Blood Gas Recommendations & Problems

Blood Gas & POC Testing Procedural Recommendations: Collection, Sampling & Pitfalls

Critical Care Testing = Whole Blood Analysis ■

Whole Blood Analysis = Many ‘Variables’ need to be ‘controlled’: Variables Include: Include ■ Prolonged contact of serum/plasma with cells ■ ‘Collection-Induced’ Hemolysis ■ Effects of Exposure to Room Air ■ Effects of Evaporation ■ Incorrect Transport/Storage Conditions (inc temperature) ■ Anticoagulants: Type/Amount/Mixing ■ Collection/Preparation/Analysis Issues

Prolonged Contact of Serum/Plasma with Cells • Most Affected Critical Care Tests: (if cells left in contact with serum/plasma): – Glucose – Lactate – K+ – Hb • Blood Gases + Others Analysis (Lytes/Metabolites): – Collect via Syringe; Cannot separate typically – Analysis should be within 10-15 minutes ideally; no more than 30 minutes maximum – No refrigeration recommended – Keep Sample Well-Mixed

Cell Contact with Plasma: Parameter Problems • Affected Parameters: – Glucose: (Glycolysis) • Cells use up Glucose while in tube; lowering Gluc values over time. • Estimated 5 % Decrease/Hour ‘on cells’ – Lactate: • Due to cellular use of Glucose over time, and with limited O2 present: Increase Lactic Acid seen. • Falsely overly high Lact can be seen on samples > 30 min old from collection. – K+: • Samples kept as WB: May miss any Hemolysis present. • Should use BG analyzer that can detect hemolysis. – Hb: • WB is proper sample for correct Hb/Hct testing. • However, proper mixing of WB sample is required to give accurate results. • Samples sitting too long may require excessive time for proper mixing.

‘Collection-Induced’ Hemolysis • Hemolysis: – “The breaking of the Red Blood Cell membrane with the cellular contents being expelled into the plasma”. – May interfere with correct measurement several POC Parameters including: • Potassium, Hb, SO2%, LDH, Billirubin – Effects on ‘Common Tests’ w/ Hemolysis: • K+ = Increased (severely) • Hb = Variable; Often Increased • SO2% = Incorrect results for measured technology.

Hemolysis Causes & Detection • Common Causes of Hemolysis Include: – – – – –

Moisture in the collection tube/syringe Mechanical destruction of cells by device Freezing of sample (ie: Icing during transport) Excessive tourniquet use/time Too vigorous mixing of sample container

• WB Samples vs Serum/Plasma: – Difficult to detect Hemolysis on WB sample • Need to rely on BG instrumentation flagging or excessive K+ value without underlying symptoms

Hemolysis Causes & Detection • Common Causes of Hemolysis Include: – – – – –

Moisture in the collection tube/syringe Mechanical destruction of cells by device Freezing of sample (ie: Icing during transport) Excessive tourniquet use/time Too vigorous mixing of sample container

• WB Samples vs Serum/Plasma: – Difficult to detect Hemolysis on WB sample • Need to rely on BG instrumentation flagging or excessive K+ value without underlying symptoms

Exposure to Room Air • Parameters Affected: – pO2 • Room Air = Higher O2 levels than syringe sample for normal range patients; Lower O2 levels in Room Air for patients receiving O2 • Exposure to Room Air can either Increase or Decrease measured pO2

– pCO2 • Room Air = Lower CO2 levels than syringe sample • Generally exposure will LOWER measured pCO2 value (although not as severe as O2-exposure)

– pH: • Effected by pCO2 changes (will change inverse to CO2)

pO2 Exposure Effects • pO2 Detailed Exposure Effects: – Effects for Normal Range pO2: • Example: If an air bubble is in syringe that is equal to only 10% of total blood volume present = Typical 30 mm Hg O2 change.

– Effects for High pO2 Patients: • Lowering of measured pO2 seen at rate of up to 2 mm Hg/min exposed for pO2’s in range of 300-400 mm Hg.

– Plastic syringes not completely ‘gas-tight’: • Up to 9 mm Hg shift pO2 seen if sample left in Plastic Syringe > 20 minutes.

Evaporation Details • Evaporation vs. Air Exposure: – Evaporation: Referring mainly to non-syringe samples, either in tube or on-analyzer-- Prolonged exposure to air resulting in evaporation of liquid from sample. – Exposure to Air: Referring mainly to syringe samples for gases where sample is mixed/exposed with room air affecting gas values.

Effects of Evaporation • Parameters Most Affected (Evaporation): – Electrolytes: • Longer exposure will have greatest impact on ‘Lytes’ (Na, K, Cl, iCa, HCO3-) • Generally will tend to ‘concentrate’ sample more resulting in HIGHER measured values • Greatest effects on Na+ and Cl- (due to higher values that can be affected more by exposure)

– Metabolites: • Gluc/Lact: If sample separated from cells, effects limited to ‘concentration’ of sample and generally INCREASE in value. • Less of an effect compared to Electrolytes.

– Hb/Hct: • Generally if samples ‘sit’ with air exposure, they tend to ‘settle’ and this results in “two-layer” (plasma & cells) • Sampling from un-mixed sample in either ‘layer’ can result in either Lower or Higher Hb/Hct values.

Transport/Storage Conditions • Samples for BG Analysis: – Not recommended to be on ice • Effects Other Parameters: Negatives: Hb/Hct sampling/mixing & Hemolysis (K+ values) • Icing does help reduce Glycolysis & O2 consumption by cells, but overall the negatives of use out-weigh the positive (Lower Glycolysis – Analysis within 15 minutes of collection • To avoid air contamination & temperature effects • Without Icing (and > 30 min analysis time): pH, pO2, HCO3-, BE = Will DECREASE pCO2 = Will INCREASE – Plastic or Glass syringes acceptable (if run w/in 15 min.) • Glass syringes recommended for longer than 30 min. analysis intervals – Proper Anticoagulants & Proper concentrations must be used (see later slides for details)

Transport/Storage Conditions • Electrolytes/Metabolites/COOx: – If gases not needed: Can collect in Syringe or Evacuated Tube – Can run WB, Serum or Plasma • WB/Plasma acceptable for TAT Considerations • Serum: Sample Handling Issues and Delays affect TAT – WB/Plasma: Anticoagulant Type & Concentration very important for accurate results (see later slides for details) – Icing samples can reduce Glycolysis (Glucose utilization), but this should only be done when not in ‘conflict’ w/ BG-analysis. – Can refrigerate/freeze non-WB samples (air-tight) for re-analysis later – Must avoid air-evaporation effects on main sample and samples on analyzers

Anticoagulants Overview Information • Anticoagulants Overview: – Sodium Heparin/Lithium Heparin: Best for Blood Gases, Chemistries

• Non-Acceptable Anticoagulants (for Gases/Lytes): – Oxalate (often used for Glucose plasma collection)= Major Lytes Binding Problems – Citrate (Coag Use) & Iodoacetate= Major ISE Binding Issues – Na/NH3 Fluoride (Gluc Plamsa Collection) = Problems with ‘ISE Interference’ typically

• Non-Anticoagulant Collection: – Serum Tubes (w/ & w/out separator): • • • •

Lytes & Chemistries OK; Anaerobic required for ICa/IMg. Unacceptable for Gases/pH Unacceptable TAT due to centrifugation required Separator Tubes: Problems w/ K+ measurements possible.

Issues with Different Types of Heparin ■

Acceptable Heparin Types: ■ ■ ■

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Dosage Recommendations: ■ ■ ■ ■

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Sodium (difficult to find; possible interferences) Lithium (most common) NH3 (rare to find) Normal Na+ and Li Heparin concentration should be no more than 15-20 IU/mL ‘Low-Dose’ Syringes Available w/ Heparin as low as 7 IU/ml. Lower dose syringes more prone to Clotting (must MIX well) “Balanced Li Hep” recommended for Creat testing ■ Use of Normal LiHep can cause decreased Creat Values

Use Dry-Heparin Pre-Coated Syringes if Possible: ■

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If adding proper amount of blood will result in expected dilution and IU final concentration Liquid Heparin (added manually) is unreliable in determining final IU concentration

Other Issues with Heparin Use ■

Under-filling can result in Heparin concentrations of up to 100 IU/mL ■

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Use of Na+ Heparin Syringes: ■

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Excess Na+ Heparin may elevate Na+ results (dependent on final concentration; usually IU concentrations up to 15 IU have little effect.)

Heparin can also bind iCa & iMg ■

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Especially common with Liquid Heparin, but can also occur with Dry Heparin

Especially true for Na+ Heparin

Dilution Errors for ‘Other’ Tests: ■

Possible if excess Liquid Heparin is present

Heparin UseGlass & Plastic Syringes •

Glass containers require more heparin than plastic: – Coag factors & platelets activate quicker on contact w/ glass versus plastic (increased heparin compensates for this). – Not ideal for measurements of iCa and iMg (plastic better).

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Specific IFCC Recommended Maximum Heparin Levels: (Note: IU/ml denotes final ‘in-syringe’ concentration of heparin to blood). – Glass: w/ Dry/Liquid Heparin = 40 - 60 IU/ml – Plastic: w/ Dry/Liquid Heparin = 12 - 50 IU/ml – For Samples for iCa/iMg Determinations: < 15 IU/ml (plastic) • Best to use “Low-Dose’, “Ca-Titrated” or “Balanced-Hep” Tubes.

IFCC= International Federation of Clinical Chemists

Interferences By Heparin •

Effects on- Na+ & BUN/Urea: – Na+ Heparin Type: • Up to 15 IU/ml heparin shows no effect. • > 1 mmol/L increase after 15 IU limit. – Li-Heparin: Type: • Little effects up to 70 IU/mL • Dilution effects (esp. with Liquid Heparin)

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Effects on pH/HCo3-Bicarbonate/Base Excess: – No effect up to 50 IU/ml • Not usually a problem using dry-heparin • Only major effects when using liquid heparin manually introduced – Increments of 100 IU/ml show the following decreases: • pH: 0 - 0.004 pH units • HCO3-: 0 - 0.3 mmol/L • BE: 0 - 0.3 mmol/L

Additional Interferences By Heparin • Effects on iCa/iMg: – Decreased Values Seen with Increased Heparin: • Due to Binding to Heparin by ‘Chelation’.

– Up to 4 IU/ml heparin: effect is < 0.01 mmol/L – For every 100 IU/ml heparin: effect is 0.13 mmol/L decrease – At about 20 IU/ml a 3.5 % decrease will be seen – Additional Problem: “Dilution Effect”: • With Heparin Concentrations > 100 IU/ml • Most values will be lower....

Anticoagulants Dilution Effects • Parameters Affected: – Electrolytes, HCO3-, CO2, Hb/Hct, Gluc, Lact, BUN: • Will Decrease due to dilution (> 100 IU/ml concentrations) • pCO2 Details: - 0.27 kPa (- 2.0 mm Hg)

– PO2/SO2: • Will increase because PO2 of heparin solution is about 20 kPa (150 mm Hg) • pO2 Details: + 0.53 kPa (+4.0 mm Hg)

– pH: Little/No Effects Due to Dilution.

Preventing Dilution Effects • To Keep Effects of Dilution Minimized: – Dead space of syringe/tube should not exceed 5 % of blood volume to be drawn. – Use primarily DRY-Heparin if possible • Use pre-coated syringes with minimum fixed heparin

– Effects of dilution primarily on plasma phase so electrolytes will be most affected • Esp. for tests with tight 'normal ranges': Na, iCa,iMg)

Sample Collection Review ■

Blood Gases: ■ ■

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Patient should be in steady state of ventilation If on Ventilator – (if possible): Settings should be unchanged for 30 min. prior to collection Collection must be anaerobic Indwelling catheters/A lines may be used for sampling

General Collection Notes: ■ ■

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In-line catheters must be thoroughly flushed before sampling A volume equal to 3 x “dead space” must be withdrawn prior to collection to guard against contamination Heparin drips should be stopped at least 30 min prior to collection and the line should also be flushed

Syringe Use/Collection ■

Immediately after collection, check for and expel any air bubbles and replace needle cap ■

Also expel any air bubbles trapped in syringe prior to sample analysis: ■

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Collect a volume of blood that is 20 x dead space volum Mix syringe by rolling in your hands a minimum of 10 times prior to analysis to suspend cells ■

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With syringe needle up onto gauze etc.

Analyze BG syringe samples promptly (under 15 minutes)

Ideal collection device for ABG’s: ■ ■

1,3,or 5 ml self filling, plastic disposable syringe Pre-filled with the appropriate type of lyophillized (dry) heparin

Capillary Tube Use/Collection • ■

Capillary Samples:

Shows characteristics of both arterial and venous samples. • Subject to room air contamination if not collected properly •

Capillary Collection Information: ■ ■ ■ ■ ■ ■

Prior to collection >>Warm skin at the site to 39 - 42 o C for 3 min (if possible) After making a single deep puncture, remove the first drop of blood and allow the blood to flow rather than squeezing it out Place the tip of the capillary into the blood drop Fill capillary without introducing air bubble Seal the end that was in the blood immediately (cap or wax) Add a metal mixing bar/flea from the other end of the tube and seal this end also

Capillary Tube Prior to Analysis

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Be sure to use a capillary with pre-coated (lyopholized) Heparin ■

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Same final IU/ml heparin concentrations apply

For capillaries immediately before analysis: ■

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Mix by dragging a magnet across the length of the tube 4-5 times Remove mixing flea Pass a wire stylette through the sample (check for clots) Use a Clot-Catcher on analyzer as final safety measure

Capillary vs. Syringe Samples ■

pH & pCO2 Results: ■ ■

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pO2 Results: ■

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Capillary samples closer to venous values

Potassium Values: ■

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Generally correlate well Capillary-Arterial Little differences seen; clinically insignificant

May be higher in capillary values due to Hemolysis

Others: ■

Generally most other POC/critical tests correlate well between capillary & syringe (arterial) samples.

Sampling Sites/Details • Blood Gases:

– Arterial Preferred: (Radial, Brachial, Femoral, Scalp, Umbilical) Capillary: (Scalp, Heel, Finger) – {Anaerobic concerns....} – Mixed Venous: (best site = Pulmonary Artery) Venous: Multiple sites; easiest collection; – poor O2

• Electrolytes/Chemistries:

– Arterial & capillary blood acceptable. – Venous Blood usually chosen (not acceptable for pO2/SO2) – Use of tourniquet must be kept to < 2 minutes (hemostasis). – No muscular activity at site of collection.

Typical ‘Expected’ Values (Main Gas Parameters) ■

Note: Values listed are for reference only in this presentation. Typically institutions will determine their own ‘Normal Values’ based on their location and population.

Test

Arterial

Capillary

Venous

pH

7.37 – 7.44

7.35 – 7.45

7.33 – 7.43

pO2

83 – 108 mm Hg

35 – 80 mm Hg

30 – 50 mm Hg

pCO2

35 – 45 mm Hg

35 – 50 mm Hg

38 – 50 mm Hg

SO2%

95-99 %

65 – 85 %

60 – 85 %

HCO3-

21– 28 mmol/L

22– 29 mmol/L

22– 29 mmol/L

Oxygenation: Assessing Oxygen Binding Oxygen Transport Determination •Definition - Oxygen Saturation (SO2 %): Amount of Hb in the blood as a percentage of the total amount of Hb bound with O2. Used to determine the effectiveness of O2 therapy and transport.

Determining Oxygen Binding to Hb: • Measurement Methods: (Direct Measurement): • (Using the difference in the wavelengths of maximum absorbance for oxyhemoglobin and de-oxyhemglobin; optical determination.)

– Trend: Pulse Oximeters:

• Best for TREND Monitoring Only • Subject to many interferences- Patient Circulation; Thickness of Skin; Movement; Sensor Contact with Skin; • Follow-up to low values = Confirmation BG w/ SO2%

– Simple: Nova BG Analyzers: 3 Wavelength Reflectance: • • • •

Accounts for O2Hb and HHB fractions in sample Not calculated; no problems with Pulse-Ox Interferances Done simply with regular BG sample in same flowpath No extra cost or consumable items to get result

– Complex: CO-Oximeters (Multi-Wavelength): • Provide direct measurements of normal & abnormal Hb fractions. • Reports variant of SO2%……..………FO2Hb

Determining Oxygen Binding to Hb: • Calculated Methods (Indirect): – Most BG Analyzers: Calculate O2-Sat: – Utilize pO2, pH, HCO3-, and input/calculated Hb value.

– Problems with Calculated Results: • Assumes "normal" O2 dissociation curve. Factors Affecting O2 Curve: (all may be abnormal in ‘sick’ patients) – Patient Temperature – pCO2 Value; HCO3– THb of Patient – pH Value

• Assumes all Hb is O2Hb (100% able to bind) – In truth, abnormal hemoglobin fractions may be present – Over-estimates SO2% with abnormal fractions possible

Fractional Oxyhemoglobin • Fractional OxyHemoglobin (FO2Hb):

– Amount of Hb in blood expressed as a fraction of the total amount of O2Hb available. Used to determine the effectiveness of O2 therapy. – Measured on some Blood Gas Analyzers similarly to SO2 %. – Usually must be determined using a full (multiple) wavelength Spectrophotometer – Comparing FO2Hb and Measured SO2% (Simple) : – FO2Hb = [O2Hb] / ([O2Hb]+[HHb]+[COHb]+[MetHb]) – SO2 % = [O2Hb] / ([O2Hb]+[HHb]) x 100 –

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Usually: FO2Hb (decimal fraction)

˜ SO % (integer percent) 2

Dangers in Use of Calculated SO2 vs. FO2Hb or mSO2%: – May overestimate true oxygen saturation in cases where abnormal hemoglobins (e.g. COHb, MetHb, HHb, etc.) are present

mSO2% as a Stand-Alone Parameter • mSO2% is frequently all that is needed for oxygen status assessment….. – It is EASY to run (run in same flowpath when doing ABG sample-Nova Analyzer) – No extra costs to run.

• Can rely on mSO2 (Reflectance Method) – If….The presence of COHb/MetHb has been ruled out by: • Clinical evaluation – No history of smoking or smoke inhalation – No evidence of metHb • Direct measurement using CO-Oximeter

• The beginning & the end: – If the sum of COHb and MetHb is less than 3-4% then SO2% gives adequate information on O2-Hb relationship

COHb & MetHb Populations In Most Parts of the World: The “In-Health” (for Oxygenation) Population Represents between 80 - 90 % of patients coming into a typical Emergency Dept, and between 40 - 70 % of the patients admitted ‘in-house’. (Except in areas with high industrial pollution, high risk workers, or toxic heating practices.)

In health, where there is minimal COHb and MetHb, SO2% and FO2Hb can be used interchangeably. Therefore, routine COOx screening of all patients is NOT medically necessary.

Quality Control Usage in POCABG Testing A Brief OverviewThings to Consider….

“QC”: What Is It? • QC = Quality Control Material: – Aqueous, protein-based, or blood-based solutions. – Usually pre-assayed for specific analyzers • Mean and Range Limits usually provided – Best materials to use are provided by analyzer manufacturer – Used to confirm proper system performance and accuracy of results – Designed to ‘mimic’ blood analysis – System should NOT be used if QC is out of limits – Proper system ‘calibration’ does NOT mean proper accuracy of results….

“QC”: When Should It Be Run? • How Often? – Local Markets Set Their Own Regulations • General Rule: QC Analysis as often as necessary to assure the user that his instrument is working….

– USA & European Markets… • The ‘Regulations’ for Blood Gases: Each 8 Hours of analyzer use with 3 levels within a 24 hour period. • Chemistry & HH Tests: 2 Levels each 8 hours of Analyzer Use.

“QC”: What Types/Materials? • What Materials To Use?:

Blood Gas Units

– Usually an AQEUOUS Material. • Most companies offer Ampoule Solutions (multiple levels)

– Nova Biomedical:

Unique Offerings….

• Typical Ampoule Controls OR • On-Board ‘Auto-QC’ Packs (multi-level packs) – Bagged QC Solutions (tonometered controls) – 35 Day Typical Use Life/Pack – Available on CCX and pHOx Product Lines

Nova External & ‘Auto’-QC Advantages/DisadvantagesExternal Versus Auto-QC: • Auto-QC: Advantages: 1. 2 3. 4. 5. 6.

Easier to Use Unlimited ‘Analysis Times’ No Operator Intervention Less temperature sensitive Guaranteed QC Compliance Use all bag QC (no waste)

Disadvantages: 1. Must run min 3 QC/Day for cost 2. Subject to more shipping effects

• External-QC: Advantages: 1. More economical for low QC analysis/day 2 Limited Shipping effects 3. ‘Blood Gas Standard’

Disadvantages: 1. 2. 3. 4. 5.

Requires Operator Intervention More staff time required Single Use Only per Ampoule Temp Sensitive to RT changes No Guarantee for QC Analysis

If You Do Not Run Controls…?? • You Run a Risk….. – Calibrations alone do NOT completely assess analyzer results – Changes in sensor or system operations can occur that can affect patient results – QC samples can indicate drifts or trends in analyzer results – QC samples can indicate ‘hidden’ analyzer problems not seen with calibration alone

• This is true for all Blood Gas & Critical Care Testing Analyzers…. SO BEWARE!!

Nova Quality Assurance Program - “QAP”

Allows Nova QC Users to Submit Their QC Data & Be Compared to Other Users of Similar Systems Intra-Laboratory Comparison A ‘free’ service to all active Nova analyzer users

Nova Quality Assurance Program - “QAP” What Is It? A Quality Assurance Program compares the performance of similar instruments by having all users sample the exact same material. Each group using the same Control Material ( same lot no.) submits data on a Monthly basis. Each member of the group (Peer Group) receives a monthly report showing the performance of their unit relative to the rest of the group. Questionable performance is followed by contact from the manufacturer’s support specialist with suggestions on improving the performance of their unit.

Nova Quality Assurance Program - “QAP” Why Consider It? There is NO COST to be in this program. (Customers only need to purchase a minimum # of Nova-Qc material/year).

QC-data easily collected & sent to Nova (Customer only send ‘statistics’ from analyzer QC; can send by e-mail/fax/mail).

Customers get the ‘manufacturers validation of performance’. Customers can see how their unit performs relative to others using the same model(s). (Comparison range limits may vary from original insert sheet limits; improve validation).

Additional support for any accreditation audit or inspection.

QAP Input Sheet: Summary Statistics

Easy Data Input from Analyzer Print-out of QC Data

QAP Web Site qap.novabio.com Allows Nova QC Users to Submit and Review Quality Control Data Online: Intra-Laboratory Comparison

A ‘free’ service to all active Nova analyzer users

Data Entry Summary Data Entry

Members who have data management systems or can calculate their Mean and Standard Deviation may use a Summary Data Entry Form. Using this form, data is submitted only once a month.

In Summary…. • Consider Many Factors that Affect Sample Results: – Sample Handling – – – – –

Anti-Coagulants Pre-Analysis Errors Room Air Exposure/Evaporation Temperature & Storage Mixing of Sample & Sample Separation

• Consider Using Measured Oxygen Saturation Assessment: – More Accurate Results – Not Affected by Patient Condition like Calculated Value

• Perform Proper Quality Control on Analyzers: – Verify Sensors Performance – Calibrations alone do NOT completely assess analyzer results – Legal Requirement in many markets now.