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Pulmonary Week 2 > ICL 2.8: Introduction to Acid-Base Physiology > Flashcards

ICL 2.8: Introduction to Acid-Base Physiology Flashcards

1
Q

what is the equation for pH?

A

pH = -log[H+]

pH = pK + log[A]/[HA]

it’s a measurement of H+ in the concentration

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2
Q

what pH is acidemia and alkalemia?

A

acidemia: pH < 7.4
alkalemia: pH > 7.4

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3
Q

what is acidosis vs. alkalosis?

A

processes that cause arterial blood pH to become higher than/lower than 7.4

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4
Q

what are the fixed/nonvolatile acid sources of acid?

A
  1. sulfuric acid
  2. phosphoric acid
  3. hydrochloric acid
  4. lactic acid
  5. acetoacetic and butyric acid

CO2 is the major volatile source of acid

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5
Q

which 3 systems in the body control pH?

A
  1. buffer systems (short term; instantaneous)
  2. lungs (minutes; removes CO2)
  3. kidneys (hours)
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6
Q

how do the kidneys balance pH in the body?

A
  1. acids are excreted as fixed acids and NH4+ if there’s acidosis
  2. reabsorption/generation/secretion of HCO3- during alkalosis

they have a long term effect on pH

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7
Q

what are the 4 major buffer systems in the body?

A
  1. extracellular bicarbonate buffer: H2CO3 ⇋ H+ + HCO3-
  2. intracellular protein buffer: HB ⇋ H+ + HHB
  3. phosphate buffer: H2PO4 ⇋ H+ + HPO4-
  4. ammonia buffer: NH4+⇋ H+ + NH3

these buffers don’t eliminate or add H+, they just keep them tied up temporarily till the body can figure stuff out

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8
Q

what is the most important extracellular buffer?

A

bicarbonate buffer

H2CO3 ⇋ H+ + HCO3-

this is important because that means this is the buffer that works the most in the blood!

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9
Q

what is the most important intracellular buffer?

A

intracellular protein buffer

HB ⇋ H+ + HHB

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10
Q

what is the henderson hasselbach equation for the bicarbonate buffer system?

A

CO2 + H2O ⇋ H2CO3 ⇋ H+ + HCO3-

pH = pK + log[HCO3-]/[CO2]+[H2CO3]

BUT H2CO3 dissociated pretty quickly so really you can kind of ignore it and the equation would be:

pH = pK + log[HCO3-]/[CO2]

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11
Q

what is the normal HCO3- concentration?

A

24 mEq/L

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12
Q

what differentiates metabolic vs. respiratory acidosis/alkalosis?

A

processes that initially alter [HCO3-] is metabolic –> the respiratory system will attempt to correct metabolic acid-base imbalance

processes that alters PCO2 is respiratory –> the kidneys will work to correct imbalances caused by respiratory disease

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13
Q

which criteria signifies respiratory acidosis vs. alkalosis and metabolic acidosis vs. alkalosis?

A

DECREASED PH
1. if PaCO2 is increased = respiratory acidosis

  1. if [HCO3-] is decreased it’s metabolic acidosis

INCREASED PH
1. if decreased PaCO2 = respiratory alkalosis

  1. if increased [HCO3-] = metabolic alkalosis

pH = pK + log[HCO3-]/[CO2]

CO2 + H2O ⇋ H2CO3 ⇋ H+ + HCO3-

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14
Q

what causes respiratory acidosis and alkalosis?

A

failure of the respiratory system to balance pH

PCO2 is the single most important indicator of respiratory inadequacy

PCO2 > 40 mmHg = respiratory acidosis

PCO2 < 40 mmHg = respiratory alkalosis

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15
Q

what conditions cause respiratory acidosis?

A

respiratory acidosis results from processes that cause CO2 retention = increased PaCO2 like:

  1. decreased alveolar ventilation –> shallow breathing, emphysema, sleep apnea, bronchospasm, respiratory center depression due to drugs or trauma
  2. decreased pulmonary fas exchange –> pulmonary edema, pneumonia, cystic fibrosis, or cardiac arrest
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16
Q

what time frame qualifies as acute vs. chronic respiratory acidosis?

A

acute = <24 hours

chronic = > 5 days

this helps you differentiate between metabolic acidosis because kidneys take longer to balance pH

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17
Q

what conditions cause respiratory alkalosis?

A

respiratory alkalosis results form processes that cause excess CO2 removal = decreased PaCO2 like:

  1. central respiratory stimulation –> anxiety, pain, fever, head trauma, brain tumors, vascular accidents, salicylates, pregnancy
  2. peripheral respiratory stimulation –> pulmonary emboli, CHF, pneumonia
  3. mechanical hyperventilation
  4. early gram negative sepsis
  5. hepatic failure
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18
Q

why does fever cause respiratory alkalosis?

A

your body thinks the rise in temperature is due to increased metabolism

so it thinks you’re making more CO2 so then it starts getting rid of more CO2 which actually leads to depression of CO2 levels since there wasn’t actually any extra CO2 to start with

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19
Q

what corrects respiratory acidosis/alkalosis?

A

to correct respiratory acid-base imbalance, renal mechanisms are stepped up

the kidneys take ~ 24 hours for compensation but there’s NO compensation for acute respiratory acidosis/alkalosis

CO2 + H2O ⇋ H+ + HCO3-

  1. in chronic acidosis kidneys retain HCO3- which leads to ↑ PaCO2 and ↑ [HCO3-]

high HCO3- indicates compensation

  1. in chronic alkalosis kidneys eliminate HCO3- which leads to ↓ PaCO2 and ↓ [HCO3-]

low HCO3- indicates compensation

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20
Q

does the kidney compensate for acute respiratory alkalosis/acidosis?

A

nope

there is no compensation for acute respiratory acidosis/alkalosis

this means [HCO3-] will be totally normal since the kidney isn’t doing anything to try and fix the respiratory alkalosis/acidosis so the only thing you’ll see is elevated/decreased PCO2

21
Q

what is the primary cause, compensatory mechanism and pH in respiratory alkalosis?

A

increased pH

primary: decreased pCO2
compensation: decreased HCO3-

CO2 + H2O ⇋ H+ + HCO3-

so when CO2 is low, there will be a shift to the left which will decreased H+ and cause alkalosis

so then to try and compensate, the kidney will excrete HCO3- to try and get things to shift back to the right and increase H+

22
Q

what is the primary cause, compensatory mechanism and pH in respiratory acidosis?

A

decreased pH

primary: increased pCO2
compensation: increased HCO3-

CO2 + H2O ⇋ H+ + HCO3-

so when there’s high CO2, there will be a shift to the right causing acidosis

so then the kidney will try and compensate and try to get things to shift to the left by increased HCO3

23
Q

what causes metabolic acidosis and alkalosis?

A

all pH imbalances except those caused by abnormal blood CO2 levels

they’re indicated by changes in [HCO3-]!!!

normal [HCO3] = 24 mEQ/mL

metabolic acidosis = <24 mEq

metabolic alkalosis = > 24 mEq/mL

24
Q

what conditions cause metabolic acidosis?

A

metabolic acidosis is anything that results from a process that causes a decrease in plasma HCO3- like:

  1. addition of readily dissociated acid –> lactic acidosis, Ketoacidosis, alcohol abuse, ingestion of toxic substances like salicylate, methylene glycol
  2. inability to excrete the normal dietary H+ load –> kidney failure
  3. external loss of [HCO3-] –> diarrhea, renal tubular acidosis
25
Q

how does lactic acidosis lead to metabolic acidosis?

A

metabolic acidosis is anything that results from a process that causes a decrease in plasma HCO3-

so in lactic acidosis, there’s increased H+ which then get neutralized via HCO3- and using all this HCO3- decreases its concentration and causes metabolic acidosis

26
Q

which conditions cause metabolic alkalosis?

A

metabolic alkalosis is anything that results from a process that causes an increase in plasma HCO3- like:

  1. excess loss of H+ from the body –> vomiting (loss of gastric HCl), hyperaldosteronism (renal loss of H+)
  2. intake of excess base (antacids)
  3. excess HCO3- reabsorption (constipation)
  4. loss of Cl- rich fluid or contraction alkalosis (diuretic abuse)
27
Q

how do the lungs try and compensate for metabolic acidosis/alkalosis?

A

respiratory rate can rise and fall depending on change in blood pH

there’s no difference in acute vs. chronic cases (compensation is abrupt so the lungs will be quick enough to react to both chronic and acute metabolic acidosis/alkalosis)

  1. increase in [H+] → more H2CO3 → CO2 blown off with air

↑ rate and depth of breathing (Kussmaul’s respiration)

  1. decrease in [H+] → less H2CO3 → retention of CO2

slow, shallow breathing

28
Q

what is the primary cause, compensatory mechanism and pH in metabolic acidosis?

A

pH is low

primary: low HCO3
compensation: low pCO2

CO2 + H2O ⇋ H+ + HCO3-

29
Q

what is the primary cause, compensatory mechanism and pH in metabolic alkalosis?

A

pH is high

primary: high HCO3
compensation: high pCO2

CO2 + H2O ⇋ H+ + HCO3-

30
Q

man with inhalant abuse. ABG:
pH = 6.95

HCO3 = 2

PCO2 = 9

Na+ = 130

Cl- = 98

diagnosis?

A

acidosis

HCO3 really low = acidosis

PCO2 really low =alkalosis

PO2 really high

metabolic acidosis with respiratory compensation – he would have tachypnea because his lungs are trying to compensate!

high anion gap (30»12)

31
Q

lady taking TUMS for peptic ulcer. ABG:

pH = 7.46

HCO3 = 34

PCO2 = 49

PO2 = 68

Na = 139

Cl = 95

primary disorder?
compensation?

A

alkalosis

high HCO3 = alkalosis

high PCO2 = acidosis

so he has metabolic alkalosis with respiratory compensation – so she’d have slower breathing

increased HCO3 is from taking all those antacids!

32
Q

what is the anion gap?

A

the difference between unmeasured anionic and cationic electrolytes

you want the sum of cations to be equal to the sum of anions in the body

cations = Na + unmeasured cations

anions = Cl- and HCO3- + unmeasured anions

[Cl-]+[HCO3-]+[unmeasured anions] = [Na+]+[unmeasured cations]

anion gap = [unmeasured anions] – [unmeasured cations] = [Na+] - ([Cl-] + [HCO3-])

33
Q

what are the major cations in the body?

A

Na+

unmeasured cations include:
1. K+

  1. Mg+2
  2. Ca+2
  3. gamma globulins
34
Q

what are the major anions in the body?

A

Cl- and HCO3-

unmeasured anions include:
1. albumin

  1. SO4-2
  2. phosphates
  3. organic anions
35
Q

what makes up most of the anion gap?

A

plasma proteins

albumin specifically is the major component of the normal anion gap!

36
Q

what is the normal anion gap value?

A

12 mEq/L

37
Q

why is the anion gap useful clinically?

A

it’s useful for diagnosing metabolic acidosis!

38
Q

what would lead to a large anion gap?

A

if you have metabolic acidosis, that means there’s a decrease in HCO3-….if HCO3- drops then one of the things that can happen to make sure the body remains electrically neutral is the unmeasured anions are going to increase

when this happens the anion gap increases because there’s increased unmeasured anions and the anion gap = [unmeasured anions] – [unmeasured cations]

ex. organic acidosis: during lactic acidosis or ketoacidosis these acids will dissociate into H+ + A- which means HCO3- will get used up trying to eliminate H+ and A- will contribute to the unmeasured anions!

39
Q

what 3 conditions result in high anion gap metabolic acidosis?

A
  1. accumulation of unmeasured anions –> lactic acidosis or ketoacidosis
  2. loss of unmeasured cations like K+ or Mg+2
  3. presence of ingested drug or toxic substances that gets metabolized to organic acids –> methanol, ethanol, salicylates, ethylene glycol, ammonium chloride

anion gap = [unmeasured anions] – [unmeasured cations]

40
Q

what conditions results in an increase of unmeasured metabolic anions?

A
  1. ketoacidosis –> diabetes mellitus, alcoholism, starvation
  2. lactic acidosis –> hypoxemia; anemia and carbon monoxide; hypovolemic, cardiogenic, or septic shock; strenuous exercise; ARDS
  3. renal insufficiency
41
Q

what is the mnemonic for conditions that can cause high anion gap metabolic acidosis?

A

CAT MUDPILES

C – carbon monoxide, cyanide, CHF, Chronic renal failure

A – ammonium chloride, alcohol ketoacidosis

T – toluene

M – methanol

U – uremia

D – diabetic ketoacidosis

P – propylene glycol, paraldehyde, paracetamol

I – iron, isoniazid

L – lactic acidosis

E – ethylene glycol

S – salicylates poisoning, starvation ketoacidosis, shock

42
Q

what is normal anion gap metabolic acidosis?

A

it results from a loss of HCO3- from the body via GI tract or kidneys like with diarrhea or renal tubular acidosis

HCO3- is replaced by Cl- so the anion gap is normal but H+ isn’t neutralized since HCl will just dissociate since it’s a strong acid and H+ will continue to accumulate

43
Q

what is the mnemonic for conditions that can cause normal anion gap metabolic acidosis?

A

HARDUPS

H – hydrochloric acid, hyperalimentation TPN

A – acetazolamide, Addison’s disease

R – RTA = renal tubular acidosis (Types I, II and IV)

D – diarrhea

U – uretosigmoid fistula

P – pancreaticoduodenal fistula, ↑parathyroidism

S – spironolactone

44
Q

what are mixed acid-base disorders?

A

when acidosis/alkalosis is NOT accompanied by appropriate compensation

so you could have:

  1. low pH (acidosis) with ↓PCO2 but not accompanied by ↓HCO3-
  2. high pH (alkalosis) with ↑HCO3- but not accompanied by ↑PCO2
45
Q

what is the delta gap?

A

delta gap = measured anion gap - baseline anion gap (12)

it’s the difference between the measured anion gap and normal anion gap

so the delta gap added to measured HCO3− should be in the normal range for HCO3− –> ↑ anion gap equal to the ↓ [HCO3-]

a positive delta gap indicates excess HCO3- accumulation (additional presence of ametabolic alkalosis)

a negative delta gap indicates excess H+ accumulation (additional presence of ametabolic acidosis)

∆Gap = AG2 - AG1 = HCO3(1) - HCO3(2)

∆Gap (AG2 - AG1) = [24 - HCO3-] because normal HCO3 is 24

46
Q

what is the anion gap and delta gap and delta delta gap for the following lab values:

Na = 139
Cl = 95
HCO3 = 34
A

AG = 139-(95+34) = 10

∆gap = AG2 - AG1 = 10 - 12 = -2

(12 is the normal anion gap)

∆∆Gap = ∆anion Gap – ∆[HCO3]

= (10-12) - (24-34)
= -2 + 10
= 8

+∆∆gap means metabolic alkalosis

47
Q

what is the equation for ∆Gap?

A

∆gap = AG2 - AG1 = HCO3(1) - HCO3(2)

48
Q

what is the equation for ∆∆Gap?

A

∆∆Gap = (AG2 - AG1) - [HCO3(1) - HCO3(2)] = ∆anion Gap – ∆[HCO3]

49
Q 
a vomiting patient who is also alcoholic show up int he ED. ABG and labs:
Na = 137
K = 3.8
Cl = 90
HCO3 = 22
pH = 7.4
PCO2 = 41
PO2  = 85

diagnosis?
AG?
∆gap?
∆∆gap?

A

AG = 137 - (90+22) = 25 –> high AG which signifies metabolic acidosis

∆gap = AG2- AG1 = 25 - 12 = 13

∆∆gap = ∆AG - ∆HCO3 = 13 - (24-22) = 13-2 = 11

+∆∆gap signifies metabolic alkalosis and accumulation of HCO3-

so he has metabolic acidosis from alcoholic ketoacidosis AND metabolic alkalosis from all the vomiting and loss of acid

Pulmonary Week 2 (9 decks)

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