SM 159a, SM 173a - Acid Base Flashcards by Madeleine (she/her) Horvath

What does the isohydric principle state?

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

The acid/base ratio of a buffer is determined by K_a 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

How well did you know this?

Not at all

Perfectly

The slope of the buffer line is defined by ______________

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

How well did you know this?

Not at all

Perfectly

What are the two types of metabolic acidosis?

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

How well did you know this?

Not at all

Perfectly

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

Why or why not?

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+

How well did you know this?

Not at all

Perfectly

What system compensates for metabolic alkylosis or acidosis?

The respiratory system

Compensates almost instantly

How well did you know this?

Not at all

Perfectly

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

Mechanically ventilated patients

How well did you know this?

Not at all

Perfectly

What is the Henderson-Hasselbalch equation?

How well did you know this?

Not at all

Perfectly

Which systems buffer metabolic acidosis or alkylosis?

Bicarbonate and non-bicarbonate buffer systems

How well did you know this?

Not at all

Perfectly

In general, what causes metabolic acidosis?

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)

How well did you know this?

Not at all

Perfectly

For every 10 mmHg of P_aCO2 change, pH will change by units in the opposite direction.

For every 10 mmHg of P_aCO2 change, pH will change by 0.08 units in the opposite direction.

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

Metabolic Alkylosis

(With expected compensatory respiratory acidosis)

How well did you know this?

Not at all

Perfectly

A decreasein unmeasuredcations will ________ the anion gap

A decreasein unmeasuredcationswillincrease the anion gap

How well did you know this?

Not at all

Perfectly

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

Adding hemoglobin would increase the buffer vaule

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

How well did you know this?

Not at all

Perfectly

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

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 P_CO2
- Ventilation decreases to compensate for increased pH
  - Goal is to increase P_CO2

How well did you know this?

Not at all

Perfectly

A decreasein unmeasuredanions will ________ the anion gap

A decreasein unmeasuredanions will decrease the anion gap

How well did you know this?

Not at all

Perfectly

A patient has ABG of 7.47/47 (34)

What acid/base process is present?

Metabolic alkylosis

How well did you know this?

Not at all

Perfectly

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

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)

How well did you know this?

Not at all

Perfectly

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

Look at arterial blood gas
Acidosis or alkylosis?
Metabolic or respiratory?
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
Perform a delta-delta analysis to uncover underlying bicarbonate excess or bicarbonate wasting states

How well did you know this?

Not at all

Perfectly

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

Metabolic acidosis

Metabolic acidosis -> Increased [H+]

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

How well did you know this?

Not at all

Perfectly

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

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

Respiratory Alkylosis

What enzyme catalyzes the bicarbonate buffer system?

Carbonic anhydrase

Catalyzes H₂O + CO₂ -> H₂CO₃

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

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

In general, what causes metabolic alkylosis?

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)

In general, what causes respiratory acidosis or alkylosis?

A primary change in P_aCO2 due to hypoventilation (acidosis) or hyperventilation (alkylosis)

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. ## Footnote **What caused the fall in HCO₃^-and pH over the 3 hr period?**

* 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.

What limits respiratory compensation for primary metabolic alkylosis?

The compensatory response to metabolic acidosis = respiratory alkylosis, achieved by **hypoventilation** This compensatory response is limited by **hypoxemia;** If the body hypoventilates to P_aO2 \< 60 mmHg, carotoid chemoreceptor activtion will work to increase ventilation, thus counteracting the compensatory respiratory acidosis.

What is the most important buffer system in the body?

The bicarbonate buffer system

How do you calculae the Anion Gap? What is the expected value?

AG = [Na+] - [Cl-] - [HCO3] Expected value = 10 +/- 2

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

A change in PaCO2 of 10 mmHg will result in a **_0.08 unit_** change in pH

An **increase** in unmeasured **cations** will ________ the anion gap

An **increase** in unmeasured **cations** will **_decrease_** the anion gap

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

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

Which systems buffer respiratory acidosis or alkylosis?

Non-bicarbonate bufferes **only**

How do you perform a delta-delta analysis?

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

Which protein contributes most signfiicantly to the anion gap?

**Albumin** Albumin is negatively chagrged Hypoalbuminemia = smaller anion gap Hyperalbuminemia = larger anion gap

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

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

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

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

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

Respiratory Acidosis

For every _10_ mmHg of P_aCO2 change, pH will change by _0.08_ units in the direction.

For every _10_ mmHg of P_aCO2 change, pH will change by _0.08_ units in the **_opposite_** direction.

What are the two types of metabolic alkylosis?

* 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

For every mmHg of P_aCO2 change, pH will change by _0.08_ units in the _opposite_ direction.

For every **_10_** mmHg of P_aCO2 change, pH will change by _0.08_ units in the _opposite_ direction.

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

pH = -log[H+]

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

Acid add-on state: MUD PILES (The patient ate something they weren't supposed to, or they are in lactic or ketoacidosis)

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

Metabolic acidosis (with expected compensatory respiratory alkylosis)

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?

~ 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

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

pH = 6.1 + log { [HCO₃^-] / (0.03 \* P_aCO2) } * Normal values * HCO₃^- = 24 * P_aCO2 = 40 * =\> **pH = 7.4**

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?

* 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

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

Bicarbonate wasting state USED CARS (Noteably: Saline administration, Diarrhea, Spironolactone)

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

Line (a)

An **increase** in unmeasured **an****ions** will ________ the anion gap

An **increase** in unmeasured **an****ions**will**_increase_** the anion gap

What is the "buffer value" of a buffer?

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