Basic Principles of Critical Care

1. ARTERIAL BLOOD GAS ANALYSIS
Gradian Health Systems
Basic Principles of Critical Care
INTERPRETATION OF LAB RESULTS

2. Disclaimer
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
Disclaimer: Gradian Health Systems cannot provide formal recommendations or indications
regarding medical care and clinical service delivery. The tables, checklists, and other clinical
documents referenced in this training have not been validated in all settings. These documents are
intended to serve as examples only. We recognize that all clinical training content and activities
must be customized to meet the needs of each facility and its clinical staff, factoring in available
resources, practitioner skill level, and other environmental considerations.
For any questions regarding the contents or applications of this training,
please contact Gradian Health Systems:
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training@gradianhealth.org

3. Module 6
Gradian Health Systems
Basics Principles of Critical Care
Interpretation of Lab Results

4. Module 6: Interpretation of Lab Results
MODULE OVERVIEW
Lesson 1 I Arterial Blood Gas Analysis
Lesson 2 I Hematological Tests
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

5. Components of the Gradian CCV SystemLesson 1: Arterial Blood Gas Analysis
Lesson Objectives
• Categorize acid-base disorders
• Describe an arterial blood gas
• Interpret an arterial blood gas
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

6. Components of the Gradian CCV SystemLesson 1: Arterial Blood Gas Analysis
Key Concepts
• pH
• PaO2
• PCO2
• Bicarbonate
• Acidosis
• Alkalosis
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

7. Components of the Gradian CCV SystemArterial Blood Gas Analysis
pH
• Normal physiological functioning of cells depends on a balance between the
concentrations of acids and bases in the blood; this is dependent on the
buffering system in the body
• Buffer is a chemical system that prevents a radical change in fluid pH by
dampening the change in hydrogen ion concentrations in the case of excess
acid or base
• Bicarbonate (HCO3-) is most important extracellular buffer
• Lungs and kidneys are important organs in maintaining acid-base balance
• Kidneys regulate the filtration and consequent reabsorption of bicarbonate,
depending on the pH
• Lungs regulate the exhalation of carbon dioxide
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

8. Components of the Gradian CCV SystemArterial Blood Gas Analysis
pH
• Carbon dioxide in the blood combines with water to form carbonic acid that
dissociates to form bicarbonate and hydrogen ions
• The hydrogen ions formed increase the acidity of the blood:
CO2 + H2O ↔ H2CO3 ↔ H+ +HCO3-
• Increasing rate and depth of breathing will result in an adjustment of arterial
PaCO2 and pH
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

9. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Acid-base Disorder Classification
• Normal blood pH is between 7.35 - 7.45
• Acidosis is a blood pH < 7.35
• Respiratory – results from retention of CO2
• Metabolic – production or ingestion of hydrogen ions; loss of bicarbonate
• Alkalosis is a pH > 7.45
• Respiratory – wash out of CO2
• Metabolic – loss of H+ or increased production / ingestion of HCO3-
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

10. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Causes of Acid-Base Disorders
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
Disorder Respiratory Metabolic
Acidosis
• Hypoventilation
• Opioid overdose
• Head injury
• Airway obstruction
• Pneumonia
• Renal failure
• Aspirin overdose
• Lactic acidosis
• Ketoacidosis
• Ethanol
Alkalosis
• Hyperventilation
• Fever
• Anxiety / panic
• Salicylate poisoning
• Excessive diarrhea and vomiting
• Antacid ingestion

11. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Normal Arterial Blood Gas
• pH  7.35-7.45
• PaO2  75-100 mmHg (10-12 kPa)
• PaCO2  35-45 mmHg (4.6-6 kPa)
• HCO3-  22-26 mEq/L
• Oxygen saturation (SpO2)  95-100%
• Base excess/deficit (BE)  -2 to +2
• Lactate  0.5-2.2
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

12. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Interpretation of Arterial blood gas
1. History and physical examination
• First indicators of acid-base disorder cause
2. Evaluate blood pH
• pH < 7.35  acidosis)
• pH > 7.45  alkalosis
3. Evaluate PaCO2
• Helps determine primary disorders
• Acidosis with an elevated PaCO2 suggests respiratory acidosis
• Acidosis with a reduced PaCO2 suggests metabolic acidosis
• Alkalosis with a reduced PaCO2 suggests respiratory alkalosis
• Alkalosis with an elevated PaCO2 suggests metabolic alkalosis
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

13. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Interpretation of Arterial blood gas
4. Evaluate HCO3-
• High (> 26mEq/L) suggests metabolic alkalosis
• Low (< 22mEq/L) suggest metabolic acidosis
5. Evaluate PaO2
• Low  hypoxemia
• High  hyperoxia
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis

14. Components of the Gradian CCV SystemArterial Blood Gas Analysis
Interpretation of Arterial blood gas
• Metabolic acidosis
• pH is low
• Bicarbonate is low
• PaCO2 is normal
• Respiratory acidosis
• pH is low
• Bicarbonate is normal
• PaCO2 is high
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
• Metabolic alkalosis
• pH is high
• Bicarbonate is high
• PaCO2 is normal
• Respiratory alkalosis
• pH is high
• Bicarbonate is normal
• PaCO2 is low
Trends in acid-base disorders
Respiratory disorders  change in pH and the PaCO2 move in opposite directions
Metabolic disorders  change in pH and the bicarbonate move in the same direction
ROME = Respiratory Opposite, Metabolic Equal

15. Components of the Gradian CCV SystemLesson 1: Summary
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
• Correct interpretation of an ABGs includes history and physical examination,
enabling the clinician to identify the possible cause of the acid-base disorder
• ROME = Respiratory Opposite, Metabolic Equal

16. Components of the Gradian CCV SystemLesson 1: Activities
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
Case Study A
A 45 year old female is seen in the outpatient department following a road traffic
accident. She is noted to be breathing rapidly. Her ABG is:
• pH: 7.49 (7.35-7.45)
• PaO2: 7.5 (10-14)
• PCO2: 3.9 (4.5-6.0)
• HCO3: 22 (22-26)
• BE: -1 (-2 to +2)
• Other values within normal range
What is your interpretation of the blood gas?

17. Components of the Gradian CCV SystemLesson 1: Activities
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
Case Study B
A 18 year old female is brought to the clinic and discloses that her mother
passed away 1 week ago. Her ABG is:
• pH: 7.50 (7.35-7.45)
• PaO2: 12.1 (10-14)
• PCO2: 3.5 (4.5-6.0)
• HCO3: 22 (22-26)
• BE: -1 (-2 to +2)
• Other values within normal range
What is your interpretation of the blood gas?
What is the difference between this patient and the previous one?

18. Components of the Gradian CCV SystemLesson 1: Activities
Basic Principles of Critical Care Training I Arterial Blood Gas Analysis
Case Study C
A 60 year old male presents with persistent vomiting and diarrhea for 4 days. His
ABG is
• pH: 7.12 (7.35-7.45)
• PaO2: 10.5 (10-14)
• PCO2: 4.5 (4.5-6.0)
• HCO3: 9 (22-26)
• BE: -17 (-2 to +2)
• Lactate: 4.0
• Potassium: 5.5
• Other values within normal range
What is your interpretation of the blood gas?