The present report underline that ignition is a potential life-threatening complication of laser surgery in non-intubated rodents under volatile anesthesia. Although accidental ignition during laser surgeries is sporadically reported in human medical literature
[
17,
20-
23], to the author’s best knowledge this is the first report in which laser-secondary ignition is described in veterinary literature.
For any fire to start, three elements must be present: heat or an ignition source, fuel and an oxidizer. The three elements constitute the so-called “fire triad” or “fire triangle”
[
24,
25]. An oxidizer is a substance that gains electrons in a red-ox chemical reaction. The most common oxidizers in the operating room are oxygen and nitrous oxide
[
25]. The most common ignition sources cited in operating room fires seem to be the electrosurgical unit
[
24], although also lasers are another common ignition source. As previously stated heat can replace the ignition source: the heat produced by the fiberoptic light source was responsible of operating room fire
[
26]. Fuels can be from alcohol based solutions, to any cloth-containing or paper-containing materials on or around the patient, including abdominal gasses
[
24].
Indeed, an oxygen-rich atmosphere, flammable materials, and ignition sources are virtually ubiquitous in the modern-day operating room
[
24].
In human medical literature, laser-secondary ignitions are mainly reported during upper airways surgeries
[
20], especially laryngeal
[
17,
22,
23] and tracheal
[
21] surgeries. On 20,000 laryngeal laser-surgical procedures, Sesterhenn and colleagues
[
27] reported 15 cases (0.075%) of tube fires. The mechanism of combustion is the initial penetration of the endotracheal tube by the laser and then the ignition of the tube. This is facilitated by the heat produced by the laser, the flow of oxygen, inflammable anesthetic agents or combustible materials
[
16,
23,
28]. We suppose that in the present cases the elements composing the “fire triangle” (oxidizer/inflammable substance/ignition source)
[
25] were: 100 per cent oxygen, sevoflurane or isoflurane and diode laser at 3–3.5
W continuous pulsation, respectively. Decrease or removal of any element of the fire triangle could have prevented fire ignition.
In a recent study 15 rats underwent resection of a 3-mm transverse area of the anterior tongue by use of a carbon dioxide laser
[
29]. The rats in the study were not exposed to inhalant anesthesia or to oxygen. It is not unexpected that no fire ignition consequent to the procedure was reported in that study. This finding corroborates the role that oxygen and inhalant gasses play in fire ignition during laser surgery.
In the present work we presented two cases in which the oxygen was administered at 100 per cent concentration. Oxygen concentrations of 50 and 75 per cent did not alter the time to ignition of surgical patties exposed to laser beam. Indeed the time to ignition felt significantly when the oxygen concentration was further increased to 100 per cent
[
30]. A previous study already demonstrated that surgical drapes present a lower time to ignition when exposed to higher oxygen concentration
[
31]. Considering such findings, ventilation with 100 per cent oxygen should be avoided when laser surgeries are performed under face mask ventilation. An alternative to 100 per cent oxygen ventilation may be the ventilation with a lower oxygen concentration (e.g. 30-60-80 per cent), as it has been suggested in human medicine to prevent atelectasis
[
32-
34]. Although lower oxygen concentrations may decrease the risk of fire ignition, specific reports investigating its impact on rodent surgery outcome are necessary before its application in clinical practice.
Intubation in rodents is, in most cases, not easily performed; therefore anesthesia is often maintained with a tight-fitting face mask connected to the breathing system
[
35,
36]. As suggested by Dave and Mahaffey
[
37] “
The use of face masks and nasal cannulae should be avoided as there is always some leakage around these devices”. In the present reports the face mask employed (Figure
) did not prevent leakage of oxygen and anesthetic gasses. Face masks similar to those employed by the authors are often used during surgeries of small exotic animals
[
35,
38,
39]. The use of tight-fitting face masks providing a hermetical seal seems necessary during laser surgery under volatile anesthesia in rodents. Anesthetic gas leakage from standard rodent non-rebreathing circuits has been demonstrated
[
40]. The use of modified face masks significantly reduced the volume of gas leakage. The masks were modified by addition of a latex diaphragm to the conical mask attached to the Mapleson E circuit
[
40]. Nevertheless, before laser can be safely employed on non-intubated animals under volatile anesthesia, specific trials focusing on the real efficacy of face masks in preventing gas leakage are necessary.
In the two cases described topical scrub was not performed with alcohol due to its intrinsic inflammable properties. Unfortunately, also most commercial chlorhexidine solutions contain alcohol, and their flammability is in direct proportion to their alcohol concentration
[
24]. Although some case reports identifying alcohol-based skin preparations as a fuel source in surgical fires have been published in human medical literature
[
41-
43], a recent study was unable to demonstrate flammability of isopropyl alcohol exposed to electrofulguration in experimental settings
[
44]. Conversely, when materials in the study were poured with chlorhexidine gluconate under saturated and damp conditions produced a spark and associated mild to moderate char
[
44]. Only water-based prep solutions such as betadine contain no alcohol and, therefore, can be considered truly nonflammable
[
24]. It should be also mentioned that the use of alcohol in surgeries of rodents is discouraged, as it could promote hypothermia
[
11,
45].
1 Giordano Nardini,2 Ivano Antonio Ciraci,1 and Paolo Selleri1
