Arterial Blood Gases

Arterial Blood GasesAn arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood from an artery. This test is used to check how well your lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.As blood passes through your lungs, oxygen moves into the blood while carbon dioxide moves out of the blood into the lungs. An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be measured before they enter body tissues. An ABG measures:Partial pressure of oxygen (PaO2). This measures the pressure of oxygen dissolved in the blood and how well oxygen is able to move from the airspace of the lungs into the blood.Partial pressure of carbon dioxide (PaCO2). This measures the pressure of carbon dioxide dissolved in the blood and how well carbon dioxide is able to move out of the body.pH. The pH measures hydrogen ions (H+) in blood. The pH of blood is usually between 7.35 and 7.45. A pH of less than 7.0 is called acid and a pH greater than 7.0 is called basic (alkaline). So blood is slightly basic.Bicarbonate (HCO3). Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.Oxygen content (O2CT) and oxygen saturation (O2Sat) values. O2 content measures the amount of oxygen in the blood. Oxygen saturation measures how much of the hemoglobin in the red blood cells is carrying oxygen (O2).

Why It Is DoneAn arterial blood gas (ABG) test is done to:Check for severe breathing problems and lung diseases, such asasthma, cystic fibrosis, or chronic obstructive pulmonary disease (COPD).See how well treatment for lung diseases is working.Find out if you need extra oxygen or help with breathing (mechanical ventilation).Find out if you are receiving the right amount of oxygen when you are using oxygen in the hospital.Measure the acid-base level in the blood of people who have heart failure, kidney failure, uncontrolled diabetes, sleep disorders, severe infections, or after a drug overdose.

How To PrepareTell your doctor if you: Have had bleeding problems or take blood thinners, such as aspirin or warfarin (Coumadin). Are taking any medicines. Are allergic to any medicines, such as those used to numb the skin (anesthetics). If you are on oxygen therapy, the oxygen may be turned off for 20 minutes before the blood test. This is called a "room air" test. If you can't breathe without the oxygen, the oxygen will not be turned off.Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form.

How It Is DoneA sample of blood from an artery is usually taken from the inside of the wrist (radial artery), but it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery). You will be seated with your arm extended and your wrist resting on a small pillow. The health professional drawing the blood may rotate your hand back and forth and feel for a pulse in your wrist.A procedure called the Allen test may be done to ensure that blood flow to your hand is normal. An arterial blood gas (ABG) test will not be done on an arm used for dialysis or if there is an infection or inflammation in the area of the puncture site.The health professional taking a sample of your blood will: Clean the needle site with alcohol. You may be given an injection oflocal anesthetic to numb that area. Put the needle into the artery. More than one needle stick may be needed. Allow the blood to fill the syringe. Be sure to breathe normally while your blood is being collected. Put a gauze pad or cotton ball over the needle site as the needle is removed. Put a bandage over the puncture site and apply firm pressure for 5 to 10 minutes (possibly longer if you take blood-thinning medicine or have bleeding problems).

How It FeelsCollecting blood from an artery is more painful than collecting it from a vein because the arteries are deeper and are protected by nerves. Most people feel a brief, sharp pain as the needle to collect the blood sample enters the artery. If you are given a local anesthetic, you may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. You may feel more pain if the person drawing your blood has a hard time finding your artery, your artery is narrowed, or if you are very sensitive to pain.RisksThere is little chance of a problem from having a blood sample taken from an artery. You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for at least 10 minutes after the needle is removed (longer if you have bleeding problems or take blood thinners). You may feel lightheaded, faint, dizzy, or nauseated while the blood is being drawn from your artery. Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken. On rare occasions, the needle may damage a nerve or the artery, causing the artery to become blocked. Though problems are rare, be careful with the arm or leg that had the blood draw. Do not lift or carry objects for about 24 hours after you have had blood drawn from an artery.ResultsAn arterial blood gas (ABG) test measures the acidity (pH) and levels of oxygen and carbon dioxide in the blood.NormalThe normal values listed herecalled a reference rangeare just a guide. These ranges vary from lab to lab and depend upon the elevation above sea level. Your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.Results continued...Results are usually available right away.Arterial blood gases (at sea level and breathing room air) 1

Partial pressure of oxygen (PaO2):Greater than 80 mm Hg (greater than 10.6 kPa)

Partial pressure of carbon dioxide (PaCO2):3545 mm Hg (4.65.9 kPa)

pH:7.357.45

Bicarbonate (HCO3):2226 mEq/L (2226 mmol/L)

Oxygen content (O2CT):1522 mL per 100 mL of blood (6.69.7 mmol/L)

Oxygen saturation (O2Sat):95%100% (0.951.00)

The normal values for children may differ from the adult values listed here.The concentration of oxygen being breathed, called the fraction of inhaled oxygen (FiO2), is also usually reported. This is only useful if you are receiving oxygen therapy from a tank or are on a ventilator.Many conditions can change blood gas levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.What Affects the TestReasons you may not be able to have the test or why the results may not be helpful include the following: You have a fever or an abnormally low body temperature (hypothermia). You have a disease that affects how much oxygen is carried in your blood, such as severe anemia or polycythemia. You smoke just before the test or breathe secondhand smoke, carbon monoxide, or certain paint or varnish removers in closed or poorly ventilated areas.What To Think About Arterial blood gas (ABG) values alone don't provide enough information to diagnose a problem. For example, they can't tell whether low levels are caused by lung or heart problems. Arterial blood gas values are most helpful when they are reviewed with other examinations and tests. An ABG test is often done for a person who is in the hospital because of severe injury or illness. The test can measure how well the person's lungs and kidneys are working and how well the body is using energy. An ABG test may be most useful when a person's breathing rate is increased or decreased or when the person has very high blood sugar (glucose) levels, a severe infection, or heart failure. If several blood samples are needed, a thin tube (arterial catheter) may be placed in an artery. Blood can then be collected when needed.

Allens Test:The blood supply to your hand normally comes from two arteries: the radial artery and the ulnar artery. Before drawing blood for an arterial blood gas test, your health professional will make sure that both arteries are open and working correctly. A procedure called the Allen test may be used to find out if the blood flow to your hand is normal.For the Allen test, the health professional drawing your blood will apply pressure to the arteries in your wrist for several seconds. This will stop the blood flow to your hand, and your hand will become cool and pale. Blood is then allowed to flow through the artery that will not be used to collect the blood sample. This is usually the ulnar artery, which is found on the outer (little finger side) of your wrist. Arterial blood gases are usually taken from the radial artery, which is found on the inner (thumb side) of the wrist.Allen test

Normal (positive)Your hand quickly becomes warm and returns to its normal color. This means that one artery alone will be enough to supply blood to your hand and fingers.

Abnormal (negative)Your hand remains pale and cold. This means that one artery is not enough to supply blood to your hand and fingers. Blood will not be collected from an artery in this hand.

If your hand remains pale and cold, the Allen test will then be performed on your other hand. If your other hand also remains pale, the blood often will be collected from another artery, usually in the groin or elbow crease.

In medicine, the Modified Allen's test, also the Modified Allen test, The hand is elevated and the patient/person is asked to make a fist for about 30 seconds. Pressure is applied over the ulnar and the radial arteries so as to occlude both of them. Still elevated, the hand is then opened. It should appear blanched (pallor can be observed at the finger nails). Ulnar pressure is released and the colour should return in 7 seconds.The Allen's test is testing for abnormal circulation. If color returns as described above, the Allen's test is considered to be "Negative" (abnormal circulation is NOT present). If color fails to return, the test is considered "Positive" (abnormal circulation is present) and theulnar artery supply to the hand is not sufficient. The radial artery therefore cannot be safely pricked/ cannulated.

Allen test. Source: http://fitsweb.uchc.edu/student/selectives/TimurGraham/Modified_Allen%27s_Test.htmlInstruct the patient to clench his or her fist; if the patient is unable to do this, close the person's hand tightly.Using your fingers, apply occlusive pressure to both the ulnar and radial arteries, to obstruct blood flow to the hand.While applying occlusive pressure to both arteries, have the patient relax his or her hand, and check whether the palm and fingers have blanched. If this is not the case, you have not completely occluded the arteries with your fingers.Release the occlusive pressure on the ulnar artery only to determine whether the modified Allen test is positive or negative.Positive modified Allen test If the hand flushes within 5-15 seconds it indicates that the ulnar artery has good blood flow; this normal flushing of the hand is considered to be a positive test.Negative modified Allen test If the hand does not flush within 5-15 seconds, it indicates that ulnar circulation is inadequate or nonexistent; in this situation, the radial artery supplying arterial blood to that hand should not be punctured.PurposeTo evaluate the efficiency of pulmonary gas exchange.To assess the integrity of the ventilatory control system.To determine the acidbase level of the blood.To monitor respiratory therapy.ProcedurePatient Preparation1 Explain the arterial blood gas analysis evaluates how well the lungs are delivering the oxygen to the blood and eliminating carbon dioxide.2 Tell the patient that the test requires a blood sample.3 Explain to the patient, who will perform the arterial puncture, when it will occur, and where the puncture site will be; radial, brachial, or femoral artery.4 Inform the patient that he may not need to restrict food and fluids.5 Instruct the patient to breathe normally during the test, and warn him that he may experience a brief cramping or throbbing pain at the puncture site.Implementation6 Use a heparinized blood gas syringe to draw the sample.7 Perform an arterial puncture or draw blood from an arterial line.8 Eliminate air from the sample, place it on ice immediately, and prepare to transport for analysis.9 Note the flow rate of oxygen therapy and method of delivery.10 Note the patients rectal temperature.Nursing Interventions11 After applying pressure to the puncture site for 3 to 5 minutes and when bleeding has stopped, tape a gauze pad firmly over it.12 If the puncture site is on the arm, dont tape the entire circumference because this may restrict circulation.13 If the patient is receiving anticoagulants or has a coagulonopathy, apply pressure to the puncture site longer than 5 minutes if necessary.14 Monitor vital signs and observe for signs of circulatory impairment.InterpretationNormal ResultsNormal ABG values fall within this ranges. Pao2 80 to 100 mm Hg (SI, 10.6 to 13.3 kPa) Paco2 35 to 45 mm Hg (SI, 4.7 to 5.3 kPa) pH 7.35 to 7.45 (SI, 7.35 to 7.45) O2CT 15% to 23% (SI, o.15 to 0.23) Sao2 94% to 100% (SI, 0.94 to 1) HCO3- -22 to 25 mEq/L (SI, 22 to 25 mmol/L)Abnormal FindingsLow Pao2, O2CT, and Sao2 levels and a high Paco2 may result from conditions that impair respiratory function, such as respiratory muscle weakness or paralysis, respiratory center inhibition (from head injury, brain tumor, or drug abuse), and airway obstruction possibly from mucus plug or a tumor.Low readings may result from bronchiole obstruction caused by asthma or emphysema, from an abnormal ventilation perfusion ratio due to partially blocked alveoli or pulmonary capillaries, or from alveoli that are damaged or filled with fluid because of disease, hemorrhage, or near drowning.When inspired air contains insufficient oxygen, Pao2, O2CT, and Sao2 decrease, but Paco2 may be normal. Such findings are common in pneumothorax, impaired diffusion between alveoli and blood.Low O2CT with normal Pao2, Sao2 and, possibly, Paco2 values may result from severe anemia, decreased blood volume, and reduced hemoglobin oxygen carrying capacity.PrecautionsWait at least 20 minutes before drawing arterial blood when starting, changing, or discontinuing oxygen therapy. After initiating or changing settings of mechanical ventilation or other extubation.Before sending the sample to the laboratory, note on the laboratory request whether the patient was breathing room air or receiving oxygen therapy when the sample is collected.Interfering FactorsExposing the sample to air increase or decrease in Pao2 and Paco2.Venous blood in sample possible decrease in Pao2 and increase Paco2.Use of Diamox, Macrodantin, and Tetracycline may decrease Paco2.Fever may cause false-high Pao2 and Paco2.ComplicationBleeding from the puncture site.