The Approach That Never Fails
Robert C Hollander, M.D.
PGY-30
Gainesville VA
1.
2.
3.
4.
5.
Acidemia v. Alkalemia
Metabolic v. Respiratory
?Anion Gap
Does the ΔAG = ΔHCO3 ?
Is there appropriate compensation?
1.
2.
3.
4.
5.
Acidemia v. Alkalemia
Metabolic v. Respiratory
?Anion Gap
Does the ΔAG = ΔHCO3 ?
Is there appropriate compensation?
Pre-supposes you have an ABG
Accurate conclusions cannot be drawn from HCO3
alone
Normal range: 7.35-7.45
If there is an abnormal pCO2, HCO3 or AG, then
7.4 is the dividing line
1.
Acidemia v. Alkalemia
2.
Metabolic v. Respiratory
5.
?Anion Gap
Does the ΔAG = ΔHCO3 ?
Is there appropriate compensation?

Ask yourself out loud (softly if others are around)
3.
4.
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What explains the acidemia? Or
What explains the alkalemia?
If HCO3
Metabolic
If pCO2
Respiratory
If both, pick one and the Foolproof Approach will catch the
other later.
2.
Acidemia v. Alkalemia
Metabolic v. Respiratory
3.
?Anion Gap
1.
Does the ΔAG = ΔHCO3 ?
Is there appropriate compensation?
4.
5.
AG = Na – (Cl + HCO3)
AG = Unmeasured Anions – Unmeasured Cations
AG= an artifact of laboratory measurement
AG allows inferences about unmeasured anions
Albumin excepted, the Unmeasured Anions are salts
of organic acids
Therefore, AG elevations
Metabolic Acidosis
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
Exceptions exists
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Methanol
Uremia
DKA
Propylene glycol (not paraldehyde)
INH (impaired hepatic clearance of lactate)
Lactic acidosis
Ethanol/Ethylene Glycol
Salicylates
Baseline
Abnormal
Sodium
136
136
Chloride
102
112
Bicarbonate
24
14
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.29
pCO2
40
29
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
Diarrhea, RTA, carbonic anhydrase inhibitors, ureteral diversions
Dilutional acidosis, post hypocapnic
4.
Acidemia v. Alkalemia
Metabolic v. Respiratory
?Anion Gap
Does the ΔAG = ΔHCO3 ?
5.
Is there appropriate compensation?
1.
2.
3.
Compensation will return the pH towards normal
Compensation is either:
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




Appropriate, or
If not, indicative of another acid-base disturbance
If Metabolic Acidosis prevails then the Winter
Formula applies, predicting the ventilatory
response (know this formula!)
pCO2 = 1.5(HCO3) + 8 ± 2
Baseline
Abnormal
Sodium
136
136
Chloride
102
102
Bicarbonate
24
14
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.29
pCO2
40
29
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
Acidemia v. Alkalemia
Metabolic v. Respiratory
?Anion Gap
1.
2.
3.
Does the ΔAG = ΔHCO3 ?
4.
Is there appropriate compensation?
5.
If ΔAG = ΔHCO3
If ΔAG ≠ΔHCO3
Rationale:
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
one METABOLIC disturbance
>1 METABOLIC disturbance
X meq acid will titrate X meq HCO3
HCO3 will fall by x, AG will rise by x
If ΔAG ≠ΔHCO3, then another metabolic disturbance accounts
for the difference
Baseline
Abnormal
Sodium
136
136
Chloride
102
92
Bicarbonate
24
14
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.29
pCO2
40
29
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
DKA + vomiting, AKA + vomiting, Sepsis + vomiting, Sepsis + NG
suction
Baseline
Abnormal
Sodium
136
136
Chloride
102
102
Bicarbonate
24
14
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.22
pCO2
40
23
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
DKA with respiratory failure (from any cause), Sepsis with
respiratory failure (pneumonia + sepsis)
Baseline
Abnormal
Sodium
136
136
Chloride
102
102
Bicarbonate
24
24
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.50
pCO2
40
32
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
Hypoxia (from any cause), pain, sepsis/endotoxemia, ASA
toxicity, anxiety (diagnosis of exclusion)
Baseline
Abnormal
Sodium
136
136
Chloride
102
92
Bicarbonate
24
31
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.36
pCO2
40
56
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
Severe COPD, OSA, Advanced neuromuscular disease
Baseline
Abnormal
Abnormal Baseline
Sodium
136
136
136
Chloride
102
92
92
Bicarbonate
24
31
31
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.50
7.38
pCO2
40
42
55
1] Acidemia v. Alkalemia
2] Metabolic v. Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] 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.
Baseline
Admission #1
A month later
Sodium
137
139
130
Chloride
105
99
93
Bicarbonate
24
21
13
Anion Gap
10
Δ Anion Gap
-
Δ Bicarbonate
-
pH
7.40
7.46
7.38
pCO2
40
21
16
1] Acidemia v.
Alkalemia
2] Metabolic v.
Respiratory
3] Anion Gap?
4] ∆ Anion Gap
5] Compensation?
Two interpretations, one unifying diagnosis