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MD3002 Physiology > Clinical Aspects of Acid-Base Control > Flashcards

Clinical Aspects of Acid-Base Control Flashcards

1
Q

What are the buffers of pH in the body?

A
  • Proteins
  • Haemoglobin
  • Carbonic acid / bicarbonate
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2
Q

How is standard bicarbonate calculated?

A

From the actual bicarbonate but assuming 37C and a paCO2 of 5.3kPa

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3
Q

What happens to the base excess in a metabolic acidemia?

A

Becomes more negative

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4
Q

What is likely to be occuring if pCO2 and bicarbonate are moving in the same direction?

A

Compensation

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5
Q

What is the anion gap?

A
  • Sum of routinely measured cations in venous blood minus routinely measured anions
  • (Na+ + K+) - (Cl- + HCO3-)
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6
Q

What are the main anions?

A
  • Chloride
  • Bicarbonate
  • Protein
  • Organic acid
  • Phosphate
  • Sulphate
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7
Q

What are the main cations?

A
  • K+
  • Na+
  • Ca2+
  • Mg2+
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8
Q

What does an increased anion gap signal?

A

Metabolic acidaemia

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9
Q

What is the normal fife anion gap?

A

16

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10
Q

What are the different types of metabolic acidosis / what are they due to?

A
  • Bodies own production (endogenous)
  • Ingestion (exogenous source)
  • Failure of excretion / regeneration bicarb by the kidneys
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11
Q

What causes a lactic acidosis?

A 
Any conditions causing hypoperfusion 
- Of the whole body: shock
- Or part of the body: femoral artery embolism 
ALSO
- Severe acute hypoxia 
- Severe convulsions (resp arrest)
- Strenuous exercise (dehydration)
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12
Q

What happens to the anion gap in lactic acidosis?

A

Increases

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13
Q

Where is lactate metabolised?

A

Liver

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14
Q

When does production of lactate increase?

A

When O2 delivery falls (consumption of lactate by the liver then falls)

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15
Q

When are lactate levels concerning?

A

When > 2 mmol/L

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16
Q

What does uncontrolled diabetes mellitus lead to?

A

Ketoacidosis (endogenous metabolic acidosis)

17
Q

What can cause ketoacidosis?

A
  • Uncontrolled diabetes mellitus
  • Alcoholic ketoacidosis
  • Starvation ketoacidosis
18
Q

Where should blood be taken from in order to measure diabetic ketoacidosis?

A

Venous

19
Q

What substances can cause an exogenous acid load?

A
  • Methanol (industrial solvent, windscreen wash)

- Ethylene glycol (anti-freeze)

20
Q

What is the effect of renal failure both acute and chronic on the anion gap?

A

Increased

21
Q

What is the effect of renal tubular acidosis on the anion gap?

A

Normal (eGFR should be more or less normal as well)

22
Q

What happens below the pylorus?

A
  • Bicarbonate secreted into gut lumen

- For every bicarbonate secreted into gut lumen an H+ ion enters ECF

23
Q

Why does the anion gap remain level in diarrhoea?

A
  • Bicarb decreases but RAAS system stimulated due to dihidration which retains Cl-
24
Q

What pathologies have a metabolic acidosis but not an increased anion gap?

A
  • Laxative abuse
  • Ileostomy
  • Colostomy
25
Q

How do the kidneys correct metabolic acidemia?

A
  • Secrete more acid (therefore also make new bicarbonate) - plasma H+ decreases (pH rises) and plasma bicarbonate rises to normal
  • But only if the metabolic acidosis is of non-renal origin and the kidneys are functioning effectively
26
Q

What is the respiration pattern called that compensates for metabolic acidosis?

A

Kussmaul respiration - a laboured deep, rapid pattern of breathing

27
Q

How long does maximal compensation take?

A

Up to 24 hours

28
Q

What 2 processes have to happen in a metabolic alkalosis?

A
  • An initiating process

- A maintaining process

29
Q

What are the most common initiating processes of metabolic alkalosis?

A

Loss of H+ ions

  • From the gut (pyloric stenosis)
  • From the kidney (furosemide, thiazide)
30
Q

What maintains an alkalosis?

A

HAV

  • Hypokalaemia
  • Aldosterone excess
  • Volume and chloride depletion group
31
Q

Describe the pathology of ploric stenosis?

A
  • In health parietal cells secrete H+ into lumen of the stomach. The bicarb is secreted into the ECF
  • Gastric fluid also contains Na+, H2O and K+ (5-10mmol/l)
  • Initially excess bicarb is spilled in the urine but accompanied by a cation
  • Worsening volume depletion results in aldosterone secretion (RAAS)
  • Na+ and water retained exacerbating hypokalaemia

MD3002 Physiology (24 decks)

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