2.4.1 Interpreting Arterial Blood Gases

Question 1

What is the expected change in pH for a chronic respiratory disturbance?

Answer 1

0.03 X (measured PaCO2-40)/10

Question 2

What are some causes of anion gap metabolic acidosis? (there is a neumonic)

Answer 2

MUDPILES

Methanol

Uremia

DKA

Paraldehyde

INH/Iron

Lactic Acidosis

Ethylene Glycol

Salicylates/Starvation

Question 3

What is the primary alteration in respiratory disorders?

Answer 3

pCO₂

Question 4

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 4

Question 5

What are the two organ systems that could lead to an acid-base disorder?

Answer 5

Kidneys and Lungs

Question 6

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 6

Question 7

Metabolic disorders lead to irregularities in which value?

Answer 7

Bicarbonate

Metabolic acidosis (HCO3 retention/overproduction); Metabolic alkalosis (HCO3 depletion)

Question 8

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 8

Question 9

What is the expected change in pH for an acute respiratory disturbance?

Answer 9

0.08 x (measured PaCO2-40)/10

Question 10

What are some causes of respiratory acidosis?

Answer 10

CNS depression

Neuromuscular disorder

Thoracic cage limitation

Acute obstruction

Chronic obstruction

Ventilator Malfunction

Question 11

What is the equation for anion gap? What is a normal value?

Answer 11

AG = Na⁺ - (Cl^- + HCO3^-)

Normal is 12 or less

Question 12

What are the normal values for pH, PCO2, and PO2?

Answer 12

pH: 7.4 (7.38-7.42)

PCO2: 40 (38-42)

PO2: 80, depends on age (104 - 0.27{age})

Question 13

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 13

Question 14

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 14

Question 15

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 15

Question 16

What two tests are needing for diagnosing an acid-base disorder?

Answer 16

Blood chemistry (electrolytes) and arterial blood gases

Question 17

What is the Henderson-Hasselbach equation?

Answer 17

pH = pKa + log [HCO3^-]/ PCO2

Question 19

What is acidemia? alkalemia?

Answer 19

Acidemia: pH < 7.35-7.45

Alkalemia: pH > 7.35-7.45

Question 20

What is the Kassirer-Bleich equation?

Answer 20

[H+] = 24 X PCO2/[HCO3^-]

Question 21

What are some of the causes of non-anion gap metabolic acidosis?

Answer 21

HARD-UP

Hyperailmentation

Acetazolamide and other carbonic anhydrase inhibitors

Renal tubular acidosis

Diarrhea

Ureteroenteric fistula

Pancreaticoduodenal fistula

Question 22

What are the two types of metabolic acidosis?

Answer 22

Anion gap

Non-anion gap (hypercholeremic)

Question 23

1. Is there a gap?
2. Is the pCO2 appropriate?
3. What are the problems?

Answer 23

Question 24

What formula is used to determine respiratory compensation?

Answer 24

The Winter Formula

expected pCO2 = (1.5 X [HCO3-]) + 8 +/- 2

Question 25

1. Is there a gap? 2. Is the pCO2 appropriate? 3. What are the problems?

Answer 25

Question 26

1. Is there a gap? 2. Is the pCO2 appropriate? 3. What are the problems?

Answer 26

Question 27

What are some causes of metabolic alkalosis?

Answer 27

Nasogastric suctioning, vomiting Diuretic therapy Cushing Syndrome - ACTH excess Hyperaldosteronism - Addison's Dz Exogenous therapy Licorice ingestion Alkali ingestion

Question 28

Put the normal values into the KB equation.

Answer 28

[H+] = 24 x 40/24 [H+] = 40 = pH of 7.4

Question 29

What is the standard approach for understanding an acid-base disorder?

Answer 29

1. Evaluate pt history 2. Review ABG * What is the pH? Acidemic or alkalemic? * Primarily respiratory or metabolic disorder? * Look at arterial PaCO2 and serum bicarbonate level * If respiratory: acute or chronic disturbance? * If metabolic: anion gap or non-anion gap? 3. Use Winter's formula to determine appropriate respiratory compensation (for metabolic acidosis)

Question 30

What are some causes of respiratory alkalosis?

Answer 30

Anxiety CNS Disorders Drugs - Salicylates, analeptics Fever, sepsis Pregnancy Liver insufficiency Hyperthyroidism