Clinical Chem 2 Blood-GAS PDF

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BLOOD GASESCLINICAL CHEMISTRY BLOOD GAS ANALYSIS Measurement of the amount of oxygen and carbon dioxide in the body It also involves the measurement of blood pH Also known as ABG or Arterial Blood Gas test Specimen of choice : Arterial Blood Provides information on how well lungs or kidneys are func...

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BLOOD GASES CLI NI CALCHEMI STRY

BLOOD GAS ANALYSIS • Measurement of the amount of oxygen and carbon dioxide in the body • It also involves the measurement of blood pH • Also known as ABG or Arterial Blood Gas test • Specimen of choice : Arterial Blood • Provides information on how well lungs or kidneys are functioning • Samples must be tested within 10 minutes after collection of small amount of blood. TERMINOLOGY Buffer

pH Hydronium ion

Hydroxyl ion

Base Excess

pCO2

Bicarbonate

pO2

• The combination of a weak acid and weak base and it’s salt. • System that resists changes in pH • A buffer of carbonic acid (H2CO3) and bicarbonate (HCO3−) is present in blood plasma, to maintain a pH between 7.35 and 7.45. • is a measure of the acidity or basicity of an aqueous solution • is the cation that forms from water in the presence of hydrogen ions. • Its excess proton being readily available for reaction with basic species. • Also known as hydroxonium • H2CO3 + H20 ----- H+ + H20+ HC03• is an anion of hydrogen that contains oxygen and one hydrogen atom with a shared electron. • The neutral form of this ion is called a hydroxyl radical. • The anion form, (OH−), is called the hydroxide anion; • it bears a single negative charge largely residing on the more electronegative oxygen. • HC03- + H20 -------- OH- + H2C03 • indicates the amount of excess or insufficient level of bicarbonate in the system. • A negative base excess indicates a base deficit in the blood and is equivalent to an acid excess. • A value outside of the normal range (-2 to +2 mEq) suggests a metabolic cause for the abnormality. • The base excess is defined as the amount of H+ ions that would be required to return the pH of the blood to 7.35. • Base excess = 0.93 (HCO3 - 24.4 + 14.8(pH - 7.4) • Partial pressure or tension of CO2 in blood. • Pressure or tension exerted by CO2 gas dissolved in arterial blood. • Index of efficiency of gas exchange in lungs. • CO2 is called a “volatile acid” because it can combine reversibly with H2O to yield a strongly acidic H+ ion and a weak basic bicarbonate ion (HCO3 -) according to the following equation: • CO2 + H2O H+ + HCO3 Normal Value: Arterial = 35 – 45 mmHg Venous = 35 – 50 mmHg Respiratory acidosis: > 45 mmHg Respiratory alkalosis:...