ABG Interpretation PDF

outlines Purpose of arterial blood gas Components of arterial blood gas Components of buffering systems Steps of ABG interpretation  Arterial Blood Gas Interpretation The ability to rapidly interpret ABG results is an essential critical care skill. ABG results reflect of oxygenat...

outlines Purpose of arterial blood gas Components of arterial blood gas Components of buffering systems Steps of ABG interpretation  Arterial Blood Gas Interpretation The ability to rapidly interpret ABG results is an essential critical care skill. ABG results reflect of oxygenation, adequacy of gas exchange in the lungs, and acid- base status.  1- Oxygenation: PaO2 is the partial pressure of oxygen dissolved in arterial blood. The normal PaO2 is 80 to 100 mmHg at sea level. The PaO2 decreases in the elderly; the value for individuals 60 to 80 years of age usually ranges from 60 to 80 mmHg.  1- Oxygenation: SaO2 refers to the amount of oxygen bound to hemoglobin. The normal saturation of hemoglobin ranges from 99 to 100 %. The SaO2 is very important because most oxygen supplied to the tissues is transported via hemoglobin  1-Oxygenation: Both the PaO2 and the SaO2 are used to assess oxygenation. Decreased oxygenation of arterial blood (PaO2 < 80 mm Hg) is referred to as hypoxemia. A patient with a PaO2 of less than 60 mmHg requires immediate intervention, unless the patient has COPD and has adapted to lower oxygen levels.. 2-Ventilation/Acid Base Status: Blood gas values that reflect ventilation and acid-base include: pH PaCO2 HCO3  2-Ventilation/Acid Base Status: PH is the concentration of hydrogen ions (H+) in the blood. The normal range for pH is 7.35 to 7.45. A pH of less than 7.35 indicates the presence of acidemia A pH of greater than 7.45 indicates presence of alkalemia. 2-Ventilation/Acid Base Status: PaCO2 is the partial pressure of carbon dioxide dissolved in arterial plasma. The normal range of PaCO2 is 35 to 45 mm Hg. The PaCO2 is regulated in the lungs. A PaCO2 of greater than 45 mm Hg indicates respiratory acidosis or hypoventilates means carbon dioxide is retained A PaCO2 of less than 35 mm Hg indicates respiratory alkalosis or hyperventilation, excess carbon dioxide is excreted by the lung. 2-Ventilation/Acid Base Status: HCO3 is the concentration of sodium bicarbonate in the blood. The normal HCO3 level is 22 to 26 mEq/L. HCO3 is regulated by the kidneys. An HCO3 level of greater than 26 mEq/L indicates metabolic alkalosis, An HCO3 level of less than 22 mEq/L indicates metabolic acidosis.  Buffer System : The body regulates acid-base balance through the buffer system. The buffer system can be described as a mechanism for the neutralization of acids.  Buffer systems Buffer systems prevent major changes in the pH of body fluids by removing or releasing H+; they can act quickly to prevent excessive changes in H+ concentration  Buffer systems Three buffer systems exist for maintaining acid-base status are in the: blood respiratory system renal system The blood buffer system is activated as the H+ concentration changes. As H+ level increases, the pH falls, resulting in acidosis. Bicarbonate (HCO3) then combines with H+ to form carbonic acid (H2CO3). Carbonic acid then breaks down into carbon dioxide (which is excreted through the lungs) and water (H2O).  The respiratory buffer system works rapidly to return the pH to normal. The lungs react to correct imbalance by altering the rate and depth of respiration The respiratory system buffer system begins to work immediately after an acid-base alteration is noted.  The respiratory buffer system Metabolic acidosis: the respiratory rate increases, causing greater elimination of CO2 from the lungs (to reduce the acid load). Metabolic alkalosis: the respiratory rate decreases, causing CO2 to be retained( to increase the acid load)  The renal buffer system works by excreting excess H+ and retaining bicarbonate. The renal buffer system activates more slowly and may take up to 2 days to regulate acid-base balance.  The renal buffer system Respiratory acidosis: kidneys excrete hydrogen ions and retention bicarbonate ions to help restore balance Respiratory alkalosis: the kidneys retain hydrogen ions and excrete bicarbonate ions to help restore balance Steps in Arterial Blood Gas Interpretation Arterial blood gas results should be interpreted systematically. The oxygenation is evaluated first. Second, the acid-base status is determined. Third, the primary imbalance is identified. Last, compensation is identified.  Step 1: Evaluate Oxygenation Oxygenation is analyzed by evaluation of the PaO2 and the SaO2. If the PaO2 is less than the expected normal range, hypoxemia exists. paO2 > 80 Normal paO2