A 73-yr-old Caucasian man was scheduled for bilateral parietal burr-holes to evacuate a subdural hematoma at the University Medical Center in Tucson, AZ—the primary teaching hospital of the University of Arizona College of Medicine. The patient had severe Parkinson’s disease treated with Sinemet® (combination of levodopa and carbidopa) (DuPont Pharma, Wilmington, DE), and postviral cardiomyopathy with a measured ejection fraction of <20%. Because of his risk factors for general anesthesia, and at the patient’s request, the burr-hole procedure was performed under monitored anesthesia care (MAC).
The patient was brought to the OR without premedication, and connected to standard monitors, including electrocardiogram, automated sphygmomanometer, pulse oximeter, and capnograph. A clear plastic mask (Model 1041 Oxygen Mask; Hudson Respiratory Care, Inc., Temecula, CA) was loosely strapped to his face, and oxygen was introduced through the mask at 6 L/min. The head was shaved, and the skin surrounding the right parietal surgical site was prepared with a commercially available surgical solution of Iodofor (0.7% available iodine) in 74% isopropyl alcohol.
After preparing the site and allowing at least 2 min drying time, as recommended in the manufacturer’s instructions, the surgical field was draped. First, the field was “squared off” using a barrier of surgical towels. Next, a layer of Ioban™ Antimicrobial Incise Drape (3M Corporation, St. Paul, MN) was applied to the skin over the field, also covering the edges of the towels. Ioban is a clear plastic adhesive drape through which an incision can be made. Ioban will not adhere to a wet surface. Then a standard paper surgical drape (Baxter, Inc., Irvine, CA) was applied over the Ioban. The paper drape covered the entire head, neck, and chest area, with a roughly 15 cm diameter hole where it adhered to the Ioban.
The burr-hole procedure on the right side of the head was uneventful, the skin was closed, and the surgical drapes and Ioban dressing were removed. The head was turned slightly to the opposite side, and the site preparation was repeated as before, using the alcohol/iodine solution and recommended drying time. Surgical towels and a new Ioban dressing were applied to the left parietal side, followed again by a paper drape. The oxygen mask was left in place with a 6 L/min flow rate. The patient was responsive but sedated when the second draping took place.
A 3-cm skin incision was made using a scalpel, cutting directly through the Ioban dressing in the usual fashion. Then the electrosurgical monopolar pencil (“Force 2” Electrosurgical Generator; Pfizer Valley Labs, Boulder, CO) was used to incise the pericranium, using a setting of 3 for cutting. During the first activation of the electrosurgical unit (ESU), a muffled “pop” was heard. This was followed almost immediately by the appearance of smoke from under the paper drapes. The surgeon acted very quickly and removed the entire drape from the patient’s head. According to the surgical team, the head was fully engulfed in a “ball of flame” as the drapes were removed. The oxygen mask was also observed to be in flames. The paper drapes themselves were not on fire, and the surgeon immediately used these to smother the flames. At the same time, the anesthesiologist turned off the oxygen flow to the mask. Observers reported that the entire fire lasted <15 s from ignition to complete extinction.
The patient appeared stunned, but was still conscious and moving after the fire was extinguished. He had obvious burns and soot on his face, neck, and upper chest. Because of the possibility of airway burns and inhalation injury, general anesthesia was induced and an endotracheal tube was placed after consultation with the patient’s family. The patient was sedated, supported with mechanical ventilation, and then transferred to the ICU.
The burns to the face and neck eventually proved to be second degree, and all areas healed without surgical intervention. However, the patient’s ICU course lasted approximately 2 mo and was complicated by pneumonia, difficulty weaning from mechanical ventilation, and intolerance to enteric feeding. Some of these problems appeared related to his preexisting conditions of Parkinson’s disease and cardiomyopathy. He was eventually transferred from the ICU to a rehabilitation center, and then home.
To determine the causes and mechanisms of this OR fire, we performed multiple laboratory simulations of the event. A full-scale manikin made of a nonflammable plastic was used to simulate the head, neck, and upper torso of the patient (Fig. 1). To provide an electrical current pathway for the ESU, a 3 × 3 cm area of the manikin’s “skin” at the surgical site was covered with a thin layer of aluminum. One corner of this piece was connected to the return pad outlet of the ESU. This aluminum skin was an artifice made necessary by the fact that the manikin’s body has a much lower electrical conductivity than the human body. For the ESU to generate the localized heating responsible for its action, an electrical current must flow from the electrode tip into the patient. This current is normally returned to the ESU through the conductive pad on the patient’s skin. This pad is incorrectly referred to as the “grounding pad.” It is not an electrical ground, and it is properly called a “return pad” or “dispersive electrode.”Figure 1
All experiments were performed under a fume hood, whose exhaust fan was activated at the end of each experiment to evacuate smoke. The experiments were photographed by a VHS video camera equipped with a continuous timer display, as well as by a 35-mm still camera.
In the first experiment, we attempted to duplicate as closely as possible the circumstances of the OR fire. The manikin was placed on a bed sheet with a small towel under the back of the head in the same manner as in the actual case. The clear plastic oxygen mask (Model 1041; Hudson Respiratory Care, Inc.) was placed over the nose and mouth, and the oxygen flow was set at 6 L/min (Fig. 1).
The head and one side of the face were prepared with the alcohol/iodine solution using the sponge applicator provided with the product. During the preparation process, we noted that a few drops of solution dripped onto the towel and bed sheet, even though we were very cautious in the application. The package insert for the solution provides the following warning: “Do not allow to pool or soak into materials and do not use around ignition sources until dry (2–3 min).” We allowed exactly 2 min for drying.
The surgical site was then covered with the Ioban occlusive drape as was done in the OR. The paper surgical drape was then placed over the Ioban, leaving a 15-cm hole over the surgical site. Oxygen concentration was measured at several locations under the drape (POET II Gas Analyzer; Criticare, Waukesha, WI) and was found to range from 35% to 50% during steady-state conditions. The Valley Labs ESU intensity was set on 3, the same setting that was used in the OR. At the time of ESU activation, both video and still cameras were operating.
In the first experiment, the ESU pencil electrode was applied to the surgical site, and sparks were observed at the tip of the electrode, as they typically appear in the OR (Fig. 2). After roughly 3 s of application, a muffled “pop” sound was heard. Five seconds later, smoke began to appear from under the paper drapes (Fig. 3). We did not interrupt the process, although it was apparently at this point in the actual case that the surgeon removed the paper drapes from the patient. After another 8 s, bright yellow flames burst through the paper drapes (Fig. 4). Within 10 s after that, the entire head and surgical drapes were involved in flame (Fig. 5). The plastic oxygen mask produced bright yellow flames and quickly melted onto the manikin’s face. The laboratory was rapidly filling with smoke, and the experiment was terminated at this point. The oxygen supply was turned off, and the fume hood fan was activated. The remaining flames were smothered with towels.
At this point we carefully inspected our manikin. The melted oxygen mask was adherent to the manikin’s face. During the actual fire, events were stopped as soon as smoke came from under the paper drapes, but the oxygen mask was melted nevertheless. The manikin’s face and neck were stained with black soot, but there was no apparent thermal damage to the plastic itself. The manikin was cleansed with soap and water, and reused in the additional experiments.
In the next three experiments, we created the same initial conditions, but filmed the events from various angles to determine precisely where the fire began and how it propagated. In one experiment, we installed a Plexiglas® sidewall so that we could see into the closed cavity formed by the surgical drape. Through this transparent wall, we observed that when the ESU ignition source was activated, the fire spread almost instantly through the closed space within the drapes. Flames were then seen originating from the towel on which the head rested, in the area whereupon some preparation solution had dripped (Fig. 6). The cup-shaped depression in the lower right of the figure is the manikin’s shoulder socket; it had no arms. The plastic mask itself ignited a few seconds later and appeared to burn with an extremely hot flame.
We tested three of the plastic masks separately from the manikin setup, and found that in the absence of oxygen flow an open flame could melt them, although they did not themselves support combustion. However, when oxygen was flowing through a mask, even at 3 L/min, the mask could be easily ignited and would burn with an intense white flame.
In the remaining experiments, we varied the initial conditions one factor at a time to determine the exact ingredients required to produce a fire of this sort. We found the following consistent results:
- 1) If there was no flow of supplemental oxygen to the plastic mask, there was no fire. The paper drapes could eventually be ignited by aggressive application of the ESU, but the resulting fire was very slow burning and would self-extinguish within seconds.
- 2) If the alcohol-based preparation solution was not used, there was no fire. Furthermore, if we allowed 5 min of drying time after solution application (the manufacturer’s recommendation is 2–3 min), there was no fire.
- 3) If there was no closed space formed by a “tent” of surgical drapes covering the head, there was no fire. The alcohol-based preparation solution, the supplemental oxygen supply, the closed tent of surgical drapes, and the electrocautery ignition source were all required ingredients to produce a fire in our simulation.