ARTERIAL BLOOD GASES ( ABG ) hhanajiaknan

Jkakakkakakkakkakkakk

1. ARTERIAL BLOOD GASES ( ABG )
ARTERIAL BLOOD GAS ANALYSIS - ABG
DR.BINCY ROMANS
MRCEM TRAINEE

2. Arterial blood gases
ABG analysis assesses a patient's partial pressure of oxygen (PaO2) and
carbon dioxide
 (PaCO2).
Henderson Hasselbalch Equation :
pH = pK + log[conjugate base]/[acid]
the most important buffer system in the body is the carbonic acid/bicarbonate
system due to the physiological control of its component parts by the lungs and
kidneys. This relationship is shown as:
CO2 + H2O H2CO3  H+ + HCO3–
↔ ↔

4. NORMAL VALUES
•pH (7.35-7.45)
•PaO2 (80-100 mmHg) (10.67-13.33 kPa )
•PaCO2 (35-45 mmHg) (4.67 – 6.00 kPa)
•HCO3 (22-26 meq/L) ( 23-28 mmol/l )
•AG : 12 +/- 2 meq/L ( 6-16 mmol/l )
•Base excess/deficit (-2 to +2)
•SaO2 (95-100%)

5. The 6 step approach
Acidemic or Alkalemic
Is the primary disturbance respiratory or metabolic
If Respiratory, is it acute or chronic
If Metabolic, is there an anion gap?
Co existing metabolic disorders?
Compensation

6. Step - 1
Acidemic or Alkalemic
Acidemic : pH < 7.35
Alkalemic : pH > 7.45
Step - 2
Is the primary disturbance Respiratory or
Metabolic

7. respiratory DISoRDERS :
Respiratory disorder will alter the PaCO2
High CO2 in acidosis ,Low CO2 in alkalosis
Respiratory Acidosis
Acute :
pH = 0.08 x (PaCO2 – 40 ) /10
Chronic :
pH = 0.03 x (PaCO2 – 40 ) /10

8. RESPIRATORY ALKALOSIS
Acute:
pH = 0.08 x (PaCO2 – 40 ) /10
Chronic :
pH = 0.03 x (PaCO2 – 40 ) /10

9. METABOLIC DISORDERS :
Step - 4
Metabolic disorder will alter the HCO3.
HCO3 < 22, metabolic acidosis
HCO3 >26 ,metabolic alkalosis
oHypovolemia with Cl- depletion
oGI loss of H+ :Vomiting, gastric suction, , diarrhea with chloride-rich fluid
oRenal loss H+ :Loop and thiazide diuretics etc
oHypervolemia, Cl- expansion
oRenal loss of H+:
  edematous states (heart failure, cirrhosis, nephrotic syndrome),
hyperaldosteronism, hypercortisolism, excess ACTH, exogenous steroids, hyperreninemia,
severe hypokalemia, renal artery stenosis, bicarbonate administration

10. METABOLIC ACIDOSIS :
CHECK ANION GAP
Anion Gap = Na- (Cl + HCO3)
Normal :12 +/- 2 meq
High Anion Gap Metabolic acidosis : AG > 12

11. Non Anion Gap acidosis : AG < 12
In a normal anion gap acidosis,
bicarbonate is lost from the gut or the
kidneys and there is a raised chloride,
which compensates for the extra
cations, thus keeping the gap normal.
This occurs as a result of reabsorption
of sodium chloride via the kidneys:

12. COMPENSATION

Metabolic acidosis:-
pCO2 = 1.5 X HCO3 + 8 +/- 2 (WHINTERS FORMULA)

Metabolic alkalosis:-
each 1mEq/L increase in HCO3- will increase 0.6mmhg of pCO2

Respiratory acidosis:-

Acute – each 10mmHg increase in pCO2 will increase 1mEqL of HCO3-

Chronic - each 10mmHg increase in pCO2 will increase 3.5mEqL of HCO3-

Respiratory alkalosis:

Acute - each 10mmHg decrease in pCO2 will decrease 2mEqL of HCO3-

Chronic - each 10mmHg decrease in pCO2 will decrease 5mEqL of HCO3-

13. REFRENCES :
RCEM LEARNING
TINTINALLI