ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

An analysis should be repeated immediately (ideally on another analyzer) if the results are: • Inconsistent with the patient’s past results and/or conditions (3) • Physiologically inconsistent values (3) (e.g., Pa O 2 >120 mm Hg for patients breathing room air) • At the extremes of the range of expected values (3). Analytic Phase The technology used to analyze pH and blood gases has developed to permit expanded utility and ease of instru- ment operation, but methodology has remained relatively unchanged. Modifications of current design have also allowed for miniaturization of the electrodes, which has enabled point of care (POC) testing. Before introduction of blood samples, the analyzer’s electrode outputs are evaluated with known high and low concentrations of buffer, solutions, and gases. If required, the analyzer is recalibrated. Some analyzers are calibrated before each test, and other instruments internally verify calibration at least every 30 minutes. Calibrations are usually referred to as one or two point, where the electrode response is adjusted at one level or at two levels (7). Because there are so many different designs, protocols, and recommendations frommanufacturers regarding calibration, the labora- tory must adhere to the manufacturer’s recommendations. The measurement of barometric pressure must be considered and is integrated into the calibration equation of the instrument. To ensure accurate calibration of the blood gas electrodes, the internal instrument barometer should be verified for accuracy at least annually against a National Institute of Standards and Technology traceable barometer and be documented. Analyte analysis begins when a blood specimen is injected or aspirated into the sample chamber for measurement. Because temperature changes affect measured results, the electrodes systems and the sample chamber are located inside a temperature-controlled block maintained at 37° C. Typically, when the blood sample contacts the electrodes in the chamber, it produces an electrical output that corresponds to a pH, partial pressure, or hematocrit value. Blood gas analyzers monitor the electrodes’ response continuously and, after a predetermined stabilization period, the instrument will display and/or print the measured results. When analysis is complete, the blood specimen is disposed of and the electrode-sensor system is flushed with a rinse solution (7). Postanalytic Phase The postanalytic phase of testing primarily encompasses reporting results. Accurate and complete documen- tation, whether performed manually or electronically, is extremely important. All patient results should be reported with the analyzer’s normal range as documented in the blood gas laboratory’s policy and procedure manual. When applicable, communication to the medical staff of critical or alert values needs to occur in a timely fashion. In addition to the blood gas results, a complete report should include the collection time, source of sample, Fi O2 level, any ventilator settings, the type and location of any fluid infusion, the collection site, and patient posture (3). Critical values or alert values are defined as test results that are markedly outside normal range and associated with impending morbidity or mortality. The blood gas laboratory policy and procedure manual should describe the procedure for reanalysis of the specimen when values are outside the critical value range. For example, the specimen should be analyzed on a different instrument (if possible) to verify results. The policy and procedure manual should also describe the protocol for how to rapidly communicate critical values to the medical staff. Documenting this communication (e.g., name of the physician or nurse contacted, as well as the person making the contact should be written on the blood gas report) is an essential component of the standards that regulate laboratories (3).

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