General Guide for interfacing Inhalation Sedation

Three main Elements of Equipment required for Inhalation Sedation:

  • Dedicated Inhalation Sedation Flowmeter: Analogue or Digital
  • Dental Scavenging; active
  • Medical Gases; oxygen & nitrous oxide

Inhalation Sedation Flowmeters

There are currently approximately 7 main types of dedicated inhalation sedation flowmeters in circulation on the U.K. and Irish marketplace.  These include: MDM (Cyprane, Fraser Sweatman or Matrx), Digital MDM (Matrx), MXR (Porter), Quantiflex Mark II (Cyprane, Fraser Sweatman), Ultra and Newport (Accutron) and Mc1 (McKesson).  Some older types such as the Quantiflex Mark I (Cyprane) do also still exist although numbers are declining.All these units require some form of mounting to hold them in the correct operating angle,
with the exception of the Accutron Newport which is a floor standing model.
The chart below sets out which mounting may be used with which flowmeter type:


Flowmeter Type Matrx 4 cyl stand Matrx tall stand* Matrx low stand* Matrx swing bkt* Matrx cabinet mount*
MDM yes yes yes yes yes
DMDM yes yes yes yes no
QRA Mark II yes yes yes yes yes
Flowmeter Type Porter 4 cyl stand Porter tall stand* Porter low stand* Porter swing bkt* Porter cab mount*
MXR yes yes yes yes yes
Flowmeter Type McK 4 cyl stand McK bracket* Mck low stand*
Mc1 yes yes  yes
Flowmeter Type Acc 4 cyl stand Acc mob stand* Acc wall arm*
Ultra yes yes yes

* For connection to pipeline system only & mounting peg also required



Scavenging of Waste Nitrous Oxide:

Excerpt from HTM02-01  (Ref 1)

Chapter 10 – Anaesthetic Gas Scavenging Disposal Systems
10.5: Active Scavenging for dental installation is an entirely different concept.
An active system is one in which there is a flow generated through the patient’s nasal mask and this carries away the waste gases exhaled by the patient.  This flow is in the order of 45 L/min and is achieved by connection of the mask (via a suitable flow-limiting adaptor) to either; a dental vacuum system or directly to an active scavenging system
(BS/EN) wall terminal.

Appendix L – Important notes for use of medical vacuum and anaesthetic gas scavenging.  Sections 8, 9 and 10 refer to Active Dental Scavenging Systems.

The above taken in conjunction with the excerpt below taken from the NIOSH Technical Report: Control of Nitrous Oxide in Dental Operatories establishes that dental scavenging should have an air flow rate at the nasal mask of 45 L/min at all times during the procedure.

‘A Scavenging system, simply defined, is a means to collect and remove excess gases to prevent them from being vented back into the operating room.  Installation of an efficient scavenging system is the most important step in reducing trace gas concentrations.  It has been demonstrated that ambient concentrations have been lowered by 90 percent through the use of an efficient system’ (Ref 2)

Explanatory note on Passive systems:This type usually consisted of 22mm clear corrugated hoses w/one way valve – gas passed from fresh gas outlet (22mm) along tubing to nasal hood on patients face with a blanking cap to prevent escape of waste gases (the nasal hood could either be blue autoclavable


Dynomite scented single use), then, as the patient exhaled, a valve opened in the expiratory hose and the expired air was forced out, by the patients normal expiratory effort, into the further length of tubing.  Commonly, this tubing was then either ‘hung’ out of the window, or connected to a low level wall exit vent block.  In more recent times, these systems were also connected to a wall mounted AGS (Anaesthetic Gas Scavenging) System such as a MEC Purair 130 or Dental 2000.  These units needed to be mounted no higher than one metre above floor level to have any efficacy.  The transfer hose from the patient needing to be level or slope downwards, thus assisting the flow of waste gases, nitrous oxide in particular, being heavier than air.  In cases where the receiver was mounted high up on the surgery wall then ‘back-flooding’ of gases did occur resulting in ambient pollution and increased staff exposure levels as a result.
Comment: This system has been around for approximately 40+ years and is not efficient, with a potential for large amounts of waste gas leakage and resulting ambient surgery pollution.  Historical note: In January 2009, Porter Instruments announced they had purchased the Matrx Nitrous Oxide Division from Midmark.  All manufacturing was transferred to the Porter factory in Hatfield, Philadelphia.  In January 2010, Porter announced that they were discontinuing the Passive breathing system – with immediate effect. The stocks of spare parts were already severely limited and this system is now obsolete.Explanatory notes on Active Systems: An active breathing system is one which has been designed by the Manufacturer to operate and withstand air flow rates of 45 L/min.  This usually results in smaller bore, thicker walled tubing than that used in passive circuits (22mm).  There are several types available including the Porter brown, A.N.S.* and Accutron system.  These are the most commonly seen types of which the Porter brown is the most popular.  For more information on the individual system, please refer to ‘Explanatory Overview of Dental Nitrous Oxide Scavenger Breathing Systems – Passive vs Active’.(Ref 3)
* The A.N.S. System is designed to deliver the NIOSH recommended scavenging flow rate of 45 L/min at 3 in. Hg.  The vacuum control block is factory pre-set and unable to be adjusted by the customer.

One of the most critical aspects of an active scavenging system is how the waste gases are vented from the surgery environment.  There are currently three methods available although these are not always suitable for all locations:

  • Suitable dental vacuum system – High Volume Port
  • Anaesthetic Gas Scavenging System terminal
  • Miniscav Unit

Dental Vacuum System – HVE: All active systems were originally designed by the Manufacturer to connect to a dental vacuum system and this is widely used in the U.S.A. for example.  However, the system has to be capable of sustaining the flow of 45 L/min during the procedure and must be vented externally from the surgery environment.  This usually means employing the high volume port which can be a problem as most dental surgeries only have one.  Connection to the low volume will not give the required draw.  Some chair Manufacturers e.g. ADEC, are addressing the issue with provision of a dual HVE option on certain chair models, however this is expensive and can only be done when the chair is being replaced.  In addition, due to exhausted gases being exposed to motor arking, it is not recommended that Tridac (Aspirade) models are used for this purpose. It is further advisable to check with the relevant equipment Manufacturer as to the suitability of any suction unit.

Anaesthetic Gas Scavenging System Terminal: Larger facilities such as hospitals and health centres may have an AGS System already fit.  This consists of a remote pump serving any number of AGS terminals.  These terminals are ‘balanced’ and normally used – for G.A. purposes with an airbrake in-line.  The air break (also known as a Barnsley Receiver) is not needed for use with an active dental breathing system as it literally ‘breaks’ the air flow rate – only offering a maximum draw of 0.5 L/min (BS 6834:1987) instead of the required 45 L/min.  Instead, the use of a simple AGS Adapter – consisting of a stainless steel AGS Probe and specially turned connecting element which allows connection of the Porter brown or other active system by interference fit, is located directly into the self-sealing valve of the AGS terminal.  The flow on the breathing system is then adjusted by means of the system flow-limiter – e.g. vacuum control block on the Pb system.  The ‘mini-flowmeter’ block indicates the ideal flow by a green area and black bobbin.  Once a fresh gas flow is established and the system is connected to the AGS, the bobbin can be adjusted to sit within the green area. (It is important to do this with the mask seated firmly on the patient’s face.)

If the facility already exists, then this is an ideal way to connect the scavenging system.  However, they are expensive to install and maintain and are really only suitable for multi surgery use.

Miniscav Unit: This unit was designed specifically to meet the purpose of dedicated active dental scavenging.  They are small, quiet (48db) and easily fit within the surgery environment only requiring a normal 240v power socket and small 16mm external vent hole to take the rigid venting assembly (15mm).  Care must be taken to ensure this vent discharges well away from ventilation inlets, opening windows etc to ensure pollution does not re-enter the building.  The unit has the advantage of flexibility and has been developed to work particularly well with the Porter brown system although it is possible to use both the ANS and Accutron system.  Maintenance is easy and cost effective, the unit requiring an annual check after the first year and service exchange including replacement hosing in the second year.

Placement of Medical Gases:   There is often confusion as to exactly how medical gas terminals – oxygen & nitrous oxide should be placed in order to correctly and easily interface with the r a equipment.  This is slightly more complicated than it originally appears and some costly mistakes have been made in recent years – in one case, the row of terminals oxygen/nitrous oxide and ags were placed on the surgery wall – directly across the room from the chair head and therefore totally inaccessible.

It is unfortunate that the current HTM 02-01 contains no guidance for terminal placement and orientation when used with inhalation sedation equipment – only G.A.  This is covered in Part A Design, installation, validation and verification; Chapter 3 Provision of terminals units  This chapter gives clearly defined terminal unit mounting orders for horizontal and vertical arrays and mounting height information, however these are mostly useless when it comes to interfacing with r a units!   It is hoped that some form of instruction regarding these will be added to any revision of HTM02-01, but due to the current economic climate and budget cuts, this is unlikely to occur any time in the near future so therefore, common sense must be made to prevail in these circumstances.

Terminal placement for inhalation sedation equipment is crucial and ideally, the r a flowmeter will be located in the triangular area from the dental chair head – usually in either a dedicated cabinet – suggested width 500mm or in the knee space area formed by the cabinetry return.  The usual mounting employed here would be either a swing arm bracket or cabinet mount depending on the type of flowmeter fit (see mounting chart on page 1).  In either case, the terminals would then be located in the rear of the cabinetry in such height and orientation as to interface with the flowmeter supply hoses.

In cases where only oxygen and nitrous oxide terminals are required then orientation is not crucial.  However height/position can be.  Most flowmeters are supplied with one metre hoses and these are usually ideal as they allow for outward movement and positioning of the head/mounting whilst in use without tangling, which can be caused by excessive length.  This can lead to wear or damage.  The normal advice is to position the terminals in a central side to side/top to bottom configuration and the HTM 02-01 orientation can be followed in this instance – whether placement is horizontal or vertical.

The position changes somewhat when an AGS terminal is ‘thrown’ into the equasion.  There are two issues here:

  • Orientation
  • Height

Orientation: This is dependant on which side of the cabinetry the r a flowmeter is mounted – the main criteria being that the ags terminal is always the furthest side away.  This obviously contradicts the HTM 02-01 orientation but is to ensure that the breathing system vacuum tubing does not become entangled with the oxygen/nitrous oxide supply hoses.  The staff need to be able to clearly view the vacuum control block and tubing at all times during the sedation procedure and this is impossible if obstructed by medical gas hosing/flowmeter etc.

Height: The height is also crucial as the ags terminal must be placed at least 12 inches from the underside of the work surface.  This is to allow correct placement of the vacuum control block and vacuum hose loop (to prevent hose kinking).  Again, no provision is made for this is HTM 02-01.

This document is offered as an initial guide to surgery planning , but if further clarification is required then please contact Customer Services on 01535 652444 or email

Ref 1: HTM 02-01
Ref 2: NIOSH Technical Report: Control of Nitrous Oxide in Dental Operatories
Ref 3: Explanatory Overview of Dental Nitrous Oxide Scavenger Breathing Systems – Passive vs Active’

Mrs J E Pickles
Issue 2 03/14

RA Medical Services Ltd