3. What is an ABG Arterial Blood Gas Drawn from artery- radial, brachial, femoral It is an invasive procedure. Caution must be taken with patient on anticoagulants. Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.
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6. Normal Arterial Blood Gas Values* PH 7.35-7.45 35-45 mm Hg PaCO 2 70-100 m Hg PaO 2 SaO 2 95-100% 22-26 mEq/L - HCO3- % MetHb <2.0% <3.0% %COHb 16-22 ml O 2 /dl CaO 2 * At sea level, breathing ambient air ** Age-dependent
7. COMPONENTS OF THE ABG pH : Measurement of acidity or alkalinity, based on the hydrogen (H+) 7.35 – 7.45 Pao 2 The partial pressure oxygen that is dissolved in arterial blood. 80-100 mm Hg. PCO 2 : The amount of carbon dioxide dissolved in arterial blood. 35– 45 mmHg HCO 3 : The calculated value of the amount of bicarbonate in the blood 22 – 26 mmol/L B.E: The base excess indicates the amount of excess or insufficient level of bicarbonate. -2 to +2mEq/L (A negative base excess indicates a base deficit in blood) SaO 2 : The arterial oxygen saturation. >95%
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18. Acceptable PaO2 Values on Room Air 60 yrs 80 mm Hg 1mm Hg/yr Age Group Accepable PaO2 (mm Hg) Adults upto 60 yrs & Children > 80 Newborn 40-70 70 yrs > 70 80 yrs > 60 90 yrs > 50
46. FULLY COMPENSATED pH paco2 Hco3 Resp.Acidosis Normal but <7.40 Resp.Alkalosis Normal but >7.40 Met. Acidosis Normal but <7.40 Met. Alkalosis Normal but >7.40
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52. PH 2,3DPG temperature CO 2 ODC to right deviation Oxygenated hemoglobin release oxygen to tissue, prevent hypoxia of the tissue. But absorbed oxygen of hemoglobin is decreased from the alveoli. Bohr effect : movement of ODC place is induced by PH.
54. Oxygen dissociation curve: SaO 2 vs. PaO 2 Also shown are CaO 2 vs. PaO 2 for two different hemoglobin contents: 15 gm% and 10 gm%. CaO 2 units are ml O 2 /dl. P 50 is the PaO 2 at which SaO 2 is 50%.
141. ELECTROLYTE SHIFTS Acidosis Compensatory Response Result - H + buffered intracellularly - Hyperkalemia Alkalosis Compensatory Response Result - Tendency to correct alkalosis - Hypokalemia cell H + K + H + K + cell
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143. Arterial Blood Gases: Test Your Overall Understanding Case 1 - Discussion OXYGENATION : The PaO 2 and SaO 2 are both reduced on room air. Since P(A-a)O 2 is elevated (approximately 43 mm Hg), the low PaO 2 can be attributed to V-Q imbalance, i.e., a pulmonary problem. SaO 2 is reduced, in part from the low PaO 2 but mainly from elevated carboxyhemoglobin, which in turn can be attributed to cigarettes. The arterial oxygen content is adequate. VENTILATION : Adequate for the patient's level of CO 2 production; the patient is neither hyper- nor hypo-ventilating. ACID-BASE : Elevated pH and HCO 3 - suggest a state of metabolic alkalosis, most likely related to the patient's diuretic; his serum K + should be checked for hypokalemia.
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145. Arterial Blood Gases: Test Your Overall Understanding Case 2 - Discussion OXYGENATION: The PaO 2 is lower than expected for someone hyperventilating to this degree and receiving supplemental oxygen, and points to significant V-Q imbalance. The oxygen content is adequate. VENTILATION: PaCO 2 is half normal and indicates marked hyperventilation. ACID-BASE : Normal pH with very low bicarbonate and PaCO 2 indicates combined respiratory alkalosis and metabolic acidosis. If these changes are of sudden onset, the diagnosis of sepsis should be strongly considered, especially in someone with a documented infection .
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147. Arterial Blood Gases: Test Your Overall Understanding Case 3 - Discussion OXYGENATION: The patient's PaO 2 is reduced for two reasons - hypercapnia and V-Q imbalance - the latter apparent from an elevated P(A-a)O 2 (approximately 27 mm Hg). VENTILATION : The patient is hypoventilating . ACID-BASE : pH and PaCO 2 are suggestive of acute respiratory acidosis plus metabolic acidosis; the calculated HCO 3 - is lower than expected from acute respiratory acidosis alone.
