Michael Patkin's

Ergonomics and Anaesthesia

Publication history, Reflections & comments



Surgery & ergonomics


Information design

Editorials, book reviews




The practice of anaesthesia involves the anaesthetist, the patient, drugs and equipment, the surgical team, and a complex hospital setting. Till now, little attention has been paid to the anaesthetist as a worker who manipulates and monitors a complicated system. As a result, there are many features of his equipment and his working environment which add avoidable stress and a liability to error.

This neglect of human factors in the working environment is very common. The scientific study of man at work is called Ergonomics. It has been applied usefully to industry and some aspects of surgery in the last thirty years. To clarify the role of Ergonomics as it may apply to anaesthesia° it is useful to have a model of man at work (Fig. 1).

                            l                         l
          (ergonomics)       (bio-engineering)

This model has three elements - anaesthetist, equipment, and patient - and two interfaces. The second of these interfaces is familiar as bio-engineering, and is concerned with the interaction between anaesthetic technology and the patient. The first interface, neglected in the past, is the province of Ergonomics.

The areas studied in Ergonomics are:
1. Equipment design.
2. Work-place lay-out
3. Environmental conditions such as lighting .
4. Related questions of shill acquisition, productivity, and safety. .

The word "Ergonomics" is derived from two Greek words, ergos = workv and nomos = basis or foundation. It was coined in 1949 by Murre1lv who led a team of scientists in England during the Second World War in the development of weapons systems. There are societies devoted to its study in most countries, and a growing number of trained ergonomists solving problems of man-machine mis-match in industry and in the armed forces. It received tremendous impetus in the United States (where it is often referred to as Human Factors Engineering) from the aerospace program.

Although there is a huge amount of data ready to be applied to fields of work such as anaesthesia, there has been lack of awareness of this data by anaesthetists and the designers of their equipment.

The ergonomics of controls and displays has special relevance as anaesthetic technology becomes more complex. It is even more important as questions arise of de-skilling certain aspects of work so they are carried out by technicians and nurses under the supervision of anaesthetists, instead of directly by the anaesthetist himself.


1. Designing eouipment to be handled

The design of many tools and knobs is more appropriate for steel-fingered pixies. Rational design must be based on the type of handgrip to be used. The more important features are: .

(a) The power grip of the hand.

Levers and handles should suit the sire and comfortable position of the hand. Their length should equal or exceed the width of the palm. They should be thick enough (3 to 4 cm.) to be gripped by the fingers and thumb securely. There should be clearance around them for the knuckles, and they should be placed to avoid wrist flexion or awkward body posture.

There should be no sharp edges or high spots, but some flattening or moulding to avoid unwanted slip and rotation. Thickening at each end of a handle (like a pommel) also prevents accidental slipping. There should be electrical insulation. The amount of force needed can be measured with a simple spring balance or kitchen-type scale, and checked against appropriate recommendations. Carrying handles must be vertically above the centre of gravity.

(b) Finger-tip grips.

A secure grip requires adequate surface area of contact' as wide as the flattened pulp of the thumb. Luer Lock connectors should have a rotating collar at least 13 mm. long, 20 mm. thick, and spaced 25 mm. from adjacent projections (AAMI draft recommendation). Many small items such as needles are awkward because of their small size, especially if stiff to turn. Some syringes are so stiff that the operator's hand wobbles with the effort of pushing the plunger in the barrel. Simple measurements with a kitchen scale suggest that a desirable stiffness for syringes is in the range of 100 to 300 grams weight. One brand of stiff syringe, no longer made, took 1600 grams weight of force, and had sharp edges on the barrel flange which made it even more awkward to use (Editorial' 1970). Such assessments are simple and valid for a wide range of operating room equipment (Patkin, 1970).

In other work such as-microsurgery, much thought went into the design of handles for needleholders during the 1970'sv with great improvement in the accuracy of work that could be done. Similar analysis for items such epidural needles may yield benefits of the same degree. There are over 50 separate criteria with which to assess the design of handles, push-buttons, and small items to be used in the fingers.


2. Work-place layout

An example of bad design often quoted is a lathe made 20 years ago. Its controls were ideally sited for aa worker four feet six inches tall, with an arm-span of eight feet, shoulders two feet wider and eye-balls on stalks eight inches long. Today the design of operating tables, anaesthetic machines' monitors, and their controls suggests the ideal build of an anaesthetist is something equally grotesque. The bulk of the soda-lime canisters on the side of a machine, drawers or other obstructions under what is meant as a work-surface and writing surface, and the distance to operating table controls and lights are all instances of engineering which may be mechanically good but which ignore the dimensions of the human who is to operate them.

These examples, and many more, suggest it is worth reviewing all aspects of anaesthetic practice to find more effective ways to arrange equipment and other facilities optimally. The size of theatres must allow room for nurses to circulate. Induction rooms, if used, may be unsuitable for left-handed anaesthetists or have outlets behind him, and be too small for treating cardiac arrest.

One of the simplest and most humane measures to take in many operating theatres is to replace the traditional anaesthetist's stool with a good-quality office chair, costing about $150. Good seating involves almost 15 separate factors. Just two of them worth mentioning are having castors on the seat' and quick height adjustment by an air-spring mechanism instead of the tedious screwing height adjustment which users of different stature don't bother to alter. One other addition, not often found on office chairs is being able to put the lumbar support horizontally, so the anaesthetist can turn on his chair and rest his forearm as well as the clinical record on it when he is writing up notes.


3. Environmental conditions — lighting and legibility

Lighting is, one of the few isolated ergonomic considerations which anaesthetists have studied because of the importance of recognising cyanosis. They are familiar with problems of different fluorescent tubes, green drapes, and darkness for endmscopy and radiology under anaesthesia. Selector switches should accompany the surgical and general theatre lighting controls on the wall panel. The need for adequate surgical lighting is only just being appreciated, though one thousand years ago the Arab physician Albucasis recommended that surgery for cataract be done by the light of the sun at noon.. This represented a lighting level of 100 000 lux, compared with the maximum of 60 000 lux now provided by manufacturers.

However there is more to lighting than its intensity and colour rendering. Contrast and glare are also important. Typical lighting levels recommended for office work are ay general illumination of 150 Iux" and local lighting of 400 lux, except less over video display screens unless shielded. Because surgical lighting is so bright, up to 80 kilolux the general theatre lighting must also be brighter. This is to have contrast between the main area of work and the surroundings less than the desirable maximum ratio of five to one.

Glare is recognised as a problem in surgery. The polished stainless surface of many stainless steel instruments has been replaced in many cases by a matte or blacked finish. Clare on the glass faces of display dials reduces legibility. Clare can be decreased by suitable changes in design and arrangement.

The design of displays is a large subject on its own, with needs for simple, legible, and standard presentation of data. Information presented to the anaesthetist may be of measured quantities or of status. Different grades of system status are best shown by indicator lights coded green, amber, red, or red flashing 3 to 5 times per second. Detailed recommendations such as this are listed in references at the end of this paper, and they also include types of audible warnings to be used.

Numerals and letters must both be legible at distances beyond 30 centimetres. The ratio of their height to their distance should be at least one to 200, and there are detailed recommendations for the style of print which makes them easiest to read, as well as the wording placed on equipment. Mistakes occur from parallax, pointers hiding numerals, scales whose direction of increase contradict the user's expectation, poIycarbonate plastic covers which reflect and scratch easily, and confusing or obscured labelling.

Displays should be grouped according to function, follow a 1ogical sequence from top to bottom and left to right, and have an obvious relation in space to the controls which alter them. Non-urgent information, such as the maker's name and model and serial numbers of equipment, should not be on the front face. Controls and displays for maintenance should be shielded, while controls which are critical to life should be handiest, and protected against accidental activation or de-activation.

Apart from lighting and vision there are other environmental factors which can affect theatre staff adversely, as well as the patient. Temperature and humidity obviously need control, and there should be simple gauges for these in operating theatres, together with an efficient hospital engineering service to maintain good working conditions.

Even low-level noise disturbs good working rhythm and may mask nocessary conversation or audible signals. Distracting chatter, noisy equipment, and inappropriate impromptu lectures may all be intrusive.

A 2 decibel mosquito hum can be enough to ruin a night's sleep and one's efficiency the next day. Similar noise in the operating theatre may be difficult to control in a teaching hospital environment.

Apart from impairing efficiency of work, factors in the environment can be downright dangerous' but this very danger has meant earlier recognition and control of such threats as anaesthetic gas pollution, electric shock, and radiation. Some attention has been paid to the work load of hospital staff in terms of lack of sleep and efficiency, but stress of all kinds has to be considered in planning the working environment of operating rooms. Problems include back injuries and tripping.


4. The ergonomics of skill in anaesthesia

The anaesthetist exercises skill in several different areas - in handling equipment and tissues, in observing and interpreting data, and in relating to colleagues. Few of these skills have been analysed in a formal way. The potential contribution of ergonomics is in the area of manual skills in anaesthesia. It is useful to illustrate this with an example of a simple everyday task - threading a needle. The essential movement in doing this skilfully is steadying the two hands together to abolish normal hand tremor. This single movement is learned in seconds. Someone who has found it difficult to thread a needle will find this lesson lasts a lifetime.

Few anaesthetic procedures have been analysed in terms of their elements. In many skills, it is the accuracy of feel rather than the 'accuracy of movement that is important. A greengrocer learns the weight of a kilogram of apples, and a postal clerk learns when a letter is likely to weight more than 20 grams, by repeated checking against a scale. A budding anaesthetist is likely to learn the resistance of vein wall through a run of haematomas. It would be surprising if gaining such skills was not quicker and less damaging if helped by learning what level of force is used. It takes about 500 grams to cut adult abdominal skin with a scalpel. The surgical apprentice has to learn not to scratch the skin awkwardly instead of incising. Other steps in technique are learned more slowly. Analogies suggest learning is quicker with better feedback, and simulated material is used for teaching intravenous and other puncture.

Understanding the forces involved, and the details of the common pattern of hand posture used by experts, should be as efficient as the use of a mechanical trainer in grooving a golf swing' seeing aa video replay of one's mistakes in many other spurts and activities or a videotape of an expert cook.

This area is much more speculative than the ones previously discussed, but the rewards are potentially great. It suggests enormous potential value from such studies. Already there are manikins used for teaching cardio-pulmonary resuscitation, and simulations of bone for trainee orthopaedic surgeons learning techniques of internal fixation.

The psychological analysis of how shills are acquired can be carried further, defining stages of learning. The first of these is the coding of individual movements, especially hand and body posture, and an example of this was given earlier. The later stages are arranging coded elements of movement into a sequence, which eventually becomes an unconscious act like the sub-routine of a computer program. Carrying this analogy further, different values for variable factors are set according to the individual task, for example fragility of tissues in older patients.


Basic implications of ergonomics for anaesthesia

The first requirement is a fresh look at the work of the anaesthetist to define his activities in a logical and detailed way. The necessary vision for a total view of this is outside the capacity of the present writerr, but certain aspects emerge to serve as a starting point. One of these is to list the functions and relations of the anaesthetic machine itself.

Functions of the Anaesthetic Machine and Related Equipment:

Circuits - gas, liquid, and electrical, both integral and added.
Displays, including alarms
Gas Reservoirs

Equipment and drug store
Work surface, writing surface

Associated functions - ventilator, gas absorption and removal

Related functions - suction, diathermy, tourniquet I.V. lines, posture of patient.
Needs for information, both everyday and for rare cases
Communication - verbal' written, transmission facilities, information storage, retrieval and display.

The problems presented are those of design, both engineering and ergonomic, especially in terms of bulk and mobility. The ergonomic needs can be considered, at least to start with, in general terms.

Human Factors Needs for Medical Devices:

1. Male and female .anthropometry (of users and patients). 2. Information processing capacity of humans
3. Simplicity, because of staff changes and stress
4. Environmental factors - light, noise, atmosphere etc.
5. Facility for speedy use
6. Mobility for transport and re-arrangement


Implications for action

If anaesthetists have been persuaded that the foregoing analysis is valid and significant, the following practical steps should be taken:

1. Organisations such as the Australian Society of Anaesthetists should formally acknowledge the relevance of ergonomics to anaesthetic equipment and work-place design and to training and analysis of skills used.

2. Organisations of anaesthetists should have an ad hoc committee and designated resource persons to relate ergonomics to anaesthesia.

3. Ergonomics should be incorporated into standards for anaesthetic equipment, a protocol of recommended design for work areas including operating theatres, recovery and intensive care areas' and a protocol for routine procedures and for training.

4. Research on ergonomics and anaesthesia should be encouraged by the suitable choice of projects for senior trainees and others likely to seek new areas for investigation.

Relevant literature

Much of the published literature in anaesthesia relates to equipment' design, but with few exceptions such as PoIlard's "Chair of Anaesthesia" (1972) and Boquet's limited ergonomic analysis (1980) the relevance of human factors has been ignored. The only systematic analysis of ergonomic factors in relation to medical devices found so far is that in the draft recommendations of the American Association for Medical Instrumentation (AAMI). On the engineering side, Hazard Alerts and other detailed reports have been prepared frequently by ECRI (the Emergency Care Research Institute) at Phildadelphia in the United States.

Surgical applications of ergonomics have been studied over many years by the present writer, especially in relation to microsurgery, where limitations of human capacity have been a basic factor, apart from technology, in determining what could be achieved.

The general literature in ergonomics is vast. A nodding acquaintance with one or two of the basic texts should prove of great interest to many practising anaesthetists because of the nature of their work.



Ergonomics in general:

Grandjean E.(1980).Fitting the Task to the Man: An Ergonomic Approach. Taylor & Francis, London.
Cakir, A.' Hart, D.J.v and Stewartr T.F.M. (1980) Visual Display Terminals: A Manual Covering Ergonomics, Workplace Design' Health and Safety, Task Organisation. John Wiley Sons, Chichester.
McCormick, E.J. (1978) Human Factors in Engineering and Design, 4th ed. Mc.Graw Hill
Applied Ergonomics (bi-monthly)

Ergonomics in Surgery:

Patkin, M (1981). Ergonomics and the Surgeon, in Clinical Science for Surgeons, edited Burnett. Butterworthn Sydney.
Patkin M. (1970). Surgical Instruments and Effort. Med.J. Aust., 1. 22S-226.
Editorial (1970). On Giving Injections. Med. J. Austv l, 194-5.

Ergonomics in Anaesthesia:

Pollard, Brian J (1972) A Chair of Anaesthesia. Anaesth. Intens. Care, 1, 161-162
Boquet, G., Bushmanv J.A.° and Davenport, H.T. The Anaesthetic Machine - A study of Function and Design (1980). Br. J. Anaesth., 52, 61-67.
Proposed AAMI "Human Engineering Guidelines and Preferred Practices for Design of Medical Devices, seventh draft, April 14, 1980° unpublished.
American National Standard Minimum Performance and Safety Requirements for Components and Systems of Continuous-Flow Anesthesia Machines for Human Use, ANSI Z79.8-1979. Lyons, G. (1980). Surgical Operating Tables in New South Wales Hospitals. Thesis, Faculty of Science (Industrial Arts), University of New South Wales.

Other References:

"Health Devices Update", published monthly by the Emergency Care Research Institute in the United States, has just been re-named "Technology for Anaesthesia", "Technology for Surgery". and so on for other fields. ECRI provides a continuing program of education, consultation' and information which no major hospital should be without, if only for legal and financial reasons.


Since writing the paper, an important article was passed on to me by Professor M.J.Cousins, of Flinders Medical Centre. Under, the title of "A New Anesthesia Delivery System'". Cooper and his co-workers at Harvard (1978) describe a prototype computer-based anaesthesia machine whose electronics and engineering break away completely from traditional mechanical systems.

It is clear such a break must be complete, because of unreliable interfaces between the two technologies. Cooper's integrated design avoids the mess of spaghetti tubing which is all too evident with add-on devices in theatres today. Its greatest value seems in presenting information to the user which avoids the need for mental re-interpretation of data, so that clinical information is presented in its most relevant and usable form. In addition, great thought has been given to the reliability of the internal workings of what is now a "black box", but even this has modular circuits which should be easy to replace as needed.

However some important questions remain in considering such a radical change. One is cost of such a proposal across the broad range of less affluent general hospitals, whose efficiency would suffer. Their continually changing staff at every level would have to learn two parallel technologies of anaesthesia. And what would the relevance of such new technology be for the bulk of less sophisticated surgery, much of it in countries struggling with sorry little budgets for health already? The crucial remaining question, the subject of the paper which follows, is how to design and manage the total system of work in operating rooms so that they are fit for humans to work in as well as be treated there. For many people less practical than Cooper it would be too easy, despite his cautions, to be diverted by the dazzling promise of this inevitable new technology-at the cost of neglect of other human factors. With such awareness, the potential rewards are enormous.



Drafts of the following paper were improved out of recognition by the criticism of colleagues at Whyalla and by Drs. E. Alfred, K. Brown, M. Cass, R. Davis, and J. Russell. Mistakes in it are mine.

Additional references

Cooper, J.B., Newbower, R. S., Moore, J.W., and Troutman, E.D. (1978). A New Anaesthesia Delivery System. Anesthesiology, 49: 310-318.
Ream, A.R. (1978). Editorial - New Directions: The Anaesthesia Machine and the Practice of Anaesthesia, ibid. 307-308.



Presented to the Annual General Meeting of the Australian Society of Anaesthetists, Melbourne, October 1981.

MichaeI Patkin FRACS
The Whyalla Hospital, South Australia 5600


Ergonomics is the scientific study of man at work. Anaesthesia has concentrated on the interface between equipment and patient, but how the operator relates to his working environment has fundamental effects" for better or worse, on this relationship.

It is convenient to consider a model of the anaesthetist at work as three elements and two interfaces:

Ergonomics has been applied widely in industry, the aero-space program, and the design of consumer items. Its application to anaesthetic practice, as well as to these other fieldsv can be considered usefully in 4 areas:

1. Equipment design for the user (especially handles, read-outs).
2. Work-place lay-out (the anaesthetic machine, seating, a more general analysis of operating tables for the surgeon as well).
3. Environmental conditions, as they affect operators as well as patient (lighting, temperature, noise).
4. Related questions of skill, productivity, safety.

Much of this is well known to anaesthetists, but in patchy fashion. An ergonomic approach to the work of the anaesthetist fills in some large gaps, and also provides an enormous fund of information with a large positive contribution to make, but neglected in the past.

Doctors are uniquely placed to bridge the interface to designers -and engineers, because 0f their background in applied anatomy and physiology. Existing design too often neglects the simplest logic of human factors - knobs designed for steel-fingered pixies, visual displays obscured through glare, poor lettering, or bad wording, equipment with a handsome stainless steel finish but awkward to grip or sit on, and failure to analyse and present the basic skill elements involved.

Other papers in this session will present various aspects of the anaesthetic-work interface. This abstract can barely introduce a new perspective of anaesthesia, but the full paper will give am overview of ergonomics, present a check-list of design features for handles, and briefly discuss the ergonomics of operating tables and seating in the operating theatre.