Acid_Base Chemistry Acids E.g carbonic acid (H 2 CO 3 ) *Most Common Bases E.g bicarbonate (HCO3-) *Most Common Buffers
Body Fluid Chemistry Arterial Blood pH = 7.35-7.45 ECF 1 molecule of carbonic acid to 20 free bicarbonate ions (1:20) Carbonic Anhydrase Equation CO 2 + H 2 0 H 2 CO 3 H + + HCO3 -
Body Fluid Chemistry CO 2 + H 2 0 H 2 CO 3 H + + HCO3 - CO2 = H+, therefore pH (more acidic) CO2 = H+, therefore pH (more basic) HCO3- = H+, therefore pH (more basic)
Body Fluid Chemistry Sources of Acids Glucose Metabolism Fat & Protein Metabolism Anaerobic Metabolism of Glucose & Fat
Body Fluid Chemistry Sources of Bicarbonate Ions Breakdown of carbonic acid Intestinal absorption of ingested HCO 3 - Pancreatic production Movement of intracellular HCO 3 - into ECF Kidney reabsorption
Regulatory Mechanisms Buffers (1 st line of defense) Chemical (HCO3-) Proteins (Hemoglobin) Respiratory (2 nd ) Hyperventilation Hypoventilation Renal (3 rd )
Age-Related Changes Older Adults Reduced effective gas exchange Decreased kidney function Medications Diuretics & Digoxin (Often taken by older adults) Both drugs increase kidney excretion of H+ ions, which can result in an increased blood pH.
Assessment Kidney function Hydration Status I/O Laboratory data Renal function blood studies Blood Urea Nitrogen (8-20mg/dL) Creatinine (0.5-1.5mg/dL) Arterial Blood Gases (ABG’s}
Acid-Base Imbalances Acidosis (pH<7.35) Respiratory Acidosis Increase CO 2 causes an increase in H+ I.e., Respiratory depression, Inadequate chest expansion, Airway obstruction. Metabolic Acidosis Overproduction of H+ Breakdown of fatty acids Lactic acid build up Under elimination of H+ (Renal failure) Underproduction of HCO3- (Renal Failure) Over elimination of HCO3- (Diarrhea)
Assessment Key Features Neuromuscular: Lethargy, confusion, skeletal muscle weakness Cardiovascular: Early acidosis: Increased HR & CO Late acidosis: Hypotension, thready pulse Respiratory: Nonvoluntary deep, and rapid respirations (Kussmaul)
Acid-Base Imbalances Alkalosis (pH>7.45) Respiratory Alkalosis Decrease CO 2 Hyperventilation Metabolic Alkalosis Increases in Bases Antacids, TPN Decreases in Acids Caused by disease or medical treatments Also prolonged vomiting
Assessment Key Features Neuromuscular: Dizziness, agitation, confusion, hyperreflexia, skeletal muscle weakness Cardiovascular: Increases myocardial irritability, HR, thready pulse Respiratory: Hyperventilation Will cause respiratory alkalosis
Putting It All Together Step one: Label the pH Step two: Find the cause of the acid base imbalance. Determine respiratory component. Determine metabolic component. Step Three: Assess for compensation. Step Four: Check the PaO2 (oxygenation) If low < 80 indicates an interference with ventilation process (evaluate the patient), supply supplemental oxygen if needed. If normal 80 – 100 indicates patient is getting enough oxygen. If PaO2 is > 100, is possible getting too much supplemental oxygen.
Case Studies Mary, 54 years old suffered an acute anterior wall myocardial infarction and is now in cardiogenic shock. ABG shows a pH of 7.27, PaCO2 38 and HCO3 14. What is her acid – base status?
Case Studies 85 year old Arthur has chronic obstructive pulmonary disease (COPD). He is currently hospitalized with an upper respiratory infection. His ABGs show a pH of 7.30, PaCO2 - 60 and HCO3 - 26. Describe his acid-base status.
Case Studies Joan a 45-year-old female sustained major trauma in an automobile accident. She has a NG tube in place that has drained 1,500 ml in the last 24 hours. ABGs show a pH of 7.53, PaCO2 42 and HCO3 34. Describe her acid- base status.
Case Studies 28-year-old woman has been admitted to your unit for a breast biopsy. While you’re explaining the procedure to her, she becomes noticeably anxious and says she feels dizzy. You note that her respirations have increased to 45 / minute. The doctor orders ABGs. After reviewing the results, pH 7.51, PaCO2 29, PO2 80, HCO3 24. What is her acid-base status?
Introduction to Compensation If compensation has occurred, the value will move in the same direction as the other components. For example, if the problem is too much base (HCO3 > 26) holding on to acid (PaCO2 > 45) will help bring the pH closer to normal.
Now Try These pH 7.46, PaCO2 47mmHg, HCO3- 34mEq/L Determine Acid-Base Imbalance Compensated or Uncompensated? pH 7.21, PaCO2 98mmHg, HCO3- 40mEq/L Determine Acid-Base Imbalance Compensated or Uncompensated?