Synonym

• ABG PaCO₂
• PaCO₂ABG
• PCO₂ ABG
• ABG PCO₂

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:

• pH: 7.35-7.45

Other related normals:

Note:

Normal reference ranges vary between laboratories; consult your laboratory.

High Result

pH > 7.45 occurs in the following conditions:

• Metabolic alkalosis
• Respiratory alkalosis

Details of Metabolic Alkalosis:

Metabolic alkalosis is characterized by a high pH with normal or high PaCO₂ and high HCO₃ levels.

Metabolic alkalosis overview:

• 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

Metabolic alkalosis causes:

• Cushing's disease
• Diarrhea
• Diuretic therapy
• Drugs such as
• Antacids
• Carbenicillin
• Carbenoxolone
• Corticosteroids
• Ethacrynic acid
• Laxative
• Mafenide
• Sodium bicarbonate
• Gastric suctioning
• Inadequate potassium intake
• Licorice (Large amounts consumed)
• Potassium-losing nephropathy
• Vomiting (Prolonged)

Details of Respiratory Alkalosis:

Respiratory Alkalosis is characterized by a high pH with low PaCO2 and normal or low HCO3 levels.

Respiratory alkalosis overview:

• 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

Respiratory alkalosis causes:

• Anemia
• Anxiety/Hyperventilation
• Carbon monoxide poisoning
• Fever
• Heart failure
• Myocardial infarction
• Neurologic disorders
• Pulmonary embolism
• Salicylate ingestion
• Shock
• Ventilator related (Excessive ventilation)

Low Result

pH < 7.35 occurs in the following conditions:

• Metabolic acidosis
• Respiratory acidosis

Details of Metabolic Acidosis:

Metabolic acidosis is characterized by a low pH with normal or low PaCO₂ and low HCO₃ levels.

Metabolic acidosis overview:

• 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

Metabolic acidosis causes:

• Decreased excretion of H⁺:
• Addison's disease
• Cystinosis
• Drugs
• Fanconi's syndrome
• Hypercalcemia
• Renal failure
• Renal tubular acidosis
• Wilson's disease
• Increased H⁺ load:
• Acid intake
• Ammonium chloride
• Ethylene glycol
• Hyperalimentation fluids
• Iron
• Isoniazid
• Metformin
• Methanol
• Paraldehyde
• Salicylates
• Sulfur
• Toluene
• High-fat/low-carbohydrate diets
• Ketoacidosis
• Alcoholism
• Diabetes
• Starvation
• Lactic acidosis
• Loss of HCO₃^-:
• GI losses
• Cholestyramine
• Diarrhea
• GI Fistula
• Ureterosigmoidostomy
• Renal losses
• Acetazolamide
• Renal tubular acidosis

Details of Respiratory Acidosis:

Respiratory acidosis is characterized by a low pH with high PaCO2 and high or normal HCO3.

Respiratory acidosis overview:

• 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

Respiratory acidosis causes:

• Asthma
• Chest injury
• Chronic obstructive pulmonary disease (COPD)
• Drug overdose (Narcotics/Sedatives)
• Neurologic diseases (Brain and Peripheral Nervous System)
• Obesity (Massive)
• Pneumonia
• Pulmonary edema

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