Do Double-fan Surgical Helmet Systems Result in Less Gown-particle Contamination Than Single-fan Designs?

Abstract

Background

Surgical helmet systems commonly are stand-alone systems with a single fan blowing air into the suit, creating positive pressure that blows particles out through areas of low resistance, possibly contaminating surgical attire and the surgical field. Two-fan systems were developed more recently to release spent air, also theoretically lowering pressure in the suit and decreasing the aforementioned risk of particle contamination. To our knowledge no study to date has measured the potential differences in gown particle contamination to support this hypothesis.

Questions/purposes

We compared a commonly used single-fan system versus a two-fan system and asked: (1) Which fan system results in less gown particle contamination? (2) Are there differences between the systems in the location of contamination?

Methods

Using an existing experimental study model, two surgeons performed five 30-minute TKA simulations comparing a single-fan to a double-fan helmet system after applying fluorescent powder to the hands, axillae, and chest. Both are two-piece hood and gown systems. The single-fan sits on top of the helmet blowing air into the suit; the double-fan system has a second fan positioned at the rear blowing out spent air. Ultraviolet light-enhanced photographs were subsequently obtained of the flexor and extensor surfaces of the arms, axillary areas, and front and back of the chest. We chose these locations because they all contain either a seam or an overlap between gown and hood or gloves through which particles can escape. The images were scored for contamination on a scale of 1 (zero specks) to 4 (> 100 specks) by three independent observers. Interobserver correlation was assessed through Spearman’s test yielding 0.91 (95% CI 0.86 to 0.94; p < 0.0001), 0.81 (95% CI 0.73 to 0.87; p < 0.0001) and 0.87 (95% CI 0.80 to 0.91; p < 0.0001) between observers 1 and 2, observers 1 and 3, and observers 2 and 3, rendering the used scale reliable. Results of the observers were averaged and compared using the Mann-Whitney U test.

Results

There was no difference in overall gown particle contamination between the systems (overall single-fan median contamination score 2.5 of 4 [interquartile range Q1-Q3 0-3.42] versus double fan 1 out of 4 (Q1-Q3 0-3); p = 0.082), but all tests showed there was contamination at the gown-glove interface. In general, there were few differences between the two systems in terms of location of the contamination; however, when comparing only the axillary regions, we found that the single-fan group (median score 3.67 [Q1-Q3 3-4]) showed more contamination than the double-fan group (2.33 [Q1-Q3 0-3.08]); p = 0.01.

Conclusion

We found no difference in gown particle contamination between a single-fan and a double-fan helmet design. However, we note that contamination was present in all tests with both systems, so surgeons should not assume that these systems provide a contamination-free environment.

Clinical Relevance

When using such helmets, the surgeon should not place items close to the axillary region because the seam of the gown may have low resistance to particle contamination. Gown designs could be improved by creating better seals, especially at the arm-body seam.

Introduction

Periprosthetic joint infection is among the most-feared complications in total joint arthroplasty because of its substantial morbidity, mortality, and cost both to the patient and society. Charnley developed the body exhaust suit in the 1960s to decrease the relatively high incidence of infection [2]. Air was aspirated from around the surgeon’s body and head, carried away via attached tubing for filtering, and fresh, clean air was then returned to the suit. The body exhaust suit created a negative-pressure, closed circuit in which possible contaminating particles from the surgeon’s skin and hair were prevented from disseminating into the operating room. Subsequent studies validated its use, including a large randomized controlled trial showing a further 90% decrease in periprosthetic joint infection with the use of a body exhaust suit in the presence of antibiotic prophylaxis and ultraclean operating rooms, leading to the widespread use of body exhaust suits [1, 7].

Recently, more attention has been paid to the design of modern stand-alone space suits. Although less cumbersome because they do not have attached tubing, these systems use a ventilated helmet that blows air into the hood and gown, creating positive pressure and the possibility of particle egress through various openings and areas of low resistance in the gown [8]. Although surgeons may perceive that space suits are the successors of body exhaust suits, modern space suits are only considered to be personal protection systems against blood spatter and debris and not as aids for decreasing periprosthetic joint infection [12]. A large retrospective analysis of the New Zealand Joint Registry conducted by Hooper et al. [6] between 1999 and 2008 showed that the incidence of periprosthetic joint infection more than doubled when modern space suits were used in almost 90,000 primary hip and knee arthroplasties compared with standard gowns. However, one more recent analysis performed between 2000 and 2014 and a similar analysis of a joint registry in the United States failed to show any difference [9, 11].

Various authors have researched the potential mechanisms of contamination by studying the gown-glove interface or the air egress pattern when using different combinations of helmet systems and gowns or togas [4, 8]. Young et al. [14] used fluorescent particles comparable in size to shed skin flakes and covered the surgeon’s hands in them before gowning and gloving to study particle migration.

Our study design was based on this experimental model, and we aimed to directly compare two modern helmet systems: one with a single fan (inflow only) and one with two fans (inflow and outflow).

We asked: (1) Which fan system results in less gown particle contamination? (2) Are there differences between the systems in the location of contamination?

Materials and Methods

Study Design

This was an experimental study investigating the presence and location of potential contamination on the surgical attire during a simulated TKA while using a single- or double-fan helmet system. To do this, we used a model previously devised by Young et al. [14], who compared different areas of low resistance such as the gown-glove interface between different gowns and helmet systems. We added the axillary areas to the comparison because of the seam present connecting the sleeve to the chest—another possible area of particle egress—but used the same type of gown in all tests.

Operation and Gown Types

We compared two helmet systems using the same two-piece hood and gown combination for each helmet type: the single-fan Stryker Flyte helmet (Kalamazoo, MI, USA) with a Stryker hood and the double-fan THI Oxygen (Feistritz im Rosenthal, Austria) with a THI hood. In our personal experience, the Stryker Flyte seems by far the most used helmet system in Belgium, though we do not possess exact numbers. The THI system is a more recent development that we chose for its double-fan design, which may potentially lower pressure inside the suit and thus reduce contamination. A Medline poly-reinforced AAMI Level 4 surgical gown (Northfield, IL, USA) was used in all tests. Following the standardized protocol used by Fraser et al. [4] and Young et al. [14], a senior surgeon (FV assisted by a resident [AV], both of whom wore the same type of helmet) performed a 30-minute TKA simulation using Sawbones. Fans were set to the maximum ventilation capacity. Five surgical procedures were performed with each helmet type. Because both surgeons were wearing the same helmet type at the same time, this resulted in 10 tests per helmet.

Fluorescent Powder as a Surrogate for Shed Skin Particles

After standard scrubbing, a fluorescent powder with an average particle size of 5 μm was evenly applied to the surgeons’ hands (Glo Germ, Hygienic Solutions, Lincoln, UK) (Fig. 1) down to the level of the distal wrist crease (Fig. 2). This powder was chosen for its close approximation of the size of shed skin particles (5 μm-15 μm) and use in previous reports [4, 14]. The presence of airborne particles 5 μm or larger in the OR is also associated with a higher bacterial count, supposedly because bacteria are 0.2 to 5 μm in size and tend to adhere to and create aggregates on particles larger than themselves [5]. Under ideal lighting and contrast conditions, such as those created with fluorescent particles under ultraviolet (UV) light, the human eye can see particles of about 50 μm in size comparing to a speck made up of at least several fluorescent particles. This means we are measuring specks that, in theory, could contain several bacteria.

Fig. 1.

This image shows application of powder to the surgeon’s hands.

Fig. 2.

The powder, seen here under ultraviolet light, extends to the level of the distal crease.

In equal measure, powder was applied to both axillary regions and the upper chest area to check whether particles escaped through the seam in the axilla or hood-gown interface (Fig. 3). After gowning and gloving, a UV light source was used to check for contamination of the gown or gloves before starting the procedure. If any contamination was present, the surgeon removed all surgical attire and re-scrubbed and re-gowned. The cuffs of the gown were placed at the level of the metacarpophalangeal joints to maximize the seal between the glove and gown by creating a large overlapping area (Fig. 4). All simulated surgical procedures were performed in the same operating room without laminar airflow.

Fig. 3.

This image shows application of powder to the chest and axilla.

Fig. 4.

The gown cuffs were placed at the level of the metacarpophalangeal joint to maximize the seal between the gloves and the gown.

Analysis

When surgery was finished, UV light-enhanced photographs were obtained of the flexor and extensor surfaces of both arms, both axillary areas, and the front and back of the hood-gown interface. We chose these locations because they present an opportunity for air and particle egress due to the presence of a seam or overlap between gown and hood or gloves. The amount of contamination was graded according to a scale previously published by Young et al. [14] and more recently used by Fraser et al. [4]: 0 (no visible specks), 1 (one to five specks), 2 (five to 10 specks), 3 (10 to 100 specks), and 4 (more than 100 specks). As noted before, one speck could theoretically contain several bacteria. All observations were independently graded by three separate observers (FV, MV, AV), who were blinded to each other’s observations. Interobserver correlation was validated through Spearman’s test yielding 0.91 between the first and second observers, 0.81 between the first and third observers, and 0.87 between the second and third observers. The results were averaged and compared using the Mann-Whitney U test, with statistical significance defined as p < 0.05. We also compared each separate area to see whether there were focal differences in contamination between both systems. We reported median results because of non-parametric distribution of the data. Analysis was performed using GraphPad Prism (version 8.2.0, San Diego, CA, USA).

Results

Pooling observations across all examined areas, we found there was no difference in overall contamination between the single-fan and double-fan helmet (overall single-fan median contamination score 2.5 out of 4 (interquartile range [IQR] Q1-Q3 0-3.42) versus double fan 1 out of 4 (IQR Q1-Q3 0-3); p = 0.082; Table 1). All tests were performed with the same gown type and all showed some degree of contamination at the gown-glove interface on the volar and dorsal aspects of the wrist (Fig. 5). The hood-gown interface showed no contamination—front or back—in four of the 10 procedures with the single-fan helmet, and in six of 10 procedures with the double-fan helmet. If contamination was present, it was typically observed at the back of the gown for the double-fan system but not in a greater concentration than in the single-fan system.

Table 1.

Median contamination (interquartile range Q1-Q3)

Fig. 5.

This image shows contamination at the gown-glove interface (arrows).

When comparing only the axillary areas, however, we found that the single-fan group (median score 3.67 [IQR Q1-Q3 3-4]) showed more contamination than the double-fan group did (2.33 [IQR Q1-Q3 0-3.08]); p = 0.01. This area was also the most contaminated of all areas in the single-fan group (Fig. 6).

Fig. 6.

This image shows an example of gross contamination at the axilla.

Discussion

Although Charnley’s introduction of the body exhaust suit resulted in lower periprosthetic joint infection rates, these results cannot be directly transferred to modern space suits because the body exhaust suit is a closed-circuit system that actively funnels off air from inside the suit to be filtered. Although modern suits are in wide use and come with one or two fans—the latter also egressing spent air into the OR—they are believed to mitigate contamination through the creation of a positive pressure environment inside the suit. We sought to identify any difference in the degree of contamination and potential differences in the location of contamination between a single- and double-fan helmet system through a previously used experimental study design, hypothesizing that the double-fan system might result in less contamination due to less pressure build-up inside the suit. We found contamination in all areas to some degree with both systems. There seemed to be more pronounced contamination around the gown-glove interface in both systems, but more so in the axillary areas for the single-fan system only.

Our study has some obvious limitations. First, particle contamination does not necessarily have a causal relationship with infection, although in a recent study, particle and microbiological emission rates in a simulated operating room proved to be higher if the surgeon wore a modern helmet system than if they wore normal operating room attire [13]. Additionally, when a body exhaust suit was compared with conventional attire during hip replacement, bacterial surface counts on settle plates placed in the OR did not differ [10]. This is possibly due to the fact that both an exhaust suit and conventional attire do little to disturb the airflow in the OR, which is not the case with modern helmet systems [8]. When comparing air-to-wound bacterial counts during total knee replacements with and without body exhaust suit, it was found that although the air bacterial count in this study was lower with the body exhaust suit (not surface counts as in the previous study), this did not translate into lower wound bacterial counts. This supports the idea that wound contamination more likely occurs from direct contact with a contaminant rather than from airborne bacteria because the air bacterial counts in modern ORs with ultraclean air are already low [14]. This renders gown-glove interface contamination more important because it comes in direct contact with the surgical site. As mentioned earlier, there is also a relationship between particle size of 5 μm or greater—corresponding with the powder used—and the number of colony forming units in the OR [5]. Thus, although the actual relationship between our synthetic particle counts and deep infection rate is unknown, it may be reasonable to assume a relationship between bacterial wound counts and deep infection [3]. Secondly, we did not include a control group without a helmet or multiple single-fan or double-fan systems, nor did we use different types of gowns. However, our goal was to compare two common single-fan and double-fan systems, and using the same gown and hood combination eliminates another variable. We chose two-piece suits over togas because they are more practical in use and most surgeons using helmets are likely to make the same decision. To our knowledge a Stryker single-fan system is the most commonly used system in Belgium, though there are undoubtedly differences on a more global scale. We compared this to a double-fan system—although it is generally less commonly used—because it presents a technical innovation that could theoretically decrease gown contamination. Finally, our sample size is small, but both other studies using this model did four and five trials per helmet/gown tested based on a power calculation of a pilot study by Young et al. [14]. Because this model represents a new area of study, we chose 10 trials to accommodate for this uncertainty.

We found there was no difference in overall gown-glove contamination between the single-fan and double-fan helmet systems using this particle model, with the numbers available. Although we reasoned that perhaps a recently developed two-fan system would produce less contamination than a commonly used single-fan system, overall, it did not. In 2016, Young et al. [15] performed a systematic review comparing contamination and deep infection rates with the use of a body exhaust suit versus a space suit. In contrast to body exhaust suits, modern-design space suits were not shown to reduce contamination or deep infection during arthroplasty. However, the authors of that study did not consider the potentially different effects of double-fan systems, and most studies on the body exhaust suit used in this review date back to the 1970s and 1980s, while new advances in OR infrastructure, air filtration, airflow and bacterial detection techniques may show different results today. Thus, there is still a need to study the impact of body exhaust suits on deep infection rates in a modern-day surgical environment to be able to accurately compare them to today’s helmets and conventional attire.

In addition to the gown-glove interface, contamination was higher in the axillary region, more so in the single-fan group than in the double-fan group. Contamination in this area is most likely related to the seam where the arm and main body of the gown are sewn together, resulting in a less-than-airtight seal. This confirms the standard practice in surgery that hands should be kept between the level of the nipples and the navel at all times, and that no objects should be placed or held in the axilla. For example, the practice of holding the dislocated leg during the posterior approach to hip surgery by clenching the foot in the assistant’s axilla should definitely be avoided. The fact that the single-fan helmet creates more contamination in this area could be because single-fan systems potentially create a larger pressure gradient inside the suit. However, this difference does not hold true at the level of the wrists, perhaps because this area is already prone to contamination due to the movements associated with the surgical procedure, regardless of pressure. Contamination in this area was reduced to zero by sealing the cuffs with tape in another study [14], but since this would disrupt the airflow and possibly influence contamination at other sites differently between both systems, we decided not to include this practice in our study. It was also observed that when the cuffs were not sealed, a stiffer gown created deeper folds, making the glove-gown seal less tight [4]. Stiffness seemed increased when more waterproof material was used. Though we used the same gowns in every test, we do not know how their relative stiffness compares with other gowns. Further studies should assess different gown materials for their stiffness and ability to create a tight seal at the gown glove interface, and seams in the axillary areas should be examined between different gowns. The least contamination was found at the front and back of the hood-gown interface, presumably because of the large overlap between the hood and gown in these areas. The back of the hood-gown interface in the double-fan group may be more prone to this contamination than that of the single-fan group because the second fan expels spent air at the back of the helmet, although we could not demonstrate this convincingly with the numbers available. However, this air egress pattern was visualized and confirmed in a recent study [8].

Conclusions

It would seem good practice to use helmet systems as personal protection when deemed advisable by the surgeon but to await more definitive studies about how these systems may influence periprosthetic joint infection risk. When making the decision to use such a system, there appears to be little difference between single-fan and double-fan systems. Nevertheless, the surgeon should also be wary of the gown-glove interface, perhaps sealing it with sterile tape, and the surgeon should never place any object near the axillae. Finally, current gown designs could be improved by creating better seals, especially at the arm-body seam, and future stand-alone helmet designs should better account for altered airflow and pressure inside the suit and the suit’s surroundings.