A respiratory care view of point-of-care blood gas and electrolyte testing.
The complex demands of support and management for the lung, a critical organ system, have made respiratory care practitioners essential players on the ICU team. Accordingly, the respiratory care profession has matured to emphasize education, investigation, credentialing, publication, and broadening of expertise.|1~
In many institutions, the operation of laboratory blood gas instruments falls under the purview of respiratory care. Knowing the levels of a patient's blood gases and electrolytes, which are measured in a similar way technologically, is of unquestioned clinical utility in monitoring many critical care patients.
Respiratory care practitioners enhance care in each phase of pulmonary management by recognizing the need for blood gas measurement, collecting the specimen, performing the analysis, and applying the results. For example, respiratory care practitioners are frequently involved in collecting blood specimens for blood gas measurements and in analyzing, interpreting, and applying the results in titration of oxygen therapy or weaning from mechanical ventilation.
During the introduction of a point-of-care blood gas/electrolyte testing program, the respiratory care practitioner who is proficient in blood gas analysis is a valuable consultant while clinicians, laboratorians, and others are being trained to work with the instruments.
In the future, interpretation of proposed Federal regulations will clarify who is permitted to perform blood gas analyses. Whoever performs point-of-care testing should approach it from the standpoint of an experienced respiratory care practitioner. Standards of quality control and quality assurance flow from the tenets of good laboratory practice and state and Federal regulations. As such, they are the same for all operators, whether from the central, Stat, or pulmonary function laboratory, the respiratory care department, or another area. As technologic advances move testing closer to the patient and into the hands of clinical staff members, these recommendations will be appropriate for even more applications.
* Pros and cons. Point-of-care clinical chemistry analyzers have brought microprocessor-based instrumentation to a new level of sophistication and ease of use yet at the same time introduced hidden complexity.|2~ Previous generations of automated blood gas instruments, marketed as reliable and easy to use by nearly anyone on the health care team, failed to live up to their potential for point-of-care application when inadequately maintained or used by undertrained personnel. Like any new rung on the ladder of technologic complexity, this one involves a tradeoff: The more highly a machine is automated, the less each operator will understand how it works and the harder it will be to perform maintenance and troubleshooting activities in-house. These problems, coupled with overconfidence in the instruments' reliability, led to too many substandard test results. Legitimate concerns arose concerning the adequacy of new technologies.|3~
Reimbursement trends and competition among manufacturers will accelerate the use of chemistry analyzers used at the point of patient care. Since personnel costs dominate their financial statements, hospitals will be drawn to any technology that improves care by facilitating testing while requiring no increase or a decrease in the number of laboratory specialists needed to operate the equipment.
Automation is not merely inevitable but desirable. In critical care, rapid turnaround of blood gas and electrolyte results is always important and often vital. Besides the strong clinical considerations, point-of-care instruments save the time of the care giver. When respiratory care practitioners, physicians, nurses, and others can obtain immediate results, patients can be assessed faster and therapeutic responses instituted sooner. Less time is wasted and medical professionals are more efficient. The technology of discrete-sample portable analyzers offers an affordable way to solve many current problems in this area.
* Keys to success. For a portable blood gas and electrolyte instrument to work successfully in the hands of an ICU team member, it must meet certain conditions:
* Appropriateness. The instrument should occupy a genuine niche in clinical medicine. It must be quick, available, and suitable for analytical use by personnel who may not be highly experienced in laboratory principles. It must require only intermittent attention from those with more expertise in clinical laboratory testing.
* Performance. Reports in peer review literature must have demonstrated that the instrument achieves suitable accuracy and precision.
* Track record. The instrument must be proved to be useful as implemented in each medical center.
* Making best use of the system. How can a hospital use a portable blood gas/electrolyte instrument to take full advantage of its strengths and mitigate its weaknesses? One practical way would be to use the instrument in an ICU or a Stat laboratory that is not staffed full time by a medical technologist or technician. Quality control and maintenance procedures would be performed at appropriate intervals by respiratory care practitioners, medical technologists, or other technical specialists. Analyses would be performed by those who attended the patient and interpreted the test results: respiratory care practitioners, physicians, nurses, and perhaps perfusionists or other health professionals.
The types of medical personnel who may legally perform these analyses vary from state to state. Because the new instruments break new ground, blurring what constitutes lab analysis and how it differs from analysis with a portable device, it may be necessary to reinterpret or amend existing regulations.
It may be feasible to have analyses performed by a great variety of health professionals, but is it desirable? That value judgment will depend partly on how intelligently the system is introduced and maintained in each institution. Points in favor of using diverse operators include quick turnaround, especially in emergencies; more efficient use of clinicians' time; and cost saving. A potential drawback is the increased difficulty of guaranteeing high-quality results when tests are performed by personnel who lack a laboratory orientation, especially if the test method requires extensive operator involvement to process a specimen or maintain the instrument.
Hospitals have been disappointed in the past by experiences with promising technologies. In this case, an advantageous mix of laboratorians and clinical care givers can provide both the requisite QA and the convenience of point-of-care analysis, as discussed in the suggested guidelines offered below.
* Personnel standards. Two main groups will be involved in use of portable analyzers: clinical and technical operators. Their training and the extent of their familiarity with the instrument differ.
* Clinical operators. Hands-on care givers who will actually perform the analyses of patient specimens include physicians, nurses, respiratory care practitioners, and others. Not included in this category are clerks, ward managers, and other nontechnical or nonclinical workers. If the instrument malfunctions, the care giver is the first line of defense. The insight of clinical operators will be crucial in detecting any discrepancies between results and clinical circumstances.
* Technical operators. Backing up the instrument but not operating it will be persons who perform maintenance activities, analyze QC samples, keep records, and generally oversee proper performance of the equipment. Their qualifications should include the quality control expertise of a professional laboratorian and familiarity with performing blood gas measurements on conventional electrode-based equipment. To acquire such knowledge and skills, respiratory care practitioners and other nonlaboratory-based technical operators will need specific training and experience in making blood gas, electrolyte, and related clinical chemistry determinations.
* Training. The responsibility for comprehensive training rests with the manufacturer. This training should include appropriate materials and in-service education.
Clinical operators should receive instruction on specimen collection and analysis, including proper and improper specimen fluids, appropriate specimen sites, collection methods and devices, acceptable types and concentrations of anticoagulant, effects of air bubbles, considerations related to the patient's body temperature, and how to avoid effects, such as incorrect methods of storing specimens, that may vitiate the analysis.|4,5~
Each clinical operator should be trained by a qualified and experienced trainer, preferably a laboratorian, who can provide personal instruction to small groups. The manufacturer should make available a videotape for later review and for the orientation of new staff members.
Technical operators should receive more extensive training by the manufacturer. Besides learning the same information as clinical operators, they should attend sessions on theory, operation, hands-on maintenance, and troubleshooting.
* Gearing up. Before the instrument is put in regular service, establish its performance characteristics and baseline quality control results. Compare these with methods used in the same institution to perform the same tests. Allow at least one week to obtain and consider all this information.
* Setting limits. To establish initial control limits using quality control ampules, run samples at the manufacturer's suggested rate, with approval from the medical director of the institution. To be statistically significant, this sampling should yield at least 20 data points for every analyte at each level at the end of a week.|6~ After recording data for each analyte, calculate the mean and standard deviation.
In subsequent clinical operation, consider the instrument out of control for a given analyte if QC results for any level are more than 3 SD from the mean or if QC results for two or more levels exceed 2 SD.|6~ If desired, more elaborate rules for determining out-of-control conditions may be applied.|7~ Consult the manufacturer's directions for additional trouble-shooting information. Disposables must be changed at the recommended frequency, not more often, to ascertain stability data at their normal life.
* Precision and accuracy. To determine the instrument's absolute accuracy for |pO.sub.2~ and |pCO.sub.2~ measurements, use a commercially available thin-film or bubble tonometer.|5~ While tonometry levels should cover the entire range of interest, they should cluster near the expected and critical ranges. Specific target value ranges and other parameters are listed in Figure I.
Use suitable standards to determine the accuracy of electrolyte measurements. For instrument systems that vary with pressure, record barometric pressure readings from the point-of-care instrument and from a mercury barometer installed in the same room. As before, record the data and then calculate the mean and standard deviation for each analyte. These results will be used as baseline performance characteristics for accuracy and precision.
* Comparisons. While results from a point-of-care blood gas/electrolyte analyzer should be similar to those obtained with instruments in the central laboratory, they should not be expected to be identical. The potential for inaccuracy and imprecision exists in all laboratory measurements.
It is best to know the deviation from truth of both the new instrument and existing instruments. For blood gases, this is most successfully accomplished by comparing the performance of existing methods and of the new method with tonometry and precision pH buffers.(5) Initial correlation studies should be performed by placing the new analyzer next to the existing analyzer. Samples should be run on the same syringe. Using this technique will minimize preanalytical error.
Once a successful side-by-side evaluation has been completed, the instruments can be separated and the evaluation can continue. Even if the new method does exhibit bias, the values identified may nevertheless be valid as long as the shift is consistent. Clinical protocols and normal ranges can then be adjusted accordingly.
For blood gas comparisons, tonometered samples from the accuracy and precision study done previously may be used. These may be adequate for the other analytes as well. For each analyte, plot the values derived from the new instrument against the values from the comparison method. Calculate regression lines. The slopes should be close to 1.0, the intercepts near 0.0, and the correlation coefficient (r) high--preferably 0.95 or more.
Plot the differences between found values and target values against tonometered values as well. Determine 95% confidence limits for the differences and evaluate their adequacy.|8~ If you identify differences between the new and existing methods, decide whether you should accept them or apply simple correction factors--that is, linear offset and proportionality--to make the results agree. Consult with the clinical users of the instrument as you make that decision. The software of some instruments does not have offset capabilities.
* Quality control. Adhere to all quality control and quality assurance measures required by the Joint Commission on Accreditation of Healthcare Organizations, the College of American Pathologists, and state and Federal agencies such as the Health Care Financing Administration. The instrument's technical operators are responsible for running, recording, and interpreting quality control results and for monitoring the use and replacement of disposable materials. The National Committee for Clinical Laboratory Standards has published a widely accepted set of recommendations on developing QC programs for blood gas instruments.|5~
A technical operator should verify appropriate operation of the instrument at the beginning of each of three shifts per day. All clinical operators should keep a log in which they record observations of instrument problems. Each such entry should include the date, time, operator's name or other identification, a description of the problem, and corrective action taken.
Technical operators should examine the log kept by those using the instruments, respond to any problems noted, and document any actions taken. Printouts derived from the instrument itself should be examined for proper calibration results. Any out-of-control results should be acted upon promptly.
The log should include the number of specimens run per shift. In addition, if required for the instrument, operators should record barometric pressure taken from both the instrument and an independent mercury barometer.
Figure II summarizes three options besides external quality control programs that supplement aqueous-based solutions. Once a day, analyze a split comparison sample on the point-of-care device and on an instrument in the central laboratory. Keep all printouts and results near the instrument.
After reviewing these records routinely, the technical operator should certify in the log book that the instrument is suitable for continued operation during the remainder of the shift--or if not, remove it from active use and attend to any problems. The log book should be reviewed and initialed at least once a week by a supervisor and at least once a quarter by the responsible physician. This program, which utilizes whole blood, augments the existing quality control program and checks the instrument with actual patient specimens.
* Overseeing performance. Enroll the point-of-care instrument in an approved proficiency testing program that provides a challenge frequency of at least quarterly. Develop a comprehensive quality assurance plan. Monitor clinical usefulness and response to errors, downtime, and other operational problems. It will be necessary for both clinical and technical operators to receive ongoing in-service education. Keeping skills at a high level requires formal orientation for new operators and frequent review for experienced ones.
As point-of-care testing for blood gases and other analytes becomes more widely used and accepted, some roles and responsibilities may shift. The goal is to keep quality of care paramount. Even when laboratorians do not perform the tests themselves, their technical supervision and team spirit will determine whether this burgeoning technology can fulfill its great promise.
1. Craig, K.C. The role of research in respiratory care. In: Chatburn, R.L., and Craig, K.C., eds., "Fundamentals of Respiratory Care Research," pp. 3-14. Norwalk, Conn., Appleton & Lange, 1988.
2. Shrout, J.B. Controlling the quality of blood gas results. Am. J. Med. Technol. 48:347-351, 1982.
3. Morris, A.H.; Kanner, R.E.; Crapo, R.O.; el al, eds. "Clinical Pulmonary Function Testing," 2nd ed., pp. 35-36. Salt Lake City, Intermountain Thoracic Society, 1984.
4. National Committee for Clinical Laboratory Standards. Percutaneous collection of arterial blood for laboratory analysis; approved standard H11-A. Villanova, Pa., NCCLS, 1985.
5. National Committee for Clinical Laboratory Standards. Blood gas preanalytical considerations: Specimen collection, calibration, and controls; tentative guideline C27-T. Villanova, Pa., NCCLS, 1989.
6. National Committee for Clinical Laboratory Standards. Internal quality control testing: Principles and definitions; approved guideline C24-A. Villanova, Pa., NCCLS, 1991.
7. Westgard, J.O.; Barry P.L.; and Hunt, M.R. A multi-rule Shewart chart for quality control in clinical chemistry. Clin. Chem. 27:493-501, 1980.
8. Bland, J.M., and Altman, D.G. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1: 307-310, 1986.
Important target values
To determine absolute accuracy for |pO.sub.2~ and |pCO.sub.2~ measurements:
Perform blood tonometry with a commercially available thin-film or bubble tonometer. Tonometry levels should be concentrated near expected and critical ranges.
Range of |pO.sub.2~ target values (adult applications near sea level)
4.67 kPa (35 mm Hg) to 13.33 kPa (100 mm Hg)
Range of |pCO.sub.2~ target values
4.0 kPa (30 mm Hg) to 8.00 kPa (60 mm Hg)
Obtain 30 tonometric measurements each for |pO.sub.2~ and |pCO.sub.2~ over a one-week trial period.
pH With the tonometry samples, analyze two levels of ampuled, NIST-traceable pH buffers at levels other than 6.840 and 7.383.
Record readings from the instrument and from a mercury barometer installed in the same room.
Quality control options
These suggested optional QC programs, to be used for point-of-care blood gas and electrolyte analyzers in addition to external programs, are listed in decreasing order of desirability.
* Run blood tonometry at one or two levels each shift. Run NIST-traceable buffers at other than pH 6.840 or 7.383 each shift. Run two levels of controls for electrolytes (or all analytes) during each shift.
* Run two levels of ampuled control material during each shift. Perform blood tonometry at one or two levels once per cartridge. Run NIST-traceable buffers at two levels per cartridge.
* Run bicarbonate buffer tonometry at two levels once per shift. Perform blood tonometry at one or two levels once per cartridge. Run NIST-traceable buffers at two levels once per cartridge.
Adapted from NCCLS document C27-T.|5~
The author, Steven L. Berlin, is technical director in the pulmonary laboratories of Alta View Hospital, Cottonwood Hospital, and LDS Hospital, Salt Lake City, Utah.
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|Title Annotation:||MLO Special Issue: Point-of-Care Testing|
|Author:||Berlin, Steven L.|
|Publication:||Medical Laboratory Observer|
|Date:||Sep 1, 1991|
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