Piped gas supply

Question 1

Piped medical gas and vacuum (PMGV) systems

Supply, pipework, outlets

Answer 1

• Gases supplied from central supply points: e.g cylinder manifold banks or liquid oxygen storage tanks
• Copper pipework system: copper is used because it prevents the degradation of hte gases and has bacteriostatic properties
• Outlet valves control the flow of gas through the hospital
• Piped supply outlets are **identified by gas colour coding, gas name and shape, and pressure **(air): safety system to ensure patient not given incorrect supply
• Outlets can be installed in various different ways: e.g. flush fitting units, surface-fitting units, on booms or pedants, suspended on a hose, or gang-mounted

Question 2

What pressures are gases supplied at?

Answer 2

Gases are supplied under pressure of 400 kPa. In addition, air is also supplied under pressure of 700 kPa

Question 3

Piped supply outlets: colour coding

Answer 3

Oxygen: white
Nitrous oxide: blue
Air (400 kPa and 700 kPA): black
Suction: yellow
Scavenging: yellow/blue (note connection to anaesthetic machine is brown)

Question 4

PMGV system outlets: how are incorrect connections prevented

Answer 4

PMGV system outlets are designed to accept matching quick connect/disconnect probes, but only the correct connector will fit: outlets have Schrader sockets with an indexing collar specific to each gas or gas mixture

Are recognised by:
* Gas colour coding
* Gas name
* Shape
* Pressure (e.g. air outlets may be 400 or 700 kPa)

Question 5

Connection between PMGV outlets and anaesthetic machine

Colour coding, British Standard

Answer 5

PMGV system outlets are connected to anaesthetic machine using flexible colour-coded hoses that are permanently fixed
* oxygen -white
* nitrous - blue
* air - black
* yellow- vacuum/suction
* brown- scavenging

British Standard states that the end of the hose connecting to the anaesthetic machine should be permanently fixed using a nut and linear union and gas-specific non-interchangeable screw threads (NISTs)

Question 6

Identify the NIST colour coded hoses

Question 7

Safety features/ tests in piped gas supply system

2 central, 3 in theatre, single hose vs tug test

Answer 7

• Isolating valves behind break glass covers (area valve service units or AVSUs) are positioned at strategic points throughout the network. In the event of fire or exposion, gas supply can be immediatly isolated and shut down
• Low pressure alarms: alarm systems usually downstream of AVSUs, monitor up to 6 gas services in normal, high and low-pressure conditions, and alarm if any faults
• Single-hose test to prevent cross connection: ensures correct gas flowing via correct flowmeter
• Reserve bank of cylinders available, usually attached to the anaesthetic machine, can be turned on in case of a central supply failure
• Tug test : performed to detect misconnection - confirms that each pipeline is correctly inserted into appropriate gas supply terminal (inadequately inserted pipes can appear to be attached, but there will be no gas flow)

Question 8

Pipes gas risks from hoses

Type with greatest risk

Answer 8

• Risk of fire from worn or damaged hoses
• Because of heavy wear and tear, risk of rupture is greates in oxygen hoses used with transport devices
• Regular inspection and replacement of all medical gas hoses every 2-5 years recommended

Question 9

Compressed medical air

Uses, pressures, supply

Answer 9

Two types:
* Clinical use - e.g. anaesthetic machine, intensive care ventilators: supplied at 400 kPa
* To drive power tools e.g. orthopaedic surgical tools or tourniquet equipment: supplied at 700 kPa
Terminal outlets for the two pressures are different, to prevent misconnection

May be supplied from
* Cylinder manifolds
* Air-supplying compressor (more economical)
* Note oil-free medical air is cleaned by filters and separators and then dried before use

Question 10

Vacuum system

Components, 3 tests for efficiency

Answer 10

Consists of
* Pump
* Receiver
* Filter: removal of 99.999% bacteria. Also used to prevent contamination by fluids, condensate and smoke

Three tests to determine efficiency of central-piped vacuum systems:
* Vacuum of at least 400mmHg below standard atmospheric pressure (-53kPa) is generated
* Each central-piped vacuum outlet should be able ot withstand a flow of free air of at least 40L/min
* A unit should take no longer than 10 seconds to generate a **vacuum (500 mmHg) **with a displacement of air of 25L/min

Question 11

Necessary features of suction devices

Answer 11

• Should be at least 2 vacuum outlets (yellow) in each operating theatre, 1 per anaesthetic room, 1 per recovery or ICU bed
• Negative pressure (i.e. degree of suctioning) can be adjusted to use (e.g. adult vs child) using a vacuum regulator
• Collection resevoir appropriately sized: sufficient capacity for aspirated material, but if too large will take a long time to generate adequate negative pressure
• Suction subing should be flexible, firm, transparent, and of sufficient internal diameter and length for optimal suction efficiency