easy understing with examples and work sheet

1. Arterial Blood Gases
AND
Venous Blood Gases
By Dr. Komal Patel
(MPT MUSCULOSKELETAL)

2. Contents:
• INTRODUCTION
• BASIC TERMINOLOGY
• NORMAL VALUES
• PHYSIOLOGY OF ACID – BASE BALANCE
• BLOOD GAS INTERPRETATION
• EXAMPLE WITH CONDITIONS
• FACTOR AFFECTING ABG

3. References
• Cardiovascular and Pulmonary physical therapy
(second edition) -JOANNE WATCHIE
• Principles and practice of CARDIOPULMONARY
PHYSICAL THERAPY (third edition)-Donna
Frownfelter

4. • Prediction of ABG values from VBG values in
patient with acute exacerbation of COPD-AHMET
AK,2006
• The Accuracy of the Central Venous Blood Gas for
Acid-Base Monitoring- Atlan J. Walkey,2010
• Tietz, Norbert (2005)Clincial Guide to Laboratory
Tests, 3rd edition

5. INTRODUCTION
• Arterial Blood Gas AND Venous Blood Gas
• Drawn from artery for ABG AND from vein for VBG
• It is an invasive procedure.
• Caution must be taken with patient on anticoagulants.

6. Conti……Case of emergency in
cardiopulmonary:
Airway Breathing Circulation

7. ABG gives idea about
Acid-Base balance
Alveolar
ventilation
Oxygenation status

8. BASIC TERMINOLOGY
• pH: It signifies free hydrogen ion concentration.
Noraml value is 7.4 (7.35 to 7.45).
• ACID: donate H+ ion. (i.e. lowers pH).
• BASE: accept H+ ion.(i.e. rises pH).
• ANION: An ion with negative charges is anion(i.e. Cl, HCO3 ) .
• CATION: An ion with Positive charges is cation (i.e. Na, K, Mg)

9. • ACIDEMIA : Acidemia means “acid blood” refers
to blood pH below normal (pH<7.35) and increased
in H+ ion concentration.
• ALKALAEMIA: means “alkaline blood” refers to
blood pH above normal(i.e. pH>7.45)and decrease in
H+ ion concentration.

10. • ACIDOSIS: Abnormal process or disease which
reduced pH due to increase in acid or decrease in
alkali is called acidosis.
• ALKALOSIS: Abnormal process or disease which
increased pH due to decrease in acid or increase in
alkali is called alkalosis.

11. Values in ABG analysis• pH [H+]
• PCO2 Partial pressure
CO2
• PO2 Partial pressure O2
• HCO3 Bicarbonate
• BE Base excess

12. Normal values
• pH 7.35 -7.45
• PaCO2 35-45 mmHg
• PaO2 80-100mmHg
• HCO3¯ 22-26mmol/l
• Base excess-2 to +2

13. PHYSIOLOGY OF ACID – BASE
BALANCE
• NORMAL body metabolism consists of
consumption of,
-Nutrients
-Exertion of acid metabolism
98% normal metabolism are from co2 reacts with water
and form carbonic acid.
Co2 +H2O H2CO3

14. • These all acid content can be exerted through lungs
during respiration.
• It is determined by using Handerson- Hasselbatch
equation.
H2O+CO2 H2CO3 H+ + HCO3
If H+ concentration occur, Kidney excreted H+ by
urine.
Resorbed by bicarbonate into blood.

15. Four Simple Steps for Analyzing
Arterial Blood Gases
Step 1:
Normal pH value :7.35 -7.45
to assess acid–base status
• pH <7.40 indicates acidosis
• pH >7.40 indicates alkalosis

16. Step 2:
Examine the PaCO2: (indicator of ventilatory status)
PaCO2 :35 to 45 mm Hg indicates adequate ventilation
• PaCO2 <30 mm Hg indicates alveolar
hyperventilation
• PaCO2 >50 mm Hg indicates alveolar
hypoventilation(ventilatory failure)

17. Step 3:
interpret the levels in relation to pH to determine the
cause of abnormal values
• PaCO2 >45 mm Hg and pH <7.40 indicate
respiratory acidosis
• PaCO2 >45 mm Hg and pH >7.40 indicate
respiratory retention of CO2 to compensate for
metabolic alkalosis

18. • PaCO2 <35 mm Hg and pH >7.40 indicate
respiratory alkalosis
• PaCO2 <35 mm Hg and pH <7.40 indicate
respiratory elimination of CO2 to compensate for
metabolic acidosis

19. Step 4:
Normal HCO3 values (22 to 26 mEq/L)
• HCO3 <22 mEq/L and pH <7.40 indicate metabolic acidosis
• HCO3<22 mEq/L and pH >7.40 indicate renal compensation
for respiratory alkalosis
• HCO3 >26 mEq/L and pH >7.40 indicate metabolic
alkalosis
• HCO3 >26 mEq/L and pH <7.40 indicate renal compensation
for respiratory acidosis

20. Step 5:
Normal value of PaO2 : 80 to 100 mm Hg
• PaO2 =60 to 80 mm Hg indicates mild hypoxemia
• PaO2 = 40 to 60 mm Hg indicates moderate
hypoxemia
• PaO2 <40 mm Hg indicates severe hypoxemia,

23. Alveolar hypoventilation
• (PaCO2) > 45
• causes of persistent hypercapnia include COPD
• diseases restricting chest wall expansion (e.g.,
kyphoscoliosis, ankylosing spondylitis, spinal cord
injury, and neuromuscular disorders)
• CNS abnormalities

24. Alveolar hyperventilation
• PaCO2 <35
• caused by an increase in respiratory drive, which can
be induced by hypoxemia
• pulmonary disease (e.g., asthma, pneumonia, and
pulmonary embolism)
• cardiovascular disorders (e.g., CHF and hypotension)
• fever, sepsis, and pregnancy.

25. Ventilatory, or hypercapnic
respiratory, failure
• PaCO2 exceeds 50 and can be precipitated by
increased work of breathing (e.g., acute or chronic
pulmonary disease causing significant ventilation–
perfusion mismatching)
• reduced energy supply (e.g., low cardiac output and
CHF)
• impaired muscular efficiency (e.g., hyperinflation of
chest, respiratory muscle weakness or fatigue, and
flaccidity of abdominal muscles)

26. Respiratory acidosis
• pH is <7.40 and PaCO2 is >45
• results from hypoventilation due to a number of
causes include
-respiratory muscle weakness or paralysis;
-reduced respiratory muscle endurance;
-restricted lung or thoracic compliance, including that
which occurs with aging; retained secretions; and
increased dead space ventilation

27. Metabolic acidosis
• pH <7.40 and HCO3<22
• result from increased acid production
(e.g., diabetes, alcohol abuse, and starvation)
• lactic acidosis (e.g., circulatory or respiratory failure,
shock, drugs and toxins, and enzyme defects)
• associated with other disorders (e.g., severe anemia,
pulmonary disease, and neoplasms)

28. • renal failure.
• loss of alkali (e.g., diarrhea, enteric fistula, ileostomy),

29. Respiratory alkalosis
• pH >7.40 and PaCO2 <35,
• which is induced by alveolar hyperventilation

30. Metabolic alkalosis
• pH >7.40 and HCO3 >26.
• e.g., vomiting, nasogastric suction, diuretic therapy,
and decrease in PaCO2 during treatment of chronic
respiratory acidosis

31. VENOUS BLOOD GAS (VBG)
• Patients who require frequent blood gas testing often
have indwelling venous catheters for the
administration of intravenous medications or the
monitoring of central vascular pressures, allowing for
repeated central venous blood gas (VBG) analysis.
multiple studies have looked to the VBG as a less
invasive alternative for routine monitoring of acid-
base status

32. Normal value
• VpO2: 30 - 50 mm Hg
• VpCO2: 40 – 52 mm Hg
• VpH: 7.31 – 7.41
• HCO3: 22 – 27 mEq/L

33. • Base Excess (BE):
-Newborn (0-7 days): -10 to -2 mmol/L
-Infant (1 week-1 year): -7 to -1 mmol/L
-Child (1-16 years): -4 to +2 mmol/L
-Adult (>16 years): -3 to +3 mmol/L
• Critical Values:
VpCO2: <15 or >70 mm Hg
VpH: <7.2 or >7.

34. Factors affecting ABG
1) Age: Neonatal
: Geriatric
2)Exercise / Increase activity from rest
3)Pregnancy
4)During sleep
5)Increase temperature
6)Change in the atmospheric pressure

35. It’s not magic understanding ABG’s, it
just takes a little practice!

36. Any Questions?

37. Practice ABG’s
1. PaO2 90 pH 7.48 PaCO2 32 HCO3 24
2. PaO2 60 pH 7.32 PaCO2 48 HCO3 25
3. PaO2 95 pH 7.30 PaCO2 40 HCO3 18
4. PaO2 87 pH 7.38 PaCO2 48 HCO3 28
5. PaO2 94 pH 7.49 PaCO2 40 HCO3 30
6. PaO2 62 pH 7.35 PaCO2 48 HCO3 27
7. PaO2 93 pH 7.45 PaCO2 47 HCO3 29
8. PaO2 95 pH 7.31 PaCO2 38 HCO3 15
9. PaO2 65 pH 7.30 PaCO2 50 HCO3 24

38. Answers to Practice ABG’s
1. Respiratory alkalosis
2. Respiratory acidosis
3. Metabolic acidosis
4. Compensated Respiratory acidosis
5. Metabolic alkalosis
6. Compensated Respiratory acidosis
7. Compensated Metabolic alkalosis
8. Metabolic acidosis
9. Respiratory acidosis