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5. ADV PHYS > Disturbances in acid-base balance > Flashcards

Disturbances in acid-base balance Flashcards

1
Q

list (3) criteria for acid-base balance in body:

A
  • arterial blood pH (7.35-7.45)
  • arterial plasma [HCO3-] normal range (22-26 mM)
  • arterial pCO2, normal range (35-45 mmHg)
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2
Q

normal values of arterial: pH, plasma HCO3-, and pCO2

A
  • pH: 7.4
  • arterial plasma HCO3-: 24mM
  • arterial pCO2: 40mmHg
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3
Q

list (2) types of disturbances to acid base balance:

A
  • respiratory og

- metabolic og

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4
Q

define respiratory disturbance:

A
  • shift pH by altering pCO2
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5
Q

define metabolic disturbance:

A
  • shift pH due to abnormal conc of HCO3-
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6
Q

changes in pCO2 what can’t buffer this? and new equation shifts

A
  • carbonate buffers can’t cont to buffering

equation shifts to R:
CO2 + H2O H + HCO3

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7
Q

if HCO3- increases how about H+?

A
  • doesn’t really affect it

- if double CO2, must double (HCO3- and H+)

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8
Q

H2CO3 will dissociate into

A
  • noncarbonate buffers bind H+
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9
Q

general body compensation to disturbed acid base balance:

A
  • ratio of [HCO3]/pCO2 towards normal = ECF pH returned to almost 7.4
  • BUT these mechanisms won’t correct cause of change (abnormal pCO2, or [HCO3-] so acid base balance not restored
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10
Q

disturbance of acid base balance only corrected when:

A
  • pH
  • pCO2
  • [HCO3-] all back to normal values
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11
Q

respiratory acidosis: how it forms

A
  • insufficient CO2 excreted through lungs to balance that prod by cells of body
  • pCO2 increases to >45 mmHg
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12
Q

respiratory acidosis: HH equation

A

when pH decreases, HCO3-/CO2 ration decreases

- arterial pH ~7.18

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13
Q

respiratory acidosis: non carbonate buffers involved

A

haemoglobin bind some additional H+

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14
Q

respiratory acidosis: how does HCO3- increase and result

A
  • increased reab/regeneration of HCO3- by kidney tubules cause HCO3- in body

= if increase [HCO3-], increase CO2

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15
Q

respiratory acidosis: balance of initial rise of pCO2, and time taken

A
  • nearly balanced by increase HCO3-
  • pH nearly normal
  • compensation slow (kidney) 2-5 days
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16
Q

respiratory acidosis: how is acid base balance properly fixed

A
  • increased excretion of CO2 through lungs
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17
Q

respiratory acidosis: list causes (3)

A
  • chronic lung diseases (bronchitis, emphysema = smokers)
  • airway obstruction, chest injury
  • inhibited central respiratory drive due to brain damage, anaesthetics, morphine (heroin), barbiturates
18
Q

respiratory alkalosis: define

A

CO2 decreased, affecting ratio

19
Q

respiratory alkalosis: if too much CO2 removed

A
  • increases ratio = pH increases (7.62)
  • noncarbonate buffers used (haemoglobin) releasing bound H+
  • reduced reab/generation of HCO3- by kidney compensates increased pH = decreases ECF [HCO3-]
  • so partially restoring pH (7.49)
  • but normal breathing needed to return acid base balance to normal
20
Q

respiratory alkalosis: list causes (3)

A
  • hypoxia at high altitudes (>4500m) increase in alveolar ventilation -> resp alk reduced pCO2 on central chemoreceptors overridden by peripheral chemoreceptors in response to low pO2
  • over breathing: due to sepsis, fever, brain damage, hysteria
  • pregnancy: over breathing due to progesterone effect on brain, lowering pCO2 to 30mmHg, to compensate [HCO3-] decreases to 18-20mM returning pH to 7.44 ‘normal’ value
21
Q

metabolic acidosis: define

A
  • acidosis caused by low ECF [HCO3-]
22
Q

metabolic acidosis: features

A
  • addition of non carbonate acid to body
  • HCO3- reduced by buffering excess acid

OR HCO3- lost directly

23
Q

metabolic acidosis: effect on equation and time taken

A
  • [HCO3-] decreases, so pH decrease (7.16)
  • fall in pH detected, peripheral chemoreceptors breathing increases = lowering pCO2
  • compensation within 12 hrs (7.29)
24
Q

metabolic acidosis: what is needed to properly correct acid base balance

A
  • increase in reabsorption and generation of HCO3-
25
Q

metabolic acidosis: list causes (4)

A
  • diarrhoea: excess secretion of HCO3- into intestine causes acidification of ECF
  • lactic acidosis: from hypoxia limiting ox phos and gluconeogenesis (esp mm and liver), assoc w strenous ex + dehydration, redist of blood flow from splanchnic circulation. also cardiac arrest causing hypoxia so emergency treatment in patient requiring CPR often includes admin of Ad and NaHCO3-
  • diabetic ketoacidosis: production of ketoacid from fatty acids, cause life threatening drop in HCO3-, starvation, alcoholic ketoacidosis (milder effects on pH)
  • renal failure leading to inadequate HCO3-, reabsorption/ regeneration by kidneys
26
Q

metabolic alkalosis: define

A
  • increased [HCO3-]
27
Q

metabolic alkalosis: features

A
  • loss of non carbonate acid

- less than usual HCO3- removed from body, so increasing pH

28
Q

metabolic alkalosis: effect and equations

A
  • increased pH from increased [HCO3-] (7.58)

- compensation by resp sys slows breathing rate, increasing pCO2 and reducing elevated pH (7.49)

29
Q

metabolic alkalosis: why doesn’t reducing [HCO3-] reabsorption by kidney correct this?

A
  • not as simple

- requires renal reab of HCO3- to continue despite excess HCO3-

30
Q

metabolic alkalosis: factors maintaining renal reabsorption of HCO3- despite elevated CSF [HCO3-] are (3)

A
  • vol depletion,
  • low K
  • aldosterone excess
31
Q

metabolic alkalosis: causes (1) and eg.

A
  • vomiting expels HCl from stomach
  • replacement of lost acid causes addition of HCO3- to ECF
  • Na and K also lost in expelled gastric fluid
  • renal reabsorption of HCO3- initially halted so excess HCO3- excreted but counter ion (Na) must also be excreted
  • eventually causes reduction in total body Na content, reduced ECF vol
  • RAS sys activated and aldosterone will increase Na reabsorption and K excretion leading to hypokalaemia and HCO3- reab = meta alk established
  • even when gastric losses cease meta alk, can’t be corrected
32
Q

metabolic alkalosis: properly correct how eg.

A
  • ECF vol is restored

- chicken soup, oral rehydration solution

33
Q

1˚ change: respiratory acidosis

A

pCO2 up

34
Q

1˚ change: respiratory alkalosis

A

pCO2 down

35
Q

1˚ change: metabolic acidosis

A

[HCO3-] down

36
Q

1˚ change: metabolic alkalosis

A

[HCO3-] up

37
Q

2˚ change: respiratory acidosis

A

[HCO3-] up

38
Q

2˚ change: respiratory alkalosis

A

[HCO3-] down

39
Q

2˚ change: metabolic acidosis

A

pCO2 down

40
Q

2˚ change: metabolic alkalosis

A

pCO2 up

41
Q

what increases pH:

A

[HCO3-]

42
Q

what decreases pH:

A

pCO2

5. ADV PHYS (10 decks)

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