Field of the Invention

The present invention relates to an air flow system for an operating theatre. Aspects of the invention are also related to an operating theatre including the air flow system and the operating theatre may be static, mobile, transportable, permanent or temporary. There is also provided a method of generating laminar air flow in an operating theatre.

Background to the Invention

Air flow systems are commonly used in operating theatres in order to provide a high degree of air purity to reduce the risk of infecting a patient, particularly if they have an open wound or body cavity during surgery.

Laminar air flow systems are desirable when deep invasive surgery is performed as such systems can ensure a particularly high level of air purity within a designated enclosed air space (e.g. in the region of the patient on the operating table). In effect, such laminar air flow systems cause the entire body of air within that space to move with uniform velocity in a single downwards direction along parallel flow lines. Turbulence within the air space is thus eliminated (or in practice, at least greatly reduced) so that any particles of impurities are flushed out of the air space.

However, traditional laminar air flow systems can be noisy and expensive to run as they require constant operation of high speed fans. Furthermore, the filters which are provided to purify the air in these systems have a limited effective lifetime and require regular replacement.

It is therefore an object of the present invention to provide an air flow system for an operating theatre which addresses at least some of the afore-mentioned problems. Statements of the Invention

According to a first aspect of the present invention there is provided an air flow system for an operating theatre comprising: at least one laminar air flow fan operable to provide laminar air flow into an operating theatre from a ceiling thereof; and a laminar flow hood configured to guide the laminar air flow into the operating theatre; wherein the laminar flow hood is configured to compress the laminar air flow so as to exploit the Bernoulli effect, resulting in the laminar air flow increasing in velocity after exiting the laminar flow hood.

In accordance with the Bernoulli effect, a decrease in pressure (such as that experienced by the air flow after it has exited the laminar flow hood and entered the larger volume of the operating theatre) will be accompanied simultaneously with an increase in the speed of the air.

Embodiments of the present invention therefore provide an air flow system configured to enhance the velocity of laminar air exiting the system and entering the operating theatre. As a result, the at least one fan may be operated at a reduced speed than would otherwise be necessary to achieve a desired velocity of air flowing in the operating theatre. Accordingly, the fan can be optimised for operation at a lower speed, with resulting energy and cost savings and a reduced entrainment risk. Furthermore, the fan will operate at a reduced noise level, thereby providing a quieter operating environment. In addition, the compression of the air in the laminar flow hood may serve to reduce turbulence thereby ensuring a more even flow.

The laminar flow hood may be generally rectangular and may have at least two opposing sides which are directed inwardly to compress the laminar air flow prior to its exit from the laminar flow hood. In some embodiments, all four sides may be directed inwardly to compress the laminar air flow.

In other embodiments, the laminar flow hood need not be rectangular and may, for example, be generally circular, oval or triangular. In which case, one, some or all portions of the hood may be directed inwardly to compress the laminar air flow prior to its exit from the laminar flow hood.

The laminar flow hood overlies substantially the entire working area of the operating theatre. It will be understood that laminar air flow is only generally required in the vicinity of a patient being operated on. Thus, the laminar flow hood may be configured to provide laminar air flow in the vicinity of an operating table. A horizontal cross- section through the laminar air flow volume may be of the order of 6 to 10m ² (e.g. 8.2m ² ). Thus, an even velocity of air may be provided across the whole cross-section area of the laminar flow hood. The patient and surgeon are therefore within the same airflow and are supplied with air having the same humidity and temperature.

The system may further comprise air return channels for returning air from near a floor of the operating theatre to an air intake of the at least one laminar air flow fan.

The system may further comprise one or more air filters configured to filter the air flowing into the operating theatre. The air filter may be located at, adjacent or upstream of an entry port for air flowing through the laminar flow hood. Accordingly, the air filter will encounter air flowing at a lower rate than that required on exit from the laminar flow hood and, as a result, the air filter will have an increased effective lifetime, when compared to a filter in a conventional system. The air filter may comprise a High- Efficiency Particulate Air (HEPA) filter. The air filter may be configured to maintain an air quality at ISO grade 5 or above.

The system may further comprise an over-pressure system configured to provide and maintain a cascade of over-pressure of air (i.e. pressure above ambient air pressure) within the operating theatre. The over-pressure system may be configured to provide an over-pressure of approximately 15 to 30 Pascals (e.g. 25 Pascals) over ambient air pressure.

The over-pressure system may comprise an over-pressure fan and ducting arranged to re-circulate air through the operating theatre via the laminar flow hood. The overpressure system may be configured to provide approximately 20 to 40 (e.g. 30) total volume changes of air per hour in the operating theatre.

The over-pressure system may be operable independently of the at least one laminar air flow fan so that over-pressure can be maintained irrespective of whether laminar air flow is required in the operating theatre.

The at least one laminar air flow fan may be configured for operation at two or more different speeds for increased flexibility. In a particular embodiment, the at least one laminar air flow fan may be configured for selective operation at either full speed or a reduced speed (e.g. set-back mode). The system may be configured such that operation of the least one laminar air flow fan is independent of the operation of the over-pressure system such that over-pressure can be maintained irrespective of whether the at least one laminar air flow fan is operating at full speed or at a reduced speed. Furthermore, due to the location of the air filter, air quality may be maintained irrespective of the operation of the at least one laminar air flow fan.

The full speed setting may be configured to provide a required laminar flow rate in a laminar flow area of the operating theatre, taking into account the acceleration of the air flow due to the Bernoulli effect. The required laminar flow rate may be approximately 0.4m/sec (e.g. 0.2 to 0.6 m/sec) at 2m above floor level and approximately 0.2m/sec (e.g. 0.1 to 0.3 m/sec) at 1 m above floor level (approximate patient level). The full speed setting may be required for operations involving deep orthopaedic surgery (e.g. hip replacements), where laminar air flow is required to minimise the risk of infection.

The reduced speed (e.g. set-back) setting may be configured to provide laminar (or non-laminar) flow at a reduced velocity within the operating theatre. In certain embodiments, the reduced speed setting may be provided by reducing the speed of operation of the at least one laminar air flow fan by at least approximately 25%, 50% or 75% when compared to the full speed setting. The reduced speed setting may allow the operating theatre to be used as a reduced velocity laminar (or non-laminar) flow operating theatre whilst continuing to provide fresh air into the operating environment and maintaining a desired pressure differential and rate of fresh air room changes (e.g. via the over-pressure system). The reduced speed setting may therefore be used to minimise energy, cost and noise levels when operations that do not require high velocity laminar air flow are performed in the operating theatre. The reduced speed setting may be required for non-invasive procedures, or invasive procedures other than deep orthopaedic surgery, such as those requiring only a local anaesthetic (e.g. nerve repair operations).

In certain embodiments, two, four, six, eight or ten laminar air flow fans may be employed. The laminar air flow fans may be symmetrically arranged with respect to the length of the laminar flow hood. In a specific embodiment, four pairs of fans may be employed. The laminar air flow fans may be of the type known as quadrant fans. The air flow system may be configured for use in a static or permanent (i.e. conventional) operating theatre or it may be configured for use in a mobile, transportable or temporary operating theatre. According to a second aspect of the present invention there is provided an operating theatre comprising an air flow system according to the first aspect of the invention. The operating theatre may be static, mobile, transportable, permanent or temporary.

According to a third aspect of the present invention there is provided a transportable medical facility comprising an operating theatre according to the second aspect of the invention.

The transportable medical facility may of the types described in WO2006/125822 or WO2007/014881 , the disclosures of which are incorporated herein by reference.

The transportable medical facility may be convertible between a compacted condition for transport on a low loading trailer and an expanded, free-standing condition for use. The transportable medical facility, when in its expanded condition, may comprising: a base structure, a roof structure and external walls, defining an enclosed working area; internal walls defining the operating theatre within the working area; and the laminar flow hood of the air flow system being provided in a portion of the roof structure overlying the operating theatre, thereby to establish a laminar airflow within the operating theatre when in use. The roof structure may have one or more air ducts formed therein, in communication with the laminar flow hood, and may optionally house one or more air conditioning and/or purifying elements.

According to a fourth aspect of the present invention there is provided a method of generating laminar air flow in an operating theatre comprising: providing an air flow system according to the first aspect of the invention; operating the at least one laminar air flow fan to provide laminar air flow into the operating theatre from a ceiling thereof; guiding the laminar air flow into the operating theatre via the laminar flow hood; and compressing the laminar air flow in the laminar flow hood so as to exploit the Bernoulli effect, resulting in the laminar air flow increasing in velocity after exiting the laminar flow hood. Brief Description of the Drawings

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a cross-sectional plan view of a transportable medical facility according to an embodiment of the present invention, when deployed for use in its expanded condition;

Figure 2 shows a cross-sectional end view of the operating theatre of the transportable medical facility of Figure 1 , illustrating operation of the air flow system in accordance with an embodiment of the present invention;

Figure 3 shows a simplified cross-sectional side view of the operating theatre of the transportable medical facility of Figure 1 , showing the compressing sides of the laminar flow hood in accordance with an embodiment of the present invention;

Figure 4 shows a top perspective view of the roof structure of the transportable medical facility of Figure 1 ; and

Figure 5 shows a cross-sectional plan view of the roof structure of Figure 4.

Detailed Description of Certain Embodiments

Figure 1 illustrates a transportable medical facility 10 convertible between a compacted condition for transport on a low loading trailer and an expanded, free-standing condition for use, according to an embodiment of the present invention, when deployed in its expanded condition. The facility 10 comprises a base 11 (not visible in Figure 1), having upstanding end members 12, a roof structure (ceiling) 13 (not visible in Figure 1) and external side walls 14, 14'. For ease of representation, the transportable medical facility 10 is shown in Figure 1 with the roof structure 13 substantially removed. The roof structure 13 will be described in more detail below with reference to Figures 4 and 5.

The external side walls 14, 14' are adapted to move in and out of the facility 10 so as to effect conversion of the facility between its expanded and compacted conditions. The side walls 14, 14' are provided with end wall portions 15, which combine with the upstanding end members 12 of the base structure 11 to form external end walls 16 of the facility 10 when said facility 10 is in its expanded condition.

An internal working area of the facility, generally indicated 17, is defined within the external side and end walls 14, 14', 16. As can be seen from Figure 1 , one side wall 14' of the facility 10 is adapted to move further from the base 11 than is the other, thus defining an auxiliary section, generally indicated 18, of the working area 17. A first pair of internal walls 19 is provided transversely across the working area 17. This first pair of walls 19, together with a second pair of internal walls 20 arranged parallel to the longitudinal axis of the facility 10, define an operating theatre 21 generally centrally within the facility 10. The first pair of internal walls 19 also serve to divide the remaining working area 17 into a pre-operational induction room 22, and a post-operational recovery room 23. Further internal walls 24 are provided within the auxiliary section 18, thus sub-dividing it into "clean" and "dirty" utility rooms 25, 26, a scrub room 27 and a changing room 28, each fitted with appropriate units, sinks, lockers, cupboards etc. 29.

In an area of the roof structure 13 substantially overlying the operating theatre 21 is provided a laminar flow hood 31 , as will be described in more detail below with reference to Figures 2 to 5. An operating table 32 is provided in the operating theatre 21 , arranged centrally beneath the laminar flow hood 31 , and substantially perpendicular to the longitudinal axis of the transportable medical facility 10.

Figure 2 shows the operating theatre 21 viewed in cross-section along the longitudinal axis of the transportable medical facility 10, illustrating operation of an air flow system 40 in accordance with an embodiment of the present invention. The laminar flow hood 31 is formed as part of the roof structure 13, and overlies substantially the entire working area of the operating theatre 21. The laminar flow hood 31 is fed by a series of air ducts 33 formed in the roof structure 13, which are divided into a central portion 34 and two outer portions 35. The central air duct portion 34 is in communication with air drawn from the ambient environment, as will be discussed in more detail below with reference to Figure 4 and 5. The outer air duct portions 35 are each in communication with a return channel 36 formed in the second pair of internal walls 20 defining the operating theatre 21. Laminar air flow fans 37 are located at the top of the return channels 36, to drive the re-circulated air from said return channels 36 into the outer air duct portions 35. Further like fans are arranged to drive the fresh air through the central air duct portion 34, as will be discussed in more detail below with reference to Figures 4 and 5.

The flow of air through the operating theatre 21 , as illustrated by the arrows in Figure 2, will now be discussed. The air ducts 34, 35 feed an entry port 50 of the laminar flow hood 31 , where the combined air streams are passed through a grid of High Efficiency Particulate Air (HEPA) filters (not shown in Figure 2). Extending into the operating theatre 21 from the entry port 50 are two opposed vertical polycarbonate sides 38 of the laminar hood 31. The sides 38 are shaped so as to impart a unidirectional downward flow to the air stream driven therethrough by the laminar air flow fans 37. As shown in Figure 2, the laminar airflow passes downwardly through substantially the entire height of the operating theatre 21 , before being channelled into the return channels 36 by inlets 39 formed in the internal walls 20 closely adjacent the floor 41 of the operating theatre 21. The action of the laminar air flow fans 37 draws the air up the return channels 36 and returns it to the outer air duct portions 35 which then feed the laminar flow hood 31 , together with replenished fresh air from the central air duct portion 34. At each pass, a proportion of the re-circulated air is carried away along the central air duct portion 34 to be expelled, as will be discussed below with reference to Figures 4 and 5.

Figure 3 shows a simplified side cross-sectional view of the operating theatre 21 and the air flow system 40 (i.e. viewed at an angle of 90 degrees with respect to Figure 2). Accordingly, it can be seen that the laminar flow hood 31 has two opposed polycarbonate sides 51 which are angled inwardly to compress the laminar air flow so as to exploit the Bernoulli effect in accordance with an embodiment of the present invention. As described above, the compressing of the laminar air flow in the laminar flow hood 31 increases the pressure such that, when the laminar air flow exits the laminar flow hood 31 and enters the larger volume of the operating theatre 21 , the pressure will drop resulting in a simultaneous increase in air velocity. Consequently, it is possible to reduce the speeds of the laminar air flow fans 37 while maintaining a desired flow rate of approximately 0.4m/sec at 2m above floor level (indicated by line 52 in Figure 3) and approximately 0.2m/sec at 1 m above floor level (indicated by line 54 in Figure 3). The flow of air through the transportable medical facility 10 will now be further discussed, referring simultaneously to Figures 4 and 5, which show different aspects of the roof structure 13. Fresh air is drawn from the ambient environment into the facility 10 by a further set of fans 37', through an inlet vent 42 provided with a pre-filter 43, and located in the upstanding member 12 of the base 11 adjacent the pre-operational induction room 22. The air is then driven by the fans 37' through an air duct 33 over the pre-operational induction room 22, provided with further pre-filters 43 in communication with the pre-operational induction room 22. The pre-filters 43 may desirably also be HEPA filters. As discussed previously, when the air duct 33 reaches the roof structure 13 overlying the operating theatre 21 , the duct 33 is split into a central portion 34 and two outer portions 35. The fresh air is channelled through the central portion 34 which feeds the laminar flow hood 31 , consisting of a grid of HEPA filters 44. Here, a proportion of the fresh air will be driven through the laminar flow hood 31 into the operating theatre 21 , combining with the re-circulated air driven through the outer air duct portions 35 by the laminar air flow fans 37 from the return channels 36, as described above with reference to Figure 2. However, a proportion of the fresh air will combine with a proportion of the re-circulated air, and be channelled into a continuation of the air duct 33 overlying the post-operative recovery room 23. This part of the air duct 33 is provided with exhaust vents 45 in communication with the post-operative recovery room 23, and ultimately the ambient environment. By the provision of sensors (not shown) in the air ducts 33, 34, 35, the return channels 36, and the operating theatre 21 , and by varying the relative power of the fans 37, 37', the ratio of re-circulated to fresh air passing through the operating theatre 21 can be controlled, as can the number of complete air changes in a given time period.

In addition, the laminar air flow fans 37 in the embodiment shown are controlled independently from the fans 37' and are configured for selective operation at either full speed - to provide laminar flow as described above with reference to Figure 3 - or a reduced speed (e.g. set-back mode) - to provide non-laminar flow when laminar flow is not required. The fans 37' can be configured to provide over-pressure air (filtered by the HEPA filters 44) into the operating theatre 21 irrespective of whether the laminar air flow fans 37 are operational.

It will be appreciated by persons skilled in the art that various modifications may be made to the above embodiments without departing from the scope of the present invention as defined by the accompanying claims. Thus, although the air flow system has been described in relation to an operating theatre in a transportable medical facility, in other embodiments the air flow system can be employed in other types of operating theatres such as those permanently provided in static hospital buildings.