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Yr 2 Sem 1 Resp > 7.1 Hypoxaemia And Respiratory Failure > Flashcards

7.1 Hypoxaemia And Respiratory Failure Flashcards

1
Q

Define hypoxaemia

A

Low pO2 in the blood

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2
Q

Define hypoxia

A

O2 deficiency at the tissue level

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3
Q

Can tissues be hypoxic without hypoxaemia? Why?

A

Yes

Anaemia, poor circulation

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4
Q

What is the normal range for O2 saturation?

A

94-98%

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5
Q

What is the normal range for pO2?

A

9.3 - 13.3kPa

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6
Q

In terms of oxygen, when is tissue damage most likely and what is this used to diagnose?

A

Respiratory failure
O2 sats <90%
pO2 <8kPa

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7
Q

Define respiratory failure

A

Impairment in gas exchange causing hypoxia with or without hypercapnia

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8
Q

Describe blood gases in type 1 respiratory failure

A 
Low pO2 (<8kPa or oxygen sats <90%)
pCO2 normal or low
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9
Q

Describe blood gases in type 2 respiratory failure

A

Low pO2

High pCO2

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10
Q

Name 5 causes of hypoxia

A

Low inspired oxygen
Hypoventilation (due to respiratory pump failure)
Ventilation/Perfusion mismatch
Disruption defect (problem with alveolar capillary membrane)
Right to left shunt (cyanotic heart disease)

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11
Q

What should alveolar ventilation be?

A

350ml x 15 (RR) = 5250ml/min

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12
Q

What should pulmonary perfusion be (pulmonary blood flow)?

A

SV X HR

70 X 70 = 4900 ml/min

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13
Q

What is reduced in hypoventilation?

A

Alveolar ventilation

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14
Q

Why does the amount of oxygen entering the blood and carbon dioxide entering the alveolus per min remain unchanged in hypoventilation?

A

Metabolic rate remains unchanged

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15
Q

What happens to blood gases in hypoventilation?

A

Hypoxaemia

Hypercapnia

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16
Q

Hypoventilation always causes hypercapnia, true or false?

A

True

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17
Q

What type of respiratory failure does hypoventilation fall into?

A

Type 2 respiratory failure

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18
Q

What can cause acute hypoventilation?

A

Opiate overdose
Head injury
Very severe acute asthma

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19
Q

How should acute hypoventilation be treated?

A

Urgent treatment

Ventilation

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20
Q

Why is chronic hypoventilation better tolerated?

A

Slow onset and progression allows time for compensation

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21
Q

What disease can cause chronic hypoventilation?

A

Severe COPD

22
Q

What respiratory centre causes can lead to hypoventilation?

A

Opiates

Head injury

23
Q

Damage to phrenic and intercostal nerves can cause hypoventilation in which pathology?

A

Guillain-Barre Syndrome

24
Q

What NMJ problem causes hypoventilation?

A

Myasthenia gravis

25
Q

What are some chronic causes of hypoventilation?

A

Muscles of respiration - myopathy, MND
Chest wall - severe obesity, kyphoscoliosis
Lung fibrosis
Late stage COPD

26
Q

What can effect the pleural cavity to cause hypoventilation?

A

Pneumothorax

Large pleural effusion

27
Q

What are the effects of hypoxaemia?

A

Impaired CNS function - confusion, irritability
Cyanosis
Cardiac arrhythmias
Hypoxic vasoconstriction of pulmonary vessels

28
Q

Clinical definition for central cyanosis

A

> 50gm/L of desaturated Hb in blood

29
Q

What does central cyanosis indicate?

A

Hypoxaemia

Seen in oral mucosa, tongue, lips

30
Q

What does peripheral cyanosis indicate?

A

Poor local circulation

31
Q

What compensatory mechanisms are there in chronic hypoxaemia?

A

Increased EPR secreted by kidney -> Polycythemia

Increased 2,3-DPG -> Shift curve to right

32
Q

What can result from chronic hypoxic vasoconstriction?

A

Pulmonary hypertension
Right HF
Cor pulmonale

33
Q

What is cor pulmonale?

A

HF secondary to pulmonary hypertension

34
Q

What are the effects of hypercapnia?

A

Respiratory acidosis
Impaired CNS function: drowsy, confused, coma, flapping tremors
Peripheral dilation: warm hands, bounding pulse
Cerebral vasodilation: headache

35
Q

How can chronic hypercapnia be compensated for?

A

Respiratory acidosis compensated by retention of HCO3 by kidney

36
Q

Describe chronic CO2 retention in brain

A

CO2 diffuses into CSF
CSF pH drops
Stimulates central chemoreceptors
Choroid plexus cells secrete HCO3 into CSF
Central chemoreceptors reset to a new higher level of CO2

37
Q

Why may treatment of hypoxia worsen hypercapnia in chronic type 2 respiratory failure?

A

O2 removes stimulus for hypoxic respiratory drive

Removes pulmonary hypoxic vasoconstriction

38
Q

Describe blood gases when V/Q <1

A

Hypoventilation
pO2 falls
pCO2 rises

39
Q

Describe blood gases when V/Q >1

A

Hyperventilation
pO2 rises
pCO2 falls

40
Q

How are central and peripheral chemoreceptors stimulated in hyperventilation?

A

V/Q ration < 1 in affected alveoli
ALVEOLAR oxygen falls and cardboard dioxide rises
Causes hypoxic vasoconstriction, diverting blood to better ventilated areas
If V/Q still <1 then that alveolar blood will mix with blood from functioning alveoli - ARTERIAL low O2, high pCO2
Stimulates receptors

41
Q

How can V/Q mismatch lead to type 1 respiratory failure?

A

Hyperventilation occurs
Unaffected segments have increased ventilation V/Q>1
- O2 content not significantly increased because the rise in pO2 only causes a small increase in dissolved oxygen and Hb is fully saturated above 10kPa (insufficient to compensate)
Drop in pCO2 and reducing in total CO2 in blood enough to compensate for any CO2 retention

42
Q

Why do V/Q mismatches arise?

A

Occurs in disorders where SOME alveoli are being poorly ventilated

43
Q

What are some disorders that may cause a V/Q mismatch?

A 
Asthma
Pneumonia 
RDS in newborn 
Pulmonary oedema
Pulmonary embolism 
(Early stage COPD)
44
Q

Why does asthma cause V/Q mismatch?

A

Variable airway narrowing

45
Q

Why does pneumonia cause V/Q mismatch?

A

Exudate in affected alveoli

46
Q

Why does RDS in newborn cause V/Q mismatch?

A

Some alveoli not expanded

47
Q

Why does pulmonary oedema cause V/Q mismatch?

A

Fluid in alveoli

48
Q

Why does pulmonary embolism cause V/Q mismatch?

A

Embolus results in redistribution of blood flow
Need to hyperventilate to meet needs
If hyperventilation cant match increased perfusion then V/Q >1
Causes hypoxaemia

(Ie lung cant ventilate the rest of the lung enough to oxygenate the extra blood flow)

49
Q

Why do you get type 1 respiratory failure if there is poor diffusion across the alveolar membrane?

A

CO2 is more soluble so its diffusion is affected less than oxygen

50
Q

Name some causes of diffuse lung fibrosis?

A

Idiopathic fibrosis alveolitis
Asbestosis
Extrinsic allergic alveolitis
Pneumoconiosis

Yr 2 Sem 1 Resp (7 decks)

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