Blood gas analyzers—the old and the new

August 2007
Feature Story

Anne Paxton

When Carla Gianoli Smith, BS, RRT-NPS, started in the respiratory care laboratory 18 years ago, blood gas analysis seemed a lot simpler. For one thing, the analyzers only tested blood gases: oxygen, acidity/alkalinity, carbon dioxide, and bicarbonates (pO₂, pH, pCO₂, HCO₃).

But some of the biggest changes at her hospital, Spectrum Health in Grand Rapids, Mich., and at others, have occurred just since 2005.

“Before that year, we had analyzers with gas tanks and manual quality control with a lot of therapist-to-therapist variability depending on how long the sample was left open and exposed to air,” says Smith, who is Spectrum’s respiratory care laboratory coordinator.

“That was the old blood gas analysis. With the new generation of instruments, everything is automatic cartridges.”

And an ever-longer test menu. At the smaller of Spectrum’s two campuses, Smith manages a Bayer 405 instrument (now a Siemens instrument), which includes tests for blood gas, glucose, hemoglobin, hematocrit, ionized calcium, electrolytes, and an entire co-oximeter panel.

“The only test we don’t report is lactic acid; they gave that up to have a more streamlined, lower-maintenance unit,” Smith says. The 405 has automatic QC run three times a day at three levels, though a therapist still has to verify it in Spectrum’s laboratory information system.

Spectrum’s larger campus has five units for different ICUs—the new Siemens (Bayer) 1265s, which are full benchtop analyzers performing blood gas, electrolytes, ionized calcium, glucose, lactic acid, hemoglobin, hematocrit, and co-oximetry.

“Each ICU customizes what they get from us. The adult medical and surgical ICUs tend to just rely on us for blood gas, but the pediatric ICU uses our machine to its full capacity all the time. They really capitalize on ‘care sets’—ordering six tests at once.” Spectrum’s 92-bed neonatal unit, one of the largest in the country, explains the demand for 70 to 100 results per day. “And it’s usually at capacity; they are just bursting,” Smith says.

“The 1265 requires more maintenance than the 405, depending on sample volume, but not a lot,” she says. “Twice a week, the glucose and lactate electrodes are checked for minimum performance, the barometer is calibrated, and the sensors are deproteinized. It all takes about an hour per week per instrument.” All other testing that the College’s Laboratory Accreditation Program requires, such as surveys, linearities, and calibration verification, are performed throughout the year and work out to less than an hour per instrument per week.

Fewer moving parts on the 1265 make her job as troubleshooter that much easier, Smith notes, because the machine does more self-maintenance. “On the older-generation machines, there were a lot of pathways you could go through from A to Z to try to figure out where an obstruction was.”

“But now, a lot of the moving parts are inside the cartridges, so if you have a problem, you just take it out and put a new one back in. You don’t have to change reagent bottles; you don’t have to snap the ampules. And Siemens has been quick to replace a failed cartridge.”

One feature that’s the same is the actual electrode module. “They’re individual sensors and can be a little fussy. They require more maintenance than the 405’s measurement cartridge because they are separate, but the upside is you can replace the bad one instead of having to replace all of them at once.”

It takes only about 120 seconds for the instrument to complete a test, from introducing the specimen to result, she reports. “Turnaround time is just a matter of getting to the bedside and the therapist being available, but I would say when the chips fall where they should, we’d have the specimen from the draw back to the bedside in under five minutes,” she estimates. “We actually haven’t done a time study lately because we’ve shown we can turn them around quickly and none of our customers have expressed dissatisfaction.”

On a per-specimen basis, the costs of testing have increased very little—about the rate of inflation. “Now we are using basically two wash cartridges, one reagent, and one QC per instrument. In the past, we were buying QC ampules, reagent bottles, wash bottles.” There can be some nuances, such as deciding whether a 450-specimen cartridge would be more cost-effective than a 700-specimen cartridge for the 405, but overall, “the new instruments did not change the cost of doing business very much.”

The instruments’ automatic QC, she says, “is one of the best things to come along in a long time. Carrying a patient assignment along with lab responsibilities could cause issues with what has more priority. When you’re busy with a patient, a lot of times your QC could be late. But now we set a schedule and QC runs automatically. I feel there is a lot less deviation in results as well.”

“Before, we would rerun specimens and run calibrations to have the result in range, and we’re having a lot less of that. We work very closely with the lab, under their license, and our pathologists run a very tight ship, setting our QC tolerance tighter than the instrument internal limits. But even in the tight ranges, our pathologists are very pleased.”

The interface with the laboratory’s Cerner LIS is through PathNet. “The system can be a little cumbersome for the bedside user, but the overall interface is very good,” Smith says. “I am able to use it for all my quality audits, historical data, and tracking, and it includes all the applications for ordering tests, canceling, or crediting them, etc.”

The hospital has a pneumatic tube system, but its use is discouraged for blood gas. “We consider the samples precious fluids, especially if a puncture was done to obtain a blood gas,” Smith explains.

Now that there are a few brands of blood gas analyzers that include tests for creatinine and bilirubin, Smith wonders whether the test menu is already too big. “You get to a point where you are just using them for convenience as opposed to needing a test stat, and I wonder, is it better to do it on a chemistry machine made for these tests? I don’t know the answer to that.”

But the only real issue for her, she says, is always going to remain an issue: the clotting of neonatal capillary samples. “You just can’t simulate neonatal blood or its components. There’s different hemoglobin, and it clots differently. We’ve talked a lot with Bayer, and we’re working with them on better draw techniques and quicker analyzation of capillary samples.”

The blood gas analysis at San Francisco General Hospital, part of the University of California at San Francisco, used to be done in the emergency department laboratory, says Alan Wu, PhD, chief of clinical chemistry. Less than a year ago it was decided to move it back to the central laboratory. “The ED wanted their space back,” Dr. Wu explains.

But some point-of-care testing remains in the OR—the same Gem 3000s made by Instrumentation Laboratory that the central laboratory has.

“We probably sacrificed a little bit of our turnaround time,” says Dr. Wu, just because the specimens have to travel farther. But the laboratory is happy with the Gem 3000s. “IL had the menu we wanted, including not just blood gases but blood electrolytes, calcium, and lactates, although we’re not doing lactates yet.”

In addition to the menu, the Gem 3000’s self-contained plug-in module for reagents was an attractive feature. “We feel it gives us more flexibility than that of the traditional blood gas instrument, where everything is piped in,” Dr. Wu says. The cost was a little more than that of the traditional laboratory-based analyzer, but not substantially more.

Dr. Wu is impressed with the quality control features, particularly IL’s proprietary Intelligent Quality Management. “One of the attractive features of the Gem 3000 is the IQM system, which is, I think, a superior approach to QC than the traditional system.”

It was an on-site inspection by the Ontario Laboratory Accreditation, or OLA, board that prompted Sudbury Regional Hospital to launch a search for a new blood gas analyzer in 2003, says Ken Onuska, PhD, clinical biochemist, Department of Laboratory Medicine and Pathology. “Following the formal review, it was obvious we had significant gaps with regard to consistent QC and documentation in the point-of-care blood gas setting.”

The laboratory, which performs about 13,000 arterial blood gas tests across three hospital sites within the city, originally ran a mix of blood gas analyzers to accommodate different testing needs, Dr. Onuska says. But a number of new laboratory accreditation requirements under OLA made point-of-care standardization—especially in the areas of documentation and user lockouts—a necessity as services began to expand.

“We have close to 200 people involved with blood gas testing, including 120 nursing staff, between 20 and 30 respiratory therapists and perfusionists, and up to 40 MLTs within the laboratory that are utilizing these instruments.”

After comparing a number of analyzers, Sudbury ended up acquiring nine IL Gem Premier 3000 analyzers, with several across the three main laboratories, two in the OR suites, one in the cardiac catheter laboratory, and one in the NICU.

“I believe we were the first large, decentralized regional laboratory in Canada to get the instrument, and we didn’t know what to expect. The Intelligent Quality Management was a pretty new concept to us. And to me as a clinical chemist, it was surprising to see how IQM technology could combine not just a software program to the integrated wet QC and biosensor electrodes of the Gem cartridge but with the overall operation of the instrument to create a virtually fail-safe blood gas testing environment.”

Dr. Onuska says informatics are essential and, ideally, every result should be electronically available in the patient’s chart. “However, most POC analyzers run as rogue analyzers using just the ticker tape, and thus workload units and utilization are nearly impossible to track,” he says. In the core laboratory, the Gems are directly interfaced to the Meditech LIS, which uses HL7 language, “but we had a bit of a shortcoming with the POC units since they required orders to be created on the fly,” Dr. Onuska says.

“Originally what we wanted was to have POC users scan themselves in before testing. Today we do have that capability, but back in 2004 we did not.” Sudbury now uses Cobas IT, a middleware solution made by Roche Diagnostics.

“Cobas IT was actually installed as part of our point-of-care Roche glucometers in 2006, but they had a Gem 3000 plug-in available for their software. So today, all the POC authorized users have to scan themselves before being able to aspirate a blood gas sample. The Cobas IT validates them and communicates back to the Gem analyzer that, ‘Okay, you’re good to go.’”

After the blood gas is run, “because the system has a fully automated QC run immediately after the aspiration and before test results are released, we know we can run an autovalidation scheme. That’s quite revolutionary in terms of blood gas analyzers.” With other instruments in the past, they aspirated blood gases two times in a row to determine precision, “but you never necessarily knew if you were accurate because you weren’t running any QC after it,” he says.

With the IL Gem 3000 analyzer, the sample has to be aspirated only once. “It runs QC immediately after the specimen, and you can set it not to release the patient result if the QC doesn’t come in within the proper range. It will come up as an IQM error and that result will not be transmitted,” Dr. Onuska says.

Once the analyzer autovalidates the results, the results are sent via Cobas IT (that converts the analyzer’s ASTM language to HL7) to the Meditech, which has a POC module that generates an order on the fly, and the patient chart is immediately populated with data.

“It sounds complicated, but the autovalidation feature is very critical in the POC setting since we have different skill sets of people running the instrument. Our medical laboratory technologist staff understands blood gases very well, but it is the other health care professional staff that can create point-of-care havoc.”

Ontario Laboratory Accreditation requires that the lab run at least one level of QC at least once per shift with all three levels tested within 24 hours. “The difficulty is that you may have an electrode off and not realize it until you run the QC, but unfortunately you’ve already run patient results, possibly eight hours ago, on the previous shift. This analyzer completely avoids that happening, essentially by trapping errors before the results.”

Staff morale is high because of the new analyzers. Laboratory staff, nurses, RTs, and perfusionists embraced the IQM technology. “Part of that is due to the analyzer’s ability to detect clots, give low sample aspiration warnings, and detect possible biosensor malfunctions—whose errors are all given in plain English within the IQM technology built into the analyzer,” Dr. Onuska says.

The intuitive touchscreen interface means quicker training of a diverse end-user group, he says. At one time, it was necessary to deal with external gas cylinders, daily QC, error documentation, and more. “Today, all those functions are automatic because of IQM.” The new instruments have not affected turnaround time. “The technology is maybe a little slower because of all the quality checks. Before, we could easily have run two blood gases in a minute, whereas now it takes approximately four minutes from aspiration to result.”

“But the big difference is uptime. The analyzer is continuously up.” In the past, he says, a chemistry charge or senior would have to spend a significant amount of time outside the laboratory addressing such problems as clogged aspiration probes, electrode drift, or re-membraning. With every such procedure, a calibration and three levels of QC were needed. But with IQM, the analyzer runs more than 100 QC per day on average, “which is an incredible amount,” and the laboratory has 100 percent compliance with OLA QC requirements and documentation of all errors.

“In the old days, you might find, when you’d go up to the POC departments, old expired QC or old expired lots of reagents being used. This is a non-issue with this analyzer, as it will physically not accept QC or materials outside the date range since it is all integrated in the Gem cartridge bar code.”

“The beauty of using the cartridge-based system is you can either upscale or downscale a department’s blood gas testing menu on the fly,” he says. Cartridges have a lifetime of between two and four weeks depending on the menu and number of tests.

The consolidation to a single analyzer from one vendor versus many different analyzers for different departmental needs as offered by other vendors led to a “big inventory management time savings,” Dr. Onuska says. In the past the laboratory had more than 60 different items in inventory to keep track of whereas now it has only four: the cartridge, the control validation product, paper for the printer, and a floppy diskette used if a cartridge fails (reimbursed by IL if the required failure data are supplied).

How much staff time does the IL technology save? Though the lab hasn’t quantified it, it’s easy to see where the savings are. There’s “no need for testing daily QC, no need to get gas cylinders, no need to document errors, and no need to deal with re-membraning, aspiration probes, pump windings, or failed electrodes since new ones are included every time you insert a new Gem cartridge,” he says—in their case 21 days.

In pediatrics, the analyzers turn out to require less sample even though their minimum sampling volume is higher. “Originally, when phasing in eight Gem 3000s, we decided to keep the old analyzer in the NICU because it had a smaller sampling volume. It only required 50 μL whereas the Gem 3000 requires 135 μL.”

“But we met with the director of pediatrics and found they were typically drawing up to three 110 μL glass tube capillaries, although they only need 50 μL, because of capillary clot and aspiration problems and the requirement to test two times in a row and the third in case one of the aspirations was not successful.”

Today, with the Gem analyzer, they draw one tube—it’s a flexible heparinized tube with a volume of 170 μL. Though it is larger, it offers a complete analysis, including not only blood gases but also, potentially, glucose, lactate, sodium, potassium, and ionized calcium. Sudbury has already ordered three of the next-generation Gem 4000 analyzers, Dr. Onuska says, which will have a much smaller minimum sample volume for capillary blood gas and a built-in co-oximeter.

The core laboratory also performs co-oximetry testing with its blood gas configuration. “The Gem OPL is an add-on; it’s not actually part of the Gem 3000 analyzer. However, it’s umbilicalled to the unit using the serial port. The nice feature is that it uses the same touchscreen interface to make the order and IT connection to incorporate the result into the patient’s chart.”

Because of the small footprint of the Gem OPL, at the point of care the laboratory uses a pole cart with a Gem 3000 plus a Gem OPL running off a battery-powered uninterruptible power supply. “Should there be someone exposed to a fire, for example carbon monoxide inhalation, typically we get a request for co-oximetry to be performed, and we use the Gem OPL.”

“It uses six wavelengths so it’s a full analyzer. The difference is it does not use classical hemolysis, but instead it uses thin-slide translucency technology where you inject 50 µL of sample into a disposable cuvette. You insert it into the analyzer and in 10 seconds it will provide you with a full co-oximetry result.”

The analyzer’s performance quality is reflected in its external QA scores, Dr. Onuska points out. “We’re part of an EQA that’s mandatory here in Ontario, and because of the IQM, we’ve never had an EQA failure. I would have thought that in four years, with nine analyzers in service, at least one analyte would be out. But we’ve had none. The CVs are very tight on this analyzer, and it’s incredibly accurate.”

Paul Guthrie, MT(ASCP), laboratory manager at the 343-bed Bronson Methodist Hospital in Kalamazoo, Mich., likes the low maintenance of the Roche blood gas analyzers. With total blood gases of 30,000 a year, about 85 percent of that performed in the main laboratory, Bronson has used two Roche Cobas b 221 analyzers (formerly called Omni) for the last two years. The Cobas b 221 is a multiparameter analyzer for blood gas, co-oximetry, electrolytes, and metabolites.

In the NICU and OR, the hospital uses Siemens RapidPoint 400 analyzers. Both the Cobas analyzers and the RapidPoint are low maintenance. The RapidPoints, which are about the size of a personal computer, “use cartridges with basically everything on them,” Guthrie reports.

The Roche instruments are moderately sized. “You wouldn’t consider them to be portable. But one thing that’s changed over the years is that blood gases no longer have large compressed gas tanks with them,” Guthrie says. “In the not-too-distant past, many machines had to have metal tanks of O₂ and CO₂ to calibrate them. But most of the new units use reagents to actually generate CO₂.”

Using middleware from Telcor, Bronson staff are now converting the Siemens RapidPoints to interface directly to the LIS. “Currently at the unit in the NICU we have the respiratory therapists manually entering the data into the LIS, and in the OR just giving a printout directly to the anesthesiologist.”

“The middleware will eliminate manual entry for the NICU, and for the OR it will put results into the medical record along with laboratory results. Currently they have a sheet on the chart that is scanned,” he explains.

“In the OR, the main thing is they want the information right now. They’re not as concerned with trending as the NICU, where they want to see how the patient is going from day to day and week to week.”

Point-of-care devices proved necessary for Bronson because the main laboratory is a quarter mile from the hospital and samples are sent by pneumatic tube. “We used to do all our blood gas testing in the laboratory until a few years ago, but there was a concern because of the distance issue.”

Even though the blood gases are sent in a special tube for stat testing, “it can take longer, particularly if there is a pneumatic tube system malfunction. There were fears that the tube system might break down, so the people in the NICU and OR wanted to ensure adequate turnaround times.”

The main feature Guthrie would like to see improved is the analyzers’ ability to handle clots. “It’s an issue of training for drawing of arterial blood. Clearing the line properly depends entirely on training, and it’s where you have potentially diluted samples with IV fluid, or falsely lower hemoglobin.”

Some of the blood gas instruments do detect clots or bubbles, but on almost any instrument, if you get a clot it can wreak havoc for a while. “You might be down until you get rid of it. So anything the manufacturers can do to get rid of it or flush it out—I’d like to see that addressed.”

With some companies reporting record unit sales in recent years, blood gas analysis is unquestionably in an expansion mode. But Smith sees a lot of variation in hospitals’ usage patterns. “When we get together at respiratory conferences, a lot have multiple blood gas instruments, some have only one.” Unlike Spectrum, “many hospital facilities will rely on the main laboratory for blood gases even though they have an ICU.”

Adding a new blood gas analyzer for each ICU worked out well for Spectrum, she says, and the hospital plans to purchase another one when its new children’s hospital opens in 2010. “But every hospital has to decide which combination is best for them.”