Download Introduction to Acid

Introduction to Acid-Base
Balance
N132
Acid_Base Chemistry
 Acids
E.g carbonic acid (H CO ) *Most Common
 Bases
E.g bicarbonate (HCO3-) *Most Common
 Buffers
2
3
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
CO2 + H20  H2CO3  H+ + HCO3-
Body Fluid Chemistry
CO2 + H20  H2CO3  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 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 data

Renal function blood studies
 Blood Urea Nitrogen (8-20mg/dL)
 Creatinine (0.5-1.5mg/dL)

Arterial Blood Gases (ABG’s}
Allen’s Test
Assessment
CO2 + H20  H2CO3  H+ + 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 & CO
 Late 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, TPN

Decreases in Acids
 Caused by disease or medical treatments
 Also prolonged vomiting
Assessment
 Key Features

Neuromuscular:


Cardiovascular:


Dizziness, agitation, confusion, hyperreflexia, skeletal
muscle weakness
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 acidbase 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?