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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
Renal acidification
Kidneys excrete acid to balance non-volatile acid generated through metabolism
26
Net acid excretion
NAE = ([Urine NH4+] + [Urine titratable acid] + [Urine HCO3-]) x Volume
27
3 main renal processes involved in acid-base balance
1) Bicarbonate reabsorption 2) New bicarbonate generation 3) H+ secretion in distal nephron
28
Acetazolamide
Carbonic anhydrase inhibitor that prevents bicarbonate from being formed from CO2 Causes metabolic acidosis Used in mountaineering to counteract alkalosis due to hyperventilation
29
Renal handling of ammonium
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
Response of the kidney to acidosis
Increased HCO3 and H+ transport along nephron Increased ammoniagenesis Increased availability of urinary buffers ---> renal compensation
31
Expected values in respiratory acidosis with renal compensation
Low pH High pCO2 High bicarbonate High base excess
32
Metabolic acidosis primary change and compensatory response
Decreased bicarbonate | Decrease in pCO2
33
Metabolic alkalosis primary change and compensatory response
Increased bicarbonate | Increase in pCO2
34
Respiratory acidosis primary change and compensatory response
Increased PCO2 | Increase in bicarbonate
35
Respiratory alkalosis primary change and compensatory response
Decreased pCO2 | Decrease in bicarbonate
36
Base excess
Amount of acid or base needed to restore pH to 7.4 Only for metabolic disturbances Positive in alkalosis and negative in acidosis
37
Normal base excess
0 | From -2 to +2
38
``` 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? ```
``` 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
Anion gap
AG = (Na + K) - (Cl + bicarb) Normal range = 14 to 16 Only useful in metabolic acidosis
40
What does a normal anion gap reflect?
Protein anions
41
What does an increased anion gap reflect?
The presence of unmeasured anions e.g. lactate, oxalate etc.
42
Approach to metabolic acidosis
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
Non-anion gap acidosis
Due to urinary acidification or loss of HCO3-
44
Key causes of acidosis with increased anion gap
Lactic acidosis Diabetic ketoacidosis Alcoholic ketoacidosis Renal failure
45
Non-renal causes of normal anion gap acidosis
Diarrhoea Ileostomy External loss of pancreatic or biliary secretions
46
Renal causes of normal anion gap acidosis
Renal tubular acidoses: - proximal - hypokalaemic distal - hyperkalaemic distal
47
Renal tubular acidosis
Defects in acid excretion Urine pH > 5.5 Urine ammonium normal
48
``` 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? ```
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
What childhood deficiency disease is associated with renal tubular acidosis?
Rickets | Vitamin D deficiency
50
If a urine pH is normal in an acidosis, what would the diagnosis be?
Renal tubular acidosis
51
What can urine anion gaps tell you about the ammonium?
In metabolic acidoses: If UAG is positive, there is not enough NH4+ If UAG is negative there is too much NH4+
52
Why are normal anion gap acidoses hyperchloremic?
When bicarbonate is low, extra chloride is needed to maintain the electrical charge because sodium will continue to be reabsorbed
53
Hyperkalemia is associated with:
Acidosis
54
Hypokalemia is associated with:
Alkalosis
55
Which 2 mechanisms describe the association between potassium and acid-base disturbances?
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
Two acidotic exceptions to the acidosis/hyperkalemia rule
Diarrhoea - because of bicarbonate and K+ loss | Renal tubular acidosis - because distal and proximal types are associated with hypokalemia
57
``` 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? ```
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
Chloride-responsive metabolic alkalosis examples
Vomiting Diuretic-induced Chronic hypercapnia recovery
59
Chloride-resistant metabolic alkalosis examples
Mineralocorticoid excess Severe hypokalemia Antacids
60
Chloride-responsive alkalosis
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
When should you use a venous blood gas?
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
Negatives of arterial blood gas
Arterial puncture is painful and risky for thrombosis and haemorrhage
63
Artefacts observed in blood gases
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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