Respiratory: Oxygen and Arterial Blood Gases

Question 1

What does Hypoxia mean?

Answer 1

 Hypoxia – lack of oxygen to tissues

Question 2

What are the causes of hypoxia?

Answer 2

Anaemic hypoxia
Perfusional hypoxia
Toxic Hypoxia
Hypoxaemic hypoxia

Question 3

What is anaemic hypoxia?

Answer 3

o Anaemic hypoxia; lack of Hb (falls below 40) means oxygen cannot bind

Question 4

What is perfusional hypoxia?

Answer 4

Poor cardiac output – O2 is able to bind to Hb but the hearts is unable to pump it round

Question 5

What is toxic hypoxia?

Answer 5

failure of release off O2 at tissue level – O2 binds to Hb and travels round body but does not release from Hb so ends up travelling round the blood

Question 6

What is hypoxaemic hypoxia?

Answer 6

low pO2 and SaO2 – people with a normal heart, normal amount off perfusion and no poison but O2 levels are low due to respiratory insufficiency

Question 7

What does hypoxaemia mean?

Answer 7

 Hypoxaemia – low oxygen levels within the blood (pO2¬ and SaO¬2 combined)

Question 8

How do you calculate the most amount of oxygen a patient can receive?

Answer 8

DO2 = CO x [(1.3 x Hb x SaO2) + 0.003 x PaO2]

Question 9

In what situations do you give the patient the most amount of oxygen they can receive?

Answer 9

Cardiac arrest
Massive trauma
Sepsis
Anaphylaxis

Question 10

What do you keep the Oxygen saturations at for a COPD patient?

Answer 10

88%-92%

Question 11

What is the general normal SaO2 range for a healthy person?

Answer 11

94%-98%

Question 12

What concentrations are important for acid-base balance?

Answer 12

pH
pCO2
HCO3

Question 13

What are the buffers used by the body?

Answer 13

Haemoglobin
Bicarbonate
Ammonium
Phosphate

Question 14

What is the pH range for when it is considered an acidaemia?

Answer 14

Less than 7.35

Question 15

What is an acidosis?

Answer 15

 Acidosis is a process causing excess acid to be present in the blood - this doesn’t necessarily produce acidaemia

Question 16

What is the pH range for when it is considered an alkalaemia?

Answer 16

Greater than 7.45

Question 17

What is an alkalosis?

Answer 17

 Alkalosis is a process causing excess base to be present in the blood – this doesn’t necessarily produce alkalaemia

Question 18

If the pH is normal, but there is a high pCO” and HCO3 how do you determine if it is a respiratory acidosis or a compensated metabolic alkalosis?

Answer 18

Check history
Monitor over a couple of hours
Metabolic acidosis is more common than alkalosis

Question 19

In what conditions would you find a Respiratory acidosis with metabolic compensation ?

Answer 19

o Chronic type 2 respiratory failure: COPD, CF, kyphoscoliosis

Question 20

In what conditions would you find a Metabolic alkalosis with respiratory compensation?

Answer 20

o Milk alkali syndrome, vomiting, severe hypokalaemia

Question 21

In what conditions would you find a Metabolic acidosis with respiratory compensation ?

Answer 21

o Sepsis, DKA, poisoning, drugs, lactate

Question 22

In what conditions would you find a Respiratory alkalosis with metabolic compensation ?

Answer 22

o Chronic hyper-ventilatory states

Question 23

What type of respiratory failure is a Uncompensated respiratory acidosis?

Answer 23

Acute Type 2 Respiratory Failure

Question 24

What type of respiratory failure is a Compensated respiratory acidosis?

Answer 24

Chronic Type 2 Respiratory failure

Question 25

What type of respiratory failure is a decompensated respiratory acidosis?

Answer 25

Acute on Chronic Type 2 Respiratory failure

Question 26

What is the anion gap?

Answer 26

if you add together the sodium and potassium, then add together the chloride and the bicarbonate you must add 12 to compensate for the addition anions found in the blood stream
Na+ + K+ = Cl- + HCO3- + 12

Question 27

In what situations/conditions does a high anion gap acidosis exist?

Answer 27

o	Alcohol (Alcohol dissociates to become a weak acid)
o	Methanol (See alcohol.  Causes blindness)
o	Uraemia (Failure to reabsorb HCO3- and excrete H+)
o	DKA (Ketones are dehydrogenated alcohols, and dissociate to acid)
o	Paraquat (Very nasty poison, universally lethal)
o	Infection (Commonest cause.  Localised tissue hypoxia leads to...)
o	Lactic Acid (Product of anaerobic respiration, and tissue necrosis)
o	Ethylene Gylcol (Antifreeze.  Quite a potent acid, no longer sold in UK)
o	Salicylates (Aspirin causes respiratory alkalosis, then metabolic acidosis)

Question 28

In what situations/conditions does a normal anion gap acidosis exist?

Answer 28

o	Addison’s Disease
o	High Output Fistulas
o	RTA I, II, IV
o	Acetazolamide Therapy
o	Diarrhoea

Question 29

What does a base excess of +2 suggest?

Answer 29

Metabolic alkalosis

Question 30

What does a base excess of -2 suggest?

Answer 30

Metabolic acidosis

Question 31

What is the base excess?

Answer 31

base excess and base deficit refer to an excess or deficit, respectively, in the amount of base present in the blood