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Spr2015_Week5 > Acid/Base Physiology > Flashcards

Acid/Base Physiology Flashcards

1
Q

what is the pH compatible with life

A

6.8-7.8

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2
Q

What does Ka describe

A

HA (weak acid) H+ + A- (conjugate base)

Ka = [H+][A-] / [HA]

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3
Q

what is henderson-hasselbalch equation

A

pH = pKa + log ([A-] / [HA])

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4
Q

pKa

A

pH where concentration of conjugate base and weak acid are equal

we want pKa near pH (best buffer to accept H+ and anions)

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5
Q

what are intracellular buffers (3)

A

1) organic phsophates
2) proteins
3) Hb

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6
Q

what are extracellular buffers (4)

A

1) proteins
2) albumin
3) phosphate
4) bicarbonate

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7
Q

what is the bicarbonate buffering system equation

A

H2O + CO2 H2CO3 H+ + HCO3-

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8
Q

what does K1 of bicarbonate buffering system describe

what enzyme catalyzes the reaction

A

H2O + CO2 H2CO3

catalyzed by carbonic anhydrase

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9
Q

what does K2 of bicarbonate buffering system describe

A

H2CO3 H+ + HCO3-

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10
Q

how can we rewrite Henderson-Hasselbalch in terms of [HCO3-]

A

assume H2CO3 rapidly converted to H+ + HCO3-

therefore,
pH = pKa + log ( [HCO3-]/[CO2] )

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11
Q

how can we rewrite
pH = pKa + log ( [HCO3-]/[CO2] )

for bicarb buffering system

A 
[CO2]  = 0.03 x PaCO2 
pKa = 6.1

pH = 6.1 + log [HCO3-] / (0.03 x PaCO2)

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12
Q

what is the pH of an arterial blood sample normally

A

substitute
[HCO3-] = 24 meq/L
PaCO2 = 40 Torr

pH = 7.40 `

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13
Q

what is normal arterial pH range

how does it change in Denver

A

normal pH = 7.38-7.43

higher in denver

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14
Q

what is normal venous pH range

A

7.34 - 7.37

lower than arterial because carrying more CO2

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15
Q

why is venous pH slightly lower and venous pCO2 slightly higher (~45 Torr) than arterial blood despite amount of CO2 being carried

A

deoxyhemoglobin is a good buffer

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16
Q

venous pH is slightly ____ than arterial blood

A

lower

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17
Q

venous pCO2 is slightly ___ than arterial blood

A

higher

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18
Q

what is acidemia

how does that affect pH

A

more acid in blood than normal

lower pH

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19
Q

what is alkalemia

how does that affect pH

A

more base (or less acid) in blood than normal

higher pH > 7.40

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20
Q

how does the body compensate to normalize pH (2 ways)

A

1) lungs regulate CO2 levels (minutes)

2) kidneys regulate bicarbonate (hours to days)

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21
Q

compensation will ____ completely correct to normal pH (nor will it over-compensate)

A

NEVER !!!

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22
Q

compensation will ____ completely correct to ____

A

normal pH or over-compensate

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23
Q

What is respiratory acidosis

how does that affect pH

due to?

A

too much CO2, incr PaCO2 in denominator

lower pH

due to ineffective ventilation

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24
Q

respiratory acidosis is acute, chronic, or both

A

both

acute before kidneys compensate

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25
Q

what are compensation rules for
1) acute resp acidosis

2) chronic resp acidosis

A

acute = for every 10 Torr incr in CO2, pH decr by 0.08

chronic = for every 1 Torr incr in CO2, HCO3- incr about 0.4 meq/L

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26
Q

too much CO2, incr PaCO2 in denominator

lower pH

due to ineffective ventilation

A

respiratory acidosis

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27
Q

a

A

a

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28
Q

what are acute causes of resp acidosis

A

1) CNS depressants (opiates, benzodiazepines, alcohol most common)
2) Respiratory muscle fatigue (increased work of breathing)

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29
Q

what are chronic causes of resp acidosis

A

1) Central hypoventilation (e.g. obesity hypo- ventilation syndrome)
2) Neuromuscular disease (e.g. ALS)
3) Chronic lung diseases (emphysema, bronchiectasis, etc)
4) Hypothyroidism

30
Q

a

A

a

31
Q

define resp alkalosis

how does that affect pH

A

too little CO2, decr PaCO2, decr denominator

higher pH

32
Q

what is resp alkalosis most commonly due to?

A

incr ventilation

33
Q

resp alkalosis can be acute, chronic, or both

A

both

34
Q

what are compensation rules
1) acute resp alkalosis

2) chronic resp alkalosis

A

SAME AS RESPIRATORY ACIDOSIS

1) acute = for every 10 Torr decrease in CO2, pH increases by 0.08
2) chronic = for every 1Torr decrease in CO2, HCO3- decreases about 0.4 meq/L

35
Q

acute causes of resp alkalosis

A

1) Pain
2) Anxiety/Panic attack
3) Fever (inflamm cascade –> resp sensing)
4) Mechanical Ventilation

36
Q

what are chronic causes of resp alkalosis

A

1) Living at altitude
2) Brain injury
3) Chronic aspirin toxicity (activ CNS)
4) Pregnancy

37
Q

too little CO2, decr PaCO2, decr denominator

higher pH

incr ventilation

A

respiratory alkalosis

38
Q

a

A

a

39
Q

define metabolic acidosis

how does that affect pH

A

too much acid, decr [HCO3-]

decr pH

40
Q

in metabolic acidosis ___ compensation is quite rapid with incr ventilation –> decr pCO2

A

respiratory compensation

–> leads to respiratory alkalosis

41
Q

in metabolic acidosis respiratory compensation is quite rapid with ___

A

incr ventilation –> decr pCO2

42
Q

compensation rules for metabolic acidosis

winter’s formula ***MEMORIZE

A

expected pCO2 = 1.5 [HCO3-] + 8 +/- 2

Winter’s formula

43
Q

2 categories of metabolic acidosis

A

1) anion gap

2) non-anion gap

44
Q

describe anion gap in metabolic acidosis
what is normal value

what does it it indicate

A

Anion Gap = [Na+] – ([Cl-] + [HCO3-])
normally 12-14

indicates additional acid that is buffered by bicarbonate, incr amount of unmeasured anions
(incr HA, decr HCO3-, incr A-)

45
Q

describe non-anion gap in metabolic acidosis

what is it caused by

A

caused by loss of bicarb

46
Q

what are causes of anion gap medically

A

1) methanol
2) uremia
3) DKA (EtOH and starvation)
4) propylene glycol
5) Isoniazid
6) lactate
7) ethylene glycol
`8) salicylates

MUDPILES

47
Q

what are causes of non-anion gap medically

A

1) GI losses = diarrhea
2) renal losses = Renal tubular acidosis
3) too much IV saline (incr Cl- with loss of bicarb)

48
Q

too much acid, decr [HCO3-]

decr pH

A

metabolic acidosis

49
Q

a

A

a

50
Q

define metabolic alkalosis

effect on pH

A

too much [HCO3-],

higher pH

51
Q

____ compensation is rapid with decr ventilation –> incr pCO2

our body will not allow us to ____ to point of hypoxemia

A

respiratory

will not hypoventilate to point of hypoxemia

52
Q

respiratory compensation is rapid with ___

A

decr ventilation –> incr pCO2

will not hypoventilate to point of hypoxemia

53
Q

compensation rules for metabolic alkalosis

A

incr [HCO3-] of 1mEq/L, incr PaCO2 by 0.7 Torr

54
Q

causes of metabolic alkalosis

A

1) vomiting or NG tube suction (loss of gastric acid)
2) Ingestion NaHCO3
3) Ingestion of other alkali (milk-alkali syndrome)
4) Hypovolemia, so-called contraction alkalosis
5) Diuretics

55
Q

CASE
what does this patient have?
why?

emphysema pt with exacerbation with wheezing, tight, shortness of breath
incr work of breathing

A

RESPIRATORY ACIDOSIS

muscles fatigue –> decr Tidal volume –> less effective ventilation, not blowing as much CO2, CO2 incr –> respiratory acidosis

56
Q

too much [HCO3-],

higher pH

A

metabolic alkalosis

57
Q

dangers of metabolic alkalosis (2)

A

1) ventricular arrhythmia

2) seizures

58
Q

dangers of metabolic alkalosis (2)

A

1) ventricular arrhythmia

2) seizures

59
Q

CASE 2
what does this patient have?

Patient presents to the ED with some nausea/vomiting past few days with the following blood gas
pH = 7.07
paco2 = 18 Torr = low
PaO2 = 78 torr = low
[HCO3-] = 5 mEq/L
A

Metabolic acidosis due to DKA

NORMAL OXYGENATION

60
Q

anion gap or non-anion gap acidosis

Patient presents to the ED with some nausea/vomiting past few days with the following blood gas
pH = 7.07= low
paco2 = 18 Torr = low
PaO2 = 78 torr = low
[HCO3-] = 5 mEq/L
[Na+] = 132 mEq/L 
[Cl-] = 94 mEq/L
glucose = 560 mg/dL
AG = 132 - (94 + 5) = 33
A

anion gap metabolic acidosis

61
Q

compensated?

Patient presents to the ED with some nausea/vomiting past few days with the following blood gas
pH = 7.07
paco2 = 18 Torr = low
PaO2 = 78 torr = low
[HCO3-] = 5 mEq/L
[Na+] = 132 mEq/L 
[Cl-] = 94 mEq/L
glucose = 560 mg/dL
AG = 132 - (94 + 5) = 33
A

use WINTER’S FORMULA
Expected PaCO2 = 1.5 (5) + 8 +/ 2 = 7.5 (round up to 8) + 8 +/- 2 = 16 +/- 2

SHOULD BE AROUND ~16 +/- 2

patient’s expected paCO2 = 18 so YES, COMPENSATED

if 24, incomplete compensation

62
Q

CASE 3
what does patient have?

Patient presents with a broken arm

pH = 7.52 = high
PaCO2 = 25 Torr = low 
PaO2 = 85 Torr 
[HCO3-]  = 21 mEq/L
A

acute respiratory alkalosis

high pH
low PaCO2

63
Q

acute or chronic?

Patient presents with a broken arm

pH = 7.52 = high
PaCO2 = 25 Torr = low 
PaO2 = 85 Torr 
[HCO3-]  = 21 mEq/L
A

acute because bicarb is not significantly reduced and paCO2 is nearly 15 points below normal and pH is about 0.12 points above normal which fits clinical rule so acute

64
Q

cause?

Patient presents with a broken arm

pH = 7.52 = high
PaCO2 = 25 Torr = low 
PaO2 = 85 Torr 
[HCO3-]  = 21 mEq/L
A

hyperventilating due to pain when ABG was drawn

65
Q

why is PaO2 higher than expected?

Patient presents with a broken arm

pH = 7.52 = high
PaCO2 = 25 Torr = low 
PaO2 = 85 Torr 
[HCO3-]  = 21 mEq/L
A

PaO2 is higher than expected because PaO2 PaO2 is what predicted by alveolar gas equation for reduced PaCO2

66
Q

CASE 3
what does he have?
N/V for past few days

pH = 7.53 = high
PaCO2 = 42 Torr
PaO2 = 110 Torr
[HCO3-] = 36 mEq/L
A

metabolic alkalosis

67
Q

is compensation appropriate?
why is he not hypoventilating?

N/V for past few days

pH = 7.53 = high
PaCO2 = 42 Torr
PaO2 = 110 Torr
[HCO3-] = 36 mEq/L
A

Metabolic alkalosis with incomplete compensation

expected PaCO2 = 14 x 0.7 = 10
[HCO3-] = 14 mEq/L and PaCO2 should incr by 0.7

INCOMPLETE but won’t hypoventilate to hypoxemia

in order to incr PaCO2 by 10 points you hypoventilate to point of hypoxemia which the resp centers in the brain generally will not allow

68
Q

cause?

N/V for past few days

pH = 7.53 = high
PaCO2 = 42 Torr
PaO2 = 110 Torr
[HCO3-] = 36 mEq/L
A

loss of gastric acid
contraction alkalosis
elevated PaO2 because he was on supplemental oxygen

69
Q

CASE 4
what does he have?

patient was stuporous
Pulse ox shows Sp02 = 85%

pH = 7.31  = high
PaCO2 = 48 = high
PaO2 = 55 Torr
[HCO3-] = 23 mEq/L
A

respiratory acidosis

70
Q

acute or chronic?

patient was stuporous
Pulse ox shows Sp02 = 85%

pH = 7.31  = high
PaCO2 = 48 = high
PaO2 = 55 Torr
[HCO3-] = 23 mEq/L
A

acute, within hours

bicarb is normal and approx 10 Torr change in PaCO2, pH has decr about 0.08

71
Q

cause?

patient was stuporous
Pulse ox shows Sp02 = 85%

pH = 7.31  = high
PaCO2 = 48 = high
PaO2 = 55 Torr
[HCO3-] = 23 mEq/L
A

urine positive for opiates = heroin

72
Q

Why is he hypoxemic?

patient was stuporous
Pulse ox shows Sp02 = 85%

pH = 7.31  = high
PaCO2 = 48 = high
PaO2 = 55 Torr
[HCO3-] = 23 mEq/L
A

Check A-a gradient

A-a gradient = (630-47) x 0.21 - 48/0.8 - 55 = 7

R = 0.8
Observed PaO2 = 55

NORMAL = 10 can incr with age

so why PaO2?
because CO2 high, alveoli only have so much room so CO2 high
no problem transfer O2 but CO2 problem

so hypoventilation causing hypoxemia
no p

Spr2015_Week5 (19 decks)

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