Blood Gases

Question 1

What are the normal pH ranges?

Answer 1

7.35-7.45 kPa

Question 2

What are the normal PaCo2 ranges?

Answer 2

4.5-6.0 kPa

Question 3

What are the normal PaO2 ranges?

Answer 3

10.5-13.5 kPa

Question 4

What are the normal HCO3 ranges?

Answer 4

21-27 kPa

Question 5

What are the normal BE ranges?

Answer 5

-2 to +2 kPa

Question 6

What would you expect to see in a respiratory acidosis?

Answer 6

Decreased pH
Increased CO2
Normal HCO3
Normal BE

Question 7

What would you expect to see in a respiratory alkalosis?

Answer 7

Increased pH
Decreased CO2
Normal HCO3
Normal BE

Question 8

What would you expect to see in a metabolic acidosis?

Answer 8

Decreased pH
Normal CO2
Decreased HCO3
Decreased BE

Question 9

What would you expect to see in a metabolic alkalosis?

Answer 9

Increased pH
Normal CO2
Decreased HCO3
Increased BE

Question 10

What does pH represent?

Answer 10

The hydrogen ion concentration

Question 11

What does HCO3 represent?

Answer 11

Assesses the metabolic component- titrated against a constant temperature and CO2

Question 12

What does Base Excess represent?

Answer 12

Is a measure of the amount of acid or base that needs to be added to a sample under standard conditions to return the pH to 7.4

Question 13

What do acid base disturbances indicate?

Answer 13

A serious underlying pathology rather than being the pathology in themselves

Question 14

How does pH affect the body?

Answer 14

Biochemical processes are very sensitive to even small changes in pH

Question 15

What are buffer systems?

Answer 15

Systems responsible for maintaining pH- such as bicardbonate, haemoglobin, phosphate and plasma proteins

Question 16

What are examples of buffer organs?

Answer 16

Lungs and kidneys

Question 17

What are some causes of respiratory acidosis?

Answer 17

Impared gaseous exchange or lung ventilation i.e. asthma, croup
Pulmonary restrictive disorders i.e. COPD
Neuromuscular diseases
CNS depression
Iatrogenic causes (inadequate mechanical ventilation)

Question 18

What are the effects of respiratory acidosis?

Answer 18

Decreases respiratory rate, shallow breathing, tachycardia
Cyanosis may be notes if accompanying hypoxaemia is present
Physical examination may demonstrate presence of wheezing, hyperinflation, decreased breath sounds, prolonged expiration etc
Mental status may be depressed in severe elevations of PaCO2- seizures may occur
Nausea and vomiting

Question 19

What are some causes of respiratory alkalosis?

Answer 19

Direct cause is always hyperventilation (pain, anxiety)
Increased metabolic rate
Brain tumour or injury

Question 20

Effects of respiratory alkalosis

Answer 20

Hypocapnoea causes a reduction in serum calcium (many of the symptoms are related to hypocalcaemia.) Calcium reduction is secondary to increased binding of calcium to albumin
Cardiac rhythm disturbances
Hypocapnoea reduces cerebral blood flow and can cause neurological symptoms, including dizziness, mental confusion, syncope and seizures
Anxiety, tachycardia and tachypnoea

Question 21

Causes of metabolic acidosis

Answer 21

Severe diarrhoea (GI losses of bicarbonate)
Renal diseases (causing inadequate re-absorption of bicarbonate and excretion of acids)
DKA
Shock
Excess alcohol consumption
High extracellular potassium (potassium enters the cell in exchange for H+ ion)

Question 22

What are the effects of metabolic acidosis?

Answer 22

Kussmaul respirations
Tachycardia
Poor perfusion
Decreased peripheral pulses
Increased capillary refill time
Decreased level of consciousness
Fatigue
Confusion
Seizures
Nausea and vomiting

Question 23

What are the causes of metabolic alkalosis?

Answer 23

Vomiting or gastric drainage
Selected diuretics causing potassium depletion which stimulates the renal tubules to secrete H+ ions
Constipation leading to increased bicarbonate absorbed
Excess bicarbonate administration

Question 24

What are the effects of a metabolic alkalosis?

Answer 24

Hypoventilation
Decreased perfusion
Confusion and lethargy
Unresponsiveness
Hyperreflexia
Tetany
Seizures
D&V