Acid-Base Disorders
Robert Fields, DO
St Joseph’s Mercy Hospital
Emergency Dept.
5 Steps is all you need





Check the pH
Find the primary disorder (Look at pCO2
and HCO3)
Calculate the anion gap (AG=Na – (HCO3
+ Cl-)
Calculate the excess anion gap (AGp - AGn
+ HCO3p = X)
Winters formula pCO2 = 1.5(HCO3-) + 8
What do you really need to do this?


ABG, with pCO2 and pH
Chem 7 with Na+, Cl-, HCO3-
STEP 1, Check the pH





Acidemia, pH < 7.35
Alkalemia, pH >7.45
Made Simpler! Acidemia<7.40>Alkalemia
Acidosis/Alkalosis vs. Acidemia/Alkalemia
Know the “normals” of the rest. (This is
not to hard as it is printed in the
computer)
STEP 2, Find the Basic Problem



Look at the pCO2 and the HCO3Respiratory problems relate to pCO2
Metabolic problems relate to HCO3-
Respiratory Acidosis





Causes
CNS depression
NMS disorders
Pulmonary edema
Ventilatory dysfunction
Respiratory Alkalosis







Causes
Anxiety
Hypoxia
CNS stimulants
Pregnancy
Sepsis
Excessive mechanical ventilation
Metabolic Alkalosis




Chloride responsive
Vomiting
Diuretics
Dehydration




Chloride unresponsive
Excess mineral
corticoid activity
Cushing's, Conn’s
The infamous licorice
ingestion
STEP 3, Check the Anion Gap
What is the Anion Gap?






Cations = Anions
Na+ + K+ etc. = HC03- + Cl- + Alb + etc
Simplified
Na+ = HC03- + Cl- + others
We will call the others, AG (anion gap)
and solve for AG.
Therefore AG = Na+ - (HCO3- + Cl-)
Increased Anion Gap
Metabolic Acidosis








Methanol
Uremia
DKA (starvation ketosis, alcohol ketosis)
Paraldehyde
INH, Iron
Lactic Acidemia (type A, B, D)
Ethanol, Ethylene Glycol
Salicylates
Columbia Encyclopedia: paraldehyde
(pârăl'dəhīd') , nervous system depressant similar to alcohol in its effects and used as a
sedative. A colorless flammable liquid with a disagreeable odor, paraldehyde produces
sleep for up to 12 hr. with little or no muscle, heart, or respiratory depression. It is often
given to alcoholics having delirium tremens, to induce sleep, and is also used to calm
psychiatric patients. Like alcohol and other depressants it is addictive (see drug
addiction and drug abuse). Paraldehyde is also used in the manufacture of synthetic
resins, as a preservative, and in preparing leather. It is produced by treating
acetaldehyde with a small amount of sulfuric acid.
Normal Anion Gap
Metabolic Acidosis
Gastrointestinal
Diarrhea
Ureteral diversion

Renal Loss
RTA
Early renal failure
Acetozolamide
Aldosterone inhibitors

12
mmol/L
24
140
104
Na+
Normal AG
Na+/Cl-
HCO3
AG
Lactic Acid Production
+
H+
+
H2CO3
H+ + HCO3-
CO2 + H2O +
Buffering Species
CO2 + H2O <----> H2CO3
carbonic anyhdrase
H2CO3 <----> HCO3- + H+
12
mmol/L
24
140
104
Na+
Normal AG
Na+/Cl-
HCO3
AG
12
mmol/L
24
24
12
140
Na+
104
104
Normal AG
Acidosis
Na+/Cl-
HCO3
AG
STEP 4, Check the Anion Gap
Excess




This is going to help you determine if
there is an alkalosis or acidosis that is
NOT related to the anion gap.
This done by doing this equation
AGp – AGn + HCO3-p = X
X should equal 24 if there is no additional
acidosis or alkalosis.
The results of Step 4
If you calculated < 20 mmol/L
There is a an acidosis present that is
unrelated to the AG.
 If you calculated >30 mmol/L there is an
alkalosis present.

What we are doing so far ?




1. Determine the pH
2. Finding primary disorder
3. Finding AG Metabolic Acidosis if not
already recognized
4. Finding Metabolic Acidosis (unrelated to
the AG) and/or metabolic Alkalosis if not
yet recognized.
So What’s Left?



Respiratory Alkalosis or Acidosis that may
have gone unrecognized.
Winter’s formula
pCO2 = 1.5 (HCO3) + 8 +-2
Examples
Example 1





pH, 7.50
pCO2, 20mm Hg
Na+, 140 mmol/L
Cl-, 103 mmol/L
HCO3-, 15
Results






Alkalemia
Primary disorder, respiratory
AG is 22, Therefore metabolic acidosis with AG.
A-ha! Two disorders are present.
Excess AG, 22- 12 + 15 = 25 , no alkalosis or
acidosis otherwise present.
Don’t need to do Winter’s as you can only have
one respiratory problem.
Clinical correlation?
Salicylate Toxicity
Example 2





pH, 7.40
pCO2, 40mm Hg
Na+, 145 mmol/L
Cl-, 100 mmol/L
HCO3-, 24
Results






pH? Normal
Primary, What Primary?
Anion Gap = 21
Excess anion gap = 21-12 + 24 =33, A
significant metabolic alkalosis is present
too!
Winter’s ? Nothing too bad here.
Clinical Correlation?
CRI (AG acidosis) with vomiting as
uremia worsened
Example 3





pH, 7.50
pCO2, 20mm Hg
Na+, 145 mmol/L
Cl-, 100 mmol/L
HCO3-, 15
Example 3





Alkalemia
Respiratory primarily
Anion Gap is 30, AG MA (MUDPILES)
Excess anion gap plus HC03 = 30-12 + 15
= 33, There it is the triple threat.
Don’t need Winter’s, respiratory
determined as primary.
Clinical Correlation



Vomiting (metabolic alkalosis)
Alcoholic ketoacidosis (AG metabolic
acidosis)
Pneumonia, (Respiratory alkalosis)
Example 4





pH, 7.10
pCO2, 50mm Hg
Na+, 145 mmol/L
Cl-, 100 mmol/L
HCO3-, 15
Example 4





Acidemia
Respiratory and Metabolic
Anion Gap is 30, you know the drill
Excess AG + HCO3 = 30-12+15=33,
Metabolic Alkalosis.
Clinical Correlation?
Clinical Correlation

DKA with vomiting, followed by aspiration
and unresponsive.
Example 5





pH 7.25
pCO2, 45
Na+, 137
Cl-, 79
HCO3-, 20
Example 5





Acidemia
Metabolic
AG=38
38-12 + 20 = 46
Winter’s ! 1.5(20) + 8 = 38
Clinical Correlation




Borhaave’s Esophageal Rupture
Anion Gap Acidosis from lactic acid and
ketoacidosis
Metabolic alkalosis from profound
dehydration and loss of gastric HCL into
chest wall
Respiratory acidosis from large pleural
effusion.
References

1991 West J. Medicine, A Practical
Approach to Acid-Base Disorders.