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Influence of laminar airflow on prosthetic joint infections: a systematic review

      Summary

      Background

      Many hospitals use ultraclean ventilation (UVC), also known as laminar airflow systems (LAF), in their operating rooms to decrease rates of surgical site infections (SSIs). However, the evidence for these systems is limited and the additional expenses for LAF are substantial.

      Aim

      To determine the effectiveness of LAF to decrease SSI rates following hip and knee prosthesis.

      Methods

      Systematic review of cohort studies investigating the influence of LAF on SSIs following hip and knee prosthesis published during the last 10 years.

      Findings

      Four cohort studies using the endpoint severe SSI following knee prosthesis and four studies following hip prosthesis were included. No individual study showed a significant benefit for LAF following knee prosthesis but one small study showed a significant benefit following hip prosthesis. However, one individual study showed significantly higher severe SSI rates following knee prosthesis and three studies significantly higher SSI rates following hip prosthesis under LAF conditions. The summary odds ratio was 1.36 (95% confidence interval: 1.06–1.74) for knee prosthesis and 1.71 (1.21–2.41) for hip prosthesis.

      Conclusions

      It would be a waste of resources to establish new operating rooms with LAF, and questionable as to whether LAF systems in existing operating rooms should be replaced by conventional ventilation systems.

      Keywords

      Introduction

      A severe surgical site infection (SSI) is one of the major complications following insertion of hip or knee prosthesis. The use of ultraclean ventilation (UVC) systems, commonly known as laminar airflow (LAF) ventilation, in operating rooms is frequently recommended for preventing SSI. For example, LAF systems are regarded as optimal for orthopaedic implant surgery in the UK. A survey carried out in the UK in 1993 showed that the majority of hospitals (63%) had ultraclean air facilities for orthopaedic implant surgery.
      • Humphreys H.
      • Stacey A.
      • Taylor E.
      Survey of operating theatres in Great Britain and Ireland.
      In New Zealand, laminar airflow systems were used in 49% of total hip replacements and 53% of total knee replacements in 2008.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      In a recent survey of German orthopaedic departments performing hip prosthesis, 69% used operating rooms with LAF.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      However, the Centers for Disease Control and Prevention/Healthcare Infection Control Practices Advisory Committee guidelines classify this point as an unresolved issue and state: ‘no recommendation is offered for performing orthopedic implant operations in rooms supplied with laminar airflow’.
      • CDC/HICPAC
      Guidelines for environmental infection control in health care facilities.
      The reason for these conflicting practices or recommendations respectively is the lack of scientific evidence clearly supporting this technology. There is a small number of studies investigating this question using clinical endpoints.
      • Charnley J.
      Postoperative infection after total hip replacement with special reference to air contamination in the operating room.
      • Nelson J.
      Five years experience with operating room clean rooms and personnel-isolator systems.
      • Salvati E.
      • Robinson R.
      • Zeno S.
      • Koslin B.
      • Brause B.
      • Wilson P.J.
      Infection rates after total hip and total knee replacements performed with and without a horizontal unidirectional filtered air-flow system.
      • Lidwell O.
      • Lowbury E.
      • Whyte W.
      • Blowers R.
      • Lowe D.
      Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study.
      • Marotte J.
      • Lord G.
      • Blanchard J.
      • et al.
      Infection rate in total hip arthroplasty as a function of air cleanliness and antibiotic prophylaxis. 10-year experience with 2,384 cementless Lord madreporic prostheses.
      However, these studies had serious limitations in that they were not comparative, had inadequate sample size, were not randomized or blinded, or included other interventions that could have affected the rate of SSIs. For example Lidwell et al. studied the use of ultraclean air and exhaust suits in orthopaedic implant surgery and found a significant reduction of deep infection rates when compared with routine practices and procedures in conventional theatres. Unfortunately this multi-centre study did not control for the administration of prophylactic antibiotics.
      • Lidwell O.
      • Lowbury E.
      • Whyte W.
      • Blowers R.
      • Lowe D.
      Effect of ultraclean air in operating rooms on deep sepsis in the joint after total hip or knee replacement: a randomised study.
      LAF technology also has high investment costs and operating expenses compared with conventional ventilation systems. A study from Italy showed a 24% increase in building costs, and a 34% increase in annual operating costs using LAF versus conventional systems.
      • Cacciari P.
      • Giannoni R.
      • Marcelli E.
      • Cercenelli L.
      Cost evaluation of a ventilation system for operating theatre: an ultraclean design versus a conventional one.
      In recent years some large cohort studies have been published. They investigated the development of SSI under routine conditions in hospitals with and without LAF.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      • Engesaeter L.
      • Lie S.
      • Espehaug B.
      • Furnes O.
      • Vollset S.
      • Havelin L.
      Antibiotic prophylaxis in total hip arthroplasty.
      • Miner A.
      • Losina E.
      • Katz J.
      • Fossel A.
      • Platt R.
      Deep infection after total knee replacement: impact of laminar airflow systems and body exhaust suits in the modern operating room.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      None of these studies identified lower SSI rates in patients in hospitals with LAF. In one study LAF use was even associated with significantly higher severe SSI rates for hip prosthesis after adjusting for many relevant SSI risk factors.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      The objective of this systematic review was to investigate the influence of LAF on the development of SSI under routine conditions as observed in cohort studies.

      Methods

      A computerized literature search of articles published before September 2011 was performed. In order to exclude outdated technology, only studies published after 2000 were considered.
      The search was conducted in the biomedical database Medical Literature Analysis and Retrieval System Online using the United States National Library of Medicine PubSearch engine using the key terms ‘infection’, ‘operating room’ and ‘hip’ or ‘knee’ without any language restrictions. Truncation was used to identify a range of similar terms. The reference lists of the retrieved articles were reviewed for additional studies. Inclusion criteria for this meta-analysis were cohort studies investigating hip and/or knee prosthesis procedures and providing data for the endpoint severe SSI and information about the ventilation system in the hospitals where these procedures were performed.
      Each study was reviewed for patient population, study design, factors adjusted in multivariate analysis, country, study period, definitions of severe SSI, follow-up period, ventilation system, number of hospitals, number of procedures and number of SSIs. Data extraction was performed independently by two of the authors using a structured form and checked for accuracy; differences were resolved by the last author. In the case of missing information, the authors tried to obtain further data by contacting the authors.
      Statistical analysis was performed using software provided by the Cochrane Collaboration (Review Manager 5.1. package, released 2011). The outcome (severe SSI) was dichotomous and the measures of effects were given as Mantel–Haenszel weighted relative risks (RRs) and 95% confidence intervals (CIs). The forest plots of comparison were created by using the fixed effect model. Heterogeneity between included studies was assessed by the χ2-test, and I2 statistics. In case of heterogeneity, the studies and the data were revalued. Finally the random effect model was applied in the forest plots to incorporate heterogeneity between studies. Moreover, funnel plots were created to assess whether publication bias occurred.
      • Sterne J.
      • Egger M.
      Funnel plots for detecting bias in meta-analysis: guidelines on choice of axis.

      Results

      The initial PubMed search in September 2011 yielded 140 articles for hip and 68 for knee prosthesis. Of these, five studies were considered for inclusion in the systematic review.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      • Miner A.
      • Losina E.
      • Katz J.
      • Fossel A.
      • Platt R.
      Deep infection after total knee replacement: impact of laminar airflow systems and body exhaust suits in the modern operating room.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      Table I provides an overview of the characteristics of the studies included. They originate from four different countries and include altogether more than 75,000 knee prosthesis procedures and more than 120,000 hip prosthesis procedures. The data extracted from the studies that were included in the meta-analysis for the effect of LAF on the risk of severe SSI in hip and knee prosthesis surgery are shown in Table II, Table III. One study is based on a national arthroplasty registry, two studies are consecutive analyses from the German national surveillance system for SSI, one study is an analysis of health insurance data and one study investigated a small consecutive cohort of patients. The data from the Norwegian arthroplasty register were not used for the final meta-analysis because of missing individual data from each group of hospitals.
      • Engesaeter L.
      • Lie S.
      • Espehaug B.
      • Furnes O.
      • Vollset S.
      • Havelin L.
      Antibiotic prophylaxis in total hip arthroplasty.
      Table ICharacteristics of studies included in the meta-analysis for the effect of LAF on the risk of severe SSI in hip and knee prosthesis surgery
      StudyStudy designAdjustment factorsPatient populationCountryStudy periodSevere SSI definitionFollow-up periodInformation about the ventilation systemNo. of hospitalsNo. of proceduresRR/OR (95% CI) for LAF (multivariate)
      Miner et al.
      • Miner A.
      • Losina E.
      • Katz J.
      • Fossel A.
      • Platt R.
      Deep infection after total knee replacement: impact of laminar airflow systems and body exhaust suits in the modern operating room.
      Retrospective cohort study (Medicare claims) with multivariate analysisNoKnee prosthesisUSA2000Deep infections requiring subsequent operations (ICD-9 diagnosis and procedure codes)90 daysLAF (vertical and horizontal together) vs no LAF; survey 200025682881.57 (0.75–3.31)
      Kakwani et al.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      Cohort studyNoneHip prosthesisUK2000–2004Reoperation for infection1 yearLAF vs non-LAF theatres1435No multivariate analysis
      Brandt et al.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      Prospective cohort study (Surveillance system); GEE methodSex, age, ASA score, wound class, duration of operation, annual frequency of procedures, hospital beds, academic status, participation in the systemHip prosthesis Knee prosthesisGermanyJan 2000–June 2004CDC definitions (deep and organ/space infections)1 year, but no complete follow upVertical LAF vs HEPA-filtered turbulent air; survey 200444

      18
      28,623

      9396
      1.63 (1.06–2.52)

      1.76 (0.80–3.85)
      Hooper et al.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      Retrospective cohort study (New Zealand Joint Registry)NoHip prosthesis

      Knee prosthesis
      New Zealand1999–2008Any revision performed within 6 months of the initial operation for infectionMinimum 6 monthsLAF vs conventional theatre6451,485

      36,826
      P < 0.001

      P < 0.001
      Breier et al.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      Prospective cohort study (surveillance system); GEE methodSex, age, ASA score, wound class, duration of operationHip (A),

      Hip (F),

      Knee prosthesis
      GermanyJuly 2004–June 2009CDC definitions (deep and organ/space infections)1 year, but no complete follow-upLAF vs conventional ventilation, survey 200948

      41

      38
      33,463

      7749

      20,554
      1.08 (0.53–2.20)

      1.25 (0.60–2.58)

      1.04 (0.40–2.73)
      LAF, laminar airflow; SSI, surgical site infection; RR, relative risk; OR, odds ratio; CI, confidence interval; ICD, International Classification of Diseases; CDC, Centers for Disease Control and Prevention; ASA, American Society of Anesthesiologists; HEPA, high-efficiency particulate air filtration; GEE, generalized estimating equation; hip (A), hip prosthesis following arthrosis; hip (F), hip prosthesis following fracture.
      Table IIProcedures and severe SSIs following knee prosthesis according to the ventilation system, extracted from four studies included in the meta-analysis for the effect of LAF on the risk of severe SSI in hip and knee prosthesis surgery
      StudyLaminar airflowConventional ventilationWeightRelative risk (Mantel–Haenszel, fixed effect model, 95% CI)Severe SSI rate (%)
      SSIAll proceduresSSIAll procedures
      Miner et al.
      • Miner A.
      • Losina E.
      • Katz J.
      • Fossel A.
      • Platt R.
      Deep infection after total knee replacement: impact of laminar airflow systems and body exhaust suits in the modern operating room.
      15351313477510.3%1.57 (0.75–3.29)0.34
      Brandt et al.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      55599322340326.2%1.42 (0.87–2.32)0.82
      Hooper et al.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      ; calculated from the authors' data
      2713,9942322,83216.3%1.92 (1.10–3.34)0.14
      Breier et al.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      9314,45636609847.2%1.09 (0.74–1.60)0.63
      Total (only severe SSI)19037,9569437,108100.0%1.36 (1.06–1.74)
      SSI, surgical site infection; LAF, laminar airflow; CI, confidence interval.
      Table IIIProcedures and severe SSIs following hip prosthesis according to the ventilation system, extracted from four studies included in the meta-analysis for the effect of LAF on the risk of severe SSI in hip and knee prosthesis surgery
      StudyLaminar airflowConventional ventilationWeightRelative risk (Mantel–Haenszel, random effect model, 95% CI)Severe SSI rate (%)
      SSIAll proceduresSSIAll procedures
      Kakwani et al.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      021292231.4%0.06 (0.00–0.95)2.1
      Brandt et al.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      24217,6579910,96639.5%1.52 (1.20–1.92)Arthrosis and fracture together: 1.12
      Hooper et al.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      ; calculated from the authors' data
      2516,9902134,49520.3%2.42 (1.35–4.32)0.09
      Breier et al.
      • Breier A.-C.
      • Brandt C.
      • Sohr D.
      • Geffers C.
      • Gastmeier P.
      Laminar airflow ceiling size: no impact on infection rates following hip and knee prosthesis.
      196 16023,017 651352 2510,446 123638.7%1.83 (1.43–2.34)Arthrosis: 0.74

      Fracture: 2.39
      Total (only severe SSI)62364,38920657,366100.0%1.71 (1.21–2.41)
      SSI, surgical site infection; LAF, laminar airflow; CI, confidence interval.
      None of the studies showed a benefit for patients operated on in hospitals with LAF systems following knee prosthesis, but one small cohort study showed a benefit following hip prosthesis.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      One individual study demonstrated a significant disadvantage for knee prosthesis patients operated under LAF conditions.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      Three studies included in the analysis for hip prosthesis showed a significant disadvantage under LAF conditions. Figures 1 and 2 show the forest plots for knee and hip prosthesis. Figure 3 is a sensitivity analysis for hip prosthesis without the small cohort study by Kakwani et al.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      Figure thumbnail gr1
      Figure 1Meta-analysis for the endpoint severe surgical site infections following knee prosthesis according to the use of laminar airflow (LAF) or not using the fixed effect model. M-H, Mantel–Haenszel; CI, confidence interval.
      Figure thumbnail gr2
      Figure 2Meta-analysis for the endpoint severe surgical site infections following hip prosthesis according to the use of laminar airflow (LAF) or not using the random effect model. M-H, Mantel–Haenszel; CI, confidence interval.
      Figure thumbnail gr3
      Figure 3Meta-analysis for the endpoint severe surgical site infections following hip prosthesis according to the use of laminar airflow (LAF) or not without the study by Kakwani et al.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      The overall relative risk for severe SSI associated with LAF for knee prosthesis was 1.36 (95% CI: 1.06–1.74), with low heterogeneity and no publication bias according to the funnel plot of comparison. The meta-analysis for hip prosthesis shows an overall relative risk for severe SSI of 1.71 (1.21–2.41) using the random effect model because of substantial heterogeneity. Excluding the small study by Kakwani et al. and using the fixed effect model because of low heterogeneity of the remaining studies, a summary relative risk of 1.71 (1.45–2.01) was calculated.

      Discussion

      The role of the operating room air as a source of infection and the need for special ventilation systems in the operating rooms have long been subjects of debate. Because of the low rates of severe SSI following joint replacement, conducting randomized trials with sufficient statistical power is unrealistic.
      • Hooper G.
      • Rothwell A.
      • Frampton C.
      • Wyatt M.
      Does the use of laminar airflow and space suits reduce early deep infection after total hip and knee replacement?.
      • Lipsett P.
      Do we really need laminar flow ventilation in the operating room to prevent surgical site infections?.
      In addition, the use of surveillance data and information from national registries instead of performing randomized trials has the advantage of observing the situation under actual rather than ideal conditions. All studies considered in this meta-analysis (each including many thousands of procedures), with the exception of one cohort study of only 435 patients, have shown no reduction in risk of severe SSI for patients operated on in LAF theatres. Pooling the data from the studies revealed a significantly higher infection risk for hip and knee prosthesis; for hip prostheses this risk was almost twice as high. Taking these results into consideration, it is not only a waste of resources to establish new operating rooms with LAF, but it may be worthwhile to investigate the replacement of laminar airflow systems in existing operating rooms with conventional ventilation systems.
      Two main explanations for the higher SSI risk associated with LAF have been discussed previously: improper positioning of operating room personnel in the airflow and lower intraoperative tissue temperatures in the surgical wound.
      • Brandt C.
      • Hott U.
      • Sohr D.
      • Daschner F.
      • Gastmeier P.
      • Rüden H.
      Operating room ventilation with laminar airflow shows no protective effect on the surgical site infection rate in orthopedic and abdominal surgery.
      Randomized trials have shown that forced-air warming substantially decreased the risk of SSI and guidelines emphasizing the importance of maintaining perioperative normothermia for prevention of SSI have been published.
      • Kurz A.
      • Sessler D.I.
      • Lenhardt R.
      Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization.
      • Melling A.
      • Ali B.
      • Scott E.
      • Leaper D.
      Effects of preoperative warming on the incidence of wound infection after clean surgery: a randomised controlled trial.
      • Forbes S.
      • Eskicioglu C.
      • Nathens A.
      • et al.
      Evidence-based guidelines for prevention of perioperative hypothermia.
      However, concerns have also been raised about the effect of forced-air warming on LAF. A recently published study demonstrated that LAF performed well within rigorous and objective standards during forced-air warming, but the endpoint of this study was the number of particle counts instead of SSI rates.
      • Sessler D.
      • Olmsted R.
      • Kuelpmann R.
      Forced-air warming does not worsen air quality in laminar flow operating rooms.
      This meta-analysis has some limitations. First, the individual studies used different definitions for severe SSI leading to a huge range of overall SSI rates in the studies, e.g. from 0.14% to 0.82% for knee prosthesis procedures. Whether patients were operated on in theatres with LAF or conventional ventilation was defined consistently in all studies. Surveillance and registry database were not originally designed to be subjected to this kind of analysis, potentially leading to bias.
      Second, 39.9% of the knee prosthesis procedures and 57.6% of hip prosthesis came from the German SSI surveillance system, but the studies from the USA and New Zealand had even higher relative risk compared to the studies from Germany. Third, many hospitals have both conventional and LAF operating rooms. In the two German studies the questionnaire asked about the ventilation technology installed in the operating rooms routinely used for the insertion of hip and knee prosthesis. Normally German hospitals use the operating room with the highest level of ventilation technology for hip and knee prosthesis surgery. Finally, the search was restricted to the PubMed database only.
      To conclude the question of whether LAF should be used in operating rooms: two individual studies and this meta-analysis have demonstrated that LAF was a risk factor for development of severe SSI. The other studies included in this meta-analysis have neither identified LAF as a risk factor nor as a protective factor. Because the organization of a randomized controlled trial seems to be very difficult, the installation of LAF into newly built operating rooms should be stopped.
      • Kakwani R.
      • Yohannan D.
      • Wahab K.
      The effect of laminar air-flow on the results of Austin–Moore hemiarthroplasty.
      Before removing existing LAF systems, our knowledge base concerning this point should be extended by showing reproducibility of the data. Many countries have well-established national surveillance systems for SSI following hip and knee prosthesis or appropriate registries, and it should be possible to repeat the method of the studies included in this systematic review in a short time period.

      Conflict of interest statement

      None declared.

      Funding sources

      None.

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