Biochemistry Acid-Base Balance Flashcards Preview

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Flashcards in Biochemistry Acid-Base Balance Deck (58):
1

Acid-Base Balance is

The regulation of Hydrogen ions

2

Acid-base metabolism

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

3

Carbon dioxide is

The major source of acid in the body
CO2 + H2O = Carbonic Acid (produces acid and base)

4

Acid produced by the body

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

5

Bases produced by the body

• Bicarbonate
• Phosphate
• Proteins
• Ammonia

6

Buffering System

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

7

Haemoglobin buffering

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

8

The Henderson – Hasselbalch equation

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

9

pH is proportional to

HCO3-/p CO2

10

HCO3 =

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

11

Compensation

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

12

Acidosis leads to

Mechanisms that compensate to increase the pH

13

Alkalosis leads to

Mechanisms that compensate to decrease the pH

14

If there is no evidence of compensation

Acute process

15

Over-compensation?

Never an over-compensation

16

Mixed disorder

Primary disorder my be mixed

17

Compensation – primary metabolic cause:

Respiratory compensation = Immediate
See slide on 76

18

Compensation = primary respiratory cause:

Metabolic compensation = Delayed
See slide on 76

19

pCO2

35-45 mmHg

20

HCO3-

23-29 mmol/L

21

Base Excess (BE)

±3 mmol/L

22

pO2 in the context of acid-base

Is immaterial in this context

23

Acidosis is a

Process which tends to produce an academia

24

Alkalosis is a

Process which tends to produce an alkalaemia

25

pH normal values

7.35-7.45

26

Acidosis is a

Process which tends to produce an academia

27

Alkalosis is a

Process which tends to produce an alkalaemia

28

pH normal values

7.35-7.45

29

Systematic Approach

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

30


Anion Gap →

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

31

Unmeasured cations (11 mmol/L)

Potassium, calcium, magnesium but they are usually constant.

32

Unmeasured (23 mmol/L)

Proteins, mostly albumin, organic acids, phosphates, sulphates

33

AG purpose

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.

34

Causes of normal anion gap acidosis

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

35

AG equation

NA+ - (Cl- + HCO-)

36

Causes of increased anion gap

Endogenous acidosis
Exogenous acidosis

37

Endogenous acidosis

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

38

Exogenous acidosis

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

39

Acideamia produces

High K+

40

Alkalaemia produces

Low K+

41

Metabolic acidosis

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

42

Metabolic acidosis

Metabolic acidosis

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

43

Metabolic acidosis

Reduced renal H+ excretion causes

Generalised renal failure
Renal tubular acidosis (RTA)

44

Metabolic acidosis

Loss of bicarbonate

Diarrhoea, pancreatic fistula, RTA

45

Metabolic alkalosis → Caused by

Gain of HCO3 and maintained by abnormal renal HCO3 absorption.

46

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

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)

47

Metabolic alkalosis → Alkalosis tends to

Depress respiration and leads to CO2 retention

48

Metabolic alkalosis → Compensation

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

49

Respiratory Acidosis → Causes

Lung Disease
Mechanical
Neurological

50

Respiratory Acidosis → Lung disease examples

Fibrosis
Oedema
Tumours
Bronchitis
Severe asthma
Pulmonary embolism

51

Respiratory Acidosis → Mechanical

Myopathies
Trauma
Pleural effusions
Pneumothorax

52

Respiratory Acidosis → Neurological

CNS depression (e.g. drugs) CNS disease

53

Respiratory Acidosis → Increased H+ due to

CO2 retention, compensated by increased bicarbonate synthesis

54

Respiratory Alkalosis → Definition

CO2 reduction due to excessive ventilation

55

Respiratory Alkalosis → Causes

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

56

Causes of High Osmolar Gap

Isotonic hyponatraemia
Glycine infusion
Chronic renal failure
Ingestions
Contrast Media

57

Isotonic hyponatraemia

Hyperlipidaemia
Hyperproteinaemia
Mannitol

58

Ingestions

Ethanol
Isopropyl alcohol
Ethylene glycol

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