Nitrous Oxide, Xenon and Oxygen Flashcards

Question

Nitrous Oxide: contraindications to use

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

Increases cerebral blood flow - avoided in patients with raised ICP

Answer 5

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.

Answer 6

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

Answer 7

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

Answer 8

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

Answer 9

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.

Answer 10

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.

Answer 11

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

Answer 12

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

Answer 13

Blocks NMDA receptors

Nitrous Oxide, Xenon and Oxygen Flashcards

(40 cards)