1. Diagnosis of Acid Base Disorders
Alok Agrawal, MD, FASN, FNKF
Clinical Associate Professor
WSU, Dayton, Ohio

2. Arterial Blood Gas
ABG’s - necessary to correctly diagnose AB disorders
Interpret ABG s in conjunction with history, PE and labs
TCo2 in the chemistry panel - more accurate
pCO2 >55, primary respiratory acidosis always present
AG> 20, primary metabolic acidosis always present

3. AB Disorders- Definitions
Acidemia : pH < 7.38
Alkalemia : pH > 7.42
Acidosis : pathologic process increasing H+
Alkalosis: pathologic process decreasing H+
Mixed Disorders : combination of 2 or more primary disorders
Compensation : physiologic processes that cause pH to move towards normal due to buffering

4. STEP 1
STEP 2
Check pCO2
Check pH
Metabolic
Acidosis
Metabolic
Acidosis
Respiratory
< 40
Metabolic
Acidosis
Respiratory
Acidosis
> 40
< 7.40
Respiratory
Acidosis
Metabolic
Alkalosis
> 7.40
Metabolic
Alkalosis
Respiratory
Alkalosis
> 40
Metabolic
Alkalosis
Respiratory
Respiratory
Alkalosis
< 40

5. STEP 3
STEP 4
Choose Formula
Identify other disorders
Metabolic
Acidosis
pCO2 = 1.5 (HCO3¯ ) + 8
± 2
STEP 5
Check Anion Gap
Respiratory
Acidosis
For every Ý of 10 in pCO2:
pH ¯ by 0.08 (Acute)
0.03 (Chronic)
HCO3¯ ­ by 1 mEq/l (Acute)
4 mEq/l (Chronic)
STEP 6
Check Urine pH
Metabolic
Alkalosis
pCO2 = 0.9 (HCO3¯ ) +16
STEP 7
For every ß of 10 in pCO2:
pH ­ by 0.08 (Acute)
0.03 (Chronic)
HCO3¯ ¯ by 2 mEq/l (Acute)
5 mEq/l (Chronic)
Generate a differential
diagnosis
Respiratory
Alkalosis

6. Normal pH pCO2 < 36 , HCO3 < 21
mixed respiratory alkalosis and metabolic acidosis
pCO2> 44, HCO3> 27
mixed respiratory acidosis and metabolic alkalosis
pCO2 ~ 40, HC03~ 24 (with anion gap)
mixed metabolic acidosis and metabolic alkalosis

7. Simple metabolic acidosis anion gap

8. Mg 2 Proteins 16 Proteins 16 Ca 5 K 5 These anions= 22 Na 140 Cl 105
Organic acids 4
Na 140
Cl 105
PO4/SO4 2
K 5
HCO3 25
These cations = 12
These anions= 22
Anion gap is
Unmeasured anions
Unmeasured cations
22 – 12 = 10
Anion gap is calculated
Na – (Cl + HcO3) or
140 – 130 = 10
Cations
Anions

9. Increased Anion gap acidosis
Methanol
Uremia
DKA
Paraldehyde ingestion, propylene glycol
Alcohol, Acetaminophen (pyroglutamic acid)
Lactic acidosis
Ethylene glycol
Salicylate , Starvation ketoacidosis

10. Causes of Low Anion Gap Decreased Unmeasured Anion
hypoalbuminemia
Increased Unmeasured Cation
myeloma- IgG, light chains, marked hypercalcemia and hypermagnesemia
Pseudohyperchloremia
li intoxication, Bromism

11. Normal anion gap acidosis
Diarrhea
Ureteral diversion
RTA, Renal failure chronic- early
Hippurate (toulene), Hyperalimentation (AA, sulfur)
Acetazolamide, ammonium chloride, topiramate
Miscellaneous - pancreatic fistula, post hypocapnia,
- dilutional (IVF)

12. Acquired Distal RTA Auto-immune disorders
Sjogrens, PBC
Hypercalciuria and Nephrocalcinosis
Hyperpara, hypervitaminosis D
Drugs
Ampho B, ifosfomide, lead, li, tetracycline, toulene
TI Diseases

13. Osmolal Gap Measured Osm- Calculated Osm ethylene glycol methanol
propylene glycol
isopropranolol

14. Lactic Acidosis Type A Type B - Metformin -Shock
- Acute severe hypoxia
- Acute severe anemia
Type B
- Metformin
- Malignancy
- Thiamine deficiency
- Cyanide
- NRTI
- Zyvox

15. Delta AG- Delta HCO3 Ratio
Ratio 1-2 : High anion gap acidosis
Ratio > 2 : HAG acidosis and metabolic alkalosis
Ratio < 1 : HAG acidosis and NAG acidosis
: DKA with ketone excretion
: CKD with anion excretion but H+
retention

16. Simple metabolic alkalosis

17. Saline responsive metabolic alkalosis
Diuretics
Adenoma
Miscellaneous- IV penicillin, Barter’s syndrome
Posthypercapnia
Emesis
NG suction

18. Saline unresponsive metabolic alkalosis
Licorice ingestion
Exogenous steroids
Alkali ingestion with low GFR
Cushing syndrome
Hyperaldosteronism

20. THANK YOU

21. Case 4a
72 yr old female with brain tumor has MS changes. Comatose with Kussmaul’s respirations. CT- IC hemorrhage with midline shifts
130/4.0/103/20
7.56/20/20
pH: 7.0

22. Simple acute respiratory alkalosis

23. Case 4b Same patient after 2 days with same breathing pattern
136/4.5/110/14
7.46/21/15
pH : 6.5

24. Simple chronic respiratory alkalosis (fully compensated)

25. Case 4c What if history was not known? 136/3.9/109/15 7.47/21/15
pH 6.0

26. Case 4c simple chronic respiratory alkalosis
mixed acute respiratory alkalosis and metabolic acidosis

27. Case 4d
ABG done 12 hours after 4a and before 4b
7.52/21/17

28. Respiratory alkalosis in which compensation not complete

29. Case 5 20 yr old male in ER - bottle of pills 140/3.5/104/8/18/1.0/90
7.35/15/8
pH: 5.0

30. Mixed elevated gap metabolic acidosis and respiratory alkalosis

31. Case 6a 57 year old with history of smoking has DOE 143/4.0/105/27
7.37/50/25
pH 5.0

32. simple chronic respiratory acidosis

33. Case 6b
One month later with respiratory distress. Has wheeze with respiratory rate of 33
142/3.9/100/33
7.29/61/33
pH : 5.0

34. Mixed acute on chronic respiratory acidosis

35. Case 7 45 year old diabetic patient with obtundation
140/5.5/97/20/20/1.1
7.01/80/20
pH : 5.0

36. Mixed acute respiratory acidosis elevated gap metabolic acidosis and metabolic alkalosis

37. Case 8
78 yr old NH pt. with vomiting for several days and fever, increasing SOB for few hours. RR is 35/mt . RLL consolidation.
138/4.2/97/28
7.69/20/26
pH:8.0

38. Mixed acute respiratory alkalosis and metabolic alkalosis

39. Case 9
20 yr old diabetic with nausea, vomiting for several days and now with fever and SOB over 8 hours
148/4.0/95/24/ 26/1.2/610
7.59/26/24
pH : 8.0, ketones

40. Respiratory alkalosis, metabolic alkalosis and elevated gap metabolic acidosis

41. Case 10
47 yr old alcoholic presents with vomiting after binge drinking for past 2 days. Swallowed large no. of diazepam pills 1 hour prior and is lethargic. RR- 8/mt and is unresponsive
136/4.4/85/29/21/1.0
7.27/62/29
pH: 5.0

42. Respiratory acidosis, elevated gap acidosis and metabolic alkalosis

43. Case 11
65 with COPD, CHF has increasing SOB,wheezing for 4 hrs. Currently on furosemide.
140/3.8/90/37/20/1.1
7.40/60/37
pH: 5.0

44. Mixed acute on chronic respiratory acidosis and a metabolic alkalosis

45. Case 12
27 yr old diabetic with SOB for 1 hour. Nausea, increased urination for 2 days. did not take insulin for 2 days. Hypercoagulable state diagnosed in hospital
136/3.6/102/12/10/1.1/700
7.40/20/13
pH: 5.0, ketones +

46. Mixed elevated gap metabolic acidosis and respiratory alkalosis