abg in easy way

1. • Mrs. Zaffar is a 35-year-old single mother, just getting off the night shift. She
reports to the ED in the early morning with shortness of breath. She has
cyanosis of the lips. She has had a productive cough for 2 weeks. Her
temperature is 102.2, blood pressure 110/76, heart rate 108, respirations
32, rapid and shallow. Breath sounds are diminished in both bases, with
coarse rhonchi in the upper lobes.
Chest X-ray indicates bilateral pneumonia.
• ABG results are:
– pH= 7.44
– PaCO2= 28
– HCO3= 24
– PaO2= 54
• Problems:
• PaCO2 is low.
• pH is on the high side of normal,
• Also, PaO2 is low, probably due to mucous displacing air in the alveoli affected
by the pneumonia

2. ABG component
• pH / pCO2 / pO2 / HCO3 /O2 Sat
Base: metabolic
Oxygenation: lungs
Acid: lungs
The sum total of the acid/base balance,
on a log scale (pH=-log[H+])

3. ABG component
pH pCO2 pO2 HCO3
ӿ
BE
Arterial 7.35-
7.45
35-45 80-100 22-26 -2 to +2
Venous 7.30-
7.40
43-50 ~45 22-26 -2 to +2
Desired Ranges
Base Excess/Base Deficit
ӿ

4. Acid Base Balance
• The body produces acids daily
– 15,000 mmol CO2
– 50-100 mEq Nonvolatile acids
• The lungs and kidneys attempt to maintain
balance

5. Determine the evaluation of
abnormal values:
Test Normal Value Value
pH 7.35-7.45 Acidosis Alkalosis
pCO2 35-45 Alkalosis Acidosis
HCO3 22-26 Acidosis Alkalosis
pO2 80-100 Hypoxemia O2 therapy
Sa O2 95-100% Hypoxemia ---------

6. The 6 important steps for
ABG Analysis.
• Is the pH normal?
• Is the CO2 normal?
• Is the HCO3normal?
• Match the Co or the HCO3 with the pH
• Does the CO or the HCO3 go the opposite
direction of the pH?
• Are the pO2 and the O2 saturation normal?

7. Step1: Analyze the pH
• The first step in analyzing ABGs is to look at
the pH
• Normal pH is 7.4, plus or minus 0.05,
• < 7.35 it is acidic if > then 7.45 , it is alkolotic.
• Label it.

8. Respiratory or Metabolic?
• After you’ve determined whether the sample is
acidic or alkaline, you need to work out if it’s due
to respiratory or metabolic causes. This is where
it can get tricky. For respiratory problems, the
CO2 will be out of the normal range,
• whereas for metabolic problems the HCO3- will
be abnormal.
• Low CO2 points to respiratory alkalosis, and high
HCO3- can indicate metabolic alkalosis.

9. Step2: Analyze the CO2
• The second step is to examine the pCO2.
Normal pCO2 levels are 35-45mmHg.
• Below 35 is alkalotic, above 45 is acidic.
• Label it.

10. ~ PaCO2 – pH Relationship
80 7.20
60 7.30
40 7.40
30 7.50
20 7.60

11. Step 3: Analyze the HCO3
• The third step is to look at the HCO3 level. A
normal HCO3 level is 22-26 mEq/L.
• If the HCO3 is below, the patient is acidic.
• If the HCO3 is above 26, the patient is alkalotic.
• Label it.

12. Step 4: Match the CO2 or the HCO3
with pH
• Match either the pCO2 or the HCO3 with the pH
to determine the acid-base disorder.
• For example, if the pH is acidic, and the CO2 is
acidotic, then the acid-base disturbance is being
caused by the respiratory system. Therefore, we
call it a respiratory acidosis . However,
• if the pH is alkalotic and the HCO3 is alkalotic, the
acid-base disturbance is being caused by the
metabolic (or renal) system. Therefore, it will be
a metabolic alkalosis.

13. Step 5: Does the CO2 or HCO3 go the
opposite direction of the pH?
• The CO2 or HCO3 go in the opposite direction of
the pH?
If so, there is compensation by that system. For
example, the pH is acidic, the CO2 is acidotic, and
the HCO3 is alkalotic.
The CO2 matches the pH making the primary
acid-base disorder respiratory acidosis.
The HCO3 is opposite of the pH and would be
evidence of compensation from the metabolic
system.

14. ROME
• Respiratory Opposite
• Metabolic Equal
• The CO2 is the respiratory component the pH is
low of the ABG, and if it is low and the pH is high
the patient would have a respiratory alkalosis.
They move in opposite directions to match.
• The HCO3 is the metabolic component of the
ABG. If the HCO3 is low and the pH is low the
patient would have metabolic acidosis. They
move in the same direction to match.

15. Step 6: Analyze the pO2 and the O2
saturation
• Evaluate the PaO2 and O2 sat.
• if they are below normal there is evidence of
hypoxemia.

16. Arterial Oxygen Tension (PaO2)
• Normal value in healthy adult breathing room
air at sea level  97 mm Hg.
•  progressively with  age
• Dependent upon
1. Fraction of inspired oxygen (FiO2)
2. Patm
• Hypoxemia is PaO2 < 80 mm Hg at Room Air

17. COMPENSATION
• The normal response of the respiratory system or
kidneys to change in pH induced by a primary acid-
base disorder

18. Compensation
• Disturbances in HCO3- (metabolic acidosis or
alkalosis) result in respiratory compensation
• while changes in CO2 (respiratory acidosis/alkalosis)
are counteracted by renal compensation
a. Renal compensation – kidneys adapt to
alterations in pH by changing the amount of HCO3-
generated/excreted. Full renal compensation takes 2-
5 days
b. Respiratory compensation – alteration in
ventilation allow immediate compensation for
metabolic acid-base disorders

19. Acid-base disorders
DISORDER PRIMARY
RESPONSES
COMPENSATORY
RESPONSE
Metabolic
acidosis
 [H+]  PH  HCO3
-  pCO2
Metabolic
alkalosis
 [H+]  PH  HCO3
-  pCO2
Respiratory
acidosis
 [H+]  PH  pCO2  HCO3
-
Respiratory
alkalosis
 [H+]  PH  pCO2  HCO3
-

20. SIMPLE VS. MIXED ACID-BASE
DISORDER
• Simple acid-base disorder – a single primary
process of acidosis or alkalosis
• Mixed acid-base disorder – presence of more
than one acid base disorder simultaneously

21. pH 7.27 acidotic
CO2 53 acidotic
pO2 50 low
O2 sat. 70% low
HCO3 24 normal

22. Respiratory Acidosis
• Carbonic acid excess caused by blood levels of
CO2 above 45 mm Hg.
• Hypercapnia – high levels of CO2 in blood
• Chronic conditions:
– Depression of respiratory center in brain that
controls breathing rate – drugs or head trauma
– Paralysis of respiratory or chest muscles
– Emphysema
22

23. Respiratory Acidosis
• Acute conditons:
– Adult Respiratory Distress Syndrome
– Pulmonary edema
– Pneumothorax
23

24. Compensation for Respiratory
Acidosis
• Kidneys eliminate hydrogen ion and retain
bicarbonate ion
24

25. Signs and Symptoms of Respiratory
Acidosis
• Breathlessness
• Restlessness
• Lethargy and disorientation
• Tremors, convulsions, coma
• Respiratory rate rapid, then gradually
depressed
• Skin warm and flushed due to vasodilation
caused by excess CO2
25

26. Treatment of Respiratory Acidosis
• Restore ventilation
• IV lactate solution
• Treat underlying dysfunction or disease
26

27. pH 7.52 alkalotic
CO2 29 alkalotic
pO2 100 normal
O2 sat. 98% normal
HCO3 23 normal

28. Respiratory Alkalosis
• Carbonic acid deficit
• pCO2 less than 35 mm Hg (hypocapnea)
• Most common acid-base imbalance
• Primary cause is hyperventilation
28

29. Respiratory Alkalosis
• Conditions that stimulate respiratory center:
– Oxygen deficiency at high altitudes
– Pulmonary disease and Congestive heart failure –
caused by hypoxia
– Acute anxiety
– Fever, anemia
– Early salicylate intoxication
– Cirrhosis
– Gram-negative sepsis
29

30. Compensation of Respiratory
Alkalosis
• Kidneys conserve hydrogen ion
• Excrete bicarbonate ion
30

31. Treatment of Respiratory Alkalosis
• Treat underlying cause
• Breathe into a paper bag
• IV Chloride containing solution – Cl- ions
replace lost bicarbonate ions
31

32. pH 7.18 acidotic
CO2 44 normal
pO2 92 normal
O2 sat. 95 normal
HCO3 16 acidotic

33. Metabolic Acidosis
• Bicarbonate deficit - blood concentrations of
bicarb drop below 22mEq/L
• Causes:
– Loss of bicarbonate through diarrhea or renal
dysfunction
– Accumulation of acids (lactic acid or ketones)
– Failure of kidneys to excrete H+
33

34. Symptoms of Metabolic Acidosis
• Headache, lethargy
• Nausea, vomiting, diarrhea
• Coma
• Death
34

35. Compensation for Metabolic Acidosis
• Increased ventilation
• Renal excretion of hydrogen ions if possible
• K+ exchanges with excess H+ in ECF
• ( H+ into cells, K+ out of cells)
35

36. Treatment of Metabolic Acidosis
• IV lactate solution
36

37. pH 7.60 alkalotic
CO2 37 normal
pO2 92 normal
O2 sat. 98% normal
HCO3 35 alkalotic

38. Compensation for Metabolic Alkalosis
• Alkalosis most commonly occurs with renal
dysfunction, so can’t count on kidneys
• Respiratory compensation difficult –
hypoventilation limited by hypoxia
38

39. Symptoms of Metabolic Alkalosis
• Respiration slow and shallow
• Hyperactive reflexes ; tetany
• Often related to depletion of electrolytes
• Atrial tachycardia
• Dysrhythmias
39

40. Treatment of Metabolic Alkalosis
• Electrolytes to replace those lost
• IV chloride containing solution
• Treat underlying disorder
40

41. pH 7.30 acidotic
CO2 30 alkalotic
pO2 68 low
O2 sat. 92% low
HCO3 14 acidotic

42. • J is a 45 years old female admitted with the severe attack of
asthma. She has been experiencing increasing shortness of
breath since admission three hours ago. Her arterial blood gas
result is as follows:
• pH : 7.22
• paCO2 : 55
• HCO3 : 25
• Follow the steps
• pH is low – acidosis
• paCO2 is high – in the opposite direction of the pH.
• Hco3 is Normal.
• Respiratory Acidosis
• Need to improve ventilation by oxygen therapy, mechanical
ventilation, pulmonary toilet or by administering bronchodilators.

43. Mr. D is a 55 years old admitted with
recurring bowel obstruction has been
experiencing intractable vomiting for
the last several hours. His ABG is:
• pH : 7.5
• paCO2 :42
• HCO3 : 33
• Metabolic alkalosis
• Management: IV fluids, measures to
reduce the excess base

44. • Mrs. H is admitted, he is kidney dialysis
patient who has missed his last 2
appointments at the dialysis centre his
ABG results:
• pH : 7.32
• paCo2 : 32
• HCO3 : 18
• Pao2 : 88
• Partially compensated metabolic
Acidosis

45. • Mr. S is a 53 year old man presented to
ED with the following ABG.
• pH : 7.51
• PaCO2 : 50
• HCO3 : 40
• Pao2 : 40 (21%O2)
• He has metabolic alkalosis
• Acute respiratory alkalosis (acute
hyperventilation).

46. Acid Base Balance
• Assessment of status via bicarbonate-
carbon dioxide buffer system
– CO2 + H2O <--> H2CO3 <--> HCO3
- + H+
– ph = 6.10 + log ([HCO3] / [0.03 x PCO2])

47. • Mr. M.K with COPD.His ABG is:
• pH : 7.35
• PaCO2 : 48
• HCO3 : 28
• PaO2 : 90
• Fully compensated Respiratory
Acidosis

48. Approach to ABGs
Analyses
Dr Syed Tousif Ahmed

49. Metabolic Alkalosis
• Bicarbonate excess - concentration in blood
is greater than 26 mEq/L
• Causes:
– Excess vomiting = loss of stomach acid
– Excessive use of alkaline drugs
– Certain diuretics
– Endocrine disorders
– Heavy ingestion of antacids
– Severe dehydration
49