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Arterial-Blood-Gas Analysis (ABG)
Arterial-Blood-Gas Analysis (ABG)
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Arterial-Blood-Gas Analysis (ABG)
Category: Blood gases and electrolytes.
Subcategory: Blood gases.
Material studied: Blood collected from an artery.
Estimated cost of test: $40.00 to $80.00.
Patient time for test: 15 minutes.
Reliability of test results: Good.
Available as home self-test? No.
BEFORE THE TEST
Purpose of test:
Evaluates gas exchange in the lungs. Measurements include:
Partial pressure of oxygen (PaO2).
Partial pressure of carbon dioxide (PaCO2).
pH to measure the acid-base level of the blood or the hydrogen ion (H+) concentration.
Oxygen content (O2CT).
Oxygen saturation (O2Sat).
Bicarbonate (HCO3-).
Measurements may be needed to make diagnosis or to monitor various treatments.
Where is test performed?
Commercial laboratory, hospital, doctor's office.
Who performs test?
Lab technician, nurse, doctor.
Risks and precautions:
Some blood may leak from the artery after blood has been withdrawn. This is usually controlled easily.
If you are treated with intermittent positive-pressure breathing, the operator should wait at least 20 minutes after treatment to draw arterial blood.
Patient preparation:
Activity--No changes necessary.
Diet--No changes necessary.
Medicines--Inform the person performing the test if you have recently taken any medications listed under Taking these drugs may affect test results. You may be asked not to take this medication before the test.
Disrobing--None required if blood is collected from an artery in the arm. Partial disrobing if a technician, nurse or doctor chooses the artery in the groin or under the armpit.
THE TEST
Sensory factors:
Touching--You will feel some minor pain when the local anesthetic is injected into the skin overlying the artery before collecting blood. You may feel slight additional discomfort when the underlying artery is punctured.
Seeing--You will see the technician, nurse or doctor prepare the skin, drape it to prevent infection and perform the arterial puncture. You will also see the basket or tray to hold the equipment, the needles, syringes, collecting tubes and bandages.
Feeling--Some degree of fear or apprehension is normal and should be expected. After the arterial puncture, apprehension will subside.
Other senses (taste, smell, hearing)--Not affected.
Equipment used:
Needles, syringes and heparinized* collecting tubes. Sterile, disposable equipment prevents contamination or spread of infection. There is no chance of becoming infected with hepatitis or AIDS virus or any other infecting germ.
Description of test:
Operator feels the artery to be punctured. Skin over the artery is cleaned with alcohol or other antiseptic on a piece of cotton.
The site is draped.
Skin is injected with a local anesthetic, such as Xylocaine.
The artery is punctured with a sterile, disposable needle attached to a disposable syringe.
Operator withdraws the needle and transfers sample from the collecting syringe into sterile tubes (identified with your name). Tubes are treated with an anti-coagulant chemical to prevent clotting.
Tubes are packed in an ice bag before transporting to the laboratory.
AFTER THE TEST
Immediate post-test care:
Apply pressure to the puncture site.
Apply tape or gauze pad over the puncture site. Don't bandage the entire circumference of any puncture site.
Activity after test:
Rest quietly for 10 minutes, applying pressure to arterial puncture site.
Resume taking any medications that were withheld before the test.
Return to pretest activities gradually.
Use warm compresses if blood collects under the puncture site or if the area becomes tender, red or painful.
Time before test results available:
1 to 2 hours if done in hospital or local lab. Several days if a distant lab analyzes samples.
TEST RESULTS
Test values:
Test results are determined by electrode analysis* and color-comparison analysis*.
Normal values:
PaO2 75 to 100mmHg
PaCO2 35 to 45mmHg
pH 7.35 to 7.42
O2CT 15 to 23%
O2 94 to 100%
HCO3- 22 to 26mEq/liter
What ABNORMAL may indicate:
Pneumothorax*.
Interstitial fibrosis*.
Severe anemia*.
Decreased blood volume and reduced hemoglobin/oxygen-carrying capacity.
Asphyxia*.
Diarrhea.
Excess ingestion of antacids.
Hyperventilation*.
Kidney disorders.
Liver disease.
Loss of electrolytes from excessive vomiting.
Respiratory stimulation by drugs.
Severe infections.
Shock.
Taking these drugs may affect test results:
Acetazolamide.
Antacids.
Bicarbonate.
Ethacrynic acid.
Hydrocortisone.
Methicillin.
Metolazone.
Nitrofurantoin.
Prednisone.
Tetracycline.
Thiazide diuretics.
Other factors that may affect test results: None expected.
*See Glossary.
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