2.4.1 Interpreting Arterial Blood Gases

Question 1

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

Answer 1

Kidneys and Lungs

Question 2

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

Answer 2

Blood chemistry (electrolytes) and arterial blood gases

Question 3

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

Answer 3

pH: 7.4 (7.38-7.42)

PCO2: 40 (38-42)

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

Question 4

What is the Henderson-Hasselbach equation?

Answer 4

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

Question 5

What is the Kassirer-Bleich equation?

Answer 5

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

Question 6

What is acidemia? alkalemia?

Answer 6

Acidemia: pH < 7.35-7.45

Alkalemia: pH > 7.35-7.45

Question 7

Put the normal values into the KB equation.

Answer 7

[H+] = 24 x 40/24

[H+] = 40 = pH of 7.4

Question 8

What are the two types of metabolic acidosis?

Answer 8

Anion gap

Non-anion gap (hypercholeremic)

Question 9

Metabolic disorders lead to irregularities in which value?

Answer 9

Bicarbonate

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

Question 10

What are some causes of metabolic alkalosis?

Answer 10

Nasogastric suctioning, vomiting

Diuretic therapy

Cushing Syndrome - ACTH excess

Hyperaldosteronism - Addison’s Dz

Exogenous therapy

Licorice ingestion

Alkali ingestion

Question 11

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

Answer 11

MUDPILES

Methanol

Uremia

DKA

Paraldehyde

INH/Iron

Lactic Acidosis

Ethylene Glycol

Salicylates/Starvation

Question 12

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

Answer 12

HARD-UP

Hyperailmentation

Acetazolamide and other carbonic anhydrase inhibitors

Renal tubular acidosis

Diarrhea

Ureteroenteric fistula

Pancreaticoduodenal fistula

Question 13

What formula is used to determine respiratory compensation?

Answer 13

The Winter Formula

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

Question 14

What is the primary alteration in respiratory disorders?

Answer 14

pCO₂

Question 15

What are some causes of respiratory acidosis?

Answer 15

CNS depression

Neuromuscular disorder

Thoracic cage limitation

Acute obstruction

Chronic obstruction

Ventilator Malfunction

Question 16

What are some causes of respiratory alkalosis?

Answer 16

Anxiety

CNS Disorders

Drugs - Salicylates, analeptics

Fever, sepsis

Pregnancy

Liver insufficiency

Hyperthyroidism

Question 17

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

Answer 17

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 18

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

Answer 18

0.08 x (measured PaCO2-40)/10

Question 19

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

Answer 19

0.03 X (measured PaCO2-40)/10

Question 20

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

Answer 20

AG = Na⁺ - (Cl^- + HCO3^-)

Normal is 12 or less

Question 21

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

Answer 21

Question 22

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

Answer 22

Question 23

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

Answer 23

Question 24

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

Answer 24

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

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

Answer 27

Question 28

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

Answer 28

Question 29

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

Answer 29