Introduction to Acid-Base Balance

N132

Acid_Base Chemistry

Acids

E.g carbonic acid (H2CO3) *Most Common

Bases

E.g bicarbonate (HCO3-) *Most Common

Buffers

Body Fluid Chemistry

Arterial Blood pH = 7.35-7.45

ECF1 molecule of carbonic acid to 20 free bicarbonate ions (1:20)

Carbonic Anhydrase Equation

CO2 + H20 H2CO3 H+ + HCO3-

Body Fluid Chemistry

COCO22 + H + H220 0 H H22COCO33 H H++ + HCO3 + 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 HCO3- Pancreatic production Movement of intracellular HCO3- into

ECF Kidney reabsorption

Regulatory Mechanisms

Buffers (1st line of defense) Chemical (HCO3-) Proteins (Hemoglobin)

Respiratory (2nd) Hyperventilation Hypoventilation

Renal (3rd)

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 dataRenal function blood studies

Blood Urea Nitrogen (8-20mg/dL) Creatinine (0.5-1.5mg/dL)

Arterial Blood Gases (ABG’s}

Allen’s Test

 

                                             

Assessment

COCO22 + H + H220 0 H H22COCO33 H H++ + HCO3 + HCO3--

pH = 7.35-7.45 (arterial) PCO2 = 35-45 mmHg HCO3- = 22-26 mEq/L PO2 = 80-100mmHg

                                             

Acid-Base Imbalances

Acidosis (pH<7.35) Respiratory Acidosis

Increase CO2 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 & COLate acidosis: Hypotension, thready pulse

Respiratory:Nonvoluntary deep, and rapid respirations (Kussmaul)

Acid-Base Imbalances

Alkalosis (pH>7.45) Respiratory Alkalosis

Decrease CO2 Hyperventilation

Metabolic Alkalosis Increases in Bases

Antacids, TPNDecreases 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?