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Renal system > Acid base balance > Flashcards

Acid base balance Flashcards

1
Q

What information is included in arterial blood gas?

A 
pH
pCO2
pO2
HCO3-
BE
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2
Q

normal pH

A

7.35-7.45

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3
Q

normal pCO2

A

5.1-5.5KPa

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4
Q

normal PO2

A

11.5-14.5kpa

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5
Q

HCO3-

A

24-28mmol/L

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6
Q

Base excess

A

0 (-1 to +1)

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7
Q

in A&E

A

use venous blood gas as less invasive, but less accurate.

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8
Q

why is acid-base important?

A 
enzyme function
electrolyte regulation
drug ionisation
good diagnostic guide 
monitoring therapy
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9
Q

acid-base

A

acid production and acid elimination balance

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10
Q

acid production

A

respiratory

metabolic

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11
Q

respiratory production of acid

A

carbonic acid from CO2

0.5kg/day

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12
Q

metabolic production. of acid

A

organic - lactic, amino, hydroxybutyric acids
inorganic - suplfuric and phosphoric
80mmol/day = inorganic

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13
Q

acidic/ alkaline secretions

A

In gastric and pancreatic physiology

if either is lost in substantial quantities acid/base disturbance can result

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14
Q

gastric

A

high H+

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15
Q

pancreatic

A

high HCO3-

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16
Q

acid elimination

A

respiratory

metabolic

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17
Q

respiratory acid elimination

A

ventilation removes CO2

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18
Q

metabolic acid elimination

A

inorganic acids - excreted by kidneys unchanged

organic acids - generally undergo liver metabolism

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19
Q

lactate metabolism

A

to CO2 and water or back to glucose in cori cycle

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20
Q

pH

A

-log[H+]

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21
Q

pH scale

A

logarithmic scale
wide range encountered so easier scale to use
a small change in pH is a big change in H+

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22
Q

pH of plasma

A

7.4

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23
Q

pH of stomach

A

2

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24
Q

how to keep pH constant?

A

buffers
respiratory
renal/ metabolic

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25
Q

what is the point of acid-base homeostasis?

A

to keep pH constant

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26
Q

time of buffers

A

immediate - seconds/ minutes

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27
Q

time of respiratory

A

rapid - minutes/ hours

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28
Q

time of renal

A

slow - hours/ days

small contribution by liver

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29
Q

what are the different types of buffers?

A

proteins
phosphate
carbonic acid/ bicarbonate

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30
Q

protein buffers

A

albumin in ECF
haemoglobin in ICF
via histidine residues

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31
Q

how do protein buffers work?

A

negatively charged when in contact with ammonium salt

hydrogen ions attracted to protein

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32
Q

phosphate buffer

A

HPO42- + H+ –> H2PO4-
interacts with free H+ ions
intracellular

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33
Q

carbonic acid/ bicarbonate

A

main extracellular buffer

involved in metabolic and respiratory regulations

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34
Q

carbonic acid/ bicarbonate equation

A

H2O + CO2 –> H2CO3 –> H+ + HCO3-
this is reversible
first step requires enzyme carbonic anhydrase to combine water and CO2

35
Q

where does CO2 come from?

A

respiratory manipulation will affect this

36
Q

where does HCO3- come from?

A

renal/ metabolic system will affect this

37
Q

respiratory system

A 
rise in CO2
positive effect on central chemoreceptors
increase firing to medulla 
stimulates ventilation 
returns pCO2 to normal
38
Q

PCO2

A

indicates the respiratory component of acid-base balance

39
Q

hypoventilation

A

increases CO2 in blood

40
Q

hyperventilation

A

decreases CO2 in blood

41
Q

renal system

A

bulk of H+ secretion and HCO3- reabsorption is in PCT

final urine acidity is determined by intercalated cells of DCT

42
Q

urine pH

A

variable 4.5-8

43
Q

impaired renal elimination

A

acid is constantly being produced and so if there is impaired renal elimination it causes acidosis

44
Q

main renal production/ secretion of H+ ions

A

CO2 and H2o –> H2CO3 –> H+ + HCO3-
H+ into tubule lumen and Na+ into tubular cell by Na+/H+ antiporter
H+ is buffered by bicarbonate, phosphate or ammonia in tubule
cotransport takes carbonate into blood with and sodium

45
Q

buffering by bicarbonate

A

filtered bicarbonate ion from glomerulus
combines with H+ ion from antiporter to form bicarbonate
carbonic anhydrase on lumen side of tubular cell which forms CO2 and H2O which can filter back into tubular cell and into blood stream and split again

46
Q

buffering by phosphate

A

filtered phosphate ion from glomerulus
combines with H+
H2PO4- excreted in urine
a buffered H+ causes an HCO3- to be added to the blood

47
Q

buffering by ammonia

A

glutamine converted to NH3 in tubular cell and filtered out into lumen
H+ ion transported out of tubular cell to lumen combines with NH3 to form NH4+
which is excreted in urine
buffered H+ ion causes HCO3- to be added to blood

48
Q

which buffering mechanism is best able to increase capacity?

A

ammonia buffering

49
Q

final regulation of H+ ions in intercalated cells

A

DCT
K+/H+ antiporter
transports potassium from lumen into intercalated cell and H+ into lumen
decreases pH in urine
potassium pumped into blood by transporter and back into intercalated cell by Na+/K+ pump

50
Q

acidosis

A

increases H+ excretion at the expense of K+ retention

51
Q

HCO3-

A

marker of metabolic disturbance not the cause

52
Q

increase H+ ions/ metabolic acid added

A

shifts carbonate equation to left

so HCO3- falls

53
Q

base excess

A

extent to which HCO3- exceeds expected value

54
Q

positive BE

A

metabolic alkalosis

55
Q

negative BE or base deficit

A

metabolic acidosis

56
Q

anion gap

A

measure to help identify the cause of metabolic acidosis - either disturbance of organic or inorganic acids
organic cause = raised anion gap
inorganic cause = normal anion gap

57
Q

calculating anion gap

A

[NA+ + K+] - [Cl- + HCO3-]

total cations must equal anions

58
Q

what is normal anion gap?

A

8-16mmol/L

59
Q

what causes the normal anion gap?

60
Q

increased anion gap

A

caused by organic metabolic acidosis

e.g. ketoacids

61
Q

acid-base compensation

A

if one system fails the other attempts to compensate
speed depends on the system involved
if underlying disease present it will not be normal again

62
Q

what are the compensatory mechanisms in acidosis?

A

respiratory

metabolic compensation

63
Q

respiratory compensation of acidosis

A

primary metabolic acidosis
increased H+ acts on peripheral chemoreceptors in aortic and carotid bodies
fires to medulla to increase ventilation
H+ cannot cross BBB

64
Q

metabolic compensation of acidosis

A

primary respiratory acidosis causes increased CO2 which causes kidney to retain additional HCO3- and excrete more H+

65
Q

alkalosis

A

opposite changes in compensation

66
Q

respiratory compensation for alkalosis

A

primary metabolic alkalosis causes reduction in H+ so reduces ventilation

67
Q

metabolic compensation for alkalosis

A

primary respiratory alkalosis
reduced CO2
more H+ retention

68
Q

what are the types of acid-base abnormalities

A

metabolic acidosis and alkalosis

respiratory acidosis and alkalosis

69
Q

primary diagnostic marker of metabolic acidosis

A

decreased HCO3-

pH dropped

70
Q

primary diagnostic marker of respiratory acidosis

A

pH dropped

CO2 increased

71
Q

primary diagnostic marker of metabolic alkalosis

A

increased HCO3-

increased pH

72
Q

primary diagnostic marker of respiratory alkalosis

A

pH increased

CO2 reduced

73
Q

3 step solution to working out acid-base imbalances

A

acidosis or alkalosis
respiratory or metabolic
compensated or not

74
Q

acidosis or alkalosis

A

look at pH

75
Q

pH for acidosis

76
Q

pH for alkalosis

77
Q

if carbon dioxide and bicarbonate affected?

A

multi system organ failure in compensation

78
Q

compensation

A

opposite thing will go in same direction as primary problem

79
Q

metabolic acidosis

A

decreased bicarbonate

compensated by decreased CO2

80
Q

metabolic alkalosis

A

increased bicarbonate

compensated by increased CO2

81
Q

respiratory acidosis

A

increased CO2

compensated by increased bicarbonate

82
Q

respiratory alkalosis

A

decreased CO2 compensated by decreased bicarbonate

83
Q

blood pH

A

only reflects ECF pH

Renal system (17 decks)

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