Introduction to Acid-Base Balance N132

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 =  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 ( mg/dL) Arterial Blood Gases (ABG’s}

Allen’s Test

Assessment CO 2 + H 2 0  H 2 CO 3  H + + HCO3 -  pH = (arterial)  PCO2 = mmHg  HCO3- = mEq/L  PO2 = mmHg

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, PaCO and HCO 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?