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Pulm by Minnie: AH Update > SM 159a, SM 173a - Acid Base > Flashcards

SM 159a, SM 173a - Acid Base Flashcards

1
Q

What does the isohydric principle state?

How does this apply to the buffer systems in the body?

A

The acid/base ratio of a buffer is determined by Ka and [H+]

Changes in [H+] will change the acid/base ratio of all buffer systems in a solution.

However, since these systems are in equillibrium, we only need to know about one system to calcualte the pH of the solution

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2
Q

The slope of the buffer line is defined by ______________

A

The slope of the buffer line is defined by the nonbicarbonate buffer systems

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3
Q

What are the two types of metabolic acidosis?

A
  • Anion Gap Metabolic Acidosis: AG > 20
    • Metabolic acidosis is due to acid accumulation
      (ex: MUD PILES)
  • Non-Anion Gap Metabolic Acidosis: AG < 20
    • Metabolic acidosis is due to bicarbonate loss
      (ex: USED CARS)
    • AG gap is normal becaue Cl- has increased to compensate
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4
Q

Would the bicarbonate buffere system function in the absense fo gas exchange and ventilation?

Why or why not?

A

No;

We must continually breathe off CO2 in order for the bicarbonate system to function.

Excreting CO2 pulls the reaction to the left (via Le Chatelier), thus minimizing the effects of added H+

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5
Q

What system compensates for metabolic alkylosis or acidosis?

A

The respiratory system

Compensates almost instantly

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6
Q

Which patients are least likely to have adequate respiratory compensation for metabolic acidosis or alkylosis?

A

Mechanically ventilated patients

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7
Q

What is the Henderson-Hasselbalch equation?

A
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8
Q

Which systems buffer metabolic acidosis or alkylosis?

A

Bicarbonate and non-bicarbonate buffer systems

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9
Q

In general, what causes metabolic acidosis?

A

Addition of a fixed acid or loss of a base

May be primary or secondary

  • Primary: acid-base process occurrs independently
  • Secondary: acid-base process occurs in response to a primary process (ex: the process is compensatory to restore pH to normal)
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10
Q

For every 10 mmHg of PaCO2 change, pH will change by units in the opposite direction.

A

For every 10 mmHg of PaCO2 change, pH will change by 0.08 ​ units in the opposite direction.

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11
Q

A change in PaCO2 of _______ will result in a 0.08 unit change in pH

A

A change in PaCO2 of 10 mmHg will result in a 0.08 unit change in pH

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12
Q

What process is occcuring if pH and PaCO2 are both increased?

A

Metabolic Alkylosis

(With expected compensatory respiratory acidosis)

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13
Q

A decreasein unmeasuredcations will ________ the anion gap

A

A decreasein unmeasuredcationswillincrease the anion gap

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14
Q

Would increasing hemoglobin concentration increase or decrease the buffer value of the nonbicarbonate buffers in the body as a whole?

A

Adding hemoglobin would increase the buffer vaule

Hemoglobin acts as a buffer, so more of it would help the body resist changes to pH

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15
Q

If we have buffers, why do we need respiratory compensation for primary metabolic alkylosis or acidosis?

A

Buffers reduce, but do not prevent changes in pH due to primary metabolic processes.

  • The small change in pH stimulates peripheral chemoreceptors
    • Ventilation increases to compensate for decreased pH
      • Goal is to decrease PCO2
    • Ventilation decreases to compensate for increased pH
      • Goal is to increase PCO2
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16
Q

A decreasein unmeasuredanions will ________ the anion gap

A

A decreasein unmeasuredanions will decrease the anion gap

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17
Q

A patient has ABG of 7.47/47 (34)

What acid/base process is present?

A

Metabolic alkylosis

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18
Q

What is the difference between a primary and secondary metabolic acid-base process?

A
  • Primary: acid-base process occurrs independently
  • Secondary: acid-base process occurs in response to a primary process (ex: the process is compensatory to restore pH to normal)
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19
Q

What steps should you take when evaluating a patient with an acid-base process?

A
  1. Look at arterial blood gas
    Acidosis or alkylosis?
    Metabolic or respiratory?
  2. a) If the patient is in metabolic acidosis, calculate the anion gap
    AG > 20 = acid add-on state
    AG < 20 = bicarbonate-wasting state
    b) If the patient is in metabolic aklylosis, evaluate for Cl- responsive (Low Cl-, Na+, FeNa in urine, low urine output) or CL- unresponseive
  3. Perform a delta-delta analysis to uncover underlying bicarbonate excess or bicarbonate wasting states
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20
Q

Low serum HCO3 indicates the presence of which acid-base process?

A

Metabolic acidosis

Metabolic acidosis -> Increased [H+]

Increased [H+] -> Le Chatelier to the left; this uses up HCO3

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21
Q

Where are Na+, Cl-, and HCO3 in the electrolyte tree?

A
22
Q

What process is occuring if pH is increased and PaCO2 is decreased?

A

Respiratory Alkylosis

23
Q

What enzyme catalyzes the bicarbonate buffer system?

A

Carbonic anhydrase

Catalyzes H2O + CO2 -> H2CO3

24
Q

How would the buffer line change if hemoglobin concentration in the body were increased?

A

Increasing hemoglobin would increase the buffering power of the non-bicarbonate buffer systems in the body.

The slope of the line would be steeper -> less change in pH, even when [HCO3-] changes

25
Q

In general, what causes metabolic alkylosis?

A

Addition of a base or loss of an acid

May be primary or secondary

  • Primary: acid-base process occurrs independently
  • Secondary: acid-base process occurs in response to a primary process (ex: the process is compensatory to restore pH to normal)
26
Q

In general, what causes respiratory acidosis or alkylosis?

A

A primary change in PaCO2 due to hypoventilation (acidosis) or hyperventilation (alkylosis)

27
Q

The rapid intravenous infusion of HCO3- into a 70 kg male initially increased arterial pH from 7.40 to 7.51 and [HCO3-] from 24 to 32 mEq/L. However, over the next 3 hr the arterial [HCO3-] decreased to
27 mEq/L and pH decreased to 7.45.

What caused the fall in HCO3-and pH over the 3 hr period?

A
  • HCO3-
    • Equilibrated throughout the extracellular space
    • Non-bicarbonate buffers
    • This wil inrease CO2
  • pH
    • Respiratory compensation for metabolic alkylosis = hypoventilation
    • However, increased CO2 due to the bicarbonate infusion will stimulate central chemoreceptors to increase respiration. This limits respiratory compensation of increased pH.
28
Q

What limits respiratory compensation for primary metabolic alkylosis?

A

The compensatory response to metabolic acidosis = respiratory alkylosis, achieved by hypoventilation

This compensatory response is limited by hypoxemia; If the body hypoventilates to PaO2 < 60 mmHg, carotoid chemoreceptor activtion will work to increase ventilation, thus counteracting the compensatory respiratory acidosis.

29
Q

What is the most important buffer system in the body?

A

The bicarbonate buffer system

30
Q

How do you calculae the Anion Gap?

What is the expected value?

A

AG = [Na+] - [Cl-] - [HCO3]

Expected value = 10 +/- 2

31
Q

A change in PaCO2 of 10 mmHg will result in a ________ change in pH in

A

A change in PaCO2 of 10 mmHg will result in a 0.08 unit change in pH

32
Q

An increase in unmeasured cations will ________ the anion gap

A

An increase in unmeasured cations will decrease the anion gap

33
Q

How would the buffer line change if hemoglobin concentration in the body were decreased?

A

Decreasing hemoglobin would decrease the buffering power of the non-bicarbonate buffer systems in the body.

The slope of the line would be less steep; changes in [HCO3-] would have a large effect on pH

34
Q

Which systems buffer respiratory acidosis or alkylosis?

A

Non-bicarbonate bufferes only

35
Q

How do you perform a delta-delta analysis?

A
  1. Calculate the ΔAG
    * *ΔAG** = AG - Expected AG = AG - 10
  2. Add ΔAG + HCO3

If ΔAG + HCO3 > 30 => additional bicarbonate excess state

If ΔAG + HCO3 < 20 => additional bicarbonate wasting condition

If ΔAG + HCO3 < 20 => No other underlying acid/base processes are present

36
Q

Which protein contributes most signfiicantly to the anion gap?

A

Albumin

Albumin is negatively chagrged

Hypoalbuminemia = smaller anion gap

Hyperalbuminemia = larger anion gap

37
Q

How can you tell if a metabolic acid/base process is appropriately compensated?

A

Winter’s formula:

If PaCO2 = 1.5 * [HCO3] + 8 , the metabolic process is perfectly compensated

OR

If the last 2 digist of PCO2 are the same as the last 2 digits of pH, the metabolic process is perfectly compensated

38
Q

High serum HCO3 indicates the presence of which acid-base process?

A

Metabolic alkylosis

Metabolic alkylosis -> decreased [H+]

Decreased [H+] -> Le Chatelier to the right; this produces HCO3

39
Q

What process is occuring if pH is decreased and PaCO2 is increased?

A

Respiratory Acidosis

40
Q

For every 10 mmHg of PaCO2 change, pH will change by 0.08 units in the direction.

A

For every 10 mmHg of PaCO2 change, pH will change by 0.08 ​ units in the opposite direction.

41
Q

What are the two types of metabolic alkylosis?

A
  • Cl- responsive metabolic alkylosis
    • Primary problem: Increase in serum bicarbonate
      • Usually associated with volume depletion
      • The kidney wants to resorb Na and Cl to reabsorb H2O
      • However, when it runs out of Cl-, it chooses to reabsorb HCO3- to restore volume
      • This comes at the cost of increased pH
    • Giving NaCl infusion can restore the patient to normal
  • Cl- unresponsive metabolic alkylosis
    • Problem = too much aldosterone or not not enough K+
      • Promotes H+ secretion in the renal epithelial cells
42
Q

For every mmHg of PaCO2 change, pH will change by 0.08 units in the opposite direction.

A

For every 10 mmHg of PaCO2 change, pH will change by 0.08 ​ units in the opposite direction.

43
Q

What is the relationship of pH and [H+]?

A

pH = -log[H+]

44
Q

If a patient has metabolic acidosis with an elevated anion gap, what is the cause?

A

Acid add-on state: MUD PILES

(The patient ate something they weren’t supposed to, or they are in lactic or ketoacidosis)

45
Q

What process is occcuring if pH and PaCO2 are both decreased?

A

Metabolic acidosis

(with expected compensatory respiratory alkylosis)

46
Q

How long does it take for the kidney to begin to compensate for respiratory acidosis or alkylosis?

How can you tell if compensation has occurred?

A

~ 3 days

  • Compensated Respiratory Acidosis
    • pH is higher than expected for the increase in PaCO2
  • Compensated Respiratory Alkylosis
    • pH is lower than expected for the decreaed PaCO2
47
Q

What is the Henderson-Hasselbalch equation for the bicarbonate buffer system?

A

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

  • Normal values
    • HCO3- = 24
    • PaCO2 = 40
    • => pH = 7.4
48
Q

A patient has ABG of 7.47/47 (34), characteristic of metabolic alkylosis.

What would you expect to see if this were a Cl- responsive metabolic alkylosis?

A
  • Low urine output
  • Low levels of the following in the urine:
    • Cl-
    • Na+
    • FeNa

Cl- responsive metabolic alkylosis is usually associated with a a low volume state; the body is reabsorbing bicarbonate to try to restore pH

49
Q

If a patient has metabolic acidosis without an elevated anion gap, what is the cause?

A

Bicarbonate wasting state

USED CARS

(Noteably: Saline administration, Diarrhea, Spironolactone)

50
Q

If there were no non-bicarbonate buffers, which line would represent the buffer line?

A

Line (a)

51
Q

An increase in unmeasured anions will ________ the anion gap

A

An increase in unmeasured anionswillincrease the anion gap

52
Q

What is the “buffer value” of a buffer?

A

The buffer value refers to the moles of H+ that must be added or removed from the solution to produce a 1 pH unit change

The highe the value, the stronger the buffer

Pulm by Minnie: AH Update (34 decks)

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