Chris Thompson  

Suction systems (AS 2120, 1977)

1) Introduction

Suction is required by anaesthetists in many situations, including:

• Airway toilet
• Scavenging of waste gases
• Pleural (-3 kPa) and other drainage systems
• Cardio-pulmonary bypass (vent & pump sucker)
• Gastric decompression, endoscopy
• Surgical suction (operative field, body cavities,TOP, Breech extraction)

Before starting every case, the anaesthetist should confirm that their sucker is working properly, and before every list that the scavenging is correctly adjusted.

2) Vacuum pump systems

a) SIMPLE

Physically sucking down a catheter, usually with a sputum trap, is often used in neonates. The haemovac is a simple, safe, spring powered suction device.

Hand or foot-operated bellows type pumps may be suitable for emergency and field situations.

b) ELECTRICALLY POWERED PORTABLE PUMPs

Disadvantages of noise, explosion hazard, need for electrical cable, and relatively high cost limit the usefulness of these devices. On the other hand, they are portable and do not require a gas source or expensive piping.

c) PIPED SUCTION from a CENTRAL PUMP

Expensive to install but cheap to run thereafter. The central pump station must have:

• Suction failure alarms, a means of adjusting the vacuum pressure to -60 kPa and a 0-100 kPa vacuum gauge complying with AS 1349.
• A minimum of two preferably identical pumps, each with hours run meters, thermal protection, isolating valves, duplicated and bypassable filter assemblies and sterilisable particle traps (marked "Biohazard").
• Automatic startup (with hysteresis) of the backup pump if suction level falls and a suction reservoir (sufficient to limit the number of times the pumps must turn on per hour during usual conditions to ten), a positive pressure blowoff valve, and several other requirements as set out in AS2896-1986.
• Adequate capacity - determined according to the minimum design airflow (which depends on hospital bed numbers). (see table below)
• Safe discharge - must comply with statutory requirements, and be vented to atmosphere above roof level of adjoining buildings, well away from any ventilation intake, window, or normally frequented areas where cigarette butts or lighted matches may be present. Max backpressure 7 kPa.

Piping must be of the usual seamless copper capable of withstanding 1400 kPa, identified by colour and name, leak and crossover tested (should maintain -85+/-1.5 kPa over 1 hour), and have isolating valves, ie comply with AS1169.

Permanent wall outlets, set at the usual 1.5 - 1.7m above the floor are differentiated from others by "Primrose Yellow" control knob and prominent identification. Outlets should be sleeve indexed. Sleeves for suction are the largest (26.9 mmOD and 23.9 ID) of all sleeve indexed fittings.

Control devices allow the user to turn suction on and off, adjust the suction level, display the suction pressure on a vacuum gauge, and have a particulate filter. The gauge must read from the patient side of the filter, and be at least 50mm diameter.

3) VENTURI SYSTEMS

Use high pressure gas (usually wall or regulated cylinder air at 400 kPa) to entrain air through a suitable venturi. Do not require electricity (unlike central suction pumps) - essential where emergency electrical power is unreliable.

Drive gas leaves the venturi at high speed, sucking with it approximately the same volume of the gas to be scavenged. Negative pressures so generated can be adjusted by varying the venturi flowrate.

Should the outlet from the venturi become obstructed, the drive gas will exit the suction line in reverse, pressurising the suction system and whatever is connected to it, ie the patient, to 400 kPa. All such venturi systems should have a positive pressure blowoff valve set at 0.5 kPa, but most do not, including devices designed to screw onto air or oxygen outlets or the twinovac.

In the operating theatres, the venturis are usually located within the wall cavity, and the outlet ducted away to some suitable discharge point.

The "Twinovac" has an adjustable venturi driven suction point. Full suction of -55 kPa is generated with oxygen flows of 22 l/m. The venturi may clog with debris from the suction jar despite the metal gauze protection. High (100 kPa) and low (25 kPa) vacuum versions ( #TM117G and #5183632) are available.

4) PERFORMANCE

Each outlet should meet the following requirements:

• 40 l/m free air flow
• 60 kPa negative pressure
• 4 second time constant (ie reaches 38 kPa (63% of final) in 4 seconds) - the ISO standard 10079-3 requires more than 60 kPa in 10s with a 2l reservoir.

5) CONTROL DEVICES AND USER ATTACHMENTS

Regardless of how the suction is generated, a control device is usually required to adjust the strength of the suction at the user attachment.

Low suction control devices must have a positive pressure relief valve set at 0.5 kPa (5 cmH20), a safety valve set at -24 kPa, and read from 0 - 25 kPa.

High suction control devices should have a relief valve set at 0.5 kPa and read 0-100 kPa.

Scavenging outlets typically only have a simple adjustable valve.

"Suction Bottles", including disposable types, are the most common user attachment. They should be at least 1.2 litres in volume, transparent, sterilisable, marked at 100 or 250 ml levels, and must incorporate some form of check valve e.g. a ping-pong ball) to prevent liquid or particulate matter entering the suction line or venturi. Never connect the suction tubing directly to the suction source.

6) HAZARDS

• Not connected or inoperable when required (esp. rapid sequence induction).
• Catheter problems, ie infection, mechanical trauma to teeth or mucosae, breakage (tip of Yankauer), airway disconnection during suction, etc.
• Explosion hazards with flammable vapours. Portable electrical devices may ignite the vapours. Conductive suction tubing is required. External venting of explosive or flammable gas mixtures must not be near a potential ignition source.
• Excessive suction, particularly with chest drains, which always require low suction.
• Pressurisation of the suction line. Obstruction of the venturi outlet in venturi suction systems without a relief valve (ie twin-o-vac and some old hospital systems) will result in driving gas pressure (400 kPa) in the suction line. Obvious disaster if you have a chest drain !
• Health hazard to those cleaning suction bottles, tubing, and central suction filters and traps.

Last updated Tuesday, December 15, 2020
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