Robert C Hollander MD PGY30 Gainesville VA The Approach That Never Fails Five Steps Acidemia v Alkalemia Metabolic v Respiratory Anion Gap Does the Δ AG Δ HCO 3 Is there appropriate compensation ID: 686704
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Slide1
The FooLproof 5-Step Approach to Acid-Base
Robert C Hollander, M.D.PGY-30 Gainesville VA
The Approach That Never Fails Slide2
Five StepsAcidemia v. Alkalemia
Metabolic v. Respiratory ?Anion GapDoes the ΔAG =
Δ
HCO
3
?
Is there appropriate compensation?Slide3
Five Steps – Step #1Acidemia v. Alkalemia
Metabolic v. Respiratory ?Anion GapDoes the Δ
AG =
Δ
HCO
3
?
Is there appropriate compensation?
Pre-supposes you have an ABG
Accurate conclusions cannot be drawn from HCO
3
alone
Normal range: 7.35-7.45
If there is an abnormal pCO
2
, HCO
3
or AG, then 7.4 is the dividing line Slide4
Five Steps – Step #2
Acidemia v. AlkalemiaMetabolic v. Respiratory ?Anion GapDoes the Δ
AG =
Δ
HCO
3
?
Is there appropriate compensation?
Ask yourself out loud (softly if others are around)What explains the acidemia? OrWhat explains the alkalemia?If HCO3 MetabolicIf pCO2 RespiratoryIf both, pick one and the Foolproof Approach will catch the other later.Slide5
Five Steps – Step #3
Acidemia v. AlkalemiaMetabolic v. Respiratory ?Anion GapDoes the
Δ
AG =
Δ
HCO
3
?
Is there appropriate compensation?AG = Na – (Cl + HCO3)AG = Unmeasured Anions – Unmeasured CationsAG= an artifact of laboratory measurementAG allows inferences about unmeasured anionsAlbumin excepted, the Unmeasured Anions are salts of organic acidsTherefore, AG elevations Metabolic AcidosisExceptions existsSlide6
Anion Gap
MethanolUremiaD
KA
P
ropylene glycol (not paraldehyde)
I
NH (impaired hepatic clearance of lactate)
L
actic acidosisEthanol/Ethylene GlycolSalicylatesSlide7
Baseline
AbnormalSodium136136
Chloride
102
112
Bicarbonate
24
14
Anion Gap10Δ Anion Gap-Δ Bicarbonate
-pH
7.40
7.29
pCO
2
40
29
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap5] Compensation?
Diarrhea, RTA, carbonic anhydrase inhibitors, ureteral diversionsDilutional acidosis, post hypocapnic
Non-Anion
Gap Metabolic AcidosisSlide8
Five Steps - #5
Acidemia v. AlkalemiaMetabolic v. Respiratory ?Anion GapDoes the
Δ
AG =
Δ
HCO
3
?
Is there appropriate compensation?Compensation will return the pH towards normalCompensation is either:Appropriate, orIf not, indicative of another acid-base disturbanceIf Metabolic Acidosis prevails then the Winter Formula applies, predicting the ventilatory response (know this formula!)pCO2
= 1.5(HCO3) + 8 ± 2Slide9
Anion Gap Metabolic Acidosis
BaselineAbnormal
Sodium
136
136
Chloride
102
102
Bicarbonate2414Anion Gap10Δ Anion Gap-
Δ Bicarbonate
-
pH
7.40
7.29
pCO
2
40
291] Acidemia v. Alkalemia2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap
5] Compensation?Slide10
Five Steps - #4Acidemia v. Alkalemia
Metabolic v. Respiratory ?Anion GapDoes the ΔAG =
Δ
HCO
3
?
Is there appropriate compensation?
If
ΔAG = ΔHCO3 one METABOLIC disturbanceIf ΔAG ≠ΔHCO3 >1
METABOLIC disturbanceRationale:
X
meq
acid will titrate
X
meq HCO3
HCO3 will fall by x, AG will rise by xIf ΔAG ≠ΔHCO3, then another metabolic disturbance accounts for the differenceSlide11
Baseline
AbnormalSodium136136
Chloride
102
92
Bicarbonate
24
14
Anion Gap10Δ Anion Gap-Δ Bicarbonate
-pH
7.40
7.29
pCO
2
40
29
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap5] Compensation?
DKA + vomiting, AKA + vomiting, Sepsis + vomiting, Sepsis + NG suctionAG Metabolic Acidosis + Metabolic AlkalosisSlide12
AG Met Acidosis + Resp
Acidosis
Baseline
Abnormal
Sodium
136
136
Chloride
102102Bicarbonate2414Anion Gap10Δ Anion Gap
-
Δ
Bicarbonate
-
pH
7.40
7.22
pCO
240231] Acidemia v. Alkalemia2] Metabolic v. Respiratory3] Anion Gap?
4] ∆ Anion Gap5] Compensation?DKA with respiratory failure (from any cause), Sepsis with respiratory failure (pneumonia + sepsis)Slide13
Respiratory Alkalosis
BaselineAbnormal
Sodium
136
136
Chloride
102
102
Bicarbonate2424Anion Gap10Δ Anion Gap-
Δ Bicarbonate
-
pH
7.40
7.50
pCO
2
40
321] Acidemia v. Alkalemia2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap
5] Compensation?Hypoxia (from any cause), pain, sepsis/endotoxemia, ASA toxicity, anxiety (diagnosis of exclusion)Slide14
Chronic Respiratory Acidosis-Compensated
BaselineAbnormal
Sodium
136
136
Chloride
102
92
Bicarbonate2431Anion Gap10Δ Anion Gap-
Δ Bicarbonate
-
pH
7.40
7.36
pCO
2
40
561] Acidemia v. Alkalemia2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap
5] Compensation?Severe COPD, OSA, Advanced neuromuscular diseaseSlide15
Metabolic Alkalosis + Resp. Alkalosis
Acute Resp. Alkalosis on Chronic Respiratory acidosis
Baseline
Abnormal
Abnormal Baseline
Sodium
136
136
136Chloride1029292Bicarbonate243131Anion Gap10
Δ
Anion Gap
-
Δ
Bicarbonate
-
pH
7.40
7.507.38pCO2404255
1] Acidemia v. Alkalemia2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap5] Compensation?
Loop diuretics or vomiting with any primary Respiratory Alkalosis
The Chronic CO2 retainer who stops retaining from either pain, hypoxia, sepsis, acute PE or any other acute Respiratory Alkalosis. Learn to recognize the
patient who starts
from an abnormal baseline.Slide16
Mixed Disturbance
BaselineAdmission #1
A month later
Sodium
137
139
130
Chloride
1059993Bicarbonate242113Anion Gap10
Δ Anion Gap
-
Δ
Bicarbonate
-
pH
7.40
7.46
7.38pCO24021161] Acidemia v. Alkalemia
2] Metabolic v. Respiratory3] Anion Gap?4] ∆ Anion Gap
5] Compensation?
Two interpretations, one unifying diagnosis