CLINICAL TIP: CLOSING THE ANION GAP

When I was a student nurse, I prayed that my instructor wouldn’t choose me for her “game show” humiliation during post-conference. She would randomly challenge us with impromptu questions like, “What’s the difference between pre-load and after-load? Tina. Can you answer?”…like she was a game show host but without the fabulous prizes.

Of course the questions in some way related to the lecture content of that week but with the gazillion things to learn, it was impossible to be fully prepared.  If you knew the answer, you were a superstar, however if you didn’t, she made you feel that you were forever unworthy of the RN title.

During the week we discussed acid-base balance, I felt prepared. There’s just something about interpreting blood gases that I “get.” To this day (24 years later), you can show me any blood gas result and I’ll be able to interpret it within a few seconds. I have a great self-learning module on blood gases. If you want a copy, just contact me by clicking here.

However, I wasn’t prepared for this question, “Who can explain the anion gap? Renee – go!” Ugh. I didn’t really pay attention to the anion gap and what the heck does it have to do with acid-base balance???

WHAT IS THE ANION GAP?

Your body spends energy everyday to maintain acid-base balance. On a macro level, it does this by holding onto or getting rid of carbon dioxide (lungs – acid) or bicarb (kidneys – base). On a micro level, it’s all about cations (positive/base) and anions (negative/acid).

The anion gap is simply the difference between the numbers of cations versus anions.

WHAT DO THE NUMBERS MEAN?

An anion gap can be high, normal, or low (rare). A high anion gap indicates a lot more anions than cations or…acidosis. When bicarb is used up to correct the acid base balance the gap widens. Metabolic causes of increasing anion gap are Diabetic Ketoacidosis, uremina, lactic acidosis (sepsis), and toxins.

HOW DO YOU USE THIS?

Let’s say you’re concerned that your patient might be going into DKA but nobody believes you: Type I, blood glucose is 400, resp. rate 24, etc. It’s a lot easier just to check an anion gap than it is to get an order for a blood gas. If the anion gap is wide (>11 mEq/L), chances are, your patient is in DKA.  If not, he’s not in DKA just yet!

BOTTOM LINE

Anion gap is useful in assessing the degree of metabolic acidosis without needing to stick a patient for an arterial blood gas. If the anion gap is >11 mEq/L, your patient is acidotic…period.

As for whether or not I became a superstar, winning to trip to Aruba (I wish) or the spawn of Satan... Well, I don’t know how I did it but I pulled out the answer from somewhere deep in my brain and said, “The anion gap reflects the level of acidosis in the body and can be an alternative to arterial blood gases in determining acid base balance.” Ding, ding, ding!! 

Although I did became a mini-superstar THAT day, my goal is to help YOU become a superstar EVERYDAY!

Thanks so much for reading. Thanks for choosing to become a nurse.

Take care and stay connected!

Renee

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