Acid-Base Disorders Worksheet
Joshua Steinberg MD for Wilson Family Practice Residency
Na+
Step #1: Gather the necessary data (Na+, Cl-, HCO3-, pH, pCO2). 1
Preferably, all obtained from the same blood sample. At Wilson, ordering an Cl
HCO3ABG and a BMP (Chem 7) will give you all of the information you need.
pH
pCO2
Step #2: Look at the pH. If it is > 7.4, then pt has primary alkalosis, proceed to
Step 3a. If pH < 7.4, then pt has primary acidosis, proceed to step 3b.
Patient has primary:
acidosis
| alkalosis
Step #3: Look at the pCO2.
3a: If PCO2 is > 40, then pt’s alkalosis is metabolic; if < 40 then respiratory.
3b: If PCO2 is > 40, then pt’s acidosis is respiratory; if < 40, then metabolic.
Primary process is:
respiratory | metabolic
Step #4: Look for disorders revealed by failure of compensation. 2
- If 1° process is metabolic alkalosis, pCO2 should be > 40, < 55 (there are several
Additional disorder:
resp.
resp.
acidosis | alkalosis
metabolic alkalosis pCO2 prediction formulas, but fraught with clinical inaccuracy/unreliability).
- If 1° process is metabolic acidosis, predicted pCO2 = (1.5 x HCO3) + 8 +/- 2.
In either case above, if actual pCO2 too high, then additional respiratory
acidosis; if actual pCO2 too low, then additional respiratory alkalosis.
- If 1° process is resp., then skip to steps 5&6 (where further metabolic disorders revealed).
-or-
no additional disorder
Step #5: Check if patient has a significant anion gap (> 12-18). (AG = Na –
Cl – HCO3.) If significantly elevated, then patient has an anion gap metabolic
acidosis in addition to (or in confirmation of) whatever Steps 2 thru 4 yielded.
Patient has | does not have
anion gap metabolic
acidosis.
Step #6: Calculate the corrected bicarb. (Pt’s gap – 12 + pt’s serum bicarb)
In addition to whatever disorders Steps 1 through 5 yielded, ...
- if corrected bicarb > 30, then pt has an underlying metabolic alkalosis;
- if corrected bicarb < 23, then pt has an underlying non-gap metabolic acidosis.
Patient has underlying
metabolic:
non gap | alkalosis
!!!!acidosis
Step #7: Figure out what’s causing the problem(s) using differentials below & knowledge of the patient
Anion Gap
Metabolic Acidosis
Non-Gap
Metabolic Acidosis
Acute Respiratory
Acidosis
Metabolic
Alkalosis
Respiratory
Alkalosis
“MUDPILERS”
“HARDUPS”
“CLEVER PD”
“CHAMPS”
• Methanol
• Uremia
• DKA/Alcoholic KA
• Paraldehyde
• Isoniazid
• Lactic Acidosis
• EtOH/Ethylene Glycol
• Rhabdo/Renal Failure
• Salicylates
• Hyperalimentation
• Acetazolamide
• Renal Tubular Acidosis
•Diarrhea
•Uretero-Pelvic Shunt
• Post-Hypocapnia
• Spironolactone
anything that causes
hypoventilation, i.e.:
• CNS Depression
(drugs/CVA)
• Airway Obstruction
• Pneumonia
• Pulmonary Edema
• Hemo/Pneumothorax
• Myopathy
Contraction
Licorice*
Endo: (Conn’s/
anything that causes
hyperventilation, i.e.:
Cushing’s/Bartter’s)*
• CNS disease
• Hypoxia
• Anxiety
• Mech Ventilators
• Progesterone
• Salicylates/Sepsis
(Chronic respiratory
acidosis is caused by
COPD and restrictive
lung disease)
Vomiting, NG suction
Excess Alkali*
Refeeding Alkalosis*
Post-hypercapnia
Diuretics*
*assoc with high urine CL levels
Step #8: Fix it!
references: all steps but #4 nearly verbatim from Dr. Erik Rupard's worksheet adaptation of Haber, A practical approach to acid-base disorders. West J Med 1991. Aug; 155:146-151; step #4 from Narins and Emmett, Simple
and Mixed Acid-Base Disorders. Medicine, vol. 59, no. 3, 1980, and multiple other sources agreeing on metabolic acidosis compensation while conflicting on metabolic alkalosis compensation!
revised last: by Dr. Steinberg at Wilson/JCFCC January 11, 2009.