Thread by @aryadoctoryet

#tweetorial time for SUPER FAST, no WINTER or (difficult) MATH evaluation of Anion-Gap Metabolic Acidosis:

THE METABOLIC SEESAW. YEE HAW.

1/12

The metabolic seesaw:

dBC dAG
———————🔺———————
(more BC)

dAG = delta Anion Gap
dBC = delta Bicarbonate.
Toward the Center = more bicarbonate

This will all make sense in a moment.

2/12

Scene: patient w/ anion-gap metabolic acidosis

Your ?: is their compensation appropriate? Do I need more labs? Who and what is a winter and why do they have a formula?!?!

Answers: seesaw only, a chemistry is all you need!

3/12

dAG: lab anion gap - 12
dBC: 22 - lab bicarb

Lab = on your chem panel.

The dAG can be thought of as the increase in acid. Which means, you’d expect an equal decrease in bicarbonate! How much did the bicarb decrease? That’s the dBicarbonate!

So, why seesaw? EZ to see 😉

4/12

For every little rung further from the center the dAG gets, the dBicarb should also get on the other side.

This makes sense since the dAG = acid rise, and dBC = base fall. More acid = less base. These should balance each other out if there is no other process happening!

5/12

Examples:

AG: 20, Bicarb: 14

dAG: 20-12 = 8
dBC: 22-14 = 8

dBC dAG
———————🔺———————
(8 from 🔺) (8 from 🔺)

There is balance in the force, this is a pure anion gap metabolic acidosis.

6/12

AG: 25, Bicarb: 20
dAG: 25-12 = 13
dBC: 22-20 = 2

dBC dAG
———————🔺———————
( 2 from 🔺) ( 13 from 🔺)

IMBALANCE: dBC wants to be 13 out like dAG is but something is pushing it up!

7/12

This means too much bicarbonate is around (remember: toward center = more bicarbonate) which means something is elevating the bicarbonate! There is a concurrent metabolic ALKALOSIS happening!

Next example:

8/12

AG: 20, Bicarb: 3
dAG: 20-12 = 8
dBC: 22-3 = 19

dBC dAG
———————🔺———————
( 19 from 🔺) ( 8 from 🔺)

IMBALANCE: dBC wants to be 8 out like dAG is but something is pushing it further down! Something is pushing DOWN the bicarbonate!

9/12

Remember, AWAY from center = less bicarbonate. Something is dropping the bicarbonate! What drops bicarb? An acid! So this something else is a concurrent metabolic acidosis!

10/12

Summary & Principles:

1. Draw your see-saw (dAG on either side)

2. Remember that the dBC wants to balance it

3. Ask, is dBC being pushed away from center by where it should be if it was balanced, or toward center by where it should be if it was balanced?

11/12

5. Toward center = more bicarb = something elevating the bicarbonate = concurrent metabolic alkalosis. Away from center = less bicarbonate = something dropping the bicarb = concurrent metabolic acidosis.

Happy seesawing!

12/12

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