Synonym

• ABG PaO₂
• PaO₂ ABG
• PO₂ ABG
• ABG PO₂

Tubes

Heparinized syringe designed for ABG

1-3 mL of arterial blood

Immediate care of specimen:

Capped, iced and immediately transported to the laboratory without exposure to air

Additional information of sample collection:

• Sample of blood is collected from radial, femoral, or brachial artery.
• In newborns, it is collected from the umbilical cord.
• May be drawn by percutaneous arterial puncture or from arterial line.
• When collecting sample from the radial artery, determine the patency of the ulnar artery using the Allen test
• Specify whether the patient was breathing room air; if not, document the amount (Lpm) and delivery (canula, mask, ETT)of any oxygen being supplied when the sample was collected
• If the patient was on oxygen, the oxygen concentration must remain constant for 20 minutes preceding the test.
• If the test is to be taken without oxygen, the oxygen must be turned off for 20 minutes before the sample is taken
• Must be analyzed within 15 minutes of collection
• Maintain specimen on ice to prevent:
• Glycolysis
• Production of lactic acid
• Fall in pH
• Rise in PCO₂

Info

ABG analysis measures:

• Partial pressure of arterial O₂ (PaO₂)
• Partial pressure of arterial CO₂ (PaCO₂)
• Arterial sample pH
• O₂ content (O₂CT)
• Arterial O₂ saturation (SaO₂)
• Bicarbonate (HCO₃^-)

Clinical

ABG analysis is done:

• To determine the acid-base level of blood
• To evaluate the efficiency of pulmonary gas exchange
• To assess the function of the ventilatory control system
• To monitor respiratory therapy

Factors that may interfere with the results of the test:

• Anemia (Severe)
• Fever
• Hypothermia
• Polycythemia
• Presence of air bubbles in the syringe

Factors that may lower the SaO₂ values without affecting the PaO₂ values include:

• Exposure to carbon monoxide (including cigarette smoking)
• Exposure to certain paint or varnish removers

4 basic conditions may be found on analysis. It is generally reasonable to examine the pH, PCO₂, HCO₃ to determine the primary process. There is typically some compensation that occurs in chronic conditions; but the pH, PCO₂ and HCO₃ will tell which process is primary and which is the compensatory mechanism.

I. Respiratory acidosis:

• Excess CO₂ retention
• pH < 7.35
• HOC₃^- > 28 mmol/L (may not be elevated in acute cases)
• PaCO₂ > 45 mmHg (> 5.3 kPa)
• Signs and symptoms such as
• Anxiety/Apprehension
• Confusion/Coma
• Excessive sweating
• Headache
• Restlessness
• Tachycardia

II. Respiratory alkalosis:

• Excess CO₂ excretion
• pH > 7.45
• HCO₃^- < 22 mmol/L (may not be diminished in acute cases)
• PaCO₂ < 35 mmHg (< 4.7 kPa)
• Signs and symptoms of:
• Anxiety
• Fear
• Lightheadedness
• Paresthesias
• Rapid, deep breathing
• Twitching

III. Metabolic acidosis:

• HCO₃^- loss and acid retention
• PH < 7.35
• HCO₃^- < 22 mmol/L
• PaCO₂ > 35 mmHg (> 4.7 kPa)
• Signs and symptoms of:
• Coma (in severe cases)
• Drowsiness
• Fatigue
• Fruity breath (if DKA)
• Headache
• Lethargy
• Nausea
• Rapid, deep breathing
• Vomiting

IV. Metabolic alkalosis:

• HCO₃^- retention
• Acid loss
• pH > 7.45
• HCO₃^- > 28 mmol/L
• PaCO₂ > 45 mmHg (> 5.3 kPa)
• Signs and symptoms such as:
• Coma (in severe cases)
• Confusion
• Irritability
• Hypertonic muscles
• Mental apathy
• Restlessness
• Seizures
• Slow, shallow breathing
• Tetany
• Twitching

Nl Result

Reference range:

• PaO₂: 80-100 mmHg (10.7-13.3 kPa)

Other related normals:

Note:

Normal reference ranges vary between laboratories; consult your laboratory.

High Result

PaO₂ > 100 mmHg (> 13.3kPa) occurs in the following conditions:

• Drugs such as
• Theophylline
• Urokinase
• Fever
• Hyperventilation
• Oxygen supplementation

Low Result

PaO₂ < 80 mmHg (< 10.7kPa) occurs in the following conditions:

• Drugs such as
• Althesin
• Barbiturates
• GM-CSF
• Isoproterenol
• Narcotics
• Sedatives
• Hypoventilation
• Cerebrovascular incident (Stroke)
• Head injury
• Flail chest/rib fractures
• Pneumothorax
• Respiratory depressant drugs
• Decreased alveolar gas exchange
• Cancer of Lung
• Compression of lung
• Resection of lung
• Respiratory distress syndrome
• Sarcoidosis
• Decreased ventilation or perfusion
• Airway obstruction (upper or lower)
• Asthma
• Bronchitis
• Bronchiectasis
• Cancer
• Chronic obstructive pulmonary disease (COPD)
• Croup
• Cystic fibrosis
• Emphysema
• Granulomata
• Pneumonia
• Pulmonary edema
• Pulmonary emboli
• Pulmonary infarction
• Shock
• Hypoxemia
• Abnormal hemoglobins
• Anesthesia
• Carbon monoxide poisoning
• Heart failure
• High altitudes
• Near drowning
• Right to left shunt
• Congenital heart disease
• Intrapulmonary venoarterial shunting
• Ventilated patients
• Obstructed ETT
• Oxygen supply not attached
• Dislodged ETT
• Pneumothorax
• Other equipment failure
• Large A-a gradient due to underlying condition

References

• Lab tests online. Blood gases[Homepage on internet] ©2001-2006 [updated 2005 Apr 25;cited 2006 Jul 11] Available from http://labtestsonline.org/understanding/analytes/blood_gases/test.html
• MedlinePlus: Medical Encyclopedia. Blood gases test [Homepage on internet] c2005 [updated 2004 Aug 16;cited 2006 Jul 11] Available from http://www.nlm.nih.gov/medlineplus/ency/imagepages/9126.htm
• MedlinePlus: Medical Encyclopedia. Blood gases [Homepage on internet] c2005 [updated 2006 May 30;cited 2006 Jul 11] Available from http://www.nlm.nih.gov/medlineplus/ency/article/003855.htm
• Nissl J, Terra RP. BCHealthGuide. Arterial blood gases [Homepage on internet] c 1995-2006 [updated 2004 Nov 19;cited 2006 Jul 11] Available from http://www.bchealthguide.org/kbase/topic/medtest/hw2343/descrip.htm