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Blood Gas Analysis: The Pros and Cons of Point-Of-Care Testing

Beth Wegerbauer
Contributing Editor

Since the first system was invented in 1957, blood gas analysis has revolutionized clinical medicine and patient care. During the 1960s, blood gas analysis became almost universally available, and blood gases were considered "the most important laboratory test for critically ill patients," according to a article by Dr. John Severinghaus, inventor of the blood gas analysis system.

Blood gas tests determine whether a patient has enough oxygen in his blood and whether or not that blood is pH balanced. The tests reveal levels of pH (indicating blood's acid/base status), pO2 (how much oxygen is dissolved in blood), PCO2 (how much carbon dioxide gas is dissolved in blood), as well as other parameters like O2 saturation and HCO3. Blood samples are collected from an artery, usually the radial artery in the wrist, but also can be taken from the brachial or femoral arteries. For infants, capillary blood may be taken from a heelstick. In addition to arterial sampling, blood gas panels can be ordered on blood drawn through a central venous line to estimate cardiac output.

Blood gas analysis is performed by trained health-care providers in a hospital, emergency room, or large clinical laboratory. These tests are "stat" tests, meaning they should be done as quickly as possible after sample collection. For arterial blood gases (ABGs), the collected sample degrades quickly and, if any testing delay is expected, it should be kept on ice and rewarmed later for accurate analysis. If, after sample collection, any air bubbles remain in the top of the syringe, they must be removed. After the needle is capped, the syringe is then placed on ice and transported for immediate analysis.

To reduce transport as well as turnaround time, especially for the most seriously ill patients, many analyzers are located in or near selected patient care settings, such as intensive care units (ICUs), operating rooms (ORs) and emergency departments. Because ABGs are the most common tests ordered in ORs and ICUs, immediate results are critical. Therefore, many health-care providers are choosing blood gas analysis that is performed via point-of-care testing (POCT), using handheld units that give a quick result at the bedside or operating table. Such handheld units can be used in non-traditional settings such as rural clinics and in ambulance or helicopter transport situations.

POCT can offer several benefits, most importantly the instant implementation of treatment decisions rather than waiting, sometimes for several hours, for the results from a more traditional central laboratory-based analyzer. By the time those results become available, the condition of the patient may have changed. In the case of POCT, immediate results mean immediate care. Specimen transport time is minimized as no staff have to leave the OR or bedside to carry a sample to the lab. In some cases, there may even be a reduction in pneumatic tube traffic. POCT also reduces the risk of preanalytical errors that may accompany traditional laboratory testing, such as the handling, labeling, and transport of samples.

Another advantage to POCT is a decrease in phlebotomy-related blood loss, an important feature in settings like the OR or ICU, where blood conservation is key. Some analyzers used in central laboratories have menus that require a minimum sample size, whereas POCT devices use smaller samples.

The reality of POCT, despite all of these benefits, is that the advantages of POCT are lost when a sample is mishandled or testing is done incorrectly. Therefore, implementation of point-of-care tests inherently demands structure and regulation (per JCAHO and CLIA regulation) to ensure quality results. POCT places a burden on department and site directors to properly identify the training needs of non-labora torians, and to ensure that they are met. Additionally, non-laboratorian staff trained on POCT methods must be monitored following the trainings in order to insure their competency with the tests. Training a diverse non-laboratorian staff (including MDs, RNs and RTs) across multiple shifts, instruments, methods, and then monitoring their competency over time is a formidable task which increases with each test introduced and with department size. It is easier to decentralize the test itself than it is to decentralize the specialized laboratory knowledge and training that goes with each test.

Lack of adequate documentation may be considered another drawback to POCT. Results from POCT devices usually appear on a screen with temporary printouts available. Those results may get mishandled or misplaced and never find their way into the patient's permanent medical record. This lack of documentation may also have an affect on potential reimbursement issues.

As health-care providers must consider each advantage and disadvantage to POCT, its technology continues to develop. The analyzers are getting faster, smaller, easier to use, and show the ability to perform accurate testing with smaller blood samples. Radiometer America, Westlake, OH, manufactures one such model, called the 1st automatic blood gas analysis system. The system combines instruments, samplers and information technology to reduce the steps in the analytical process, improve patient and operator safety, and minimize errors. It consists of the safePICO pre-barcoded arterial sampler that helps to remove air bubbles and avoid contact with patient blood while reducing the risk of needlesticks with an onboard safety device; FLEXLINK software to help ensure correct sample, patient, and operator identification; and the FLEXQ module on the ABL800 FLEX analyzer to help reduce errors through automatic identification and mixing of samples.

Abbott Laboratories, Abbott Park, IL, produces the widel y used i-STAT 1 handheld system, which gives results in as little as two minutes using as little as two drops of blood along with a test cartridge. The system is capable of performing a comprehensive panel of critical tests and, according to the manufacturer, is simple to learn and operate.

Of course, the decision to use POCT instead of a central laboratory depends on various factors unique to a particular hospital or health-care setting. One thing is for certain, the transfer of blood gas analysis from the laboratory to the ICU and OR will profoundly effect critical care, just as the introduction of laboratory-based blood gas analyzers did more than 40 years ago.

Beth Wegerbauer is a medical writer and editor with 12 years of experience covering the clinical laboratory field.

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