1. Arterial Blood Gas Analysis

2. What is an Arterial Blood Gas (ABG)?
The components
pH / PaCO2 / PaO2 / HCO3 / O2sat / BE
Desired ranges
pH –
PaCO2 – mmHg
PaO2 – mmHg
HCO3 –
O2sat – %
Base excess – +/-2 mEq/L

3. Why Order an ABG? Aids in establishing a diagnosis
Helps guide treatment plan
Aids in ventilator management
Improvement in acid/base management allows for optimal function of medications
Acid/base status may alter electrolyte levels critical to patient status/care

4. Logistics When to order an arterial line Where to place – The options
Need for continuous BP monitoring
Need for multiple ABGs
Where to place – The options
Radial
Femoral
Brachial
Dorsalis Pedis
Axillary

5. Acid Base Balance The body produces acids daily 15,000 mmol CO2
mEq Nonvolatile acids
The lungs and kidneys attempt to maintain balance

6. Acid Base Balance
Assessment of status via bicarbonate-carbon dioxide buffer system
CO2 + H2O <--> H2CO3 <--> HCO3- + H+
ph = log ([HCO3] / [0.03 x PCO2])

7. The Terms Acids Bases Acidemia Acidosis Alkalemia Alkalosis
Respiratory
CO2
Metabolic
HCO3
Bases
Alkalemia
Alkalosis
Respiratory
CO2
Metabolic
HCO3

8. Respiratory Acidosis ph, CO2, Ventilation Causes CNS depression
Pleural disease
COPD/ARDS
Musculoskeletal disorders
Compensation for metabolic alkalosis

9. Respiratory Acidosis Acute vs. chronic
Acute – Little kidney involvement. Buffering via titration, via Hb for example.
pH by 0.08 for 10mmHg  in CO2
Chronic – Renal compensation via synthesis and retention of HCO3 (Cl to balance charges  hypochloremia)
pH by 0.03 for 10mmHg in CO2

10. Respiratory Alkalosis
 pH,  CO2,  Ventilation
 CO2   HCO3 ( Cl to balance charges  hyperchloremia)
Causes
Intracerebral hemorrhage
Salicylate and progesterone drug usage
Anxiety   lung compliance
Cirrhosis of the liver
Sepsis

11. Respiratory Alkalosis
Acute vs. chronic
Acute – HCO3 by 2 mEq/L for every 10mmHg  in PCO2
Chronic – Ratio increases to 4 mEq/L of HCO3 for every 10mmHg  in PCO2
Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH

12. Metabolic Acidosis  pH,  HCO3
hours for complete activation of respiratory compensation
 PCO2 by 1.2mmHg for every 1 mEq/L  HCO3
The degree of compensation is assessed via the Winter’s Formula
 PCO2 = 1.5(HCO3) +8  2

13. The Causes Metabolic gap acidosis Non-gap metabolic acidosis
M – Methanol
U – Uremia
D – DKA
P – Paraldehyde
I – INH
L – Lactic acidosis
E – Ehylene glycol
S – Salicylate
Non-gap metabolic acidosis
Hyperalimentation
Acetazolamide
RTA (Calculate urine anion gap)
Diarrhea
Pancreatic fistula

14. Metabolic Alkalosis  pH,  HCO3
 PCO2 by 0.7 for every 1mEq/L  in HCO3
Causes
Vomiting
Diuretics
Chronic diarrhea
Hypokalemia
Renal failure

15. Mixed Acid-Base Disorders
Patients may have two or more acid-base disorders at one time
Delta gap
Delta HCO3 = HCO3 + Change in anion gap
>24 = metabolic alkalosis

16. The Steps Start with the pH Note the PCO2 Calculate anion gap
Determine compensation

17. Sample Problem #1
An ill-appearing alcoholic male presents with nausea and vomiting
ABG – 7.4 / 41 / 85 / 22
Na – 137 / K- 3.8 / Cl- 90 / HCO3- 22

18. Sample Problem #1 Anion gap = 137 - (90 + 22) = 25
 Anion gap metabolic acidosis
Winter’s Formula = 1.5(22) + 8  2
= 39  2
 Compensated
Delta gap = = 15
= 37
 Metabolic alkalosis

19. Sample Problem #2
A 22-year-old female presents for attempted overdose. She has taken an unknown amount of Midol containing aspirin, cinnamedrine, and caffeine. On the exam she is experiencing respiratory distress.

20. Sample Problem #2 ABG – 7.47 / 19 / 123 / 14
Na – 145 / K- 3.6 / Cl- 109 / HCO3- 17
ASA level – 38.2 mg/dL

21. Sample Problem #2 Anion gap = 145 - (109 + 17) = 19
 Anion gap metabolic acidosis
Winter’s Formula = 1.5 (17) + 8  2
= 34  2
 Uncompensated
Delta gap = = 9
= 26
 No metabolic alkalosis

22. Sample Problem #3
47-year-old-male experienced crush injury at construction site
ABG – 7.3 / 32 / 96 / 15
Na – 135 / K-5 / Cl- 98 / HCO3- 15 / BUN- 38 / Cr- 1.7
CK – 42, 346

23. Sample Problem #3 Anion gap = 135 - (98 + 15) = 22
 Anion gap metabolic acidosis
Winter’s Formula = 1.5 (15) + 8  2
= 30  2
 Compensated
Delta gap = = 12
= 27
 Mild metabolic alkalosis

24. Sample Problem #4
1-month-old male presents with projectile emesis x 2 days
ABG – 7.49 / 40 / 98 / 30
Na – 140 / K- 2.9 / Cl- 92 / HCO3- 32

25. Sample Problem #4 Metabolic alkalosis, hypochloremic
Winter’s Formula = 1.5 (30) + 8  2
= 53  2
 Uncompensated