Visitors to the operating rooms of virtually any large hospital in the developing world are likely to encounter expensive equipment in pristine condition lying unused in nearby storerooms. Typically found among these items are brand-new anesthetic machines, complete with sophisticated monitoring devices, which have been manufactured and transported at great expense. Yet, these devices often remain unused because the machines are not designed for use in the conditions that prevail locally. To function, they require uninterrupted supplies of oxygen and electricity, as well as regular attention by highly skilled electronic engineers to perform essential servicing and maintenance. In the absence of one or more of these essential requirements, the anesthetic machines, however expensive, cannot function.
The squandering of resources to produce machines that are unsuitable, and then transporting these devices to isolated hospitals in poor countries where they cannot be used, is clearly environmentally harmful, yet this practice has continued unchecked for many years. A World Health Organization report in 2010 stated that up to 75% of medical equipment supplied to developing countries failed to work.1 Efforts to stop this waste, or even slow it down, have been largely unsuccessful, partly because many have vested interests in maintaining the status quo, and partly because acceptable alternatives have been unavailable.
Until recently, most research in this field has been directed toward the upper end of the market, whereas the needs of the poor have been largely ignored. As a result, anesthetic machines capable of overcoming the additional hazards found in isolated hospitals in poor countries received little attention, and research in this area attracted little funding.
The precursor of the Glostavent® (Diamedica UK Ltd., Barnstable, UK), known as the Oxyvent, was first described in 1997.2 It was specifically designed, after consultations with anesthetists working under difficult conditions, to enable them to overcome the additional problems they faced.
To meet their requirements, the Glostavent, as it later became known, was frequently modified to increase efficiency and versatility without increasing its cost.3
It incorporates 3 additional components not found on standard continuous-flow machines:
- A drawover breathing system to enable inhalational anesthesia to be delivered when no pressurized gases are available.
- A ventilator that is gas driven and can function in the absence of electricity.
- An oxygen concentrator to eliminate dependency on cylinders of oxygen.
THE DRAWOVER BREATHING SYSTEM
To deliver an inhalational anesthetic to a patient, a carrier gas passes through a vaporizing chamber containing the anesthetic in liquid form, where it is vaporized. In continuous-flow anesthesia, the carrier gas is pushed across by pressure from a cylinder or central supply situated upstream of the vaporizer. Alternatively, it can be drawn through the vaporizer by subatmospheric pressure generated downstream of the vaporizer by the patient’s inspiration or by the expansion of bellows, as in drawover anesthesia.
The essential features of a drawover system are illustrated in the triservice apparatus (Fig. 1).
They include the following:
- A reservoir tube, open to the atmosphere at one end for the entrainment of air and with a side port for supplementation with oxygen if it is available.
- Vaporizers with low resistance to enable spontaneous respiration to occur.
- A self-inflating bag with a valve to direct the flow of gas toward the patient when the bag is compressed.
- A nonrebreathing valve close to the patient’s airway. This ensures that expired gas cannot re-enter the breathing system and that the inspired gases from the anesthetic machine cannot be diluted with room air.
These valves also ensure that the gas mixture can only pass through the vaporizing chamber once so that accumulation of volatile agent cannot occur.
With the advent of reliable central gas supplies, more sophisticated ventilators, and anesthesia delivery systems, continuous-flow anesthesia has gained steadily in popularity to the extent that drawover anesthesia is now seldom used in modern well-equipped hospitals. Consequently, drawover anesthetic equipment was not developed to the same extent as continuous-flow equipment, and in some quarters, has come to be regarded as obsolete.
However, this is certainly not the case whenever anesthesia has to be administered in circumstances in which the supply of pressurized gases is unreliable or nonexistent. This includes isolated hospitals in poor countries, after natural disasters, or in the presence of military or terrorist activities.
In these circumstances, the use of drawover equipment has enabled inhaled anesthesia to be administered safely using atmospheric air as the carrier gas. As a result, there has been a resurgence of interest in drawover equipment in recent years, with new models such as the Glostavent, manufactured by Diamedica UK Ltd., (Barnstaple, United Kingdom) (Fig. 2) and the TTM Anesthesia Unit.a
THE GAS-DRIVEN VENTILATOR
The ability to provide automatic ventilation to the lungs is a desirable feature of an anesthetic machine and is essential if it is also required for the treatment of respiratory failure in an intensive care or recovery unit. Most modern ventilators are powered by electricity, but, as described previously, this is often unavailable in poorer countries.
Gas-driven ventilators offer an alternative, but they can be extremely extravagant in their requirement for oxygen. Many require a volume of drive gas equal to or greater than the entire minute volume of the patient.4
The Diamedica ventilator was designed to reduce the volume of drive gas required. Under normal circumstances, when electricity is available, the pressure required can be provided at no extra cost by oxygen from the concentrator. If the electricity supply fails and the concentrator is no longer able to generate oxygen, the reserve oxygen cylinder automatically takes over as source of the driving gas. The Diamedica ventilator requires a drive gas volume of only approximately one-seventh of the patient’s minute volume.5
Additional conservation of oxygen is achieved by recycling this oxygen. After it has driven the bellows, it is collected and returned to the breathing system, enabling an Fraction of Inspired Oxygen (FIO2) in excess of 30% to be delivered without additional supplementation.
THE OXYGEN CONCENTRATOR
Among the essential features required for providing an anesthetic service is a reliable supply of oxygen. In remote hospitals in poor countries, oxygen is usually supplied in individual cylinders, which are expensive6 and difficult to transport over long distances on poor roads. Thus, the supply is frequently interrupted.
However, atmospheric air costs nothing, it does not require transport, and the supply is unlimited. Consequently, it is both economically and environmentally sound to use atmospheric air as the source of oxygen. This is done by means of an oxygen concentrator similar to the types used for domiciliary oxygen therapy.7 Room air is filtered and compressed to a pressure of 20 psi before passing through canisters containing zeolite, in which nitrogen is removed and the residual oxygen delivered to the patient.
The use of oxygen concentrators in hospitals has been investigated in parts of Canada, where an oxygen cost saving of 62%8 has been described.
The concentrator used in the Glostavent has been adapted and improved for use during anesthesia. It can produce a flow rate of 8 L/min of 95% oxygen as well as 8 L/min of air while requiring just 400 W of electricity. The output pressure of 20 psi is sufficient to drive a mechanical ventilator. Thus, it is the source of both oxygen and air for the patient to breathe and of power to drive the ventilator.
The concentrator is designed to require minimal intervention from the operator. The sponge filter at the air intake port requires washing daily, but the zeolite, unlike soda lime, does not become exhausted, continually regenerates, and can last for years.
CONSERVATION OF OXYGEN
In addition to the economies listed above, the volume of oxygen used in a drawover breathing system can be further reduced by the scrupulous avoidance of any waste and maximal conservation of available oxygen.
One of the features of the drawover breathing system as used in the triservice apparatus and the early versions of the Glostavent is the open-ended reservoir tube with its side port for supplementary oxygen (Fig. 3).
During expiration, the nonrebreathing valve at the patient’s airway automatically closes, and the forward movement of the anesthetic mixture through the system ceases. Consequently, the flow of oxygen, which is continuous, is diverted into the reservoir tube to be included in the next breath. To maximize the FIO2, the flow rate of supplementary oxygen is increased to fill the reservoir tube, but this inevitably allows spillage of oxygen through the open end of the tube during expiration.
To eliminate this, the original open-ended reservoir has been modified by 3 simple additions9 (Fig. 4):
- A flap valve at the open end of the reservoir tube. This prevents any oxygen from escaping into the atmosphere and ensures that every liter supplied is delivered to the patient.
- A 2 L reservoir bag to increase the volume of the reservoir.
- A pressure relief valve set at 5 cm H2O to prevent overdistension of the reservoir bag.
If the flow of supplementary oxygen entering the reservoir exceeds the rate at which the contents are inhaled by the patient, then the pressure in the reservoir rises, the flap valve closes, and no oxygen is wasted. The oxygen flow rate is then adjusted to prevent an increase in pressure sufficient to open the pressure relief valve and waste oxygen.
CONVERSION TO A CONTINUOUS-FLOW SYSTEM
An additional advantage of the modified reservoir described above is that it enables the drawover breathing system to be readily converted to a continuous-flow system if this is required.
Drawover anesthesia depends on an airtight seal at the patient’s airway for the generation of subatmospheric pressure. However, in certain circumstances, such as when inhalation must be induced in an uncooperative patient, an airtight fit may be impossible to achieve, and continuous flow of the anesthetic mixture may be required.
Using the modified reservoir described above, conversion to continuous flow occurs automatically as the oxygen flow rate increases until the flap valve closes and the mixture is directed to the patient. No other equipment is required.
MANAGEMENT OF ELECTRICAL FAILURE
The electricity supply in isolated parts of the world can be unreliable, with frequent interruptions sometimes occurring several times a day. To minimize this disruption, the Glostavent features an uninterruptable power supply unit. In effect, this acts to store electricity so that the supply can continue for an additional period of up to 20 minutes after the interruption.
In addition to these interruptions, there are commonly major voltage fluctuations as high as 40% in either direction. Delicate electronic apparatus cannot cope with fluctuations of this magnitude and rapidly cease to function. However, the uniterruptible power supply, which is an integral component of the Glostavent, is capable of smoothing out these fluctuations so that the oxygen concentrator can continue to function normally.
If the electricity supply is interrupted for more than 20 minutes, an audible alarm on the oxygen concentrator indicates that it has ceased to function, either as a source of oxygen for the patient or of pressure to drive the ventilator. A reserve cylinder of oxygen situated at the rear of the Glostavent (type E containing approximately 680 L) then takes over both the supply of oxygen for the patient and of pressure to drive the ventilator. This changeover occurs automatically and requires no intervention by the anesthetist.
SELECTION OF ANESTHETICS
Nitrous oxide is commonly used to provide the analgesic component of inhalational anesthesia. It is supplied in cylinders that, like oxygen cylinders, are expensive to purchase and transport. However, in drawover anesthesia, nitrous oxide is not used. The analgesic component can be provided IV.
Because nitrous oxide is considered a serious pollutant of the atmosphere,10 the use of anesthetic techniques that can prevent pollution are important, not only for reducing atmospheric pollution via the greenhouse effect, but also by avoiding the cost of production and transport of heavy and bulky nitrous oxide cylinders.
In place of nitrous oxide, air is now commonly used in combination with oxygen to avoid high FIO2 levels and the possibility of subsequent damage to the respiratory tract. Whereas in continuous-flow breathing systems, a constant supply of cylinders of compressed air is required at considerable extra cost, in draw-over anesthesia, room air can be used, which costs nothing and requires no transport.
Standard plenum vaporizers are not suitable for drawover anesthesia because of their high resistance to spontaneous respiration. The Diamedica drawover vaporizer (DDV1), a low-resistance vaporizer designed for use with halothane or isoflurane, is more accurate than the Oxford Miniature Vaporizer (OMV), which was used in drawover anesthesia for many years.11
In response to requests from armed forces and various aid agencies, a separate vaporizer (DDV2) is also available for use with sevoflurane, and this too has been shown to be accurate over the wide range of conditions likely to be encountered.12
Trilene is still requested by anesthetists in parts of Africa, where it is popular because of its analgesic properties and low cost. A new vaporizer calibrated for trilene has been introduced recently and is now available as well.
CONSERVATION OF RESOURCES AND REDUCTION OF POLLUTION
The Glostavent incorporates a drawover breathing system. The primary advantage of this system is that it enables inhaled anesthesia to be administered in situations in which continuous-flow anesthesia is not possible because of the absence of compressed gases.
The use of the drawover breathing system affects both the environment and the overall cost of anesthetic administration. When compared with the use of a circle system with low flows of fresh gas, it is immediately obvious that the volume, and therefore the cost, of the volatile agent is greater. There is also an increase in atmospheric pollution although pollution within the operating room itself can now be avoided by use of the Diamedica valve situated on the anesthetic machine.13
Although these disadvantages cannot be ignored, they should not be viewed in isolation because they are more than balanced by other relevant factors. A closer examination reveals that there are in fact many additional factors affecting both pollution and cost that are not immediately obvious but that nevertheless need to considered when the 2 systems are compared.
First, with a circle system, when the flow of fresh gas is reduced to a rate below the patient’s minute volume, it is mixed with expired gases. The composition of the resulting mixture is therefore unknown, and additional equipment in the form of gas analyzers is required for continuous monitoring of the concentration of oxygen, carbon dioxide, and the volatile agent in use.
Gas analyzers are extremely expensive, and, moreover, require regular servicing and maintenance by highly trained technicians without which they cannot function. The presence in the operating room of expensive monitors with no function represents a monumental waste of resources that continues unabated in many countries.
In contrast to a drawover system, continuous-flow machines require an uninterrupted supply of compressed gases. Cylinders of oxygen, nitrous oxide, and/or compressed air are required that are not needed in drawover anesthesia. The additional expense of manufacture and transport of these cylinders over distances that can be very great must also be considered.
Furthermore, soda lime must be purchased and regularly replenished when using the circle system, whereas in drawover anesthesia, it is not used at all.
With the circle system, expired gases re-enter the breathing system, which requires using filters or sterilization of the breathing system after use. In contrast, drawover anesthesia can be administered safely without any of these additional expenses.
Given all of these factors, the apparent savings from use of the circle system are more than balanced by the additional expenses incurred.14
COMPARISON WITH TOTAL INTRAVENOUS ANESTHESIA
Although the use of total IV anesthesia (TIVA) has its advocates, drawover anesthesia remains extremely popular with those administering anesthesia in hazardous situations. In a recent survey among British Military anesthetists, 39 of 40 elected to continue to use drawover techniques in preference to TIVA.15
It is notoriously difficult for the anesthetist to predict exactly when a surgeon is going to finish operating. Occasionally, a surgeon will unexpectedly announce that an operation is coming to an imminent conclusion. When using TIVA, any anesthetic remaining in the syringe at this time is discarded to avoid possible contamination of subsequent patients. In contrast, any volatile agent remaining in a vaporizer at the conclusion of an operation is not wasted but saved and can be used on subsequent patients.
Electronic monitors have become an integral component of modern anesthetic machines, and although they have undoubtedly contributed to patient safety, they have also added considerably to cost. Furthermore, they require regular calibration and servicing to maintain their accuracy and effectiveness as well as a supply of electricity that is reliable and uninterrupted. Because none of these requirements is likely to be met in isolated hospitals in poor countries or in disaster situations, savings can be made by foregoing these expensive monitors and anesthetic machines and relying instead on clinical observation and simple, battery-driven monitors such as the Lifebox oximeter (Acare Co Ltd., New Taipei City, Taiwan). In addition, the following safety features are inherent in the drawover system:
- The gas mixture leaving the vaporizer passes directly to the patient, and its composition is unchanged. The presence of the nonrebreathing valve at the patient’s airway and the unidirectional valve on the self-inflating bag ensure that the gas mixture cannot re-enter the vaporizing chamber during either controlled or spontaneous respiration. The concentration of the volatile agent will therefore remain unaltered.
- It is impossible to administer a hypoxic mixture inadvertently. This is because the atmospheric air drawn in has a concentration of 21% to which supplementary oxygen may then be added. Therefore, the resulting concentration of oxygen will be higher not lower than the original 21%.
- The carbon dioxide concentration depends solely on the patient’s respiration, which can be observed readily. It is not affected by the state of the soda lime, as in the circle system, in which expired soda lime can be ineffective and can lead to hypercarbia. Similarly, it is not dependent on high flows of fresh gas as in some other breathing systems.
THE PORTABLE VERSION OF THE GLOSTAVENT
An anesthetic machine such as the Glostavent, which can function safely in isolated hospitals with few facilities, will enable many operations to be performed locally that might otherwise have required transport over long distances to larger and better-equipped hospitals. The savings in time, money, and improvement in patient care and comfort can be considerable.
After catastrophic events, such as earthquakes, typhoons, and military or terrorist activities, emergency surgery may be required where there are no facilities, and everything needed has to be carried to the patient. For use in these circumstances, a portable version of the Glostavent is available (Fig. 5). It consists of a simple drawover system presented in a rigid hand-held container and weighing just 10 kg.16
Using a portable Glostavent, a charity such as Mercy Flyers,b for example, is able to transport a mobile team consisting of a surgeon and an anesthetist to an isolated hospital, confident that they can complete an operating list with the facilities for safe anesthesia.
In addition to what has already been published and is in use, the following improvements are now available and awaiting publication.
Helix Portable Ventilator
This is a time-cycled, volume-limited, pressure generator. Because it is gas driven, it can function independently of the supply of mains electricity. It can be driven by an oxygen cylinder or an oxygen concentrator. In the absence of either, a rechargeable battery-powered compressor is now also available. A single oxygen concentrator could run 3 or 4 ventilators (Fig. 6).
A stainless steel vaporizer calibrated for trilene is now available after requests from anesthetists, mainly from rural hospitals. Trilene is still used for general anesthesia in parts of Africa, where it remains popular, mainly because of its analgesic properties and low cost compared with other volatile agents.
Low-Pressure Oxygen Storage Reservoir
Cylindrical aluminium vessels on wheels are now available in 2 sizes: 20 and 100 L. These can be filled with oxygen that has been produced by an oxygen concentrator. It is then compressed to 5 bar and stored at this pressure. It can subsequently be used to provide both driving gas for the ventilator and supplementary oxygen for the patient in the event of an electrical power failure.
Oxygen Flushing Device
A frequent complaint by users of drawover anesthesia is the absence of a means of flushing the system with oxygen in an emergency situation. An oxygen flushing device, which is unique to drawover anesthetic equipment, is now available on the Glostavent anesthetic machine.
Additional Vaporizer for Portable Version of Glostavent
A new version of the original Diamedica Portable Anesthetic Machine (DPAO1) has been introduced to improve versatility. The original version had a single vaporizer calibrated for either halothane or isoflurane. A second version (DPAO2) is identical except that the vaporizer is calibrated for sevoflurane. The DPAO3 is a slightly larger version designed to accommodate both vaporizers.
The Glostavent is a self-contained unit specifically designed to enable general anesthesia to be administered safely and economically when support facilities are limited or nonexistent. This has been made possible by eliminating dependence on unreliable factors, such as the supply of oxygen and electricity and the availability of highly trained technicians.
The Glostavent has evolved slowly into its present form in response to helpful suggestions from many anesthetists experienced in difficult situations throughout the world and with close cooperation with engineers who were able to ensure that the function of every component was based on sound engineering principles.17
As the Glostavent has gradually evolved, every opportunity has been taken to reduce extravagance and waste, to conserve supplies whenever possible, and to encourage reliance on simple clinical monitoring rather than on sophisticated gadgetry.
With the introduction of the Glostavent, the availability of inhalational anesthesia in the poorest and most isolated parts of the world has been increased, not by spending more money but by spending less. This has been made possible by the selection of simple components that have each been specifically designed to overcome the difficulties encountered locally and contributed to savings on transport, fuel, and manufacturing costs.
Name: Roger J. Eltringham, MB, ChB, FFARCS.
Contribution: This author helped write the manuscript.
Attestation: Roger J. Eltringham approved the final manuscript.
Conflicts of Interest: This author has no conflicts of interest to declare.
Name: Robert C. Neighbour, MSc, CEng, FIET.
Contribution: This author helped write the manuscript.
Attestation: Robert C. Neighbour approved the final manuscript.
Conflicts of Interest: Robert C. Neighbour reported a conflict of interest with Diamedica, Managing Director of Diamedica (UK) Ltd., the manufacturer of the Glostavent.
This manuscript was handled by: Maxime Cannesson, MD, PhD.