Review of unusual patient care experiences is a cornerstone of medical education. Each month, the AQI-AIRS Steering Committee abstracts a patient history submitted to the Anesthesia Incident Reporting System (AIRS) and authors a discussion of the safety and human factors challenges involved. Real-life case histories often include multiple clinical decisions, only some of which can be discussed in the space available. Absence of commentary should not be construed as agreement with the clinical decisions described. Feedback regarding this article can be sent by email to email@example.com. Report incidents or download the AIRS mobile app at www.aqiairs.org.
Case 2020-1: Transnasal Humidified High Flow Nasal Oxygen – Managing the Risk of Fire
A 74-year-old man presented for surgical removal of a basal cell carcinoma on the forehead and repair of the resulting skin defect. He had a past medical history of myocardial infarction, type 2 diabetes and mild chronic renal failure. His BMI was 40 and blood tests unremarkable except that the creatinine and glucose levels were mildly raised. In view of his comorbidities, instead of general anesthesia, a local anesthetic technique was used, with sedation and high-flow humidified nasal oxygen (HFNO). HFNO was favoured over lower-flow oxygen via nasal prongs because it provides continuous positive airway pressure (CPAP) and it was thought likely to be more effective in maintaining SaO2 during any periods of apnea or hypopnea.
The HFNO was applied at 30 l/min of 100 percent oxygen and the sedation given until he tended to fall asleep while still responding to stimuli. Local anesthetic was injected, and then the patient’s skin was prepped with aqueous chlorhexidine and the operative site draped, in a manner that sealed the drapes to the skin. Wet swabs were placed over the patient’s eyebrows. The procedure was started.
After the skin lesion had been removed and a small flap raised to fill the defect, there was some bleeding that was hard to control, and the surgeon had difficulty visualizing the surgical field. The patient’s head was turned slightly and then diathermy was used on the bleeding point. There was a flash and one of the patient’s eyebrows caught fire. The fire was quickly extinguished with one of the wet swabs. At this point, it was noted that during the procedure the drape had lifted, possibly during the repositioning of the head.
The patient was reviewed by the Burns Unit at the hospital. There was a flash burn on the eyebrow which was not full thickness and did not require a skin graft. The patient made a full recovery.
In the report of this incident, it was suggested that the high-flow oxygen may have contributed to this fire directly and also indirectly by drying the wetted eyebrow. Given the humidification of the oxygen used in this application, the latter possibility seems unlikely. On the other hand, it is well known that the use of any form of supplemental medical oxygen does increase the risk of fire, both in the O.R. and at home.1 Of course, oxygen is only one element of the fire triad, and the other two (heat and fuel) are also needed. Furthermore, fires can occur in room air without supplemental oxygen, so vigilance is required in all cases (and eyebrows are a good example of a fuel that will ignite readily in room air). The incidence of surgical fires and the general guidelines of managing this risk were discussed in detail in “Case 2016-2: Surgical Flash Fire” and recently in a substantial review in Anesthesiology.2 This particular case was actually reported to WebAIRS (www.anztadc.net – AIRS’ sister incident reporting system in Australia and New Zealand). It has been previously described in a letter to Anaesthesia and Intensive Care.3
At home, fires may result from oversights such as smoking a cigarette while consuming home oxygen from nasal prongs. The cigarette, instead of smouldering, bursts into flames. This has been described by a patient as “the cigarette just exploded on lighting.”1,2 In the O.R., the use of supplementary oxygen during surgery on the head, neck and airway under sedation increases the risk of fire. In fact, Case 2016-2 was very similar to the present case, but with conventional nasal oxygenation. Discussion of the role of oxygen in the generation of flash fires during surgery typically focuses on the concentration of oxygen. In fact, although this is relevant, it is actually the rate of delivery of oxygen to the other two components of the fire triad that really matters. This can be understood when one thinks of using bellows or blowing on the glowing embers of a fire to assist its ignition. The percentage of oxygen is actually lower in expired air than in room air, but the amount of oxygen delivered per unit time to the nascent fire is increased. Clearly, delivering oxygen at 30 l/m substantially increases the amount of oxygen potentially delivered to a source of fuel (eyebrows) and ignition (diathermy). Increasing the percentage concentration percentage of oxygen increases this amount still further. Although some devices allow HFNO to be delivered at varying concentrations, others can only deliver 100 percent oxygen. There are many reasons not to administer a higher concentration of oxygen than each individual patient requires, so devices that can only deliver 100 percent oxygen are not ideal for administering supplemental oxygenation during sedation.
The fire-related risks of HFNO have been stressed by Cooper et al.4 Fisher and Paykel Healthcare Limited (Panmure, Auckland 1741, New Zealand) who make the Optiflow device (one of the products available for the delivery of HFNO) state: “To avoid burns … Do not use the system near any ignition source, including electrosurgery, electrocautery or laser surgery instruments. Exposure to oxygen increases the risk of fire.” Their message, very well illustrated by this case, is clear: the use of diathermy close to a source of fuel (the eyebrows in this case) is dangerous in any level of oxygen, even room air. Increasing the available supply of oxygen increases the risk.
Onwochei et al. have reported a case of intra-oral ignition of monopolar diathermy during HFNO.5 During the use of monopolar diathermy, an arc arose from the diathermy tip to titanium dental implants, causing a brief ignition and a burn on the polytetrafluoroethylene (insulated ridge grip of the diathermy shaft). Neither patient nor the staff were burned. Perhaps surprisingly, this report to webAIRS, and one other also reported to webAIRS,2 are the only ones we can find in which an actual burn (albeit a minor one) has been sustained in association with the use of HFNO.
A factor that is sometimes overlooked in discussions of surgical fires is that of the turnover of air in an O.R. In the U.S., 20 air changes per hour are recommended.2 This will disperse oxygen to some extent, even with HFNO, as long as there are no drape folds that can trap and create pockets of oxygen (as detailed below). However, in office-based facilities, this level of ventilation may not be present, and the risk of accumulation of oxygen may therefore be greater than in an O.R.
HFNO is unquestionably a valuable addition to the options available for the management of surgical patients in various situations. Among other things, it can substantially increase apnea time over that provided by simple apneic oxygenation. In fact, it has been used to facilitate intratracheal surgery without the need of any kind of endotracheal tube or jet ventilation.6 This is possible because live human flesh does not ignite readily. Thus, in theory, if no other fuel is touched by the beam of the laser used in such surgery, all should be well. On the other hand, it would only take a momentary failure in attention in the use of the laser, perhaps involving a swab or a plastic tube, to end up with a dangerous fire. From a human factor viewpoint, a key message is that it only requires a slight variation from safe practice for a potentially disastrous problem to occur.
It seems likely that oxygen supplied by HFNO could accumulate in cavities or spaces created under surgical drapes. It could also create such cavities through positive pressure, which might cause the drapes to lift.3 Also, depending on proximity to the nasal catheters, oxygen might well flow into the surgical field.3 One can speculate that if a fire were to start, the rising hot air might entrain surrounding air, and if that air contained a higher concentration of oxygen being delivered at high flow, it might accelerate the combustion and set up a vicious circle. In fact, the relatively modest extent of the fire described here actually calls into question whether the primary source of oxygen in the case was, simply, room air – one might expect a much more flamboyant fire if the HFNO had actually been entrained. This possibility does not diminish the importance of the message, of course: on the contrary, to restate the point, there is a risk of fire whenever diathermy is used near a source of fuel, and eyebrows ignite easily.
Several strategies can be used to reduce the risk of fire when supplemental oxygen is used during a surgical procedure. These depend on managing the three elements of the fire triangle. As a source of heat, bipolar diathermy may be safer than monopolar. When used while gripping tissues, it is likely to produce heat rather than an arc. However, it may still ignite a fire in the presence of abundant oxygen. Thought must be given to sources of fuel. Again, in this case, a wet swab was placed over the eyebrows to reduce their flammability. Alcohol containing surgical preparation fluids should ideally be avoided (as was done in this case). If used, care must be taken to ensure that they dry properly before diathermy is used. The advice to reduce the concentration of oxygen to the minimum required is sound, but as already explained, this alone does not eliminate the risk of fire. If it is necessary for diathermy to be used in proximity to a fuel source, all supplemental oxygen should be turned off for at least two minutes before this is done. Even then, ignition may occur, so other steps are also needed. If at all possible, diathermy and ignitable fuel sources should be kept well apart.
In summary, HFNO is a valuable addition to the techniques available for managing the oxygenation of patients in various anesthetic situations. Given its potential to deliver large quantities of oxygen per unit time to a source of ignition, there is particular need for vigilance in respect to potential fires whenever HFNO is used. The risk of fire must be kept firmly in mind whenever surgery is performed around the head and neck, whether supplementary oxygen is used or not.