key: cord-0987688-egesy7t0
authors: Buggisch, Jonathan R.; Göhler, Daniel; Le Pape, Alain; Roger, Sébastien; Ouaissi, Mehdi; Stintz, Michael; Rudolph, Andreas; Giger-Pabst, Urs
title: Experimental Model to Test Electrostatic Precipitation Technology in the COVID-19 Era: A Pilot Study
date: 2020-09-03
journal: J Am Coll Surg
DOI: 10.1016/j.jamcollsurg.2020.08.759
sha: 4a2feb2268b656214a888bdf581d6646b7574fc5
doc_id: 987688
cord_uid: egesy7t0

OBJECTIVE: In the COVID-19 crisis, laparoscopic surgery is in the focus as a relevant source of bioaerosol release. The efficacy of electrostatic aerosol precipitation (EAP) and continuous aerosol evacuation (CAE) to eliminate bioaerosols during laparoscopic surgery was verified. METHODS: Ex-vivo laparoscopic cholecystectomies (LCs) were simulated +/- EAP or CAE in a pelvitrainer equipped with swine gallbladders. Release of bioaerosols was initiated by performing high-frequency electrosurgery with a monopolar electro hook (MP-HOOK) force at 40 W (MP-HOOK40) and 60 W (MP-HOOK60), as well as by ultrasonic cutting (USC). Particle number concentrations (PNC) of arising aerosols were analyzed with a condensation particle counter (CPC). Aerosol samples were taken i) within the pelvitrainer near to the source, ii) outside the pelvitrainer at the working trocar and iii) in the breathing zone of the surgeon. RESULTS: Within the pelvitrainer, MP-HOOK40 (6.4 x 10(5) cm(-3)) and MP-HOOK60 (7.3 x 10(5) cm(-3)) showed significant higher median PNCs compared to USC (4.4 x 10(5) cm(-3)) (p = 0.001). EAP lead to a significant decrease of the median PNCs in all three groups. A high linear correlation with Pearson correlation coefficients of 0.852, 0.825 and 0.759 were observed by comparing MP-HOOK40 (+/- EAP), MP-HOOK60 (+/- EAP) and USC (+/- EAP), respectively. During ex-vivo LC and CAE, significant bioaerosol contaminations of the operating room occurred. Ex-vivo LC with EAP lead to a considerable reduction of the bioaerosol concentration. CONCLUSION: EAP was found to be efficient for intraoperative bioaerosol elimination and reducing the risk of bioaerosol exposure for surgical staff.

Exposure of surgical staff in operating room facilities by surgically induced aerosols, which are released during surgical procedures such as high-frequency electrosurgery and ultrasonic cutting (USC), represents a potential health risk [1, 2] . Fractions of released aerosols can reach the breathing zone of health care workers [3] , especially when they are close (i.e., in the nearfield) to the surgical field. In a survey among operating room facility health care workers in the USA, 99 % of the responders reported to be within 5 ft (1.52 m) from the aerosol source [4, 5] . Furthermore, health authorities report about 500,000 health care workers, who are exposed regularly to surgical-induced aerosols annually in the USA [6] .

Surgically induced aerosols can contain viral DNA (HPV, HIV, Hep B) but also viable tumor cells thus questioning the general protection of surgical teams when operating such patients [7, 8, 9, 10] . In the course of the COVID-19 pandemic, it is therefore reasonable to assume that such bioaerosols might harbor a relevant risk to infect surgical staff by the coronavirus SARS-CoV-2 [11, 12, 13, 14] . Some experts tend to assume currently that laparoscopic surgery could increase surgeon risk of exposure to aerosolized coronaviruses since the capnoperitoneum itself is a potential source of aerosols [15] . Moreover, a recently performed study reports higher levels of SARS-CoV-2 RNA concentrations in the peritoneal fluid than in the respiratory tract [16] . While there is no societal consensus on limiting or restricting laparoscopic surgery, there is expert consensus to minimize any risk of coronavirus transmission by a restrictive use of high-frequency electrosurgery and ultrasonic cutting (USC) devices and the use of active aerosol evacuation or passive filter systems during laparoscopic surgery [17, 18] .

Electrostatic aerosol precipitation (EAP) technology is widely used in industry as a filtration device that removes fine particles, like dust and smoke, from exhaust gases using the force of an induced electrostatic charge. More recently, EAP technology is now also available as a commercial and medically approved system. Its efficiency has been demonstrated to maintain visual surgical field clarity by bioaerosol clearance in the abdominal cavity during laparoscopic surgery [19] . Although EAP is not widely known in the community of laparoscopic surgeons, this technology has a potential to minimize, considerably, the exposure risk of surgical-induced aerosols for surgical staff. Thus, this ex-vivo pilot study focuses on the efficacy of EAP to eliminate surgical-induced bioaerosols. Its efficacy is furthermore compared to the intraoperative use of continuous aerosol elimination (CAE) by active filtering of the capnoperitoneum, which is currently one of the most widely used technologies for bioaerosol elimination during laparoscopic surgery.

The authorization from the Health Department of Bochum, Germany, was obtained to experiment with fresh post mortal animal tissue. The tissue specimens were disposed of after the experiments in accordance with the German law (Tierische Nebenprodukte-Beseitigungsgesetz). The experiments were performed in compliance with the German coronavirus containment rules at the Aesculap Akademie GmbH in Bochum, Germany. Mühlheim/Donau, Germany) that was modified to a total volume of 9 L CO 2 at a capnoperitoneal pressure of 12 mmHg. The modified pelvitrainer was equipped with fresh liver and attached gallbladder of a German land race pig (volumetry by water displacement analyses at room temperature revealed a median liver volume of 2.0 (1.7 -2.1) L).

Accordingly, the capnoperitoneal volume within the pelvitrainer was about 7 L and thus approximately 2 times higher than the one for humans. The specimen was placed on the return electrode plate attached to an electrosurgical generator in the right upper quadrant of the pelvitrainer. To mimic more realistic conditions within the pelvitrainer, the inner surface of the pelvitrainer was coated with a fine layer (1.5 m 2 surface area) of nitrocellulose membrane, which was previously soaked with an aqueous 0. 

To generate typical surgical-induced bioaerosols, particle release was initiated by the simulation of ex-vivo LCs. Standardized incisions of the gallbladder peritoneum in the sulcus between the gallbladder fundus and the Glisson's capsule were performed for a duration of 3 s by means of high frequency electrosurgery (HFE) using a monopolar electrocautery endohook (MP-HOOK) and ultrasonic cutting (USC) device.

The operated devices and parameters to perform ex-vivo LCs were used as follows: • ultrasonic scalpel (USC), standard cutting mode

To characterize the efficacy of electrostatic aerosol precipitation (EAP) a commercial and medically approved EAP system (Ultravision TM , Alesi Surgical, Cardiff, UK) was used to eliminate surgically induced bioaerosols during performed laparoscopic cholecystectomies. The operated EAP system is composed of a generator unit (high voltage of 7500-9500 V, current of ≤ 10 µA), a stainless-steel brush electrode (Ionwand, Alesi Surgical, Cardiff, UK) and a return electrode connected to the return plate. The brush electrode produces electrons, which ionize present gas molecules [20] . The formed electrical field between brush electrode and grounded surface lead i) to unipolar field charging of the aerosol particles (efficient particle charging down to approx. some tenth of nanometers, [21] ) by the gas ions and ii) to transportation of the particles on the field lines to the grounded surface (called electrostatic deposition). Also charged particles that escape the electrical field will be deposed more efficiently than non-charged particles. This is due to the induction of image charges on present dipole water molecules on wet surfaces that lead to increased attractive forces [22] . Accordingly, the inner surface of the pelvitrainer was moistened as described above.

In this study, the brush electrode was introduced into the pelvitrainer cavity by subcostal puncture via a needle (diameter of 3 mm). The tip was pushed forward to the surgical field as close as possible not interfering with the following surgical manipulations. For all experiments, the positions of the brush electrode and the trocars were kept constant, since the distance between brush electrode and bioaerosol source effects the deposition efficiency. For the purpose of comparison, all laparoscopic cholecystectomies experiments were performed with and without electrostatic aerosol precipitation (EAP).

Previous studies have shown that surgical-induced aerosols can span over a considerably wide size range from a few nanometers to several micrometers, but the highest particle number quantities were found to be between 40 nm and 200 nm [5] . To characterize the surgical-induced bioaerosols in this study, a water-based condensation particle counter (CPC Model 3789, TSI Inc., Shoreview, USA) was operated at a flow rate of 0.6 L/min for determining the total particle number concentration (PNC) in a size range from 7 nm to 1000 nm. The CPC operation parameters were kept constant over all experiments. 

To keep particles losses by electrostatic effects [23] constant, a conductive tube (Tygon, Saint-Gobain, France) of 60 cm length was used for aerosol sampling. In the case of primary release characterization from the agitated tissue, the sample tube was connected to the Luer side tap of the subxyphoidal trocar by pushing the tube over the Luer outlet. In the case of secondary release from the capnoperitoneum, the inlet of the aerosol sampling tube was fixed with a tripod in a static position 2 cm laterally from the inlet of the 12 mm working trocar.

Aerosol sampling in the breathing zone of the surgeon (for exposure characterization) was realized via a tripod at a height of 70 cm centered above the 12 mm trocar for the endoscope (umbilicus).

Beside the differences in the sampling locations, there were also some differences in the experimental procedures. Primary release characterization within the pelvitrainer was performed over a time frame of 100 s with ambient air instead of carbon dioxide. Analyses were performed for monopolar electrocautery endo-hook at 40 Watt (MP-HOOK40), 60 Watt (MP-HOOK60) and ultrasonic scalpel (USC) with and without EAP. Between each experiment, the pelvitrainer was restored by purging with particle free air (based on a high efficiency particulate air filter). Both secondary release characterization at the main working trocar and exposure characterization in the surgeon's breathing zone were performed over a time frame of 12 min for MP-HOOK60 in an established capnoperitoneum at a capnoperitoneal pressure of 12 mmHg. In contrast to EAP, continuous aerosol/smoke evacuation (CAE) is a well-known and suggested procedure to reduce surgical-induced aerosols during laparoscopic surgery [18] . In addition to analyses with and without EAP, the efficacy of CAE at a carbon dioxide flow rate of 12 L/min (SHE SHA Level 2) was studied for MP-HOOK60 outside the pelvitrainer immediately at the working trocar. 

The concentration data of the bioaerosols within the pelvitrainer have to be doubled when approximating the measured data of this study to typical human capnoperitonea, since the capnoperitoneal volume for humans is approx. 3.5 L that is the half of the volume of the used pelvitrainer (i.e., pelvitrainer volume of 9 L minus 2 L liver volume). In Fig. 2 with EAP does not show considerably high short-term PNC peak events.

There is a major lack of interest and knowledge among surgeons that the exposure to surgical-induced aerosols represents a potential health risk [24, 25] . Due to economic reasons, hospital administrations urge surgeons to minimize intervention times. Accordingly, surgical techniques like systems for high frequency electrosurgery (HSF) and ultrasound cutting (USC) are operated at high energy levels to achieve faster tissue transection and sealing. This is accompanied by the formation of highly concentrated and sometimes toxic bioaerosols. To further reduce costs, also the use of aerosol elimination systems is often avoided. But in the course of the COVID-19 pandemic, the potential risk to acquire COVID-19 by exposure with coronavirus laden surgical aerosols has raised major concern and uncertainty among surgeons. In the meantime, national and international expert committees and professional societies have published their recommendations for avoiding unnecessary bioaerosol generation and guidelines for exposure protection [15, 17, 18, 26] . However, unknown to most surgeons, electrostatic aerosol precipitation (EAP) as used for example to improve drug deposition during Pressurized Intraperitoneal Aerosol Chemotherapy [20, 22] is a cost-efficient and effective method for the elimination of surgical-induced aerosols during laparoscopic surgery.

In this study, the efficacy of EAP was analyzed by ex-vivo simulations on a clinically relevant experimental setup with a phantom for laparoscopic procedures by characterizing the particle number concentration of surgical-induced bioaerosols i) within the laparoscopic cavity (primary release from tissue), ii) outside the laparoscopic cavity near the working trocar (secondary release from the cavity) and iii) in the breathing zone (exposure) of the surgeon. During the incision of the used swine gallbladder peritoneum by high-frequency electrosurgery with a monopolar electro hook (MP-HOOK) force at 40 W (MP-HOOK40) respectively 60 W (MP-HOOK60) and by ultrasonic cutting (USC), a considerable release of particles was determined within the laparoscopic cavity.

In daily practice, the energy settings for laparoscopic cholecystectomy with monopolar electrosurgery in the U.S. are generally in the 25 to 30 Watt range [27] . Since such low energy settings did not allow adequate tissue transection of cadaveric swine gall bladders in our ex-vivo Pelvitrainer model, higher energy settings of 40 and 60 Watt were used for this present study. Additionally, to our very best knowledge, power settings for monopolar cholecystectomy in many German hospitals and German surgical training centers, such as the Aesculap Academy in Bochum, are generally between 40 to 60 Watt.

The highest PNC was observed for MP-HOOK60. A trend towards a lower PNC was determined for MP-HOOK40. However, this difference was statistically not significant. A significant lower PNC occurred for USC in standard cutting mode as well as power settings.

These findings are in line with the results of previous work, which showed for monopolarbased instruments higher particle release rates than for USC [11, 28, 29] . Despite USC has been shown to produce less aerosol particles than mono-and bipolar cutting devices, the COVID-19 pandemic has raised new concerns about the use of USC. This is due to the generation of aerosols composed of tissue, blood and blood degradation products that could be identified up to 40 cm from the source [11] .

The results of this study show that a continuous operation of EAP significantly lowers the pandemic, only a condensation particle counter was operated. Thus, the considerable release of particles during ex-vivo LC limited the incision time for release characterization to 3 s to avoid a passing of the concentration limit of the operated device. For studying particle release and exposure of surgical-induced bioaerosols for long-term or repeated LCs in future work, beside size-selective aerosol-analytical instruments also appropriate aerosol dilution measures [30, 31] should be used. However, with regard to the coronavirus, released particles/droplets equal or larger than the virus (65 -125 nm) are of relevance [32] . The determined particle number concentrations alone can only serve as an indicator for a lowered risk to get infected by aerosolized virus particles encountered during laparoscopic surgery. It is therefore necessary to carry out follow-up studies on in-vivo laparoscopic animal models with a detailed characterization of generated bioaerosols.

Conclusion EAP is an efficient method to eliminate generated bioaerosols already at the surgical site and minimizes potential bioaerosol exposure to surgical staff. EAP is currently the most efficient method for aerosol evacuation and elimination. In the light that a previous study reported the efficient capture of viruses and its concomitant deactivation using electrostatic precipitation technology [33] , EAP should become even more promising in the future. 

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We are thankful to Aesculap Akademie GmbH, Bochum, Germany for providing the infrastructure and technical equipment to simulate laparoscopic cholecystectomies.Especially to Mrs. Angela Krug, Training Manager at Aesculap Akademie GmbH, Bochum, Germany for her important help to organize and perform the experiments. We also thank to Mr. Björn Betz and Patrick Perez, BOWA-electronic GmbH & Co, Gomaringen, Germany for providing the smoke evacuation system and the electrostatic aerosol precipitation device.Furthermore, we also thank Robert C. Meltvedt, MD, Surgeon, for the native English correction of our manuscript. Finally, Florian Dahlkötter and Carsten Kykal from TSI GmbH, Aachen, Germany is to thank for organizing and providing a condensation particle counter as well as for its operation briefing.

Jonathan Buggisch and Urs Giger-Pabst: study design, experiments, data acquisition, data analysis, drafting and critical revision for important intellectual content of the manuscript