This document provides information on interpreting blood gases, including normal values for pH, PaCO2, PaO2, HCO3, and base excess. It describes causes and features of respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. Various treatments are discussed for different acid-base imbalances. A section on arterial blood sampling and the Allen test is also included. The document ends with sample case studies to test the reader's understanding of interpreting blood gas results.

1. Quick interpretation of Blood
Gases
Dr. P K Maharana

2. Normal Values
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pH 7.4 ( range 7.34 – 7.44)
H+
35 – 45 mmol / L
PaCO2 40mmhg (35-45)
PaO2 100mmHg( 75 – 100)
HCO3 24 mEq/L(22- 26)
Base Excess -2 to +2 mmol /L

3. pH
• Acidosis  pH < 7.35
• Alkalosis  pH > 7.45

4. Changes in pH, PCO2 & HCO3
Respiratory Acidosis
High PaCO2 ( > 45)
Low pH ( < 7.35)
Normal Bicarbonate
Respiratory Alkalosis
Low PaCO2
High pH
Normal Bicarbonate
Respiratory Acidosis with
Compensatory Metabolic Alkalosis
High PaCO2
Normal pH
High Bicarbonate
Metabolic Acidosis
Normal PaCO2
Bicarbonate Low
Low pH
Metabolic Alkalosis
Normal PaCO2
Bicarbonate High
pH high
Metabolic Acidosis with
compensatory Alkalosis
PCO2 High
Bicarbonate High
pH Low

5. Anion Gap
• This is useful in any cause of metabolic acidosis.
In plasma, the sum of the cations (sodium plus
potassium) is normally greater than that of the
anions (chloride plus bicarbonate) by
approximately 14 mmol/L (normal range 10-18
mmol/L).
• This is known as the anion gap. In some
disorders, either the positive or negative ions
may increase, leading to a change in the anion
gap

6. Raised Anion gap Metabolic
Acidosis
• Accumulation of acids, for example:
• Ketoacids in diabetic ketoacidosis (DKA).
• Lactic acid, eg shock, infection.
• Drugs/toxins, eg salicylates, ethylene glycol,
methanol.
MUDPILES' mnemonic (methanol, uraemia, DKA, paraldehyde,
infection/ ischaemia / isoniazid, lactic acidosis, ethylene
glycol/ethanol, salicylates/starvation).

7. Normal Anion Gap Metabolic
Acidosis
• Loss of bicarbonate or ingestion of acid,
for example:
• Gastrointestinal tract (GIT) causes, eg
diarrhoea, pancreatic fistula.
• Renal tubular acidosis.
• Addison's disease.
• Drugs, eg carbonic anhydrase inhibitors

8. Arterial Blood Samples
• Contraindications for
Radial Artery
Puncture :• Infection
• Unable palpate the
pulse
• Coagulation Disorder
• Positive Allen Test
• Samples can be
drawn from Radial,
Femoral, Brachial or
from an Arterial Line

9. Allen Test

10. Respiratory Acidosis
Causes :• CNS depression due to Head Injury
• CNS depression due to drugs ( sedatives,
narcotics, anesthesia).
• Impaired respiratory muscle function( spinal
cord injury, neuromuscular diseases, muscle relaxants)
• Pulmonary Diseases ( pneumonia, atelectasis,
pneumothorax, bronchial obstruction, pulmonary oedema,
pulmonary embolism)
• Hypoventilation (due to Pain, Abdominal distention,
chest wall injury or deformity)

11. Treatment of Respiratory Acidosis
• Treatment of Cause.
• O2 therapy
• Respiratory support ( Mechanical
Ventilation)

12. Respiratory Alkalosis
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(pH > 7.45, PaCO2 < 35 mmHg)
Causes :Physiological Hyperventilation( fear, pain,
anxiety)
Medications.( Respiratory Stimulants)
Increased Metabolic states (fever, sepsis,
pregnancy, thyrotoxicosis)
Central Nervous System Lesions

13. Treatment
• Treatment of underlying cause.
• Patients should be monitored for
exhaustion & respiratory muscle fatigue
leading to respiratory failure.

14. Metabolic Acidosis
(pH <7.35, Bicarbonate < 22 mmol/L)
Causes:Renal Failure.
Diabetic ketoacidosis.
Starvation.
Anaerobic Metabolism.
Ingestion of Salicylates.

15. Signs & Symptoms
• Nausea, Vomiting
• Kussmaul’s Breathing
• Headache, confusion, lethargy,
restlessness, stupor, coma.
• Hypotension, warm flushed skin,
Dysrhythmias

16. Treatment
• Treatment of the cause.
• Presence of metabolic acidosis should
spur a search for hypoxia somewhere
in the body.
Hypoxia Anaerobic Metabolism
Acidosis
The only way is to improve tissue perfusion.
Once tissue perfusion is restored look for
other causes.

17. Treatment Acidosis (cont-)
• Routine use of Sodium Bicarbonate
should be avoided as it leads to alkalosis
& Hypernatremia.
• It only should be used in bicarbonateresponsive acidosis, like renal failure.

18. Metabolic Alkalosis
•
pH > 7.45, Bicarbonate > 29 mEq /L
Causes:A) Excess of Base  Ingestion of Antacids,
Excess use of bicarbonates, Use of
Lactate in dialysis.
B) Loss of Acids Protracted vomiting,
Gastric suction, hypochloremia, excess
use of diuretics, high level of
Aldosterone.

19. Treatment of metabolic Alkalosis
• It is one of the most difficult situation to
treat. In a hospitalized patient mostly
iatrogenic.
• Acetazolamide ( diamox) is the drug
commonly used to treat but the effects are
slow.

20. Case Study
1. pH 7.21,
pCO2 60
HCO3 24
a. Normal
b. Respiratory acidosis without compensation
c. Metabolic acidosis with partial compensation
d. Respiratory acidosis with complete
compensation
2.pH 7.50
pCO2 29
HCO3 24
A. Normal
B. Respiratory acidosis with compensation
C. Respiratory alkalosis without compensation
D. Metabolic alkalosis with partial compensation
3. pH 7.28
pCO2 40
HCO3 18
A. Respiratory acidosis without compensation
B. Respiratory alkalosis with partial compensation
C. Metabolic alkalosis with partial compensation
D. Metabolic acidosis without compensation

21. Case Study
4.pH 7.45
pCO2 26
HCO3 16
A. Normal
B. Respiratory acidosis fully compensated
C. Respiratory alkalosis fully compensated
D. Metabolic alkalosis fully compensated
5. pH 7.33
pCO2 60
HCO3 34
A. Normal ABG values
B. Respiratory acidosis without compensation
C. Respiratory acidosis with partial compensation
D. Respiratory acidosis with full compensation
6. pH 7.48
pCO2 42
HCO3 30
A. Metabolic acidosis without compensation
B. Respiratory alkalosis with partial compensation
C. Respiratory alkalosis with full compensation
D. Metabolic alkalosis without compensation

22. Case study
7.pH 7.38
pCO2 38
HCO3 24
A. Respiratory alkalosis
B. Normal
C. Metabolic Alkalosis
D. None of the above
8.. pH 7.21
pCO2 60
HCO3 24
A. Normal
B. Respiratory acidosis without compensation
C. Metabolic acidosis with partial compensation
D. Respiratory acidosis with complete compensation
9. pH 7.48
pCO2 28
HCO3 20
A. Respiratory alkalosis with partial compensation
B. Respiratory alkalosis with complete compensation
C. Metabolic alkalosis without compensation
D. Metabolic alkalosis with complete compensation

23. Question Answer.
1.The solution that would be most alkalotic
would be the one with a pH of
A. Four
B. Seven
C. Nine
D. Fourteen
2.The normal pH range for blood
is
A. 7.00 – 7.25
B. 7.30 – 7.40
C. 7.35 – 7.45
D. 7.45 – 7.55
3.The respiratory system compensates for
changes in the pH level by responding to
changes
in the levels of:
A. CO2
B. H2O
C. H2CO3
D. HCO3
4. The kidneys compensate for acid-base
A. Hydrogen ions
B. Carbonic acid
C. Sodium Bicarbonate
D. Water
imbalances by excreting or retaining:

24. Question & Answer
All of the following might be a cause of
respiratory acidosis except the followings
A. Sedation
B. Head trauma
C. COPD
D. Hyperventilation
A patient with a prolonged episode of
nausea, vomiting and diarrhea has an
ABG ordered on admission. You might
expect the results to show
A. Metabolic acidosis
B. Metabolic alkalosis
C. Respiratory acidosis
D. Respiratory alkalosis
A calculated ABG value that indicates
excess or insufficiency of sodium
bicarbonate in the system is:
A. HCO3
B. Base excess
C. PaO2
D. pH
You are reviewing the results of an ABG.
Both the pH and the CO2 values are
abnormal. The primary problem is:
A. Respiratory
B. Renal
C. Metabolic
D. Compensation