ABG Basics

Obtaining an Arterial Blood Sample.  The raidal artery is the most frequently used artery for ABG's Paramedics, physicians, nurses (RNs), and respiratory technicians / technologists are the persons most likely to be trained to perform arterial blood gas samples.  The Allen test for collateral circulation is routinely performed first, to be sure the patient can tolerate temporary blockage of the radial artery. Modified Allen Test   To Determine that collateral circulation is present from the ulnar artery in the event that thrombosis of the radial artery should occur. a) Position the patient's arm on a flat surface with the wrist supported on a rolled towel. Severe extension should be avoided as it will obliterate a palpable pulse. b) Compress both the radial and ulna arteries with the index and middle fingers of both your hands for several seconds. c) Ask the patient to clench and unclench their fist until blanching of the skin occurs. d) Release pressure on the ulnar artery and assess for the return of skin colour within 5 to 15 seconds. Return of colour within this time frame signifies a positive Allen's test. e) If ulnar filling is poor or no flushing occurs do not proceed but try the other arm for a suitable site. Documentation of inadequate circulation in the affected extremity must be done. f) If the Modified Allen's test is positive you may proceed with the arterial puncture.Have the patient make a fist.  Using fingertips, press moderately against the wrist to find the radial or ulnar arteries. CONTRAINDICATIONS/CONCERNS FOR ARTERIAL PUNCTURE: Anticoagulant therapy History of a clotting disorder (haemophilia) History of arterial spasms following previous punctures Severe peripheral vascular disease Abnormal or infectious skin processes at or near the puncture sites Arterial grafts   Prepare for the Procedure The patient's medical record must be assessed carefully for any of the above and the physician notified. Check for physician's order. Check the patient's medical record for latex allergy  Pick up requisition and patient label. Gather Equipment EQUIPMENT NEEDED: Plastic bag ABG kit Butterfly needle Alcohol swabs  Betadine Swabs Ice Vacutainer with Leur adapter 2" x 2" gauze sponge Gloves Appropriate Bed protector  Collection tubes Appropriate identification labels Appropriate lab requisitions Identify the patient. Explain the procedure and its purpose. Instruct the patient to report excessive pain during the procedure. Assess the patient by checking vital signs.  Check for collateral circulation, using the Allen Test.  Prepare the site: a) Place a bed protection sheet under the site, ensure towel is in place. b) Glove -- use plastic glove if latex allergy indicated. c) Cleanse the puncture site by starting in the centre of the target area with the alcohol prep pad, scrub in a circular motion from the inside to outside. Ensure that the rolled towel is still in position under the patient's wrist to help stabilize the site. Do not apply tension to the wrist as the artery can become compressed. Have the patient make a fist. Locate the radial artery on the thumb side of the wrist, using the index finger and middle fingers of the left hand.  Palpate the artery to determine its size, depth and direction.  Never use the thumb, because it has its own pulse and can be confused with the patients. Clean the site using alcohol first and then povidone iodine.  Prep the fingers that will be used for palpitation.  Allow to dry, being careful not to touch the site. If an anesthetic was used, infiltrate the skin over the selected site, entering the skin with the needle at about 10-dregrees with the surface of the skin.  Pull back slightly on the plunger to check of you have punctured a vein. (if a vein has been punctured, you will have to perform the procedure again) Otherwise, expel the anesthetic into the skin forming a raised wheel.  Wait about 1 to 2 minutes to take effect. Take the drawing syringe, and expel the remaining heparin, being careful not to draw air back into the syringe.  Hold it in the dominant hand as if your were holding a dart. Locate the artery and insert the needle bevel up into the skin at about 45-degree angle, at about 5 to 10 mm distal to the finger locating the artery.  Direct the needle away form the hand with the bevel facing the flow of blood. As you insert the needle slowly deeper into the wrist, you may feel a "pop" and a flash of blood will appear in the hub of the needle.  At this point, stop advancing the needle further.  Once the artery is punctured, arterial pressure will push up the hub of the syringe and a pulsating flow of blood will easily fill the syringe.  It is not necessary to pull back on the plunger.  Hold the syringe very still until the amount of blood needed has been collected.Note: Suspect venous puncture if pulsation is minimal and blood dark in colour. If you missed the artery, slowly withdrawal the needle out to just below the skin and re-insert again.  Do not probe with the needle, as this can be very painful and can lead to a hematoma, thrombus formation and damage to the artery itself.  Never ask the patient to apply the pressure.  This is because the patients may not apply enough pressure. After the amount of blood has been collected, quickly withdraw the needle and immediately place direct pressure on the puncture site using a dry gauze pad.  Never allow the Examine the sample carefully and expel any air you may see or suspect.  Then place it in the rubber or latex square. After the 2 to 5 minutes of pressure holding on the puncture site, remove the syringe from the rubber or latex square and replace the needle with the luer cap. Label the specimen and place it in ice or the cool block. Difficulties in obtaining a sample may occur if: a) The patient is alkalotic or acidotic; an irritable or constricted vessel is more difficult to puncture b) Hypotension exists with a weak or absent pulse on palpation. c) The patient is younger. The absence of atherosclerosis implies a healthy, muscular, 'bouncy' artery which may not be particularly easy to penetrate d) The patient suffers from diseases such as Parkinsons', etc. e) The patient is afraid and tense. This can be dealt with by reassuring the patient and re-explaining the procedure and its purpose.   Complications Discomfort Generally, arterial punctures are painful and the patient will feel some discomfort or pain sometime after the procedure.  This is true even if a local anesthetic was used. Infection Improper or failure to use antiseptic can and most likely will cause infection. Hematoma Because the blood is under considerable pressure in the arteries, blood is initially more apt to leak from an arterial puncture than from a venipuncture site.  However, arterial puncture sites tend  be close more rapidly due to the elastic nature of the arterial wall.  This elasticity tends to decrease with age, therefore, the probability of a hematoma formation is greater in older patient or in patients receiving anticoagulants. Arteriospasm The artery muscle can be irritated by needle penetration which can cause a reflex constriction of the artery or arteriospam.  The condition is transitory but may make it difficult to obtain a specimen. Thrombus formation Injury to the intima of the artery can lead to clot (thrombus) formation.  A large thrombus can obstruct the flow of blood and impair circulation. Problems with the integrity of the ABG The following are problems that can cause erroneous result in ABG analysis. Air bubbles - If not removed immediately, oxygen from the bubbles can diffuse into the sample and CO2 can escape, changing the results. Delay in cooling - Blood cells continue to consume oxygen and nutrients and produce acids and carbon dioxide at room temperature.  If the specimen remains at room temperature for more then 5 to 10 minutes, the pH, blood gases, and glucose values will change. Cooling to between 1ºC to 5ºC slows the metabolism and helps stabilize the specimen.  Processing the specimen as soon as possible after collection will ensure the most accurate results. Venus blood mixed in ABG sample - Normal arterial blood is brightred, whereas venus blood is slightly darker in color.  Sometimes it is difficult to distinguish between arterial and venous blood in patients with poor oxygen content.  This will make their arterial blood appear as dark as venous blood.  The best way to be certain that a specimen is arterial is if the blood pulses into the syringe.  In some cases, such as with low cardiac output, a specimen may need to be aspirated.  In such instances, it is hard to be certain that the specimen is really arterial. Improper anticoagulant - Heparin is the accepted anticoagulant for ABGs.  Oxalates, EDTA and citrates may alter results, especially pH. Too much heparin can cause erroneous results due to acidosis and too little can result in clotting. Specimen Rejection Inadequate volume of specimen for the test Clotted Incorrect or no identification Wrong syringe used Delay in delivering the sample for analysis Not placed in ice Air bubbles COMPLICATIONS: 1. Embolism. 2. Arterial occlusion (prolonged spasm). 3. Haematoma -- this can substantially be minimized if pressure is held at the puncture site for at least five minutes. 4. Localized infection and/or bacteremia. 5. Distal ischemia. 6. Thrombosis. 7. Numbness of the hand. DOCUMENTATION: MUST INCLUDE: 1. Date and time of procedure. 2. The site chosen. 3. The patient's tolerance of the procedure. 4. The Fi02 the patient is on at the time the sample is drawn. CHART BY EXCEPTION: 1. Adverse side effects of the procedure. 2. Length of time pressure applied, if greater than 5 minutes. 3. Any negativity in Modified Allen's test. **All attempts successful and unsuccessful must be documented.** COMPLICATIONS OF ARTERIAL PUNCTURE:   COMPLICATION CAUSE ACTION Arteriospasm May occur secondary to pain or anxiety. Reassure patient; explain procedure and purpose. Hematoma Leakage of blood into tissue due to lack of sufficient elastic tissue to seal puncture site, especially in elderly. Ensure using small diameter needle. Ensure proper technique in holding site X5 minutes post-puncture. Hemorrhage Patient receiving anticoagulant therapy or patients with known blood coagulation disorders. Two minutes after pressure is released inspect site for bleeding oozing or seepage of blood; continue pressure until bleeding ceases. A longer compression time is necessary. Infection of Health Care Provider Contact with virus, infections contained in blood of infected patients. Universal blood & body fluid precautions should be implemented. All blood samples from all patients must be treated with full precautions. Nosocomial Bacteraemia Inadequate cleansing prior to puncture. Ensure appropriate cleansing technique. Distal ischemia No collateral circulation. Only proceed with puncture after patient has a (+) Allen's Test. Numbness of hand Nerve damage. Ensure proper technique. Palpate artery well, do not redirect when needle lies deep within tissue. Sepsis Infection/inflammation adjacent to puncture site. Avoid sites indicating presence of infection or inflammation. Basic Conditions Diagnosed by ABG's Respiratory Acidosis Anything which prevents the body from getting rid of excess CO2, increases acid which decreases pH Respiratory Alkalosis Anything which makes to body lose CO2, decreases acid, which increases pH Metabolic Alkalosis Anything which increases HCO3 increases base which increases pH Metabolic Acidosis Anything which decreases HCO3 decreases base which decreases pH ABG Normal Values pH 7.35-7.45 PO2 80-100 mm hg PCO2 35-45 mm hg  HCO3 22-26 mEq/L SaO2 97-100% (also known as SAT)- Arterial values Pulse Oxygen Normal 95-100% This number is similar to the Sa02 or SAT from ABG Many MD’s write orders to increase O2 as needed to keep pulse oxygen above 92% for patients who do not have COPD Basic steps to interpret classic ABG results First memorize the normal values for pH, CO2 and HCO3  Understand that CO2 acts as an acid and HCO3 acts as a base. These two are essentially opposite of each other and the body tries to keep the pH in a narrow range in order to survive. It does this by varying the amounts of CO2 and HC03. Know that a low pH indicates too much acid, or not enough base Know that a high pH indicates not enough acid, or too much base           To analyze patient results Look at each of the patient values and draw arrows (for high or low beside each of them)  Look at pH and determine if it is alkalosis or acidosis  (If pH is low it is some type of acidosis, If pH is high, it is some type of alkalosis) Determine what is causing the problem. In order to do this you have to understand basic physiology.  If you can't breath, you can't get rid of CO2 and CO2 acts as an acid in the body. So if the patient is in acidosis and  CO2 is high, it’s respiratory acidosis. If the patient is not having a C02 problem, it is probably the other type of acidosis - metabolic. In this case, it is not too much acid which is the problem, but rather not enough base to buffer the body's normal C02. HCO3 acts as a base in the body. Therefore if HCO3 is low it causes  metabolic acidosis. This can be caused by the body using up a lot of HCO3 (diabetics) or loosing a lot of HCO3 in the urine, etc.   So what if the pH is high - It is some type of alkalosis  Determine the cause of the alkalosis. Again, remember that C02 is an acid and not enough acid would make the person go into alkalosis. So if CO2 is low, its respiratory alkalosis  - meaning that for some reason they are breathing too much (or too fast) and breathing off too much CO2 - Hyperventilation, etc. However, another cause for alkalosis is too much base. HCO3 is the base for the body.  If  HCO3 is high, its metabolic alkalosis (a number of disease conditions can cause this to happen).  OK, so what if the pH is normal or near normal, but the CO2 and HCO3 are way off. This happens when the body manages to compensate for the problems in one system (such as the respiratory system) but creating more of the other componet.  How do you know if the patient is in some type of compensated process? Anytime CO2 and HCO3 are going the same direction (either both high or both low), it is a compensated process - such as partially compensated respiratory acidosis (both CO2 and  HCO3 are high).   So to sum it all up. Look at pH and determine if it is high or low (alkalosis or acidosis) If pH is low it is some type of acidosis If CO2 is high, it’s respiratory acidosis If HCO3 is low it’s metabolic acidosis If pH is high it is some type of alkalosis If  CO2 is low, its respiratory alkalosis If  HCO3 is high, its metabolic alkalosis Anytime CO2 and HCO3 are going the same direction (either both high or both low), it is a compensated process - such as partially compensated respiratory acidosis (both CO2 and HCO3 are high) Example problem pH 7.33 O2 60 CO2 48 HCO3 25 SaO2 90%   The pH is low so this is acidosis The CO2 is high so this must be respiratory acidosis The Bicarb is normal so the acidosis is not being compensated for by the renal system yet.