Cremo 6: Simple acid base disturbances

Question 1

What is the difference between an -EMIA and an -OSIS? I.e. acidemia vs acidosis.

Answer 1

Acidemia refers to what the blood is doing.

Acidosis refers to a pathological process that causes pH to change.

Question 2

What causes respiratory acidosis or alkalosis?

Answer 2

Pathological change in PaCO2. Often caused by abnormal function of the lung.

Question 3

What causes metabolic acidosis or alkalosis?

Answer 3

Pathological change in [HCO3-]

Question 4

ph =

Answer 4

pka + log(kidney/lung)
pka + log([HCO3-]/PaCO2)
pka + log(metabolic/respiratory)

Question 5

What does a Davenport diagram tell you?

Answer 5

How blood will respond to changes in PaCO2

Question 6

What does the steeper buffer line of blood reflect?

Answer 6

Reflects the presence of more non-volatile buffering power

Question 7

What causes respiratory acidosis or alkalosis?

Answer 7

Pathological changes in PaCO2

Question 8

In respiratory acidosis, there is a slight increase in [HCO3-] when pH decreases, but is SMALL compared to (blank)

Answer 8

Change in [HCO3-] during metabolic-oses

Question 9

Common clinical causes of acute respiratory acidosis

Answer 9

• non-pulmonary causes
• upper airway obstruction
• severe asthma attack
• COPD
• pneumonia

Question 10

With respiratory alkalosis, there is a slight decrease in [HCO3-], but this is SMALL compared to (blank)

Answer 10

Change in [HCO3-] that occurs in metabolic-oses

Question 11

Respiratory alkalosis can be caused by an increase in central drive to breathe. What variable increases?

Answer 11

VA

Question 12

Four conditions that act as abnormal ventilatory stimuli to increase central drive to breathe

Answer 12

1. arterial hypoxemia or hypoxia
2. direct stimulation of pulmonary mechano and chemo receptors by lung disease
3. chemical or physical factors that directly stimulate the medullary respiratory center
4. psychological factors

Question 13

Most common pulmonary diseases can lead to (blank)

Answer 13

respiratory alkalosis

Question 14

Why can hypoxemia cause respiratory alkalosis?

Answer 14

Think about it. Central chemoreceptors sense increase in PaCO2 in blood and respond by increasing ventilation.

Question 15

The same diseases that cause respiratory alkalosis can cause respiratory acidosis. Discuss.

Answer 15

So, in the beginning of the disease, strength wins. Many pulmonary diseases will progress from alkalosis to acidosis if they are severe enough to decrease muscle strength and increase load enough to tip the balance.

Question 16

What wins in respiratory acidosis: strength or load?

Answer 16

Load!

Question 17

What wins in respiratory alkalosis: strength or load?

Answer 17

Strength!

Question 18

How does the blood respond to changes in addition of strong acid or base (EAP)?

Answer 18

[HCO3-] will increase or decrease along the isopleth! No change in PaCO2, because it is fixed.

Question 19

In hypobicarbonatemia, there is a decrease in pH. What two things can cause this to occur?

Answer 19

Increase in EAP

Reduced net acid excretion due to renal defects

Question 20

Gastrointestinal cause of acidosis?

Answer 20

Think diarrhea. Lots of stool, so loss of bicarb :( So, increase in HCO3- secretion by lower gut to try to compensate. This causes a concomitant increase in H+ delivered to blood. Meanwhile, blood HCO3- is consumed. Acidosis.

Question 21

Hypoxia as a metabolic cause of acidosis. Discuss.

Answer 21

So, complete metabolism of organic acid production requires O2. During hypoxia, organic acids will build up, because they cannot be metabolized. This causes acidosis.

Question 22

Vomiting causes (blank)

Answer 22

Alkalosis

Question 23

Recall, respiratory acidosis and alkalosis cause (blank) changes in HCO3-, while metabolic acidosis and alkalosis cause (blank) changes in HCO3-

Answer 23

small; large

Question 24

pH down by 0.07

HCO3- up slightly (~1 mM)

Answer 24

Acute respiratory acidosis

Question 25

pH up by 0.08

HCO3- down slightly (~2 mM)

Answer 25

Acute respiratory alkalosis

Question 26

Purpose of any compensation, whether it be by the lung or kidney.

Answer 26

Return the pH toward normal. It will not go back to 7.4 as long as the disturbance is still present.

Question 27

Respiratory acidosis and alkalosis can be acute or chronic, but metabolic acidosis and alkolosis cannot. Why?

Answer 27

Respiratory compensation to metabolic conditions is very fast.

Question 28

Chronic respiratory acidosis.
In Phase 1, body buffers respond within the first ten minutes of an increase in PCO2.
Phase 2 occurs much more slowly. What does it involve?

Answer 28

Renal mechanisms: increase H+ excretion (new bicarb production), increase bicarb reabsorption

Question 29

Primary change: fall in [HCO3-]

Rapid compensatory change: fall in PaCO2

Answer 29

Metabolic acidosis

Question 30

Expected rapid compensatory response by lung during metabolic acidosis

Answer 30

PaCO2 = 1.5 x [HCO3-] + 8 ± 2 (Winter’s Formula)

Question 31

Primary change: rise in [HCO3-]

Compensatory change: rise in PaCO2

Answer 31

Metabolic alkalosis

Question 32

Expected rapid compensatory response by lung during metabolic alkalosis

Answer 32

PaCO2 = 0.7 [HCO3-] + 20 (+/- 5)

Question 33

What is the rule of thumb for determining acute respiratory alkalosis?

Answer 33

Rule is that for every 10 mm Hg decrease in PaCO2, there is a 0.8 increase in pH

Question 34

What is the rule of thumb for determining acute respiratory acidosis?

Answer 34

Rule is that for every 10 mm Hg increase in PaCO2, the pH goes down by 0.07

Question 35

Equation for anion gap

Answer 35

Gap = Na+ - (Cl- + HCO3-) where HCO3 is really the value of CO2

Question 36

What is Winters formula for metabolic acidosis (predicting change in PaCO2)

Answer 36

1.5 x [HCO3-] + 8 ± 2