Paolo Selleri, DMV, PhD, and Nicola Di Girolamo, DMV, MSC Objective—To determine whether face mask fit during anesthesia affects the occurrence of fire episodes during laser surgery in nonintubated cadaveric rodents under volatile anesthesia. Design—Adaptive single-center randomized controlled trial with an interim analysis. Sample—100 dead rats intended for animal consumption. Procedures—Rat carcasses were randomly allocated to undergo simulated anesthetic procedures with 2 face masks: open mask versus tight-fitting mask. Under volatile anesthesia, 4 cutaneous surgeries were performed (skin biopsies at 3 different sites and resection of a pinna) by means of a diode laser on each carcass. A single interim analysis of 50 rats was planned a priori to drop an arm of the study in the case of a highly significant difference in the incidence of fire events. Surgeries would have continued with the other face mask until completion of the study. Univariate and multivariate analyses were performed. Results—Overall, 25 surgeries were performed with open face masks and 75 with tightfitting masks. During 400 surgical procedures on 100 rat carcasses, 11 (11%; 95% confidence interval, 5.62% to 18.83%) fire events occurred. Ten fire events occurred with the open masks, and 1 fire event occurred with the tight-fitting masks (relative risk, 30.0; 95% confidence interval, 4.0 to 222.8). All of the fire events occurred on different carcasses when cheek skin biopsy was performed. Procedure time, body weight, and surgeon did not significantly concur in the prediction of fire events. Conclusions and Clinical Relevance—Modification of open masks by the addition of a latex diaphragm significantly reduced the occurrence of fire ignition during laser surgery. Results suggested that open masks should not be used for laser surgery of nonintubated rodents during volatile anesthesia. Additionally, results indicated that surgical lasers should be avoided for facial surgery of nonintubated anesthetized rodents, even if tight-fitting masks are used. (J Am Vet Med Assoc 2015;246:639–644)
F
ire events caused by the use of electric devices during surgery are underreported1 and potentially devastating accidents in human2 and veterinary3 hospitals. Almost any electrical device may act as an ignition source,4,5 but electrosurgical devices and lasers represent the most common sources of operating room fires.6 Reports2,7–10 of fire events during laser surgery are scattered throughout the scientific literature. Lasers are subdivided into 4 classes (I to IV), depending on their ability to inflict damage to the skin or eyes. Class IV includes surgical and other cutting lasers, which may pose fire hazards.11–13 In human surgery, the most frequent fires occur during laser surgery of the pharynx, larynx, or trachea.2,7–10 However, accidental fires may occur during any surgical procedure, such as in dermatologic surgery,14 ocular surgery,15 facial16 and maxillofacial surgery,17 or neurosurgery18 as well as during endoscopic procedures in gastroenterology,19 laparoscopy,20 or proctology.21 Although most fires may be minor incidents, in a 2009 report,22 the Emergency Care Research Institute estimated that each year in the United States, 20 to 30 operating room fires in human From the Clinica per Animali Esotici, Centro Veterinario Specialistico (CVS), Via Sandro Giovannini 53, Roma, Italy. Presented in part at the 1st International Conference on Avian, Herpetological and Exotic Mammal Medicine, Wiesbaden, Germany, April 2013. The authors thank Drs. Tommaso Collarile and Alessandra Carnimeo for assistance with surgical procedures and Dr. Raffaele Melidone for gross evaluation of carcasses. Address correspondence to Dr. Di Girolamo ([email protected]). JAVMA, Vol 246, No. 6, March 15, 2015
ABBREVIATION CI CONSORT
Confidence interval Consolidated Standards of ReportingTrials
patients are disabling or disfiguring and 1 or 2 are fatal. Few scientific studies1,23,24 have been performed to characterize and identify the contributing factors to operating room fires in human medicine. Recently, 2 episodes of fire ignition occurred during laser surgery in pet rodents at our hospital.3 Small rodents are among the most widely used animals in medical research.25 Furthermore, pet rodents are an important portion of the specialty pet population in US homes.26 Besides hamsters, gerbils, and guinea pigs,26 high-quality medical care for the common fancy rat (Rattus norvegicus) is increasingly requested.27 Therefore, surgeries on these animals are a common aspect of clinical and laboratory medicine. The use of surgical lasers in exotic animal medicine is not novel.28–30 In pet rodents, it has been advised by several experienced surgeons,31,32 mainly because it may shorten surgical times and prevent development of hypothermia, which is a frequent complication in anesthetized rodents.33–35 Beyond anecdotal opinions, results of an in vivo experimental study36 that evaluated use of the CO2 laser for surgery in laboratory rodents suggest rapid postoperative healing of skin incisions. Furthermore, when excision of cutaneous tumors by means of laser, scalpel blade, and diaScientific Reports
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A randomized controlled trial of factors influencing fire occurrence during laser surgery of cadaveric rodents under simulated mask anesthesia
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thermy was compared in mice, the group exposed to laser surgery experienced significantly lower tumor recurrence and significantly lower perioperative mortality rates.37 Considering our recent report3 in which laser secondary ignition provoked severe burns in one rodent and lethal burns in another, urgent evidence on the safety of laser surgeries during volatile anesthesia in rodents was considered needed. Fire ignition has been reported in nonintubated rodents maintained under volatile anesthesia.3 Although the maintenance of anesthesia in rodents is generally performed without complications by administration of fluorinated inhalation anesthetics,38 endotracheal intubation in rodents is not easily performed; therefore, anesthesia is often maintained with a face mask connected to the anesthetic system in clinical practice39–43 as well as in laboratory settings.35,38,44 In a 2006 study45 of laboratory rats anesthetized with isoflurane, the amount of gas leakage in the operating room produced by different face masks was quantified. Several studies have demonstrated the contribution of oxygen to fire ignition in the operating room.46–48 Consequently, the use of masks that prevent or minimize gas leakage may reduce or prevent fire events. Therefore, the purpose of the study reported here was to evaluate whether the use of different face masks and the distance of the surgical site from the breathing circuit may affect the occurrence of fire episodes during laser surgery in nonintubated rodents under volatile anesthesia. Our specific hypotheses were that open masks would produce a higher incidence of fire ignition and that the closer the surgical site is to the face mask, the higher the incidence of fire episodes. Materials and Methods Animals—The use of live animals was considered unnecessary for the purpose of this study. Use of live rats has been effectively replaced49 with a cadaveric model (ie, dead rats bred for animal consumption). The dead rats were obtained frozen from a commercial retailer that produces feeder rats for snakes, birds of prey, and other carnivores. Fully defrosted carcasses were used after thawing at room temperature (22°C) the night before the surgical procedures. Carcasses that underwent fire burns were sent to a board-certified veterinary pathologist for gross examination. Ethical protocol review and approval were not required because the use of dead animals or parts of animals is not covered by either the US Public Health Service Policy on Humane Care and Use of Laboratory Animals or European Directive 2010/63 for the protection of animals used for scientific purposes. Outcome—The primary outcome measure was the difference in incidence of fire events occurring with an 640
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open mask or modified tight-fitting mask. Secondary outcome measures were the effect of several factors (ie, surgical site, procedure time, body weight, and surgeon) on the occurrence of fire ignition and the gross appearance of any burns. Design, sample size, and randomization—An adaptive single-center randomized controlled cadaveric trial was planned according to CONSORT 201050 recommendations (Figure 1; Online Supplement available at http://avmajournals.avma.org/toc/javma/246/6). Two arms were initially planned and differed with regard to the anesthetic mask type: open mask versus tight-fitting mask. The sample size was calculated for achieving a desired power at the end of the study. Sample size calculations were performed to provide 90% power to detect a difference of 20% in fire ignition between 2 arms, assuming a 2-sided α of 0.05. Thus, the minimal anticipated sample size was 43 subjects/group. A dropout rate of 10% during the trial was estimated owing to any possible interference. Therefore, 100 dead rats ranging in body weight from 62 to 154 g (2.2 to 5.4 oz; median, 116 g [4.1 oz]; interquartile range, 105 to 127 g [3.7 to 4.5 oz]) were purchased from the frozen rat supplier. A drop-the-loser design was used to rapidly eliminate the mask type that would provoke significantly more fire events. A priori, an interim analysis with the Haybittle-Peto boundary51,52 was planned at 50 rats. Thus, convincing evidence for dropping one of the arms of the study was defined as a difference in treatment effect (ie, episodes of fire ignition) of Z = 3.2 (corresponding to P = 0.001).51 If 1 arm was dropped following the interim analysis, the study would have continued with a single arm to keep evaluating the effect of different surgical sites on fire episodes. Allocation of the rats to the different arms (open mask vs tight-fitting mask) was performed with a computer programa by one of the authors (ND) by means of stratified
Figure 1—Study flow diagram for an adaptive, single-center randomized controlled trial of factors influencing fire occurrence during laser surgery of dead rats (n = 100) under simulated volatile anesthesia. The interim analysis performed after 50 rats were randomized to 2 treatment groups (open mask [OM] vs tight-fitting mask [TM]) found a significantly (P < 0.001) higher incidence of fire occurrence in the OM group. Therefore, the OM arm of the trial was dropped, and the remaining 50 dead rats continued in the trial to additionally evaluate the TM. JAVMA, Vol 246, No. 6, March 15, 2015
Face masks—The open mask was the cylindrical disposable plastic sensor of a commercial respiratory monitor,b analogous to handcrafted open masks used in prior reports.3,39,40,54 Internal diameter aperture of the mask measured 16 mm (external diameter, 22 mm), and internal diameter of the inlet port measured 13 mm (external diameter, 16 mm). Total length of the mask was 59 mm, and it was inserted in the breathing circuit for a length of approximately 15 mm. The tight-fitting mask was created by modifying the open mask by adding a simple latex diaphragm manufactured from the thumb portion of a commercially available surgical glove (small size),c as described elsewhere.45 Briefly, the thumb was removed with ordinary scissors and then stretched over the orifice of the open mask. On the latex diaphragm, an aperture large enough to contain the nose of the rat carcass (approx 5 mm) was made with scissors. The face masks were connected to a nonrebreathing circuit. Surgical procedures—Surgical procedures were performed at the Clinica per Animali Esotici, Roma, Italy. Each rat carcass was placed on a heating pad as typical during standard surgical procedures.35 The carcass was placed in (left) lateral recumbency, and one of the masks (open mask vs tight-fitting mask) was positioned simulating a typical anesthetic episode. Maintenance of general anesthesia was simulated by administering 2.5% isoflurane and 0.8 L of oxygen/min through an adjustable dial to regulate the output of isoflurane (concentration range, 0 to 5%)d coupled with a separate oxygen flow meter (range, 0.2 to 4 L/min), as in conventional rodent surgical procedures.55,56 Three of the 4 surgeries simulated the excision of skin biopsies: circular, 5-mm-diameter areas of the cutis were removed on the hind limb, forelimb, and cheek. The fourth surgery simulated excision of the external ear: at the base of the ear pinna, a full-thickness incision was performed. The 4 sites were surgically prepared by means of shaving and scrubbing with chlorhexidinee and sterile saline (0.9% NaCl) solution. Chlorhexidine was used because its flammability has already been evaluated in a controlled trial.57 A diode laserf transduced by an optic fiber was used in contact, continuous mode at 4 W.58 The optic fiber was 400 µm in diameter with a conical tip. The laser tip was at a distance of approximately 0.5 cm from the epithelial surface during laser exposure. The surgeon performed the 4 surgeries with the optic fiber stabilized by a holding pencil and with an Adson-Brown tissue forceps. Surgeries were performed in a random order as described. Procedure time was measured for each rat as the time that elapsed from the first incision to the conclusion of the fourth excision. If fire ignition occurred, the chronometer was paused until the surgical simulation could start again. JAVMA, Vol 246, No. 6, March 15, 2015
Surgeons wore protective eyeglasses, sterile latex surgical gloves of appropriate size, and surgical masks. A mobile smoke evacuation system was activated during the procedures. In case of fire ignition, the emergency maneuver consisted of turning off the oxygen and, if necessary, pouring saline solution on the carcass.3 Statistical analysis—Statistical analyses were performed with 2 commercial software programs.a,g The proportion of fire events occurring in each treatment arm (open mask vs tight-fitting mask) was compared by means of a Fisher exact test. Difference of frequency of fire events between the surgical sites was evaluated with the Cochran Q test.59 A logistic regression model was fitted at the rat level (n = 100) to determine evidence of contribution of procedure time, body weight, and surgeon (independent variables) to the prediction of the outcome fire event (dependent variable). Values are reported as the incidence of fire (percentage of the total number of animals and procedures) with 95% CI and relative risk. Two-tailed values of P < 0.05 were considered significant. Results Interim analysis—The interim analysis performed for 50 rats (after 200 surgical interventions) showed a significantly higher incidence of fire events in the group undergoing volatile anesthetic procedures with an open mask. Of 25 surgical procedures, 10 episodes (40%; 95% CI, 21.13% to 61.33%) of fire ignition occurred with the open mask, but no episodes (0%; 95% CI, 0% to 13.72%) of fire ignition occurred with the tightfitting mask (Fisher exact test; P < 0.001). Because of the high rate of ignition observed in the open mask group, that arm of the trial was dropped as planned in the protocol (Figure 1). Trial—Overall, 11 fire events occurred during 400 surgical interventions in 100 rats (11%; 95% CI, 5.62% to 18.83%). All of the fire events (n = 11) occurred on different carcasses. The first 10 fire events occurred with the open mask. Following the dropping of the open mask arm, 1 fire event occurred with the tight-fitting mask (1/75 [1.33%; 95% CI, 0.03% to 7.20%]). Fire occurrence was significantly associated with exposure to the open mask (relative risk, 30.0; 95% CI, 4.0 to 222.8; P < 0.001). All of the fire events (n = 11) occurred when the cheek skin biopsy was performed. The surgery site significantly affected the occurrence of fire events (Cochran Q = 33.0; P < 0.001). Median procedure time was 159 seconds (range, 86 to 367 seconds; interquartile range, 130 to 208 seconds). Procedure time, body weight, and surgeon did not significantly (overall logistic regression fit; P = 0.604) concur in the prediction of fire events. All of the carcasses in which fire ignition occurred during the surgery had grossly similar burns. The lesions comprised most of the face, with the nose being completely carbonized. In a few cases (n = 2), the forelimbs and the pectoral region were also burned. The first step of the emergency procedure (ie, turning off oxygen) was sufficient to stop fire ignition in all instances. Discussion In this randomized controlled cadaveric trial, modification of open masks by the addition of a latex diaphragm Scientific Reports
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block randomization, with each block composed of 4 rats. Considering that the effect of the diode laser can be influenced by tissue color,53 the randomization was stratified per coat color (hooded black vs hooded gray and albino) to reduce the chance of imbalance between the 2 arms. Because of the nature of the study, it was impossible to blind the surgeons to the allocation of rats to tight-fitting mask and open mask groups. The order in which surgical interventions were performed on each of the carcasses was assigned by means of block random allocation, with each rat representing a block. Then, each carcass was assigned to 1 of the 4 surgeons by simple random allocation with a 4-sided die.
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significantly reduced the occurrence of fire ignition during general anesthesia in rat carcasses. Ten fire events occurred with the open masks during cheek biopsy by means of surgical laser, whereas 1 fire event occurred with the tight-fitting masks (relative risk, 30.0; 95% CI, 4.0 to 222.8). We therefore suggest that open masks not be used during laser surgery of nonintubated rodents undergoing volatile anesthesia. Furthermore, we suggest that it is not safe to perform facial surgeries with laser devices in small animals anesthetized with tight-fitting masks. Among the adverse events or accidents that may occur during cutaneous surgeries, fire ignition is probably one of the more frustrating, in that it is unexpected by the surgeon and the animal owner. Despite initial enthusiasm for the use of surgical lasers in small exotic animals,29,30 the risk with the use of these devices has not been systematically evaluated. Although many reports47,60–63 of experiments focusing on flammability of topical preparations, surgical drapes, and endotracheal tubes have been published in human medical literature, to our knowledge, this is the first study in which factors concurrent to laser-secondary ignition during surgery have been investigated in rodents. In the present study, the conditions that provoked fire ignition during clinical activity3 were easily replicated. Our results confirmed that cutaneous laser surgery in rodents under volatile mask anesthesia poses actual risk of operating room fire. In the present trial, we opted to use a cadaveric model to simulate rodent anesthesia and surgery. Although live animal models were used for similar purposes in the past,64 we believe it is unnecessary and unethical to use live animals.49 Considering that the anesthetic protocol and the surgical preparation used in this study are successfully employed in our clinical activities as well as in clinical42 and laboratory practice,35,56 we believe that the cadaveric model adequately simulated standard anesthesia and surgery. In the human medical literature, laser-secondary ignitions are mainly reported during upper airway surgery,7 specifically during laryngeal2,65,66 and tracheal67 surgeries. In the present study, fire ignition in rodents during shortduration facial surgeries with an open mask had a higher incidence than has been reported for laryngeal and tracheal surgical procedures in humans.7,68 In fact, the incidence of tube ignition in humans during laryngeal and tracheal surgery ranges from 0.075% (15 cases/20,000 surgical procedures)68 to 1.6% (4 cases/250 patients),7 whereas the incidence of fire events in the present study during facial laser surgery in nonintubated rodents was 40% (10/25). Incidence of fire ignition with the tight-fitting mask in the present study (1.3% [1/75]) was similar to the incidence observed during laryngeal and tracheal surgery in humans.7,68 Therefore, facial laser surgery in rodents appears to pose a similar or higher fire risk than laryngeal and tracheal laser surgery in humans. Results of the present study confirmed that fire develops from the outlet of the anesthetic system, as suggested by our previous case report.3 This hypothesis was supported by the significantly higher incidence of fire events during facial surgery, the adequacy of turning off oxygen to interrupt fire ignition, and the localization of the burns in the carcasses; in all 11 cases, the most severe lesions were located on the nose and, to a lesser degree, other facial regions. Localization and gross appearance of burns were similar to lesions that spontaneously occurred in our earlier report.3 642
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In the present trial, fire events did not occur during the 300 surgeries performed on the ear, forelimb, and hind limb. All of the fire events occurred during facial surgeries. On the basis of this finding, it should not be concluded that surgeries performed a greater distance from the mask do not carry risk of fire ignition. In fact, in our previous report,3 fire ignition occurred during removal of a mass from the forelimb of a hamster. Therefore, even though we did not observe a similar event in the present study, fires may also occur when surgeries are performed in regions other than the face and proper caution should be observed. Results of the present trial demonstrated a striking difference in the incidence of fire ignition depending on the type of mask used. The use of face masks in clinical surgery of rodents is not novel, as Frye et al54 in 1967 described the manufacture of a face mask by use of waste materials and its use for the maintenance of anesthesia in small animals. To date, open masks are still widely used for the maintenance of anesthesia in small animals,69–71 especially rodents.35,40,41 The impact of oxygen concentration on the occurrence of fire during laser surgery has been evaluated elsewhere.48 In a recent survey,6 81% of operating room fires in human patients occurred while supplemental oxygen was in use. It has also been demonstrated that decreasing oxygen concentration or flow rates increases the time required to ignite a fire.24 Theoretically, the open mask and the tight-fitting mask used in this study differed only for the volume of oxygen and of volatile anesthetic agent that diffused into the operating field.45 Although standard open masks allow substantial gas leakage, the simple modification proposed by Smith and Bolon45 significantly reduces gas leakage. Therefore, we hypothesize that in the present study, the reduction of gas leakage corresponded to a decrease in incidence of fire ignition. Therefore, tight-fitting masks should always be preferred when laser surgeries are performed. Although this trial was performed on rats, risks of fire ignition should be considered in every small animal in which intubation is not easily performed and face masks are commonly used.69–71 Furthermore, every situation in which the surgical site is near to the face mask should be considered risky. It should also be considered that the addition of a latex diaphragm with an appropriately sized opening will substantially reduce but not eliminate leakage of gases from nonrebreathing circuits.45 This minimal gas loss could explain the single case of fire ignition that occurred in the present trial with the tight-fitting mask. Because there is some evidence that decreasing oxygen concentration would minimize occurrence of fire events,1,48 the association of a tight-fitting mask with lower oxygen concentrations may avoid fire events. Future studies in which oxygen is administered at lower concentrations (eg, 21% or 50%) during these procedures are suggested. In the present study, the dead rodents underwent anesthetic procedures with oxygen and isoflurane because this is a common protocol both in clinical42 and in laboratory practice.35,56 Because of nonflammability, halothane and its successor halogenated agents were an immediate success over previous inhalation anesthetics when introduced.72,73 Halogenation renders compounds less flammable, but some halogenated agents can be ignited in circumstances that are clinically difficult to reproduce.74 Experimentally, halogenated anesthetics increase the oxygen concentration necessary to support the combustion of the most common endotracheal tube materials, therefore minimizing the risk of airway fire.75 The role that isoJAVMA, Vol 246, No. 6, March 15, 2015
a. b. c. d. e. f. g.
SPSS, version 18.0, SPSS Inc, Chicago, Ill. ERM-8010, V-12-2-05-109, Vetronic Services, Torquay, Devon, England. Ansell Ltd, Tamworth, Staffordshire, England. Penlon Sigma Delta, Penlon Ltd, Abingdon, Oxfordshire, England. Clorexyderm, ICFpet, Palazzo Pignano, Italy. Veilure S9, Lasering Srl, Modena, Italy. MedCalc, version 12.2.1, MedCalc Software, Mariakerke, Belgium.
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Barker SJ, Polson JS. Fire in the operating room: a case report and laboratory study. Anesth Analg 2001;93:960–965. Chou AK, Tan PH, Yang LC, et al. Carbon dioxide laser induced airway fire during larynx surgery: case report. Chang Gung Med J 2001;24:393–398. Collarile T, Di Girolamo N, Nardini G, et al. Fire ignition during laser surgery in pet rodents. BMC Vet Res 2012;8:177. ECRI Institute. Hazard report: using external defibrillators in oxygen-enriched atmospheres can cause fires. Health Devices 2005;34:423–425. Williams DM, Littwin S, Patterson AJ, et al. Fiberoptic light source induced surgical fires: the contribution of forced-air warming blankets. Acta Anaesthesiol Scand 2006;50:505–508. Smith LP, Roy S. Operating room fires in otolaryngology: risk factors and prevention. Am J Otolaryngol 2011;32:109–114. Snow JC, Norton ML, Saluja TS, et al. Fire hazard during CO2 laser microsurgery on the larynx and trachea. Anesth Analg 1976;55:146–147. Burgess GE III, LeJeune FE Jr. Endotracheal tube ignition during laser surgery of the larynx. Arch Otolaryngol 1979;105:561–562. Hirshman CA, Smith J. Indirect ignition of the endo-tracheal tube during carbon dioxide laser surgery. Arch Otolaryngol 1980;106:639–641. Cozine K, Rosenbaum LM, Askanazi J, et al. Laser-induced endotracheal tube fire. Anesthesiology 1981;55:583–585. Fry TR. Laser safety. Vet Clin North Am Small Anim Pract 2002;32:535–547. Parker S. Laser regulation and safety in general dental practice. Br Dent J 2007;202:523–532. Takac S, Stojanović S. Classification of laser irradiation and safety measures [in Croatian]. Med Pregl 1998;51:415–418. Wald D, Michelow BJ, Guyuron B, et al. Fire hazards and CO2 laser resurfacing. Plast Reconstr Surg 1998;101:185–188. Ho SY, French P. Minimizing fire risk during eye surgery. Clin Nurs Res 2002;11:387–402. Rosenfield LK, Chang DS. Flash fires during facial surgery: recommendations for the safe delivery of oxygen. Plast Reconstr Surg 2007;119:1982–1983.
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17. Assael LA. The need for national patient safety goals for ambulatory oral and maxillofacial surgery. J Oral Maxillofac Surg 2007;65:1–2. 18. Meltzer HS, Granville R, Aryan HE, et al. Gel-based surgical preparation resulting in an operating room fire during a neurosurgical procedure: case report [Erratum published in J Neurosurg 2005;103(suppl 1):96]. J Neurosurg 2005;102:347–349. 19. Sidebotham GW, Cantelmi F, Stoffa DM, et al. Flammability of intestinal gases during nitrous oxide anesthesia. In: Chou TC, Royals WT, Steinberg TA, eds. Flammability and sensitivity of materials in oxygen-enriched atmospheres. Vol 8. West Conshohocken, Pa: American Society for Testing and Materials, 1995;477–485. 20. Greilich PE, Greilich NB, Froelich EG. Intraabdominal fire during laparoscopic cholecystectomy. Anesthesiology 1995;83:871–874. 21. Bigard MA, Gaucher P, Lassalle C. Fatal colonic explosion during colonoscopic polypectomy. Gastroenterology 1979;77:1307–1310. 22. ECRI Institute. New clinical guidance for surgical fire prevention. Health Devices 2009;38:314–332. 23. Roy S, Smith LP. Device-related risk of fire in oropharyngeal surgery: a mechanical model. Am J Otolaryngol 2010;31:356–359. 24. Roy S, Smith LP. What does it take to start an oropharyngeal fire? Oxygen requirements to start fires in the operating room. Int J Pediatr Otorhinolaryngol 2011;75:227–230. 25. Kohn DF, Clifford CB. Biology and diseases of rats. In: Fox JG, Anderson LC, Loew FM, et al, eds. Laboratory animal medicine. 2nd ed. New York: Academic Press, 2002;121–165. 26. Shepherd AJ. Results of the 2006 AVMA survey of companion animal ownership in US pet-owning households. J Am Vet Med Assoc 2008;232:695–696. 27. Haines VL. The ancient rat. Vet Clin North Am Exot Anim Pract 2010;13:95–105. 28. Mader DR. Use of laser in exotic animal medicine. Vet Pract News 2000;12:1. 29. Hernandez-Divers SJ. Diode laser surgery: principles and application in exotic animals. Semin Avian Exot Pet Med 2002;11:208–220. 30. Rupley AE, Parrott-Nenezian T. The use of sugical laser in exotic and avian practice. Vet Clin North Am Small Anim Pract 2002;32:703–721. 31. Capello V. Common surgical procedures in pet rodents. J Exot Pet Med 2011;20:294–307. 32. Bennett RA. Soft tissue surgery. In: Quesenberry KE, Carpenter JW, eds. Ferrets, rabbits, and rodents clinical medicine and surgery. 3rd ed. St Louis: Saunders Elsevier, 2012;373–391. 33. Reijnders K, English SJ, Krishna MC, et al. Influence of body temperature on the BOLD effect in murine SCC tumors. Magn Reson Med 2004;51:389–393. 34. Grahn DA, Heller MC, Larkin JE, et al. Appropriate thermal manipulations eliminate tremors in rats recovering from halothane anesthesia. J Appl Physiol 1996;81:2547–2554. 35. Taylor DK. Study of two devices used to maintain normothermia in rats and mice during general anesthesia. J Am Assoc Lab Anim Sci 2007;46:37–41. 36. Wang Z, Devaiah AK, Feng L, et al. Fiber-guided CO2 laser surgery in an animal model. Photomed Laser Surg 2006;24:646–650. 37. Peled I, Shohat B, Gassner S, et al. Excision of epithelial tumors: CO2 laser versus conventional methods. Cancer Lett 1976;2:41–45. 38. Cesarovic N, Nicholls F, Rettich A, et al. Isoflurane and sevoflurane provide equally effective anaesthesia in laboratory mice. J Am Assoc Lab Anim Sci 2010;44:329–336. 39. Lichtenberger M, Ko J. Anesthesia and analgesia for small mammals and birds. Vet Clin North Am Exot Anim Pract 2007;10:293–315. 40. Hawkins MG, Graham JE. Emergency and critical care of rodents. Vet Clin North Am Exot Anim Pract 2007;10:501–531. 41. Longley LA. Anaesthesia of exotic pets. Philadelphia: Saunders Elsevier, 2008. 42. Wenger S. Anesthesia and analgesia in rabbits and rodents. J Exot Pet Med 2012;21:7–16. 43. Lennox AM, Bauck L. Small rodents: basic anatomy, physiology, husbandry, and clinical techniques. In: Quesenberry KE, Carpenter JW, eds. Ferrets, rabbits, and rodents clinical medicine and surgery. 3rd ed. St Louis: Saunders Elsevier, 2012;339–353. 44. Yuan Y, Fei L, Yue-min W, et al. Respiratory face mask: a novel and cost-effective device for use during the application of myocardial ischemia in rats. J Zhejiang Univ Sci B 2009;10:391–394. 45. Smith JC, Bolon B. Isoflurane leakage from non-rebreathing roScientific Reports
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flurane played in the present study is uncertain because no direct comparison of incidence of fire ignition with or without isoflurane was performed. It is possible that different laser settings may somehow change the occurrence of fire ignition. In the present study, we used the settings that resulted in the best healing of incisions in rat oral mucosa,58 which was also the lowest power that permitted ease of incising skin and subcutaneous tissues. It is possible that higher laser settings would increase the incidence of fire ignition. There is compelling evidence that the use of a surgical laser for facial surgery under inhalation anesthesia delivered via an open mask carries an extremely high risk of fire ignition. On the basis of the results of this trial and in view of our previous case report3 describing 2 patients, we suggest that an open face mask should never be used when laser surgeries are performed on small animals, as suggested for human patients.1 Furthermore, lasers should also be avoided for facial surgery of nonintubated rodents, even if tight-fitting masks are used. Although the risks of operating room fires may never be eliminated, educating veterinarians and operating room personnel on this subject may minimize these risks.
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dent anaesthesia circuits: comparison of emissions from conventional and modified ports. Lab Anim 2006;40:200–209. Wolf GL, Sidebotham GW, Lazard JL, et al. Laser ignition of surgical drape materials in air, 50% oxygen, and 95% oxygen. Anesthesiology 2004;100:1167–1171. Goldberg J. Brief laboratory report: surgical drape flammability. AANA J 2006;74:352–354. Dhar V, Young K, Nouraei SA, et al. Impact of oxygen concentration and laser power on occurrence of intraluminal fires during shared–airway surgery: an investigation. J Laryngol Otol 2008;122:1335–1338. Russell WMS, Burch RL. The principles of humane experimental technique. London: Methuen, 1959. Schulz KF, Altman DG, Moher D, et al. CONSORT 2010 Statement: updated guidelines for reporting parallel group randomised trials. Ann Intern Med 152(11):726-732. Epub 2010 Mar 24. Geller NL, Pocock SJ. Interim analyses in randomized clinical trials: ramifications and guidelines for practitioners. Biometrics 1987;43:213–223. Schulz KF, Grimes DA. Multiplicity in randomised trials II: subgroup and interim analyses. Lancet 2005;365:1657–1661. Stratigos AJ, Alora MB, Urioste S, et al. Cutaneous laser surgery. Curr Probl Dermatol 1998;10:130–172. Frye FL, Cucuel JP, Uno T. A gas anesthesia adapter for small animals. J Am Vet Med Assoc 1967;151:843–844. Morrison ML, Blackwood JE, Lockett SL, et al. Surviving blood loss using hydrogen sulfide. J Trauma 2008;65:183–188. Picq CA, Clarençon D, Sinniger VE, et al. Impact of anesthetics on immune functions in a rat model of vagus nerve stimulation. PLoS ONE 2013;8:e67086. Arefiev K, Warycha M, Whiting D, et al. Flammability of topical preparations and surgical dressings in cutaneous and laser surgery: a controlled simulation study. J Am Acad Dermatol 2012;67:700–705. D’Arcangelo C, Di Nardo Di Maio F, Prosperi GD, et al. A preliminary study of healing of diode laser versus scalpel incisions in rat oral tissue: a comparison of clinical, histological, and immunohistochemical results. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:764–773. Cochran WG. The comparison of percentages in matched samples. Biometrika 1950;37:256–266. Sosis MB. What is the safest endotracheal tube for Nd-YAG laser surgery? A comparative study. Anesth Analg 1989;69:802–804.
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61. Stouffer DJ. Fires during surgery: two fatal incidents in Los Angeles. J Burn Care Rehabil 1992;13:114–117. 62. Eggen MA, Brock-Utne JG. Fiberoptic illumination systems can serve as a source of smoldering fires. J Clin Monit 1994;10:244–246. 63. Smith LP, Roy S. Fire/burn risk with electrosurgical devices and endoscopy fiberoptic cables. Am J Otolaryngol 2008;29:171–176. 64. Ossoff RH, Duncavage JA, Eisenman TS, et al. Comparison of tracheal damage from laser-ignited endotracheal tube fires. Ann Otol Rhinol Laryngol 1983;92:333–336. 65. Santos P, Ayuso A, Luis M, et al. Airway ignition during CO2 laser laryngeal surgery and high frequency jet ventilation. Eur J Anaesthesiol 2000;17:204–207. 66. Wang HM, Lee KW, Tsai CJ, et al. Tracheostomy tube ignition during microlaryngeal surgery using diode laser: a case report. Kaohsiung J Med Sci 2006;22:199–202. 67. Komatsu T, Kaji R, Okazaki S, et al. Endotracheal tube ignition during the intratracheal laser treatment. Asian Cardiovasc Thorac Ann 2008;16:e49–e51. 68. Sesterhenn AM, Dunne AA, Braulke D, et al. Value of endotracheal tube safety in laryngeal laser surgery. Lasers Surg Med 2003;32:384–390. 69. Fisher PG. Exotic mammal renal disease: diagnosis and treatment. Vet Clin North Am Exot Anim Pract 2006;9:69–96. 70. Lennox AM. Emergency and critical care procedures in sugar gliders (Petaurus breviceps), African hedgehogs (Atelerix albiventris), and prairie dogs (Cynomys spp). Vet Clin North Am Exot Anim Pract 2007;10:533–555. 71. Hawkins MG, Pascoe PJ. Anesthesia, analgesia, and sedation of small mammals. In: Quesenberry KE, Carpenter JW, eds. Ferrets, rabbits, and rodents clinical medicine and surgery. 3rd ed. St Louis: Saunders Elsevier, 2012;429–451. 72. Raventos J. Action of fluothane: a new volatile anesthetic. Br J Pharmacol 1956;11:394–410. 73. Vitcha JF. A history of forane. Anesthesiology 1971;35:4–7. 74. Leonard PF. The lower limits of flammability of halothane, enflurane, and isoflurane. Anesth Analg 1975;54:238–240. 75. Cohen DL, Motahdi S, Wolf GL, et al. The effect of volatile anesthetics upon the flammability of endotracheal tubes. Anesth Analg 1998;86(suppl):201.
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F
ire events caused by the use of electric devices during surgery are underreported1 and potentially devastating accidents in human2 and veterinary3 hospitals. Almost any electrical device may act as an ignition source,4,5 but electrosurgical devices and lasers represent the most common sources of operating room fires.6 Reports2,7–10 of fire events during laser surgery are scattered throughout the scientific literature. Lasers are subdivided into 4 classes (I to IV), depending on their ability to inflict damage to the skin or eyes. Class IV includes surgical and other cutting lasers, which may pose fire hazards.11–13 In human surgery, the most frequent fires occur during laser surgery of the pharynx, larynx, or trachea.2,7–10 However, accidental fires may occur during any surgical procedure, such as in dermatologic surgery,14 ocular surgery,15 facial16 and maxillofacial surgery,17 or neurosurgery18 as well as during endoscopic procedures in gastroenterology,19 laparoscopy,20 or proctology.21 Although most fires may be minor incidents, in a 2009 report,22 the Emergency Care Research Institute estimated that each year in the United States, 20 to 30 operating room fires in human From the Clinica per Animali Esotici, Centro Veterinario Specialistico (CVS), Via Sandro Giovannini 53, Roma, Italy. Presented in part at the 1st International Conference on Avian, Herpetological and Exotic Mammal Medicine, Wiesbaden, Germany, April 2013. The authors thank Drs. Tommaso Collarile and Alessandra Carnimeo for assistance with surgical procedures and Dr. Raffaele Melidone for gross evaluation of carcasses. Address correspondence to Dr. Di Girolamo ([email protected]). JAVMA, Vol 246, No. 6, March 15, 2015
ABBREVIATION CI CONSORT
Confidence interval Consolidated Standards of ReportingTrials
patients are disabling or disfiguring and 1 or 2 are fatal. Few scientific studies1,23,24 have been performed to characterize and identify the contributing factors to operating room fires in human medicine. Recently, 2 episodes of fire ignition occurred during laser surgery in pet rodents at our hospital.3 Small rodents are among the most widely used animals in medical research.25 Furthermore, pet rodents are an important portion of the specialty pet population in US homes.26 Besides hamsters, gerbils, and guinea pigs,26 high-quality medical care for the common fancy rat (Rattus norvegicus) is increasingly requested.27 Therefore, surgeries on these animals are a common aspect of clinical and laboratory medicine. The use of surgical lasers in exotic animal medicine is not novel.28–30 In pet rodents, it has been advised by several experienced surgeons,31,32 mainly because it may shorten surgical times and prevent development of hypothermia, which is a frequent complication in anesthetized rodents.33–35 Beyond anecdotal opinions, results of an in vivo experimental study36 that evaluated use of the CO2 laser for surgery in laboratory rodents suggest rapid postoperative healing of skin incisions. Furthermore, when excision of cutaneous tumors by means of laser, scalpel blade, and diaScientific Reports
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A randomized controlled trial of factors influencing fire occurrence during laser surgery of cadaveric rodents under simulated mask anesthesia
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thermy was compared in mice, the group exposed to laser surgery experienced significantly lower tumor recurrence and significantly lower perioperative mortality rates.37 Considering our recent report3 in which laser secondary ignition provoked severe burns in one rodent and lethal burns in another, urgent evidence on the safety of laser surgeries during volatile anesthesia in rodents was considered needed. Fire ignition has been reported in nonintubated rodents maintained under volatile anesthesia.3 Although the maintenance of anesthesia in rodents is generally performed without complications by administration of fluorinated inhalation anesthetics,38 endotracheal intubation in rodents is not easily performed; therefore, anesthesia is often maintained with a face mask connected to the anesthetic system in clinical practice39–43 as well as in laboratory settings.35,38,44 In a 2006 study45 of laboratory rats anesthetized with isoflurane, the amount of gas leakage in the operating room produced by different face masks was quantified. Several studies have demonstrated the contribution of oxygen to fire ignition in the operating room.46–48 Consequently, the use of masks that prevent or minimize gas leakage may reduce or prevent fire events. Therefore, the purpose of the study reported here was to evaluate whether the use of different face masks and the distance of the surgical site from the breathing circuit may affect the occurrence of fire episodes during laser surgery in nonintubated rodents under volatile anesthesia. Our specific hypotheses were that open masks would produce a higher incidence of fire ignition and that the closer the surgical site is to the face mask, the higher the incidence of fire episodes. Materials and Methods Animals—The use of live animals was considered unnecessary for the purpose of this study. Use of live rats has been effectively replaced49 with a cadaveric model (ie, dead rats bred for animal consumption). The dead rats were obtained frozen from a commercial retailer that produces feeder rats for snakes, birds of prey, and other carnivores. Fully defrosted carcasses were used after thawing at room temperature (22°C) the night before the surgical procedures. Carcasses that underwent fire burns were sent to a board-certified veterinary pathologist for gross examination. Ethical protocol review and approval were not required because the use of dead animals or parts of animals is not covered by either the US Public Health Service Policy on Humane Care and Use of Laboratory Animals or European Directive 2010/63 for the protection of animals used for scientific purposes. Outcome—The primary outcome measure was the difference in incidence of fire events occurring with an 640
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open mask or modified tight-fitting mask. Secondary outcome measures were the effect of several factors (ie, surgical site, procedure time, body weight, and surgeon) on the occurrence of fire ignition and the gross appearance of any burns. Design, sample size, and randomization—An adaptive single-center randomized controlled cadaveric trial was planned according to CONSORT 201050 recommendations (Figure 1; Online Supplement available at http://avmajournals.avma.org/toc/javma/246/6). Two arms were initially planned and differed with regard to the anesthetic mask type: open mask versus tight-fitting mask. The sample size was calculated for achieving a desired power at the end of the study. Sample size calculations were performed to provide 90% power to detect a difference of 20% in fire ignition between 2 arms, assuming a 2-sided α of 0.05. Thus, the minimal anticipated sample size was 43 subjects/group. A dropout rate of 10% during the trial was estimated owing to any possible interference. Therefore, 100 dead rats ranging in body weight from 62 to 154 g (2.2 to 5.4 oz; median, 116 g [4.1 oz]; interquartile range, 105 to 127 g [3.7 to 4.5 oz]) were purchased from the frozen rat supplier. A drop-the-loser design was used to rapidly eliminate the mask type that would provoke significantly more fire events. A priori, an interim analysis with the Haybittle-Peto boundary51,52 was planned at 50 rats. Thus, convincing evidence for dropping one of the arms of the study was defined as a difference in treatment effect (ie, episodes of fire ignition) of Z = 3.2 (corresponding to P = 0.001).51 If 1 arm was dropped following the interim analysis, the study would have continued with a single arm to keep evaluating the effect of different surgical sites on fire episodes. Allocation of the rats to the different arms (open mask vs tight-fitting mask) was performed with a computer programa by one of the authors (ND) by means of stratified
Figure 1—Study flow diagram for an adaptive, single-center randomized controlled trial of factors influencing fire occurrence during laser surgery of dead rats (n = 100) under simulated volatile anesthesia. The interim analysis performed after 50 rats were randomized to 2 treatment groups (open mask [OM] vs tight-fitting mask [TM]) found a significantly (P < 0.001) higher incidence of fire occurrence in the OM group. Therefore, the OM arm of the trial was dropped, and the remaining 50 dead rats continued in the trial to additionally evaluate the TM. JAVMA, Vol 246, No. 6, March 15, 2015
Face masks—The open mask was the cylindrical disposable plastic sensor of a commercial respiratory monitor,b analogous to handcrafted open masks used in prior reports.3,39,40,54 Internal diameter aperture of the mask measured 16 mm (external diameter, 22 mm), and internal diameter of the inlet port measured 13 mm (external diameter, 16 mm). Total length of the mask was 59 mm, and it was inserted in the breathing circuit for a length of approximately 15 mm. The tight-fitting mask was created by modifying the open mask by adding a simple latex diaphragm manufactured from the thumb portion of a commercially available surgical glove (small size),c as described elsewhere.45 Briefly, the thumb was removed with ordinary scissors and then stretched over the orifice of the open mask. On the latex diaphragm, an aperture large enough to contain the nose of the rat carcass (approx 5 mm) was made with scissors. The face masks were connected to a nonrebreathing circuit. Surgical procedures—Surgical procedures were performed at the Clinica per Animali Esotici, Roma, Italy. Each rat carcass was placed on a heating pad as typical during standard surgical procedures.35 The carcass was placed in (left) lateral recumbency, and one of the masks (open mask vs tight-fitting mask) was positioned simulating a typical anesthetic episode. Maintenance of general anesthesia was simulated by administering 2.5% isoflurane and 0.8 L of oxygen/min through an adjustable dial to regulate the output of isoflurane (concentration range, 0 to 5%)d coupled with a separate oxygen flow meter (range, 0.2 to 4 L/min), as in conventional rodent surgical procedures.55,56 Three of the 4 surgeries simulated the excision of skin biopsies: circular, 5-mm-diameter areas of the cutis were removed on the hind limb, forelimb, and cheek. The fourth surgery simulated excision of the external ear: at the base of the ear pinna, a full-thickness incision was performed. The 4 sites were surgically prepared by means of shaving and scrubbing with chlorhexidinee and sterile saline (0.9% NaCl) solution. Chlorhexidine was used because its flammability has already been evaluated in a controlled trial.57 A diode laserf transduced by an optic fiber was used in contact, continuous mode at 4 W.58 The optic fiber was 400 µm in diameter with a conical tip. The laser tip was at a distance of approximately 0.5 cm from the epithelial surface during laser exposure. The surgeon performed the 4 surgeries with the optic fiber stabilized by a holding pencil and with an Adson-Brown tissue forceps. Surgeries were performed in a random order as described. Procedure time was measured for each rat as the time that elapsed from the first incision to the conclusion of the fourth excision. If fire ignition occurred, the chronometer was paused until the surgical simulation could start again. JAVMA, Vol 246, No. 6, March 15, 2015
Surgeons wore protective eyeglasses, sterile latex surgical gloves of appropriate size, and surgical masks. A mobile smoke evacuation system was activated during the procedures. In case of fire ignition, the emergency maneuver consisted of turning off the oxygen and, if necessary, pouring saline solution on the carcass.3 Statistical analysis—Statistical analyses were performed with 2 commercial software programs.a,g The proportion of fire events occurring in each treatment arm (open mask vs tight-fitting mask) was compared by means of a Fisher exact test. Difference of frequency of fire events between the surgical sites was evaluated with the Cochran Q test.59 A logistic regression model was fitted at the rat level (n = 100) to determine evidence of contribution of procedure time, body weight, and surgeon (independent variables) to the prediction of the outcome fire event (dependent variable). Values are reported as the incidence of fire (percentage of the total number of animals and procedures) with 95% CI and relative risk. Two-tailed values of P < 0.05 were considered significant. Results Interim analysis—The interim analysis performed for 50 rats (after 200 surgical interventions) showed a significantly higher incidence of fire events in the group undergoing volatile anesthetic procedures with an open mask. Of 25 surgical procedures, 10 episodes (40%; 95% CI, 21.13% to 61.33%) of fire ignition occurred with the open mask, but no episodes (0%; 95% CI, 0% to 13.72%) of fire ignition occurred with the tightfitting mask (Fisher exact test; P < 0.001). Because of the high rate of ignition observed in the open mask group, that arm of the trial was dropped as planned in the protocol (Figure 1). Trial—Overall, 11 fire events occurred during 400 surgical interventions in 100 rats (11%; 95% CI, 5.62% to 18.83%). All of the fire events (n = 11) occurred on different carcasses. The first 10 fire events occurred with the open mask. Following the dropping of the open mask arm, 1 fire event occurred with the tight-fitting mask (1/75 [1.33%; 95% CI, 0.03% to 7.20%]). Fire occurrence was significantly associated with exposure to the open mask (relative risk, 30.0; 95% CI, 4.0 to 222.8; P < 0.001). All of the fire events (n = 11) occurred when the cheek skin biopsy was performed. The surgery site significantly affected the occurrence of fire events (Cochran Q = 33.0; P < 0.001). Median procedure time was 159 seconds (range, 86 to 367 seconds; interquartile range, 130 to 208 seconds). Procedure time, body weight, and surgeon did not significantly (overall logistic regression fit; P = 0.604) concur in the prediction of fire events. All of the carcasses in which fire ignition occurred during the surgery had grossly similar burns. The lesions comprised most of the face, with the nose being completely carbonized. In a few cases (n = 2), the forelimbs and the pectoral region were also burned. The first step of the emergency procedure (ie, turning off oxygen) was sufficient to stop fire ignition in all instances. Discussion In this randomized controlled cadaveric trial, modification of open masks by the addition of a latex diaphragm Scientific Reports
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block randomization, with each block composed of 4 rats. Considering that the effect of the diode laser can be influenced by tissue color,53 the randomization was stratified per coat color (hooded black vs hooded gray and albino) to reduce the chance of imbalance between the 2 arms. Because of the nature of the study, it was impossible to blind the surgeons to the allocation of rats to tight-fitting mask and open mask groups. The order in which surgical interventions were performed on each of the carcasses was assigned by means of block random allocation, with each rat representing a block. Then, each carcass was assigned to 1 of the 4 surgeons by simple random allocation with a 4-sided die.
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significantly reduced the occurrence of fire ignition during general anesthesia in rat carcasses. Ten fire events occurred with the open masks during cheek biopsy by means of surgical laser, whereas 1 fire event occurred with the tight-fitting masks (relative risk, 30.0; 95% CI, 4.0 to 222.8). We therefore suggest that open masks not be used during laser surgery of nonintubated rodents undergoing volatile anesthesia. Furthermore, we suggest that it is not safe to perform facial surgeries with laser devices in small animals anesthetized with tight-fitting masks. Among the adverse events or accidents that may occur during cutaneous surgeries, fire ignition is probably one of the more frustrating, in that it is unexpected by the surgeon and the animal owner. Despite initial enthusiasm for the use of surgical lasers in small exotic animals,29,30 the risk with the use of these devices has not been systematically evaluated. Although many reports47,60–63 of experiments focusing on flammability of topical preparations, surgical drapes, and endotracheal tubes have been published in human medical literature, to our knowledge, this is the first study in which factors concurrent to laser-secondary ignition during surgery have been investigated in rodents. In the present study, the conditions that provoked fire ignition during clinical activity3 were easily replicated. Our results confirmed that cutaneous laser surgery in rodents under volatile mask anesthesia poses actual risk of operating room fire. In the present trial, we opted to use a cadaveric model to simulate rodent anesthesia and surgery. Although live animal models were used for similar purposes in the past,64 we believe it is unnecessary and unethical to use live animals.49 Considering that the anesthetic protocol and the surgical preparation used in this study are successfully employed in our clinical activities as well as in clinical42 and laboratory practice,35,56 we believe that the cadaveric model adequately simulated standard anesthesia and surgery. In the human medical literature, laser-secondary ignitions are mainly reported during upper airway surgery,7 specifically during laryngeal2,65,66 and tracheal67 surgeries. In the present study, fire ignition in rodents during shortduration facial surgeries with an open mask had a higher incidence than has been reported for laryngeal and tracheal surgical procedures in humans.7,68 In fact, the incidence of tube ignition in humans during laryngeal and tracheal surgery ranges from 0.075% (15 cases/20,000 surgical procedures)68 to 1.6% (4 cases/250 patients),7 whereas the incidence of fire events in the present study during facial laser surgery in nonintubated rodents was 40% (10/25). Incidence of fire ignition with the tight-fitting mask in the present study (1.3% [1/75]) was similar to the incidence observed during laryngeal and tracheal surgery in humans.7,68 Therefore, facial laser surgery in rodents appears to pose a similar or higher fire risk than laryngeal and tracheal laser surgery in humans. Results of the present study confirmed that fire develops from the outlet of the anesthetic system, as suggested by our previous case report.3 This hypothesis was supported by the significantly higher incidence of fire events during facial surgery, the adequacy of turning off oxygen to interrupt fire ignition, and the localization of the burns in the carcasses; in all 11 cases, the most severe lesions were located on the nose and, to a lesser degree, other facial regions. Localization and gross appearance of burns were similar to lesions that spontaneously occurred in our earlier report.3 642
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In the present trial, fire events did not occur during the 300 surgeries performed on the ear, forelimb, and hind limb. All of the fire events occurred during facial surgeries. On the basis of this finding, it should not be concluded that surgeries performed a greater distance from the mask do not carry risk of fire ignition. In fact, in our previous report,3 fire ignition occurred during removal of a mass from the forelimb of a hamster. Therefore, even though we did not observe a similar event in the present study, fires may also occur when surgeries are performed in regions other than the face and proper caution should be observed. Results of the present trial demonstrated a striking difference in the incidence of fire ignition depending on the type of mask used. The use of face masks in clinical surgery of rodents is not novel, as Frye et al54 in 1967 described the manufacture of a face mask by use of waste materials and its use for the maintenance of anesthesia in small animals. To date, open masks are still widely used for the maintenance of anesthesia in small animals,69–71 especially rodents.35,40,41 The impact of oxygen concentration on the occurrence of fire during laser surgery has been evaluated elsewhere.48 In a recent survey,6 81% of operating room fires in human patients occurred while supplemental oxygen was in use. It has also been demonstrated that decreasing oxygen concentration or flow rates increases the time required to ignite a fire.24 Theoretically, the open mask and the tight-fitting mask used in this study differed only for the volume of oxygen and of volatile anesthetic agent that diffused into the operating field.45 Although standard open masks allow substantial gas leakage, the simple modification proposed by Smith and Bolon45 significantly reduces gas leakage. Therefore, we hypothesize that in the present study, the reduction of gas leakage corresponded to a decrease in incidence of fire ignition. Therefore, tight-fitting masks should always be preferred when laser surgeries are performed. Although this trial was performed on rats, risks of fire ignition should be considered in every small animal in which intubation is not easily performed and face masks are commonly used.69–71 Furthermore, every situation in which the surgical site is near to the face mask should be considered risky. It should also be considered that the addition of a latex diaphragm with an appropriately sized opening will substantially reduce but not eliminate leakage of gases from nonrebreathing circuits.45 This minimal gas loss could explain the single case of fire ignition that occurred in the present trial with the tight-fitting mask. Because there is some evidence that decreasing oxygen concentration would minimize occurrence of fire events,1,48 the association of a tight-fitting mask with lower oxygen concentrations may avoid fire events. Future studies in which oxygen is administered at lower concentrations (eg, 21% or 50%) during these procedures are suggested. In the present study, the dead rodents underwent anesthetic procedures with oxygen and isoflurane because this is a common protocol both in clinical42 and in laboratory practice.35,56 Because of nonflammability, halothane and its successor halogenated agents were an immediate success over previous inhalation anesthetics when introduced.72,73 Halogenation renders compounds less flammable, but some halogenated agents can be ignited in circumstances that are clinically difficult to reproduce.74 Experimentally, halogenated anesthetics increase the oxygen concentration necessary to support the combustion of the most common endotracheal tube materials, therefore minimizing the risk of airway fire.75 The role that isoJAVMA, Vol 246, No. 6, March 15, 2015
a. b. c. d. e. f. g.
SPSS, version 18.0, SPSS Inc, Chicago, Ill. ERM-8010, V-12-2-05-109, Vetronic Services, Torquay, Devon, England. Ansell Ltd, Tamworth, Staffordshire, England. Penlon Sigma Delta, Penlon Ltd, Abingdon, Oxfordshire, England. Clorexyderm, ICFpet, Palazzo Pignano, Italy. Veilure S9, Lasering Srl, Modena, Italy. MedCalc, version 12.2.1, MedCalc Software, Mariakerke, Belgium.
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Barker SJ, Polson JS. Fire in the operating room: a case report and laboratory study. Anesth Analg 2001;93:960–965. Chou AK, Tan PH, Yang LC, et al. Carbon dioxide laser induced airway fire during larynx surgery: case report. Chang Gung Med J 2001;24:393–398. Collarile T, Di Girolamo N, Nardini G, et al. Fire ignition during laser surgery in pet rodents. BMC Vet Res 2012;8:177. ECRI Institute. Hazard report: using external defibrillators in oxygen-enriched atmospheres can cause fires. Health Devices 2005;34:423–425. Williams DM, Littwin S, Patterson AJ, et al. Fiberoptic light source induced surgical fires: the contribution of forced-air warming blankets. Acta Anaesthesiol Scand 2006;50:505–508. Smith LP, Roy S. Operating room fires in otolaryngology: risk factors and prevention. Am J Otolaryngol 2011;32:109–114. Snow JC, Norton ML, Saluja TS, et al. Fire hazard during CO2 laser microsurgery on the larynx and trachea. Anesth Analg 1976;55:146–147. Burgess GE III, LeJeune FE Jr. Endotracheal tube ignition during laser surgery of the larynx. Arch Otolaryngol 1979;105:561–562. Hirshman CA, Smith J. Indirect ignition of the endo-tracheal tube during carbon dioxide laser surgery. Arch Otolaryngol 1980;106:639–641. Cozine K, Rosenbaum LM, Askanazi J, et al. Laser-induced endotracheal tube fire. Anesthesiology 1981;55:583–585. Fry TR. Laser safety. Vet Clin North Am Small Anim Pract 2002;32:535–547. Parker S. Laser regulation and safety in general dental practice. Br Dent J 2007;202:523–532. Takac S, Stojanović S. Classification of laser irradiation and safety measures [in Croatian]. Med Pregl 1998;51:415–418. Wald D, Michelow BJ, Guyuron B, et al. Fire hazards and CO2 laser resurfacing. Plast Reconstr Surg 1998;101:185–188. Ho SY, French P. Minimizing fire risk during eye surgery. Clin Nurs Res 2002;11:387–402. Rosenfield LK, Chang DS. Flash fires during facial surgery: recommendations for the safe delivery of oxygen. Plast Reconstr Surg 2007;119:1982–1983.
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flurane played in the present study is uncertain because no direct comparison of incidence of fire ignition with or without isoflurane was performed. It is possible that different laser settings may somehow change the occurrence of fire ignition. In the present study, we used the settings that resulted in the best healing of incisions in rat oral mucosa,58 which was also the lowest power that permitted ease of incising skin and subcutaneous tissues. It is possible that higher laser settings would increase the incidence of fire ignition. There is compelling evidence that the use of a surgical laser for facial surgery under inhalation anesthesia delivered via an open mask carries an extremely high risk of fire ignition. On the basis of the results of this trial and in view of our previous case report3 describing 2 patients, we suggest that an open face mask should never be used when laser surgeries are performed on small animals, as suggested for human patients.1 Furthermore, lasers should also be avoided for facial surgery of nonintubated rodents, even if tight-fitting masks are used. Although the risks of operating room fires may never be eliminated, educating veterinarians and operating room personnel on this subject may minimize these risks.
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59. 60.
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JAVMA, Vol 246, No. 6, March 15, 2015
