Ultraclean Air Research Articles

532Effect of mobile unit ultra-clean laminar air flow system (LAF) on microbial contamination in urological surgery procedures. Preliminary results

532Effect of mobile unit ultra-clean laminar air flow system (LAF) on microbial contamination in urological surgery procedures. Preliminary results

Aerobiology in the operating room and its implications for working standards

Two novel operating room (OR) ventilation concepts, i.e. the upward displacement or thermal convection system and the exponential ultra-clean laminar air flow (LAF) designed to function without extra walls, were evaluated from a bacteriological point of view. The thermal convection system (17 air changes/h) was compared with conventional ventilation (16 air changes/h) with an air inlet at the ceiling and evacuation at floor level. The exponential LAF was compared with the vertical ultra-clean LAF and the horizontal ultra-clean LAF, both with extra side walls. The comparison was made using strictly standardized simulated operations and, except for the horizontal LAF, it was performed in the same OR where the type of ventilation was changed. In the different areas important for surgical asepsis, the thermal system resulted in a twofold to threefold increase in bacterial air and surface counts compared to the conventional system (statistical significance = p < 0.05-0.0001). The bacteriological efficiency of the exponential LAF was equal to the horizontal and vertical LAF units with extra walls in the OR, and all three systems easily fulfilled the criteria for ultra-clean air, i.e. bacteria-carrying particles < 10/m3. In the areas important for surgical asepsis the turbulent ventilation systems yielded highly significant correlation between air and surface contamination (p < 0.02-0.0006). No such correlation existed in the LAF systems.

Application of Core Biopsy in Revision Arthroplasty for Deep Infection

A preliminary core biopsy was performed in 168 consecutive joint arthroplasties (141 hips and 27 knees) before revision for suspected deep infection. Data of the core biopsy and subsequent revision procedures were available for 159 cases. Biopsies and revisions were all performed by one surgeon, and the exchange procedures were all undertaken in an ultra clean air enclosure. Biopsy material was cultured both aerobically and anaerobically and the results compared to that of the specimens obtained at the subsequent exchange procedure. In 116 patients (70%), the culture and sensitivity results were identical in samples from core biopsy and samples obtained during revision procedure (either no growth or growth of same organisms). When compared to intraoperative specimen report, 25 biopsies (15%) gave an apparently false-positive result. In 16 instances, a false-negative result was seen, but repeat biopsy in 4 of these cases was positive. The final diagnosis of infection was made using all available clinical and investigative data. When compared to final diagnosis, the sensitivity of core biopsy was 88%, the specificity was 91%, and the accuracy was 89%. Core biopsy was successful in identifying the organisms with the sensitivities to antibiotics in 80% of the disease-positive cases, hence, offering the opportunity to add the most appropriate antibiotic to bone cement during the exchange procedure.

Wound ventilation with ultraclean air for prevention of direct airborne contamination during surgery.

Despite the novelties in operating room ventilation, airborne bacteria remain an important source of surgical wound contamination. An ultraclean airflow from the ceiling downward may convey airborne particles from the surgical team into the wound, thus increasing the risk of infection. Therefore, similar ventilation from the wound upward should be considered. We investigated the effect of wound ventilation on the concentration of airborne particles in a wound model during simulated surgery. Randomized experimental study simulating surgery with a wound cavity model. An operating room of a university hospital ventilated with ultraclean air directed downward. Particles 5 microm and larger were counted with and without a 5-cm deep cavity and with and without the insufflation of ultraclean air. With the surgeon standing upright, no airborne particles could be detected in the wound model. In contrast, during simulated operations, the median number of particles per 0.1 cu ft reached 18 (25th and 75th percentiles, 12 and 22.25) in the model with a cavity and 15.5 (25th and 75th percentiles, 14 and 21.5) without. With a cavity, wound ventilation markedly reduced the median number of particles to 1 (range, 0 to 1.25; P < .001). To protect a surgical wound against direct airborne contamination, air should be directed away from the wound rather than toward it. This study provides supportive evidence to earlier studies that operating room ventilation with ultraclean air is imperfect during surgical activity and that wound ventilation may be a simple complement. Further clinical trials are needed.

Computerized control of the procedure for detecting and removing airborne particles in operating rooms.

Surgical-site infections are still a major problem in modern medicine. Normal skin fora of patients or healthcare workers causes more than half of all infections following clean surgery, but the importance of airborne particles in this setting remains controversial. The use of ultraclean air in operating rooms has been shown to reduce infection rates significantly. High efficiency particlulate air (HEPA) filters are used in some modern operating rooms. Although the uses of HEPA filters, the air quality should be controlled by another device to make safe the air in operating rooms and intensive care units. In this study, a computerized system was established to control the cleanliness of the air by measuring the presence of airborne particles of varying sizes and numbers in operating rooms. When the maximum values are exceeded, the system warns the authorized people by phone, sound, or displays.

Bacterial contamination of surgical gloves by water droplets spilt after scrubbing

Wound infection and deep sepsis can have disastrous consequences, particularly in orthopaedic surgery. Strict protocols, ultra-clean air, prophylactic antibiotics, and impervious gowns and drapes, have all been shown to diminish wound infection. However it remains a common and significant problem. The water droplets spilt from the surgeons hands after meticulous scrubbing with povidone iodine were cultured. The permeability of the surgical glove packaging to Gram-positive bacteria was also investigated. The water droplets from the surgeon's arms contained environmental and potentially pathogenic bacteria including a micrococcus, a coliform and coagulase-negative staphylococci. The paper packaging for the range of sterile surgical gloves tested was discovered to be permeable to Gram-positive bacteria. In conclusion accidental water droplet contamination of surgical gloves is a potential source of infection. Alternative recommendations are made.

Convection warmers—a possible source of contamination in laminar airflow operating theatres?

This work results from concerns that forced-air convection heaters applied to patients in the operating theatre might interfere with ultra-clean ventilation system and thus be a potential source of wound contamination. Air samples were taken in the operative field and the bacterial load calculated by estimating the number of colony forming units per cubic metre of air (cfu/m 3). Six tests were carried out, two in empty theatres and four during standard orthopaedic operating lists. Differences were seen between empty theatres and those standing empty for short periods during busy operating lists. Increases were seen on entry to theatre of staff and patients with the convection heaters off. A further small rise was seen after the convection heaters were turned on when applied to patients. This study showed that use of warm air convection heaters on patients produced a small increase in the number of colony forming units in ultra-clean air theatres but the levels were unlikely to have clinical significance. By far the greatest effect on numbers was movement and presence of the patient and theatre staff in the theatre.

Environmental controls in operating theatres

Surgical-site infection is the leading complication of surgery. Normal skin flora of patients or healthcare workers causes more than half all infections following clean surgery, but the importance of airborne bacteria in this setting remains controversial. Modern operating theatres have conventional plenum ventilation with filtered air where particles ≥5μm are removed. For orthopaedic and other implant surgery, laminar-flow systems are used with high-efficiency particulate air (HEPA) filters where particles ≥0.3μm are removed. The use of ultra-clean air has been shown to reduce infection rates significantly in orthopaedic implant surgery. Few countries have set bacterial threshold limits for conventionally ventilated operating rooms, although most recommend 20 air changes per hour to obtain 50–150 colony forming units/m3 of air. There are no standardized methods for bacterial air sampling or its frequency. With the use of HEPA filters in operating theatre ventilation, there is a tendency to apply cleanroom technology standards used in industry for hospitals. These are based on measuring the presence of particles of varying sizes and numbers, and are better suited than bacterial sampling. Environmental bacterial sampling in operating theatres should be limited to investigation of epidemics, validation of protocols, or changes made in materials which could influence the microbial content.

Mobile zoned/exponential LAF screen: a new concept in ultra-clean air technology for additional operating room ventilation

A mobile screen (0.5×0.4m) producing ultra-clean exponential LAF (air-flow central zone 0.6m/s and peripheral zone 0.4m/s) was investigated as an addition to conventional turbulent/mixing operating room ventilation. The evaluation was performed during strictly standardized sham operations reflecting conditions during major surgery. The study consisted of a pilot experiment designed to give high counts of sedimenting aerobic colony forming units (cfu). In a second main study, recording dust particles, air-borne and sedimenting aerobic cfu, the screen was associated with optimal operating room clothing.In the pilot experiment the use of the screen resulted in a substantial reduction of sedimenting bacteria from 3835–4940 to 0–390cfu/m2/h. In the main study, the use of the additional LAF reduced the surface contamination from 416–329 to 7–78cfu/m2/h up to 1.6m from the screen (P=0.001–0.0001). Measured in the wound area the screen reduced the air counts of bacteria from 9–14 to 0.2–0.4cfu/m3 (P=0.008–0.0001) and a marked reduction of air-borne dust particles was recorded (P=0.007–0.009).In conclusion, the additional mobile LAF screen reduced the counts of aerobic air-borne and sedimenting bacteria-carrying particles as well as dust particles to the levels gained with complete ultra-clean LAF room ventilation. Thus, the screen might prove a valuable addition to operating room ventilation as well as in other areas where asepsis is essential.

Inconsistent correlation between aerobic bacterial surface and air counts in operating rooms with ultra clean laminar air flows: proposal of a new bacteriological standard for surface contamination

The relationship between surface contamination (cfus/m2/h) with particles carrying aerobic bacteria and corresponding air contamination rates (cfus/m3) was evaluated in operating rooms (OR) equipped with ultra clean vertical or horizontal laminar airflow (LAF). For the evaluation we collected data during strictly standardized sham operations using non-woven disposable or cotton clothing. Air contamination in the wound and instrument areas (Casella slit sampler) was related to the surface contamination rate (settle plates) in the same areas and in addition, on the patient chest.Typically, the mean surface counts were 20–70 cfus/m2/h and the air counts 1–2 cfus/m3in disposable clothing experiments, whilst the use of cotton clothing resulted in higher counts of 100–200 cfus/m2/h (wound P>0·05, patient P>0·05, instruments P<0·01) and 4 cfus/m3(P<0·02–0·001). In the vertical LAF, taking both disposable and cotton clothing operations together, the surface and air contamination rates (surface/air ratio SAR) were highly correlated (P =0·02–0·004) and the ratio varied between 18:1 and 50:1 with a mean for wound air of 36:1. Using only disposable clothing in the vertical LAF, the number of significant correlations was reduced. With cotton clothing experiments in vertical LAF and in the horizontal LAF using disposable clothing, no significant correlation between surface and air contamination was found.The wide variation of SAR values and the inconsistent relationship between surface and air counts indicates that measurement of OR air contamination represents an unhelpful method for assessment of surgical site contamination in LAF units. We propose instead that colony counts on sedimentation plates is a clinically more relevant indicator of bacterial OR contamination in LAF units. In addition to the current bacteriological standard for ultra clean OR air of (<10 cfus/m3) we suggest a corresponding standard for the surface contamination rate of <350 cfus/m2/h.

The Surgical Isolation Bubble System and patient temperature during ventriculoperitoneal shunt insertion in preterm and term newborn infants.

The ultraclean air environment in a plastic isolator has been used in cerebrospinal fluid shunt interventions in an attempt to reduce the incidence of infections. The blower that maintains a continuous flow of filtered air in the operative field may create body temperature changes. In this study we assessed the temperature before, during and at the end of the operation in preterm and term infants in whom ventriculoperitoneal shunts were being placed. There were 12 preterm and 9 term infants. The duration of the operative intervention ranged from 25 to 50 min. In the preterm infants the mean initial temperature was 36.2+/-0.2 degrees C, and the final temperature was 35.7+/-0.2 degrees C. This difference was not significant. The initial temperature in the term infants was 36.26+/-0.2 degrees C, and the final temperature was 35.9+/-0.3 degrees C, also not significantly different. The surgical isolation bubble system does not alter the temperature of preterm and term infants significantly during ventriculoperitoneal shunt procedures performed within the operative times seen in this study.

Zoned exponential, vertical and horizontal ultra-clean laminar airflows. No differences in bacteriological efficiency.

We compared the novel zoned exponential ultra-clean operating room ventilation, needing no extra side-walls with the traditionally used ultra-clean air systems having vertical or horizontal laminar airflow, but requiring extra side-walls. The three units were evaluated with regard to elimination of particles with focus on airborne and sedimenting bacteria-carrying particles (colony forming units, cfu) during rigidly standardized sham operations. Although minor differences were recorded inside the ultra-clean airflows, the three systems were comparable with regard to bacteriological efficiency and ensured a low air and surface contamination (0.05-4 cfu/m3 and 7-72 cfu/m2/h, depending on the site of sampling). We conclude that all three systems fulfilled well the criteria for ultra-clean air (< 10 cfu/m3), but that exponential airflow is the most versatile alternative, as additional side-walls around the operating area can be omitted.

OPTIMISATION OF ULTRACLEAN AIR

The use of ultraclean air (UCA) in operating theatres reduces the infection rate after joint replacement but some cases of infection still occur. We investigated one possible source of contamination, namely the setting up of instruments in a conventional plenum-ventilated preparation room. We measured bacterial fallout using agar settle plates and compared instruments set up in the preparation room with those set up in the UCA theatre, assessed the effect of covering instruments after preparation and compared fallout during their preparation with total fallout throughout the operation. Our findings showed that covering the instruments reduced total bacterial fallout fourfold by reducing the exposure time, particularly during periods of increased activity and bacterial dispersal. Preparation in the UCA theatre and subsequent covering of the instruments reduced total fallout 28-fold. All measurable bacterial fallout occurred during the setting up and not during surgery.

Deep infection after primary hip arthroplasty: results after treatment of 10 patients

In the period 05.06.79 -31.12.91, 2037 primary total hip arthroplasties were performed, all in ultra-clean air, wearing body-exhaust system suits and all patients recieving Meticillin as prophylactic antibiotics. None of the non-cemented arthroplasties were infected and 0.61% of the cemented hip arthoplasties were infected giving a total incidence of deep infection after total hip arthroplasty in our clinic of 0.49%. The microorganism most commonly cultured was Staph. aureus, but in one hip Listeria was cultured, which is extremely rare. In the 10 patients with deep infection the infection reccurred in 30%. Patients with a revision prosthesis in situ at follow-up, had an average Harris-hip score of 79, and radiographs showed no signs of loosening or persistant infection. The rate of deep infection and the patients' condition after the revision procedures in our series are comparable to other published series.

AIR CONTAMINATION DURING SKIN PREPARATION AND DRAPING IN JOINT REPLACEMENT SURGERY

Despite the use of ultraclean air, there are still cases of infection in total joint arthroplasty. One possible route by which bacteria may enter the wound is indirectly by contamination of instruments during skin preparation and draping. We found that bacterial air counts were 4.4 times higher during preparation and draping for hip or knee arthroplasty using an unscrubbed, ungowned leg holder than during the operation itself. With the leg holder scrubbed and gowned during preparation and draping, the air counts were reduced but were still 2.4 fold greater than intraoperatively. On some occasions, the air counts during preparation and draping exceeded the standards for ultraclean air irrespective of the attire of the leg holder. We recommend that the leg is held by a scrubbed and gowned member of the team. More importantly, we consider that instrument packs should be opened only after skin preparation and draping have been completed.

Risk of airborne transmission in an operating theatre containing four ultraclean air units

This study shows that a single, large, operating theatre (barn) containing four ultraclean operating units (cabins), was highly effective in reducing the number of airborne bacteria in the operating fields providing all occupied ultraclean cabins were functioning correctly. The air flows and bacterial counts during operations within the cabins met the current standard for ultraclean systems (HTM 2025 1994) and there was no evidence of mixing of air between cabins. It is, however, recommended that air flows are regularly checked for compliance with the standard. If failure occurs in any single ultraclean unit, surgery in that cabin should cease as contaminated air may enter from the barn and surrounding cabins. Routine microbiological sampling should not be necessary providing there is no evidence of filter leakage. An operating theatre with several ultraclean operating tables in a single room would appear to be a viable proposition for the future. Considerable savings are likely in revenue costs as much of the air is reused and support services are shared.

Ultraviolet radiation and the control of airborne contamination in the operating room

Ultraviolet irradiation has been employed in operating rooms for more than half a century in attempts to reduce airborne bacterial contamination. Safety considerations have limited its intensity to 25–30 μw cm −2 and at this level no more than a fourfold reduction has resulted. In recent studies intensities up to 300 μw cm −2 have been used without untoward effects, and, at the highest intensity, contamination as low as that obtained with ultraclean air ventilation systems was obtained. However this was only achieved in an operating room where the level of airborne contamination before the introduction of the radiation was already much lower (around one-fifth) than that usually observed, and the reduction attributable to the radiation was still only about 12-fold.

Prophylaxis against infection in orthopaedic practice

Prophylaxis against surgical infections is based upon reducing the number of microorganisms which access the wound, and on augmenting normal host defence mechanisms. There is no reason to challenge the importance of the principles of asepsis or of wound excision following injury. The last two decades have seen the growth of prophylaxis using antimicrobial agents and ultra-clean air systems. Although the available data offer less support for their effectiveness than might be supposed from the general acceptance of these measures, it is concluded that use of short-term systemic antibiotic prophylaxis against wound infection is currently justified in open fractures and whenever implants are being inserted. As coagulase negative staphylococci develop increasing resistance to routinely used systemic agents, the use of antibiotic impregnated bone cement appears logical. The case for ultra clean air laminar airflow systems as a cost effective means of reducing infection rates is, despite its plausibility, controversial at the present time.

Long-term results of revision hip arthroplasty. Survival analysis with special reference to the femoral component

We report a clinical and radiological survival analysis of 148 consecutive revisions of hip arthroplasties. All patients referred were offered revision if it was indicated and they were medically fit. About one-third (32%) had had at least one previous revision, and about one-third had an established deep infection. The revisions were performed in ultra-clean air with body-exhaust suits. The usual method of fixation was by contained and pressurised cement of standard viscosity, to which appropriate antibiotics had been added in infected cases. Some patients had cementless revision. Clinical failure meant that one or both of the implants had been removed; radiological failure was assessed from serial radiographs. The clinical survival at ten years was 95%. The Merle D'Aubigné and Postel rating for pain improved from a mean of 2.9 to 5.2; and in Charnley group A and B cases, walking ability improved from 2.3 to 4.3. In contrast to some reports we also found good radiological survival; this was 90.5% for cemented femoral stems. Isoelastic revision stems inserted without cement gave poor results.

Infection and interposition between ultraclean air source and wound.

Infection and interposition between ultraclean air source and wound.