ABGs: What patients need to know

The following was originally published at healthcentral.com/copd on June 29, 2015

What is an Arterial Blood Gas

So you have COPD, and now your doctor wants you to have an Arterial Blood Gas (ABG). So what is an ABG, and how do the results benefit you?

An ABG is a special blood draw that requires arterial blood, or freshly oxygenated blood from your lungs. The test shows your oxygen levels, which show how effective your lungs are at oxygenating, or taking the gas oxygen (O2) from the air you inhale and getting it into your bloodstream.

These include.

• PaO2. This is the partial pressure of arterial oxygen. Normal is 80-100, although greater than 60 is usually acceptable. 
• SaO2. This is how saturated your arterial blood is with oxygen (O2). Normal is 98%, although 90-100 is deemed acceptable. Sometimes 88-92 is acceptable for COPD. 

All the cells and tissues of your body, such as those that make up your heart, need oxygen to make the energy needed for them to function. Lacking enough oxygen, your heart may stop working properly and make you feel winded or short of breath. So monitoring your oxygen levels from time to time when you have a disease like COPD is important.

If your oxygen levels are low, your doctor may prescribe oxygen therapy to help you breathe easier and live longer with your lung disease.

The test also shows how effective your lungs are at ventilating, or taking the gas carbon dioxide (CO2) from your blood and allowing you to get rid of it when you exhale.

This is shown as.

• PaCO2. This is the partial pressure of arterial carbon dioxide (CO2). The normal range is 35-45.

An elevated PaCO2 level may indicate how severe your flare-up is, how much your disease has progressed, or even what stage of COPD you are in. It can help doctors decide how best to treat your flare-up. It can also help doctors decide how your treatment regime is working over time and whether adjustments need to be made.

The results also show.

• HCO3 (Bicarbonate). This is a buffer that keeps your pH from getting too acidic. A normal range is 22-26. 
• pH. This measures hydrogen ions (H+) in your blood. A normal value is 7.35 to 7.45. Your PaCO2 and HCO3 are constantly adjusted by your body to maintain a normal pH.

So an ABG requires arterial blood. The best place to draw it is from the radial artery in your wrist. The second best place is the brachial artery on the anterior side of your elbow.

An advantage of drawing blood from an artery is that arteries are deeper and less likely to roll than veins, plus they pulsate, which sometimes makes arterial blood easier to obtain. A disadvantage is arteries are surrounded by more nerves than veins, sometimes making arterial pokes more uncomfortable than venous pokes.

As an asthmatic, I’ve had the test performed on me more than once, and I can honestly say it’s really not that bad. As a respiratory therapist who has been drawing them for 20 years, I can honestly say that most people tolerate the poke just fine.

The test is also not performed very often, because most laboratory tests require only venous blood. Still, for the occasional times doctors recommend for you to have this test done, the results can go a long way to helping them help you live better with it.

Further Reading:

• Understanding Oxygen Levels
• Do You Need Oxygen Therapy
• The Natural Progression of COPD
• Stages of COPD

Lab Nazis

I hate lab.  I hate every thing about the lab.  I even hate the people.  I hate every thing about lab.  I dread going to lab with my ABG results.  I dread it more than anything else in this field.

Okay, so I don't hate all the people.  I love the lab techs. I love the good folks who draw blood.  They generally have good people skills; they have to.  Yet there are people in the lab, who all they do is look at machines all day.  Those people tend to be choleric and dry in personality.

Okay, so not all, but many.  Enough to make the milieu of the lab seem hot and tense.  And it's not just the lab where I work my full time job, it's every lab I've ever walked into.  The people are focused on numbers, machines and tasks and don't give a rats butt about the whole picture. To them the number tells the whole story.  If a machine shows a CO2 of 60, that value is critical.  It doesn't matter that the patient is a COPD retainer with a normal CO2 of 55.

They also develop their raw, dry, pining personalities because they are forced, by all the companies and government agencies forcing tons of new regulations every day, to worry about being shut down.  Yes, there is a reason they are the way they are, as I wrote about in this post.

There's a reason there are 300,000 not needed steps in entering blood gas results and resulting them into the computer system.  It's because people who have no clue about reality are making rules and regulations.  The lab folks, the lab Nazis as I call then, are that way for a reason.  They don't intent to become Nazis, it's just what they become.  It's like if you hang out with rats all day, you become one by default.

Okay, enough lab bashing.  Seriously, folks, I find no place more stressful and tense than hospital laboratories.  It has to be the most stressful job in the world, worrying about numbers being correct; worrying about machines working properly; worrying that you meet the 289,000 stupid, moronic, regulations.  (Yes, 19,000 of those regulations might actually be necessary).

I know I'm being unfair by saying I hate the people who work in lab, because it's probably not true.  What I hate is what they become, and how they are so obsessed with numbers that they lose track of reality.  But, in their defense, it's not always their fault.  It's the fault of the morons in Washington who can't keep their noses out of our healthcare system.

I think drawing ABGs was better in the old days when ABG machines were inside RT Caves.  Surely we grunted and groaned while maintaining and fixing them, but that stress was nothing compared to what we have to deal with in the lab. Sometimes I wonder if we should have kept our mouths shut and kept it the way it was, and continued to live in happy RT lalal land.

Okay, go ahead and rip my editorial to shreds if you choose.  This is my opinion only.  I am simply terrified of the lab, like my three-year-old daughter is scared of the Ferris Wheel.  I get the ABGbies every time I go there (yes, that was a funny).

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Cord blood gases trivial answers

Now, let's see how well you did on trivia questions from earlier today.  The answers are in red.

Let's see how much you guys have been paying attention to my blog. What follows are two cord blood gases and a few questions:

A.

• pH 7.36
• CO2 42.8
• PO2 33.7
• SO2 80.5
• FO2Hb 75.7
• HCO3 23.8
• BE -1.1

B.

• pH 7.27
• CO2 58.8
• PO2 12.3
• SO2 19.5
• FO2Hb 18.8
• HCO3 26.3
• BE -1.3

Questions

1. Which one of the above is arterial and which one is venous?  B is venous and A is Arterial

2. Are these results normal or critical?  Normal

3. What did you use for the basis to answer question #2? Or, how do you determine if a cord blood gas is critical?  pH is greater than 7.1.  If the pH is less than 7.1 it shows the baby probably took an anoxic hit during delivery and didn't have time to recover prior to birth.  A pH of greater than 7.1 shows the baby may have taken an anoxic hit, but it occurred prior to delivery and the baby had time to recover.  

4. If you can only draw venous or arterial from the cord, which would you rather have: venous or arterial? Arterial. This is blood from the mom.  

5. Do cord blood gases have clinical significance?  No.  They are used for litigation purposes only to prove the baby did or did not take an anoxic hit during the delivery.  Arterial blood gases get doctors off the hook in about 75 percent of cases.  

How to keep your lab from failing inspections

ABG machines are a great device to have around, particularly in emergency situations. Yet recently the lab bosses have created new recommendations and policies for us to follow that are very inconvenient. However, as I have learned, a necessary evil.

An article in the May 10, 2010, issue of the AARC Times by John Campbell, "Preventing 'proficiency Referral' from happening to your health care organization," does a great job of detailing the importance of proper ABG and ABG machine handling in order to pass laboratory inspections to prevent mandatory lab closure.

We all have shortcuts, some of which we choose not to share for obvious reasons. One shortcut of many RTs in my department is we do so few ABGs that we rarely placed a sticker with the patient's name on them. We also rarely heeded the yellow warning lights on the ABG machine that warned that the equipment must be checked before further ABGs can be reported by the machine.

However, a recent crackdown has changed our behavior. The new policy is as follows:

• Identify patient
• proper sanitisers
• label syringe
• Check for yellow light on ABG machine
• If yellow, fix problem or run maintenance
• If question mark on ABG report throw it away.
• Run monthly control (every RT must do this once a year)

Some of those rules are common sense, although some are a pain in the arse, particularly the check the yellow light and do maintenance. You see, we used to have the ABG machine in the RT Cave, and the reason we gave it to lab was so we wouldn't have to do this anymore.
So here we are learning how to do it once again. In a way, it seems we might as well take care of it ourselves. Yet the RT Boss has decided it's best off in lab where they can do the appropriate check on it, after all, he noted, "They are the lab equipment experts."
Actually, I know of many RT departments that run their own ABG machine, and they do so just fine. So, technically speaking, there is no reason we can't do it ourselves. But, be it as it may, it's no longer our machine.
Inspections of labs are made at least once a year by MANY companies, including the Centers of Medicare and Medical Services (CMS), or some other CMS contracted agency commonly called CLIA inspection or by some other accredited agency that is deemed qualified to do these things such as the College of American Pathologies or the Joint Commission.
Once an inspection is done the hospital must not lapse, because new inspectors could arrive at anytime.
The reason for inspections are obvious: machines are expected to be accurate. Results are important for obvious reasons, and inspections -- however annoying or redundant -- are needed.
Here are some of the things inspectors look for:

• Only qualified and selected individuals handle and draw samples and run machine, etc.
• One person in charge of device responsible for making sure things are done in accordance to policies.
• ABGs are labeled properly. The inspectors are known to look in waste dispensers to make sure syringes are labeled.
• Proper documentation
• Critical values are noted and highlighted on ABG results
• A note on ABG stating that doctor or nurse was notified of critical values
• All staff rotate doing controls
• Problems immediately reported to lab director or medical director

Refusal or failure of procedure or evaluation will or MAY result in closing of the lab, which would mean we RTs would be unable to use the ABG machine. ABGs would have to be run to other hospitals and run through their ABG machine.
According to Campbell, "CMS gives 5 days notice to offending labs that its CLIA certificate is being revoked. This notice will hold that the proficiency referral was intentional even if, in fact, it was not. This notice can come by mail or even face, and the 5 day period also includes weekends."
Campbell notes there is an appeals process, yet CMS usually wins. Likewise, lab closings are reported to local newspapers, which can provide a bad image to the hospital. He notes monetary costs can be staggering, from $500,000 to a million in legal fees, decreased credibility and image, decrease confidence in your facility, and inability to run labs at your hospital.
So, however annoying, follow the ABG policy set at your hospital.

ABG interpretation made easy: Oxygenation

An arterial blood gas can help you determine how well patient is oxygenating. Essentially, all you have to do is memorize the following chart.

	PaO2	SpO2
Normal	80-100	95-99%
Mild Hypoxemia	60-79	90-94%
Moderate Hypoxemia	40-59	75-89%
Severe Hypoxemia	< 40	< 75%

Oxygen Therapy.  Using oxygen therapy to improve oxygenation.  It generally involves inhaling an FiO2 greater than that which is contained in room air.

Fraction of Inspired Oxygen (FiO2).  This is the percent of oxygen in the air inhaled.  Room air contains 21% FiO2.  Oxygen Therapy may supply an FiO2 from 22-100%, depending on the device used. To learn more, check out "Oxygen Therapy Made Easy."

Goal of Oxygenation.  Most protocols now recommend the least amount of supplemental oxygen to maintain an SpO2 of 90% and a PaO2 of 60.  For some patients with lung disease, lower SpO2s may  be acceptable. For instance, with some cases of advanced COPD, an SpO2 of 88% may be acceptable.

Responsive Hypoxemia.  Supplemental oxygen improves oxygenation levels.  Or, increasing FiO2 increases SpO2 and PaO2 to acceptable levels.

Refractory Hypoxemia.  Supplemental oxygen does not improve oxygenation levels.  Or, increasing FiO2 does not result in an increase in SpO2 and PaO2.  It's commonly described as an SpO2 of less than 60 despite receiving 100% FiO2.

Hypoxemic Respiratory Failure.  Failure of the heart and lungs to oxygenate the blood despite the application of supplemental oxygen via oxygen therapy.

• PaO2 less than 60 on 50% or greater FiO2
• PaO2 less than 40 on any FiO2

Desired FiO2.  Calculated:  Desired PaO2 + Known FiO2 divided by known PaO2

How to use ABG results to determine if oxygen therapy is working over time. 

1. Expected PaO2 = FiO2 * 5
• Example.  If a patient is on 100% oxygen, you should expect a PaO2 of 500.  If the PaO2 is only 200, you know the patient is not oxygenating well.  
2. Actual PaO2/ Expected PaO2 = % of patient expected PaO2:
• Should be recorded daily 
• Shows if patient is oxygenating better
• Better indicator than simply looking at actual PaO2 and FiO2
• Normal = zero (patient requiring no supplemental oxygen)

Examples of % expected PaO2: (Despite lower PaO2, patient still oxygenating better)

• January 1 PO2 40 on 100% FiO2 = 80%
• January 5 PO2 60 on 40% FiO2 = 30%
• January 6 PO2 55 on 50% FiO2 = 20%

Another example of % expected PaO2 (PO2 look good, but is patient really oxygenating?)

• January 1 PaO2 200 on 100% FiO2 = 40%
• January 5 PaO2 100 on 100% = 20%
• January 6 PaO2 100 on 90% = 22%
• January 10 PaO2 55 on 80% = 13%

You don't necessarily need to use these formulas to see if patient oxygenating well, yet sometimes they can be useful. Especially for the more complicated cases, it helps to see the numbers and the trends.

Post originally published on 8/11/10 on respiratory therapy cave; updated by Rick Frea for accuracy and simplicity.

Further Reading

• ABG interpretation made easy: interpretation of acid base balance 
• The ABG lexicon
• Learn about the 4-5-6, 7-8-9 rule
• Oxyhemoglobin Dissociation Curve
• How to know if your patient is a CO2 retainer
• Cord Blood Gases made easy
• The argument against ABGs
• What is an ABG
• Respriatory Therapy Formulas

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