Acid/Base Physiology Flashcards by A B

what is the pH compatible with life

6.8-7.8

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What does Ka describe

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

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

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what is henderson-hasselbalch equation

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

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pKa

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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what are intracellular buffers (3)

1) organic phsophates
2) proteins
3) Hb

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what are extracellular buffers (4)

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

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what is the bicarbonate buffering system equation

H2O + CO2 H2CO3 H+ + HCO3-

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what does K1 of bicarbonate buffering system describe

what enzyme catalyzes the reaction

H2O + CO2 H2CO3

catalyzed by carbonic anhydrase

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what does K2 of bicarbonate buffering system describe

H2CO3 H+ + HCO3-

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

assume H2CO3 rapidly converted to H+ + HCO3-

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

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

for bicarb buffering system

[CO2]  = 0.03 x PaCO2 
pKa = 6.1

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

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what is the pH of an arterial blood sample normally

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

pH = 7.40 `

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what is normal arterial pH range

how does it change in Denver

normal pH = 7.38-7.43

higher in denver

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what is normal venous pH range

7.34 - 7.37

lower than arterial because carrying more CO2

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

deoxyhemoglobin is a good buffer

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venous pH is slightly ____ than arterial blood

lower

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venous pCO2 is slightly ___ than arterial blood

higher

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what is acidemia

how does that affect pH

more acid in blood than normal

lower pH

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what is alkalemia

how does that affect pH

more base (or less acid) in blood than normal

higher pH > 7.40

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

1) lungs regulate CO2 levels (minutes)

2) kidneys regulate bicarbonate (hours to days)

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

NEVER !!!

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compensation will ____ completely correct to ____

normal pH or over-compensate

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What is respiratory acidosis

how does that affect pH

due to?

too much CO2, incr PaCO2 in denominator

lower pH

due to ineffective ventilation

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respiratory acidosis is acute, chronic, or both

both

acute before kidneys compensate

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what are compensation rules for 1) acute resp acidosis 2) chronic resp acidosis

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

too much CO2, incr PaCO2 in denominator lower pH due to ineffective ventilation

respiratory acidosis

what are acute causes of resp acidosis

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

what are chronic causes of resp acidosis

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

# define resp alkalosis how does that affect pH

too little CO2, decr PaCO2, decr denominator higher pH

what is resp alkalosis most commonly due to?

incr ventilation

resp alkalosis can be acute, chronic, or both

both

what are compensation rules 1) acute resp alkalosis 2) chronic resp alkalosis

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

acute causes of resp alkalosis

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

what are chronic causes of resp alkalosis

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

too little CO2, decr PaCO2, decr denominator higher pH incr ventilation

respiratory alkalosis

# define metabolic acidosis how does that affect pH

too much acid, decr [HCO3-] decr pH

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

respiratory compensation --> leads to respiratory alkalosis

in metabolic acidosis respiratory compensation is quite rapid with ___

incr ventilation --> decr pCO2

compensation rules for metabolic acidosis winter's formula ***MEMORIZE

expected pCO2 = 1.5 [HCO3-] + 8 +/- 2 | Winter's formula

2 categories of metabolic acidosis

1) anion gap | 2) non-anion gap

describe anion gap in metabolic acidosis what is normal value what does it it indicate

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-)

describe non-anion gap in metabolic acidosis | what is it caused by

caused by loss of bicarb

what are causes of anion gap medically

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

what are causes of non-anion gap medically

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

too much acid, decr [HCO3-] decr pH

metabolic acidosis

# define metabolic alkalosis effect on pH

too much [HCO3-], higher pH

____ compensation is rapid with decr ventilation --> incr pCO2 our body will not allow us to ____ to point of hypoxemia

respiratory will not hypoventilate to point of hypoxemia

respiratory compensation is rapid with ___

decr ventilation --> incr pCO2 will not hypoventilate to point of hypoxemia

compensation rules for metabolic alkalosis

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

causes of metabolic alkalosis

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

CASE what does this patient have? why? emphysema pt with exacerbation with wheezing, tight, shortness of breath incr work of breathing

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

too much [HCO3-], higher pH

metabolic alkalosis

dangers of metabolic alkalosis (2)

1) ventricular arrhythmia | 2) seizures

dangers of metabolic alkalosis (2)

1) ventricular arrhythmia | 2) seizures

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 ```

Metabolic acidosis due to DKA NORMAL OXYGENATION

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 ```

anion gap metabolic acidosis

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 ```

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

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 ```

acute respiratory alkalosis high pH low PaCO2

acute or chronic? Patient presents with a broken arm ``` pH = 7.52 = high PaCO2 = 25 Torr = low PaO2 = 85 Torr [HCO3-] = 21 mEq/L ```

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

cause? Patient presents with a broken arm ``` pH = 7.52 = high PaCO2 = 25 Torr = low PaO2 = 85 Torr [HCO3-] = 21 mEq/L ```

hyperventilating due to pain when ABG was drawn

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 ```

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

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 ```

metabolic alkalosis

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 ```

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

cause? N/V for past few days ``` pH = 7.53 = high PaCO2 = 42 Torr PaO2 = 110 Torr [HCO3-] = 36 mEq/L ```

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

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 ```

respiratory acidosis

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 ```

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

cause? patient was stuporous Pulse ox shows Sp02 = 85% ``` pH = 7.31 = high PaCO2 = 48 = high PaO2 = 55 Torr [HCO3-] = 23 mEq/L ```

urine positive for opiates = heroin

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 ```

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

Acid/Base Physiology Flashcards

(72 cards)