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My Primary Deck > Nitrous Oxide, Xenon and Oxygen > Flashcards

Nitrous Oxide, Xenon and Oxygen Flashcards

1
Q

Nitrous Oxide: MAC

A

105%

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2
Q

Nitrous Oxide: B:G coefficient

A

0.47

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3
Q

Nitrous Oxide: Critical temperature and critical pressure

A

36.5°C and 72 bar

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4
Q

Dose-response curve for volatile agents

A

20% below MAC - almost all patients move in response to surgical stimulus
20% above MAC - less than 5% of patients move

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5
Q

Xenon vs Nitrous Oxide: blood:gas solubility

A

Xenon B:G 0.114

N2O B:G 0.47

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6
Q

Xenon vs Nitrous Oxide: MAC

A

Xenon MAC 65-70%

N2O MAC 103%

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7
Q

Xenon vs Nitrous Oxide: Flamability

A

Xenon is non-flammable

Nitrous oxide is flammable

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8
Q

Nitrous Oxide: SVP at 20°C

A

52 bar (5200 kPa)

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9
Q

Entonox: SVP at 20°C

A

52 bar (stored as a liquid so gauge will continue to read 52 bar until the liquid is exhausted)

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10
Q

Oxygen: Critical Temperatue

A

-119°C

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11
Q

Oxygen toxicity: normobaric

A

Can cause atelectasis, tracheobronchitis and even ARDS at FiO2 >0.6
FiO2 = 1.0 can cause damage to healthy lungs in 12-24 hours

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12
Q

Oxygen toxicity in the neonate

A

Retinopathy of prematurity caused by retrolental hyperplasia
Necrotising enterocolitis
Bronchopulmonary dysplasia
Intracranial haemorrhage

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13
Q

Oxygen: boiling point

A

-183°C

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14
Q

Oxygen: manufacture

A

Fractional distillation of air

Oxygen concentrator using zeolite mesh to adsorb nitrogen from atmospheric air (produces 97% oxygen)

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15
Q

Xenon: CNS effects

A

May be used to enhance CT images in the brain
Not recommended for neurosurgery due to variable increase in ICP
Has significant analgesic properties

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16
Q

Xenon: cardiovascular effects

A

Does not alter myocardial contractility

May cause small decrease in heart rate

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17
Q

Xenon: respiratory effects

A

Reduces respiratory rate
Increases tidal volume
Does not cause diffusion hypoxia

18
Q

Xenon: metabolism

A

Not metabolized in the body; excreted via the lungs

19
Q

Xenon: manufacture

A

Fractional distillation of air - very expensive (2000 times the cost of N2O)

20
Q

Xenon: MAC

A

MAC 71%

21
Q

Xenon: Blood:Gas coefficient

A

B:G 0.14 (extremely quick onset and offset)

22
Q

Entonox: pseudocritical temperature

A

Cylinder: -7°C, most likely at 117 bar
Pipeline: less that -30°C at 4.1 bar

23
Q

Entonox: composition

A

50:50 mix of N2O and O2 - effectively dissolve into each other and do not behave in a way predicted from their individual properties - the Poynting Effect

24
Q

Nitrous Oxide: metabolism

A

Less than 0.01%

25
Q

Nitrous Oxide: contraindications to use

A

Nitrous oxide will cause rapid expansion of any air filled space therefore contraindicated in pneumothorax, air embolus

26
Q

Nitrous Oxide: toxicity

A

Cobalt ion present in Vitamin B12 is oxidised by N2O so that it is unable to act as a co-factor for methionine sythetase, resulting in reduced synthesis of methionine, thyidine, tetrahydrofolate and DNA.
Few hours exposure: megaloblastic bone marrow
Few days exposure: agranulocytosis
Few years exposure (e.g. unscavanged dental practices): neurological syndromes resembling subacute degeneration of the spinal cord

27
Q

Nitrous Oxide: the Concentration Effect

A

As N2O is the only agent used in sufficiently high concentrations, a disproportionate rise in alveolar fraction is observed when compared with inspired fraction. This leads to the second gas effect - used alongside other induction agents, the high uptake of N2O will lead to increased concentration of oxygen and volatile agent, reducing induction time

28
Q

Nitrous Oxide: CNS effects

A

Increases cerebral blood flow - avoided in patients with raised ICP

29
Q

Nitrous Oxide: cardiovascular effects

A

Mild direct myocardial depressant effects counterbalanced by increased sympathetic activity.
Therefore in health very little change. However, in cardiac failure with no sympathetic drive can cause reduced cardiac output.

30
Q

Nitrous Oxide: respiratory effects

A

Causes small fall in tidal volume that is offset by increased respiratory rate

31
Q

Nitrous Oxide: manufacture

A

Nitrous oxide is manufactured by heating ammoninum nitrate to 250°C
NH4NO3 –> N2O + 2H2O

Impurities such as NH3, N2, NO, NO2 and HNO3 are removed by passage through scrubbers, water and caustic soda

32
Q

Filling ratio

A

Weight of the fluid in the cylinder divided by the weight of the water required to fill the cylinder (NB weight!)

In the UK = 0.75
In hotter climates = 0.67 to avoid cylinder explosion

33
Q

Nitrous Oxide and air filled cavities

A

It expands air-filled cavities because it is 40 times as soluble as nitrogen; thus, it passes from the blood into the cavity faster than nitrogen can diffuse out. This can double the size of a pneumothorax in 10 minutes at a concentration of 70%. Also expands air embolism and may cause pneumoencephalocoele after neurosurgery.

34
Q

Nitrous Oxide: occular surgery

A

The use of nitrous oxide during general anaesthesia in gas-filled eyes may have disastrous visual results caused by gas expansion and elevated intraocular pressure. The gases SF6 and C3F8 are most commonly used. Patients must be advised of the potentially catastrophic results of undergoing general anaesthesia before their intraocular gas bubble has resorbed. The use of nitrous oxide for patients with intraocular gas should be avoided. It may be prudent for patients with intraocular gas to wear notification bracelets warning anaesthetists about the presence of intraocular gas lest emergency surgery be needed by a patient unable to advise anaesthesia personnel about the potential danger.

35
Q

Carbon Dioxide: Production

A

Either oxidisation of carbon containing substances or heating calcium or magnesium carbonate

36
Q

Carbon Dioxide: Density

A

1.98kg/m3 (about 1.5 times that of air)

37
Q

Carbon Dioxide: Critical Temperature

A

31.2°C

38
Q

Carbon Dioxide: Critical Pressure

A

73.8 bar

39
Q

Carbon Dioxide: Boiling Point

A

-79°C

40
Q

Nitrous Oxide: Mechanism of Action

A

Blocks NMDA receptors

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