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Genitourinary > Acid-base disturbance > Flashcards

Acid-base disturbance Flashcards

1
Q

pH equations

A 
pH = -log[H+]
[H+] = 10^(-pH)
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2
Q

Blood pH levels

A

Normal: 7.35 - 7.45
Acidaemia: <7.35
Alkalaemia: >7.45

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3
Q

Buffer

A

Minimises pH changes due to addition or removal of H+

Only removes H+ temporarily - doesn’t remove from body

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4
Q

pK of buffer

A

pH at which [A-] = [HA]

pH = pK + log([A-]/[HA])

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5
Q

2 buffers in the blood

A

Bicarbonate - most important

Proteins e.g. albumin and haemoglobin

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6
Q

Respiratory control of pCO2

A

Increased pCO2 = acidosis

Decreased pCO2 = alkalosis

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7
Q

Blood gas measured quantities

A

pH
pCO2
pO2

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8
Q

Blood gas calculated quantities

A

HCO3-

Base excess

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9
Q

Respiratory disturbances

A

CO2 retention = respiratory acidosis

Hyperventilation = respiratory alkalosis

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10
Q

Metabolic disturbances

A

Decreased HCO3- = metabolic acidosis

Increased HCO3- = metabolic alkalosis

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11
Q

Metabolic acidosis indicators

A

Low pH

Low bicarbonate

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12
Q

Metabolic acidosis causes

A

Increased acid production
Decreased acid excretion
Bicarbonate loss

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13
Q

Lactic acidosis

A

Type of metabolic acidosis
Hypoxia
Poor tissue perfusion
CO or cyanide poisonsing

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14
Q

Diabetic ketoacidosis

A

Insulin resistance decreases glucose uptake. Without glucose, the body uses fat for energy which produces ketones
Ketones are acidic bodies that build up and cause acidosis

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15
Q

2 things that can cause decreased acid excretion

A

Renal failure and renal tubular acidosis

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16
Q

2 things that can cause bicarbonate loss

A

Severe diarrhoea

Ileostomy

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17
Q

Rare causes of metabolic acidosis

A 
Methanol poisoning
Ethylene glycol poisoning
Genetic disorders
Alcoholic ketoacidosis
Glue sniffing
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18
Q

Two causes of metabolic alkalosis

A

Ingestion of sodium bicarbonate

Loss of stomach acid due to vomiting

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19
Q

What do these values indicate?
pH: 7.54
Bicarbonate: 33
pCO2: 5.2

A

Metabolic alkalosis

High pH with high bicarbonate and normal pCO2

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20
Q

What do these values indicate?
pH: 7.33
Bicarbonate: 25
pCO2: 6.5

A

Acute respiratory acidosis

Low pH with normal bicarbonate and high pCO2

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21
Q

What do these values indicate?
pH: 7.50
Bicarbonate: 23
pCO2: 4.0

A

Acute respiratory alkalosis

High pH with normal bicarbonate and low pCO2

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22
Q

What do these values indicate?
pH: 7.28
Bicarbonate: 14
pCO2: 4.0

A

Metabolic acidosis

Low pH with low bicarbonate and low pCO2

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23
Q

What do these values indicate?
pH: 7.07
Bicarbonate: 16
pCO2: 7.5

A

Mixed respiratory and metabolic acidosis

Low pH with low bicarbonate and high pCO2

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24
Q

Acidotic breathing

A

When low pH from metabolic acidosis stimulates ventilation which lowers pCO2 to compensate, bringing pH up towards normal but not completely

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25
Q

Renal acidification

A

Kidneys excrete acid to balance non-volatile acid generated through metabolism

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26
Q

Net acid excretion

A

NAE = ([Urine NH4+] + [Urine titratable acid] + [Urine HCO3-]) x Volume

27
Q

3 main renal processes involved in acid-base balance

A

1) Bicarbonate reabsorption
2) New bicarbonate generation
3) H+ secretion in distal nephron

28
Q

Acetazolamide

A

Carbonic anhydrase inhibitor that prevents bicarbonate from being formed from CO2
Causes metabolic acidosis
Used in mountaineering to counteract alkalosis due to hyperventilation

29
Q

Renal handling of ammonium

A

Ammonium generated from glutamine in proximal tubule cells, then secreted into lumen
Most ammonium reabsorbed in the thick ascending limb with the rest going into the collecting duct
NH4+ trapped and secreted

30
Q

Response of the kidney to acidosis

A

Increased HCO3 and H+ transport along nephron
Increased ammoniagenesis
Increased availability of urinary buffers
—> renal compensation

31
Q

Expected values in respiratory acidosis with renal compensation

A

Low pH
High pCO2
High bicarbonate
High base excess

32
Q

Metabolic acidosis primary change and compensatory response

A

Decreased bicarbonate

Decrease in pCO2

33
Q

Metabolic alkalosis primary change and compensatory response

A

Increased bicarbonate

Increase in pCO2

34
Q

Respiratory acidosis primary change and compensatory response

A

Increased PCO2

Increase in bicarbonate

35
Q

Respiratory alkalosis primary change and compensatory response

A

Decreased pCO2

Decrease in bicarbonate

36
Q

Base excess

A

Amount of acid or base needed to restore pH to 7.4
Only for metabolic disturbances
Positive in alkalosis and negative in acidosis

37
Q

Normal base excess

A

0

From -2 to +2

38
Q 
A patient with chronic lung disease is admitted with these values:
pH: 7.30
pCO2: 9.0
Bicarb: 33
BE: +6
They are ventilated in ICU with these values:
pH: 7.55
pCO2: 5.2
Bicarb: 33
BE: +10
What kind of disturbance is this?
A 
On admission:
pH is low
pCO2 is high
Bicarb is high
BE is high
This is a respiratory acidosis with metabolic compensation.
After ventilation:
pH is high
pCO2 is normal
Bicarb is high
BE is high
Respiratory component has been corrected but metabolic compensation remains, causing chronic metabolic alkalosis
This is called post-hypercapnic alkalosis
39
Q

Anion gap

A

AG = (Na + K) - (Cl + bicarb)
Normal range = 14 to 16
Only useful in metabolic acidosis

40
Q

What does a normal anion gap reflect?

A

Protein anions

41
Q

What does an increased anion gap reflect?

A

The presence of unmeasured anions e.g. lactate, oxalate etc.

42
Q

Approach to metabolic acidosis

A

1) confirm by looking for low pH with low bicarb
2) Check serum anion gap
3) if anion gap normal, check urine anion gap

43
Q

Non-anion gap acidosis

A

Due to urinary acidification or loss of HCO3-

44
Q

Key causes of acidosis with increased anion gap

A

Lactic acidosis
Diabetic ketoacidosis
Alcoholic ketoacidosis
Renal failure

45
Q

Non-renal causes of normal anion gap acidosis

A

Diarrhoea
Ileostomy
External loss of pancreatic or biliary secretions

46
Q

Renal causes of normal anion gap acidosis

A

Renal tubular acidoses:

  • proximal
  • hypokalaemic distal
  • hyperkalaemic distal
47
Q

Renal tubular acidosis

A

Defects in acid excretion
Urine pH > 5.5
Urine ammonium normal

48
Q 
A patient presents with these values:
Na: 140
K: 3.6
Cl: 115
pH: 7.2
pCO2: 4.0
bicarbonate: 11
Base excess: -17
What type of disturbance is this and what other test should you perform?
A

Anion gap = (NA + K - Cl - HCO3
Anion gap = 17
The anion gap is normal, so this is a metabolic acidosis with a normal anion gap
You should do a urine anion gap to confirm.

49
Q

What childhood deficiency disease is associated with renal tubular acidosis?

A

Rickets

Vitamin D deficiency

50
Q

If a urine pH is normal in an acidosis, what would the diagnosis be?

A

Renal tubular acidosis

51
Q

What can urine anion gaps tell you about the ammonium?

A

In metabolic acidoses:
If UAG is positive, there is not enough NH4+
If UAG is negative there is too much NH4+

52
Q

Why are normal anion gap acidoses hyperchloremic?

A

When bicarbonate is low, extra chloride is needed to maintain the electrical charge because sodium will continue to be reabsorbed

53
Q

Hyperkalemia is associated with:

A

Acidosis

54
Q

Hypokalemia is associated with:

A

Alkalosis

55
Q

Which 2 mechanisms describe the association between potassium and acid-base disturbances?

A

1) K+ movement into cells displaces H+ (hyperkalemia causing acidosis) and vice versa (acidosis causing hyperkalemia)
- The same is true of hypokalemia and alkalosis
2) H+ and K+ compete with each other for secretion. If one is secreted, the other is retained.

56
Q

Two acidotic exceptions to the acidosis/hyperkalemia rule

A

Diarrhoea - because of bicarbonate and K+ loss

Renal tubular acidosis - because distal and proximal types are associated with hypokalemia

57
Q 
A patient presents with these values:
Na: 140
K: 2.5
Cl: 88
pH: 7.55
pCO2: 5.8
bicarbonate: 37
Base excess: +14
What type of disturbance is this?
A

This is metabolic alkalosis with some respiratory compensation.
Classic example of alkalosis with chloride depletion, confirmed by urine electrolytes.
Commonly caused by frequent vomiting and laxative abuse which overexcretes HCl.

58
Q

Chloride-responsive metabolic alkalosis examples

A

Vomiting
Diuretic-induced
Chronic hypercapnia recovery

59
Q

Chloride-resistant metabolic alkalosis examples

A

Mineralocorticoid excess
Severe hypokalemia
Antacids

60
Q

Chloride-responsive alkalosis

A

In metabolic alkalosis, kidneys attempt to increase HCO3- loss, but if chloride is depleted HCO3- needs to be retained to balance electrical charge
If chloride isn’t replaced, this can’t be corrected - kidney keeps reabsorbing HCO3- inappropriately, maintaining alkalosis

61
Q

When should you use a venous blood gas?

A

When pCO2 is not needed and severe circulatory failure is not present
If a patient doesn’t have reasonable perfusion, the values won’t be similar is venous and arterial tests so you have to do an arterial blood gas

62
Q

Negatives of arterial blood gas

A

Arterial puncture is painful and risky for thrombosis and haemorrhage

63
Q

Artefacts observed in blood gases

A

Air in blood-gas syringe can show falsely low pCO2

Delayed separation of plasma from RBCs which can show false lactic acidosis

Genitourinary (6 decks)

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