Surgical site infections (SSIs) following total joint replacement surgery make up the most feared complication, presenting a significant burden in terms of patient morbidity and additional related costs [1
]. Many factors increase the risk of SSIs, including patient-related, procedural-related, and management-related factors [1
]. In particular, in order to preserve the indoor air quality provided by heating, ventilation, and air conditioning (HVAC), reducing operator movement in the operating theatres during surgical activity is recommended, e.g., keeping operating theatre doors closed, except as needed for passage of equipment, personnel, and the patient, limiting the number of personnel entering the operating theatre to those necessary, and minimize personnel traffic during operations [1
]. Microbial contamination of the surgical site is a necessary precursor of SSIs and the air in operating theatres (OTs) represents an important vehicle for SSI-related microorganisms which can fall directly into the wound or land on exposed surfaces and subsequently be transferred into the wound [5
]. A Medical Research Council study found a significant correlation between microbial air contamination, wash-out bacterial count, and the incidence of SSIs [6
]. Therefore, the use of ultra-clean, ventilated OTs with unidirectional airflow was recommended in orthopedic implant surgeries, with maximum air microbial contamination values during operation of 10 colony-forming units per cubic meter (CFU/m3
) when measured by active sampling [8
], and 350 CFU/m3
] and 2 CFU/9-cm-plate/h when measured by passive sampling [12
]. As for particle contamination, an ISO 5 class, i.e., below 3520 particles ≥ 0.5 µm/m3
, is recommended for hip arthroplasty surgery operating theatres [4
]. However, in 2008, a retrospective study unexpectedly showed significantly higher SSI rates after hip prosthesis implantation when using unidirectional airflow ventilation compared with turbulent (mixing) ventilation [17
], and a subsequent meta-analysis [18
] performed within the framework of developing World Health Organization (WHO) global guidelines [1
] for the prevention of surgical site infections showed no difference in risk between unidirectional airflow ventilation and turbulent ventilation for hip SSIs following total hip arthroplasty [18
]. On the basis of this meta-analysis, WHO guidelines suggest that unidirectional airflow ventilation systems “should not be used to reduce the risk of SSI for patients undergoing total arthroplasty surgery”, even though “the strength of this recommendation was considered to be conditional, considering the very low quality of the supporting evidence” [1
]. Several criticisms were aimed at the studies included in the meta-analysis [19
]; in particular, none of them contained an assessment of air microbial contamination, or took into consideration that, despite unidirectional airflow ventilation, microbial air contamination could still have exceeded recommended threshold values, thereby reducing the effectiveness of the ventilation system.
Different studies showed the strong influence of the amount of people present in the OT and their movements and the influence of doors opening and closing on microbial contamination, air pressure, and microclimatic conditions. Furthermore, surgical staff behavior has a strong impact on indoor air quality and ventilation effectiveness in OTs equipped with HVAC systems with unidirectional turbulent flow [22
]. In particular, the ISChIA study [22
] showed a correlation between the number of times the door was opened, the number of people in the OT, and microbial air contamination, highlighting a high level of contamination that exceeded the current threshold values in OTs supplied with unidirectional airflow, which was even higher than the microbial contamination values obtained in conventionally ventilated OTs in some case4s. Other studies showed that in currently used, conventionally ventilated OTs, it was possible to obtain microbial contamination levels lower than the HTM 03-01 recommended values of ≤180 CFU/m3
during surgical activity [22
]. However, during bad OT management, these values could also very much exceed the recommended levels [22
]. From this background research, the aim of the present study was to evaluate microbiological and particle air contamination and microclimate parameters in order to highlight the influence of incorrect behavior on air quality in a conventionally ventilated OT during hip arthroplasties and to compare the obtained results with current standards.
3.1. Biological Sampling
shows the microbial contamination values obtained at the different sampling points, i.e., at the rest condition and during the two simulated hip arthroplasties.
No fungi were isolated during the R condition active or passive sampling. During surgical activity, the microbial contamination values increased at all sampling points. During the operation performed with the surgical team behaving correctly, the CFU/m3 increased 6.5 times, 7.7 times, and 7.2 times at the operating table, HVAC exhaust grille, and entrance door of the OT, respectively, while the IMA values increased from 0 to 2, from 0 to 6, and from 2 to 4, respectively. The lowest values were obtained at the operating table using both CFU/m3 and IMA (13 CFU/m3 and 2 IMA); the maximum CFU/m3 value (29 CFU/m3) was recorded at the entrance door of the OT, while the maximum IMA value (6 IMA) was recorded at the exhaust grille.
During surgical activity under incorrect behavior conditions, a further increase in air microbial contamination was observed, reaching values of 74, 44, and 93 CFU/m3, and 8, 8, and 16 IMA at the operating table, the exhaust grille, and the entrance, respectively.
No fungi were isolated during the C condition, while fungi were isolated by active sampling during NC condition at the operating table (1 CFU/m3 of Penicillium spp.).
The air sampling performed in the corridor during routine operational conditions yielded 50 CFU/m3.
3.2. Particle Counting
At the operating table, the number of particles ≥0.5 μm/m3
increased from 1,848 P/m3
(corresponding to ISO class 5) in the R condition to 64,783 P/m3
(corresponding to ISO class 7) during the C condition and to 82,696 P/m3
(corresponding to ISO class 7) during the NC condition. Particle air contamination increased by 27.6% during the NC condition compared to the C condition (Table 1
3.3. Microclimatic Measurements
shows the median and average values of microclimatic parameters under the R, C, and NC conditions and the different measured points. Standard deviations with respect to the average values are also given.
Time series of the indoor air temperature, humidity, and CO2
concentration values recorded in the different conditions, i.e., R, C, and NC, are given in Figure 2
, Figure 3
and Figure 4
shows the air temperature values measured at the operating table, at the exhaust grille, and at the entrance door, including radiant temperature values measured at the operating table.
In particular, during the R condition, the maximum and minimum air temperature values were 20.30 °C and 20.22 °C at the operating table, 20.02 °C and 19.98 °C at the entrance door, and 20.54 °C and 20.46 °C at the exhaust grille. The maximum and minimum radiant temperature values were 20.69 °C and 20.65 °C at the operating table. During the C condition, the maximum and minimum air temperature values were 21.02 °C and 20.82 °C at the operating table, 20.70 °C and 20.46 °C at the entrance door, and 21.02 °C and 20.9 °C at the exhaust grille. The maximum and minimum radiant temperature values were 21.32 °C and 21.24 °C at the operating table. During the NC condition, the maximum and minimum air temperature values were 21.30 °C and 21.10 °C at the operating table, 20.90 °C and 20.71 °C at the entrance door, and 21.30 °C and 21.10 °C at the exhaust grille. The maximum and minimum radiant temperature values were 21.60 °C and 21.41 °C at the operating table.
provides the relative humidity values recorded at the operating table, exhaust grille, and entrance door. The maximum value (67.1%) was recorded at the exhaust grille during the R condition, while the lowest value (63.40%) was recorded at the operating table during the NC condition. The highest values were generally detected at the exhaust grille, while the lowest values were recorded at the operating table.
concentration values in ppm measured at the operating table for all of the OT conditions are provided in Figure 4
. The maximum value (542 ppm) was recorded during the C condition, while the lowest value (409 ppm) was recorded during the R condition.
This study describes an approach of evaluating biological, particle, and microclimatic air quality in conventional operating theatres, which was applied during two simulated hip arthroplasties in two different conditions of surgical staff behavior. The surgical staff behavior had a strong impact on indoor air quality and ventilation efficacy in operating theatres equipped with effective HVAC systems with unidirectional or turbulent flow.
As in other recent studies [22
], microbial contamination during surgical activity was lower than the recommended values of 180 CFU/m3
and 25 IMA [10
]. Pasquarella et al. demonstrated that 80 CFU/m3
could be reached during operational conditions [29
], and Vonci et al. demonstrated that 50 CFU/m3
could be recorded in operating theatres equipped with turbulent flow ventilation at 15 air changes per hour [44
]. In a recent revision, Stockwell et al. reported a microbial air contamination of 20 CFU/m3
in hospital areas equipped with conventional mechanical ventilation systems [45
In this study we obtained microbial contamination levels below the recommended values even in the NC condition, showing that currently used turbulent HVAC systems are more efficient than those in the past, as highlighted in previous studies [22
]; therefore, keeping operational threshold values of 180 CFU/m3
and 25 IMA could lead to an underestimation of the risk. In particular, it was shown that some turbulent OTs complied with ISO 5 class [46
During the surgical operation performed under the C condition, we obtained values of 13 CFU/m3
and 2 IMA, which were similar to the threshold values recommended in unidirectional airflow ventilated operating theatres (10 CFU/m3
and 2 IMA) [10
], thereby supporting the evidence stating that current HVAC systems are more efficient and can reach the same air quality as that obtained by unidirectional airflow systems under correct surgical behavior conditions.
The bacteria contamination values (50 CFU/m3
) recorded in the corridor during routine operational conditions were lower than the values observed during the NC conditions at the operating table and door entrance, which were 74 and 93 CFU/m3
respectively. These findings were consistent with the results of a previous study [29
] which showed, in some cases, not significant differences between bacterial air contamination in the OT and in the corridor, and even bacterial air contamination higher in the OT than in the corridor in one case.
The particle counting results further confirmed the higher efficiency of currently used turbulent HVAC systems, with similar particle numbers as the recommended levels for unidirectional airflow plants in R conditions and the maintenance of ISO 7-required levels during C and NC conditions for ≥0.5 µm sized particles.
Microbial air contamination, which was measured both by active and passive samplings, and ≥0.5 µm-particle contamination consistently yielded the lowest values under “at rest” conditions and the highest values under “incorrect” conditions.
From a microclimatic point of view, different studies demonstrated the strong influence of total traffic flow and the number of people present in an OT. There was evidence of an important variation in the OT microclimate (i.e., deviation from the standard limit values), which was strictly connected to behavior of surgical teams. In particular, there was a strong relationship between the ventilation system, its air flow scheme, and staff behavior, and the air motion and air temperature field in high-performance hospital OTs equipped with HVAC systems with unidirectional and turbulent flow. Therefore, the need for training and control of surgeon/medical and nursing staff should be emphasized [25
In this study, the local increase of air motion and the turbulence effects induced by staff presence under the C condition was evident. When comparing trends for the R and C conditions, the velocity values recorded at the operating table were different and the air motion was increased by staff presence during the C condition; a further increment during the NC condition was observed. At the entrance door, a reduction in the air velocity from the R condition to the C condition was followed by air motion stabilization during the NC condition. These effects were typical of a turbulent motion mainly characterized by flow field irregularity of the main variables and diffusivity, i.e., irregularities due to a rapid mixing of fluid portions. The turbulent motion determined a certain dispersion of the air velocity values in the studied conditions, namely, R, C, and NC, as deduced from the Table 2
The air temperature showed the lowest mean values at the entrance door due to the turbulent effects. The data dispersion at the operating table was influenced by surgical staff presence and behavior. The average radiant temperature values at the operating table were consistently higher than those achieved by the thermohygrometers. The highest air temperature values were recorded at the operating table, which was clearly due to surgical staff presence and movements, as it was also confirmed by the highest values of the air radiant temperature at the same sampling point. The sliding door opening/closing phases did not seem to have a substantial impact on the temperature. The temperature variations over time were low. From comparisons of the three conditions (R, C, and NC), the variation of the air temperature had a similar trend over time, thereby proving that the turbulent flow ventilation scheme immediately affected the whole environment.
The relative air humidity variations over time were low, corresponding to average values in the range of 63%–68% for all of the different OT conditions that were studied.
CO2 concentration levels in the OT were affected by the presence of the surgical team for the C condition, mainly by the opening/closing door and incorrect behavior of the surgical team (NC condition). CO2 values observed during the C condition showed a fluctuating trend, but they continued to increase over time in the NC condition.
The dispersion of CO2 concentration measurements appeared high. The difference was clearer for the data acquired for the C and NC conditions, when the medical staff remained inside the room and opening/closing of the door occurred. The standard deviations for the C and NC conditions were 3 and 6 times that computed for the R condition, respectively.
The obtained results were also in accordance with evidence in the literature, demonstrating that air flow patterns and air velocity and temperature distributions were disrupted by the amount, behavior, and upright and bending positions of surgical staff [20
The microclimatic parameters agreed with current recommendations [10
], although variations during the NC condition were observed.
Our study shows the negative influence of the surgical team’s incorrect behavior on operating theatre microbial and particle air contamination and microclimatic parameters. The microbial contamination values were much lower than the current recommended threshold values for operational conventionally ventilated operating theatres during simulated hip arthroplasties with the surgical team behaving incorrectly. This highlights the need for a revision of these threshold values. During operations where the surgical team behaved correctly, very low microbial contamination was detected, with results not too far from those recommended for the unidirectional air flow plant system.
This contribution is important considering the wider use of conventional operating theatres for hip arthroplasties, particularly in light of the ongoing debate regarding unidirectional air flow ventilating systems as a risk factor for surgical site infections in hip arthroplasties. To our knowledge, this study is the first to evaluate air quality in OTs including both sampling methods (i.e., active and passive) and microclimate monitoring. The obtained results represent a useful basis for further simulated interventions, during which the modification of particle and microbiological contamination and variations in the microclimatic parameters influenced by incorrect behavior could be thoroughly assessed. The use of this approach for real hip arthroplasties with a wider collection of comparable data will provide important knowledge regarding the air quality in current conventional operating theatres, potentially leading to a revision of the threshold values.
Whichever HVAC system is installed, it is essential to guarantee operating theatre air quality. Poor management of the HVAC or incorrect operator behavior could undermine this economic investment and expose patients to the risk of surgical site infections. In this regard, air microbiological monitoring can be a useful tool to assess air quality, test the effectiveness of preventive measures, and identify hazardous situations.