of Critical Care. 18(1):31-7, 2003 Mar.

  22. Pre-analytical – Sample • Sample Error: Contamination by venous blood • Know normal venous blood values • pH=7.38 ; PvO2=40 torr, PvCO2=46 torr, SvO2=75% • Small amount of venous blood can make a significant difference (esp in PaO2) • Cross check • Patient’s clinical status & ABG picture • PaO2 & SaO2 vs. SpO2

  23. Pre-analytical – Sample • Sample Error: Hemolysis of the sample • Study demonstrated 1.2% in adult patients and 8.5 in pediatric of ABG samples with various degrees of hemolysis Clin Chem Lab Med 2011;49(5):931–932

  24. Pre-analytical – Sample • Sample Error: contamination by heparin • Excessive heparin will drop PCO2 values • Anticoagulant • Lyophilized lithium heparin is recommended • If liquid heparin (sodium or lithium, 1,000 units/mL of blood) is used, excess heparin (all except that filling the dead space of the syringe and needle) should be expelled and a blood sample of 2-4 mL be drawn

  25. Pre-analytical – Sample • Sample Error: Delay in analysis • Cellular process • Consumes O2 & generates CO2 • Quantitative Effect • @ 37 C in 1 hr • pH fall 0.05 units • PaCO2 5 torr • PaO2 fall depends on initial level • if high (>300 torr) will    precipitously • if lower (100 torr) will    20 torr/hr • if low (< 60 torr) will  but < 20torr/hr

  26. Pre-analytical – Sample • Sample Error: Delay in analysis • Normal RBCs not responsible for significant metabolism • Metabolic activity predominantly • Leukocytes & reticulocytes • Example: • WBC=276,000 cells/mm3 PaO2 from 130 to 58 torr in 2 minutes • WBC=450,000 cells/mm3 PaO2 to 0

  27. Pre-analytical – Sample • Current guidelines related to icing sample • If blood gas analysis will not be performed within 30 minutes after specimen collection, ice the sample • Procedures for the Collection of Arterial Blood Specimens: H11-A4 • Specimens held at room temperature must be analyzed within 30 minutes of drawing; iced samples should be analyzed within 1 hour. • AARC’s CPG Sampling for Arterial Blood Gas Analysis

  28. Analytical • Follow manufacturer’s instructions carefully when introducing sample • Improper introduction can cause erroneous results, especially from air bubbles, clots, or leaks • Repeat analysis if; • Inconsistent with patient’s past results and/or condition • Internally inconsistent (pH, CO2, HCO3) • At the extreme range of expected values

  29. Analytic • Operator error • Failure to label sample • Equipment malfunction • Analysis with out-of-control instrument • QC material and Levey-Jennings Plots • Failure to mix an sample • Gently rotate for a minimum of 2 minutes • Can raise the pH of a sample by 0.11 units • Calculated SaO2 and CaO2 • Erroneous in the presence of dyshemoglobins

  30. Analytical Interferences • PO2: nitrous oxide, halothane, isoflurane • Interferences with Co-oximetry • Sulfhemoglobin • Methylene Blue • Fetal hemoglobin • Turbidity: hyperlipemia

  31. Post - Analytical • Comment on the quality of the specimen, transportation or delays in analysis • Accurate transcription (review process) • Meeting the expectations of the customer • Satisfaction surveys

  32. Post - Analytical • Post-analysis sample management (disposal) • Posting data to the record in a timely fashion (i.e. turn-around time) • Validating EMR report with lab data

  33. Quality Control in the Lab • Clinical Laboratory Improvement Act 1988 • Law!! • Enforced by the CDC, CLIAC, and CMS

  34. Quality Control in the Lab • Daily QC with Levy-Jennings plots • John Westgard PhD • www.westgard.com

  35. Westgard’s Rules for Quality Control • Rule 1: (1 : 2s).......One Value outside ± 2 s.d. • No action required, still considered “in control” • Rule 2-6 considered “out of control” corrective action required • Rule 2: (1 : 3s).......One value outside ± 3 s.d. • Rule 3: (2 : 2s).......Two consecutive values outside ± 2 s.d. • Rule 4: (R : 4s).......Range from highest to lowest values > 4 s.d. • Rule 5: (4 : 1s).......Four consecutive values outside ± 1 s.d. • Rule 6 : (10 x).......10 consecutive values falling on one side of the mean

  36. Levy-Jennings Plot: “In control”

  37. Levy-Jennings Plot: Rule 1 • Rule 1: (1 : 2s).......One Value outside ± 2SD • No action required, still considered “in control”

  38. Levy-Jennings Plot: Rule 2 • Rule 2: (1 : 3s).......One value outside ± 3 SD

  39. Levy-Jennings Plot: Rule 3 • Rule 3: (2 : 2s).......Two consecutive values outside ± 2SD

  40. Levy-Jennings Plot: Rule 4 Rule 4: (R : 4s).......Range from highest to lowest values > 4SD

  41. Levy-Jennings Plot: Rule 5 • Rule 5: (4 : 1s).......Four consecutive values outside ± 1SD

  42. Levy-Jennings Plot: Rule 6 • Rule 6 : (10 x).......10 consecutive values falling on one side of the mean

  43. CLSI’s Quality Systems QSE: Assessment • College of American Pathologist • Inter-laboratory comparison – Blinded samples • Inter-laboratory comparison – Daily QC materials (provided by vendor) • Institutional comparison – Other lab within the same institution

  44. Selection process Installation Calibration log Maintenance log Troubleshooting log Service and repair log Training Documentation and review CLSI’s Quality Systems QSE: Equipment

  45. CLSI’s Quality Systems QSE – Customer Focus

  46. What’s these mean to you? • Any shortfall in the “Path of workflow” can effect the quality of the test results • Practitioners need to be knowledgeable about the current quality models as they relate to ABG’s

  47. Questions?