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LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS. dr. Husnil Kadri, M.Kes Biochemistry Departement Medical Faculty Of Andalas University Padang. Arterial Blood Gases . Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management

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LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS

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Laboratorium interpretation of acid base electrolites disorders
LABORATORIUM INTERPRETATION OF ACID-BASE & ELECTROLITES DISORDERS

dr. Husnil Kadri, M.Kes

Biochemistry Departement

Medical Faculty Of Andalas University

Padang


Arterial blood gases
Arterial Blood Gases

  • 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 – (with antikoagulant)

    • A. Radial

    • A. Femoral

    • A. Brachial

    • A. DorsalisPedis

    • A. Axillary


The components
The Components

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


Arterial blood gases1
Arterial Blood Gases

  • Reflect oxygenation, gas exchange, and acid-base balance

  • PaO2 is the partial pressure of oxygen dissolved in arterial blood

  • SaO2 is the amount of oxygen bound to hemoglobin


Base excess
Base Excess

Definition: The amount of a strong acid (like HCl) needed to bring blood to 7.40.

  • Assumes 100% oxygenation, 37oC, and pCO2 of 40.

Normal = 0

Used to calculate the metabolic component of an acid-base disturbance.


Base excess calculations
Base Excess calculations

Calculated the same way, in practice, as SID:

Buffer Base (SID) = HCO3- + A-

HCO3 calculated by pH & pCO2 (blood gas machine)

A- calculated using pH & hemoglobin (whole blood)

OR A- calculated using albumin & phos (plasma)

BE = Buffer Base – “expected buffer base”

(expected if pH = 7.4 and pCO2 = 40)



Is it respiratory or metabolic

Respiratory Acidosis

Respiratory Alkalosis

Metabolic Acidosis

Metabolic Alkalosis

Increased pCO2 >50

Decreased pCO2<30

Decreased HCO3 <18

Increased HCO3 >30

Is it Respiratory or Metabolic?


Compensated or uncompensated what does this mean
Compensated or Uncompensated—what does this mean?

  • Evaluate pH—is it normal? Yes

  • Next evaluate pCO2 & HCO3

    • pH normal + increased pCO2 + increased HCO3 = compensated respiratory acidosis

    • pH normal + decreased HCO3 + decreased pCO2 = compensated metabolic acidosis


Compensated vs uncompensated
Compensated vs. Uncompensated

  • Is pH normal? No

  • Acidotic vs. Alkalotic

  • Respiratory vs. Metabolic

    • pH<7.30 + pCO2>50 + normal HCO3 = uncompensated respiratory acidosis

    • pH<7.30 + HCO3<18 + normal pCO2 = uncompensated metabolic acidosis

    • pH>7.50 + pCO2<30 + normal HCO3 = uncompensated respiratory alkalosis

    • pH>7.50 + HCO3>30 + normal pCO2 = uncompensated metabolic alkalosis


Causes of acidosis

Respiratory

Hypoventilation

Impaired gas exchange

Metabolic

Ketoacidosis

Diabetes

Renal Tubular Acidosis

Renal Failure

Lactic Acidosis

Decreased perfusion

Severe hypoxemia

Causes of Acidosis


Causes of alkalosis

Respiratory

Hyperventilation due to:

Hypoxemia

Metabolic acidosis

Neurologic

Lesions

Trauma

Infection

Metabolic

Hypokalemia

Gastric suction or vomiting

Hypochloremia

Causes of Alkalosis


Mixed metabolic acidosis and chronic respiratory alkalosis
Mixed Metabolic Acidosis and Chronic Respiratory Alkalosis

Examples:

  • Sepsis

  • Addition of respiratory alkalosis to metabolic acidosis further decreases HCO3- but pH may remain normal

  • Lactic acidosis plus respiratory alkalosis due to severe liver disease, pulmonary emboli, or sepsis


Mixed metabolic alkalosis and chronic respiratory acidosis
Mixed Metabolic Alkalosis and Chronic Respiratory Acidosis

Examples:

  • Patient with COPD receiving glucocorticoids or diuretics

  • pCO2 and HCO3- are increased by both conditions, but pH is neutralized


Mixed alkalosis severe
Mixed Alkalosis, Severe

Example:

  • Postoperative patient with severe hemorrhage stimulating hyperventilation [respiratory alkalosis] plus massive transfusion and nasogastric drainage [metabolic alkalosis]


Mixed chronic respiratory acidosis and acute metabolic acidosis
Mixed Chronic Respiratory Acidosis and Acute Metabolic Acidosis

Examples:

  • COPD [chronic respiratory acidosis] with severe diarrhoea [metabolic acidosis]. pH is too low for pCO2 of 55 mmHg in chronic respiratory acidosis, indicating low pH due to mixed acidosis, but HCO3- effect is offset


Mixed metabolic acidosis and metabolic alkalosis
Mixed Metabolic Acidosis and Metabolic Alkalosis Acidosis

Examples:

  • Gastroenteritis with vomiting [metabolic alkalosis] and diarrhoea [metabolic acidosis due to loss of HCO3-]; surprisingly normal findings with marked volume depletion




Summary of pure and mixed acid base disorders
Summary of Pure and Mixed Acid-Base Disorders Acidosis

Source: Adapted from Friedman HH. Problem-oriented medical diagnosis, 3rd ed. Boston: Little, Brown. 1983


References
References Acidosis

  • Anisman, S. Base Excess & Strong Ion Theories. ppt. 2003.

  • Klee, V. Arterial Blood Gas Analysis.ppt. 2012.

  • Perkins, J. ABG Interpretation. ppt. 2012.

  • Rashid, FA. Respiratory Mechanisms in Acid-Base Homeostasis.ppt. 2005.


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