The indications for and the value of blood gas analysis are the same for all ages, but more care should be taken with senior samples and standards.
There is much discussion about the growing elderly population in the United States, but what exactly does that mean? By how much is it growing? Why does it matter? According to the US Census Bureau, it matters, at least in part, because the growth will change the makeup of the US population and therefore its health care patients.
Statistical analysis by the Census Bureau has shown that the number of people 65 years and older in the United States grew by a factor of 11 from 1990 to 1994 while the population as a whole increased only by a factor of 3.1 This meant that in 1994, one in eight Americans was elderly.1 By 2030, the US Census Bureau predicts that one in every five Americans will be 65 or older.
Individuals 85 years of age and older—the “oldest old,” as the bureau categorizes them—are the fastest-growing group among the elderly.1 From 1964 to 1990, this group grew 284%, versus 100% for those 65 years of age and older and 45% for the population as a whole. The implications are already being felt in medicine, where the growing population of elderly is, in some instances, taxing resources.
Volume is not the only problem. The elderly often present with complications related to their age, medications, and/or medical histories. Geriatric conditions can be complex, involving more than one anatomical system. But diagnoses still rely on the available tools. Blood gas analysis—or arterial blood gas (ABG) analysis—is one of those tools.
Used routinely to measure the amounts of oxygen and carbon dioxide in the blood as well as its pH, ABG analysis provides insight into the workings of the lungs and their interaction with the kidneys. Ventilation, respiration, metabolism, and acid-base balance can be assessed. The information is clinically valuable, particularly in determining if immediate—and life-saving—actions are needed to correct the pH.
For the elderly, the implications and follow-up are the same as with every other age group. Any history of respiratory problems can suggest the need for a blood gas analysis. But sample takers and result analysts should take into account the age of the patient, particularly if the patient is among the oldest old. Consideration of the unique challenges presented by the geriatric patient will help to produce the most accurate results for physicians and the most comfortable experience for patients.
Indications and Utilization
The indications for blood gas analysis are the same across all age groups. “The indications don’t have much to do with age. It’s the same for all—you need to assess ventilation, oxygenation, or acid-base status,” says Charles Emerman, MD, chair of emergency medicine at MetroHealth Medical Center in Cleveland, Ohio.
In general, patients who are admitted to the emergency department with respiratory distress or a history of associated ailments often have blood gasses ordered as part of their initial workups. The test is useful in assessing respiratory disease and other pulmonary-related conditions.
Blood gas analysis can also help to manage patients receiving oxygen therapy. Patients in critical care units may have the test ordered routinely, “such as in the morning, particularly if the patient is on assisted ventilation,” observes Anne Gorski, RN, BSN, clinical manager for Radiometer America Inc, of Westlake, Ohio.
The frequency with which blood gasses are ordered often depends more on an institution’s protocols rather than general trends. “I think that it falls upon the local environment. Some places are well educated on the use [of arterial blood gas analysis] and others aren’t,” says John Ancy, MA, RRT, senior clinical consultant with Instrumentation Laboratory in Lexington, Mass.
Emerman concurs. “It’s a little bit of an uncomfortable test for the patients to undergo, and it takes a little more time than a venipuncture,” he says, suggesting that, as a result, there is the potential that blood gasses should be ordered more often. Pulse oximetry may sometimes be used instead, but its results are limited to oxygenation information and do not address acid-base normality.
Senior Sample Taking
|John Ancy, MA, RRT|
Some caregivers may be deterred by the sample-taking process. “It’s not an invasive procedure, but it is not painless, either,” says Mike Samoszuk, MD, chief medical officer at Roche Diagnostic Corp, based in Indianapolis.
It is easy to draw samples from patients with arterial lines already in place, but new patients can pose a greater challenge, particularly if they are elderly. Simply selecting a site in an older patient can be a challenge. Ancy observes that the basic Allen test can be difficult to perform in a population that typically has cold hands and poor perfusion everywhere.
The stick is also a challenge. “Skin becomes less elastic with age, and there is a greater tendency to have rolling vessels,” says Gorski. The artery movement is due to reduced connective tissue.
Hardening arteries pose another challenge, “especially in the presence of atherosclerosis,” says Ancy. Repeated arterial punctures can also deform the artery, thickening the wall and shrinking the lumens.
Patients on aspirin will require special care. “[It] takes fully 7 days for the anticoagulation effect [of aspirin] to be reversed in most individuals. So you really need to hold the site gently but firmly to prevent subcutaneous bleeds [after the puncture],” says Ancy.
Throughout the process, patients themselves may be difficult. Geriatric patients can have impaired eyesight, hearing, or neurological capacities. They may be confused, scared, and anxious. “They are not always good historians regarding what is going on with them, and they may have to be prompted to get the right information,” says Gorski. Their medical histories can be complicated. Elderly patients may have chronic illnesses or previous incidents, such as a stroke.
Caregivers should take the time to evaluate this condition and respond accordingly. “You can’t just rush into a room and draw a blood gas. You may have to repeat yourself a few times to reassure the patient,” says Gorski.
Ideally, the draw will not have to be repeated as well. “You certainly don’t want to repeat a sample unnecessarily,” says Ancy, adding, “Caregivers will often do everything they can to avoid having to repeat a sample. With older folks, you really have to take the time to explain the procedure and really be aware of the patient’s condition. It can add time to perform the procedure, but I think it’s well worth it.”
|Mike Samoszuk, MD|
The same care might be needed in the interpretation of blood gas analysis results for the elderly. Although some clinicians feel the current standards are adequate, others feel the issue could require more research.
“Maybe we are not using the best guidelines. The normal standards are based on patients seen on a routine basis. Now, that population is so much older that it might be an area open to new research,” says Gorski.
Blood gas analysis takes into account a number of factors, including pH, oxygen pressure, and carbon dioxide and bicarbonate levels. “There are various formulas used to interpret and decide what type of balance the patient has and what the cause could be. These formulas are very sophisticated and taught in medical school,” says Samoszuk.
Acid-base status presents a particular challenge. “It requires a series of calculations to determine respiratory alkalosis/acidosis and metabolic alkalosis/acidosis,” says Samoszuk. Many analyzers will perform these calculations automatically.
“The cobas b 221 blood gas system automatically maps the patient’s acid-base status on a grid that can be updated each time the patient is tested, so the health care provider can view the result trend over time to track patient progress,” says Samoszuk.
pH results should be stable. Acid-base references do not change with age. “The pH and CO2 really don’t change appreciably with aging,” notes Ancy. Oxygen pressure, however, might do so.
“Clinicians need to be aware that a normal Po2 for someone who is 40 is not the same for someone at 80 or 90, or even the centenarians we see,” says Ancy. He suggests more latitude in interpreting Po2.
“Some of the [literature] indicates that for every 10 years past the age of 10, the Po2 drops by 5. If that happens, by the time one gets to 80, the number is low,” says Ancy. Although Ancy would not consider a Po2 of 80 mm Hg low in an 80-year-old patient, he would like to see more research. In discussing the mechanism that lowers oxygen pressure levels in the aging, Ancy questions whether there has “ever been a truly great study done on that.”
In general, the whole patient should be considered—not only the basic demographics, such as age, but also medical status. Elderly cases may be complicated by comorbidities, multiple medications, and complicated medical histories, such as cardiovascular incidents or COPD.
For instance, many elderly patients are anemic. “This condition can affect the results of the blood gas analyzer,” says Samoszuk, noting some instruments may correct for this factor. For instance, the cobas b 221 co-oximeter takes 512 wavelength readings to obtain an accurate reading for hemoglobin and hemoglobin derivates.
What analyzers don’t currently do well is adjust for age, a problem more associated with the available tables than the capabilities of the analyzers. “You have to work with the medical director to decide at what level you want to adjust the Po2 values for age,” says Ancy.
A reliable analyzer is key to avoiding repeat draws. “If the results are in question, that might cause the physician or nurse to have to do another arterial puncture,” says Ancy.
|Anne Gorski, RN, BSN|
The results must be accurate because the information has such great clinical value. The data reveals information about a patient’s ventilation capabilities, oxygenation levels, and metabolism. “Many times a patient comes into the hospital complaining of shortness of breath. A blood gas will tell you if it’s related to hypoxemia, some other condition, or a combination of issues,” says Ancy.
In addition to the diagnostic data, the results of a blood gas analysis are also key to making decisions regarding treatment. “The test helps diagnose a patient, so the physician can institute the proper treatment modalities,” says Gorski, citing respiratory therapy, medications, and nursing care orders as areas that will reflect the blood gas analysis results.
Naturally, those results are wanted as quickly as possible. “As soon as you institute the proper care, the better the outcome,” says Gorski, suggesting a shorter hospital stay is just one way in which patient care improves.
Often, the response to an abnormal blood gas result is the same, whether the patient is young or old, but again, caregivers will want to take care to make elderly patients feel comfortable. “It’s the same treatment, but a different way of instituting it,” says Gorski, adding that caregivers must remain cognizant of the need to modify care depending on the patient.
She suggests caregivers learn more about the elderly because medicine will continue to serve them in greater numbers. “You can’t treat the elderly like children or the average-age patients. It is its own specialty now,” says Gorski. Keeping in mind the numbers from the US Census Bureau, this is not surprising and, rather than present a challenge, can present an opportunity.
Renee Diiulio is a contributing writer for RT. For further information, contact [email protected]
- Hobbs FB. The elderly population. Population profile of the United States. US Census Bureau. July 8, 2008. Available at: [removed]www.census.gov/population/www/pop-profile/elderpop.html[/removed]. Accessed December 2, 2008.