Marcus Nesbeth PA-C

 ABG: is a test that measure the arterial Oxygen and Carbon dioxide concentration, acidity, and oxyhemoglobin saturation.  Note that HCO3 from the ABG is a calculated value and should not be used in the interpretation soley.  Instead the HCO3 from the Chemistry panel should be used.  Important test for ICU Patients with critical illness and respiratory diseases.

 To evaluate acute respiratory distress and assist in determining therapeutic interventions.  To document the existence and severity of a problem with oxygenation or carbon dioxide exchange.  To analyze acid-base balance.  To evaluate the effectiveness of respiratory interventions, for eg., continuous ventilatory assistance or oxygen therapy.

 Proceed with caution and avoid arterial sticks in the following circumstances:  Previous surgery in the area  Pts on anticoagulants or with known coagulopathy. Or pts on fibrinolytics or candidates for it.  Skin infection or other damage to the skin (eg. Burns, cellulitis) at he puncture site.  Decreased collateral circulation  Severe atherosclerosis, aneurysm, or vasospasms  Severe injury to the extremity

 3-5 ml sterile syringe with freely movable plunger  25 gauge, 5/8inch needle for radial, brachial, dorsalis pedis, and femoral sticks.  Antiseptic skin preparation ( betadine..)  3ml syringe with 25 gauge, 5/8 inch needle for 1% lidocaine w/o epinephrine (optional)  Container of crushed ice for sample transport  Sterile Gloves.  Possible goggles or eye protection  Heparin 1:1000 if syringe is not heparinized

 The preferred site in most pts is the Radial Artery  Check for patency of collateral circulation with the Allen’s Test  Prep the skin in an aseptic manner and put on gloves  Position the Extremity:  Radial: Stabilize the wrist over a small rolled towel or washcloth. The wrist should be dorsiflexed about 30 degrees.  Brachial: Place a rolled towel under the pt’s elbow while hyperextending the elbow. Rotate the pt’s wrist outward.

AnatomyRadial artery puncture

Brachial Artery PunctureFemoral Artery Puncture

 Palpate the pulse and determine the point of maximal impulse.  Inject 0.2 – 0.3ml of 1% lidocaine subcutaneously on either side and above the artery (optional).  Palpate the selected artery with the balls of two fingers, and immobilize it with these fingers along its course.  Grasping the syringe as if holding a pencil. Direct the needle with the bevel up, and puncture the skin slowly at approximately a degree angle to the radial or brachial artery ( degrees to the femoral artery).

 Watch the needle hub constantly for the appearance of blood.  When blood appears, stop advancing the needle, and allow the blood to flow freely into the syringe.  If the syringe fails to fill after an initial flash of blood both walls of the artery may have been pierced.  Withdraw the needle slightly until the tip reenters the artery and blood flows into the syringe.

 Obtain a sample of 2 to 3 ml. Remove the needle from the artery.  Immediately apply direct pressure to the puncture site with dry gauze for 3 to 5mins.  And at least 10mins for pts taking anticoagulants, fibrinolytics, or glycoproteins.  Hold the syringe with the needle tip upright and expel any air bubbles. Tapping the syringe may help expel bubbles clinging to the sides.

 Most common are bleeding, hematoma, and thrombosis formation.  Compression neuropathies may occur secondary to hematomas.  Nerve injury may occur with inadvertent puncture of the nerve.  If air bubbles are not removed from the sample, the PO2 can increase and yield inaccurate test results.  The blood sample may clot if the heparin and blood are not mixed adequately.

 pH  pCO mm Hg  HCO mEq/L

FICTION!  A pCO 2 < 40 mm Hg always implies a respiratory alkalosis

 A patient cannot have a metabolic acidosis and a metabolic alkalosis simultaneously  FICTION!

 A patient with a metabolic acidosis will have a compensatory respiratory alkalosis

 Step 1. Is there an acidemia or alkalemia?

 Step 2.Is the primary process metabolic or respiratory?

 Step 3:If the primary process is respiratory, is it acute or chronic?

 This step is only applied if the primary cause is respiratory.  For each 10mm Hg that the pCO 2 changes, the pH should move in the opposite direction. If the pCO 2 drops, the pH should rise, and vice versa.  The amount that the pH changes tells us whether the change is acute or chronic.  A change in the pH of 0.08 for each 10mm Hg indicates an ACUTE condition.  A change in the pH of 0.03 for each 10mm Hg indicates a CHRONIC condition.

 Step 4:Is there an anion gap?  Na + - (Cl - + HCO 3 -) > 12?

 Step 5:Is the respiratory compensation adequate?  Expected pCO 2 range = [1.5(measured HCO 3 - )]+8+/- 2

 This step is only applied if the primary cause is metabolic (acidosis or alkalosis)  Expected pCO 2 = (1.5 * serum HCO 3 - ) + 8 [+/- 2]  If metabolic acidosis: If measured pCO 2 > expected pCO 2, a respiratory acidosis is present in addition to the already diagnosed metabolic acidosis.  If metabolic alkalosis: If measured pCO 2 > 55, a respiratory acidosis is present in addition to the already diagnosed metabolic alkalosis.

 Step 6:Are there any other metabolic disturbances?  Corrected HCO 3 - = (Measured HCO 3 - ) + (AG-12)

 This step is only applied if there is an increased anion gap metabolic acidosis (if you had to do the math in step 4)  Corrected HCO 3 - = Measured HCO (anion gap - 12)  If corrected HCO 3 - < 24, a second acidosis is present in addition to the already diagnosed metabolic acidosis.  If corrected HCO 3 - > 24, there is a co-existing metabolic alkalosis in addition to the already diagnosed metabolic acidosis.  If corrected HCO 3 - = 24, then the already diagnosed metabolic acidosis is the sole problem.

 30 year old female BMT patient with neutropenic fever has been receiving multiple antibiotics including amphotericin B. You are called to the bedside for her fevers, rigors, and dyspnea  Na + 125Cl HCO  pH 7.07pCO 2 28 K + 2.5

 Step 1. Is there an acidemia or alkalemia? Acidemia

 Step 2.Is the primary process metabolic or respiratory?  pCO 2 = 28 should drive pH ↑  HCO 3 - = 8 should drive pH ↓

 Step 3: If the primary process is respiratory, is it acute or chronic?  Skip this step as primary process is metabolic !

 Step 4:Is there an anion gap?  Na + - Cl - - HCO 3 - > 12? = 17 Anion Gap Metabolic Acidosis

 Step 5:Is the respiratory compensation adequate?  Expected pCO 2 range = [1.5(measured HCO 3 - )]+8+/- 2  [1.5 (8) +8] +/- 2 = [18-22]  pCO 2 = 28, therefore this is a Respiratory Acidosis even though the value is below 40!!

 Step 6:Are there any other metabolic disturbances?  Corrected HCO 3 - = (Measured HCO 3 - ) + (AG-12) (8) + (17-12) = 13 Since this is below the normal range after correction, there is a non anion gap acidosis

 60 y/o male presents to the ED from a nursing home. You have no history other than he has been breathing rapidly and is less responsive than usual.  Na + 123Cl - 99HCO  pH 7.31pCO 2 10

 Step 1. Is there an acidemia or alkalemia?  Acidemia

 Step 2.Is the primary process metabolic or respiratory?  pCO 2 = 10 should drive pH ↑  HCO 3 - = 5 should drive pH ↓

 Step 3:If the primary process is respiratory, is it acute or chronic?  Skip this step as primary process is metabolic !

 Step 4:Is there an anion gap?  Na + - Cl - - HCO 3 - > 12? = 19 Anion Gap Metabolic Acidosis

 Step 5:Is the respiratory compensation adequate?  Expected pCO 2 range = [1.5(measured HCO 3 - )]+8+/- 2 [1.5 (5) +8] +/- 2 = [13.5 – 17.5] pCO2 = 10, therefore it IS a respiratory alkalosis (as a 2nd process)

 Step 6:Are there any other metabolic disturbances?  Corrected HCO 3 - = (Measured HCO 3 - ) + (AG-12) (5) + (19-12) = 12 Since this does not correct bicarbonate back to normal, there is a normal anion gap acidosis

 42 y/o female has the flu for four days with incessant vomiting. She presents to the ED two days after stopping insulin due to no food intake  Na + 130Cl - 80HCO  pH 7.21pCO 2 25

 Step 1. Is there an acidemia or alkalemia?  Acidemia

 Step 2.Is the primary process metabolic or respiratory?  pCO 2 = 25 should drive pH ↑  HCO 3 - = 10 should drive pH ↓

 Step 3:If the primary process is respiratory, is it acute or chronic?  Skip this step as primary process is metabolic!

 Step 4: Is there an anion gap? Na + - Cl - - HCO 3 - > 12? = 40!! Anion Gap Metabolic Acidosis

 Step 5:Is the respiratory compensation adequate?  Expected pCO 2 range = [1.5(measured HCO 3 - )]+8+/- 2 [1.5 (10) +8] +/- 2 = [ ] pCO2 = 25, therefore this is normal respiratory compensation

 Step 6:Are there any other metabolic disturbances?  Corrected HCO 3 - = (Measured HCO 3 - ) + (AG-12) (10) + (40-12) = 38 Since this over corrects bicarbonate there is a metabolic ALKALOSIS!!

 Methanol  Uremia  Diabetic ketoacidosis  Paraldehyde  Isopropyl alcohol & Iron  Lactic acidosis  Ethylene glycol  Salicylates & Starvation  Rhabdomyolysis

 Diarrhea  Ureteral diversion  Renal tubular acidosis  Proximal  Distal  Mineralcorticoid deficiency  Carbonic anhydrase inhibitor  Acetazolamide  Mefenamic acid  Post hypocapneic state

 Early renal failure  Renal disease  SLE interstitial nephritis  Amyloidosis  Hydronephrosis  Sickle cell nephropathy  Acidifying agents  Ammonium chloride  Calcium chloride  Arginine  Sulfur toxicity