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Diagnosing Acid Base Disorders

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Diagnosing Acid Base Disorders Powered By Docstoc
					Diagnosing Acid Base Disorders
     (without your PDA)
                         Daniel Dilling, MD




Adapted from: Morganroth, M. Journal of Critical Illness; 5(2):138-54.
    When to be suspicious…
   and 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!!!
       The elements of the ABG
•   pH
•   pCO2
•   pO2
•   HCO3-
•   Base excess/deficit
•   O2 saturation
•   Methemoglobin, Carboxyhemoglobin
       The elements of the ABG
•   pH
•   pCO2
•   pO2
•   HCO3-
•   Base excess/deficit
•   O2 saturation
•   Methemoglobin, Carboxyhemoglobin
       The elements of the ABG
•   pH
•   pCO2
•   pO2
•   HCO3-
•   Base excess/deficit
•   O2 saturation
•   Methemoglobin, Carboxyhemoglobin
                        pH   pCO2   HCO3-


Metabolic acidosis


Metabolic alkalosis


Respiratory acidosis


Respiratory alkalosis
        Metabolic Acidosis
Anion gap         Non-anion gap
M                U
U                S
D                E
P                D
I                C
L                A
E                R
S                S
Anion Gap Metabolic Acidosis
M   Methanol                  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
Anion Gap Metabolic Acidosis
M   Methanol                  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
Anion Gap Metabolic Acidosis
M   Methanol                  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
    Non-Anion Gap Metabolic
           Acidosis
U     Uretero-Sigmoid
S       diversions (GI bicarbonate loss)
E     Ethanol or Enocrinopathies
D     Diarrhea
C     Carbonic Anhydrase Inhibitors
A     Hyper-Alimentation

R     RTA
S     Saline
            Metabolic Alkalosis
Vomiting or NG suction
Fluid volume contraction (“contraction alkalosis”)
Hypokalemia
Cushing’s Disease, glucocorticoid, mineralocorticoid
Post-chronic hypercapnia
Bartter’s or Gitelman's Syndrome
Massive blood transfusion (what preservative?)
Ingestion or administration of bicarbonate
    – “Milk-alkali Syndrome”
            Respiratory Acidosis
             (Hypoventilation)
• CNS                                   • Musculoskeletal or
   – Sedatives (iatrogenic or street)     neurologic
   – Obesity-hypoventilation               – Kyphoscoliosis
                                           – Guillain-Barre (flaccid
• Pleural Disease                            paralysis)
   – Effusion, PTX                         – Myesthenia Gravis
• Intrinsic Lung Disease                   – Botulism
   –   COPD                                – Polymyositis
   –   ARDS                                – Multiple sclerosis
   –   PE                                  – ALS
   –   Pneumonia                        • Other
                                           – OSA
          Respiratory Alkalosis
Catastrophic CNS event
Anxiety or Pain
Early asthma exacerbation
Sepsis
PE
Cirrhosis
Pulmonary Fibrosis
Pregnancy
Salicylates
Progesterone
 Six Step Approach to Acid-Base
    Analysis (fewer than AA!)
1. Is the patient acidemic or alkalemic?
2. Is the overriding disturbance respiratory or
   metabolic?
3. If respiratory… is it acute or chronic?
4. If metabolic… is there an high anion gap?
5. If metabolic… is the respiratory system
   compensating appropriately?
6. Is there a second metabolic disturbance present?
                 Six Step Approach
1. Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?
5.   If metabolic… is the respiratory system compensating appropriately?
6.   Is there a second metabolic disturbance present?
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?

2. Is the overriding disturbance respiratory or
   metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?
5.   If metabolic… is the respiratory system compensating appropriately?
6.   Is there a second metabolic disturbance present?
                Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?


3. 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

4.   If metabolic… is there an high anion gap?
5.   If metabolic… is the respiratory system compensating appropriately?
6.   Is there a second metabolic disturbance present?
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
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?

4. If metabolic… is there an high anion gap?
     Anion gap = (Na+) – (Cl- + HCO3-)
     A normal anion gap is

5.   If metabolic… is the respiratory system compensating appropriately?
6.   Is there a second metabolic disturbance present?
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?

4. If metabolic… is there an high anion gap?
     Anion gap = (Na+) – (Cl- + HCO3-)
     A normal anion gap is 12

5.   If metabolic… is the respiratory system compensating appropriately?
6.   Is there a second metabolic disturbance present?
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?

5. If metabolic… is the respiratory system
   compensating appropriately?
     1.5 (HCO3-) +8 +/- 2 should equal pCO2
6.   Is there a second metabolic disturbance present?
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?

5. 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

6.   Is there a second metabolic disturbance present?
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?
5.   If metabolic… is the respiratory system compensating appropriately?

6. Is there a second metabolic disturbance?
     •   “Delta anion gap” vs. “Delta bicarbonate”
     •   Measured HCO3- + (delta anion gap) should equal 24
                 Six Step Approach
1.   Is the patient acidemic or alkalemic?
2.   Is the overriding disturbance respiratory or metabolic?
3.   If respiratory… is it acute or chronic?
4.   If metabolic… is there an high anion gap?
5.   If metabolic… is the respiratory system compensating appropriately?

6. 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
                          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…
1o metabolic acidosis +AG
 o                             5 + (19-12) = 12
1 respiratory alkalosis
 o                                      This is less than 24…
1 metabolic acidosis -AG
                        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
1o metabolic acidosis +AG
 o                             10 + (40 - 12) = 38
1 metabolic alkalosis
                                         This is more than 24…
                         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…
1o metabolic acidosis +AG
 o                             8 + (17-12) = 13
1 respiratory acidosis
 o                                      This is less than 24…
1 metabolic acidosis -AG
                          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…
1o respiratory acidosis
                            7.40 – 7.18 = 0.22
 (acute on chronic)
                                           0.22 is between 0.12
                                           and 0.32…
                         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…
1o metabolic acidosis +AG
 o                             17 + (25-12) = 30
1 respiratory acidosis
 o                                       This is more than 24…
1 metabolic alkalosis

				
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posted:8/27/2011
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