What is an ABG?

 Arterial Blood Gas is a lab that shows us the status of a patient’s chemical balance  In general lab with be drawn from an artery by a RT not a nurse  However nurses are responsible for the analysis of the lab and the reaction to the analysis

Main Components of ABG

 pH-Measures hydrogen ion (H+) concentration  PCO2-Partial pressure of CO2 in arteries  HCO3-Measures serum bicarbonate

Normal Values of ABG

 pH-7.35-7.45

 PCO2-35-45mmHg  HCO3-22-26 mEq/l

Abnormal ABG Readings

 The body will work hard to balance any abnormal values within the acid-base system  How the body works to do this depends on the issue:  CO2 is controlled by the lungs  HCO3 is controlled by the kidneys

Compensated Vs Uncompensated

 If the body can work to balance the issue through the lungs or kidneys it will result in a normal pH  Other values in the ABG will be ABNL however do not matter since there not an overall effect on the pH  This is a compensated ABG  Allow the body to continue the balance and monitor patient closely

Step 1

 Look at the pH-if abnormal you have an uncompensated disturbance  Now figure out if the disturbance is acidosis or alkalosis-this will determine the treatment  Acidosis is pH below7.35 and results from adding H+ an acid  Alkalosis is pH above 7.45 and results from decrease in H+ an acid

Step 2

 When in ROME…  Respiratory Opposite-the HCO3 is normal and the arrows for the pH and PCO2 point in opposite directions  Metabolic Equal-the PCO2 is normal and the arrows for pH and HCO3 point in the same direction

Step 3

 Put all your findings together to determine the overall imbalance  Example: pH 7.29 PCO2 50 HCO3 26  What is this patient’s condition?

 pH 7.29  PCO2 50  HCO3 26  Respiratory acidosis

Answer

More Practice

 pH 7.50, PCO2 30, HCO3 26  pH 7.30, PCO2 42, HCO3 20  pH 7.48, PCO2 42, HCO3 32  pH 7.29, PCO2 55, HCO3 26

Primary Cause of Imbalances

 Respiratory acidosis-hypoventilation  Metabolic acidosis-addition of large amounts of fixed acids to body fluids-Ketoacidosis with diabetes  Respiratory alkalosis-hypoventilation  Metabolic alkalosis-retention of base or loss of acid through body fluids

Other Important Values on ABG

 PaO2-The partial pressure of oxygen that is dissolved in arterial blood.

 The normal range is 80 to 100 mm Hg.

 SaO2-The arterial oxygen saturation.

 The normal range is 95% to 100%.

Oxyhemoglobin Dissociation Curve

Refers to the relationship between oxygen and hemoglobin Normal-oxygen has affinity for hemoglobin until it reaches tissues in need of oxygen Once it reaches the tissues the oxygen releases itself from the hemoglobin and becomes available for use (all of this is good)

Changes in Oxyhemoglobin Dissociation Curve

 Certain conditions in the body can change the relationship between oxygen and hemoglobin  This change can lead to oxygen leaving hemoglobin before reaching tissues in need (shift to right)  Or cause the oxygen and hemoglobin to bond so tightly it cannot be released in tissues (shift to left)  Shift to left is worse for the patient-beware SPO2 will be normal however patient will be hypoxic

Causes for Shifts

 Shift to the right: acidosis, fever, elevated CO2 levels, and increased 2,3-diphosphoglycerate (2,3-DPG, a by product of glucose metabolism)  Shift to the left: hypothermia, alkalosis, low PCO2, and decrease in 2,3-DPG