AAOS Bulletin - June, 2006

Laminar air flow in the operating room

How effective is it in reducing infection?

By Richard P. Evans, MD

Surgical site infection (SSI), a leading complication of surgery, is particularly devastating and expensive to treat when it occurs in orthopaedic implant surgery. With the current trend toward pay-for-performance standards, orthopaedic surgeons must consider taking advantage of all available potential infection control measures. Both airborne bacteria and other sources of bacterial contamination must be reduced to a minimum to achieve optimal SSI rates.

Several studies have shown a reduced infection rate in orthopaedic implant surgeries performed in ultra clean air facilities and body exhaust suits.1-5 Decades of laminar flow operating room ventilation in combination with other infection control measures have improved infection rates; however, no uniform opinion about laminar flow efficacy has developed.

Laminar air flow results in a statistically significant reduction in airborne bacterial colony forming units (CFU)4, but a decrease in infection rates with statistical significance has not been shown. This is due to the number of uncontrolled variables in operating room infection control. The Centers for Disease Control and Prevention (CDC) also confirms that variables during multiple evaluations of laminar flow may have “confounded the associations.” Based on this, some authors have disputed the results of studies showing laminar flow efficacy.6, 7

Uncontrolled variables include improved air turnover in traditional operating rooms, standardization of prophylactic antibiotics, behavioral change in personnel and awareness and elimination of other vectors of wound contamination. Laminar flow technology itself has evolved through the years.

Improvement of laminar flow technology has presented its own evaluation challenge. This technology has evolved from fiberglass wall packs to High-Efficiency Particulate Air (HEPA) filtration systems. HEPA-filtered laminar air flow can be provided by vertical air-flow systems and by unidirectional horizontal flow from wall-mounted units, with and without curtains or sliding walls. Because each system has its own associated problems of air-flow disruption, newer “exponential laminar flow” systems have been developed in which the air flow takes the form of an upside-down trumpet. It is difficult to establish specific system comparisons and recommendations, however, because studies that document the merits of any one system do not include system design data.

The use of body exhaust suits in laminar flow theaters provides patients with additional protection from bacterial shedding, hair, exposed skin and mucus membranes of operating personnel.8, 9 Body exhaust suits may also prevent the patient from contaminating operating room personnel, although this reverse isolation protection is still unstudied.

A continual decrease in general postoperative infection rates—and specifically in total joint arthroplasties—has resulted from the use of laminar flow with body exhaust suits, prophylactic antibiotics, improved surgical techniques and multiple other infection control measures. Because of the simultaneous evolution of multiple factors aimed at reducing intra operative infection, a long-term homologous study with the power to determine the isolated effect of a specific laminar flow system is unlikely. With an infection rate of about 1 percent in orthopaedic implant operations, only a very large homologous series of surgical cases would show statistical significance.

Nevertheless, the literature, as a whole, remains compelling. Many total joint surgeons prefer to use laminar flow and body exhaust suits when they are available.


The analysis of surgical laminar air systems worldwide has resulted in specific standards. Examples are the UK Health Technical Memorandum (HTM 2025) in the United Kingdom and territories and the German VDI Standards, both of which are being amended to comply with the International Standards Organization (ISO) 14644.

The CDC suggests that both ultraclean air and antimicrobial prophylaxis can reduce the incidence of SSI in orthopaedic implant operations. Current CDC recommendations include the recommendation to consider performing orthopaedic implant operations in clean air and body exhaust suits.10

Additionally, the National Institutes of Health Office of Research Services, Division of Engineering Services, recently concluded that systems that provide laminar flow regimes represent the best option for contamination control in the operating room.11

Richard P. Evans, MD, is chief of adult reconstruction surgery at the department of orthopaedics, University of Arkansas for Medical Science. He can be reached at rpevans@uams.edu


1. Charnley J. Postoperative infection after total hip replacement with special reference to air contamination in the operating room. Clin Orthop 1972;87:167.

2. Lidwell OM. Clean air at operation and subsequent sepsis in the joint. CORR 1986; 211:91-102.

3. Nelson CL. Environmental bacteriology in the unidirectional operating room. Arch Surg 1979;114:826.

4. Nelson JP, Glassburn AR, Talbott RD, McElhinney JP. The effect of previous surgery, operating room environment, and preventive antibiotics on post-operative infection following total hip arthroplasty. CORR 1980;147:167-69.

5. Salvati EA, Robinson RP, Zino SM, Koslin BL, Brause BD, Wilson PD. Infection rates after 3,175 total hip and total knee replacements performed with and without a horizontal unidirectional filtered air flow system. J Bone Joint Surg 1982;64-A (4):525-35.

6. Franco JA, Baer H, Enneking WF. Airborne contamination in orthopedic surgery. Clin Orthop 1977;122:231-43.

7. Laufman H. Air-flow effects in surgery. Arch Surg 1979;114(7):826-30.

8. Dharan S, Pittet D. Environmental controls in operating theaters. J Hosp Inf 2002;51:79-84.

9. Owers KL, James E, Bannister GC. Source of bacterial shedding in laminar flow theaters. J Hosp Inf 2004;58;230-2.

10. Hospital Infections Program, Centers for Disease Control and Prevention. Guideline for prevention of surgical site infection. Infection Control and Hospital Epidemiology 1999; 20(4):247-78.

11. Memarzadeh F, Manning A. Reducing Risks of Surgery, ASHRAE Journal 2003; Feb; 28-33.

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