10_HST110 Acid-Base Disorders 2017

Question 1

Normal plasma PCO2

Answer 1

37 – 44 mm Hg

Question 2

Name the 4 simple Acid-Base Disorders

Answer 2

Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis

Question 3

Metabolic Acidosis: Decrease in plasma [HCO3-]

Caused by what 3 conditions? Compensated by what 2 mechanisms?

Answer 3

1. Adding H+ to body (eg, lactic acidosis, ketoacidosis)
2. Losing HCO3- (eg, diarrhea)
3. Kidneys not secreting enough H+ to replenish HCO3- (renal tubular acidosis)

Compensation

1. Lungs hyperventilate to decrease PCO2
2. Kidneys secrete excess H+, reabsorb more HCO3-

Question 4

The addition of certain acids generates anions that can increase the anion gap. How is this calculated?

Answer 4

[Na+] – [Cl-] – [HCO3-] = [UA] – [UC] = 3-12 mEq/L Normally

Question 5

Metabolic Alkalosis: Increase in plasma [HCO3-]

Caused by what 3 conditions? Compensated by what 2 mechanisms?

Answer 5

1. Adding HCO3- to body
2. Losing H+ (eg, vomiting, GI suction, diuretics*)
3. Volume contraction

Compensation

1. Lungs hypoventilate to increase PCO2
2. Kidneys secrete less H+, reabsorb less HCO3-

Question 6

Repiratory Acidosis: Increase in PCO2

Caused by what 2 conditions? Compensated by what mechanism?

Answer 6

1. Hypoventilation (eg, drugs, muscle weakness, COPD)
2. Impaired gas diffusion

Compensation
1. Kidneys secrete more H+, reabsorb and generate more HCO3- (over days)

Question 7

Respiratory Alkalosis: Decrease in PCO2

Caused by what condition? Compensated by what mechanism?

Answer 7

1. Hyperventilation
   * Stimulation of respiratory center (eg, drugs (aspirin), sepsis)
   * High altitude
   * Emotional responses (pain, fear, stress)

Compensation
Kidneys secrete less H+, reabsorb and generate less HCO3- (over days)

Question 8

Approaching Acid-Base disorders. What lab values does one need to make a diagnosis?

Answer 8

Arterial blood gas (ABG) for pH/PCO2/HCO3-

Basic Chemistry Panel: Na+,K+,Cl-,HCO3-

Question 9

What are the 5 steps to diagnose acid-base disorders?

Answer 9

1. What is the pH?
2. What is the primary disturbance? i.e. Metabolic or Respiratory?
3. What is the anion gap?
4. Is there appropriate compensation?
5. What is the delta-delta gap?

Question 10

pH < 7.37 = (X) (not acidosis)
pH > 7.44 = (Y) (not alkalosis)

“-emia” describes the state of the blood
“-osis” describes a process that can result in acidemia or alkalemia

Answer 10

X = ACIDEMIA 
Y = ALKALEMIA

Question 11

Metabolic acidosis = [HCO3-] < (X)
Metabolic alkalosis = [HCO3-] > (X)
Respiratory acidosis = PCO2 > (Y)
Respiratory alkalosis = PCO2 &laquo_space;(Y)

Answer 11

X = 25
Y = 40

Question 12

Anion gap = Na+ - (Cl- + HCO3-

AG > 12 may indicate AG acidosis
AG > (X) always indicates AG acidosis

Answer 12

X = 20

Question 13

Causes of elevated anion gap acronym

Answer 13

MUDPILES (see notes for details)

Question 14

Causes (of Metabolic Acidosis) with NORMAL Anion Gap (Acronym)

Answer 14

HARDUPS

Question 15

What are the compensation mechanisms for metabolic or respiratory acid-base issues?

Answer 15

Metabolic acidosis/alkalosis?
Respiratory compensation (hyperventilation or hypoventilation)

Respiratory acidosis/alkalosis?
Metabolic compensation (increase or decrease in renal bicarbonate reabsorption)

Question 16

COMPENSATION

Metabolic acidosis:
Decrease in PCO2 = (X) x decrease in [HCO3]

Metabolic alkalosis:
Increase in PCO2 = (Y) x increase in [HCO3]

Alternatively, Winter’s formula:
Expected PCO2 = (Z)
Only useful for metabolic acidosis

Answer 16

X = 1.3
Y = 0.6
Z = 1.5 x [HCO3] + 8 ± 2

Question 17

COMPENSATION for Respiratory Process (acute (hrs))

Answer 17

• Acidosis -> Increase in ΔHCO3 for every ΔPCO3 of 10 = 1

* Alkalosis -> Decrease in ΔHCO3 for every ΔPCO3 of 10 = 2

Question 18

COMPENSATION for Respiratory Process (chronic (days))

Answer 18

• Acidosis -> Increase in ΔHCO3 for every ΔPCO3 of 10 = 4

* Alkalosis -> Decrease in ΔHCO3 for every ΔPCO3 of 10 = 5

Question 19

Delta-Delta gap is based on the principle of (X)

Answer 19

X = electroneutrality

Question 20

When should you calculate the delta-delta gap?

Answer 20

When you have an anion gap metabolic acidosis

Question 21

What is the underlying balance in Delta-Delta gap calculations?

Answer 21

Every 1 point increase in anion gap should be accompanied by a 1 mEq/L decrease in HCO3-

Δ Anion gap = Δ HCO3

Question 22

If Δ Anion gap does not equal Δ HCO3, what are the 3 scenarios in the setting of metabolic acidosis?

Answer 22

Δ Anion gap = Δ HCO3 implies simple anion gap acidosis

Δ Anion gap < Δ HCO3 implies non-anion gap metabolic acidosis

Δ Anion gap > Δ HCO3 implies underlying metabolic alkalosis