Biochemistry Acid-Base Balance

Question 1

Acid-Base Balance is

Answer 1

The regulation of Hydrogen ions

Question 2

Acid-base metabolism

Answer 2

Production of H+ via metabolism of carbs and fats etc. input into the system buffered by factors and output via the lungs and kidneys.

Question 3

Carbon dioxide is

Answer 3

The major source of acid in the body

CO2 + H2O = Carbonic Acid (produces acid and base)

Question 4

Acid produced by the body

Answer 4

• Carbonic acid (from CO2)
• Hydrochloric acid – stomach
• Lactic acid
• Alpha-ketoacids
• Uric acid
• Proteins

Question 5

Bases produced by the body

Answer 5

• Bicarbonate
• Phosphate
• Proteins
• Ammonia

Question 6

Buffering System

Answer 6

Bicarbonate = most important
Haemoglobin (intracellular)
Proteins (extracellular)
Phosphate (kidneys)
Ammonia (kidneys)

Question 7

Haemoglobin buffering

Answer 7

CO2 from tissue respiration absorbed in erythrocyte releasing Hco3
See diagrams pg 75

Question 8

The Henderson – Hasselbalch equation

Answer 8

pH = pKa + log (HCO3)/0.23 x pCO2

Question 9

pH is proportional to

Answer 9

HCO3-/p CO2

Question 10

HCO3 =

Answer 10

Base=kidneys=metabolic
Increased Hco3 = increased pH (alkalosis)
Reduced HCo3 = decreased pH (acidosis)

Question 11

Compensation

Answer 11

A change in pH outside the normal range causes the body to attempt to compensate to return pH towards normal.

Question 12

Acidosis leads to

Answer 12

Mechanisms that compensate to increase the pH

Question 13

Alkalosis leads to

Answer 13

Mechanisms that compensate to decrease the pH

Question 14

If there is no evidence of compensation

Answer 14

Acute process

Question 15

Over-compensation?

Answer 15

Never an over-compensation

Question 16

Mixed disorder

Answer 16

Primary disorder my be mixed

Question 17

Compensation – primary metabolic cause:

Answer 17

Respiratory compensation = Immediate

See slide on 76

Question 18

Compensation = primary respiratory cause:

Answer 18

Metabolic compensation = Delayed

See slide on 76

Question 19

pCO2

Answer 19

35-45 mmHg

Question 20

HCO3-

Answer 20

23-29 mmol/L

Question 21

Base Excess (BE)

Answer 21

±3 mmol/L

Question 22

pO2 in the context of acid-base

Answer 22

Is immaterial in this context

Question 23

Acidosis is a

Answer 23

Process which tends to produce an academia

Question 24

Alkalosis is a

Answer 24

Process which tends to produce an alkalaemia

Question 25

pH normal values

Answer 25

7.35-7.45

Question 26

Acidosis is a

Answer 26

Process which tends to produce an academia

Question 27

Alkalosis is a

Answer 27

Process which tends to produce an alkalaemia

Question 28

pH normal values

Answer 28

7.35-7.45

Question 29

Systematic Approach

Answer 29

1. Look at the pH – is the primary acidosis or alkalosis? 2. Check the Co2 (respiratory indicator) – is the pH change explained by a rise or fall in pCO2? 3. Check the HCO3 – is the ph change explained by a rise or fall in HCO3? 4. Is there any evidence of compensation? 5. Calculate Anion Gap if metabolic acidosis present

Question 30

Anion Gap →

Answer 30

→ Calculated difference between the serum anions that are measured in a chemistry profile an the unmeasured anions.

Question 31

Unmeasured cations (11 mmol/L)

Answer 31

Potassium, calcium, magnesium but they are usually constant.

Question 32

Unmeasured (23 mmol/L)

Answer 32

Proteins, mostly albumin, organic acids, phosphates, sulphates

Question 33

AG purpose

Answer 33

Is used in the differential diagnosis of metabolic acidosis. | The body does not generate an AG to compensate for a primary disorder – AG is part of a primary disorder.

Question 34

Causes of normal anion gap acidosis

Answer 34

HCO3 has been removed from the extracellular space due to renal or GI HCO3 losses: 1. diarrhoea 2. Pancreatic fistula 3. Ammonia or alimentation eg TPN 4. Carbonic anhydrase inhibitor 5. Renal tubular acidosis 6. Ureterosigmoidostomy 7. Endocrine – hypoaldosteronism → Compensatory hyperchloraemia

Question 35

AG equation

Answer 35

NA+ - (Cl- + HCO-)

Question 36

Causes of increased anion gap

Answer 36

Endogenous acidosis | Exogenous acidosis

Question 37

Endogenous acidosis

Answer 37

Uraemia (renal failure) – no regeneration of HCO3- build up of organic acids normally excreted by the kidney Ketoacidosis – diabeti or alcoholic Lactic acidosis

Question 38

Exogenous acidosis

Answer 38

By intoxication: 1. Acetyl-salicylic acid (aspirin) 2. Biguanides (metformin) 3. Breakdown products of poisons (ethylene glycol and methanol)

Question 39

Acideamia produces

Answer 39

High K+

Question 40

Alkalaemia produces

Answer 40

Low K+

Question 41

Metabolic acidosis

Answer 41

Increased rate of H+ production Acid ingestion Reduced renal H+ excretion Loss of bicarbonate

Question 42

Metabolic acidosis Metabolic acidosis

Answer 42

Ketoacidosis Diabetic or alcoholic lactic acidosis form hypoxia poisoning Inherited organic acidosis

Question 43

Metabolic acidosis Reduced renal H+ excretion causes

Answer 43

Generalised renal failure | Renal tubular acidosis (RTA)

Question 44

Metabolic acidosis Loss of bicarbonate

Answer 44

Diarrhoea, pancreatic fistula, RTA

Question 45

Metabolic alkalosis → Caused by

Answer 45

Gain of HCO3 and maintained by abnormal renal HCO3 absorption.

Question 46

Metabolic alkalosis → Metabolic alkalosis is almost always due to and examples of this causes

Answer 46

Volume contraction • Vomiting, gastric aspiration, diuretics • Profound hypokalaemia • Renal failure: poor filtration and therefore poor excretion • Hyperaldosteronism: via increased H secretion and hypokalaemia (Na/K exchanger) • Excess alkali administration (iatrogenic)

Question 47

Metabolic alkalosis → Alkalosis tends to

Answer 47

Depress respiration and leads to CO2 retention

Question 48

Metabolic alkalosis → Compensation

Answer 48

Partial compensation since associated hypoxia overrides this effect and stimulates respiration.

Question 49

Respiratory Acidosis → Causes

Answer 49

Lung Disease Mechanical Neurological

Question 50

Respiratory Acidosis → Lung disease examples

Answer 50

``` Fibrosis Oedema Tumours Bronchitis Severe asthma Pulmonary embolism ```

Question 51

Respiratory Acidosis → Mechanical

Answer 51

Myopathies Trauma Pleural effusions Pneumothorax

Question 52

Respiratory Acidosis → Neurological

Answer 52

CNS depression (e.g. drugs) CNS disease

Question 53

Respiratory Acidosis → Increased H+ due to

Answer 53

CO2 retention, compensated by increased bicarbonate synthesis

Question 54

Respiratory Alkalosis → Definition

Answer 54

CO2 reduction due to excessive ventilation

Question 55

Respiratory Alkalosis → Causes

Answer 55

Fall in oxygen (anaemia, CCF, altitude) Pulmonary pathology (infection, oedema) Central stimulation (Sepsis, toxins, trauma) Voluntary, psychogenic, anxiety, pain

Question 56

Causes of High Osmolar Gap

Answer 56

``` Isotonic hyponatraemia Glycine infusion Chronic renal failure Ingestions Contrast Media ```

Question 57

Isotonic hyponatraemia

Answer 57

Hyperlipidaemia Hyperproteinaemia Mannitol

Question 58

Ingestions

Answer 58

Ethanol Isopropyl alcohol Ethylene glycol