CPR 59-60 - Respiratory Acid Base and Clinical Cases

Question 1

Differentiate acidemia/alkalemia from acidosis/alkalosis.

Answer 1

Acidema/Alkalemia refers to a condition where the blood is at a pH below 7.35 or above 7.45 respectively.

Acidosis/Alkalosis refers to a condition where the blood pH has decreased/increased relative to what it was previosly.

Often, including in this class, these terms are used interchangeably

Question 2

How does acidosis and alkalosis affect excitable tissues?

Answer 2

Acidosis causes hypoexcitability (CNS depression)

Alkalosis causes hyperexcitability (tetany)

Question 3

What are the 3 lines of defense against pH changes in order of which happens first?

Answer 3

1. Buffering
2. Changes in ventilation
3. Changes in renal handling of H+ & HCO3-

Question 4

How do blood pH, pCO2, [H+], and [HCO3-] levels change in a person with acute respiratory acidosis? Chronic respiratory acidosis?

Answer 4

Acute respiratory acidosis will have high pCO2, [H+], and [HCO3-] with low pH. Chronic respiratory acidosis will also have those things but pH won’t be as low and [HCO3-] will be even higher due to renal compensation.

Question 5

How do pCO2, blood pH, and [HCO3-] levels change for someone with acute respiratory alkalosis? Chronic respiratory alkalosis?

Answer 5

Acute respiratory alkalosis has decreased pCO2 and [HCO3-] and increased pH. Chronic respiratory alkalosis has all of the same things but pH will not be as high due to renal compensation.

Question 6

Draw out a rough Davenport diagram and indicate where respiratory/metabolic acidosis and alkalosis would be found. Also indicate where respiratory/renal compensations would be found.

Answer 6

Question 7

Answer 7

Question 8

Mr Smiths arterial blood has the following characteristics; PCO2 50 mm Hg, pH 7.31 HCO3 - 26 mM. What is the diagnosis?

Answer 8

Respiratory acidosis

Question 9

A 62 year old patient’s arterial blood has the following values; PCO2 60, pH 7.32, HCO3 - 32 mM, what is the likely cause?

Answer 9

Respiratory acidosis with renal compensation

Question 10

The laboratory provides the following report on arterial blood from a patient PCO2 28 mm Hg, pH 7.25, HCO3 - 25 mM, what is the likely problem?

Answer 10

Lab error

Question 11

Answer 11

B

Question 12

Answer 12

C

Question 13

Answer 13

COPD with emphysema

FEV1 indicates obstructive instead of restrictive

Question 14

Answer 14

Functional Residual Capacity

When supine abdominal contents push into thoracic cavity. When standing those contents are suspended and pull down on diaphragm which leads to an increase in lung compliance and FRC

Question 15

Answer 15

Blood flow distribution

Because the RV is a relatively low pressure pump, pulmonary blood flow is highly dependent on gravity. Therefore, standing changes blood flow patterns

Question 16

Answer 16

Decreased radial tension

The decreased radial tension leads to a smaller airway. Combine this with the forcefulness of coughing and a large increase in flow velocity develops. This helps to rip some of the mucus build-up from the airways.

Question 17

Answer 17

Patchy hyperlucency in the lung fields

Question 18

Why is patch hyperlucency seen on Mrs. M’s chest radiograph?

Answer 18

Emphysema is a loss of lung tissue. Any time tissue is lost and replaced with air increased lucency will be seen on a radiograph.

Question 19

Answer 19

Widening of costophrenic angle

Loss of elastic recoil of the lungs because of emphysema allows the diaphragm to lie flatter and lower. Refer to image

Question 20

Answer 20

7

Emphysema eats away at lung tissue which will degrage the radial tension tracts and increase compliance. Chest wall recoil shouldn’t be affected.

Question 21

How will an increase in lung compliance affect FRC and why?

Answer 21

FRC occurs at the point where chest wall recoil is equal to lung recoil. An increase in lung compliance means a decrease in lung elasticity and therefore and lung recoil. Because of this lung recoil is equal to chest recoil at a larger volume. This leads to an increase in FRC. Refer to image

Question 22

Answer 22

Pulmonary edema

Pulmonary edema is the presence of an increased amount of interstitial fluid in the lungs. This causes the lungs to stiffen up and lose compliance.

Question 23

Also explain what causes this starling force change

Answer 23

Increased hydrostatic pressure

The emphysema leads to a decrease in pulmonary vasculature cross-sectional area. This will increase pulmonary resistance and pressure.

The emphysema will also lead to some alveoli becoming hypoxic which will cause hypoxia mediated vasoconstriction. This will also increase pulmonary resistance and pressure.

Question 24

Answer 24

Residual volume

Due to the decrease in lung elastance the airways collapse quickly during exhalation.

Question 25

Answer 25

Increased anterioposterior diameter

Question 26

Answer 26

Respiratory acidemia

Question 27

Answer 27

Metabolic alkalosis

Question 28

How can you tell if metabolic compensation is occurring with respiratory acidemia?

Answer 28

The bicab levels. If they’re normal then it’s pure respiratory acidosis. If they’re high then renal metabolic compensation is present

Question 29

Answer 29

Patient has an increased A-a gradient

Question 30

Answer 30

Normal A-a gradient with low pO2 and high pCO2

Question 31

Answer 31

She will likely have elements of all of these but V/Q is the real driving force of her hypoxemia