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ANESTHESIA PRACTICE 2 > ACID-BASE REGULATION > Flashcards

ACID-BASE REGULATION Flashcards

1
Q

define acid

A

any substance that acts as a proton (H+) donor

AH A- + H+

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2
Q

name 3 strong acids

A

hydrogen chloride (HCl), sulfuric acid (H2SO4), phosphoric acid (H3PO4)

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3
Q

name 2 weak acids

A

carbonic acid (H2CO3), acetic acid (CH3COOH)

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4
Q

define base

A

any substance that acts as a proton recipient

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5
Q

name 3 strong bases

A 
sodium hydroxide (NaOH), potassium hydroxide (KOH)
B + H+  BH+
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6
Q

name 3 weak bases

A

sodium bicarbonate (NaHCO3), ammonia (NH3), sodium acetate (CH3COONa)

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7
Q

define pH

A

negative decimal logarithm of the hydrogen ion (H+) concentration
pH = -log [H+]

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8
Q

what is the normal pH range of blood?

A

7.35 – 7.45

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9
Q

what is the human basal metabolism rate of CO2 production?

A

13 moles/day (>20 moles with activity)

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10
Q

what values of pH will not sustain life?

A

pH 7.8

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11
Q

what are the mechanisms of equalizing pH?

A
  • buffering
  • respiratory (rapid response to pH disturbance to temporize the problem)
  • renal (ultimate excretion and/or reabsorption of acids (H+)/bases (HCO3-))
  • bone (fast and slow response systems built in to store/release needed elements)
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12
Q

describe buffering

A

weak acids and bases can dissociate, therefore donating/accepting an exogenous proton

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13
Q

define K (dissociation constant)

A

K = (H+ x A-) / (HA)

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14
Q

define the hendersen- hasselbach equation

A

pH = pK + log(A- / HA)

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15
Q

define the steps of the bicarbonate buffer system

A

CO2 + H2O H2CO3 H+ + HCO3-

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16
Q

how is the pH of the bicarbonate system determined?

A

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

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17
Q

why is bicarbonate such an efficient buffer?

A

2-sided elimination (CO2 and HCO3-)

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18
Q

what is the pK of bicarbonate?

A

6.1

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19
Q

which proteins in the protein buffer system have positively charged side groups?

A

lysine (Lys, K), histidine (His, H), asparagine (Asn, N)

20
Q

which proteins in the protein buffer system have negatively charged side groups (negatively charged at physiologic pH)?

A

glutamate (Glu, E), aspartate (Asp, D)

21
Q

why is the protein buffer system not very efficient?

A

concentrations in plasma are too low for clinical significance

22
Q

define the steps in the phosphate buffer system

what is the pKa?

A

H2OP4- H+ + HPO4(2-)

pKa = 7.21

23
Q

where is phosphate buffer system most/least efficient?

A

most efficient in intracellular environment

least efficient in plasma (concentration too low for clinical significance)

24
Q

define the hemoglobin buffer system

A

hemoglobin rich in histamine with a pKa of 6.8
* exists both as potassium salt or a weak acid
* H+ + KHb HHb + K+
(can serve as both proton acceptor (base) or donor (acid)

25
Q

what is the second most important plasma buffer after bicarbonate?

A

hemoglobin buffer

26
Q

describe the importance of bone as a buffering system

A
  • most of bone is acellular hydorxyapatite crystal (can serve as a CO2 reservoir)
  • most important in chronic metabolic acidosis
  • generally a slower-responding buffer system
27
Q

define acidemia

A

pH value lower than normal reference

28
Q

define alkalemia

A

pH value higher than normal reference

29
Q

define adicosis

A

excess of acid

30
Q

define alkalosis

A

excess of alkali

31
Q

define respiratory (in terms of pH balance)

A

disorder involves CO2

32
Q

define metabolic (in terms of pH balance)

A

disorder involves all body acids except CO2

33
Q

define anion gap

A

difference between sum of major cations and anions

* Na+ - (Cl- + HCO3-) = 8-12mmol/l (normally)

34
Q

what is the expected compensation for metabolic acidosis?

A

decrease PaCO2 = 1.2 x [decrease in HCO3-]

35
Q

what is the expected compensation for metabolic alkalosis?

A

increase PaCO2 = 0.7 x [increase in HCO3-]

36
Q

what is the expected compensation for acute/chronic respiratory acidosis (increased PaCO2)?

A

acute: increase [HCO3-] 1mmol/L for every 10mmHg increase in PaCO2
chronic: increase [HCO3-] 4mmol/L for every 10mmHg increase in PaCO2

37
Q

what is the expected compensation for acute/chronic respiratory alkalosis (decreased PaCO2)?

A

acute: decrease [HCO3-] 2mmol/L for every 10mmHg decrease in PaCO2
chronic: decrease [HCO3-] 4 mmol/L for every 10mmHg decrease in PaCO2

38
Q

what are the renal causes of non-gap metabolic acidosis?

A
  • renal tubular acidosis

* carbonic anhydrase inhibitor diuretics

39
Q

what are the GI causes of non-gap metabolic acidosis?

A
  • severe diarrhea
  • uretero-enterostomy or obstructed ileal conduit
  • drainage of pancreatic or biliary secretions
  • small bowel fistula
40
Q

what are some other causes of non-gap metabolic acidosis?

A

addition of HCl or NH4Cl

41
Q

name three causes of metabolic alkalosis

A
  1. addition of base to ECF
    * milk-alkali syndrome
    * excessive NaHCO3 intake
    * massive blood transfusion (citrate)
  2. chloride depletion
    * loss of acidic gastric juice (vomiting)
    * diuretics (furosemide/thiazide – impair Cl reabsorption)
  3. potassium depletion
    * hyperaldosteronism (increased tubular Na+ reabsorption/K+ and H+ excretion)
    * cushing’s syndrome
    * kaliuretic diuretics
    * excessive licorice intake (glycyrrhizic acid)
42
Q

name three causes of respiratory acidosis caused by impaired CO2 elimination

A
  1. CNS depression
    * drug depression of resp. center
    * CNS trauma or tumor
    * hypoventilation of obesity
  2. nerve or muscle disorders
    * myasthenic syndromes
    * muscle relaxant drugs
  3. mechanical
    * chest trauma
    * pneumothorax
    * restrictive lung disease
    * aspiration
    * upper airway obstruction
    * laryngospasms
    * bronchospasm/ asthma
    * inadequate mechanical ventilation
43
Q

name two causes of respiratory acidosis caused by overproduction of CO2

A
  1. hypermetabolic disorders
    * malignant hyperthermia
    * fever
  2. increased intake
    * rebreathing exhaled gas
    * absorption from laparoscopy
44
Q

name four causes of respiratory alkalosis

A
  1. central causes (direct via respiratory center)
    * injury/stroke
    * hyperventilation (anxiety, pain, fear, stress)
    * various drugs/endogenous compounds
  2. hypoxemia
    * respiratory stimulation via peripheral chemoreceptors
  3. pulmonary causes (act via intrapulmonary receptors)
    * PE, pneumonia, asthma, pulmonary edema
  4. latrogenic (act directly on ventilation)
    * excessive controlled ventilation
45
Q

what is the albumin/malnourishment anion gap correction formula?

A

anion gap + (2.5 * (4-albumin))

ANESTHESIA PRACTICE 2 (5 decks)

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