We all go through it. It is almost a rite of passage for those responsible for arterial blood gas (ABG) laboratories. What is it? It is the stress we endure prior to our laboratory’s inspection. Whether it is the College of American Pathologists (CAP), The Joint Commission, or the Clinical Laboratory Improvement Amendments (CLIA) team coming to town, we check and double check our policies and procedures to make sure we have our “ducks in order.” A key component to any preparation process is making sure we are aware of and understand the newest Clinical and Laboratory Standards Institute (CLSI) guidelines. Why? Because many of the inspector’s checklist items are based on CLSI recommendations. There are three CLSI guidelines that are written specifically for ABG laboratories: H11-A4, Procedures for the Collection of Arterial Blood Specimens1; H4-A6, Procedures and Devices for the Collection of Diagnostic Capillary Blood Specimens2; and C46-A2, Blood Gas and pH Analysis and Related Measurements.3 We have been involved in CLSI for years, serving in a variety of committee and leadership roles, but certainly one of our charges is to make sure these ABG guidelines are reviewed by respiratory care practitioners. These guidelines routinely go through the revision process, the latest being C46-A2, which was just published in 2009. We will briefly review the highlights from these documents to familiarize you with their content and, we hope, entice you to examine them more thoroughly.
Arterial Blood Specimen Collection
The collection of arterial specimens is a core competency for respiratory therapists. CLSI published the first proposed standard for the collection of arterial blood specimens in 1980. The first approved edition was published in 1985 and has been updated over the years with the fourth edition (H11-A4) published in 2004.1 Each of these documents has involved the expertise of respiratory therapists. The standard focuses on the quality system essentials (QSEs) specific to arterial sample collection and the path of workflow. The primary focus is to address the collection of whole blood specimens for blood gas, electrolyte, and metabolic determinations. The appendices include multiple illustrations that are helpful in the instruction of both students and respiratory therapists.
Quality System Essentials
A key to the CLSI’s portfolio is HS1-A2, A Quality Management System for Health Care,4 and, although it is not the focus of this article, an introduction is warranted. This guideline describes an overall quality system model that includes the path of workflow concept and quality system essentials. In any quality system, one needs to look at all aspects of the path of workflow, which in the laboratory means we need to assess the preanalytical, analytical, and postanalytical process. In each of these phases of the work performed are quality system essentials. The 12 QSEs function as the building blocks that are necessary to support any laboratory’s path of workflow.
The specific QSEs noted in CLSI’s Procedures for the Collection of Arterial Blood Specimens guideline are: personnel, process control, process improvement, and documents and records. In the QSE Personnel, a process should exist for training of new and existing employees. Collection of arterial specimens is generally a competence that should be assessed annually. Changes in procedure or identified training needs should prompt an update for existing employees.
One aspect of the process control QSE relates to interferences that need to be considered. Multiple substances have the potential to interfere with the measurement of blood gases, electrolytes, and other metabolites. Understanding these interfering substances related to the measurement and equipment is a critical element of the training procedures. Examples of known substances include ice (cooling), heparin, sodium thiopental, dopamine, ethanol, isoniazide, and sodium fluoride. The guideline reviews each interfering substance and potential impact on blood gases, electrolytes, glucose, and lactate results.
|Table. H11-A4 Procedures for the Collection of Arterial Blood Specimens.|
Documents and records must address the test request form. In order to have a meaningful interpretation of the results reflecting the patient’s condition at the time of specimen collection, multiple pieces of information should be present. Additional information may be required by regulatory or institutional policies. Examples of data to collect include patient’s full name, identification number, date and clock time of sampling, clinical indication, oxygen delivery, and mechanical ventilation parameters.
A periodic assessment of the quality system should be performed, and improvements in process made as appropriate. Quality indicators across the path of workflow can be identified and monitored (Table). The information from these indicators will drive improvement activities or changes in process.
Path of Workflow
The ABG laboratory’s path of workflow includes test ordering, patient preparation, selection of the site for arterial puncture, equipment, procedure, handling and transport of the specimen, and specimen receipt and processing. Attention to the details in each of these areas is key to preventing preanalytical errors. Test ordering should be consistent with institutional polices and address all components required on the test request form. Correct patient identification is essential and is addressed in the CLSI document, Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture.5
Patient assessment and clarification of the clinical indication is a fundamental skill particularly important to respiratory therapists. Attention to this element is a primary preventive strategy to eliminate preanalytical error. All precollection conditions should be confirmed prior to specimen collection. Generally, 20 to 30 minutes of steady state breathing on the required Fio2 is recommended prior to sample collection. Documentation as defined by institutional policy and best practice should be included on the requisition form. Explanation of the procedure to the patient is completed in a pleasant and reassuring manner.
Selection of the site for the arterial puncture includes assessment of collateral blood flow, accessibility and size of the artery, and periarterial tissue. The CLSI document clearly outlines equipment required to collect an arterial specimen. Hazards of the procedure include vasovagal response, arteriospasm, hematoma, thrombosis, and embolism. Regardless of the frequency of the hazard, each therapist should be well informed in preventive techniques, recognition, and treatment of each. Procedures for arterial punctures, arterial cannulation, and collection from arterial lines are reviewed in detail.
Handling and transport of the arterial specimen is another opportunity for respiratory therapists to prevent preanalytical error. The use of a coolant and impact on results are imperative to understand. If a specimen is analyzed within 30 minutes, a plastic syringe is recommended. The standard and best practice is to transport the specimen at room temperature and analyze the specimen. The specimen should not be cooled.1,3 If the analysis is delayed longer than 30 minutes, the specimen should be immersed in a coolant after collection and glass syringes are recommended. This should be the exception to normal practice.
Collection of Diagnostic Capillary Blood Specimens
H4-A6, Procedures and Devices for the Collection of Diagnostic Capillary Blood Specimens,2 is a document addressing the collection of capillary blood specimens. It was initially published in 1977, with the most recent update in the sixth edition published in 2008. The standard reviews all components of the path of workflow, including site selection, collection procedure, handling capillary tubes, and identification and labeling. It also addresses the devices and analyte variations between skin puncture and venipuncture specimens. Statistical and clinical differences have been reported between skin puncture and venous blood in the concentrations of glucose, potassium, total protein, and calcium. All but glucose has been found to be lower in skin puncture blood. As respiratory therapists appreciate, there are significant differences between the composition of skin puncture blood and specimens collected by arterial puncture.
The potential sites for collection for infants less than 1 year of age include the lateral or medial plantar surface of the heel. A heel puncture must not exceed 2.0 mm. A specific procedure should be used for arterialization of the site. A warm, moist towel or other warming device is used to cover the site for 3 to 5 minutes at a temperature that does not exceed 42°C. This procedure will increase the blood flow sevenfold. It does not burn the skin and will result in insignificant changes for routinely tested analytes with the exception of Po2. The Po2 is expected to be lower in the capillary sample. Low blood flow and high Po2 will increase the difference between the capillary sample and an arterial puncture sample. Engineering controls such as using plastic tubes and work practice controls minimize risk to the health care personnel collecting the specimen. Respiratory therapists obtaining capillary blood specimens should complete a review of the standard as part of training and whenever updates are available.
C46-A2, Blood Gas and pH Analysis and Related Measurements3 was updated and published earlier this year. We served as advisors to the writing committee for this revision. It has a comprehensive review of the concepts and definitions and would be a great reference for your staff. If they do not know the definition of p50, they can find it in the guideline, and they can also find the difference between “p50 standard” and “p50 actual.” This guideline also covers preanalytical considerations, including sampling, which overlaps some of the recommendations from the collection guideline H11-A4, but it is certainly applicable to the analysis process. This section expands on the recommendation of using plastic syringes that are kept at room temperature and analyzed within 30 minutes, by noting that samples collected for special studies (eg, shunt studies) should be analyzed within 5 minutes. The guideline emphasizes that, during the analysis, manufacturer’s instructions should be carefully followed when introducing a sample into the instrument. Incorrect introduction of a sample can cause erroneous results, especially by contamination from air bubbles. The samples should also be repeated if any of the following conditions exist:
- the results are inconsistent with the patient’s past results and/or conditions;
- the results are internally inconsistent (eg, the sum of Po2 + Pco2 >150 torr with the patient breathing room air);
- values are at the extremes of expected (eg, pH <7.2 or >7.6).
There is an excellent review of analytical interferences, specifically listing interferences for all variables measured. As an example, interference of Po2 sensors with anesthetic gases has been reported. Nitrous oxide, halothane, and isoflurane are capable of diffusing across the gas permeable membrane of the Po2 sensor, resulting in high Po2 readings. Also reviewed are the interferences with measurement of electrolytes and with co-oximetry. The comprehensive list of interferences is impressive and a great resource for your staff.
The guideline covers blood gas analyzer calibration and quality control. One subject that is often confusing and covered extensively is traceability. According to the guideline, “reference materials shall be traceable to SI units of measurement or to certified reference materials.” If traceable standards do not exist, then traceability can be met by use of certified materials, use of specified methods or consensus standards, and/or participation in an interlaboratory comparison program. Certainly, participation in an interlaboratory comparison program such as those provided by CAP would then meet the requirements of traceability. The section also reviews both surrogate sample controls, such as tonometry, aqueous, and emulsion control solutions, and nonsurrogate or alternative quality control. The latter is electronic QC, automated procedural controls, or automated internal checks. These types of controls might check all or a portion of the analytical components each time a patient sample is analyzed and can be used in conjunction with or in place of external control materials.
CLSI’s mission is to develop best practices in clinical and laboratory testing and promote their use throughout the world, using a consensus-driven process that balances the viewpoints of industry, government, and the health care professions. Respiratory therapists involved in ABG testing should be aware of the CLSI guidelines that directly affect their practice. We hope this review heightens your awareness of and motivates you to investigate the guidelines further, so you are prepared for the “dreaded” inspection.
The authors represent respiratory therapists in the CLSI; Blonshin served previously on the board of directors and currently serves as chair of the Working Group on QSE Equipment. Mottram is currently serving as chair of the Area Committee on Quality System and Laboratory Practice.
Carl D. Mottram, BA, RRT, RPFT, is the director, pulmonary function laboratories and pulmonary rehabilitation program, and assistant professor of medicine, Mayo Clinic, Rochester, Minn. Susan Blonshine, BS, RRT, RPFT, AE-C, is president and CEO, TechEd Consultants Inc, Mason, Mich. For further information, contact [email protected].
- Blonshine S, Fallon KD, Lehman CM, Sittig S. Procedures for the Collection of Arterial Blood Specimens; Approved Standard—4th Ed. H11-A4. Clinical and Laboratory Standards Institute. Available at: www.clsi.org/Source/Custom/Currentdocs.cfm?Section=Current_Versions_of_CLSI_Documents. Accessed September 8, 2009.
- Procedures and Devices for the Collection of Diagnostic Capillary Blood Specimens; Approved Standard—6th Ed. CLSI H4-A6. Clinical and Laboratory Standards Institute. Available at: www.clsi.org/Source/Custom/Currentdocs.cfm?Section=Current_Versions_of_CLSI_Documents. Accessed September 8, 2009.
- Blood Gas and pH Analysis and Related Measurements; Approved Standard—2nd Ed. C46-A2. Clinical and Laboratory Standards Institute. Available at: www.clsi.org/Source/Custom/Currentdocs.cfm?Section=Current_Versions_of_CLSI_Documents. Accessed September 8, 2009.
- A Quality Management System Model for Health Care; Approved Standard—2nd Ed. HS1-A2. Clinical and Laboratory Standards Institute. Available at: www.clsi.org/Source/Custom/Currentdocs.cfm?Section=Current_Versions_of_CLSI_Documents. Accessed September 8, 2009.
- Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture; Approved Standard—6th Ed. H3-A6. Clinical and Laboratory Standards Institute. Available at: www.clsi.org/Source/Custom/Currentdocs.cfm?Section=Current_Versions_of_CLSI_Documents. Accessed September 8, 2009.