Abg presentation

Pediatric Lectures

1. Arterial Blood Gas Analysis
Overview

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
•Assessment of status via bicarbonate-
carbon dioxide buffer system
–CO
2
+ H
2
O <--> H
2
CO
3
<--> HCO
3
-
+ H
+

6. The Terms
•ACIDS
–Acidemia
–Acidosis
•Respiratory
­CO
2
•Metabolic
¯HCO
3
•BASES
–Alkalemia
–Alkalosis
•Respiratory
¯CO
2
•Metabolic
­HCO
3

7. Respiratory Acidosis
•¯ph, ­CO
2,
¯Ventilation
•Causes
–CNS depression
–Pleural disease
–COPD/ARDS
–Musculoskeletal disorders
–Compensation for metabolic alkalosis

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. The Steps
•Start with the pH
•Note the PCO
2
•Calculate anion gap
•Determine compensation