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NME > Kidney: Acid-Base bBlance > Flashcards

Kidney: Acid-Base bBlance Flashcards

1
Q

What kind of relationship between pH and plasma concentration of CO2

A

Inversely proportional (one goes up the other goes down)

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2
Q

What kind of relationship between pH and HCO3-?

A

Directly proportional

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3
Q

Normal body pH (extracellular fluid)

A

7.35-7.45

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4
Q

What fluctuations of pH does death occur?

A
  • <6.8 (acidosis)
  • > 8.0 (alkalosis)
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5
Q

2 types of sources of acid generation:

A
  • carbolic (volatile) acids (15,000mmol/day)
  • non-carbolic (non-volatile) acids
    (70mmol/day)
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6
Q

Sources of acid generation: carbolic acids:

A
  • generated from metabolism of carbs and
    fats
  • produced as CO2 and converted to H+ and
    HCO3-
  • reconverted back to CO2 in lungs and
    eliminated by the lungs through the loss of
    CO2
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7
Q

Sources of acid generation: Non-carbolic acids:

A
  • generated from metabolism of sulphur
    containing amino acids (proteins)
  • buffered with HCO3- before eliminated by
    the kidneys through loss of H+
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8
Q

2 types of mechanisms of dealing with acid (H+) load:

A
  • buffering
  • elimination
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9
Q

Dealing with acid (H+) load: buffering (seconds):

A
  • bicarbonate in extracellular fluid
  • HPO42- in intracellular fluid
  • carbonate in bones
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10
Q

Dealing with acid (H+) load: elimination:

A
  • increased respiratory drive to increase CO2
    excretion
  • acute response
  • increased hydrogen ion secretion by
    kidneys = chronic sustained response
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11
Q

3 systems

A
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12
Q

Normal ranges:
- blood pH
- urine pH
- blood HCO3-
- blood pCO2

A

Blood pH = 7.35 to 7.45
Urine pH = 4.6 to 8

Blood [HCO3-] = 22 – 26 mmol/L
Blood pCO2 = partial pressure of CO2 = 4.7 – 6.0 kPa
(35 – 45 mmHg)

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13
Q

Renal excretion of acid load in the PCT

A
  • all parts of the nephron can excrete acid
  • main sites are PCT and intercalated cells of
    cortical collecting ducts
  • limited H+ secretion
  • **Na+/H+ exchanger rebasorbs Na+ and
    excretes H+
  • ammonium is secreted into tubular fluid by
    re-absorbing Na+
  • 80%-990% filtered bicarb is re-absorbed
    into systemic circulation
  • pH of ultrafiltrate falls from 7.4 to 6.7 at
    end of PCT
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14
Q

Renal excretion of acid load in cortical collecting ducts:

A
  • HPO42- is most prevalent filtered buffer in
    DCT
  • not lipid soluble
  • DCT urinary pH <5.8
  • intercalated alpha cell
  • ammonium excretion both in PCT and
    direct diffusion of lipid soluble ammonia
    constitutes a major adaptive response to
    acid load
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15
Q

Maintaining renal tubular cell pH:

A
  • decrease in extracellular bicarb
  • increases grad across basolateral
    membrane
  • diffusion out of cell
  • hence lowers tubular cellular pH
  • bicarb constant re-absorption creates
    gradient allowing H+ ions to be secreted
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16
Q

Causes of acid base disorders

A

if diabetes then may present with diabetic ketone acidosis
sepsis causes lactate production
renal failure

17
Q

Case 1: A 28 year old diabetic lady is admitted with high blood sugars following a viral illness.

Arterial blood gas on admission:
PH 7.0 (7.35-7.45), PCO2 3.5 Kpa (4.7-6.0), Bicarbonate 18 mmol/L (22-26)

A
  • metabolic acidosis with compensation
  • ph= acidic
  • CO2 = low = metabolic
  • bicarb = low

pH acidic hence she is acidotic, CO2 low because hypoventilating, kidneys compensating

hence diabetic ketoacidosis

18
Q

Metabolic acidosis with compensation mechanisms

A
19
Q

Case 2: A 72 year old female is admitted with exacerbation of COPD.

Arterial blood gas on admission
PH 7.0 (7.35-7.45), PCO2 8.5 Kpa (4.7-6.0), Bicarbonate 32 mmol/L (22-26)

A
  • pH = low = acidosis
  • CO2 = high = respiratory
  • Bicarb = high = compensation (kidnery re-
    absorbing to combat acid)

respiratory acidosis with compensation

20
Q

Respiratory acidosis with compensation

A
21
Q

Case 3: A 28 year with profuse vomiting for 2 days following a kebab meal.

Arterial blood gas on admission
PH 7.90 (7.35-7.45), PCO2 6.5 Kpa (4.7-6.0), Bicarbonate 32 mmol/L (22-26)

A
  • pH = high = alkalosis
  • CO2 = high = not respiratory but
    compensation
  • bicarb = high = metabolic

Metabolic alkalosis with compensation

22
Q

Metabolic alkalosis with compensation

A
23
Q

Case 4: A 18 year anxious medical student is admitted with palpitations and light headedness a day before their final examination. He was tachypnoeic on admission with respiratory rate of 28/min.

Arterial blood gas on admission
PH 7.90 (7.35-7.45), PCO2 3.2 Kpa (4.7-6.0), Bicarbonate 20 mmol/L (22-26)

A
  • pH = high = alkalosis
  • CO2 = low = alkali = respiratory
  • Bicarb = low = less rebasorbed =
    compensation

Respiratory alkalosis with compensation

24
Q

What are the compensatory responses?

Disorder: Metabolic acidosis

Primary abnormality: rise in plasma acid conc

A) Hyperventilation
B) Reduced ventilation
C) Renal Hydrogen excretion
D) Buffering of acid in extracellular fluid,
cells and bones

A

A) more breathing, expel CO2, acid
C) remove H+
D) combat H+

25
Q

What are the compensatory responses?

Disorder: Metabolic alkalosis

Primary abnormality: rise in plasma bicarb conc

A) Hyperventilation
B) Hypoventilation
C) Reduced renal Hydrogen excretion
D) Reduced renal bicarb re-absorption

A

B) we want acid so we want CO2 so we
hypoventilate
D) we dont want alkali so lower re-uptake of
bicarb

26
Q

What are the compensatory responses?

Disorder: Respiratory acidosis

Primary abnormality: rise in CO2

A) increase renal H+ excretion
B) increase buffering CO2 within Hb
C) Loss of bicarb in urine
D) increased renal bicarb re-absorption

A

A) want to remove acid
B) want to combat acid
D) want more alkali re-uptake

27
Q

What are the compensatory responses?

Disorder: Respiratory alkalosis

Primary abnormality: reduction of CO2

A) increased renal bicarb re-absorption
B) reduced renal H+ excretion
C) Reduced renal ammonium excretion
D) increased renal bicarb excretion

A

B) want acid
D) want to remove alkali

28
Q

Metabolic acidosis is frequently associated with hyperkalaemia or hypokalaemia?

A

Hyperkalaemia (high K+)

29
Q

Metabolic alkalosis is frequently associated with hyperkalaemia or hypokalaemia?

A

Hypokalaemia

30
Q

Metabolic acidosis treatment

A
  • IV sodium bicarb
  • IV furosemide (esp if passing urine)
  • dialysis
31
Q

Metabolic alkalosis treatment:

A
  • IV sodium or Iv potassium chloride
32
Q

Respiratory acidosis treatment:

A

ventilation

33
Q

Respiratory alkalosis treatment:

A

breathing into a paper bag (hyperventilating)

34
Q

Respiratory alkalosis compensation

A

NME (52 decks)

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