It is the case that the human eye is best adapted for vision in natural light. However, many complex activities are now undertaken in controlled environments like operation theatres which require artificial lighting to be used. Consequently, much effort has been made to try to generate lighting systems which can emulate (or some claim improve upon) natural lighting. The human eye works primarily in contrast to identify objects and to give them context. When contrast is lost, visual performance and hence human performance begins to fail. Contrast can be provided by colour or the amount of light being received by the eye having been reflected from visual targets.
Following are quick tips that are intended to provide prospective purchaser of operation theatre lights with general guidance on the technical, operational, and economic considerations to be taken into account in selecting the most appropriate product for their operation theatre set up.
Background
Effective and successful performance within the operating theatre is enhanced by having lighting which does not cause visual, operational and environmental difficulties such as glare, shadowing or visual stress. The operating theatre environment requires a combination of satisfactory ambient lighting and effective direct and indirect task lighting. The ability to adjust these lighting levels and change their characteristics will enable theatre staff to be more effective. Incorrect or poor lighting can impact on the patient, through poor performance and impaired effectiveness which may cause lengthened procedures through uncertainty or even errors. The wellbeing of the surgeon, the anesthetist and support team may also be adversely affected, whilst the quality and safety of the working environment will be impaired by poor ambient lighting.
Surgical lighting is vitally important within the operating theatre to allow those working to have a clear vision of the surgical site and working area, and able to rely on the performance of the lighting equipment.
In a survey of surgeon’s preferences for changes to the operating theatre, lighting was commented on as one of the most important.
Many theatres traditionally used for open surgery are now also being employed for minimally invasive surgery, microscopic surgery & cardiac surgery. Due to these multifunctional requirements of various specific types of surgery, lighting requirement within these theatres becomes more complex.
Lighting Selection
An important decision to be made when investing in theatre lights is whether each operating theatre will need identical lighting equipment or whether the lighting will need to be specific to surgical disciplines. If all lights are the same, this simplifies the selection process and will often reduce the installation and maintenance costs. Training and product familiarity will also improve efficiency. Uniform equipment across a number of theatres will also allow staff flexibility in moving between different operating theatres. However, deciding upon one manufacturer and one model may prove difficult, due to functional variations between individual surgeons and between surgical methods. A compromise can be made, whereby one manufacturer is chosen and a number of different models or modules selected according to individual theatre requirements.
The variations in technical and design specifications across the range of manufacturer products make the selection of one specific model extremely difficult. Often, clinical preference will influence the features of lights required, based on the positive characteristics or limitations of existing lights. Manufacturers use technical measurements to convey illumination and other features; however, objective interpretation of these criteria by clinicians and procurement teams are often difficult.
To facilitate the correct choice, information from many sources must be gathered in order that the specified criterion for the final product meets the needs and requirements of those responsible for using and maintaining the equipment. Decisions are often made through gathering information from visiting trade exhibitions, experience and by consulting with colleagues from other hospitals.
Selection Team
Healthcare professionals involved in the decision making include:
Surgeons: Those from different specialties will have different illumination needs.
Nurses and OT Assistants: They are more concerned about the maneuverability, adjustment ease and simplicity of changing light handles.
Biomedical Engineers: They will look into the technical specifications, quality of the product, the electrical supply, mounting and suspension of lights.
Architects & Engineers: They will look into aesthetics and structural aspects of the installation.
Purchase & Finance: They will negotiate and look into taxes and payments.
Basic Objectives
There are three key areas under which decisions and priorities should be made when determining a suitable operating theatre light. These are:
Adjustability: The design of the lighting unit and how it can adapt to meet individual requirements.
Brightness: The amount of light delivered by a source in order to illuminate a specific surgical area.
Control: Selection of a good design and an appropriate light source will help the system integrate into the operating theatre environment. However, flexibility and adjustability in the lighting system (amount of light and spread of light)will accommodate a wider range of tasks and activities.
Each of these elements will have an influence on the purchasing decisions for operating theatre lighting.
Technical Considerations
Before we start going into various aspects of operation theatre lighting, it’s important to understand few technical terminologies.
Lux (lx): The unit of measurement for the amount of light at a given point and is measured using a lux meter at that point. One lux is equal to one lumen per square meter.
Colour Rendition Index (Ra & R9): The effect the light source has on the appearance of coloured objects (tissue for example). This is a measure of the quality of light; natural daylight has a CRI value of 100. The closer an operating theatre light CRI value is to 100, the better its ability to render true colours to the human eye. It is important to appreciate how well the light renders a saturated deep red colour (R9) which will allow the surgeon to recognize details better in the area of the wound and to distinguish between tissue colours and arterial or venous blood.
Colour Temperature (K): The perceived coolness or warmth of light measured in Kelvin. Some LEDs permit the ability to adjust colour temperature, which allows a surgical team to manipulate the light characteristics and hence facilitate tissue differentiation.
Central Illuminance (Ec): The Illuminance (lx) at 1m distance from the light emitting surface in the light-field center and is measured in lumens per square meter. For good performance, it is important that the light is capable of achieving both a high illuminance and good colour rendition simultaneously.
Light Field Centre: The point in the light field (lighted area) where illuminance reaches maximum lux. It is the reference point for most measurements.
Depth of Illumination: The distance under the light emitting area where the illumination reaches20% of the central illuminance.
Shadow Dilution: Refers to the light’s ability to minimize the effect of obstructions. An absence of cast shadow or coloured shadow is described as perfect shadow dilution.
Light Field Diameter: Diameter of the light field around light field center, ending where the illuminance reaches 10% of central illuminance.
Fail Safe: The backup possibility in case of interruption of the main power supply.
Lighting Specifications
There is a range of technical specifications which are important to be aware of when making purchasing decisions.
Lamp Technology
There are typically three basic types of lamps used in an operating theatre environment – Incandescent, Gas Discharge and Light Emitting Diodes (LED). Incandescent and gas discharge lamps have traditionally been the main lamp types, utilizing halogen, tungsten, xenon, and quartz. However, other types of lighting now emerging onto the market in several forms, particularly LEDs. LEDs are small semiconductors which emit light when an electrical current is passed through them. An LED unit contains multiple lamps, which can either be all white, or a combination of white and multi-colored lamps. Using a combination of colours allows the surgeon to adjust the lamps to produce the desired colour output.
Lighting Design
In addition to the differences in light source, there are many variations in the design of the equipment. Operating theatre lights are designed in single and multiple light heads which can be fixed in different ways within the operating theatre, for instance all, ceiling, track mounted or a floor standing version with a mobile base. Major operating lights should always be supplied as a “main” and “satellite” pair, as their use in combination is the major tool in reducing shadow from the surgical team. Single lamps, used in isolation may not provide the required light output desired for a surgical procedure. However, when used in conjunction with other light heads, offer the flexibility to adapt to a wide range of procedures. Therefore, when interpreting technical specifications, it is important to examine the light head configurations in addition to the individual output from each lamp. It is also important to examine other operational considerations and features of the light, for example, heat production. Heat production from individual lamps may be within acceptable limits. However, if several lamps and satellites are used, the accumulated effect may exceed the desired level.
Surgical lights can be controlled manually using dimmer switches on lamp arm or wall panel. Many lighting systems now allow for other equipment such as cameras, mics or monitors to be mounted on the arms or integrated into the light heads. All medical lights should have a non-glass or ceramic ‘anti-shatter screen’ between the lamp and the patient. This prevents fluids from being splashed onto the lamp and protects the patient from bits of broken glass in case the lamp bursts.
Heat is produced from the light source in the form of infra-red which is felt by any person in the field of radiation. This can provide an uncomfortable working environment not only for the surgeon but the whole surgical team as well as the patient. It may also hamper the operation by causing the wound tissue to dry out, especially during longer procedures. There is also the possibility of burns to staff, as well as patients when the light source is directed in one place for a long period of time.
Radiant energy defines the radiation being directed to the patient, including the visible light energy which is the largest component. Heat from the light can also affect other equipment including laminar airflow (ultra clean ventilation), and thermal buoyancy. The shape of some lamp heads or systems can affect the laminar airflow when moved. Some light sources, such as halogen lighting, are inefficient because of the amount of energy consumed which leads to heat.
LED lights offer significant benefits in this respect since they do not produce heat at the light source. The life of the light source is also important, with LED lamps offering a service life far greater than incandescent light sources. This can impact greatly the cost of the light over its service life. To minimize damaging heat effects, surgical lights are designed to dissipate the heat at the light source away into the operating room. This is performed in a number of ways including the use of filters or lenses that pass visible light but not heat. Reflectors within the light head also reflect visible wavelengths of light toward the surgical site and transmit heat away from it. Heat may also be transferred by conduction, convection, radiation, or a combination of these. Reducing heat, particularly in the area of the surgeon’s head, provides a more comfortable environment with the potential to improve surgical team performance and theatre efficiency, which would also improve patient outcomes. However, it is important that all these technologies are maintained in good working order and in sound condition and that regular checks are made to ensure safe operation, as the consequences of failure to the patients can be severe.
Light Arms
The light arms which hold the light head is a very important factor to be considered before the purchase of operation theatre lights. They should maintain the position of the light head without drifting. They should not be smooth and not entangle. They should be easy to maneuver with one hand of the surgeon or nurse. The arm length should be such that they can reach any part of the body where the surgeon wants to operate.
Audio Visual Equipment
Many surgical lights are designed to be an integrated component of the whole operating theatre environment. Some manufacturers offer video cameras, monitors and mics mounted directly in the light head or on surrounding equipment.
Cabling, Power Source and Fail Safe
Trip hazards should be eliminated as far as possible. Cabling of AV accessories such as cameras and monitors should be integrated into the operating theatre light arms and not attached externally where they are an infection control hazard and a trip hazard. There are requirements to ensure that operating lights are ‘equipotential’ bonded. This ensures that the light is earthed to the same clean earth potential as other equipment in the room. Major operating lights should always be installed with separate and parallel power supply systems to ensure that one lamp lead will continue to function in the event of the failure of any one component. Robust system designs should be fault tolerant of the first fault. It is never acceptable to run both lighting heads from a single power supply. All operating theatre lighting should always be supplied with an independent and dedicated three-hour emergency uninterrupted power supply to ensure safe continuation of procedures in the event of a power failure.
Infection Control
It is important that lighting equipment, especially handles can be sterilized. The ease of cleaning the lighting systems should be investigated before purchase. The design of operating theatre lights should minimize cracks, crevices, and visible fixings so as to provide clean, clear easy surfaces for cleaning. Surfaces for the build-up of dust and debris should be minimized. The design should also take into account an easy, effective and safe cleaning regime without the requirement for aggressive chemicals, whilst providing sterile controls for movement and control of the light functions.
Warranty and Maintenance
It is important that practices and procedures are put in place to ensure safe operating of medical equipment. It is recommended that operating lights have 6 monthly safety inspections on all elements of the device. If the theatre light uses a battery backup system, this must also be checked. A three-hour battery backup is a minimum standard; systems should be checked as part of the service to make sure it is functioning correctly. A full discharge test should be performed to establish that the lights can still operate for at least three hours from a full charge.
Conclusion
Operating theatre lighting is a system which is very worthy of ergonomics scrutiny. Not only does it involve complex technology which needs to be operated and optimized but it also seeks to enhance, or at least limit the restrictions to, the human body at work. The operating theatre is a demanding workplace which requires high levels of vigilance for long periods of time, often in compromised physical positions whilst applying force. The demands upon the user are great. Technology, such as lighting, is used to assist the surgical team in ensuring the conditions are as beneficial as possible. However, often benefits are matched by associated drawbacks – for instance, more light which helps the vision of the work is normally accompanied by heat, which can cause attrition in the body. These factors need to be carefully balanced to ensure that the best performance is delivered. Theatre lighting is a complex issue both from a technical, performance and systems perspective. Aspects of human vision account for significant amounts of scientific publications in human factors, whilst there is still healthy debate over precise mechanisms and optima for visual performance. Additionally, the increase in the age of the workforce (and population at large) has placed new emphasis on age-related deterioration of sight as employers try to adapt to the needs of more elderly workers.
The unifying means of evaluating visual performance, and lighting as a function of that, is through user evaluation. Through investigation of the relationship between the user, the tasks they undertake and the environment in which they are conducted, it is possible to quantify the performance of lighting both empirically and subjectively. It is significant that once lighting systems are installed, their performance will be judged by the users not on a set of measurable criteria, but on their “adequacy”, which will be a function of the user’s preferences.
Failure to ensure that these preferences are met can lead to costly consequences – including reduced performance derived from the visual strain, increased error rate from poor acuity or unsupported vigilance levels, reductions in safety from an inferior lighting through inability to adjust the lights or additional capital expenditure if the lights are deemed unusable.
Whilst lighting performance can be described by the technical criteria associated with the equipment’s design, its effectiveness will be measured by the users. Accordingly, purchase of lighting on the basis of specification alone is an unreliable and possibly highly flawed approach. The inclusion of informed users early in the procurement process will help ensure that the final purchases made are fit for purpose and offer the best value when all criteria are aggregated. These criteria need to be greater than just price and technical values.
It is also true that new and emergent technology offers potential benefits but also significant difficulties. Assessing the benefits of untested technology will be high uncertainty and hence unappealing to risk-averse procurement professionals.
Accordingly, step changes in performance may be severely hampered despite offering the potential for much greater rewards. Without the ability to experience system performance in situ, users are unlikely to be able to determine the likely benefits for themselves and so will demand systems that they know and trust.
These factors combine to reinforce the need for greater user involvement, not only in the purchasing process but also in maintaining a high level of current knowledge such that they are informed, contributors. Since these users are ultimately the individuals who will determine whether the system is satisfactory or not, largely on the basis of subjective performance, the relatively small cost involved in such involvement can be offset by the potential financial consequences of poor fit between the user and the equipment.
