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ABG ANALYSIS 4/27/2017
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Purpose of ABG Analysis:
To evaluate how effective the lungs are in bringing oxygen to the blood and removing carbon dioxide from it. 4/27/2017
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Radial artery is the most frequently used artery for ABGs
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Allen’s Test Patient clenches fist
Apply firm pressure to radial & ulnar arteries Patient relaxes hand Release pressure on the ulnar artery Palm should flush within 5-15 secs Purpose of the test is to check for patency of the ulnar artery to make sure there is adequate palmar collateral circulation should the radial artery become occluded. You’re looking for a positive Allen’s Test. 4/27/2017
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Arterial Blood Sampling
Prep site Pierce skin over arterial at a 60-90° angle Obtain 3 mL of blood without air bubbles Twirl syringe to mix heparin with sample Place in ice Hold pressure for 5-10 minutes Wait 30 minutes before drawing sample if O2 setting changed 4/27/2017
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Documentation Must Include: Chart By Exception:
Presence of positive Allen’s Test Date and time of procedure Site chosen Patient’s tolerance to procedure FiO2 patient is on at the time the sample is drawn Chart By Exception: Adverse side effects of procedure Length of time pressure applied, if greater than 5 minutes Negative Allen’s Test 4/27/2017
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Key to body’s response to acid-base imbalance is:
Hydrogen Ion Concentration When H+ HCO3- + H+ H2CO3 CO2 + H2O When H+ CO2 + H2O H2CO3 HCO3- + H+ When H+ increases, HCO3 combines with H+ to form H2CO3 (carbonic acid), The carbonic acid breaks down to CO2 and H20. The lungs react first to blow off the excess CO2. The kidneys react last by excreting H+ and retaining HCO3. When H+ decreases, CO2 and H2O combine to form carbonic acid, which then breaks down into H+ and HCO3. The lungs retain CO2 making it available to the buffer system and the kidneys excrete HCO3 and recirculate H+. PH os solutions is 1-14 (7 is considered neutral). Blood is slightly alkaline 7/ Buffers in the body: carbonic acid, monohydrogen-dehydrogen, phosphate excrete sodium biphosphate in urine, a weak acid), intracellular plasma protein, hgb buffers(shift CL in & out of RBCS in exchange for bicarb 4/27/2017
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Normal ph is maintained by 1 part carbonic acid to 20 pts bicard
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Components of ABG pH- Hydrogen ion concentration in plasma
PaCO2- Partial pressure of CO2 dissolved in plasma HCO3- Bicarbonate concentration in plasma PaO2- Partial pressure of O2 dissolved in plasma Base Excess- The amount of base Normal values: Ph PCO HCO PO Saturation BE +_ 2 Venous: PCO240-45 HCO PO Sat 60-85 4/27/2017
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Interpretation of ABGs
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pH pH reflects the hydrogen ion (H+) concentration of plasma pH range
0= pure acid 14= pure base 7.0 =neutral (equal parts acids/base) Normal pH in the blood = 4/27/2017
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Acidosis Decrease in pH resulting from an increase in hydrogen ion concentration H+ Reverse relationship: Low ph, high H+ ions 4/27/2017
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Alkalosis Increase in pH resulting from a decrease in hydrogen ion concentration 4/27/2017
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FOUR STEPS to evaluate ABGs
1. Evaluate each number 2. Check pH to determine cause of imbalance 3. Find value that matches acid-base status of pH 4. Determine extent of compensation: Absent Partial Complete 4/27/2017
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Step 1 evaluating each number
Is the pH on the acid or alkaline side? What does the PaCO2 show? What does the HCO3 show? Does the PaO2 show hypoxemia? PO2 hgb CO2 What is the normal acid to base balance in the body? 1-20 HCO3 ph Base acid Buffer 4/27/2017
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Step 2 Is the pH on the acid or alkaline side?
Normal pH pH < 7.40 = acidosis pH > 7.40 = alkalosis pH levels below 6.8 and above 7.8 are considered incompatible with life. Normal ph 4/27/2017
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Step 3 Does the PaCO2 match the pH?
Normal PaCO mm Hg PaCO2 > 45 PaCO2 < 35 4/27/2017
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Step 3 Does the HCO3 match the pH?
Normal HCO mEq/L HCO3 < 22 HCO3 > 26 4/27/2017
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Which System is Involved?
Lungs (Respiratory) Kidneys (Metabolic) The system that is the problem has the value that matches the pH. The other value that doesn’t match the pH, corresponds to the system that will compensate for the imbalance. 4/27/2017
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Step 4 What is the extent of compensation?
Absent - value that doesn’t match the pH is normal Partial - value that doesn’t match the pH & pH are above or below normal Complete - value that doesn’t match the pH is above or below normal, but the pH is normal Partial= the value that doesn’t match is moving in the opposite direction,but the PH still isn’t normal 4/27/2017
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Metabolic System compensates for the Respiratory System
Respiratory acidosis Kidneys re-absorb more bicarbonate Respiratory alkalosis Kidneys excrete more bicarbonate 4/27/2017
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Respiratory System compensates for Metabolic abnormalities
Metabolic acidosis Hyperventilation lowers PaCO2 so the ratio of Bicarbonate to Carbonic acid returns to normal Metabolic alkalosis Hypoventilation so the PaCO2 rises and the ratio of Bicarbonate to Carbonic Acid returns to normal 4/27/2017
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Oxygen Oxygen is carried in the blood in two ways:
In combination with hemoglobin Dissolved in plasma PaO2 is the measurement of dissolved oxygen in the arterial blood. PaO2 is not necessary for the 4 step ABG analysis, but you should always check your patient’s PaO2. The most important thing to remember about PaO2 is that hypoxemia kills. Decrease PaO2 will ultimately result in acid-base imbalance. Without oxygen, anaerobic metabolism takes place and large amounts of lactic acid accumulates causing acidosis. 97% bound by Hgb 3% dissolved in plasma 4/27/2017
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PaO2 Normal on room air 80-100 mm Hg Mild hypoxemia = 60-80 mmHg
Moderate hypoxemia = mmHg Severe hypoxemia = below 40 mmHg 4/27/2017
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Does the PaO2 show hypoxemia?
Is the client hypoxemic? Is the client’s PaO2 or SaO2 low? Is the client anemic? For every year > 60 y.o. PaO2 decreases by 1 mm Hg. No one should have a PaO2 < 50. Normal PaO2 is Normal SaO2 is 4/27/2017
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ABG Example pH 7.48 PaCO2 32 HCO3 22 Normal Uncompensated Respiratory Alkalosis 4/27/2017
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Acid-Base Disorders ABG Disorder Possible Causes Signs and Symptoms
Respiratory Acidosis CNS depression (barbiturate or sedative OD) Asphyxia Hypoventilation COPD Respiratory muscle weakness (Guillain-Barre) Chest wall abnormality (obesity) Diaphoresis Headache Tachycardia Confusion Restlessness Apprehension Resp acidosis occurs whenever there is hypoventilation. A build up of CO2 causes carbonic acid to accumulate in the blood (CO2 + H2O=H2CO2=H+ HCO3-) CNS depression from drugs, injury Hypoventilation due to pulmonary, cardiac, musculoskeletal, or neuromuscular disease COPD, Barbituate or sedative OD, atelectasis, Guillain-Barre), pneumonia, chest wall abnormality, mechanical ventilation Treat; make them breath! Narcan, Ventilator CDB 4/27/2017
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Acid-Base Disorders ABG Disorder Possible Causes Signs and Symptoms
Respiratory Alkalosis Hyperventilation Respiratory stimulation (septicemia, encephalitis, brain injury, salisylate poisoning) Gram-negative bacteremia Rapid, deep respirations Paresthesias Light-headedness Twitching Anxiety Fear Hyperventilation from anxiety, pain or improper ventilator settings; sepsis. Have a carbonic acid deficit Hyperventilation from hypoxia, PE, fear pain, exercise, fever Stimulated respiratory center caused by septicemia, encephalitis, brain injury, ASA poisoning Treat: adjust vent settings, treat sepsis or anxiety 4/27/2017
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Acid-Base Disorders ABG Disorder Possible Causes Signs and Symptoms
Metabolic Acidosis HCO3- depletion from diarrhea Excessive production of organic acids Inadequate excretions of acids from renal disease DKA, Lactic acidosis Shock, GI fistulas Rapid, deep breathing Fruity breath Fatigue Headache Lethargy Nausea Vomiting Coma Have a base bicarbonate deficit. Occurs when an acid other than carbonic acid accumilates in the body, or when bicarbonate is lost by body fluids Excessive production of organic acids from hepatic disease, endocrine disorders, shock or drug intoxication DKA, Lactic adic, starvation, severe diarrhea, renal tubular disease, renal failure GI fistulas shock 4/27/2017
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Acid-Base Disorders ABG Disorder Possible Causes Signs and Symptoms
Metabolic Alkalosis Loss of hydorchloric acid from vomiting or NG suctioning Loss of hydrogen ions due to increased renal excretion from diuretic therapy Excessive alkali ingestion Slow, shallow respirations Muscle twitching Hypertonic muscles Restlessness Tetany (convulsion) Coma Base bicarbonate excess. Occurs when a loss of acid (prlonged vomiting or gastric suction), or a gain in bicarbonate (ingestion of baking soda) Severe vomiting, Excess if gastric suctioning Diuretic therapy, potassium deficit, Excess intake NAHCO3, excessive mineralcorticoids 4/27/2017
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ABG Case Studies Exercises 4/27/2017
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A patient was admitted to the ICU after suffering a stroke
A patient was admitted to the ICU after suffering a stroke. The third day, the patient is more lethargic than the day before. His lung sounds are diminished in the lower lobes. ABGs are drawn and the following results were obtained. pH 7.33 PaCO2 55 HCO3 29 PaO2 60 Partially compensated respiratory acidosis. Caused by alveolar hypoventilation so paCO2 increased. Treatment is TCDB, chest physiotherapy, aerosol therapy or nasotracheal suctioning. 4/27/2017
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What is the ABG result for the CVA patient?
Comp. resp. acidosis with mild hypoxemia Part. Comp. resp. acidosis with mild hypoxemia Part. Comp. metabolic acidosis with mod. hypoxemia Comp. metabolic alkalosis with mod. hypoxemia Partially compensated respiratory acidosis. 4/27/2017
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A postop cholecystectomy patient is hyperventilating due to anxiety and pain. She complains of tingling and numbness in her fingers. Her ABG values are as follows: pH 7.55 PaCO2 28 HCO3 24 PaO2 90 Uncompensated respiratory alkalosis. Caused by alveolar hyperventilation which decreases paC02. Treatment is administer pain medication and have patient breathe regularly and deeply. 4/27/2017
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What is the ABG result for the S/P cholecystectomy patient?
Comp. resp. alkalosis with normal oxygenation Part. comp. resp. alkalosis with mild hypoxemia Uncomp. Resp. alkalosis with normal oxygenation Comp. metabolic alkalosis with mild hypoxemia 4/27/2017
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A patient has acute tubular necrosis, brought on by cardiopulmonary arrest. His ABG results are as follows: pH 7.32 PaCO2 34 HCO3 17 PaO2 95 Partially compensated metabolic acidosis. Caused by the fact the kidneys can’t synthesize ammonia and ammonia is needed to excrete H+. Also HCO3 decreases because it’s used up to buffer the H+. Treatment is IV NaHCO3 and directic therapy. 4/27/2017
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What is the ABG result for the ATN patient?
Comp. resp. acidosis with normal oxygenation Comp. metabolic alkalosis with normal oxygenation Uncomp. metabolic acidosis with mild hypoxemia Part. comp. metabolic acidosis with normal oxygenation 4/27/2017
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A patient has a history of pancreatitis
A patient has a history of pancreatitis. He has been vomiting for several days PTA. He presently has a NGT to suction. His ABG values are as follows: pH 7.52 PaCO2 49 HCO3 40 PaO2 93 Uncompensated metabolic alkaosis. Volume depletion from vomiting or NGT suctioning causes loss of H+, Cl- and K+. Treatment is NaCl and KCl replacement. 4/27/2017
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What is the ABG result for the patient with pancreatitis?
Part. comp. metabolic alkalosis with normal oxygenation Comp. metabolic acidosis with normal oxygenation Comp. respiratory alkalosis with normal oxygenation Part. comp. resp. alkalosis with normal oxygenation 4/27/2017
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A patient has a history of smoking three packs of cigarettes for 40 years and has a history of COPD. His ABG’s are as follows: pH 7.35 PaCO2 70 HCO3 30 PaO2 55 4/27/2017
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What is the ABG result for the COPD patient?
Part. comp. resp. acidosis, mod. hypoxemia Comp. metabolic alkalosis, mod. hypoxemia Comp. resp. acidosis, mod. hypoxemia Part. comp. metabolic acidosis, mod. hypoxemia 4/27/2017
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Thank you. 4/27/2017
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