OP Vent2 - The study of air and energy consumption in order to optimize the bacteriologic conditions in operation rooms equipped with LAF/TAF ventilation during total hip and knee surgery

The OP Vent 2 project was initiated in 2017 and completed in the late summer of 2021. The project is a logical extension of the OP Vent 1 project and is characterized by studies of actual conditions during surgical operations. 

The aim of the OP Vent 2 project is to investigate the two typically used ventilation systems, LAF and TAF, in operating rooms at Danish hospitals.
The project has uncovered the energy consumption of knee and hip surgeries, as well as the possibilities for reducing this. In addition, we have measured the quality of the air in the LAF and TAF rooms, and whether it has been complied with in accordance to the applicable requirements and recommendations.

The results of the project provide an overall value by indicating energy savings and reduction of the risk of contamination during operations.

The project uncovers broadly through analysis of a number of parameters that have been collected in connection with 51 completed knee and hip surgeries at 15 Danish hospitals.

The project has been staffed with highly qualified specialized resources, which are based on a practical everyday life that primarily spans the medical, energy technical and ventilation construction fields.

The results of the project are presented through lectures, scientific publications and directly to authorities, organizations and the business community.

Study conclusion

Our study showed that:

Health professional

• LAF-ventilated operating rooms reduced CFU numbers compared to TAF in live surgery      
• All LAF rooms provided ultra-clean air with an active CFU number below 10 CFU / m³  while the TAF rooms had too high values ​​in 56% of (9/16) the surgeries      
• Staff behavior, including number and total number of opening of doors, did not affect CFU counts      
• Increased physical volume of the operating room resulted in a decrease in the number of CFUs      

Technical

• Operating expenses were less in the LAF room      
• Simulation showed that it-is possible to save up to 50% of the total energy consumption in the operating room. 

Energy issue
As the healthcare sector is one of the major emitters of greenhouse gases, OP Vent 2 intervenes in the global challenge of rising temperatures and derives from this the goals of the “Paris Agreement 2015” with the reduction of greenhouse gases [2]. Nationally, the more concrete goals of reducing greenhouse gas emissions by 55 percent by 2030 and reducing CO2 emissions by 39% compared to the level in 2005 [3] are thus embraced.

Larger public buildings account for a significant share of Denmark's total energy consumption. In particular hospitals are an energy-intensive type of building, which amounts to 90% of the regions' total energy consumption. Especially ventilation is an energy-intensive building installation, which accounts for 20% of the hospitals' electricity consumption.

There are several different types of ventilation systems for operating rooms in hospitals, each of which serves different purposes. Common to them is to maintain an atmospheric indoor climate, which primarily aims to prevent bacteria and particle transport, which increases the risk of the occurrence of infections, and secondarily ensures work efficiency for hospital staff and patient comfort.

Ventilation in operating rooms is particularly interesting, as it contains the strictest requirements for ventilation and the derived cleanliness of operating rooms. It is estimated that there is a significant energy saving potential.

There are primarily two ventilation principles used in operating rooms. The conventional principle, called TAF - Turbulent Air Flow, which ventilates the room and the laminar, directional air injection LAF , which forms an area around the operating bed. In addition, there are other variants, but the project does not relate to these, as there were no operating rooms that could be included in the project.

For both principles, an overpressure must be maintained to ensure that contaminated air from surrounding rooms does not enter the operating room.

The two ventilation systems are used under the assumption that the blown ultra-clean filtered air in the operating room reduces the risk of infection.

The project investigates the energy aspects around the 2 ventilation principles, including savings potentials which are compared with the healthcare issues.

The healthcare issues
The burden of musculoskeletal conditions worldwide and in Denmark is great. It is among the top five in terms of cost and one of the most common causes of sick leave and related loss of productivity to the economy and life of many countries. One of the very common conditions is hip and knee osteoarthritis (OA), which in end-of-clinical stages is treated with artificial hip or knee.

Artificial hip and knee is one of the most common orthopedic procedures in Denmark and worldwide with more than 20,000 surgeries in DK and over 1 million procedures performed in the United States.

The most feared complication after artificial hip and knee surgery is prosthetic infection (PJI) [4-5]. PJI is associated with high morbidity resulting in prolonged hospitalization and it has devastating effects on patients' lives as it is disabling and may require reoperations with risk of significant side effects [6-8]. It has a high economic impact with increased health care costs and mortality. During the operation, bacteria can come through the air, so-called airborne infections.

Prevention of PJI is of the utmost importance, which is why in-depth knowledge of causes and influencing factors are important. As related to the organizational conditions, ventilation and air quality in the operating room is one of the factors that play a significant role in contamination during the operation.

Air quality, which contributes to a good level of hygiene, cannot stand alone, but a number of other areas, such as patient susceptibility, clothing, behavior, room execution and design, cleaning, purification, disinfection and sterilization methods are also crucial [1]. At the same time, the nature of the intervention is important for permissible amounts of infectious particles in the room air. Among other things the project considers the limit values ​​for the bacterial concentration in operating rooms.

Thus, limiting the number of particles also reduces the number of bacteria.

Motivation for the project
OP Vent 2 is a continuation of the OP-Vent 1 project, where the study was performed as a mockup, i.e. without patients, and with the use of a heated doll and simulated complete performances of hip surgeries in real operating rooms.

The study showed that it was possible to reduce the amount of ventilation by 50%, and the related energy consumption by approx. 40%, without compromising the number of microorganisms (CFU) in operating rooms with LAF.

In contrast, it was not possible to reduce ventilation in operating rooms with TAF without an increase in CFU. At the same time, it was found in TAF rooms at 100% ventilation that it was not possible to maintain a microbiological environment that complied with the applicable guidelines. [9]

Given that several of the new super hospitals are planned with operating rooms with TAF-rooms, we found it important to analyze the energy consumption and the presence of microorganisms in both the LAF and TAF rooms during proper surgeries and during simultaneous measurements of microorganisms.

The perspective with this is to uncover the possibility of reducing energy consumption through better control of the ventilation systems. In addition to the possible large energy savings, there may also be patient and societal savings by using LAF rather than TAF if LAF reduces the risk of contamination.

Purpose of the OPVent 2project
The overall aim is to investigate the presence of microorganisms on the LAF - and TAF surgeries measured during real-life operations and to calculate energy usage. The specific purposes are

1. to examine the number of CFUs at surgeries performed in the LAF - and TAF rooms
2. to examine the importance of behavior measured as door- and piercing cabinets - openings in the operating room
3. to measure energy consumption at each surgery
4. to calculate possible savings in energy consumption by optimizing a number of parameters

The project has been carried out at 15 hospital registers, where 51 knee and hip surgeries have been performed in operating rooms with either LAF or TAF ventilation.

 Measurements & behavior
In connection with the operations, many measurements have been carried out. Energy technical conditions, such as pressure, energy uptake in installations and temperature conditions and the bacteriological ones through collection and subsequent analysis of particles using agar plates, have been included in the study. Both active and passive data collection have been used while observing current standards and recognized methods.

Behavior of the surgical staff, the number of openings of doors and piercing cabinets, as well as the number of people and their clothing, were noted during the operation and are also included in the study.

Energy consumption and operating savings
As all the measured plants are constructed differently, optimization calculations and simulations have been performed separately on all plants.

Enhancement levels have been simulated for the 15 operating rooms, which were examined:

The result of calculations and energy simulations shows an energy saving compared to the current situation of 338,000 kWh / year, equivalent to DKK 366,000 / year. CO2 emissions reduced by 7.5 ton / year. Percentage savings are 34% on operating costs and 31% on energy consumption. CO2 emissions are reduced by 23%.

Energy and operating savings, divided into LAF and TAF, show the largest percentage reduction for the LAF rooms with a difference of up to 4% down to the TAF rooms.

Savings without compromising the microbiological safety in connection with air change, LAF air volumes and speed etc., which are unchanged during the operation.

With the exception of operating cost energy in the “As is” situation, LAF rooms are the cheapest in energy operation with the lowest energy consumption through 2 calculated optimization phases. LAF 28,800 kWh / year versus TAF of 41,200 kWh / year.

In percentage terms the energy savings are:

• LAF: (51,913 - 28,844) / 51,913 · 100% = 44%
• TAF: (59,216 - 41,264) /59,216 · 100% = 30%

Microbiological average values for active air sampling and passive sedimentation are also significantly lower for LAF than for the TAF rooms.

TAF - rooms are a factor of 15 higher than the LAF - rooms in the active air sampling measurements and factor 6 higher in passive sedimentation.

All LAF rooms complied with the existing air quality requirements, while 56% (9/16) of the surgeries at TAF rooms had too many microorganisms ( CFUs ).

Economic perspectives
In connection with new constructions as well as renovations, a holistic economic approach should be taken.

It is important to price the two systems - LAF and TAF - alike. This means that if there is air and gas outlets, extra lights, electrical connections in the bridge engineering, etc in the LAF, the price for this is also included in the TAF system to be able to compare the costs.

One must also consider the air volumes, plant and duct sizes, space conditions for the ducts, insulation of ducts, fire dampers, the control, etc., as all this also influences on the price difference. 

The energy costs must also be included, including ensuring operational monitoring and maintenance. There is significant energy savings by ensuring continuous optimum operation of the ventilation systems in the operating rooms, and that without compromising the microbiological safety of the room - and thereby patient safety.