Diagnosing Acid Base Disorders without your PDA

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Diagnosing Acid Base Disorders(without your PDA)

• Daniel Dilling, MD

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When to be suspiciousand get an arterial blood
gas

• Most often indicated after an abnormal
  electrolyte panel
• Low total CO2
• High anion gap
• Acute or chronic respiratory failure
• Evaluate an ingestion
• Always draw one at the same time as the
  electrolyte panel!!!

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The elements of the ABG

• pH
• pCO2
• pO2
• HCO3-
• Base excess/deficit
• O2 saturation
• Methemoglobin, Carboxyhemoglobin

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The elements of the ABG

• pH
• pCO2
• pO2
• HCO3-
• Base excess/deficit
• O2 saturation
• Methemoglobin, Carboxyhemoglobin

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The elements of the ABG

• pH
• pCO2
• pO2
• HCO3-
• Base excess/deficit
• O2 saturation
• Methemoglobin, Carboxyhemoglobin

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HCO3-

• pCO2

pH
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis
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Metabolic Acidosis
Anion gap
Non-anion gap

• M
• U
• D
• P
• I
• L
• E
• S

• U
• S
• E
• D
• C
• A
• R
• S

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Anion Gap Metabolic Acidosis
Methanol
M
Formic
U
Uremia
Sulfuric, Phosphoric, Uric
D
DKA (AKA)
Acetone, Acetoacetate, B-hydroxybuteric
P
Paraldehyde
Organic acids
I
INH
????
L
Lactic (from what?)
Lactic
E
Ethylene Glycol
Oxalic, Glycolic
S
Salicylates
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Anion Gap Metabolic Acidosis
Methanol
M
Formic
U
Uremia
Sulfuric, Phosphoric, Uric
D
DKA (AKA)
Acetone, Acetoacetate, B-hydroxybuteric
P
Paraldehyde
Organic acids
I
INH
????
L
Lactic (from what?)
Lactic
E
Ethylene Glycol
Oxalic, Glycolic
S
Salicylates
11
Anion Gap Metabolic Acidosis
Methanol
M
Formic
U
Uremia
Sulfuric, Phosphoric, Uric
D
DKA (AKA)
Acetone, Acetoacetate, B-hydroxybuteric
P
Paraldehyde
Organic acids
I
INH
????
L
Lactic (from what?)
Lactic
E
Ethylene Glycol
Oxalic, Glycolic
S
Salicylates
Salicylic, Lactic
12
Non-Anion Gap Metabolic Acidosis
U
Uretero-Sigmoid diversions (GI bicarbonate
loss)
S
E
Ethanol or Enocrinopathies
D
Diarrhea
C
Carbonic Anhydrase Inhibitors
A
Hyper-Alimentation
R
RTA
S
Saline
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Metabolic Alkalosis

• Vomiting or NG suction
• Fluid volume contraction (contraction
  alkalosis)
• Hypokalemia
• Cushings Disease, glucocorticoid,
  mineralocorticoid
• Post-chronic hypercapnia
• Bartters or Gitelman's Syndrome
• Massive blood transfusion (what preservative?)
• Ingestion or administration of bicarbonate
• Milk-alkali Syndrome

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Respiratory Acidosis(Hypoventilation)

• Musculoskeletal or neurologic
• Kyphoscoliosis
• Guillain-Barre (flaccid paralysis)
• Myesthenia Gravis
• Botulism
• Polymyositis
• Multiple sclerosis
• ALS
• Other
• OSA

• CNS
• Sedatives (iatrogenic or street)
• Obesity-hypoventilation
• Pleural Disease
• Effusion, PTX
• Intrinsic Lung Disease
• COPD
• ARDS
• PE
• Pneumonia

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Respiratory Alkalosis

• Catastrophic CNS event
• Anxiety or Pain
• Early asthma exacerbation
• Sepsis
• PE
• Cirrhosis
• Pulmonary Fibrosis
• Pregnancy
• Salicylates
• Progesterone

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Six Step Approach to Acid-Base Analysis (fewer
than AA!)

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• Acute, pH should change 0.08 (pCO2-40) / 10
• Chronic, pH should change 0.03 (pCO2-40) / 10
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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• Acute, pH should change 0.08 (pCO2-40) / 10
• Chronic, pH should change 0.03 (pCO2-40) / 10
• So.. if the pCO2 is 80
• the change is 80 40 40
• 40 / 10 4
• the pH should change by 0.08 (4) 0.32
• if acute
• the pH should change by 0.03 (4) 0.12
• if chronic

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• Anion gap (Na) (Cl- HCO3-)
• A normal anion gap is
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• Anion gap (Na) (Cl- HCO3-)
• A normal anion gap is 12
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• 1.5 (HCO3-) 8 /- 2 should equal pCO2
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• 1.5 (HCO3-) 8 /- 2 should equal pCO2
• If higher, then respiratory acidosis is also
  present
• If lower, then respiratory alkalosis is also
  present
• Is there a second metabolic disturbance present?

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance?
• Delta anion gap vs. Delta bicarbonate
• Measured HCO3- (delta anion gap) should equal
  24

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Six Step Approach

• Is the patient acidemic or alkalemic?
• Is the overriding disturbance respiratory or
  metabolic?
• If respiratory is it acute or chronic?
• If metabolic is there an high anion gap?
• If metabolic is the respiratory system
  compensating appropriately?
• Is there a second metabolic disturbance?
• Delta anion gap vs. Delta bicarbonate
• Measured HCO3- (delta anion gap) should equal
  24
• If less than 24, then there is a non-gap
  acidosis present
• If more than 24, then there is a metabolic
  alkalosis present

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Problem 1
TRIPLE ACID-BASE DISORDER
123
99
ABG 7.31/10/100/8
4.0
5
AG 19
1.5 (5) 8 /- 2
15.5 /- 2
The measured pCO2 is less than 13.5
acidosis
1o metabolic
AG
5 (19-12)
12
alkalosis
1o respiratory
This is less than 24
1o metabolic acidosis -AG
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Problem 2
130
80
ABG 7.20/25/100/8
4.0
10
AG 40
1.5 (10) 8 /- 2
23 /- 2
The measured pCO2 is the same as the calculated
acidosis
1o metabolic
AG
10 (40 - 12)
38
1o metabolic alkalosis
This is more than 24
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Problem 3
125
100
ABG 7.07/28/100/10
2.5
8
AG 17
1.5 (8) 8 /- 2
20 /- 2
The measured pCO2 is more than 22
acidosis
1o metabolic
AG
8 (17-12)
13
acidosis
1o respiratory
This is less than 24
1o metabolic acidosis -AG
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Problem 4
135
93
ABG 7.18/80/100/28
4.0
30
80 40 40
0.03 (40/10) 0.12
if chronic
0.08 (40/10) 0.32
if acute
acidosis
1o respiratory
7.40 7.18 0.22
(acute on chronic)
0.22 is between 0.12 and 0.32
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Problem 5
TRIPLE ACID-BASE DISORDER
140
98
ABG 7.14/45/100/18
4.0
17
AG 25
1.5 (17) 8 /- 2
25.5 /- 2
The measured pCO2 is more than 27.5
acidosis
1o metabolic
AG
17 (25-12)
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acidosis
1o respiratory
This is more than 24
1o metabolic alkalosis