Acid base balance

Question 1

What is an acid?

Answer 1

Electrolytes that release H+ when dissolved

Question 2

What is a base?

Answer 2

Electrolytes that release ions that combine with H+

Question 3

What is normal serum pH?

Answer 3

7.35-7.45

Question 4

What is a volatile acid?

Answer 4

Gas, produced via cellular metabolism and excreted by lungs as CO2

Question 5

What is a non-volatile acid?

Answer 5

Liquid, produced via cellular metabolism excreted by the kidneys such as:

Lactic acid (anaerobic breakdown) 
Keto acid (fat breakdown)
Sulphuric/phosphoric acid (Protein breakdown)

Question 6

What is the function of buffers?

Answer 6

Minimize changes in pH

Chemical and physiological buffers

Question 7

What are the 3 chemical buffers?

Answer 7

1) Carbonic acid-bicarbonate buffer system
2) Phosphate buffer system
3) Protein buffer system

Question 8

What is the first line of defense against pH changes?

Answer 8

Chemical buffers, specifically the carbonic acid-bicarbonate buffer system

Question 9

How does the carbonic acid bicarbonate buffer system work?

Answer 9

Acid: Base ratio is 1:20 with pH 7.40, so strong acids are neutralized by HCO3- and strong bases are neutralized by H2CO3+

More common to have more strong acids than strong bases enter the body

Question 10

How does the phosphate buffer system work?

Answer 10

PO4 is able to bind to 2 H+ ions or release them to maintain pH

Becomes H2PO4 or HPO4

Question 11

How does the protein buffer system work?

Answer 11

Blood buffer, is most abundant buffer in the body.

Majority of CO2 travels in blood as H+ and HCO3-, H+ can bind to hemoglobin/RBCs which seal of H+ and prevent changes to serum pH

Question 12

What are the 2 physiological buffers?

Answer 12

1) Lungs

2) Renal system

Question 13

How do the lungs act as a physiological buffer?

Answer 13

Takes mins to react, regulates CO2.

In acidosis –> Respiratory centers in the medulla triggers increase RR to blow off CO2

In alkalosis –> Medulla triggers decrease RR to retain CO2

Question 14

How do the kidneys act as a physiological buffer?

Answer 14

Directly eliminate H+ by controlling HCO3- and H+ secretion and reabsorption. Is the most effective buffer, but takes longest.

Question 15

What happens when the kidneys move H+ from blood to urine?

Answer 15

It exchanges with another positive ion (e.g. K+)

Therefore risk of hyperkalemia in pts with profound acidosis.

Question 16

What happens when nephrons have to move too much H+ out into urine?

Answer 16

When nephron pH < 4.5 (too much secretion of H+), tubular necrosis and kidney damage occurs

Question 17

What happens when the kidneys move HCO3- from blood to urine?

Answer 17

Cl- is exchanged.

Recall lasix blocks Cl- reabsorption at the ascending LOH so urinary losses of Cl- eventually exceeds bicarbonate losses leading to metabolic alkalosis.

Question 18

What causes metabolic acidosis?

Answer 18

PH < 7.35, pHCO3- < 22

1) Accumulation of non-resp acids (lactic acid, DKA, renal failure, ingestion of acids, ASA)
2) Loss of base (diarrhea, prolonged vomiting)

Question 19

How is metabolic acidosis treated?

Answer 19

Underlying cause, sodium bicarb, HD

Question 20

What causes respiratory acidosis?

Answer 20

pH < 7.35, pCO2 > 45

Accumulation of volatile acids (CO2 retention, resp depression, airway obstruction, resp failure)

Question 21

How is respiratory acidosis treated?

Answer 21

Treat cause, ventilate increase RR, assess sedation

Question 22

What causes metabolic alkalosis?

Answer 22

pH > 7.45, HCO3- > 28

1) Accumulation of bases (antacids, diuretics causing loss of Cl-, blood transfusions due to citrate breaking down to HCO3-)
2) Loss of non-volatile acids (vomiting stomach contents, NG suction)

Question 23

How is metabolic alkalosis treated?

Answer 23

Usually not treated but acetazolamide can be used to decrease HCO3- production (low evidence)

Question 24

What causes respiratory alkalosis?

Answer 24

pH > 7.45, pCO2 < 35

Loss of volatile acids (alveolar hyperventilation decreases CO2, hypoxemia, over ventilation)

Question 25

How is respiratory alkalosis treated?

Answer 25

Underlying cause, sedation, if ventilated then correct RR and Vt