3. What’s the first thing you
look at on your BMP?
If you could only hear one number from the ER to
decide what your next steps may be, what would you
want to know?
Because: If you have an elevated anion gap, you
100% – no questions asked – have an ANION GAP
METABOLIC ACIDOSIS
Na
K
Cl
Bi
BUN
Cr
Glu
AG
4. What’s your ddx for an
AGMA?
I don’t do MUDPILES – there are 4 MAIN things
Lactate
Ketones
Uremia (renal failure)
Alcohols
*PSA: Don’t forget salicylates (less common, but
should be wary, if concomitant resp alkalosis)
5. So what do you order to
work this ddx up?
Lactate order a lactate
Ketones order a UA or beta-hydroxybutyrate
Uremia (renal failure) just look at your BUN
Alcohols order MEASURED serum osm + EtOH
*And a salicylate level if indicated
6. What should we look at
next?
We want to decide if the AGMA is the ONLY process
going on
Now we calculate the delta/delta
Na
K
Cl
Bi
BUN
Cr
Glu
AG
7. Delta bicarb / Delta gap
Typically use 24 for normal bicarb, 12 for AG
Disclaimer: chronic retainers will have a higher
baseline bicarb – so pay attention to baseline
Also, certain conditions may have a lower AG
Don’t forget! Correct AG for albumin
Corrected AG = 2.5 x (4 – albumin)
8. Delta bicarb / Delta gap
Delta bicarb = 24 – your patient’s bicarb
Delta AG = Your patient’s AG – 12
Example:
Bicarb of 18 delta is 6 (24-18)
AG of 18 delta is 6 (18-12)
So this represents a PURE ANION GAP ACIDOSIS
9. But what if it’s not equal?
Example:
Bicarb 6 delta 18
AG 18 delta 6
So what is causing the discrepancy?
This must be a NON anion gap acidosis!
This is more “acidy” than you would expect for that
increase in anion gap
Add 6+6, still 12 (acidosis) OR 6/18 (<1 – acid)
10. What’s your ddx for a
NAGMA?
To keep things simple, just remember 5 categories:
1. GI loss
Diarrhea, ECF, ureteral diversion
2. Renal loss
Diuretics like acetazolamide
3. Iatrogenic
NS
4. “Weird Stuff”
RTA I, RTA II, RTA IV
5. Adrenal Stuff
Addison’s (DEFICIENCY) – this is a type 4 RTA
11. But what if it’s not equal?
Example:
Bicarb 18 delta 6
AG 24 delta 12
So what is causing the discrepancy?
This must be a metabolic alkalosis!
This is more “alky” than you would expect for that
increase in anion gap
Add 12+18, that’s 30 (alkalosis) OR 12/6 (>1 – alk)
12. What’s your ddx for a
metabolic alkalosis?
Again, simple, SAME 5 categories:
1. GI loss
Vomiting, NGT suction
2. Renal loss
Diuretics like lasix
3. Iatrogenic
TUMS, alka seltzer
4. “Weird Stuff”
Barter’s, Gittleman’s, Liddle’s
5. Adrenal Stuff
Conn’s, Cushing’s (EXCESS), even steroids
13. Okay, so you’ve solved the
BMP…what about the gas?
pH α bicarb / CO2
AKA pH and bicarb go in same direction
pH and CO2 go in opposite directions
Step – by – Step
1: -emia?
2: CO2 direction?
3: is it compensated?
14. Quick review of respiratory
causes…
Resp acidosis = CO2 goes up, pH goes down
Resp alkalosis = CO2 goes down, pH goes up
Please remember! The –osis is the PROCESS,
The –emia is the outcome!
17. 2 ‘formulas’ to actually
memorize…
Winter’s
Expected CO2 = (1.5 * bicarb) + 8 +/- 2
Use this for metabolic alkalosis pt’s w/ resp comp
Chronic retainer
10:4
For every 10 up in CO2, 4 up in bicarb
19. Examples?
Last tip! >> Who else can help you in the BMP?
Remember those intercalated cells in the collecting
duct?! Jk, but really…
They have a bicarb/chloride exchanger
Bicarb goes down, Chloride goes up (& vice verse)
Na
K
Cl
Bi
BUN
Cr
Glu
AG
20. Problem #1
A 25 y/o F found down at a
party is brought to the ER.
On exam she is somnolent
and not arousable to voice
or sternal rub. She opens
her eyes to pain makes
incomprehensible sounds
and withdraws to pain.
Initial Tox screen positive
for opiates. Alcohol level is
at 250 mg.
VS: 36.0 C, HR 90, BP
110/50, RR 6, SpO2: 85%
ABG on room air: 7.06/36/50
135
5.5
100
10
42
1.4
112
25
AGMA – pure
Respiratory acidosis – not
appropriately compensating
21. Problem #2
You’re called about a 43
y/o M with HIV/AIDS (CD4
40/4%) being treated for
cryptococcal meningitis
who has become
increasingly altered over
the past two days. On
exam he is tachypneic
without accessory muscle
use. He has been treated
with 5-FU and
amphotericin for the past
week.
VS: 37.0 C, HR 70, BP
140/80, RR 20, SpO2: 98%
on 2 L
ABG on room air: 7.25/30/90
143
3.0
122
13
60
3.0
90
8
NAGMA
Respiratory alkalosis –
appropriately compensating
22. Problem #3
A 36 y/o M with major
depressive disorder, a
history of EtOH withdrawal
and alcohol abuse presents
to the ER intoxicated and
minimally responsive. He
remained in the ED for 20
hours waiting on a bed
upstairs. He has become
agitated, belligerent and
combative despite IM
haloperidol,
diphenhydramine, and
lorazepam. He was started a
lorazepam drip. He’s
minimally arousable and
appears to be having a
tougher time breathing.
VS: 37.7 C, HR 80, BP
195/90, RR 22, SpO2: 91%
on NRB
ABG on current settings:
7.35/35/80
145
3.0
106
19
32
1.6
60
20
AGMA + Met Alkalosis
Respiratory alkalosis –
appropriately compensating
23. Problem #4
A 65 y/o F with
emphysema and obesity
hypoventilation syndrome
who presents with
worsening shortness of
breath.
VS: 37.4 C, HR 94, BP
155/85, RR 18, SpO2: 94%
on 2 Lpm
ABG on current settings:
7.25/66/70
138
4.8
95
28
20
1.1
260
15
AGMA + Met Alkalosis
Respiratory acidosis – this pt
is a chronic retainer
