Arterial Blood Gas Analysis

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     1  Arterial Blood Gas Analysis Vanessa Klee MSIV
     2  What is an ABG? The Components pH / PaCO2 / PaO2 / HCO3 / O2sat / BE Desired Ranges pH - 7.35 - 7.45 PaCO2 - 35-45 mmHg PaO2 - 80-100 mmHg HCO3 - 21-27 O2sat - 95-100% Base Excess - +/-2 mEq/L
     3  Why Order an ABG? Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management Improvement in acid/base management allows for optimal function of medications Acid/base status may alter electrolyte levels critical to patient status/care
     4  Logistics When to order an arterial line -- Need for continuous BP monitoring Need for multiple ABGs Where to place -- the options Radial Femoral Brachial Dorsalis Pedis Axillary
     5  Acid Base Balance The body produces acids daily 15,000 mmol CO2 50-100 mEq Nonvolatile acids The lungs and kidneys attempt to maintain balance
     6  Acid Base Balance Assessment of status via bicarbonate-carbon dioxide buffer system CO2 + H2O <--> H2CO3 <--> HCO3- + H+ ph = 6.10 + log ([HCO3] / [0.03 x PCO2])
     7  The Terms ACIDS Acidemia Acidosis Respiratory ?CO2 Metabolic ?HCO3 BASES Alkalemia Alkalosis Respiratory ?CO2 Metabolic ?HCO3
     8  Respiratory Acidosis ?ph, ?CO2, ?Ventilation Causes CNS depression Pleural disease COPD/ARDS Musculoskeletal disorders Compensation for metabolic alkalosis
     9  Respiratory Acidosis Acute vs Chronic Acute - little kidney involvement. Buffering via titration via Hb for example pH ?by 0.08 for 10mmHg ? in CO2 Chronic - Renal compensation via synthesis and retention of HCO3 (?Cl to balance charges ? hypochloremia) pH ?by 0.03 for 10mmHg ?in CO2
     10  Respiratory Alkalosis ?pH, ?CO2, ?Ventilation ? CO2 ? ? HCO3 (?Cl to balance charges ? hyperchloremia) Causes Intracerebral hemorrhage Salicylate and Progesterone drug usage Anxiety ? ?lung compliance Cirrhosis of the liver Sepsis
     11  Respiratory Alkalosis Acute vs. Chronic Acute - ?HCO3 by 2 mEq/L for every 10mmHg ? in PCO2 Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg ? in PCO2 Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH
     12  Metabolic Acidosis ?pH, ?HCO3 12-24 hours for complete activation of respiratory compensation ?PCO2 by 1.2mmHg for every 1 mEq/L ?HCO3 The degree of compensation is assessed via the Winter’s Formula ? PCO2 = 1.5(HCO3) +8 ? 2
     13  The Causes Metabolic Gap Acidosis M - Methanol U - Uremia D - DKA P - Paraldehyde I - INH L - Lactic Acidosis E - Ehylene Glycol S - Salicylate Non Gap Metabolic Acidosis Hyperalimentation Acetazolamide RTA (Calculate urine anion gap) Diarrhea Pancreatic Fistula
     14  Metabolic Alkalosis ?pH, ?HCO3 ?PCO2 by 0.7 for every 1mEq/L ? in HCO3 Causes Vomiting Diuretics Chronic diarrhea Hypokalemia Renal Failure
     15  Mixed Acid-Base Disorders Patients may have two or more acid-base disorders at one time Delta Gap Delta HCO3 = HCO3 + Change in anion gap >24 = metabolic alkalosis
     16  The Steps Start with the pH Note the PCO2 Calculate anion gap Determine compensation
     17  Sample Problem #1 An ill-appearing alcoholic male presents with nausea and vomiting. ABG - 7.4 / 41 / 85 / 22 Na- 137 / K- 3.8 / Cl- 90 / HCO3- 22
     18  Sample Problem #1 Anion Gap = 137 - (90 + 22) = 25 ? anion gap metabolic acidosis Winters Formula = 1.5(22) + 8 ? 2 = 39 ? 2 ? compensated Delta Gap = 25 - 10 = 15 15 + 22 = 37 ? metabolic alkalosis
     19  Sample Problem #2 22 year old female presents for attempted overdose. She has taken an unknown amount of Midol containing aspirin, cinnamedrine, and caffeine. On exam she is experiencing respiratory distress.
     20  Sample Problem #2 ABG - 7.47 / 19 / 123 / 14 Na- 145 / K- 3.6 / Cl- 109 / HCO3- 17 ASA level - 38.2 mg/dL
     21  Sample Problem #2 Anion Gap = 145 - (109 + 17) = 19 ? anion gap metabolic acidosis Winters Formula = 1.5 (17) + 8 ? 2 = 34 ? 2 ? uncompensated Delta Gap = 19 - 10 = 9 9 + 17 = 26 ? no metabolic alkalosis
     22  Sample Problem #3 47 year old male experienced crush injury at construction site. ABG - 7.3 / 32 / 96 / 15 Na- 135 / K-5 / Cl- 98 / HCO3- 15 / BUN- 38 / Cr- 1.7 CK- 42, 346
     23  Sample Problem #3 Anion Gap = 135 - (98 + 15) = 22 ? anion gap metabolic acidosis Winters Formula = 1.5 (15) + 8 ? 2