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Cardio > Biochemistry Acid-Base Balance > Flashcards

Biochemistry Acid-Base Balance Flashcards

1
Q

Acid-Base Balance is

A

The regulation of Hydrogen ions

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2
Q

Acid-base metabolism

A

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

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3
Q

Carbon dioxide is

A

The major source of acid in the body

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

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4
Q

Acid produced by the body

A
  • Carbonic acid (from CO2)
  • Hydrochloric acid – stomach
  • Lactic acid
  • Alpha-ketoacids
  • Uric acid
  • Proteins
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5
Q

Bases produced by the body

A
  • Bicarbonate
  • Phosphate
  • Proteins
  • Ammonia
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6
Q

Buffering System

A 
Bicarbonate = most important
Haemoglobin (intracellular)
Proteins (extracellular)
Phosphate (kidneys)
Ammonia (kidneys)
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7
Q

Haemoglobin buffering

A

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

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8
Q

The Henderson – Hasselbalch equation

A

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

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9
Q

pH is proportional to

A

HCO3-/p CO2

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10
Q

HCO3 =

A

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

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11
Q

Compensation

A

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

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12
Q

Acidosis leads to

A

Mechanisms that compensate to increase the pH

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13
Q

Alkalosis leads to

A

Mechanisms that compensate to decrease the pH

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14
Q

If there is no evidence of compensation

A

Acute process

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15
Q

Over-compensation?

A

Never an over-compensation

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16
Q

Mixed disorder

A

Primary disorder my be mixed

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17
Q

Compensation – primary metabolic cause:

A

Respiratory compensation = Immediate

See slide on 76

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18
Q

Compensation = primary respiratory cause:

A

Metabolic compensation = Delayed

See slide on 76

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19
Q

pCO2

A

35-45 mmHg

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20
Q

HCO3-

A

23-29 mmol/L

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21
Q

Base Excess (BE)

A

±3 mmol/L

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22
Q

pO2 in the context of acid-base

A

Is immaterial in this context

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23
Q

Acidosis is a

A

Process which tends to produce an academia

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24
Q

Alkalosis is a

A

Process which tends to produce an alkalaemia

25
Q

pH normal values

A

7.35-7.45

26
Q

Acidosis is a

A

Process which tends to produce an academia

27
Q

Alkalosis is a

A

Process which tends to produce an alkalaemia

28
Q

pH normal values

A

7.35-7.45

29
Q

Systematic Approach

A
  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
Q

Anion Gap →

A

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

31
Q

Unmeasured cations (11 mmol/L)

A

Potassium, calcium, magnesium but they are usually constant.

32
Q

Unmeasured (23 mmol/L)

A

Proteins, mostly albumin, organic acids, phosphates, sulphates

33
Q

AG purpose

A

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
Q

Causes of normal anion gap acidosis

A

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
Q

AG equation

A

NA+ - (Cl- + HCO-)

36
Q

Causes of increased anion gap

A

Endogenous acidosis

Exogenous acidosis

37
Q

Endogenous acidosis

A

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

38
Q

Exogenous acidosis

A

By intoxication:

  1. Acetyl-salicylic acid (aspirin)
  2. Biguanides (metformin)
  3. Breakdown products of poisons (ethylene glycol and methanol)
39
Q

Acideamia produces

A

High K+

40
Q

Alkalaemia produces

A

Low K+

41
Q

Metabolic acidosis

A

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

42
Q

Metabolic acidosis

Metabolic acidosis

A

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

43
Q

Metabolic acidosis

Reduced renal H+ excretion causes

A

Generalised renal failure

Renal tubular acidosis (RTA)

44
Q

Metabolic acidosis

Loss of bicarbonate

A

Diarrhoea, pancreatic fistula, RTA

45
Q

Metabolic alkalosis → Caused by

A

Gain of HCO3 and maintained by abnormal renal HCO3 absorption.

46
Q

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

A

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
Q

Metabolic alkalosis → Alkalosis tends to

A

Depress respiration and leads to CO2 retention

48
Q

Metabolic alkalosis → Compensation

A

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

49
Q

Respiratory Acidosis → Causes

A

Lung Disease
Mechanical
Neurological

50
Q

Respiratory Acidosis → Lung disease examples

A 
Fibrosis
Oedema
Tumours
Bronchitis
Severe asthma
Pulmonary embolism
51
Q

Respiratory Acidosis → Mechanical

A

Myopathies
Trauma
Pleural effusions
Pneumothorax

52
Q

Respiratory Acidosis → Neurological

A

CNS depression (e.g. drugs) CNS disease

53
Q

Respiratory Acidosis → Increased H+ due to

A

CO2 retention, compensated by increased bicarbonate synthesis

54
Q

Respiratory Alkalosis → Definition

A

CO2 reduction due to excessive ventilation

55
Q

Respiratory Alkalosis → Causes

A

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

56
Q

Causes of High Osmolar Gap

A 
Isotonic hyponatraemia
Glycine infusion
Chronic renal failure
Ingestions
Contrast Media
57
Q

Isotonic hyponatraemia

A

Hyperlipidaemia
Hyperproteinaemia
Mannitol

58
Q

Ingestions

A

Ethanol
Isopropyl alcohol
Ethylene glycol

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