Synonym
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:
| Conv. Units | SI Units |
|---|
| pH | 7.35-7.45 | |
| PaCO2 | 35-45 mmHg | 4.7-5.3kPa |
| PaO2 | 80-100 mmHg | 10.7-13.3 kPa |
| HCO3- | 22-28 mEq/L | 22-28 mmol/L |
| Base Excess | -3 to 3+ mmol/L | |
| SaO2 | > 92% | |
Altitude affects PaCO2 and PaO2 due to hyperventilation to maintain oxygen saturation. For example, at 1 mile of altitude, the PaCO2 normal will decrease to 32-40 mmHg and the PaO2 will decrease to 65-75 mmHg.
Note:
- Normal reference ranges vary between laboratories; consult your laboratory.
High Result
Please see the specific sections on ABG for the following for interpretation of high results on each of these items:
Low Result
Please see the specific sections on ABG for the following for interpretation of low results on each of these items:
References