Worksheet for Solving Acid-Base Problems
Joel Gordon M.D., Professor, Dept of Internal Medicine, Carver College of Medicine, University of Iowa
Deborah DeWaay M.D., Assistant Professor, Dept of Internal Medicine, Medical University of South Carolina
1) Step 1: Gather the necessary data (basic metabolic panel and ABG)
a)
b)
c)
Make sure the HCO3- from the BMP and the ABG are within 2 (if not the results are uninterpretable.)
H2O + CO2  [H+] + [HCO3-]
“Normal” – pH = 7.4(7.38-7.42), pCO2 = 40 (38-42), HCO3- = 24 (22-26)
pH | pCO2 | HCO3-
2) Step 2: Look at the pH
a)
b)
If pH >7.4, then patient is alkalemic
If pH <7.4, then patient is acidemic
Patient has a primary:
Acidosis/Alkalosis
3) Step 3: Determine the primary etiology
a)
b)
c)
d)
Look at the pCO2:
i) Is it consistent with an acidosis, >40?
ii) Is it consistent with an alkalosis, <40?
Look at the HCO3-:
i) Is it consistent with an acidosis, <24?
ii) Is it consistent with an alkalosis, >24?
Does the pCO2 or the HCO3- explain the pH?
If both explain the pH  the patient has two disorders
Primary process is:
Respiratory/Metabolic
4) Step 4: If primary respiratory disorder, determine whether acute or chronic
a)
b)
Respiratory acidosis:
i) Acute: for every one point increase in pCO2 above 40, there should be a pH decrease of 0.008
ii) Chronic: for every one point increase in pCO2 above 40, there should be a pH decrease of 0.003
Respiratory alkalosis:
i) Acute: for every one point decrease in pCO2 above 40, there should be a pH increase of 0.008
ii) Chronic: for every one point increase in pCO2 above 40, there should be a pH increase of0.003
Respiratory Process:
Acute/Chronic
Acute < 24 hours
Chronic > 3 days
5) Step 5: Calculate the anion gap
a)
b)
c)
d)
[Na+] – ([HCO3-] + [Cl-]) = ________ . Normal is 8-12 mEq/L
Correct the anion gap for albumin. For every1 gm/dL drop in albumin below 4.0 gm/dL, there is a
corresponding ↓2.5 meq/L in the anion gap
Calculate the excess anion gap, also called the ∆∆ gap Excess/∆∆ gap = actual anion gap – 10 [normal
AG]
If the patient has a PRIMARY anion gap metabolic acidosis:
i) Calculate the corrected or potential HCO3-. This tells you what the HCO3- would be if the anion gap is
corrected for.
ii) The corrected or potential HCO3- = ∆∆ gap + measured serum HCO3(1) If >26 = a metabolic alkalosis
(2) If <22 = a non-anion gap metabolic acidosis
Anion Gap Present:
YES /NO
Non-gap Acidosis Present
YES /NO
Metabolic Alkalosis Present
YES /NO
6) Step 6: Identify concomitant disorders
a)
b)
If there is a PRIMARY metabolic disorder, is there also a respiratory disorder?
i) Calculate the expected pCO2. The expected pCO2 = ∆ pC02 + 40
(1) Metabolic acidosis: ∆ pCO2=1.2 x ∆ HCO3[the CO2will decrease one unit for every 1.2 unit decrease in HCO3-]
(2) Metabolic alkalosis: ∆ pCO2=0.7 x ∆ HCO3[the CO2 will increase one unit for every 0.7 unit increase in HCO3-]
ii) If actual pCO2 > expected pCO2  concomitant respiratory acidosis
iii) If actual pCO2< expected pCO2  concomitant respiratory alkalosis
If there is a PRIMARY respiratory disorder, is there also a metabolic disorder?
i) Calculate the expected HCO3-. The expected HCO3- = ∆ HCO3- + 24.
(1) Respiratory Acidosis:
(a) Acute: ΔHCO 3 - = 1 mEq/L↑/10mmHg↑pCO 2
[the HCO 3 - will go up 1mEq/L for every 10mmHg the pCO 2 goes up above 40].
(b) Chronic: ΔHCO 3 - = 3 mEq/L↑/10mmHg↑pCO 2
[the HCO 3 - will go up 3 mEq/L for every 10mmHg the pCO 2 goes up above 40].
(2) Respiratory Alkalosis:
(a) Acute: ΔHCO 3 - = 2 mEq/L↓/10mmHg↓pC0 2
[HCO 3 - will go down 2 mEq/L for every 10mmHg the pCO 2 goes down below 40].
(b) Chronic: ΔHCO 3 - = 4 mEq/L↓/10mmHg↓pCO 2
[HCO 3 - will go down 4 mEq/L for every 10mmHg the pCO 2 goes below 40].
ii) If actual HCO3- < expected HCO3-  concomitant metabolic acidosis
iii) If actual HCO3- > expected HCO3-  concomitant metabolic alkalosis
Resp. Acidosis Present
YES /NO
Rep. Alkalosis Present
YES /NO
Metabolic Acidosis Present
YES /NO
Metabolic Alkalosis Present
YES /NO
STEP 7: Figure out what’s causing the problem(s)
Anion Gap
Metabolic Acidosis
GOLD MARK
G: Glycols (Ethylene &
Propylene)
O: Oxoproline
L: L-Lactate
D: D-Lactate
M: Methanol
A: Aspirin
R: Renal Failure
K: Ketoacidosis (EtOH,
Starvation, DKA)
Non-Gap Metabolic
Acidosis
ACCRUED
A: Acid load
C: Carbonic Anhydrase
Inhibitors
C: Chronic Kidney
Disease (Renal Failure)
R: Renal Tubular
Acidosis
U: Ureteroenterostomy
E: (Volume) Expansion
D: Diarrhea
Acute Respiratory
Acidosis
CHOMPP
C: CNS depression
H: Hemo/pneumothorax
O: Obstruction (airway)
M: Myopathy
P: Pneumonia
P: Pulmonary edema
Anything that causes
Hypoventilation or
Chronic respiratory acidosis
(COPD and restrictive lung
disease)
Metabolic Alkalosis
Respiratory Alkalosis
CLEVER PD
C: Contraction
L: Licorice
E: Endo (Conn’s,
Cushing’s, Bartter’s)
V: Vomiting
E: Excess Alkali
R: Refeeding Alkalosis
P: Post-hypercapnea
D: Diuretics
CHAMPS
C: CNS disease
H: Hypoxia
A: Anxiety
M: Mechanical ventilators
P: Progesterone:
Pregnancy and Liver
Disease
S: Salicylates/Sepsis
Anything that causes
hyperventilation