25.4 Low Flow + Machine Check

Question 1

a) What are the advantages (15%) of low-flow anaesthesia?

Answer 1

Advantages:

1&raquo_space; Economy
(reduced volatile use).

2&raquo_space; Heat and moisture conservation
(less relevant when HME used).

3&raquo_space; Pollution reduction
(chlorine-containing volatiles cause
ozone destruction).

Question 2

a) What are the disadvantages (20%) of low-flow anaesthesia?

Answer 2

Disadvantages:
» Carbon dioxide absorber required.

> > Gas analysis required
(increasing difference between
inspired gas concentrations and
rotameter levels as anaesthesia continues).

> > Leak-free circle system required
(so not suitable for mask anaesthesia or
if LMA poorly fitting or
if uncuffed tube with large leak).

> > Slow response to changed setting on vaporiser.

> > Accumulation of unwanted gases:
• Substances exhaled by patient:
alcohol, methane, carbon monoxide,
acetone, therefore contraindicated
in intoxication, diabetic
ketoacidosis, carbon monoxide poisoning.

• Products of reaction with absorbents,
e.g. carbon monoxide production resulting from reaction of desflurane and dry baralyme.

Question 3

b) Describe how a circle system should be checked before each anaesthetic? (45%)

Answer 3

> > Visual inspection:
ensure correct configuration and assembly,
no foreign material in tubing,
no leaks in reservoir bag.

> > Manually check: ‘push & twist’ all connections.**

> > Pressure leak test:
between 20 and 60 cm H2O,
occlude patient end and squeeze reservoir bag, ensuring no leak.

> > Carbon dioxide absorber:
inspect contents,
ensure adequate supply and
ensure the colour indicates
sufficient absorption capacity.

> > Correct gas outlet selected**.

> > Two-bag test
(after ventilator and vaporisers checked):

• Attach a second bag on patient end
(ensure angle piece and filter attached).

• Set fresh gas flow to 5 l/min and manually ventilate – check whole breathing system patent and unidirectional valves are moving appropriately.

Check function of APL by squeezing both bags together.

• Turn on ventilator. Turn off fresh gas flow. Turn on and off each
vaporiser in turn – there should be no loss of volume.

Question 4

c) What other components of the anaesthetic work-station must be checked before each anaesthetic?
(20%)

Answer 4

> > Breathing system:
• System patent, leak-free, two-bag test.

• Vaporisers correctly fitted, filled,
leak free, plugged in if necessary.

• Alternative systems (Bain, T-piece) checked.

• Correct gas outlet selected.
» Ventilator:
functioning and correctly configured.

> > Airway equipment:
full range required, working, with spares.

> > Suction: clean, functioning.