WO2010100559A1

WO2010100559A1 - Surgical instrument table ventilation devices and methods

Info

Publication number: WO2010100559A1
Application number: PCT/IB2010/000461
Authority: WO
Inventors: Dan Kristensson; Pal Svensson
Original assignee: Airsonett Ab
Priority date: 2009-03-05
Filing date: 2010-03-05
Publication date: 2010-09-10

Abstract

The present invention relates to a device and a method for maintaining cleanliness of a surgical instrument table surface and avoiding contamination thereof due to in-mixing of ambient air, relying on a downward-directed laminar flow of cooled air having a velocity determined by the difference in temperature between the air at the point of emission from the ventilation device and the air at the surface of the surgical instrument table.

Description

Surgical instrument table ventilation devices and methods

Field of the invention

The present invention relates in general to devices and methods for ventilation of surgical instrument tables and in particular to devices and methods that utilize surface feedback stabilization of a clean-air zone generated by temperature- limited/controlled laminar air flow.

Background Surgical site infections (SSIs) are the second most common cause of hospital acquired infections. 1.5% to 20% of surgical operations leads to a Surgical Site Infection (SSI), depending on the type of surgical procedure and the wound classification.

Patients who develop SSl suffer significant debilitation and increased risk. Patients with SSIs have up to 60% increased likelihood of hospitalization in an intensive care unit. Patients with SSIs have 5 times greater likelihood of readmission to the hospital and 2 times greater risk of death than patients without SSIs.

Societal costs for SSI's are substantial. European studies shows that the average extended length of stay for an infected patient is 9.8 days. The cost per SSI patient is between €1,862 to €4,047 in direct hospital costs alone. From 30 million surgical procedures a year the resulting numbers of SSIs amounts to 0.45 to 6 million, giving rise to a total SSI cost in Europe of somewhere between €1.47 to €19.1 billion/year. Studies from USA show similar figures with an average extended length of stay for an infected patient of somewhere between 7 to 10 days. The cost per SSI patient between $8,200 to $42,000 including indirect costs. With approximately 0.5 million SSI cases per year, total SSI cost in USA in the USA is in the range between $1 to $10 billion/year.

The primary contributing cause to development of surgical site infection (SSI) is generally acknowledged to be bacterial contamination of the operating room air either directly contaminating the patient's wound or indirectly by contaminating sterile surgical equipment.

In the operating room or theater, surgical instrument tables are considered equally as important as wound-sites as specific zones requiring ultra-clean air. A variety of surgical instrument table clean-air ventilation devices are known and used in the art. The sterile air trolley of EP0079122 provides a sterile surface having a large number of vents that provide an upward airflow of sterilized air. This device suffers from intermingling of ambient air caused by the plurality of air outlets. Further, when sterile objects are placed on the trolley air outlets will be blocked causing more turbulence from the uneven air distribution. The widely used TOUL-300 ™ ventilation system, and the air cleaning devices and methods of US6811593, blow laminar air horizontally across the surgical instrument table. The mobile laminar box of DE 20018765 provides a downward directed laminar air flow over an instrument table. However, these devices suffer from significant turbulent intermingling of ambient air.

Ventilation systems for surgical instrument tables have previously relied upon force- blowing of laminar air flow which has been filtered by high efficiency particulate air (HEPA) filters. In-mixing of contaminated ambient air with filtered air typically diminishes the ultimate efficiency of HEPA filtration.

These traditional laminar air flow devices require an impulse to set a stream of clean air in motion. This impulse needs to survive from the surface of the air delivery device to the protection area. While it is simple to set a flow of clean laminar air into motion, it is nearly impossible to control its stable motion through a volume of ambient air for any long distance. The velocity at the protection area needs to be high enough to break body convection currents and to pass objects in the air flow path. Further, the filtered air flow velocity must be sufficiently high to cater to differences in density between the filtered and ambient air. This often calls for a high impulse to secure a sufficient and lasting air velocity at the protection area, preferably 0.2 to 0.4 m/s. Whether clean-air is force-blown from a vertical position upward or downward to the instrument table or from a horizontal position across the instrument table, the high air velocities required inevitably invoke turbulent in-mixing of ambient, contaminated air.

An excellent illustration of the deficiencies of traditional laminar flow ventilation devices is provided by published studies using the widely used TOUL-300 ™ surgical instrument table ventilation system. Thore and Berman report bacterial deposition rates across the surface of a TOUL-300 ™ surgical instrument table in "Further bacteriological evaluation of the TOUL mobile system delivering ultra-clean air over surgical patients and instruments," Journal of Hospital Infection (2006) 63:185. As shown, reduction factor is decreased by distance from the horizontal laminar air flow screen (see figure 1). This illustrates the turbulent intermingling of contaminated ambient air into the clean-air flows generated by the TOUL-300 ™ table.

The concentration of particles at various locations on the TOUL-300 ™ table during surgery is shown in Figure 1. An investigation regarding the effect of TOUL-300 ™ on the particle concentration and airflows around the table was performed during surgery using a TOUL-300 placed in line with the operating table (The TOUL-300 ™ blowing towards the wound area). At these 3 distances, the measurements were repeated for different distances from the table centerline. As shown in Figure 1 , at the middle and end of the table, significant particle counts were readily detected. The particle concentration for other parts of the room was 36843 particles / m3, for particles 0.3um and larger. Particle measurements were performed at 3 different distances from the air emitter of the TOUL-300.

The deficiencies of the TOUL-300 ™ system can readily be understood as arising from turbulent in-mixing of contaminated ambient air. This device utilizes HEPA- filtered air distributed via flat laminar air flow (LAF) screens. The air velocities at the surface of the screen are between 0.5-0.7 m/s. For a plane, isothermal free jet half of the spreading angle is 11° < α 22°, i.e., the air flow increases by distance from the screen by in-mixing of ambient, contaminated air. Figure 2A shows a schematic illustration of air flows generated by the TOUL-300 ™ system and figure 2B illustrates ambient in-mixing produced by the device. Because of the turbulent in-mixing problem, these conventional LAF surgical instrument table ventilation devices cannot meet the highest standards for cleanliness, specifically, for example, the ISO 5 standard for particle counts (according to ISO 14644-3), less than 3520 particles /m3, and a bacterial count of less than 5 CFU/m3 (according to ISO 14698-1 and -2).

Summary of the invention

It is surprisingly found that when temperature-limited/controlled laminar air flow is used to ventilate a surgical instrument table from a close distance, the clean-air flow is reflected by the surface of the table in such manner as to stabilize the clean air zone. Turbulent intermingling of ambient air can be completely avoided without requirement for curtains or other enclosures. The advantage achieved is that in- mixing of contaminated ambient air is avoided.

Methods and devices are provided whereby in-mixing of ambient air is avoided using temperature controlled laminar air flow (TLA) of e.g. HEPA filtered air.

A substantially laminar, descending flow of filtered air is maintained with a velocity determined by the air-temperature difference between the supplied air and the ambient air at the level of the surgical instrument table.

In preferred embodiments, air-temperature of the filtered supply air can be carefully adjusted to maintain the velocity-determining difference in air-temperature within the optimum range of 0.3 to 3° C, preferably 0.3 to 1° C.

In yet another embodiment, temperature control is facilitated by a thermoelectric cooler (TEC) using the Peltier effect with reversible polarity, whereby the supply air can be alternately cooled or heated.

Thus, being able to at the same time avoiding contamination due to in-mixing of ambient air can be avoided thereby maintaining cleanliness of the surgical instrument table with respect to particles and bacterial counts. Description of the drawings

Figure 1 shows particle concentrations achieved at different locations of a surgical instrument table ventilated by the TOUL-300 ™ system.

Figure 2(A) shows clean air flows generated by the TOUL-300 ™ system.

Figure 2 (B) shows a schematic illustration of ambient air intermingling into clean air flows generated by the TOUL-300 ™ system.

Figure 3 shows a schematic illustration of surface feedback stabilization of a clean- air zone generated by temperature-limited/controlled laminar air flow.

Figure 4 illustrates an embodiment of a device according to the invention.

Figure 5 illustrates embodiments of filtered air-stream temperature adjustment units.

Figure 6 illustrates alternative systems for dissipation of excess heat from the air- stream temperature adjustment unit.

Figure 7 illustrates functioning of one embodiment of a nozzle.

Detailed description of the preferred embodiments Temperature-limited/controlled laminar air flow has a reduced tendency for turbulent in-mixing of ambient air, compared with conventional laminar air flow. Air from a filter device is cooled to a lower temperature than the air in the desired protected area such that the clean air which will provide a clean-air zone at a lower temperature, ideally 0.3-3° C cooler, than the ambient air surrounding the protected zone. The cooled, clean air is driven by a minimal impulse, sufficient only to overcome resistance in the filter and air supply system. The cooled, clean air sinks slowly downwards into the protected area. The higher density of the cooled air limits and impacts its downward velocity. The initial velocity need not be greater than the velocity required at the protected area and, accordingly, the tendency for turbulent in-mixing is minimized.

We have discovered that, surprisingly, when temperature-limited/controlled laminai air flow is used to ventilate a surgical instrument table from a close distance, the table reflects the laminar flow. Rather than creating turbulence, this actually stabilizes the clean-air zone, preventing any possibility of turbulent in-mixing at the table edges and ensuring high cleanliness over the entire surface of the table. This principle, surface feedback stabilization of a clean-air zone generated by temperature-limited/controlled laminar air flow, is illustrated in Figure 3. It appears that the open geometries with open sides give an even distribution of the airflow in all directions and a surprisingly stable clean air zone.

Nozzles suitable for delivering temperature-limited/controlled laminar air flow are known in the art and may be used to practice methods and devices of the invention, provided they are situated at close distance from a surgical instrument table. Ideally, the air supply device is situated < 0.5 m above the instrument table surface. In some embodiments, the air supply device may be situated between 0.3 to 0.7 m above the table surface, or optionally up to 1.0 m above the table surface or even more.

Air flow velocities at the surface of the table are ideally between 0.03 - 0.30 m/s, preferably between 0.15 - 0.30 m/s. Appropriate air flow volumes will vary depending on the size and shape of the surgical instrument table, but will typically fall in the range 25 - 750 m3/hr, preferably within the range 100-500 m3/hr.

Other, alternative arrangements of preferred embodiments may be used in avoiding in-mixing of ambient air at the surface of surgical instrument tables. The air delivery nozzle, which can be spherical or flat or other shape, can be placed straight above the surgical instrument table, as shown in figures 3 and 4. However, it can also be slightly tilted and placed slightly off the center above the surgical instrument table. It can be placed aside the surgical instrument table directing an impulse horizontally towards the surgical instrument table. In all settings gravity (temperature difference) defines a substantially downward directed air stream (after initial forced impulse has been counteracted by friction with ambient air). The downward directed supply air stream have sufficient velocity to displace conflicting in-mixing of ambient air as illustrated in Figure 3. The preferred distance between the nozzle and the surgical instrument table is preferably within the range of about 20 cm to 70 cm.

In one embodiment, the invention provides a ventilating or air treatment device for surgical instrument tables comprising

- an air treatment device comprising at least one filter device and at least one device for cooling air transmitted from the filter device to a temperature lower than that of the air at the surface of the surgical instrument table

- characterized in that

- the ventilation device provides a downward-directed laminar flow of cooled air having velocity determined by the difference in temperature between the air at the point of emission from the ventilation device and the ambient air at the level of and above the surface of the surgical instrument table, and the surface of the surgical instrument table stabilizes and widens the clean air zone provided by the air treatment device, and

- the zone of clean air at the outer edges of the surgical instrument table is substantially unaffected by turbulent intermingling of ambient air.

Other embodiments are further characterized in that

- the device provides a zone of clean air that encompasses the entire surface and edge of the table in which zone the count of particles <0.5 um in size, or more preferably <0.3 um in size, is less than 3520 particles /m3 and in which the count of bacteria is <5 CFU/m3.

In yet another embodiment the device may be movable within the premises.

In yet another embodiment the device may have means for addition of moisture, odours, trace components and/or medicine to the purified air stream.

In yet another embodiment the device may be further characterized by an electronic filter identification system. In yet another embodiment the device may have one or more filters provided by one physical unit.

In yet another embodiment the device may comprise communication means between the air temperature adjustment system and the one or more filters is such that supply air is cooled before or after filtration.

In yet another embodiment the device may further be characterized by having an air-temperature adjustment unit comprising a system for dissipation of excess heat selected from the group consisting of convection, radiation, active convection, and active liquid cooling.

When used as described, the temperature-limited/controlled laminar air flow ventilation system for surgical instrument tables can provide a clean air zone that meets the highest standards for cleanliness, the ISO 5 standard for particle counts and a bacterial count of less than 5 CFU/m3, over the entire surface of the table.

In some embodiments, the invention provides methods for avoiding in-mixing of ambient air at surgical instrument tables and providing a controlled cleanliness of surgical instrument tables with respect to particles and bacterial counts comprising

- Taking air from a premises into an air treatment device

- Adjusting the air-temperature and purifying a flow of air in said device by adjusting the temperature either before or after filtration using one or more HEPA filters

- Discharging the purified air stream through an air supply device, situated above or adjacent to the surgical instrument table, as a substantially laminar descending air flow with a velocity determined by the difference in air- temperature between the supplied air and the ambient air as measured at the level of the surgical instrument table wherein said difference in air-temperature is maintained within a range of about 0.3 to 3° C, preferably 0.3 to 1° C. In preferred embodiments of methods of the invention, it is not necessary to provide two partial air streams of purified air, one of which is cooled, the other heated as known from the art, cf. US 6.702.662.

TLA devices of the invention preferably provide a descending stream of filtered air that has sufficient velocity to overcome in-mixing of ambient air as shown in Figure 3.

In preferred embodiments, an airtreatment device according to the invention utilizes TLA to generate a descending and substantially laminar flow of filtered air. This provides a controlled surgical instrument table that is substantially free of in-mixed, contaminated ambient air, thus having limited particles counts and bacterial counts. A suitable device comprises at least one of each of the following: (1) an air inlet, (2) a filter, (3) a blower, (4) an air-temperature adjustment system, (5) an air- temperature control system, (6) an air supply nozzle, and (7) a housing, Figure 4.

The one or more air inlets (1) in Figure 4 are preferably placed near the floor level of the premises in which the device is utilized, where the layer of coolest air is situated. Alternatively air inlets may be placed higher up in the room, although this typically results in higher energy consumption in that warmer layers of air must be cooled. Preferably, the air inlets are configured in such manner as to keep emission of sound waves during operation to the lowest practicable levels. The more openings in the device housing, the greater the noise levels perceived by the user will be. In some embodiments, the air inlets may be associated with a pre-filter that also serves as a sound damper. In other embodiments, a HEPA filter that provides ultimate filtration of the supply air may be situated directly at the air inlets.

The filter (2) in Figure 4 is preferably a high efficiency particulate air filter, preferably HEPA class H11 , or higher if needed. In other embodiments, any suitable filter media or device adapted to filter particles or gases unwanted at the surgical instrument table may be used. Including for example any combinations of fiberglass and/or polymer fiber filters, or electro static filters, or hybrid filters (i.e. charging incoming particles and/or the filter media), or radiation methods (i.e. UV-light), or chemical and/or fluid methods, or activated carbon filters or other filter types.

While filter effectiveness is preferably high and stable over time, the resistance to ε flow, or "pressure drop" generated by the filter is preferably kept low. Increased pressure drop generated by the filter, the device housing, the air delivery nozzle and other components and air channels of the device calls for increased blower speed which in turn generates unwanted noise. In preferred embodiments, pressure drop of a suitable filter is generally lower than 50 Pa. When using the preferred embodiment of HEPA filter using fiberglass or polymer fiber filter media, pressure drop is generally minimized by maximizing the active filter media area.

In preferred embodiments, HEPA filters are comprised of randomly arranged fibres, preferably fiberglass, having diameters between about 0.5 and 2.0 micron, and typically arranged as a continuous sheet of filtration material wrapped around separator materials so as to form a multi-layered filter. Mechanisms of filtration may include at least interception, where particles following a line of flow in the air stream come within one radius of a fibre and adhere to it; impaction, where large particles are forced by air stream contours to embed within fibres; diffusion, where gas molecules are impeded in their path through the filter and thereby increase the probability of particle capture by fibres. In some embodiments, the filter itself may comprise the air supply nozzle through which supply air is delivered.

Alternatively or complementary to a HEPA filter, any suitable air treatment system can be used, including at least a humidifier or a dehumidifier, ionizer, UV-light, or other system that provides air treatment beneficial at the surgical instrument table.

Preferred embodiments of a device according to the invention comprise an electronic filter identification system. When a filter becomes clogged with particles, its effective area is decreased and its pressure drop accordingly increased. This results in lower airflow, which reduces overall effectiveness of the device. Accordingly it is preferable that users change the filter within the recommended service interval. To facilitate proper use, preferred embodiments provide a filter management system that indicates when a filter should be changed. Each filter can be equipped with a unique ID that permits the TLA device to distinguish previously used filters from unused ones. Filter identification systems can be provided RFID, bar codes, direct interconnections, attachements such as iBUTTON ™ circuits on < circuit board on the filter. It might also be possible to read or read and store other data than the serial number on the filter by this system. Information about the most appropriate airflow according to the filter type can for instance be supplied with the filter and be read automatically by the system.

The blower (3) generates air flow needed to feed a sufficiently large stream of air and to create pressure sufficient to overcome the pressure drop generated by the device. The blower may be of any suitable design, preferably comprising a fan impeller/blower rotor driven by an electric motor. Preferred embodiments are adapted so as to generate minimal noise during operations.

Blower noise is generally minimized by maximizing the size of the rotating rotor and minimizing the rotation per minute.

In preferred embodiments the fan generates a flow of filtered air through the device of less than 500 m3/h, such as less than 400 m3/h, preferably less than 300 m3/h, such as less than 250 m3/h, more preferably less than 225 m3/h, such as less than 200 m3/h, and even more preferably less than 175 m3/h, such as less than 150 m3/h.

The temperature adjustment system (4) in figure 4 cools and/or warms the supply air. In preferred embodiments, both heating and cooling are provided by a thermoelectric Peltier module. As is known in the art, a Peltier module can provided both heating and cooling depending on the polarity of the applied voltage or the direction of its operating current. In some embodiments, heating can be provided by an electric radiator, an electric convector or other type of heating methods, while cooling is provided by compressor (i.e. by using the Carnot process), or by fresh water cooling or other cooling means. The temperature adjustment system preferably generates as little pressure drop as possible, preferably it has sufficiently large emission surfaces so as to avoid unwanted condense water when cooling in warm and humid conditions, and is preferably able to maintain a cooling power that is stable over time and with minimc short term variations of supply air-temperature.

In preferred embodiments, heating/cooling is evenly distributed by means of heat pipes. Fins mounted on the heat pipes, with short distance to heat/cool source, can cover a wide cross section area of the air flow. Because the distance to the heat/cool source is short, efficient heat exchange can be achieved using relatively thin fins. In contrast, relatively thicker fins with lower thermal resistance are required using extruded heat sinks because of the longer distance to the heat source. Accordingly, the heat pipe system can effectively provide heat/cool transfer to a cross section area of air flow with comparably thinner fins resulting in lower air resistance and minimized pressure drop. Further, the short distance to the heat/cool source using heat pipes leads to an evenly distributed surface temperature which makes more efficient heat transfer per unit fin area. This leads to smaller temperature differences and thereby less risk of condense water accumulating on cooler areas of the fins.

It will be readily understood by one skilled in the art that a variety of different schemes for temperature adjustment may be employed. In systems that utilize a TEC, excess heat can be dissipated in variety of ways, including passive or active convection or active liquid cooling.

Preferred embodiments can stably maintain an air-temperature difference of supply air relative to ambient air at the level of the surgical instrument table with a minimal fluctuation. Fluctuation of the air-temperature difference is preferably kept within the range of the margin of measurement error, preferably ±0.1 ⁰C. This stable air- temperature difference is preferably maintained at some point within the range of about 0.3 to 1° C. In this manner, descending air stream velocity can be "delicately balanced" between excessive velocity, which creates unwanted drafts, and sufficient velocity, which is just enough to avoid in-mixing currents of ambient air at the surgical instrument table.

The temperature control system (5) in Figure 4 maintains a stable air-temperature difference between the descending supply air stream enveloping the surgical instrument table and the ambient air as measured at the level of the surgical instrument table. In one preferred embodiment, the temperature control system comprises two sensors and a control unit. One temperature sensor is placed in the supply air channel just after the temperature adjustment device (4). A second sensor is placed in such manner as to measure ambient air at the level of the surgical instrument table but outside the effective stream of supply air. The control unit is preferably programmed to collect data from the two sensors and to regulate voltage applied to the Peltier element so as to maintain a temperature difference within the optimal range. Sensors are preferably protected from any kind of radiation from surfaces so as to provide an accurate air-temperature measurement. Preferably, sensors have high sensitivity and minimal error margin, ±0,05°C.

The air supply nozzle (6) in Figure 4 delivers a substantially laminar stream of supply air with minimal in-mixing of ambient air. In order that velocity of the supply air stream may be determined by difference in air-temperature from ambient air at the level of the surgical instrument table, supply air preferably exits the nozzle with velocity (i.e., dynamic pressure) that is just sufficient to overcome nozzle "impulse" (i.e., resistance). This initial dynamic pressure of supply air is rapidly diminished by static pressure of ambient air until a point is reached at which gravity alone (i.e., air- temperature difference) determines the rate of further descent. The nozzle preferably has minimal impulse whereby supply air may exit the nozzle with minimal dynamic pressure and, accordingly, whereby the point at which air-temperature difference alone determines the rate of further descent is reached well before the supply air stream reaches the surgical instrument table. In some embodiments, the nozzle (6) can be replaced by or made in combination with one or more filters (2) as an integral part of the air supply nozzle or as the sole part delivering supply air. A wide variety of nozzle shapes and sizes can be used. However, the rate at which initial velocity of supply air is diminished by static pressure of ambient air is affected by nozzle shape. Pitch length refers to the distance from the surface of the nozzle at which the cumulative effect of static pressure of ambient air counterbalances the dynamic pressure of supply air that has been set into flow with impulse just sufficient to overcome resistance in the nozzle. Preferably, a suitable nozzle has minimal pitch length. This permits gravity (i.e., air-temperature difference) to control the downward air flow velocity at a point well above the surgical instrument table. Short nozzle pitch length also ensures that supply air flow will introduce minimal disturbance of ambient air which in turn minimizes turbulences that arise when supply air meets still, standing ambient air. In preferred embodiments, nozzle pitch length ends well before the surgical instrument table.

Preferably the pitch length, as defined by an air velocity of <0,2 m/s, should reach less than 20 cm from the air delivery device. In any case, the pitch length is preferably no longer than the distance between the air supply nozzle and the surgical instrument table. The prime factors determining the actual pitch length are shape of the nozzle and the composition the materials shaping the nozzle. A preferred nozzle is described in WO2005/017419, which is hereby incorporated by reference in entirety. An air delivery nozzle with a substantially spherical shape as described is likely to cater for a larger effective operative area as compared to a flat air delivery nozzle, given identical air flow. However, both flat or spherical shaped nozzles can be used.

The substantially spherical shape has the advantage of being compact. Further the shape forces the air flow to be distributed over an increasing surface area. This reduces pitch length, in that the decrease in air velocity is dependent on friction between the supply air and ambient air. The spherical surface distributes supply air flow to a surface are that increases with approximately the square of the distance from the nozzle centre. The increasing surface area forces the velocity to decrease with approximately 1/( the square of the distance from the nozzle centre) giving the spherical nozzle a natural character with a short pitch length. In contrast, a flat delivery nozzle generates an air flow with a constant distribution area and a correspondingly longer pitch length.

Any alternative nozzle with similar characteristics of minimal pitch length and low disturbance of ambient air may be used.

Figure 4 illustrates a preferred embodiment of a device according to the invention. Ambient air (symbolized by shaded arrows, indicating flowing air) is taken in through the air inlet (1), which is situated at floor level at the bottom of the housing (7). Intake air is filtered by the filter (2), driven by action of the blower (3). An air- temperature adjustment device (4) is situated so as to provide both cooling and heating of the filtered supply air stream. The device comprises a Peltier element with reversible voltage polarity connected via heat pipes to two sets of fins. One set of fins serves primarily to distribute cooling effect in the supply air stream while the other set of fins serves primarily to provide dissipation of excess heat generated by the Peltier module. Parts of or the whole air-temperature adjustment device (4) may be situated before the filter (2) and/or the blower (3). Parts of or the whole air- temperature adjustment device (4) may also be situated in other parts of the device such as the nozzle (6). The temperature control device (5) comprises a control unit (square) and two sensors (circles). One sensor is placed in the supply air stream while the other is placed in such manner so as to measure ambient air temperature at the level of the surgical instrument table zone but outside the supply air stream. The control unit, informed by air temperature measurements from the sensors, regulates the temperature adjustment unit so as to maintain a stable air-temperature difference between the supply air and ambient air at the level of the surgical instrument table. Supply air is driven by action of the blower (3) out of the nozzle (6) with minimal impulse.

Figure 5 shows, in greater detail, an air-temperature adjustment unit (4) of a preferred embodiment. Figure 5A shows a TEC system with extruded heat sinks. In this system the TEC (9) distributes generated cooling effect on one side by interfacing an extruded heat sink (8). On the other side of the TEC heat is dissipated to a similar extruded heat sink (10). Figure 5B shows a heat pipe system. Here the TEC (12) interfaces a connection block (14) with at least the same area as the TEC. From here the cooling effect is transported to the fins by a heat pipe (13). At the warm side (15) the heat is transferred in the same way. The Peltiere element is normally fitted with thermal grease or a thermal pad which increases the thermal conductivity of the thermal interface by compensating for the irregular surfaces of the components.

Figure 6 shows alternative systems for dissipating excess heat generated by the air- temperature adjustment unit. In a preferred embodiment using a TEC system, excess heat can be dissipated by convection, as shown in Figure 6a, by radiation, as shown in Figure 6b, by active convection, as shown in Figure 6c, or by active liquid cooling, as shown in Figure 6d. These alternative systems may act alone or in combination (i.e. by combining convection with radiation)

Figure 7 illustrates functioning of the nozzle (6) of the preferred embodiment shown in Figure 4. S schematic illustration of the functioning of the nozzle shown is described in WO2005/017419.

Supply air is initially forced out of the nozzle with a slight velocity, about 0.2 m/s, just sufficient to overcome resistance in the nozzle. The spherical surface distributes supply air flow to a surface area that increases with approximately the square of the distance from the nozzle centre. Friction with ambient air dissipates the air flow velocity up to the pitch length, after which further descent of the supply air stream is determined by air-temperature difference (gravity) .

The preferred embodiments described are exemplary only and not intended to limit the scope of the invention as defined by the claims.

Claims

1. A ventilating device for surgical instrument tables comprising an air treatment device comprising at least one filter device and at least one device for cooling air transmitted from the filter device to a temperature lower than that of the air at the surface of the surgical instrument table characterized in that

- the ventilation device provides a downward-directed laminar flow of cooled air having velocity determined by the difference in temperature between the air at the point of emission from the ventilation device and the air at the surface of the surgical instrument table, and

- the surface of the surgical instrument table stabilizes and widens the clean air zone provided by the air treatment device, and

2. An air-treatment device for maintaining cleanliness of a surgical instrument table surface and avoiding contamination thereof due to in-mixing of ambient air comprising

- one or more air inlets - one or more filters

- a blower

- an air temperature adjustment system adapted to provide either heating or cooling of a supply air stream

- an air supply nozzle adapted to discharge a substantially laminar air flow, and

- a housing, wherein the air treatment device is adapted to provide a substantially laminar descending purified air flow having velocity determined by a difference in air temperature between the supplied air and ambient air as measured at the level of the surgical instrument table zone.

3. A device according to claim 2 wherein the device does not provide two partial air streams of purified air, one of which is cooled, the other heated.

4. A device according to claims 1 to 3 characterized in that the device provides a zone of clean air that encompasses the entire surface and edge of the surgical instrument table in which zone the count of particles <0.5 um in size, or more preferably <0.3 um in size, is less than 3520 particles /m3 and in which the count of bacteria is <5 CFU/m3.

5. A device according to claims 1 to 4 characterized in that the difference in temperature between the air at the point of emission from the ventilation device and the ambient air at the level of the surface of the surgical instrument table is between 0.3 ⁰C and 3°C, preferable between 0.3 ⁰C and 1°C.

6. A device according to claims 1 to 5 characterized in that the downward-directed laminar flow of cooled air has a velocity between 0.03 to 0.30 m/s, preferable between 0.15 m/s to 0.30 m/s.

7. A device according to claims 1 to 6 characterized in that the total air-flow volume is between the range 25 - 750 m3/hr, preferably within the range 100-500 m3/hr.

8. A device according to claims 1 to 7 characterized in that the device is situated at a level of about 0.2 to 1.0 m, preferably 0.2 to 0.7 m above the surgical instrument table.

9. A device according to claims 1 to 8 further characterized in that it is mobile for being movable within a premises.

10. A device according to claims 1 to 9 further characterized by having means for addition of moisture, odours, trace components and/or medicine to the purified air stream.

11. A method for maintaining cleanliness of a surgical instrument tables and avoiding contamination thereof due to in-mixing of ambient air comprising

- taking air from a premises into an air treatment device - adjusting the air-temperature and purifying a flow of air in said device by adjusting the temperature either before or after filtration using one or more HEPA filters

- discharging the purified air stream through an air supply device, situate above or adjacent to the surgical instrument table, as a substantially laminar descending air flow with velocity determined by the difference in air- temperature between the supplied air and the ambient air at the level of the surgical instrument table zone wherein said difference in air-temperature is maintained within a range of about 0.3 to 1⁰ C.

12. A method according to claim 11 wherein the ventilating device is situated at a level of about 0.2 to 1.0 m, preferably 0.2 to 0.7 m above the surgical instrument table.

13. A method according to claim 10-12 wherein the flow of filtered air through the ventilating device is less than 750 m3/hr, preferably less than 500 m3/h.

14. Use of a device according to claim 1-10 for maintaining cleanliness of surgical instrument tables and avoiding contamination thereof due to in-mixing of ambient air.

15. A method of doing business including a claim, statement or direction in advertisements, manuals, package inserts or other printed or broadcasted material that contamination of a surgical instrument table surface can be reduced or removed by reducing in-mixing of ambient air at the surface of surgical instrument tables.

16. A method according to claim 14 wherein a device according to claim 1-9 is used.