Blood gas analysis


Blood Gas Analysis Technology Focused on Point-of-Care Testing

An emphasis on accuracy and quick test results has helped shape current blood gas analysis technology, as smaller handheld devices and advancements in diagnostic sensors have allowed a focus on testing at the point-of-care.

By Phyllis Hanlon

Blood Gas testingIn 1958, the medical world welcomed the first functioning blood gas analyzer, a large, stationary, three-channel instrument that incorporated a Clark pO2 electrode, the Stow-Severinghaus pCO2 electrode, and a pH electrode. Two years later, several companies began to manufacture these medical monitoring devices, and by 1966, blood gas analysis was widely used in clinical settings, surgery, anesthesia, and intensive care. Some 20 years later, manufacturers began producing more competent devices.

During the ensuing years, technology has revolutionized the industry. Unwieldy tabletop analyzers have shrunk in size, while increasing their analytic capabilities. Still designed to monitor lung function by measuring partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2), as well as acid/base levels, bicarbonate (HCO3-), and oxygen content and saturation, these newer blood gas analyzers offer expanded menus, quicker, accurate results with less operator intervention, and growing compatibility with electronic medical records systems and other technologies.

Gold standard

Thomas Mayer, BA, RPSGT, CPFT, CRT, a member of the COPD Foundation Educational Review Working Group (ERWG) and a respiratory therapist at the Sleep Center at St. Anthony’s Medical Center in St Louis, considers blood gas analysis the gold standard in patient monitoring. “Invasive blood gas analysis has many qualities. If you know something about the patient, you can determine, by the values (high, low, or something else), how to put the information together and see the direction the diagnosis might be headed,” he said. “You can make a decision once you see if the trends are holding up.”

At St. Anthony’s Sleep Center, blood gas analyzers are situated in 12 locations throughout the facility. “They are technically adept at keeping track of things that we did manually before. The science of running the machine is more technologically advanced and our training system has gotten easier. We just pull data from the machine,” Mayer said. With this type of advanced system, fewer staff members need to be trained on the machine.

Also used in the intensive care unit, the emergency department, operating rooms, catheterization lab, and preoperative situations, blood gas analysis helps to monitor mechanically ventilated patients, according to Dennis Matricardi.

“Values from arterial blood gas tell you how to make changes on a mechanical vent,” said Matricardi, a senior analyst for MD Buyline, a 30-year veteran in the laboratory field, who is also registered by the American Society of Clinical Pathology as a specialist in microbiology and a diplomat in laboratory management.

Kathey Leibold, another senior analyst for MD Buyline with 20 years’ experience in several areas of respiratory therapy with a special emphasis on critical care, noted that traditional analyzers are located in a central lab where lab staff document quality control measures during every shift, in compliance with guidelines set by The Joint Commission or the College of American Pathologists.

The process for traditional blood gas analysis requires a trained and credentialed therapist to draw the sample and deliver it as quickly as possible to the lab where it is analyzed and the results recorded. “This process could take as long as 2 hours,” Matricardi said. “When results are needed to determine treatment options, 2 hours could be too long. Changes occur quickly so you have to have those values immediately.”

Potential for errors

No doubt, a lab-based system has its benefits and drawbacks. According to Cheryl K. Daly, RPFT, supervisor, pulmonary diagnostics, QS & Compliance at Lee Memorial Health System—which comprises four acute care hospitals, in Fort Myers, Fla—in spite of the range of capabilities, preanalytical errors do commonly occur in a lab. For instance, patient identification mistakes, such as incorrect labeling of the specimen, can lead to posting the results to the wrong medical record, she pointed out.

In some cases, sample integrity may be compromised. Daly indicated that a therapist with poor technique or an inability to palpitate a pulse might accidentally obtain a venous or mixed venous sample, instead of an arterial sample. If these samples contain clots, the results will not be dependable. She pointed out that samples must be visually inspected and all clots removed prior to analysis.

“Clots can cause analyzer problems, such as calibration drifts and quality control failure. Samples should be mixed gently for 2 minutes and then again at the time of analysis,” she said. “Too much liquid heparin in a small sample can also cause dilution of the sample, which can falsely lower the total hemoglobin and hematocrit results.”

Air bubbles in a sample also might raise concerns about contamination, according to Daly. “Bubbles can drastically affect the pCO2 and mostly the pO2 results, rendering inaccurate results up or down, depending on the clinical status of the patient,” she said. “This can result in serious and inaccurate prescription options and decisions for that patient.”

Icing, which has its supporters and detractors, can impact a blood sample as well, causing cellular metabolism and inaccurate electrolytes if reported with blood gases. “We should only ice samples if a significant delay in analysis is anticipated. Icing can lower high pO2 values. Time is the most important factor for transportation of the sample,” Daly said.

Mayer, on the other hand, has always iced samples. “Across the board, from my anecdotal standpoint, icing works to reduce volatility,” he said.

Trends in devices

Appropriate treatment in the ICU and trauma center, based on blood gas values, depends upon convenience and fast, accurate turnaround times, according to Daly. “It’s all about the instruments being available at or near the patient’s bedside,” she added.

At Lee Memorial Health System, analyzers are placed and maintained strategically throughout the hospitals and critical care units. “We utilize 30-minute turnaround criteria for a stat blood gas to be reported from the time the order was placed in the electronic medical record,” she said, adding that results might be available much quicker, sometimes within 5 to 10 minutes, if a therapist is already working in that unit.

According to Daly, point-of-care (POC) devices are becoming more prevalent in the clinical setting. “Where analyzers used to be large benchtop systems, often located only in the clinical laboratories, they have become physically smaller and smaller using the most current nanotechnology. Miniature electrodes are being permanently loaded onto very small cartridges, sometimes as small as the palm of your hand,” she said. “More parameters than ever before are now available on these analyzers. This allows respiratory therapists to provide these services in a much quicker turnaround. The instrumentation is easier to use, requiring less hands-on from the clinical person.”

Paul D’Orazio, director of Critical Care Analytical in R&D at Instrumentation Laboratory in Bedford, Mass, credits the evolution of sensors for the expansion of analyzer menus. For instance, sensor developments enable the devices to make pH, gases, and electrolyte measurements simultaneously based on the electroactive nature of the analytes.

To further enhance the capabilities of an analyzer, biosensors have been developed. Biosensors recognize the presence of a biological molecule and transform concentration into a measurable electrochemical signal.

Enhanced functionality of these multianalyte, critical care models made for use at the bedside has enabled them to replace classical three-channel lab-based instruments. D’Orazio explained that these POC devices have proven successful for three reasons: menus on these models have been expanded to include the most urgent critical care analytes with a fast turnaround time; all the systems accept whole blood as a sample and require little or no maintenance; and most have integrated, automated quality control features.

Built-in quality control

A quality control (QC) program, which evaluates an analyzer’s performance, functioning, and ability to detect errors that may affect accuracy or precision, possibly leading to clinically significant errors, is not only important, but also mandated by state and federal regulations.
But maintenance methods for blood gas devices differ, depending on the delivery system. “Surveillance is performed continually [by staff for lab-based systems]. Calibration is performed frequently, quality control samples run, results monitored, troubleshooting and maintenance tasks performed throughout the day on a 24/7 basis for most locations,” Daly said.

According to D’Orazio, manufacturers of instruments for critical care testing have developed several new approaches to QC. “The impetus for this change has been twofold: first, to simplify QC processes for increased acceptance of systems in POC environments; and second, to make QC an ongoing, continuous process,” he wrote in a 2008 paper on the subject, noting that little has changed in the last 5 years. “Most modern critical analyzers include a high degree of instrument self-diagnostics, for example, system integrity checks to assure proper functioning of mechanical components, such as pumps and valves, detection of occlusions within the fluidic system, and checks of the electronics and microprocessor communications.”

D’Orazio cites three approaches to QC for cartridge-based point of care analyzing systems that have hit the market in recent years. The electronic QC (EQC) uses a built-in or external simulator to monitor the electronic components of the analyzer. While simple to use, quick, and inexpensive, the EQC doesn’t examine actual sensing reactions or sampling-related functions. This type of analyzing is done usually before a new lot of testing cartridges is accepted for clinical use.

The automatic QC (AQC) system assays on-board surrogate samples that the user selects. When the device fails to recover an analyte concentration, corrective actions might automatically occur, including “extra flushing of the sensor cartridge fluid pathways, sensor recalibration, and parameter shut-off for persistent QC failure,” according to D’Orazio. This particular model requires no user intervention, but may fail to detect errors that occur between assays of the QC materials.

Continuous QC integrates automatic checks each time an on-board reagent or patient sample is tested, said D’Orazio. He noted that this system also checks for patterns in the sensor signal, which might indicate compromised integrity of the sample.

“If a situation outside of acceptable limits is detected, a corrective action, specific to the source of the error, will be initiated,” he said, noting that the device could be temporarily disabled until the situation is corrected.

Since no operator intervention is necessary, continuous QC is able to automatically test the performance of the entire analytical system as it measures each patient’s sample. D’Orazio noted, “An ongoing, real-time QC program, which is free of operator intervention, will be the most successful QC program at point-of-care.”

Some systems on the market integrate CO-oximetry, which allows the user to measure hemoglobin and fractional components of hemoglobin simultaneously with other critical care analytes, D’Orazio added.

User satisfaction

An added benefit to these advanced POC analyzers is a reduction in the amount of training needed to operate the device. Since the instrumentation is less cumbersome, it requires less troubleshooting and maintenance. “Changing electrodes now is a matter of changing out a cartridge instead of the tedious, and now outdated, task of re-membraning and changing out of electrodes. QC is now run electronically or automatically instead of the therapist having to report to the instrument every 8 hours to perform the procedures,” Daly explained.

“Clots are automatically detected and cleared from the system, requiring less maintenance. The instruments are more automated as far as sampling also, which allows for less human error due to variance in technique. There is less therapist intervention needed.”

The multiple benefits of handheld devices, which include ease-of-use and turnaround time, make them ideal for clinicians, and POC systems have been gaining traction in the market.

In addition, POC devices can transmit information securely and automatically, which reduces the chance of transcription errors. Also, because values are immediately delivered to the device and the EMR, the issue of icing samples becomes moot.

Cost may be another deciding factor when hospitals are considering purchasing blood gas instrumentation. According to Matricardi of MD Buyline, tabletop models can cost anywhere between $30,000 and $100,000. “Handheld models cost approximately $7,000. Single-use cartridges run about $10 each time you do a blood gas analysis, but they are user friendly and quick,” he said.

Future integration

Blood gas analysis hails as one of the preferred patient monitoring systems; however, combination blood gas and pulse oximetry therapy has its advantages as well. Blood gas offers a look at one moment in time, while oximetry offers continuous monitoring.

Mayer sees blood gas analysis as the anchor, to be used in conjunction with pulse oximetry.

“Blood gas can establish the patient’s status. Once you do a blood gas, you get a baseline number. Then use pulse oximetry to verify and monitor the patient noninvasively. This may reduce the need to do more frequent blood gases. All devices used in conjunction serve as a monitoring system for the patient, keeping them on track and in maximum health,” he said. “You are getting a rolling real-time movie picture with less complicated numbers over time. The pulse oximeter also provides saturated blood hemoglobin numbers.”

While blood gas analysis may be combined with other monitoring methods into one device in the future, the present instrumentation is capable of integrating with EMRs in many situations, which can improve workflow and reduce errors.

“Lee Memorial Health System introduced Epic, our electronic medical record with several upgrades and physician order entry system-wide within the last 2 years. It has improved workflow because all blood gas results are available in one place in the EMR, for all patients across the system at any time,” Daly said. “The ability to interface our results from the analyzer to our lab information systems has been instrumental in reducing reporting errors. We evolved from using a completely paper-oriented system to a 100% paperless report,” Daly explained.

For now, POC blood gas instrumentation appears to be the next trend. In 2012, researchers from Belgium conducted an analytical performance evaluation on four cartridge-type blood gas analyzers: Siemens RP405; Instrumentation Laboratory’s GEM Premier 4000; Radiometer’s ABL90 FLEX, which served as comparator; and Roche’s Cobas b 123.1 The study examined the precision factor of these POC devices for pH, pCO2, pO2, ionized calcium, potassium, glucose, lactate, and total hemoglobin, as compared to traditional blood gas analyzers.

Overall, the four devices produced clinically acceptable results, although there were some discrepancies. But the researchers noted that analytical performance, ease of use, and low maintenance demonstrate that these instruments are suitable for lab use as well as for POC use. RT 


Phyllis Hanlon is a contributing writer for RT Magazine. For further information, contact rtmagazine@nullallied360.com


References

  1. De Koninck AS, De Decker K, Van Bocxlaer J, Meeus P, Van Hoovels L. Clin Chem Lab Med. 2012 Feb 1; 50(6):1083-91.