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Acid base balance Flashcards

(83 cards)

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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
what is the point of acid-base homeostasis?
to keep pH constant
26
time of buffers
immediate - seconds/ minutes
27
time of respiratory
rapid - minutes/ hours
28
time of renal
slow - hours/ days | small contribution by liver
29
what are the different types of buffers?
proteins phosphate carbonic acid/ bicarbonate
30
protein buffers
albumin in ECF haemoglobin in ICF via histidine residues
31
how do protein buffers work?
negatively charged when in contact with ammonium salt | hydrogen ions attracted to protein
32
phosphate buffer
HPO42- + H+ --> H2PO4- interacts with free H+ ions intracellular
33
carbonic acid/ bicarbonate
main extracellular buffer | involved in metabolic and respiratory regulations
34
carbonic acid/ bicarbonate equation
H2O + CO2 --> H2CO3 --> H+ + HCO3- this is reversible first step requires enzyme carbonic anhydrase to combine water and CO2
35
where does CO2 come from?
respiratory manipulation will affect this
36
where does HCO3- come from?
renal/ metabolic system will affect this
37
respiratory system
``` rise in CO2 positive effect on central chemoreceptors increase firing to medulla stimulates ventilation returns pCO2 to normal ```
38
PCO2
indicates the respiratory component of acid-base balance
39
hypoventilation
increases CO2 in blood
40
hyperventilation
decreases CO2 in blood
41
renal system
bulk of H+ secretion and HCO3- reabsorption is in PCT | final urine acidity is determined by intercalated cells of DCT
42
urine pH
variable 4.5-8
43
impaired renal elimination
acid is constantly being produced and so if there is impaired renal elimination it causes acidosis
44
main renal production/ secretion of H+ ions
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
buffering by bicarbonate
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
buffering by phosphate
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
buffering by ammonia
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
which buffering mechanism is best able to increase capacity?
ammonia buffering
49
final regulation of H+ ions in intercalated cells
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
acidosis
increases H+ excretion at the expense of K+ retention
51
HCO3-
marker of metabolic disturbance not the cause
52
increase H+ ions/ metabolic acid added
shifts carbonate equation to left | so HCO3- falls
53
base excess
extent to which HCO3- exceeds expected value
54
positive BE
metabolic alkalosis
55
negative BE or base deficit
metabolic acidosis
56
anion gap
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
calculating anion gap
[NA+ + K+] - [Cl- + HCO3-] | total cations must equal anions
58
what is normal anion gap?
8-16mmol/L
59
what causes the normal anion gap?
albumin
60
increased anion gap
caused by organic metabolic acidosis | e.g. ketoacids
61
acid-base compensation
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
what are the compensatory mechanisms in acidosis?
respiratory | metabolic compensation
63
respiratory compensation of acidosis
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
metabolic compensation of acidosis
primary respiratory acidosis causes increased CO2 which causes kidney to retain additional HCO3- and excrete more H+
65
alkalosis
opposite changes in compensation
66
respiratory compensation for alkalosis
primary metabolic alkalosis causes reduction in H+ so reduces ventilation
67
metabolic compensation for alkalosis
primary respiratory alkalosis reduced CO2 more H+ retention
68
what are the types of acid-base abnormalities
metabolic acidosis and alkalosis | respiratory acidosis and alkalosis
69
primary diagnostic marker of metabolic acidosis
decreased HCO3- | pH dropped
70
primary diagnostic marker of respiratory acidosis
pH dropped | CO2 increased
71
primary diagnostic marker of metabolic alkalosis
increased HCO3- | increased pH
72
primary diagnostic marker of respiratory alkalosis
pH increased | CO2 reduced
73
3 step solution to working out acid-base imbalances
acidosis or alkalosis respiratory or metabolic compensated or not
74
acidosis or alkalosis
look at pH
75
pH for acidosis
<7.35
76
pH for alkalosis
>7.45
77
if carbon dioxide and bicarbonate affected?
multi system organ failure in compensation
78
compensation
opposite thing will go in same direction as primary problem
79
metabolic acidosis
decreased bicarbonate | compensated by decreased CO2
80
metabolic alkalosis
increased bicarbonate | compensated by increased CO2
81
respiratory acidosis
increased CO2 | compensated by increased bicarbonate
82
respiratory alkalosis
decreased CO2 compensated by decreased bicarbonate
83
blood pH
only reflects ECF pH

Renal system (17 decks)

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