5. Scavenging Flashcards
Scavenging system:
the basic arrangement comprises collection, transfer, receiving and disposal systems.
Collection system
: this is usually a shroud that is connected to the APL or
expiratory valves of the ventilator via a 30-mm connector (which prevents
confusion with components of the breathing system).
Transfer system
Receiving system
Transfer system: this comprises wide-bore tubing to remove the gases.
— Receiving system: this is a reservoir system, which is protected against excessive
pressures by valves. The positive pressure relief valve is set at 1,000 Pa (1 kPa); the
negative pressure relief valve is set at –50 Pa (0.05 kPa).
Disposal system:
subatmospheric pressure to eject the gases is generated by a fan
which develops a low-pressure high-volume system which can vent 75 l min–1.
Other ejector systems include vacuums and venturi devices
Passive systems:
Passive systems: the components of the system are as described earlier, and the
gases are vented to atmosphere either by the patient’s spontaneous respiratory
efforts or by the mechanical ventilator.
Active systems
: the basic components of the system are again as described , but
the vacuum created by a fan or a pump in the disposal system draws the
anaesthetic gases through the system. It is important that the negative pressures
so generated cannot be transmitted to the patient
Purpose of scavenging
: the safe removal of waste theatre gases is a health and safety
issue and, since 1989, with the government introduction of Control of Substances
Hazardous to Health (COSHH), has been a legal requirement.
It is only the local environment that is protected, because the gases are pollutants that are vented
unchanged to atmosphere. Most are potent greenhouse gases.
Staff health issues
s: some studies have identified increased risks of spontaneous
abortion in women exposed to trace concentrations of anaesthetic gases, and also
that male anaesthetists were more likely to father daughters than sons. There was,
in addition, the suggestion of an increase in haematological malignancies. The
association is not strong, because other studies have not replicated these data.
Moreover, many millions of general anaesthetics are given annually in the
developed world and were this to be a real problem, then its provenance would
be a lot more obvious.
Other Means of Minimizing Operating Theatre Pollution
Theatre air changes (at least 15 times per hour).
Substitution of total intravenous anaesthesia (TIVA) and regional anaesthesia for
inhalational anaesthesia.
Use of low- and ultra-low-flow breathing systems.
Maximum Permitted Exposure Levels
Nitrous oxide: 100 parts per million (ppm)
Sevoflurane and desflurane: 50 ppm. As yet there are no maximum limits;
COSHH states that their similarity to enflurane means that 50 ppm would be
appropriate.
Halothane: 10 ppm.
— USA: in America, the permitted maximum for all halogenated volatiles is
2 ppm.
