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BL MRCS Part B > Airway > Flashcards

Airway Flashcards

1
Q

what techniques count as simple airway management?

A

Head tilt: forehead and occiput
Chin Lift: fingers under mandible
Jaw thrust: pull on mandible, thumbs on chin
Airway adjuncts: oro-, nasopharyngeal airways

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2
Q

What techniques count as definitive airway?

A

Endotracheal tube

surgical airway

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3
Q

What is the oxygen cascade, and roughly what are the values in kPa?

A

Oxygen cascade is the incremental drop of O2 between atmosphere and blood

  1. Atmosphere: 21.0
  2. Trachea: 19.8
  3. Alveolus: 14.0
  4. ABG: 13.3
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4
Q

What is Henry’s Law?

A

Gas content of solution = solubility x partial pressure

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5
Q

What are the constituents of haemoglobin?

A
  1. Haem moiety

2. Globin chain: 2x alpha and beta chains with 2,3-BPG

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6
Q

What other molecules bind to Hb aside from oxygen?

A
  1. CO
  2. Protons
  3. 2,3-BPG - forms bonds between chains
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7
Q

Where does haemopoesis take place?

A
  1. yolk sac: gestation
  2. bone marrow: shortly after birth
  3. Extramedullary: liver and spleen (pathological)
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8
Q

what are the axis of the oxygen dissociation curve?

A

X: pO2 (mmHg)
Y: % Hb saturation

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9
Q

Why does the oxygen dissociation curve have a sigmoid curve?

A

cooperative binding: one bind facilitates next bind

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10
Q

What is the Bohr effect?

A

shifting of the oxygen curve to the right:

reduced affinity to oxygen, therefore more O2 in tissues

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11
Q

What causes right shift of the O2 dissociation curve?

A
  1. Temperature increase
  2. Acidity increase
  3. 2,3-BPG increase (chronic hypoxia)
  4. CO2 increase
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12
Q

What causes left shift of the O2 dissociation curve?

A

foetal curve is to the left

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13
Q

Why does foetal haemoglobin shift the O2 curve to the left?

A

gamma subunit replaces the beta, and cannot form bonds with 2,3-BPG.
allows it to take up O2 from maternal haemoglobin

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14
Q

What is FiO2 and FiCO2 in the atmosphere?

A 
FiO2 = 21% (0.21)
FiCO2 = 0.035% (0.00035)
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15
Q

How is O2 transported in the body?

A

99% Haemoglobin

1% solution

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16
Q

How is CO2 transported in the body?

A

85-90% bicarbonate ions
5-10% carbamino compounds (plasma proteins)
5% dissolved in solution

17
Q

Explain the CO2 cascade?

A
  1. Atmosphere: 0.03kPa
  2. Alveoli: 5.30kPa
  3. ABG: 5.30kPa
  4. VBG: 6.10kPa
  5. Exhaled: 4kPa
18
Q

How does CO2 transport differ between arterial and venous blood?

A

Arterial: more bicarbonate
Venous: more plasma protein

19
Q

How does CO2 become bicarbonate ions?

A

CO2 + H2O = H2CO3 = HCO3- + H+

20
Q

What enzyme is responsible for turning CO2 into bicarbonate?

A

carbonic anhydrase

21
Q

What is chloride shift

A
  1. CO2 is converted to bicarbonate inside the RBC
  2. This penetrates the membrane unlike H+
  3. Chloride moves in opposite direction into cell
  4. In order to maintain pH
22
Q

Why is haematocrit of venous blood greater than arterial?

A

bicarbonate and chloride shift causes increase in oncotic pressure of red cell

23
Q

If the O2 dissociation curve is sigmoidal, what shape is the CO2 dissociation curve?

A

Curvilinear

24
Q

What are the Bohr and the Haldane effects? and how are they related

A

Bohr effect is decreasing affinity to oxygen (right shift) due to pCO2, acidity, temperature etc.
Haldane effect is downward shift of CO2 as PaO2 affinity rises.

25
Q

What is the equation that links PaO2 and PaCO2?

A

Alveolar Gas equation:

this is normally around 0.8, influenced by respiratory rate

26
Q

How does pulse oximetry work?

A

Red and Infrared LED absorbed at different ratios by the RBCs depending on oxygenation status. A ratio is calculated

27
Q

How is Oxygen dangerous in a chronic retainer?

A
  1. may cause apnoea
  2. chronically raised CO2 rely on O2 for respiration.
  3. excess O2 leads to no respiratory drive and therefore apnoea
  4. Oxygen may also cause hypoxic pulmonary vasoconstriction -> V/Q mismatch
28
Q

What are the pitfalls of O2 pulsometer?

A
  1. poor peripheral perfusion
  2. pigments eg nail varnish
  3. may be affected by rhythm
  4. delay of about 20 seconds
  5. not accurate below 70%
29
Q

What is methaemoglobin?

A

Fe3+ rather Fe2+ as carrier which is worse at carrying O2
May be genetic cause
treated with methylene blue

30
Q

How do you measure efficacy of ventilation?

A

End-tidal CO2

31
Q

What are they types of surgical airway?

A

3 types:

  1. Needle cricothyroidotomy
  2. Cricothyroidotomy
  3. Trachoestomy
32
Q

What are the indications for a surgical airway?

A
  1. failed intubation eg oedema

2. traumatic damage/fracture to larynx

33
Q

Anatomically, where do you site a surgical airway?

A

Median Cricothyroid Ligament
This is the anterior, thicker section of cricothyroid membrane
Located 2nd -> 5th tracheal rings

BL MRCS Part B (4 decks)

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