Acid - Base Balance

Question 1

Acid Base Balance

Answer 1

Acid-base balance is carefully regulated to maintain a normal pH via multiple mechanisms

Question 2

pH

Answer 2

• Inverse logarithm of the H+ concentration

- If the H+ are higher in number, the pH is low (acidic); if the H+ are lower in number, the pH is high (alkaline)

Question 3

pH (cont’d)

Answer 3

The pH scale ranges from 0 to 14: 0 is very acidic, 14 is very alkaline
Each number represents a factor of 10
- If a solution moves from a pH of 6 to 5, the H+ have increased 10 times

Question 4

pH (cont’d)

Answer 4

Acids are formed as end products as protein, carbohydrate, and fat metabolism
To maintain the body’s pH (7.35- 7.45) the H+ must be neutralized or excreted
The bones, lungs, and kidneys are the major organs involved in the regulation of the acid and base balance

Question 5

Buffering Systems

Answer 5

A buffer is a chemical that can bind excessive H+ or OH- without a significant change in pH
A buffering pair consists of a weak acid and its conjugate base
The most important plasma buffering systems are the carbonic acid - bicarbonate pair
- CO2 + H2O H2CO3 H + HCO3

Question 6

Carbonic Acid - Bicarbonate Pair

Answer 6

Operates in the lung and the kidney
The greater the partial pressure of carbon dioxide, the more carbonic acid is formed
- At a pH of 7.4 the ratio of bicarbonate to carbonic acid is 20:1
- Bicarbonate and carbonic acid can increase or decrease, but the ratio must be maintained

Question 7

Carbonic Acid - Bicarbonate Pair (cont’d)

Answer 7

If the amount of bicarbonate decreases, the pH decreases, causing a state of acidosis
The pH can be returned to normal if the amount of carbonic acid also decreases
- This type of pH adjustment is referred to as compensation

Question 8

Carbonic Acid - Bicarbonate Pair (cont’d)

Answer 8

The respiratory system compensates by increasing ventilation to expire carbon dioxide or by decreasing ventilation to retain carbon dioxide
The renal system compensates by producing acidic or alkaline urine

Question 9

Other Buffering Systems

Answer 9

Protein buffering (hemoglobin)
- Proteins have negative charges, so they can serve as buffers for H+
Renal buffering
- Secretion of H+ in the urine and reabsorption of HCO3-
Ion exchange (between ICF and ECF)
- Exchange of K+ for H+ in acidosis and alkalosis

Question 10

Acid- Base Imbalances

Answer 10

Normal arterial blood pH
- 7.35-7.45
- Obtained by ABG sampling
Acidosis
- Systemic increase in H+ concentration or decrease in bicarbonate
Alkalosis
- Systemic decrease in H+ concentration or increase in bicarbonate

Question 11

Bicarbonate

Answer 11

HCO3: anion electrolyte
Normal: 21-28 mmol/L
Regulated by the kidney
Combines with H+
Neutralizes (buffers) acidity
- 28 too much bicarb or note enough acid

Question 12

Carbonic Acid

Answer 12

A weak acid
The primary blood buffer
Neutralizes H+, maintains pH
Forms either H+ and HCO3, or H2O and CO3

Question 13

Carbon Dioxide

Answer 13

Normal 35-45 mm Hg
A gas exhaled by the lungs
Diffuse easily across the alveoli
Elimination directly related to ventilation
- 45 hypoventilation - retaining acid

Question 14

Acidosis and Alkalosis

Answer 14

Four categories of acid-base imbalances

• Respiratory acidosis: elevation of pCO2 as a result of ventilation depression
• Respiratory alkalosis: depression of pCO2 as a result of alveolar hyperventilation
• Metabolic acidosis: depression of HCO3- or an increase in non carbonic acids
• Metabolic alkalosis: elevation of HCO3- usually caused by an excessive loss of metabolic acids

Question 15

Acidosis and Alkalosis (cont’d)

Answer 15

Four categories of acid-base imbalances

• Metabolic acidosis: depression of HCO3- or an increase in non carbonic acids
• Metabolic alkalosis: elevation of HCO3- usually caused by an excessive loss of metabolic acids

Question 16

Anion Gap

Answer 16

Used cautiously to distinguish different types of metabolic acidosis
By rule, the concentration of anions (-) should equal the concentration of cations (+); not all normal anions are routinely measured

Question 17

Anion Gap (cont’d)

Answer 17

Normal anion gap:
Na+ + K+ = Cl- + HCO3 + 10 to 12 mEq/L (other miscellaneous anions [the ones we don’t measure]: phosphates, sulfates, organic acids, etc.)

Question 18

Respiratory System

Answer 18

Regulates carbonic acid by eliminating or retaining carbon dioxide
Increase in carbon dioxide or hydrogen ions stimulates the respiratory centre in the brain to increase rate and depth of respirations
- Eliminates carbon dioxide, carbonic acid levels falls, and pH levels become normal

Question 19

Respiratory System

Answer 19

Alkalosis depresses the respiratory centre

• Causes rate and depth of respirations to decrease
• Carbon dioxide is retained
• Retained carbon dioxide combines with water
• Carbonic acid levels fall, and pH levels become normal

Question 20

Renal System

Answer 20

Regulates bicarbonate levels in extracellular fluid to excrete or retain hydrogen ions
Excessive hydrogen ions causes pH levels to fall
- Kidneys excrete hydrogen ions and retain bicarbonate

Question 21

Renal System

Answer 21

Excessive bicarbonate levels cause the kidneys to retain hydrogen ions and excrete bicarbonate to restore acid-base balance

Question 22

Example:

Answer 22

The primary acid-base imbalance moves the pH away from normal limits

If pCO2 is increased, and pH is below normal … Respiratory acidosis

Question 23

Example:

Answer 23

The primary acid-base imbalance moves the pH away from normal limits

If HCO3 is increased, and pH is above normal … Metabolic alkalosis

Question 24

Example:

Answer 24

pH : 55 - acidosis
HCO3: 24 - normal

Respiratory Acidosis

Question 25

Example:

Answer 25

pH: 7.5 - alkalosis
pCO2: 42 - normal
HCO3: 31 - alkalosis

Metabolic Alkalosis

Question 26

Compensation

Answer 26

One mechanism moves the pH away from normal causing the primary imbalance

The compensatory mechanism attempts to correct the pH in the opposite direction

Question 27

Compensation

Answer 27

Both the pCO2 and HCO3 will be abnormal
If decreased HCO3 causes an acidosis, (decrease in pH)
Then a decreased pCO2 will compensate, attempting to create an alkalosis (increased pH)

Question 28

Partial Compensation (incomplete compensation)

Answer 28

pCO2 and HCO3 are abnormal
pCO2 moves pH in one direction
HCO3 moves the pH in the opposite direction
pH is outside of normal range

Question 29

Full Compensation (complete compensation)

Answer 29

pCO2 and HCO3 are abnormal
pCO2 moves pH in one direction
HCO3 moves the pH in the opposite direction
pH is within normal range

Question 30

Lab/ Diagnostic Studies: Acid-Base imbalances

Answer 30

ABG studies
Serum electrolytes
Serum creatinine and BUN
Electrocardiogram

Question 31

Metabolic Acidosis: Treatment

Answer 31

Medications
- Administer bicarbonate, lactate, acetate, or citrate solutions
Teach proper DM care to prevent ketoacidosis
Obtain treatment for alcoholism with proper diet and medications
Manage renal failure with diet and dialysis
Prevent or treat diarrhea

Question 32

Metabolic Alkalosis: Treatment

Answer 32

Medications
- Administer potassium chloride and sodium chloride solutions
- Administer dilute hydrochloric acid or ammonium chloride for critically high pH
Teach how to prevent and manage acute gastroenteritis or vomitting, the advantages of a potassium-rich diet or potassium supplements, and to avoid use of antacids

Question 33

Respiratory Acidosis: Treatment

Answer 33

Medications
- Administer bronchodilator medications
- Administer antibiotics
- Administer medications to reverse narcotic and anesthetic effects
Teach to avoid respiratory infections, to immunize against pneumococcal pneumonia and influenza, and to obtain treatment for narcotic or drug abuse

Question 34

Respiratory Alkalosis: Treatment

Answer 34

Medications
- Administer a sedative or antianxiety medication
Teach to decrease anxiety, to seek counselling, and to identify hyperventilation and how to treat it