This document provides information about arterial blood gases (ABGs), including the components measured in an ABG, reasons for ordering an ABG, acid-base balance and disorders, and examples of how to analyze ABG results. It defines the components of an ABG as pH, PaCO2, PaO2, HCO3, O2 sat, and BE. Acid-base disorders are classified as respiratory (affecting PaCO2) or metabolic (affecting HCO3). Mixed disorders can involve both. Case examples demonstrate analyzing ABG results to identify acid-base disorders and degree of compensation.

1. Vanessa Klee MSIV

2. What is an ABG? The Components pH / PaCO 2 / PaO 2 / HCO 3 / O 2 sat / BE Desired Ranges pH - 7.35 - 7.45 PaCO 2 - 35-45 mmHg PaO 2 - 80-100 mmHg HCO 3 - 21-27 O 2 sat - 95-100% 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 -- 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 CO 2 50-100 mEq Nonvolatile acids The lungs and kidneys attempt to maintain balance

6. Acid Base Balance Assessment of status via bicarbonate-carbon dioxide buffer system CO 2 + H 2 O <--> H 2 CO 3 <--> HCO 3 - + H + ph = 6.10 + log ([HCO 3 ] / [0.03 x PCO 2 ])

7. The Terms ACIDS Acidemia Acidosis Respiratory  CO 2 Metabolic  HCO 3 BASES Alkalemia Alkalosis Respiratory  CO 2 Metabolic  HCO 3

8. Respiratory Acidosis  ph,  CO 2,  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 CO 2 Chronic - Renal compensation via synthesis and retention of HCO 3 (  Cl to balance charges  hypochloremia) pH  by 0.03 for 10mmHg  in CO 2

10. Respiratory Alkalosis  pH,  CO 2,  Ventilation  CO 2   HCO 3 (  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 -  HCO 3 by 2 mEq/L for every 10mmHg  in PCO 2 Chronic - Ratio increases to 4 mEq/L of HCO 3 for every 10mmHg  in PCO 2 Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH

12. Metabolic Acidosis  pH,  HCO 3 12-24 hours for complete activation of respiratory compensation  PCO 2 by 1.2mmHg for every 1 mEq/L  HCO 3 The degree of compensation is assessed via the Winter’s Formula  PCO 2 = 1.5(HCO 3 ) +8  2

13. The Causes Metabolic Gap 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,  HCO 3  PCO 2 by 0.7 for every 1mEq/L  in HCO 3 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 HCO 3 = HCO 3 + Change in anion gap >24 = metabolic alkalosis

16. The Steps Start with the pH Note the PCO 2 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 / HCO 3 - 22

18. Sample Problem #1 Anion Gap = 137 - (90 + 22) = 25  anion gap metabolic acidosis Winters Formula = 1.5(22) + 8  2 = 39  2  compensated Delta Gap = 25 - 10 = 15 15 + 22 = 37  metabolic alkalosis

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

20. Sample Problem #2 ABG - 7.47 / 19 / 123 / 14 Na- 145 / K- 3.6 / Cl- 109 / HCO 3 - 17 ASA level - 38.2 mg/dL

21. Sample Problem #2 Anion Gap = 145 - (109 + 17) = 19  anion gap metabolic acidosis Winters Formula = 1.5 (17) + 8  2 = 34  2  uncompensated Delta Gap = 19 - 10 = 9 9 + 17 = 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 / HCO 3 - 15 / BUN- 38 / Cr- 1.7 CK- 42, 346

23. Sample Problem #3 Anion Gap = 135 - (98 + 15) = 22  anion gap metabolic acidosis Winters Formula = 1.5 (15) + 8  2 = 30  2  compensated Delta Gap = 22 - 10 = 12 12 + 15 = 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 / HCO 3 - 32

25. Sample Problem #4 Metabolic Alkalosis, hypochloremic Winters Formula = 1.5 (30) + 8  2 = 53  2  uncompensated