The document focuses on arterial blood gas (ABG) analysis, discussing its components, mechanisms of maintaining normal blood pH, and interpretation of ABG values. It outlines common acid-base disorders, including respiratory acidosis, alkalosis, and metabolic acidosis, and details the physiological responses of the respiratory and renal systems in maintaining acid-base balance. Additionally, it provides guidelines for analyzing ABG values and understanding the relationships between pH, PaCO2, and HCO3.

1. Arterial Blood Gas(ABG)
Analysis
Medical Surgical Nursing III
8th
August 2024
2022 cohort
By. D. Kamalizeni

2. Learning Objectives
•Describe the components of ABG analysis
•Describe mechanisms that maintain the
normal blood pH
•Describe steps to ABG analysis
•Interpret selected ABG values

3. Overview of ABG analysis
•Essential component/part of diagnosing and
managing patient`s oxygenation status and
acid-base balance
•Highly dependent on knowledge of:
Genesis of parameters being analyzed

4. Pre-liquisite knowledge base continues..,
Normal ranges of such parameters
What abnormal parameters are likely to
indicate
Suggested interventions to resolve such
abnormalities
When further assessment is indicated

5. Measures of ABG
•pH
•Respiratory function(PaCO2, PaO2, SaO2)
•Metabolic function (Bicarbonate, Base
excess)
•Is compensation occurring? And which way?

6. Measure of pH
•Deals with measure of acidity/alkalinity of
blood
•Inversely proportion to no of hydrogen
ions; the more the hydrogen ions, the lower
the pH (acidity) and the fewer the no of
hydrogen ions, the higher the pH (alkali)

7. Measure of pH continues…,
•Measured on a scale from 1 (very acidic) to 14
(very alkalotic)
•A liquid with pH of 7 is neutral; neither acidic nor
alkalotic
•Normal pH range for blood is 7.35 – 7.45; which
must be maintained for normal cellular
functioning

8. Maintenance of the normal blood pH
•Self-regulated
•Uses delicate buffer mechanisms:
1.Respiratory response
2.Renal response

9. Buffer mechanisms continues.., (revision)
•Resp and renal systems together form
the physiological buffer systems that
control pH by regulating amount of acid
or base in the body

10. Respiratory response (revision)
• Co2 is the normal bi-product of metabolic activity
• It is carried in blood to the lungs for excretion
• While in the blood(erythrocytes), CO2 combine with H2O
to form carbonic acid(H2CO3) (write this chemical
reaction)
• This Carbonic acid dissociates into Hydrogen ions and
bicarbonate ions: (write this reaction )
• pH will change according to level of H2CO3 in the blood

11. Respiratory response CTs…,,
•Deviations in blood CO2 triggers the resp syst
to either increase or decrease rate & depth of
resp until appropriate conc of CO2 is re-
established
•Activation of the resp to compensate for any
of such deviations occurs within 1 – 3minutes

12. Renal response
•To maintain normal ranges of blood pH, kidneys
excrete or retain bicarbonate
•When pH decreases (acidic), kidneys retain
bicarbonate (HCO3, as pH rises (alkalotic),
kidneys excrete HCO3
•This response occur from hrs to days following
the deviation

13. The common acid-base disorders
1. Respiratory acidosis
• Caused by accumulation of CO2 in the blood
• Mostly attributed by conditions that results into hypoventilation like:
i. CNS depression 2nd
to HI, medication
ii. Impaired resp muscle functioning
iii. Pulmonary disorders like asthma
iv. Pain, chest trauma
v. Abdominal distension

14. 2.Respiratory alkalosis
•Defined as pH greater than 7.45, PaCO2 less than 33
mmHg
•Caused by any condition that cause hyperventilation
like:
i. Anxiety, fear,
ii. Pain
iii. Increased metabolic demands
iv. Medication like resp stimulants

15. 3. Metabolic acidosis
• Defined with reference to reduced bicarbonate level with pH of less
than7.35
• Mostly caused by either a deficit of a base in the blood or an excess of
acids other than CO2
• Mostly caused by:
Renal failure
DKA
Starvation

16. 4. Metabolic alkalosis
•Defined with reference to increased bicarbonate
levels with pH greater than 7.45
•May result from ingestion of more antacids,
excess use of bicarbonate
•Usually iatrogenic in nature in hospitalized
patients; (complications from related
therapeutic interventions) like gastric suction

17. Components of ABGs
pH
• Measurement of acidity or alkalinity based on hydrogen ions present
• Normal range is 7.35 – 7.45
PaO2
• O2 that is dissolved in blood
• Normal range is 80 -100 mm Hg
SaO2
• Arterial O2 saturation; ranging from 95% to 100%

18. Components of ABGs
HCO3
•Amount of bicarbonate in the blood
•Normal ranges: 22 to 26 mEq/litre
PaCO2
•Amount of CO2 dissolved in the arterial blood
•Ranges from 35 to 45 mm Hg

19. Steps to ABG analysis/interpretation
•Evaluates both oxygenation status and acid-base
balance; however each represent separate conditions
•Acid-base evaluation requires a focus on three of the
reported; pH, PaCO2, HCO3.
Step one
Assess pH to determine if blood is within normal range;
alkalotic or acidic

20. Interpretation of ABG CTs…,
Step 2
•If blood is alkalotic or acidic; then determine if it is
caused by a respiratory or metabolic problem
•With resp problem, if pH decreases below 7.35 then
PaCO2 should rise and if pH rises above 7.45, PaCO2
should fall (explain)
•Therefore, compare pH and PaCO2 values; if pH and
PaCO2 are moving in opposite direction, then the
problem is respiratory in nature

21. Interpretation of ABG CTs…,
Step 3
•Finally assess HCO3 value
•With metabolic problem, as pH rises, the HCO3 should
rise and as pH reduces, HCO3 should also reduce.
•So at this step, compare the 2 values(pH and HCO3);
•If both are moving in same direction, then problem is
primarily metabolic in nature

22. Summary of the relationships btn pH, PaCO2
and HCO3
pH PaCO2 HCO3 EXPLAIN
Respiratory
acidosis
Decreasing increasing normal
Respiratory
alkalosis
Increasing decreasing normal
Metabolic
acidosis
Decreasing Normal decreasing
Metabolic
alkalosis
increasing normal increasing

23. Example
Nabanda asthmatic patient has the following arterial blood gas values:
pH = 7.22
PaCO2 = 55 mm Hg
HCO3 = 25 mEq/litre
Analyse the above values and institute appropriate interventions for
Nabanda

24. Analysis of Nabanda`s ABG
Step 1
• PH of 7. 22 is low; decreasing; (normal is 7.35-7.45), therefore we have
acidosis
Step 2
• PaCo2 of 55mmHg is high (normal is 35-45 mmHg) and moving in opposite
direction with pH.
Step 3
• HCO3 is 25 mEq/l which is normal( normal is22 -26mEq/l);
• Therefore, acidosis is present(low pH); PaCO2 is high reflecting a resp
problem which is respiratory acidosis

25. Management of Naphiri basing on the
analysed ABG
Plan
• Improve ventilation status by:
 providing O2 (Mechanical ventilation)
pulmonary toilet,
administration of bronchodilators & steroids

26. Scenarios for self practice
Analyse the following ABGs and manage accordingly:
1. pH = 7.50; PaCO2 = 42 mmHg; HCO3 = 33mEq/l
2. pH = 7.32; PaCO2 =32 mmHg; HCO3 = 18 mEq/l
3. pH = 7.35; PaCO2 = 48 mmHg; HCO3= 28 mEq/l

27. ADDITIONAL INFORMATION ON ABG (JUST TO
KNOW)
Compensation in acid-base
imbalance

28. Compensation in acid-base imbalance
• Occurs in acid-base imbalance that exists over a long time
• The body tries to overcome either a resp or metabolic dysfunction
• Done in attempt to return the pH into the normal range
• Patient can be:
1. Uncompensated: (pH outside the normal range)
2. Partially compensated( as above)
3. Fully compensated(pH within normal, other parameters may still
remain abnormal)

29. Fully compensated states
pH PaCO2 HCO3
Respiratory acidosis Normal but less than 7.40 Increasing increasing
Respiratory alkalosis Normal, but more than
7.40
decreasing decreasing
Metabolic acidosis Normal but less than 7.40 decreasing decreasing
Metabolic alkalosis Normal but more than
7.40
increasing increasing

30. Partially compensated states
pH PaCO2 HCOH
Respiratory acidosis Decreasing increasing increasing
Respiratory alkalosis Increasing decreasing decreasing
Metabolic acidosis Decreasing decreasing decreasing
Metabolic alkalosis increasing increasing increasing

31. Differences btn partially and fully
compensated states
•In compensated states, pH falls either on the low
or high side of neutral
•Noting where the pH falls within the normal
range helps in determining whether the original
acid-base imbalance was acidosis or alkalosis

32. Example
• Patient with kidney problem has the following ABG values:
pH = 7.32
PaCO2 = 32
HCO3 = 18

33. Interpretation
• pH(7.32) is low, therefore we have acidosis
• PaCO2 is low(32). (Normally we would expect the 2 values (pH and
PaCO2) to move in opposite direction)
• pH and PaCO2 moving in same direction reflects that the acid base
disorder is primarily metabolic
• Low PaCO2 & low pH reflects that the lungs are compensating to blow
off CO2 (both moving in same direction)
• Therefore this ABG denotes a partially compensated metabolic
acidosis (pH, PaCO2 and HCO values decreasing; refer to table above)