1. ABG CASE STUDIES & INTERPRETATION
Dr. Saidunnisa M.D.,
Associate Professor in
Biochemistry

2. It’s not magic understanding ABG’s, it just takes a little practice!

3. Acid base imbalances Metabolic acidosis Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis

4. Metabolic
METABOLIC ACIDOSIS: Decrease the HCO3- --> the pH goes down.
Compensation: Respiratory Alkalosis (hyperventilation) will bring the pH back near normal. Hyperkalemia (K+ increased)
Causes: Diarrhea, DKA, LA, renal failure.
METABOLIC ALKALOSIS: Increase the HCO3- --> the pH goes up.
Compensation: Respiratory Acidosis (hypoventilation) can help to bring the pH back near normal.Hypokalemia (K+ decreased)

5. METABOLIC ALKALOSIS CAUSES:
Vomiting: Lose enough stomach acid to produce alkalosis.
Diuretics: Loop diuretics and thiazides can lead to hypokalemia > secondary metabolic alkalosis.
Antacids overuse

6. ANION GAP
Essentially, the difference between the concentrations of cations (Na+ primarily +k+) and anions (Cl-, HCO3-) in the blood.
High Anion Gap: Metabolic Acidosis. It indicates that you have added acids to the blood: salicylic acid, formic acid, lactic acid, oxalic acid, sulfuric acid.
Normal Anion Gap: Respiratory Acidosis. It occurs when you ultimately become acidotic because of losing HCO3-.

7. Causes of anion gap metabolic acidosis
Methanol
Uremia
Diabetic ketoacidosis
Paraldehyde
Isopropyl alcohol
Lactic acidosis
Ethylene glycol
Salicylates
Rhabdomyolysis

8. The Delta/Delta:  AG/  HC03
Rationale:
For each unit INCREASE in AG (above normal), HC03 should DECREASE one unit (below normal)
“Normal” values: AG = 18, HC03 = 24

9. Respiratory
RESPIRATORY ACIDOSIS: Increase the PCO2---> the pH goes down. Hypoventilation. Compensation: Metabolic Alkalosis can help bring the pH back near normal.
Causes: pneumonia, Bronchitis, Asthma, COPD.
RESPIRATORY ALKALOSIS:Decrease the PCO2-> the pH goes up. Hyperventilation. Compensation: Metabolic Acidosis can help bring the pH back near normal.

10. RESPIRATORY ALKALOSIS
Causes:
High altitude.
Neuromuscular disease
Respiratory center depression
Inadequate mechanical ventilation
Sepsis
Burns

11. ABG Disorders Disorder Change Compensation Respiratory Acidosis Pa CO2
HCO3
(Metabolic alkalosis)
Respiratory Alkalosis
(Metabolic acidosis)
Metabolic Acidosis
(Respiratory alkalosis)
Metabolic Alkalosis
Pa CO2 (Respiratory acidosis)

12. Metabolic acidosis

13. Metabolic acidosis
Metabolic acidosis: Is caused by a decrease in HCO3- concentration in blood.
Causes:
Increased production of acids: LA, kA, Salicylate poisoning.
Loss of HCO3-: Via GIT eg Diarrhea and kidneys RTA.
Blood profile: pH decreased
[HCO3-] decreased
Pco2 decreased

14. Buffering: Excess acids are buffered in both ECF and ICF.
In ECF buffered primarily by HCO3- thus decreasing the [HCO3-] and causing decrease in pH predicted by H-H equation.
In ICF excess acids are buffered by organic phosphate and proteins usually H+ is for exchanged K+ causing hyperkalemia.

15. Compensation:
Respiratory compensation: decrease in pH stimulates respiratory center causing hyperventilation which produces decrease in PCO2.
Renal Compensation: excess H+ is excreted as titratable acid and NH4+.
Treatment: lactate containing solution which converts HCO3- ion the liver.

16. Assessment of acid base status
Direct arterial blood measurements: ABG pH
pCO2
pO2
Derived measures:
Bicarbonate (HCO3-)
Normal Values:
pH = (7.4)
HCO3-= mEq / L (24mEq / L)
pCO2 = mm Hg (40mm Hg )
Anion Gap: (18)
NB: use heparinised blood, measured within 10 minutes

17. Metabolic alkalosis

18. Respiratory acidosis

19. Respiratory Alkalosis

20. Metabolic Acidosis
pH 7.30
PaCO
HCO

21. Metabolic Alkalosis
pH 7.50
PCO
HCO

22. Respiratory Acidosis
pH 7.30
PaCO
HCO

23. Respiratory Alkalosis
pH 7.50
PaCO
HCO

24. What are the compensations?
Respiratory acidosis  metabolic alkalosis
Respiratory alkalosis  metabolic acidosis
In respiratory conditions, therefore, the kidneys will attempt to compensate and visa versa.
In chronic respiratory acidosis (COPD) the kidneys increase the elimination of H+ and absorb more HCO3. The ABG will Show NL pH, CO2 and HCO3.

25. Buffers kick in within minutes.
Respiratory compensation is rapid and starts within minutes and complete within 24 hours. Kidney compensation takes hours and up to 5 days.

26. Acid base disorder-worksheet

27. Practice ABG’s

28. Answers to Practice ABG’s
1. Respiratory alkalosis
2. Respiratory acidosis
3. Metabolic acidosis
4.Compensated Respiratory
acidosis
5. Metabolic alkalosis
6. Compensated Respiratory
7.Compensated Metabolic alkalosis 8. Metabolic acidosis 9. Respiratory acidosis 10. Metabolic alkalosis

29. Work sheet Diarrhea may lead to----------?
Acid loss due to vomiting and gastric suction may lead to ____ alkalosis?
Overuse of ____ may lead to metabolic alkalosis?

30. STEPS OF ASSESSING ABG
STEP 1: Diagnose whether it is acidosis or alkalosis- (pH will help)
STEP 2: Diagnose whether it is metabolic or respiratory(Look at the value of bicarbonate and pCO2)
STEP3:Diagnose whether compensated or non compensated

31. STEPS OF ASSESSING ABG
STEP4: Diagnose whether AG is normal or elevated(apply the formula) [Na+ + K+] + [cl- + HCO3-]
STEP 5: Diagnosis
Always confirm with possible cause by reading the history

32. PROBLEMS FOR DISCUSSION

33. Problem#1 Discuss the probable diagnosis.
67 year female known diabetic for past 20years presented with sudden onset of severe chest pain and Shortness of breath.
ABG analysis showed:
pH 7.36
PCO2 33 mmHg
HCO3 18 mmol/L
Discuss the probable diagnosis.

34. Problem #2 His ABG shows the following Na+140 / Cl- 104 K+7.0 pH: 6.95
A 30-year old man with DM presents with H/O polyuria, polydipsia, fever, cough, and purulent sputum.
His ABG shows the following
Na+140 / Cl- 104
K+7.0
pH:
pCO2 : 33
Hco3 : 7.0
Discuss the probable diagnosis.

35. Problem#3
45 year old male was admitted to the emergency room with complaints of mild vomiting, associated with disorientation and muscular weakness. His blood investigations showed the following
pH = Na -137meq/l
HCO3-=16mEq / L Cl-108meq/l
pCO2 = 34mm Hg K -5.8 meq/l
Glucose =685mg/dl urea -49 mg/dl
Discuss the probable diagnosis.

36. Problem #4
60 year male presents to the ED from a nursing home. You have no history other than he has been breathing rapidly and is less responsive than usual.
Na Cl- 99 HCO3- 5
pH pCO2 10
Discuss the probable diagnosis.

37. Problem # 5
60year old man was admitted with severe abdominal pain, which started some 2 hours back. Clinically he was in a state of shock with distended abdomen. Femoral pulses could not be palpable His ABG shows the follows pH : 7.05 pCO2: 26.3 mmHg HCO3: 7 mmol/L Discuss the probable diagnosis.

38. Problem #6
Young woman was admitted with history of head injury There was Fracture skull along with cerebral injury The Respiratory rate 38/min 3 days later her ABG was: pH: 7.44 pCO2 : 29.3 mmHg HCO3: 19 mmol/L Discuss the probable diagnosis.

39. Problem# 7
A 58-year old man with cirrhosis and Type II DM presents with fever, abdominal pain and vomiting. His ABG shows the following Na+149 /K+ 3.0 pH 7.31 Cl- 112/ HCO3- 12 pCO2 19 Discuss the probable diagnosis.

40. Any Questions?

41. Problem-8
A women who had been vomiting for 3 days was taken to the emergency department, where the following blood values were measured:
pH: 7.5
Pco2: 48 mm of Hg
HCo3-: 37meq/l
What acid base disorder she have? Does she have a simple or a mixed acid base disorder?

42. Problem-9 ABG analysis:
A 56 year old woman has a 15 year history of type-I DM. A recent viral infection results in loss of appetite, fever, and vomiting. Physical examination reveals her mucous membranes are dry and she has decreased skin turgor. She is breathing deeply and rapidly. A urine sample contains glucose and ketones.
ABG analysis:
pH: Na+: 132meq/l,
k+ : 5.9meq/l cl-: 94
Pco2: 18 mm of Hg
HCo3-: 5meq/l
What acid base disorder she have? Does she have a simple or a mixed acid base disorder?

43. Problem-10
A 35 year old man is admitted to the hospital for evaluation of severe epigastric pain. For several days prior to admission he had persistent nausea and vomiting. The following blood values are obtained:
pH: Na+: 137meq/l,
k+ : 2.8meq/l cl-: 82
Pco2: 45 mm of Hg
HCo3-: 37meq/l
What acid base disorder she have? Does she have a simple or a mixed acid base disorder?

44. Problem-11
A 68 year old man has smoked three packs of cigarettes per day for 40 years. He had frequent episodes of asthmatic bronchitis. The following blood values are obtained:
pH: Na+: 139meq/l,
Cl-: 95meq/l
Pco2: 70 mm of Hg
HCo3-: 33meq/l
What acid base disorder she have? Does she have a simple or a mixed acid base disorder?

45. Problem-12 A patient has the following arterial blood values: pH: 7.33
Pco2: 70 mm of Hg
HCo3-: 36meq/l
What acid base disorder she have? Does she have a simple or a mixed acid base disorder?