Acid Base Balance

Question 1

What is the degree of increase in hydrogen ions as the pH decreases?

Answer 1

10 fold increase

Question 2

What is the normal pH range?

Answer 2

7.35-7.45

Question 3

What 2 processes need to be combated to maintain pH?

Answer 3

CO2 production from oxidative metabolism

Acid production from break down of dietary phosphoproteins and sulphur-containing proteins

Question 4

What is the process of CO2 metabolism to remove CO2 from cells? What byproduct can potentially cause a problem for the cell?
What process combats this?

Answer 4

CO2 diffuses into the plasma and then is taken up by erythrocytes

CO2 binds to H2O in erythrocyte to form carbonic acid

Carbonic anhydrase breaks down carbonic acid to form HCO3- and H+

H+ combines with HbO2 which displaces O2 (O2 released from RBC)

HCO3- = problem i.e. upsets electrical balance in cell 
Therefore= HCO3- exits RBC in exchange for Cl-

Question 5

Why is CO2 metabolism an open system?

Answer 5

The metabolic pathway can go in bother directions
I.e. cells= CO2 taken up by RBC and O2 released
Lungs= O2 taken up and CO2 released

Question 6

What role do enzymes have in imbalances?

Answer 6

Enzymes have rate limiting steps that can be dysregulated and leave to acid-base imbalances

Question 7

What 2 process are involved in hydrogen ion metabolism?

Answer 7

Extracellular buffering and respiratory compensation using bicarbonate, phosphate and proteins

Renal excretion of H+ and HCO3- regeneration

Question 8

What are the 3 buffering systems in the body? Where are these buffering systems located in body?

Answer 8

Bicarbonate
Phosphate
Protein

Plasma =bicarbonate
ECF= bicarbonate + proteins
Erythrocytes = bicarbonate, Hb, inorganic phosphates + organic phosphates
Intracellular fluid= bicarbonate + proteins + inorganic phosphate

Question 9

Why are kidneys important in maintaining acid-base balance?

Answer 9

Bicarbonate regeneration in distal tubule to ensure sufficient buffer available

Excretion of H+ via acidification of urine with ammonia breakdown to enable increased HCO3- formation in the peritubular plasma

Question 10

What is a simplified version of the Henderson-Hasselbach equation?
Using this equation what are the 2 possible scenarios which cause an acidosis and an alkalosis?

Answer 10

pH= HCO3/PCO2

Acidosis (low ph)
Fall in HCO3 with normal PCO2
Rise in PCO2 with normal HCO3

Alkalosis (high Ph)
Rise in HCO3 with normal PCO2
Fall in PCO2 with normal HCO3

Question 11

What occurs in metabolic compensation?

Answer 11

Body alerts the other component contributing to pH which has not been affected by the disease process in order to return the pH back within the normal range

Question 12

What is the compensatory response to metabolic acidosis?

How might a patient present?

Answer 12

Respiratory stimulation to increase respiratory rate to lower PCO2
(Can appear to be panting or puff breathing)
Can take 12-24 hours

Question 13

What are is the compensatory mechanism for metabolic alkalosis?

Answer 13

Respiratory depression to increase PCO2

12-24 hours

Question 14

What is the compensatory response for respiratory acidosis?

Answer 14

Renal compensation to increase HCO3

Question 15

What is the compensatory mechanism for respiratory alkalosis?

Answer 15

Renal compensation to decrease the concentration of HCO3

Question 16

How can you determine whether the primary process is respiratory or metabolic?

Answer 16

High PCO2= px retaining CO2 i.e. RESPIRATORY

Low HCO3= metabolic

Note: normal or low CO2 means it is NOT respiratory but does not immediately indicate that it is metabolic i.e. need to look at HCO3 levels for that

Question 17

If patient has respiratory acidosis, how can you decide if they have compensated? How do you distinguish between complete and partial compensation?

Answer 17

HCO3 should be high to indicate that kidneys are compensating

Complete and partial differentiated based on how close the pH is to normal

Question 18

What condition classically presents as an acute/uncompensated respiratory acidosis? What results would you expect to see?

Answer 18

Acute asthma attack

Low pH
High CO2
Normal HCO3 i.e. not had time to compensate

Question 19

The causes of metabolic acidosis fit into 3 broad categories. What are the categories and give examples of associated conditions?

Answer 19

1. Increased H+ load 
Ketoacidosis 
Lactic acidosis 
Salicylate drugs 
Methanol 
Ethanol 
Ethylene glycol 

2. Decreased H+ secretion
   Renal failure
   RTA
   Mineralocorticoid deficiency

3.Loss of HCO3
Diarrhoea
RTA

Question 20

What are the 2 main categories which causes metabolic alkalosis? Give examples of conditions for each.

Answer 20

1. Loss of H+
   Vomiting
   Mineralocorticoid excess (Cushings or Conns)
   Bartters severe K+ deficiency
2. Excessive HCO3 intake
   Oral or IV therapy

Question 21

What are the examples of conditions which can cause respiratory acidosis?

Answer 21

Emphysema
Bronchitis
Asthma

Guillain-Barré syndrome

Trauma
Infection
Tumours

Sedatives
Anaesthetics

Mechanical ventilation

Question 22

What conditions can cause respiratory alkalosis?

Answer 22

Hyperventilation

Pneumonia 
Asthma 
CCF
Embolism 
Mechanical ventilation 

Trauma 
Infection 
Tumour 
Septicaemia 
Liver failure 
Drugs 
Hysterical

Question 23

Young patient with type 1 diabetes presents to A+E with following results: 
pH 7.21 
PCO2 3.8 (4.7-6.0)
HCO3 12.0 (24-30)
PO2 13.1 (10.6-13.3) 

What is the most likely explanation for these results?

Answer 23

Low ph= acidosis
Low HCO3= metabolic acidosis
Low CO2= indicates partially compensated

Partially compensated diabetic ketoacidosis