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Immediate Life Support and Critical illness > Airway and breathing > Flashcards

Airway and breathing Flashcards

1
Q

What are the primary functions of the lungs?

A
  • Oxygenation
  • CO2 elimination
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2
Q

What is minute volume?

A

Tidal volume x Respiratory Rate

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3
Q

What is alveolar ventilation?

A

Portion of the minute volume that takes part in gas exchange

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4
Q

What is dead space?

A

PArt of minute volume which is wasted, either because it remains in the large airways or goes to parts of the lung where there is inefficient gas exchange

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5
Q

When is gas exchange in the lung most efficient?

A

When the ventilation/perfusion ratio approximately equals 1

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6
Q

What is shunting?

A

When perfusion>ventilation - wasted perfusion

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7
Q

What is alveolar dead space?

A

When ventilation > perfusion - wasted ventilation

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8
Q

What happens to CO2 levels in the blood if alveolar ventilation fails?

A

Levels will increase

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9
Q

What proportion of tidal volume remains in the large airways?

A

30%

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10
Q

What is anatomical dead space?

A

Air which remains in large airways and doesnt participate in gas exchange

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11
Q

What is physiological dead space?

A

In diseases such as emphysema, areas of the lung may be ventilated, but not perfused

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12
Q

What does CO2 retention indicate?

A

Lower alveolar ventilation

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13
Q

What is the physiological response to an increase in total dead space?

A

Compensation by increasing overall minute volume - particularly tachypnoea

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14
Q

Why does shunt have less of an impact on CO2 elimination than reduced alveolar ventilation?

A

In a diseased lung, if some blood flow to the lungs bypasses ventilated regions more CO2 will be removed in the remaining ventilated part, again due to the concentration gradient from blood to alveoli

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15
Q

What is arterial concentration of CO2 largely determined by?

A

Alveolar ventilation over the whole lungs

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16
Q

Why do those experiencing significant shunt become hypoxic?

A

As there is a limit on how much oxygen can be carried in each ml of blood, increasing alveolar ventilation cannot compensate for an area of shunt with poor oxygenation since blood leaving the well ventilated area cannot have greater than 100% saturation of O2. Therefore, arterial oxygenation is very sensitive to shunt

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17
Q

Why can hypoxia occur if total dead space increases?

A

Causes effective hypoventilation, largely due to an increase in alveolar CO2 levels (based on alveolar gas equation - PAO2=FiO2(PB−PH2O)−PaCO2/RQ)

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18
Q

What is important to remember with regard to hypoxia and determining whether shunt or increased dead space is the cause?

A

If is often difficult, and can be a combination of the two in different areas of the lungs. Just get on and treat the patient!!!

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19
Q

What are the main groups of causes of retention of CO2?

A
  • Normal/increased resp drive
  • Decreased resp drive
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20
Q

What are causes of normal/increased respiratory drive which can lead to CO2 retention?

A

Anything which increases dead space

  • Pulmonary oedema
  • Contusion
  • Pneumonia
  • Lung collapse
  • Pneumothorax
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21
Q

How do patients intitially cope with increased alveolar dead space?

A

Increase respiratory effort to maintain tidal volume

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22
Q

What can the onset of hypercapnia in those with lung pathologies caused by increased alveolar dead space indicate?

A

May signify patient is becoming exhausted or simply unable to compensate further and that their effective alveolar ventilation is failing

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23
Q

What are causes of decreased repiratory drive which can lead to CO2 retention?

A
  • Opiods
  • Alcohol
  • Benzodiazepines
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24
Q

Does type II respiratory failure with chronic CO2 retention occur in isolated acute pulmonary pathology?

A

No

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25
Q

What are 2 key questions to ask when thinking about CO2 retention?

A
  • Are opioids involved?
  • Is there previous history of chronic lung pathology?
26
Q

What pulmonary pathologies can lead to an increase in shunting and therefore hypoxia?

A
  • Pulmonary oedema
  • Contusion
  • Pneumonia
  • Pneumothorac
  • Large airway collapse
27
Q

What is the effectiveness of O2 administration dictated by from a physiological perspective?

A

Degree of absolute shunting (blood completely bypassing ventilated lung)

28
Q

What are “shunt gases” and why are they called that?

A

Low O2 and Low CO2 - Large increases in shunt can occur with any acute lung pathology. The primary lung abnormality is hypoxia - this stimulates respiration to the extent that alveolar ventilation increases and CO2 falls

29
Q

What is hypoxia most commonly caused by; dead space or shunting?

A

Shunting

30
Q

What circulatory problems can cause respiratory failure?

A
  • Gross disturbance of pulmonary circulation (PE - fat, thrombus, amniotic fluid)
  • Systemic hypotension - hypovolaemia, sepsis, vasodilation or pump failure

THESE ALL CAUSE DEAD SPACE, SHUNT and HYPOXIA

31
Q

Why is assessment of circulation an important part of management of a patient with respiratory failure?

A

Gross distrubances in pulmonary circulation or systemic hypotension leads to dead space, shunt and hypoxia

32
Q

What is an easier way to remember what shunt is?

A

Wasted perfusion

33
Q

What is an easier way to remember what dead space is?

A

Wasted ventilation

34
Q

What criteria are used to determine if someone is at risk of respiratory failure?

A

SpO2 < 94% + PaO2 < 10kPa

or Tachypnoea RR > 25/min

35
Q

What are warning signs of respiratory failure?

A
  • Rising RR
  • Complaining of SOB
  • Use of accessory muscles of respiration
  • Indrawing of tissues at root of the neck
  • Falling SpO2
36
Q

If someone was determined as having inadequate (RR reduced/irregular) breathing on breathing assessment, how would you manage it?

A
  • Bag and mask ventilation - 100% oxygen
  • Check pulse
37
Q

What would you consider doing if airway or breathing was deemed to be inadequate?

A

Call an anaeasthatist

38
Q

What would you look for when assessing the airway?

A
  • Obstruction
  • See-saw movement of the chest/abdomen
  • Anything in the mouth
  • Cyanosis
  • Oxygen mask - is it misting
39
Q

When should you give oxygen in a critically ill patient?

A

Whether breathing is adequate or not - Critically-ill patients should receive high-flow oxygen

40
Q

What should you do if breathing is absent or inadequate?

A

Immediate Atrificial ventilation with bag and mask, and call 2222

41
Q

What is the general consensus with delivering high flow 02 to CO2 retainers?

A

There is a risk of further CO2 retention, but the priority should always be relief of life threatening hypoxia. Hypoxia is more common and more rapidly fatal than CO2 retention

42
Q

What are regarded as essential tests to do in someone with respiratory failure?

A

CXR and ABG

43
Q

How would you assess someones breathing as part of an ABCDE assessment?

A

SO RIPPA

  • SpO2 and Oxygen requirment
  • Respiratory Rate
  • Inspection - End of bed, front and back of chest, including trachea etc.
  • Palpation
  • Percussion
  • Ausculation
44
Q

What are groups of causes of hypoxaemia?

A
  • Hypoventilation
  • VQ mismatch
  • R->L Shunt
  • Diffusion impairment
  • Reduced FiO2
45
Q

What is the alveolar gas equation?

A

Equation is used to calculate the alveolar oxygen partial pressure:

  • PAO2 = FiO2(PB−PH2O)−PaCO2/RQ
    • PAO2 = Alveolar oxygen concentration
    • FiO2 = inspired oxygen fraction
    • PB = barometric pressure
    • PH2O = partial pressure water
    • PaCO2 = partial pressure CO2 in arterial blood
    • RQ - respiratory quotient

Knowing the PaO2 allows calculation of the alveolar-arterial O2 gradient (A-a gradient) - using blood gas analysis

46
Q

What is the importance of calculating the alveolar-arterial oxygen gradient?

A

The A-a gradient, together with the PaO2 and PaCO2, allows systematic evaluation of hypoxemia, leading to a concise differential diagnosis. ABG provides an initial assessment of oxygenation by measuring the PaO2. The A-a gradient is an extension of this, for by calculating the difference between the PAO2 and the PaO2 we are assessing the efficiency of gas exchange at the alveolar-capillary membrane

47
Q

Can hypoxaemia caused by V/Q mismatch be overcome by increasing FiO2?

A

Yes

48
Q

Can hypoxaemia caused by shunting be overcome by increasing FiO2?

A

No - Since shunted blood is not exposed to alveoli/ventilated, and blood which is exposed to ventilated areas will already be saturated with 100% oxygen, hypoxemia caused by a shunt cannot be overcome by increasing FiO2

49
Q

What characterisitics help define hypoventilation as a cause of hypoxaemia?

A
  • Readily increases with small increases in FiO2
  • PaCO2 is elevated

An exception to this is when prolonged hypoventilation leads to atelectasis, which can increase A-a gradient

50
Q

What A-a gradient is hypoventilation characterised by?

A

Normal A-a gradient

51
Q

What A-a gradient is hypoxaemia caused by low FiO2 characterised by?

A

Normal A-a gradient

52
Q

What A-a gradient is hypoxaemia caused by R->L shunting characterised by?

A

Elevated A-a Gradient

53
Q

What A-a gradient is hypoxaemia caused by V/Q mismatch characterised by?

A

Elevated A-a gradient

54
Q

What A-a gradient is hypoxaemia caused by diffusion abnormalities characterised by?

A

Elevated A-a gradient

55
Q

What are examples of pathological physiological shunts?

A
  • Atelectasis
  • Pneumonia
  • Pulmonary oedema
  • ARDS
56
Q

What factors can contribute to the development of hypercapnia?

A
  • Decreased minute volume/hypoventilation
  • Increased dead space
  • Increased CO2 production
57
Q

How does COPD cause increazsed alveolar dead space?

A

Destruction of pulmonary capillaries, resulting in wasted ventilation

58
Q

What are the cerebral effects of hypercapnia?

A
  • Increased RR, followed by depressed consciousness and RR
  • Increased cerebral blood flow and ICP

Together, these can lead to seizures, coma and death

59
Q

What effect does hypercapnia have on oxygen dissociation?

A

Shifts curve to the right, leading to increased release of oxygen to tissues (Bohr Effect)

60
Q

What is the body’s main buffer for respiratory acidosis?

A

Protein - primarily haemoglobin. NOT BICARBONATE

61
Q

Under what circumstances might you suspect someone to have acute hypercapnic respiratory failure?

A

Those with risk of hypoventilation or increased dead space (e.g. COPD) who present with SOB, changed mental status, new hypoxaemia and/or hypersomnolence

Immediate Life Support and Critical illness (6 decks)

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