Background: The objective of an operating room (OR) ultra-clean ventilation system is to eliminate or reduce the quantity of dust particles and colony-forming units per cubic meter of air (CFU/m³). To achieve this, ultra-clean goal high air change rates per hour are required to reduce the particle load and number of CFU/m³. Aim: To determine the air quality in an ultra-clean OR during surgery, in terms of the number and type of microorganism and quantity of dust particles in order to establish a benchmark. Methods: Number of CFUs and the quantity of dust particles were measured. For measuring the CFUs, sterile extraction hoses were positioned at the incision, the furthest away positioned instrument table, and the periphery. At these locations, air was extracted to determine the quantity of dust particles. Findings: The number of CFU/m³ and particles was on average at wound level ≤1 CFU/m³ resp. 852.679 particles, at instrument table ≤1 CFU/m³ resp. 3.797 particles and in the periphery ≤8 CFU/m³, resp. 4.355 particles. Conclusion: The number of CFUs in the ultra-clean area is below the defined ultra-clean level of ≤10 CFU/m³ for ultra-clean surgery. The quantity of dust particles measured during surgery was higher than the defined ISO 5.

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Background
The operating room (OR) department is one of the most energy-intensive departments of a hospital. The majority of ORs in the Netherlands have an air-handling installation with an ultra-clean ventilation system. However, not all surgeries require an ultra-clean OR.

Aim
To determine the effect of reducing the air change rate on the ventilation effectiveness in ultra-clean ORs.

Methods
Lower air volume ventilation effectiveness (VELv) of conventional ventilation (CV), controlled dilution ventilation (cDV), temperature-controlled airflow (TcAF) and unidirectional airflow (UDAF) systems were evaluated within a 4 × 4 m measuring grid of 1 × 1 m. The VELv was defined as the recovery degree (RD), cleanliness recovery rate (CRR) and air change effectiveness (ACE).

Findings
The CV, cDVLv and TcAFLv ventilation systems showed a comparable mixing character in all areas (A, B and AB) when reducing the air change rate to 20/h. Ventilation effectiveness decreased when the air change rate was reduced, with the exception of the ACE.
At all points for the UDAF-2Lv and at the centre point (C3) of the TcAFLv, higher RD10Lv and CRRLv were measured when compared with the other examined ventilation systems.

Conclusions
The ventilation effectiveness decreased when an ultra-clean OR with an ultra-clean ventilation air-supply system was switched to an air change rate of 20/h. Reducing the air change rate in the OR from an ultra-clean OR to a generic OR will reduce the recovery degree (RD10) by a factor of 10–100 and the local air change rate (CRR) by between 42% and 81%.@en

This thesis explores different ventilation systems used for operating rooms (OR). Entrainment test methods are used in most European standards to determine the protected zone whereas the air quality in the periphery is often excluded. Furthermore, these measurements are mostly carried out in an at-rest situation where intermittent sampling during operation should be required. Most ORs in the Netherlands have an air handling system with an ultra-clean ventilation system (UCV). ORs are energy-intensive departments, where air handling systems consume the most. Relatively simple adjustments can be made to the air handling system to reduce energy, such as expanding relative humidity limits and introducing operational clock times. Lowering outside air quantity has the biggest impact on energy reduction, lowering the OR classification the least. Reducing the air change rate in the OR from an ultra-clean to a generic OR will reduce the recovery degree and the local air change rate. Lowering the air change rate in operating rooms could harm comfort conditions and (ultra-clean) air quality. The capital and operational expenditures of air handling installations with an UCV-system are higher than those with a conventional system. The investment pays for itself when 2 to 4 surgical wound infections are prevented over the lifetime of the OR. The type of surgery should be a leading consideration in determining the typology of the air handling system and the type of air supply system. Absence of evidence that surgical site infections are prevented in ORs equipped with UCV-systems is not evidence that these are not prevented. @en

This article investigates the efficacy of temperature-controlled airflow systems in modern operating rooms for contaminant control, a critical factor in preventing surgical site infections. We have conducted experimental measurements in an operating room equipped with temperature-controlled ventilation to map the airflow field and contaminant dispersion (airborne particles with diameters ranging from 0.5 to 1 μm). The results were used to validate the computational fluid dynamics code, which was then employed to simulate and examine different conditions, including contaminant release locations and air supply rates. Realizable k-epsilon and passive scalar models were utilized to simulate airflow and airborne particle phases. We assessed the airflow distribution and contaminant dispersion, utilizing indices such as ventilation and air change efficiency scales. The analysis provided quantitative insights into the distribution and removal of contaminants, as well as the speed at which the room air was replaced. Contamination was found to be effectively reduced when contaminants were released near exhaust outlets or under central unidirectional inlets. The presence of the operating table caused a big distortion of the central downward airflow, forming a horizontal air barrier at the periphery. Under this unique interior configuration, an appropriate air supply ratio between central and periphery zones was required to achieve optimal overall ventilation performance.@en

When making a decision on the operating room air handling installation and type of air supply system, it is relevant to know the expenditures of the different air handling installations and air supply systems. The aim of this study was to determine the capital and operational expenditures of air handling installations equipped with an ultra-clean or with a conventional system. To compare the technical requirements of Dutch air handling installations with European standards and guidelines, and evaluate the costs of surgical site infections in comparison with the capital expenditures. This study fills a gap in knowledge, detailed technical information and costs of air handling installations and air supply systems from multiple completed projects of 24 hospitals were collected, analyzed and compared. Per OR capital expenditures increase by €62,491 to €139,018 when an air handling installation with an ultra-clean system is compared to a conventional system, which is 3%–7% of the total construction costs of a completely new OR department. The yearly increase in operational expenditures per OR with an ultra-clean system compared to a conventional system was €673 to €1,896. The capital and operational expenditures of air handling installations with an ultra-clean system are higher than those with a conventional system. The technical specifications of the ORs studied in the Netherlands correspond to European standards and guidelines. When the impact on patient suffering and costs associated with surgical site infections are weighed against the investment required for an air handling installation with an ultra-clean system, it is worth considering.

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Ultra-clean ventilation systems are used in the operating room (OR) to reduce the quantity of airborne bacteria in the ultra-clean area, and reduce the incidence of surgical site infections (SSIs). When the number of colony-forming units (CFUs) in the ultra-clean (protected) area is too high, this is considered a risk factor for SSIs.@en

The authors regret that they have missed during the review process that the legend belonging to figure 6a, 6b, 6c and 6d is not shown. It is necessary to show the legenda otherwise the readers cannot interpret the graphs. Apologies that we missed it during the review process of the article. The legend belonging to figure 6 is:[Formula presented] The authors would like to apologize for any inconvenience caused.

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Background: Entrainment test methods are described in most European standards and guidelines to determine the protected area for ultra-clean ventilation (UCV) systems. New UCV systems, such as temperature-controlled airflow (TcAF) and controlled dilution ventilation (cDV) systems, claim the whole operating room (OR) to be ultra-clean. However, current test standards were not developed to assess ventilation effectiveness outside the standard protected area. Aim: To assess and compare the ventilation effectiveness of four types of OR ventilation systems in the ultra-clean area using a uniform test grid.
Methods: Ventilation effectiveness of four ventilation systems was evaluated for three different ultra-clean (protected) areas: the standard protected area (A); the area outside the standard protected area (B); and a large protected area (AB). Ventilation effectiveness was assessed using recovery degree (RD), cleanliness recovery rate (CRR) and air change effectiveness (ACE). Findings: RD, CRR and ACE were significantly higher for the unidirectional air flow (UDAF) system compared with the other systems in area A. In area B, the UDAF and cDV systems were comparable for RD and CRR, and the UDAF and conventional ventilation (CV) systems were comparable for ACE. In area AB, the UDAF and cDV systems were comparable for CRR and ACE, but significant differences were found in RD.
Conclusion: In area A, the ventilation effectiveness of the UDAF system outperformed other ventilation systems. In area B, the cDV system was best, followed by the UDAF, TcAF and CV systems. In area AB, the UDAF system was best, followed by the cDV, TcAF and CV systems. @en