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
Arterial Blood Gases (ABG’s)
• Reflect oxygenation
• Adequacy of gas exchange in the lungs
• Acid - base balance
CO2
pH
O2
Garbage in, Garbage out!
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)
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)
ABG Laboratory Standards
CLSI’s Path of Workflow
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”
Errors in the Total Test Process
23%
15%
62%
Pre-analytical
Analytical
Post-analytical
Clinical Chemistry 53:7 1338–1342 2007
Pre-analytical Errors
• Personnel
• Patient identification and preparation
• Sample collection, container, and procedure
• Sample handling, transport, and storage
Pre-analytical - Personnel
• Job qualifications
• Job descriptions
• Orientation
• Training
• Competency assessment
• Continuing education
• Performance appraisal
Pre-analytical - Patient and sample
identification
• Two identifiers or electronic
barcode
• Sample label
•Name and medical number (birth
date or personal identification
number)
•Date
Pre-analytical – Patient Variables
• Patient’s full name
• Identification number
• Birth date/age
• Location of the patient
• Date and clock time of sampling
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.
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
Pre-analytical - - Sample collection,
container, and procedure
• Common
•Radial artery
•Dosrsalis pedis
•Brachial
•Femoral
• Uncommon
•anterior peroneal,
axillary and superficial
temporal
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.
Pre-analytical - ABG Sample Collection
• Syringe
•Dry lithium heparin
•Engineered sharps
protection (one-handed)
•20-25 gauge short-bevel
needles (radial)
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.
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.
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.
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
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
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
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 < 20 torr/hr
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
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
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
• Operator error
Analytic
• 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
Analytical Interferences
• PO2: nitrous oxide, halothane, isoflurane
• Interferences with Co-oximetry
• Sulfhemoglobin
• Methylene Blue
• Fetal hemoglobin
• Turbidity: hyperlipemia
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
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
Quality Control in the Lab
• Clinical Laboratory
Improvement Act
1988
•Law!!
•Enforced by the
CDC, CLIAC, and
CMS
Quality Control in the Lab
• Daily QC with LevyJennings plots
• John Westgard PhD
• www.westgard.com
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
Levy-Jennings Plot: “In control”
ABG QC
PaO2
63
Series1
58
+2 STD
-2 STD
53
48
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Days
Levy-Jennings Plot: Rule 1
ABG QC
PaO2
63
Series1
58
+2 STD
-2 STD
53
48
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Days
Rule 1: (1 : 2s).......One Value outside ± 2SD
No action required, still considered “in
control”
Levy-Jennings Plot: Rule 2
ABG QC
PaO2
63
Series1
58
+2 STD
-2 STD
53
48
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Days
•Rule 2: (1 : 3s).......One value outside ± 3 SD
Levy-Jennings Plot: Rule 3
PaO2
ABG QC
64
62
60
58
56
54
52
50
48
Series1
+2 STD
-2 STD
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Days
•Rule 3: (2 : 2s).......Two consecutive
values outside ± 2SD
Levy-Jennings Plot: Rule 4
ABG QC
PaO2
63
Series1
58
+2 STD
53
-2 STD
48
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Days
Rule 4: (R : 4s).......Range from highest to lowest
values > 4SD
Levy-Jennings Plot: Rule 5
ABG QC
PaO2
63
Series1
58
+2 STD
-2 STD
53
48
0 1
2 3 4
5 6 7
8 9 10 11 12 13 14 15
Days
•Rule 5: (4 : 1s).......Four consecutive values outside
± 1SD
Levy-Jennings Plot: Rule 6
ABG QC
PaO2
63
Series1
58
+2 STD
-2 STD
53
48
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
Days
•Rule 6 : (10 x).......10 consecutive values falling
on one side of the mean
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
CLSI’s Quality Systems
QSE: Equipment
• Selection process
• Installation
• Calibration log
• Maintenance log
• Troubleshooting log
• Service and repair log
• Training
• Documentation and
review
CLSI’s Quality Systems
QSE – Customer Focus
Knowledge and Technical Skills
Called-in for Scheduled Appt. Time
25
25
20
20
15
15
Routine Lab
Special Lab
Routine Lab
Special Lab
10
10
5
5
0
0
Prior to
On-time
30 mins late
1 hour late
>1 hr late
Excellent
Very good
Good
Fair
Poor
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
Questions?