Arterial Blood Gas Analysis Overview. What is an ABG? The Components –pH / PaCO 2 / PaO 2 / HCO 3...
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Transcript of Arterial Blood Gas Analysis Overview. What is an ABG? The Components –pH / PaCO 2 / PaO 2 / HCO 3...
Arterial Blood Gas Analysis
Overview
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
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
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
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
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])
The Terms
• ACIDS– Acidemia– Acidosis
• Respiratory CO2
• Metabolic HCO3
• BASES– Alkalemia– Alkalosis
• Respiratory CO2
• Metabolic HCO3
Respiratory Acidosis
• ph, CO2, Ventilation
• Causes– CNS depression– Pleural disease– COPD/ARDS– Musculoskeletal disorders– Compensation for metabolic alkalosis
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
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
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
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
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
Metabolic Alkalosis
• pH, HCO3
• PCO2 by 0.7 for every 1mEq/L in HCO3
• Causes– Vomiting– Diuretics– Chronic diarrhea– Hypokalemia– Renal Failure
Mixed Acid-Base Disorders
• Patients may have two or more acid-base disorders at one time
• Delta GapDelta HCO3 = HCO3 + Change in anion gap
>24 = metabolic alkalosis
The Steps
• Start with the pH
• Note the PCO2
• Calculate anion gap• Determine compensation
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
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 = 1515 + 22 = 37
metabolic alkalosis
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.
Sample Problem #2
• ABG - 7.47 / 19 / 123 / 14• Na- 145 / K- 3.6 / Cl- 109 / HCO3- 17
• ASA level - 38.2 mg/dL
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
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
Sample Problem #3
• Anion Gap = 135 - (98 + 15) = 22 anion gap metabolic acidosis
• Winters Formula = 1.5 (15) + 8 2= 30 2
compensated• Delta Gap = 22 - 10 = 12
12 + 15 = 27 mild metabolic alkalosis
Sample Problem #4
• 1 month old male presents with projectile emesis x 2 days.
• ABG - 7.49 / 40 / 98 / 30• Na- 140 / K- 2.9 / Cl- 92 / HCO3- 32
Sample Problem #4
• Metabolic Alkalosis, hypochloremic• Winters Formula = 1.5 (30) + 8 2
= 53 2 uncompensated