Arterial blood gas analysis
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Arterial Blood Gas Analysis. Overview. What is an ABG?. The Components pH / PaCO 2 / PaO 2 / HCO 3 / O 2 sat / BE Desired Ranges pH - 7.35 - 7.45 PaCO 2 - 35-45 mmHg PaO 2 - 80-100 mmHg HCO 3 - 21-27 O 2 sat - 95-100% Base Excess - +/-2 mEq/L. Why Order an ABG?.

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What is an abg
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
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
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
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 balance1
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
The Terms

  • ACIDS

    • Acidemia

    • Acidosis

      • Respiratory

        CO2

      • Metabolic

        HCO3

  • BASES

    • Alkalemia

    • Alkalosis

      • Respiratory

        CO2

      • Metabolic

        HCO3


Respiratory acidosis
Respiratory Acidosis

  • ph, CO2, Ventilation

  • Causes

    • CNS depression

    • Pleural disease

    • COPD/ARDS

    • Musculoskeletal disorders

    • Compensation for metabolic alkalosis


Respiratory acidosis1
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
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 alkalosis1
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
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
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
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
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


The steps
The Steps

  • Start with the pH

  • Note the PCO2

  • Calculate anion gap

  • Determine compensation


Sample problem 1
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 11
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


Sample problem 2
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 21
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 22
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
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 31
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
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 41
Sample Problem #4

  • Metabolic Alkalosis, hypochloremic

  • Winters Formula = 1.5 (30) + 8  2

    = 53  2

     uncompensated


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