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The utility of local smoke evacuation in reducing surgical smoke exposure in spine surgery: a prospective self-controlled study
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The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study Ning Liu MD MPH , Nick Filipp Ph.D. CIH , Kirkham B. Wood MD PII: DOI: Reference:
S1529-9430(19)30997-0 https://doi.org/10.1016/j.spinee.2019.09.014 SPINEE 58023
To appear in:
The Spine Journal
Received date: Revised date: Accepted date:
19 June 2019 13 September 2019 16 September 2019
Please cite this article as: Ning Liu MD MPH , Nick Filipp Ph.D. CIH , Kirkham B. Wood MD , The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study, The Spine Journal (2019), doi: https://doi.org/10.1016/j.spinee.2019.09.014
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Title page The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study
Ning Liu MD MPH1 Nick Filipp Ph.D. CIH2 Kirkham B. Wood MD1* 1. Stanford University School of Medicine, Department of Orthopaedic Surgery 2. BSI, Environmental, Health, and Safety Services and Solutions
*Contact information of the corresponding author Kirkham B. Wood MD Stanford Outpatient Clinic, 450 Broadway Street, M/C 6342, Redwood City, CA 94063 [email protected] Office: (650)721-7620
Author disclosures: NL: Nothing to disclose. NF: Consulting fee: Stanford University (D, $30,000) KBW: Royalties: Globus (B, $10,000); Consulting: Life Spine (B, $10,000), Alphatec Spine (B, $10,000), K2M (B, $10,000). Funding Disclosure(s) Statement: Dr. Nick Filipp received consulting fee from Stanford University (paid to the BSI, an industrial hygiene company) for experimental design, evaluation of the operating room configuration, and data management in this study. Dr. Ning Liu and Dr. Kirkham B. Wood did not receive financial support for this work. The results of this study are not biased in this regard.
ABSTRACT BACKGROUND CONTEXT: Exposure to surgical smoke remains a potential occupational health concern to spine operating room personnel. Using a smoke evacuator (local exhaust ventilation) is currently regarded as a primary means of protection, yet few studies have evaluated its utility in actual surgeries. OBJECTIVE: To examine the utility of two common types of local smoke evacuators, a para incisional evacuator and a smoke evacuation pencil, in reducing surgical smoke exposure in spine surgery. STUDY DESIGN: A prospective self-controlled study. PATIENT SAMPLE: After the pre-estimation of sample size, 51 consecutive spine surgeries (25 and 26 patients using the para incisional smoke evacuator and the smoke evacuation pencil, respectively) were enrolled between February 2018 and March 2019. OUTCOME MEASURES: Two outcome measures were used to evaluate the level of surgical smoke exposure, which was defined as the concentration of ultrafine smoke particles in the air (number of particles per cm3, ppc) around the operating table: (a) the average smoke level was the arithmetic mean of all measurements recorded during the surgery; and (b) the peak smoke level was the highest measurement recorded. METHODS: Consecutive surgeries that involved bilateral symmetrical surgical exposure of the spine via a posterior midline incision were evaluated. Cauterized smoke was evacuated by two smoke evacuators: a “para incisional evacuator,” which used a flat broad suction pad positioned immediately adjacent to the incision (25 patients), and a “surgical smoke evacuation pencil” which is an incorporated part of the electrocautery (26 patients). The level of smoke exposure
was measured separately when surgically exposing the two sides of the spine: starting with one side (determined randomly) with the smoke evacuator being turned on and, then, the other side with the smoke evacuator off. The results were compared between the two sides. RESULTS: The para incisional smoke evacuator significantly reduced the average smoke level by an average of 59.7% [287 (IQR: 126, 526) vs. 1177 (IQR: 395, 2702), P<0.001]. The surgical smoke evacuation pencil also reduced the average smoke level by an average of 44.1% [917 (IQR: 448, 1936) vs. 1605 (IQR: 775, 4280), P<0.001]. Both evacuators significantly reduced peak smoke levels as well. CONCLUSIONS: This study provides evidence supporting the utility of local smoke evacuation in reducing surgical smoke exposure in spine surgery. Such technology may help to improve the occupational health protection for spine operating room workers.
Keywords surgical smoke; spine surgery; local evacuation ventilation; smoke evacuator; surgical smoke pencil; exposure control
Exposure to surgical smoke, which is generated by using an electrocautery device during surgeries, remains a potential occupational health hazard for spine operating room (OR) personnel including surgeons, nurses, anesthesiologists, and technologists [1,2]. Although smoke generation is mostly limited to the exposure stage of the surgery, it can be significant in major open procedures such as posterior cervical or thoracolumbar fusions. Nationwide, an estimated
500,000 clinicians of various disciplines are exposed to surgical smoke each year [3,4], as are patients who receive non-intubated anesthesia [4]. Among the chemical substances found in surgical smoke, at least eight are Criteria Pollutants (e.g., carbon monoxide) or Hazardous Air Pollutants (e.g., acrylonitrile) as defined by the United States Environmental Protection Agency [3,5,6], and some (e.g., benzene) are recognized carcinogens [3]. Such smoke can be physically irritative, and may also disseminate infectious pathogens when the spinal lesion per se is infected.1 Although the definite health effects of surgical smoke exposure have yet to be ascertained, the “Precautionary Principle” in public health suggests that such risk should be mitigated whenever possible [7]. While no federal law or regulation exists addressing the potential hazards of surgical smoke, relevant professional societies and government agencies have recommended the use of some form of “local exhaust ventilation”, which is typically implemented by providing suction to a smoke capture device (also referred to as “smoke evacuator”) that targets the surgical site [1,2,8]. In June 2018, Rhode Island became the first U.S. state regulating surgical smoke exposure by law, now requiring all hospitals to use a local evacuator in surgeries that generate cauterized smoke [9]. Earlier that same year, at the petition of its Nursing Association, California initiated the process to develop an occupational health standard for surgical smoke regulation, and has also considered local exhaust ventilation as the primary means of protection [8,10]. Few studies, however, have examined the actual utility of such smoke evacuators in a real clinical setting. One perceived barrier is that the smoke evacuator’s effect can be easily confounded by such factors as the magnitude of surgery, surgeon techniques, and the dynamic configuration of the operating room that vary among surgeries [11], especially when smoke generation is mild. Spine surgery, however, presents a potentially favorable setting for just such
a study. Most spine procedures are performed symmetrically in a posterior midline incision, and the smoke generation is usually significant when electrocautery is used to expose the spine, both helping to reduce confounding through a self-controlled study design that would evaluate smoke evacuation separately while operating on the two sides of the spine. Therefore, this study aims to examine the utility of two currently marketed types of local smoke evacuators in reducing surgical smoke exposure in spine surgery. The first is a broad flat suction pad positioned immediately adjacent to the surgical incision and is referred to as “para incisional evacuator”; the other is the “smoke evacuation pencil” in which the surgical pencil (the electrocautery) is equipped with a built-in smoke suction fitting. Our primary hypothesis was that, for each smoke evacuator, the level of surgical smoke measured would be different with and without its usage.
Methods Enrollment and setup of surgeries After being granted a waiver by the university Institutional Review Board, the study was conducted prospectively in consecutive surgeries. The eligibility criterion was elective open spine surgeries that involved bilateral symmetrical exposure of the spine in a posterior midline incision. The surgeries were performed in one orthopaedic operating room with a laminar airflow system. Surgical smoke was generated by a conventional electrocautery (ForceFX, Valleylab, Boulder, CO) under the coagulate mode and output power of 35 watts. As aforementioned, two kinds of smoke evacuators were examined, separately in two surgery cohorts.
The para incisional smoke evacuator (miniSQUAIR, Nascent Surgical Inc, Eden Prairie, MN) is a flat broad suction pad positioned immediately adjacent (within five centimeters) to the incision along with the surgical sheets (Figure 1, left). It has a pre-sterilized nine-inch wide flat air intake with a cell foam core. The smoke generated is carried through a corrugated flexible tube to an ultra-low penetration air (ULPA) filter incorporated within the smoke evacuation system (Figure 1, left). The smoke evacuator works steadily and continuously, but can be turned on and off as needed. The hand-held Yankauer suction was used in routine fashion for fluid collection. The smoke evacuation pencil (Valleylab, Covidien, Minneapolis, MN) has an “all-in-one” design wherein a smoke evacuation cannula is assembled as part of, and squarely above the electrocautery stem of, the surgical pencil (Figure 1, right). When the evacuation was turned on, the smoke was evacuated in a continuous fashion (in the “continuous” mode of the device) and captured by the ULPA filter. The hand-held Yankauer suction was used as usual. In using both evacuators, the level of the suction airflow was set at medium. Measurement of the exposure to surgical smoke The level of smoke exposure during surgery was monitored in real-time fashion by a condensation particle counter (P-TRAK Model 8525, TSI Inc, Shoreview, MN) which measures the concentration of ultrafine particles (UFPs), whose diameters are between 0.02 and 1 μm, in the air (number of particles per cm3, ppc). The particle counter was trialed by the authors in several settings for a general concept of concentrations of environmental UFPs. While the baseline UFP count in the operating room was typically below five, it varied greatly from 2,080 in the senior author’s office to 27,500 ppc in the hospital garage.
The particle counter was calibrated per the manufacturer’s specifications, and a “zero check” to verify instrument operation was performed before each surgery. As in previous studies [11,12], and per our OR regulations, the particle counter (the tip of its sampling tube) was positioned at a fixed position at the anesthetist’s side, at the edge of the sterilized surgical area but inside the downward laminar air flow zone and within five feet of the incision (Figure 1). The smoke level was measured only during the surgery’s first stage when the electrocautery is used to expose the spine. It was measured separately when surgically exposing the two sides of the spine: starting with one side (determined randomly) with the smoke evacuator being turned on and, then, the other side with the smoke evacuator off. Regarding which side to start with, it was determined using a random-number table wherein we randomly picked a number and started with it to relate the starting side to whether the number was even or odd [13]. In this way, the smoke level was compared in a self-controlled fashion: one level recorded when surgically exposing one side of the spine with the smoke evacuator on was compared with another recorded when exposing the other side of the spine with the smoke evacuator off (Figures 1 and 2). All surgeries were performed by the same senior surgeon who switched positions to expose both sides of the spine using identical surgical technique. This position transition took at least one minute which was, from previous study [14] and our experience, enough for the smoke level to return to the baseline. The smoke evacuator and the particle counter were controlled by the circulating nurse following the progression of surgery and surgeon instructions. Study items and sample size estimation The study items included (a) the average smoke level which is a “cumulative time-average concentration” of the smoke particles during the surgery [12] and (b) the peak smoke level which
is the highest point concentration recorded thereof (Figure 2). The latter was also qualitatively rated as whether it exceeded 100,000 ppc, which has been defined as a “heavy smoke plume” by previous studies [1,14]. The type and range (number of operated segments) of the surgeries were documented, but other patient information was not, per our IRB. For both smoke evacuators, because no previous studies exist for spine surgery, the sample size (number of surgeries) needed was estimated using prior data from breast surgery [12] and a previous estimation that surgical smoke removal devices can reduce smoke particle counts by an average of 60% [15]. It was calculated in a power-analysis approach using the formula 2(σ12 + σ22)(2.8/Δ)2 where σ1 and σ2 were the standard deviations of the smoke level when the smoke evacuator was turned on and off, respectively, and Δ was the estimated difference of smoke level between the two smoke evacuation states (on or off) [16]. In this way, for both smoke evacuators, the sample size needed to detect a statistically significant reduction of smoke exposure with 80% study power was estimated to be 25 surgeries (patients). The performance of the para incisional smoke evacuator was examined in the first 25 consecutive eligible surgeries and that of the smoke evacuation pencil, the next 26 surgeries. Statistical analysis Descriptive statistics were reported in median with 25% and 75% quantiles (interquartile range, IQR). Wilcoxon signed-rank test was used to compare the level of smoke exposure between the two groups (the two sides of the same spine surgery), one with the smoke evacuator being turned on and the other, off. R version 3.4.3 (R Foundation for Statistical Computing, Vienna, Austria) was used for data analysis. The α value was set at 0.05.
Results Per the pre-estimated sample size, 25 and 26 consecutive spine surgeries were prospectively enrolled for evaluating the para incisional smoke evacuator and the surgical pencil, respectively. All were performed through a single open posterior midline incision. The characteristics of the surgeries were summarized in Table 1. In both cohorts, the median time spent for exposing the two sides of the spine -with the smoke evacuator on and off, respectively- was not significantly different. The para incisional smoke evacuator For the para incisional smoke evacuator, the average smoke level measured when the smoke evacuator was turned on was significantly lower than that when the smoke evacuator was off [287 (IQR: 126, 526) vs. 1177 (IQR: 395, 2702), P<0.001, Figure 3]. This difference was equivalent to an average smoke reduction rate of 59.7% (IQR: 33.4%, 84.9%) in the 25 surgeries. The peak smoke level was also significantly reduced [1080 (IQR: 571, 1900) vs. 24400 (IQR: 5120, 64453), P<0.001, Figure 3], representing an average smoke reduction rate of 95.9% (IQR: 57.9%, 98.7%) in the 25 surgeries. The peak smoke level exceeded 100,000 ppc in three (12%) of the 25 surgeries, all when the smoke evacuator was turned off. Such exposure was not observed in any surgery while the smoke evacuator was turned on (Figure 3). The smoke evacuation pencil Similar results were observed for the smoke evacuation pencil. Both the average [917 (IQR: 448, 1936) vs. 1605 (IQR: 775, 4280), P<0.001] and peak [10991 (IQR: 2493, 35196) vs. 68150 (IQR: 17191, 93125), P<0.001] smoke levels were significantly reduced. The former was reduced by
an average of 44.1% (IQR: 8.4%, 73.9%) in the 26 surgeries and the latter, 75.3% (IQR: 14.2%, 87.9%) (Figure 4). The peak smoke level exceeded 100,000 ppc in seven (26.9%) of the 26 surgeries, five of which when the smoke evacuator was turned off (Figure 4). Comparing the two smoke evacuators The smoke reduction rates for both the average and peak smoke levels were compared between the two evacuators. For the average smoke level, the average smoke reduction rate of the para incisional evacuator [59.7% (IQR: 33.4%, 84.9%)] did not differ significantly from that of the evacuation pencil [44.1% (IQR: 8.4%, 73.9%), P=0.134]. For the peak smoke level, however, the average smoke reduction rate of the para incisional evacuator [95.9% (IQR: 57.9%, 98.7%)] was significantly greater than that of the evacuation pencil [75.3% (IQR: 14.2%, 87.9%), P=0.019].
Discussion To our knowledge, this is the first study that has evaluated the efficacy of suction evacuators in reducing surgical smoke exposure in spine surgery. The para incisional smoke evacuator and the smoke evacuation pencil significantly reduced the smoke exposure, by an average of 59.7% and 44.1%, respectively, during open posterior spine surgeries. Although surgical smoke has been recognized as a potential health risk for decades [2], previous studies were mostly limited to the identification or description of the problem per se [1,3,4,11,12,14,17,18]. The number of chemicals that have been identified in electrosurgical smoke ranged from 41 to 377 in literature, and has increased over time with the improvement of
detection technology [3, 4,17]. Procedures such as laser hair removal have been reported to produce toxic substances such as acetonitrile and acrylonitrile that exceeded their permissible air concentrations set by the Occupational Safety and Health Administration [4]. In studies that used UFP in describing surgical smoke exposure [4,11,12,14,18], the levels can increase by 2.9 to 1800 times during a procedure depending on the layout of the operating room and the nature of the procedure. Another study using the Air Quality Index as the outcome measure recorded “very unhealthy” and “hazardous” air qualities during open urological surgeries [19]. Few studies, however, have evaluated the utility of smoke control measures in an actual surgical setting. Such efforts were often limited by the effect of confounding from other associated factors of smoke production [11,12]. For example, in laser hair removal procedures, some inherent aspects of the procedure, such as body part and operation time, were found to be more influential on the level of smoke exposure than the use of smoke evacuation per se [11]. As a result, while using a local smoke evacuator is believed by stakeholders including policymakers as a primary means of occupational health protection [8,9,10], the current best available evidence is mostly based on laboratory experiments [17,18] and inequivalent comparisons among highly heterogenous surgeries [11,12]. The present study, therefore, made use of the symmetry of the spine to assess smoke evacuation under as identical conditions as possible. Such an equivalent comparison was further facilitated by limiting the study to the surgery’s first stage, surgical exposure of the spine, which is composed of highly standardized surgical maneuvers, with significant and constant smoke generation. With the prospective design and randomization of the starting spinal side, our study provides level-1 evidence [20] supporting the utility of smoke evacuators in actual spine surgeries. Furthermore, the substantial smoke reduction observed in both devices may still
underestimate their effectiveness as our study was performed under the OR ventilation system and with the use of the Yankauer suction which also contribute to smoke clearance and may, therefore, decrease the relative performance of the evacuator [4,11,14]. Previous research has suggested that a smoke evacuator achieves higher reduction rates when higher levels of smoke exposure are present [18]. In actual practice, using a local smoke evacuator can add a meaningful layer of protection against surgical smoke. It should be noted that our measurements of smoke were obtained at the anesthetist’s side of the surgical drapes; the “actual” exposure of the scrubbed personnel could thus be much higher. In urological surgeries, for example, the average concentration of smoke particles in the air increased by 13 times when the smoke particle counter was moved closer to the surgical site from 48 to 16 inches [19]. Also, careful risk assessment should consider the exposure over time: low dose exposure on a regular basis is still concerning. For some substances (e.g., carbon monoxide) found in surgical smoke, the National Institute for Occupational Safety and Health has recommended ceiling levels that should not be exceeded at any time [21]. Although such chemicals were not examined in the present study, several of our surgeries had a peak UFP concentration above 100,000 ppc which is regarded as heavy exposure. As aforementioned, when such perceived albeit uncertain risks present, some form of prudent primary prevention should be considered. It is important to note that this study was not designed to identify the “best” smoke evacuator. Such a study objective would require a head-to-head comparison between, and concurrent use of, the two evacuators in the same patient. But our preliminary comparison of the two evacuators seems to suggest more efficient smoke evacuation using the para incisional evacuator. However, the performance of a specific device may not necessarily represent that of other devices of the
same type. Some “pencils” with surgeon-oriented ergonomic designs, such as the PlumePen Elite (ConMed, Lancaster NY), are not available at our institution and were not studied. In real practice, other aspects of the smoke evacuators such as noise, costs, and user experience [2,22] should be considered as well. Also, the choice of a particular device must be considered in the practical context of a particular surgery. The para incisional evacuator, for example, may not be practical in surgeries with more than one surgical approach; some of the “pencils” may interfere with surgeon visibility due to the suction tubing’s high profile. Both types of devices would seem to be of limited use in minimally invasive spine surgery using tubular retractions. Finally, just as few “best” surgical techniques exist for a certain clinical entity, the use of smoke evacuation devices is not a rigid and fixed choice, and is dependent upon the type of surgery and surgeon preference. In any surgical specialty, the use of an instrument or device can almost always be optimized by the treating surgeon and his/her assistant. The implication of our study should be limited to the collective utility of local smoke evacuation technology in spine surgery, although it may also be generalizable to other surgical disciplines. This study has limitations. Firstly, the smoke evacuation was limited to the surgery’s first stage, the exposure stage, and the effectiveness of the smoke evacuator throughout the whole procedure was not examined. Also, how well UFP count actually serves as a proxy for the chemicals in surgical smoke is uncertain [17, 23]. As a research study, we examined the utility of two smoke evacuators through a purely technical approach. Improved evidence-based decision-making in this regard still requires research in multiple areas, including health outcomes of long-term exposure to surgical smoke and quantified exposure to toxic substances thereof. More studies from other surgeons at other centers are needed to lend more credence to our results. We hope that our study can serve as a starting point or reference for such future efforts.
In conclusion, using local surgical smoke evacuation systems can significantly reduce the UFP concentration during spine surgeries. This may have meaningful implications for the occupational safety for OR personnel.
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Figure legends
Figure 1 Title: Overhead view of the surgery using local smoke evacuation Legend: The surgeries were performed by the senior surgeon (A) and the assistant (B). Surgical smoke was evacuated by the para incisional smoke evacuator (C, on the left) or the smoke evacuation pencil (D, on the right). The level of smoke exposure was measured by an ultrafine particle counter (E) placed at the anesthetist’s side of the surgical drapes, with its sampling tube within five feet of the incision.
Figure 2 Title: An illustrative case of the change of smoke particle concentration during surgery Legend: This is a screenshot of the exported data of one surgery. It shows the change of the smoke particle concentration (number of particles per cm3, ppc) over time, with the blue and red color representing that with the smoke evacuator (local evacuation ventilation, LEV) on and off, respectively. The particle counter performed one measurement per second. The average smoke level under one smoke evacuation status (on or off) was the arithmetic mean of all measurements under that evacuation status; and the peak smoke level was the highest measurement (in this case, 20,600 ppc) recorded during the surgery.
Figure 3 Title: Average and peak levels of surgical smoke exposure by smoke evacuation status (evacuator on vs. off) when using the para incisional smoke evacuator Legend: The upper and lower graphs show the average and peak smoke levels, respectively, by smoke evacuation status (evacuator on vs. off) The graphs on the left show the aggregate data and those on the right show the data of individual surgeries.
Figure 4 Title: Average and peak levels of surgical smoke exposure by smoke evacuation status (evacuator on vs. off) when using the smoke evacuation pencil Legend: The upper and lower graphs show the average and peak smoke levels, respectively, by smoke evacuation status (evacuator on vs. off) The graphs on the left show the aggregate data and those on the right show the data of individual surgeries.
Table 1. Characteristics of the surgeries for evaluating the two smoke evacuators Type of local smoke evacuator Para incisional smoke evacuator
Smoke evacuation pencil
# of surgeries
25
26
Time frame of
02/2018~09/2018
09/2018~03/2019
4 (range: 1-14)
4 (range: 1-16)
Type of
23 thoracolumbar decompressions with
23 thoracolumbar decompression with
surgeries
(20), or without (3), fusion, one cervical
(17), or without (6) fusion, two cervical
laminectomy and fusion, and one
laminectomy and fusion, and one
coccygectomy
coccygectomy
13 left; 12 right
13 left; 13 right
Surgical time
17 (IQR: 11, 32) vs. 20 (IQR: 12, 39),
19 (IQR: 15, 26) vs. 17 (IQR: 15, 26),
(minutes) by
P=0.247].
P=0.989].
surgeries Average # of operated segments
Starting side of surgery
side* * The time spent on surgically exposing one side of the spine (with the smoke evacuator on) vs. that spent on the other side of the spine (with the smoke evacuator off)
The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study Ning Liu MD MPH , Nick Filipp Ph.D. CIH , Kirkham B. Wood MD PII: DOI: Reference:
S1529-9430(19)30997-0 https://doi.org/10.1016/j.spinee.2019.09.014 SPINEE 58023
To appear in:
The Spine Journal
Received date: Revised date: Accepted date:
19 June 2019 13 September 2019 16 September 2019
Please cite this article as: Ning Liu MD MPH , Nick Filipp Ph.D. CIH , Kirkham B. Wood MD , The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study, The Spine Journal (2019), doi: https://doi.org/10.1016/j.spinee.2019.09.014
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Title page The Utility of Local Smoke Evacuation in Reducing Surgical Smoke Exposure in Spine Surgery: A Prospective Self-Controlled Study
Ning Liu MD MPH1 Nick Filipp Ph.D. CIH2 Kirkham B. Wood MD1* 1. Stanford University School of Medicine, Department of Orthopaedic Surgery 2. BSI, Environmental, Health, and Safety Services and Solutions
*Contact information of the corresponding author Kirkham B. Wood MD Stanford Outpatient Clinic, 450 Broadway Street, M/C 6342, Redwood City, CA 94063 [email protected] Office: (650)721-7620
Author disclosures: NL: Nothing to disclose. NF: Consulting fee: Stanford University (D, $30,000) KBW: Royalties: Globus (B, $10,000); Consulting: Life Spine (B, $10,000), Alphatec Spine (B, $10,000), K2M (B, $10,000). Funding Disclosure(s) Statement: Dr. Nick Filipp received consulting fee from Stanford University (paid to the BSI, an industrial hygiene company) for experimental design, evaluation of the operating room configuration, and data management in this study. Dr. Ning Liu and Dr. Kirkham B. Wood did not receive financial support for this work. The results of this study are not biased in this regard.
ABSTRACT BACKGROUND CONTEXT: Exposure to surgical smoke remains a potential occupational health concern to spine operating room personnel. Using a smoke evacuator (local exhaust ventilation) is currently regarded as a primary means of protection, yet few studies have evaluated its utility in actual surgeries. OBJECTIVE: To examine the utility of two common types of local smoke evacuators, a para incisional evacuator and a smoke evacuation pencil, in reducing surgical smoke exposure in spine surgery. STUDY DESIGN: A prospective self-controlled study. PATIENT SAMPLE: After the pre-estimation of sample size, 51 consecutive spine surgeries (25 and 26 patients using the para incisional smoke evacuator and the smoke evacuation pencil, respectively) were enrolled between February 2018 and March 2019. OUTCOME MEASURES: Two outcome measures were used to evaluate the level of surgical smoke exposure, which was defined as the concentration of ultrafine smoke particles in the air (number of particles per cm3, ppc) around the operating table: (a) the average smoke level was the arithmetic mean of all measurements recorded during the surgery; and (b) the peak smoke level was the highest measurement recorded. METHODS: Consecutive surgeries that involved bilateral symmetrical surgical exposure of the spine via a posterior midline incision were evaluated. Cauterized smoke was evacuated by two smoke evacuators: a “para incisional evacuator,” which used a flat broad suction pad positioned immediately adjacent to the incision (25 patients), and a “surgical smoke evacuation pencil” which is an incorporated part of the electrocautery (26 patients). The level of smoke exposure
was measured separately when surgically exposing the two sides of the spine: starting with one side (determined randomly) with the smoke evacuator being turned on and, then, the other side with the smoke evacuator off. The results were compared between the two sides. RESULTS: The para incisional smoke evacuator significantly reduced the average smoke level by an average of 59.7% [287 (IQR: 126, 526) vs. 1177 (IQR: 395, 2702), P<0.001]. The surgical smoke evacuation pencil also reduced the average smoke level by an average of 44.1% [917 (IQR: 448, 1936) vs. 1605 (IQR: 775, 4280), P<0.001]. Both evacuators significantly reduced peak smoke levels as well. CONCLUSIONS: This study provides evidence supporting the utility of local smoke evacuation in reducing surgical smoke exposure in spine surgery. Such technology may help to improve the occupational health protection for spine operating room workers.
Keywords surgical smoke; spine surgery; local evacuation ventilation; smoke evacuator; surgical smoke pencil; exposure control
Exposure to surgical smoke, which is generated by using an electrocautery device during surgeries, remains a potential occupational health hazard for spine operating room (OR) personnel including surgeons, nurses, anesthesiologists, and technologists [1,2]. Although smoke generation is mostly limited to the exposure stage of the surgery, it can be significant in major open procedures such as posterior cervical or thoracolumbar fusions. Nationwide, an estimated
500,000 clinicians of various disciplines are exposed to surgical smoke each year [3,4], as are patients who receive non-intubated anesthesia [4]. Among the chemical substances found in surgical smoke, at least eight are Criteria Pollutants (e.g., carbon monoxide) or Hazardous Air Pollutants (e.g., acrylonitrile) as defined by the United States Environmental Protection Agency [3,5,6], and some (e.g., benzene) are recognized carcinogens [3]. Such smoke can be physically irritative, and may also disseminate infectious pathogens when the spinal lesion per se is infected.1 Although the definite health effects of surgical smoke exposure have yet to be ascertained, the “Precautionary Principle” in public health suggests that such risk should be mitigated whenever possible [7]. While no federal law or regulation exists addressing the potential hazards of surgical smoke, relevant professional societies and government agencies have recommended the use of some form of “local exhaust ventilation”, which is typically implemented by providing suction to a smoke capture device (also referred to as “smoke evacuator”) that targets the surgical site [1,2,8]. In June 2018, Rhode Island became the first U.S. state regulating surgical smoke exposure by law, now requiring all hospitals to use a local evacuator in surgeries that generate cauterized smoke [9]. Earlier that same year, at the petition of its Nursing Association, California initiated the process to develop an occupational health standard for surgical smoke regulation, and has also considered local exhaust ventilation as the primary means of protection [8,10]. Few studies, however, have examined the actual utility of such smoke evacuators in a real clinical setting. One perceived barrier is that the smoke evacuator’s effect can be easily confounded by such factors as the magnitude of surgery, surgeon techniques, and the dynamic configuration of the operating room that vary among surgeries [11], especially when smoke generation is mild. Spine surgery, however, presents a potentially favorable setting for just such
a study. Most spine procedures are performed symmetrically in a posterior midline incision, and the smoke generation is usually significant when electrocautery is used to expose the spine, both helping to reduce confounding through a self-controlled study design that would evaluate smoke evacuation separately while operating on the two sides of the spine. Therefore, this study aims to examine the utility of two currently marketed types of local smoke evacuators in reducing surgical smoke exposure in spine surgery. The first is a broad flat suction pad positioned immediately adjacent to the surgical incision and is referred to as “para incisional evacuator”; the other is the “smoke evacuation pencil” in which the surgical pencil (the electrocautery) is equipped with a built-in smoke suction fitting. Our primary hypothesis was that, for each smoke evacuator, the level of surgical smoke measured would be different with and without its usage.
Methods Enrollment and setup of surgeries After being granted a waiver by the university Institutional Review Board, the study was conducted prospectively in consecutive surgeries. The eligibility criterion was elective open spine surgeries that involved bilateral symmetrical exposure of the spine in a posterior midline incision. The surgeries were performed in one orthopaedic operating room with a laminar airflow system. Surgical smoke was generated by a conventional electrocautery (ForceFX, Valleylab, Boulder, CO) under the coagulate mode and output power of 35 watts. As aforementioned, two kinds of smoke evacuators were examined, separately in two surgery cohorts.
The para incisional smoke evacuator (miniSQUAIR, Nascent Surgical Inc, Eden Prairie, MN) is a flat broad suction pad positioned immediately adjacent (within five centimeters) to the incision along with the surgical sheets (Figure 1, left). It has a pre-sterilized nine-inch wide flat air intake with a cell foam core. The smoke generated is carried through a corrugated flexible tube to an ultra-low penetration air (ULPA) filter incorporated within the smoke evacuation system (Figure 1, left). The smoke evacuator works steadily and continuously, but can be turned on and off as needed. The hand-held Yankauer suction was used in routine fashion for fluid collection. The smoke evacuation pencil (Valleylab, Covidien, Minneapolis, MN) has an “all-in-one” design wherein a smoke evacuation cannula is assembled as part of, and squarely above the electrocautery stem of, the surgical pencil (Figure 1, right). When the evacuation was turned on, the smoke was evacuated in a continuous fashion (in the “continuous” mode of the device) and captured by the ULPA filter. The hand-held Yankauer suction was used as usual. In using both evacuators, the level of the suction airflow was set at medium. Measurement of the exposure to surgical smoke The level of smoke exposure during surgery was monitored in real-time fashion by a condensation particle counter (P-TRAK Model 8525, TSI Inc, Shoreview, MN) which measures the concentration of ultrafine particles (UFPs), whose diameters are between 0.02 and 1 μm, in the air (number of particles per cm3, ppc). The particle counter was trialed by the authors in several settings for a general concept of concentrations of environmental UFPs. While the baseline UFP count in the operating room was typically below five, it varied greatly from 2,080 in the senior author’s office to 27,500 ppc in the hospital garage.
The particle counter was calibrated per the manufacturer’s specifications, and a “zero check” to verify instrument operation was performed before each surgery. As in previous studies [11,12], and per our OR regulations, the particle counter (the tip of its sampling tube) was positioned at a fixed position at the anesthetist’s side, at the edge of the sterilized surgical area but inside the downward laminar air flow zone and within five feet of the incision (Figure 1). The smoke level was measured only during the surgery’s first stage when the electrocautery is used to expose the spine. It was measured separately when surgically exposing the two sides of the spine: starting with one side (determined randomly) with the smoke evacuator being turned on and, then, the other side with the smoke evacuator off. Regarding which side to start with, it was determined using a random-number table wherein we randomly picked a number and started with it to relate the starting side to whether the number was even or odd [13]. In this way, the smoke level was compared in a self-controlled fashion: one level recorded when surgically exposing one side of the spine with the smoke evacuator on was compared with another recorded when exposing the other side of the spine with the smoke evacuator off (Figures 1 and 2). All surgeries were performed by the same senior surgeon who switched positions to expose both sides of the spine using identical surgical technique. This position transition took at least one minute which was, from previous study [14] and our experience, enough for the smoke level to return to the baseline. The smoke evacuator and the particle counter were controlled by the circulating nurse following the progression of surgery and surgeon instructions. Study items and sample size estimation The study items included (a) the average smoke level which is a “cumulative time-average concentration” of the smoke particles during the surgery [12] and (b) the peak smoke level which
is the highest point concentration recorded thereof (Figure 2). The latter was also qualitatively rated as whether it exceeded 100,000 ppc, which has been defined as a “heavy smoke plume” by previous studies [1,14]. The type and range (number of operated segments) of the surgeries were documented, but other patient information was not, per our IRB. For both smoke evacuators, because no previous studies exist for spine surgery, the sample size (number of surgeries) needed was estimated using prior data from breast surgery [12] and a previous estimation that surgical smoke removal devices can reduce smoke particle counts by an average of 60% [15]. It was calculated in a power-analysis approach using the formula 2(σ12 + σ22)(2.8/Δ)2 where σ1 and σ2 were the standard deviations of the smoke level when the smoke evacuator was turned on and off, respectively, and Δ was the estimated difference of smoke level between the two smoke evacuation states (on or off) [16]. In this way, for both smoke evacuators, the sample size needed to detect a statistically significant reduction of smoke exposure with 80% study power was estimated to be 25 surgeries (patients). The performance of the para incisional smoke evacuator was examined in the first 25 consecutive eligible surgeries and that of the smoke evacuation pencil, the next 26 surgeries. Statistical analysis Descriptive statistics were reported in median with 25% and 75% quantiles (interquartile range, IQR). Wilcoxon signed-rank test was used to compare the level of smoke exposure between the two groups (the two sides of the same spine surgery), one with the smoke evacuator being turned on and the other, off. R version 3.4.3 (R Foundation for Statistical Computing, Vienna, Austria) was used for data analysis. The α value was set at 0.05.
Results Per the pre-estimated sample size, 25 and 26 consecutive spine surgeries were prospectively enrolled for evaluating the para incisional smoke evacuator and the surgical pencil, respectively. All were performed through a single open posterior midline incision. The characteristics of the surgeries were summarized in Table 1. In both cohorts, the median time spent for exposing the two sides of the spine -with the smoke evacuator on and off, respectively- was not significantly different. The para incisional smoke evacuator For the para incisional smoke evacuator, the average smoke level measured when the smoke evacuator was turned on was significantly lower than that when the smoke evacuator was off [287 (IQR: 126, 526) vs. 1177 (IQR: 395, 2702), P<0.001, Figure 3]. This difference was equivalent to an average smoke reduction rate of 59.7% (IQR: 33.4%, 84.9%) in the 25 surgeries. The peak smoke level was also significantly reduced [1080 (IQR: 571, 1900) vs. 24400 (IQR: 5120, 64453), P<0.001, Figure 3], representing an average smoke reduction rate of 95.9% (IQR: 57.9%, 98.7%) in the 25 surgeries. The peak smoke level exceeded 100,000 ppc in three (12%) of the 25 surgeries, all when the smoke evacuator was turned off. Such exposure was not observed in any surgery while the smoke evacuator was turned on (Figure 3). The smoke evacuation pencil Similar results were observed for the smoke evacuation pencil. Both the average [917 (IQR: 448, 1936) vs. 1605 (IQR: 775, 4280), P<0.001] and peak [10991 (IQR: 2493, 35196) vs. 68150 (IQR: 17191, 93125), P<0.001] smoke levels were significantly reduced. The former was reduced by
an average of 44.1% (IQR: 8.4%, 73.9%) in the 26 surgeries and the latter, 75.3% (IQR: 14.2%, 87.9%) (Figure 4). The peak smoke level exceeded 100,000 ppc in seven (26.9%) of the 26 surgeries, five of which when the smoke evacuator was turned off (Figure 4). Comparing the two smoke evacuators The smoke reduction rates for both the average and peak smoke levels were compared between the two evacuators. For the average smoke level, the average smoke reduction rate of the para incisional evacuator [59.7% (IQR: 33.4%, 84.9%)] did not differ significantly from that of the evacuation pencil [44.1% (IQR: 8.4%, 73.9%), P=0.134]. For the peak smoke level, however, the average smoke reduction rate of the para incisional evacuator [95.9% (IQR: 57.9%, 98.7%)] was significantly greater than that of the evacuation pencil [75.3% (IQR: 14.2%, 87.9%), P=0.019].
Discussion To our knowledge, this is the first study that has evaluated the efficacy of suction evacuators in reducing surgical smoke exposure in spine surgery. The para incisional smoke evacuator and the smoke evacuation pencil significantly reduced the smoke exposure, by an average of 59.7% and 44.1%, respectively, during open posterior spine surgeries. Although surgical smoke has been recognized as a potential health risk for decades [2], previous studies were mostly limited to the identification or description of the problem per se [1,3,4,11,12,14,17,18]. The number of chemicals that have been identified in electrosurgical smoke ranged from 41 to 377 in literature, and has increased over time with the improvement of
detection technology [3, 4,17]. Procedures such as laser hair removal have been reported to produce toxic substances such as acetonitrile and acrylonitrile that exceeded their permissible air concentrations set by the Occupational Safety and Health Administration [4]. In studies that used UFP in describing surgical smoke exposure [4,11,12,14,18], the levels can increase by 2.9 to 1800 times during a procedure depending on the layout of the operating room and the nature of the procedure. Another study using the Air Quality Index as the outcome measure recorded “very unhealthy” and “hazardous” air qualities during open urological surgeries [19]. Few studies, however, have evaluated the utility of smoke control measures in an actual surgical setting. Such efforts were often limited by the effect of confounding from other associated factors of smoke production [11,12]. For example, in laser hair removal procedures, some inherent aspects of the procedure, such as body part and operation time, were found to be more influential on the level of smoke exposure than the use of smoke evacuation per se [11]. As a result, while using a local smoke evacuator is believed by stakeholders including policymakers as a primary means of occupational health protection [8,9,10], the current best available evidence is mostly based on laboratory experiments [17,18] and inequivalent comparisons among highly heterogenous surgeries [11,12]. The present study, therefore, made use of the symmetry of the spine to assess smoke evacuation under as identical conditions as possible. Such an equivalent comparison was further facilitated by limiting the study to the surgery’s first stage, surgical exposure of the spine, which is composed of highly standardized surgical maneuvers, with significant and constant smoke generation. With the prospective design and randomization of the starting spinal side, our study provides level-1 evidence [20] supporting the utility of smoke evacuators in actual spine surgeries. Furthermore, the substantial smoke reduction observed in both devices may still
underestimate their effectiveness as our study was performed under the OR ventilation system and with the use of the Yankauer suction which also contribute to smoke clearance and may, therefore, decrease the relative performance of the evacuator [4,11,14]. Previous research has suggested that a smoke evacuator achieves higher reduction rates when higher levels of smoke exposure are present [18]. In actual practice, using a local smoke evacuator can add a meaningful layer of protection against surgical smoke. It should be noted that our measurements of smoke were obtained at the anesthetist’s side of the surgical drapes; the “actual” exposure of the scrubbed personnel could thus be much higher. In urological surgeries, for example, the average concentration of smoke particles in the air increased by 13 times when the smoke particle counter was moved closer to the surgical site from 48 to 16 inches [19]. Also, careful risk assessment should consider the exposure over time: low dose exposure on a regular basis is still concerning. For some substances (e.g., carbon monoxide) found in surgical smoke, the National Institute for Occupational Safety and Health has recommended ceiling levels that should not be exceeded at any time [21]. Although such chemicals were not examined in the present study, several of our surgeries had a peak UFP concentration above 100,000 ppc which is regarded as heavy exposure. As aforementioned, when such perceived albeit uncertain risks present, some form of prudent primary prevention should be considered. It is important to note that this study was not designed to identify the “best” smoke evacuator. Such a study objective would require a head-to-head comparison between, and concurrent use of, the two evacuators in the same patient. But our preliminary comparison of the two evacuators seems to suggest more efficient smoke evacuation using the para incisional evacuator. However, the performance of a specific device may not necessarily represent that of other devices of the
same type. Some “pencils” with surgeon-oriented ergonomic designs, such as the PlumePen Elite (ConMed, Lancaster NY), are not available at our institution and were not studied. In real practice, other aspects of the smoke evacuators such as noise, costs, and user experience [2,22] should be considered as well. Also, the choice of a particular device must be considered in the practical context of a particular surgery. The para incisional evacuator, for example, may not be practical in surgeries with more than one surgical approach; some of the “pencils” may interfere with surgeon visibility due to the suction tubing’s high profile. Both types of devices would seem to be of limited use in minimally invasive spine surgery using tubular retractions. Finally, just as few “best” surgical techniques exist for a certain clinical entity, the use of smoke evacuation devices is not a rigid and fixed choice, and is dependent upon the type of surgery and surgeon preference. In any surgical specialty, the use of an instrument or device can almost always be optimized by the treating surgeon and his/her assistant. The implication of our study should be limited to the collective utility of local smoke evacuation technology in spine surgery, although it may also be generalizable to other surgical disciplines. This study has limitations. Firstly, the smoke evacuation was limited to the surgery’s first stage, the exposure stage, and the effectiveness of the smoke evacuator throughout the whole procedure was not examined. Also, how well UFP count actually serves as a proxy for the chemicals in surgical smoke is uncertain [17, 23]. As a research study, we examined the utility of two smoke evacuators through a purely technical approach. Improved evidence-based decision-making in this regard still requires research in multiple areas, including health outcomes of long-term exposure to surgical smoke and quantified exposure to toxic substances thereof. More studies from other surgeons at other centers are needed to lend more credence to our results. We hope that our study can serve as a starting point or reference for such future efforts.
In conclusion, using local surgical smoke evacuation systems can significantly reduce the UFP concentration during spine surgeries. This may have meaningful implications for the occupational safety for OR personnel.
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Figure legends
Figure 1 Title: Overhead view of the surgery using local smoke evacuation Legend: The surgeries were performed by the senior surgeon (A) and the assistant (B). Surgical smoke was evacuated by the para incisional smoke evacuator (C, on the left) or the smoke evacuation pencil (D, on the right). The level of smoke exposure was measured by an ultrafine particle counter (E) placed at the anesthetist’s side of the surgical drapes, with its sampling tube within five feet of the incision.
Figure 2 Title: An illustrative case of the change of smoke particle concentration during surgery Legend: This is a screenshot of the exported data of one surgery. It shows the change of the smoke particle concentration (number of particles per cm3, ppc) over time, with the blue and red color representing that with the smoke evacuator (local evacuation ventilation, LEV) on and off, respectively. The particle counter performed one measurement per second. The average smoke level under one smoke evacuation status (on or off) was the arithmetic mean of all measurements under that evacuation status; and the peak smoke level was the highest measurement (in this case, 20,600 ppc) recorded during the surgery.
Figure 3 Title: Average and peak levels of surgical smoke exposure by smoke evacuation status (evacuator on vs. off) when using the para incisional smoke evacuator Legend: The upper and lower graphs show the average and peak smoke levels, respectively, by smoke evacuation status (evacuator on vs. off) The graphs on the left show the aggregate data and those on the right show the data of individual surgeries.
Figure 4 Title: Average and peak levels of surgical smoke exposure by smoke evacuation status (evacuator on vs. off) when using the smoke evacuation pencil Legend: The upper and lower graphs show the average and peak smoke levels, respectively, by smoke evacuation status (evacuator on vs. off) The graphs on the left show the aggregate data and those on the right show the data of individual surgeries.
Table 1. Characteristics of the surgeries for evaluating the two smoke evacuators Type of local smoke evacuator Para incisional smoke evacuator
Smoke evacuation pencil
# of surgeries
25
26
Time frame of
02/2018~09/2018
09/2018~03/2019
4 (range: 1-14)
4 (range: 1-16)
Type of
23 thoracolumbar decompressions with
23 thoracolumbar decompression with
surgeries
(20), or without (3), fusion, one cervical
(17), or without (6) fusion, two cervical
laminectomy and fusion, and one
laminectomy and fusion, and one
coccygectomy
coccygectomy
13 left; 12 right
13 left; 13 right
Surgical time
17 (IQR: 11, 32) vs. 20 (IQR: 12, 39),
19 (IQR: 15, 26) vs. 17 (IQR: 15, 26),
(minutes) by
P=0.247].
P=0.989].
surgeries Average # of operated segments
Starting side of surgery
side* * The time spent on surgically exposing one side of the spine (with the smoke evacuator on) vs. that spent on the other side of the spine (with the smoke evacuator off)