Arterial Blood Gas Analysis (ABG)

Purpose of the test:
*Evaluates gas exchange in the lungs (Measurements may be needed to make diagnosis or to monitor various treatments)

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Some blood may leak from the artery after blood has been withdrawn.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:
None required if blood is collected from an artery in the arm. Partial disrobing is necessary if a technician, nurse or doctor chooses the artery in the groin or under the armpit.

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.
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.
Tubes are packed in an ice bag before transporting to the laboratory.

Immediate post-test care:
Apply pressure to the puncture site; Apply tape or guaze 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; 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.

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
Ethancrynic acid
Hydrocortisone
Methicillin
Metolazone
Nitrofurantoin
Prednisone
Tetracycline
Thiazide diuretics

Other factors that may affect test results:
None expected

Time before test results available:
Test requires only a few minutes in the laboratory. Time before results are reported to the doctor varies from a few minutes to a few days.

Normal Values:
Adult indirect bilirubin levels--1.1 mg/dl or less
Adult direct bilirubin levels--Less than 0.5 mg/dl
Total bilirubin in a newborn--1 to 12mg/dl

What "high" or "increased" may indicate:
Congenital enzyme deficiencies (Gilbert's disease)
Liver damage
Severe hemolytic anemia
Obstruction of bile ducts from stones or tumors
If over 20mg/dl in a newborn, exchange transfusion may be needed

Taking these drugs may affect test results:
Aminophenol
Anti-malarials
Ascorbic acid
Dextran
Epinephrine
Ethoxazene
Histidine
Indican
Isoproterenol
Levodopa
Methyldopa
Novobiocin
Phenazopyridine
Phenelzine
Primaquine
Rifampin
Streptomycin
Sulfa drugs
Theophylline
Tyrosine

Other factors that may affect test results:
Exposure to direct sunlight or ultraviolet light may increase bilirubin levels.
Failure to fast overnight

Source: Complete Guide to Medical Tests and the Merck Manual