Possibilities of Endoscopic Diagnosis of Airway Burn in Inhalation Trauma

The diagnostic standard for airway burn in inhalation trauma is bronchoscopy. Determining the severity of a burn of the respiratory tract within first 24 hours is difficult due to the multiple foci of fixed soot, therefore, this procedure is possible only after its removal. Optimization of the standard method of sanitation bronchoscopy in case of airway burn by removing soot with endoscopic forceps and brushes significantly increase the efficacy of primary endoscopic diagnosis, which amounts to 74.9%. The most common mistakes in diagnosing the severity of mucosal damage are associated with a burn of the 1st degree.


INTRODUCTION
Inhalation trauma (IT) is a multifactorial injury to the human respiratory system when inhaling hot air and smoke, which is based on damage to the mucous membrane of the respiratory tract, lung parenchyma, and the general toxic effect of combustion products on the human body [1][2][3][4].
Bronchoscopy is recognized as the gold standard for the diagnosis of airway burns (AB) in IT, which makes it possible to assess the severity of damage to the mucous membranes of the airways [5][6][7][8][9][10] . Difficulties in endoscopic diagnosis of the severity of AB on the 1st day after injury are associated with the impossibility of visualizing the mucous membrane, which in most cases is covered with soot deposits. The mucous membrane is cleared of soot only by day 5-7 [11]. So, according to G.A. Mayorov (2005), the efficiency of primary endoscopic diagnostics is 57.3% [12].
Aim of study: to evaluate the effectiveness of primary diagnostic bronchoscopy in patients with burns of the respiratory tract mucosa during IT.

MATERIAL AND METHODS
From 2013 to 2017, 344 patients with IT were treated at the Moscow Burn Center of the N.V. Sklifosovsky Research Institute for Emergency Medicine. The study included 179 patients who underwent two or more diagnostic bronchoscopies.
There were 99 (55.3%) men and 80 (44.7%) women. The patients' age ranged from 16 to 90 years, the median age was 55 years. IT was isolated in 79 patients (44.1%) and was combined with skin burns in 100 patients (55.9%). The total area of skin burns ranged from 0.1 to 80% of the body surface (b.s.), the median was 13% b.s.
Endoscopic diagnosis of AB was based on the classification suggested by Y.V. Sinev and A. Y. Skripal, according to which there are four degrees of severity, depending on the depth of damage to the mucous membrane: catarrhal (1 st ), erosive (2 nd ), ulcerative (3 rd ), and necrotic (4 th ) [13].
All patients with AB underwent primary diagnostic and therapeutic bronchoscopy within first 3 hours after hospitalization in the course of intensive therapy according to the standard method through the upper respiratory tract, performing irrigation of the mucous membrane of the epiglottis, vocal folds and carina with 2% lidocaine solution at a dose of 6.0 ml, or through an endotracheal tube under intravenous sedation [14]. A 0.01% solution of dioxidine or miramistin in a volume of 80 ml was used as a sanitizing solution. We have optimized the standard procedure for the rehabilitation of bronchoscopy in the case of AB. The first step was washing off soot casts from the mucous membrane with antiseptic solutions. Then, while maintaining the deposition of soot on the mucous membrane, they proceeded to the second stage, which consisted in mechanical removal of soot using endoscopic forceps and brushes. Endoscopic forceps captured the soot casts and removed it, and in the case of using an endoscopic brush, traction movements were performed with the brush, which made it possible to mechanically clean the mucous membrane from soot. Repeated diagnostic and therapeutic bronchoscopies were performed every 24 hours until the mucous membrane of the tracheobronchial tree (TBT) was completely cleared of soot.

RESEARCH RESULTS
In primary diagnostic bronchoscopy, 1s t degree AB was detected in 18 patients (10.1%), 2 nd ABin 138 (77.1%), 3 rd ABin 21 (11.7%), and 4 th degree ABin 2 (1.1%) (see Table). The endoscopic picture of AB of the 1 st degree and severity in primary bronchoscopy was characterized by a moderate or large amount of liquid mucous secretion with an admixture of soot in the lumen of the TBT. The mucous membrane of the larynx, trachea and bronchi was hyperemic, edematous, soot deposition was partially or completely removed during debridement (Fig. 1). After repeated bronchoscopy, the diagnosis of 1 st degree AB was confirmed only in 7 patients (38.9%) out of 18, and in 11 (61.1%) after complete removal of soot foci, acute erosions were revealed and the 1 st degree of AB was changed to 2 nd .
For AB of the 2 nd severity, a small or moderate amount of viscous mucous secretion with an admixture of soot in the lumen of the TBT was characteristic. The mucous membrane of the TBT was brightly or moderately hyperemic, slightly or moderately edematous, with multiple foci of fixed soot and confluent lesions, which were partially or completely removed during sanitation. With the complete removal of soot, multiple acute erosions with a clean bottom or covered with a light thin layer of fibrin were visualized (Fig. 2). After repeated bronchoscopy, grade 2 AB was confirmed in 109 (79%) patients out of 138 (see Table). In 29 patients (21.0%), the diagnosis of 2 nd degree AB was not confirmed with repeated broncoscopy. In 6 patients (20.7%) out of 29 we failed to completely remove soot during the first endoscopic examination, so it was removed during repeated bronchoscopy: no damage to the mucous membrane was found, and the 2 nd degree AB was changed to 1 st . In 23 patients (79.3%) of 29, after the removal of soot, superficial ulcerative defects without clear contours were visualized: the 2 nd degree of AB was changed to the 3 rd degree (see Table).
In patients with grade 3 AB, no discharge was found in the lumen of the trachea and bronchi. The mucous membrane of the trachea and bronchi was covered with multiple confluent deposits of fixed soot, which was difficult to remove by bronchoscopy. Mucous membrane of the respiratory tract was pale or slightly hyperemic, "dry", the edema was not expressed. The soot was not removed in any patient during the initial endoscopic examination. After repeated bronchoscopy and complete removal of soot on the mucous membrane, superficial ulcerative defects were determined: grade 3 AB was confirmed in 16 patients (76.2%) out of 21 (Fig. 3). When erosions were detected and there was no ulcerative lesion of the mucous membrane, the 3rd degree of AB was changed to 2 nd in 5 patients (23.8%) (see Table). The endoscopic picture of grade 4 AB at the initial examination was characterized by the absence of c the walls of the trachea and bronchi were covered with a dense grayish-black eschar, which was not removed during debridement (Fig. 4). After primary bronchoscopy, grade 4 AB was accurately diagnosed in 2 patients on day 1. In general, the degree of AB was initially confirmed in 134 patients (74.9%), and in 45 patients (25.1%) during primary bronchoscopy, it was not possible to remove soot completely and the degree of AB was corrected with secondary bronchoscopies. In 34 patients (75.6%) of 45, after complete removal of soot, the degree of AB was changed to a more severe one.
We studied the timing of complete cleansing of the mucous membrane of the TBT from soot in case of AB of the 1 st , 2 nd and 3 rd degrees of severity (Fig. 5). In 1 st degree AB, on the 1 st day, the mucous membrane of the respiratory tract was washed and cleaned from soot in 6 patients (46.1%), on the 2 ndin 5 (38.5%), on the 3 rdin 1 (7.7%) and on the 4 th day also in 1 patient (7.7%). As it turned out, even with 1 st degree AB, we failed to remove soot more than in 15% of patients fail within first 2 days.
In AB of the 2 nd degree on the 1 st day, the mucous membrane of the respiratory tract was washed and cleared of soot in 57 patients (45.6%), on the 2 ndin 40 (32.0%), on the 3 rdin 13 (10.4%). It took more than 4 days to remove soot in case of 2 nd degree AB in 15 patients (12.0%).
With grade 3 AB, the soot was removed in 11 patients (28.2%) on the 1 st day, on the 2 nd dayin 12 (30.8%), on the 3 rd dayin 2 patients (5.1%). It took more than 4 days to remove soot from the mucous membrane of the TBT in 14 patients (35.9%).
Thus, in AB of the 1 st and 2 nd degrees, the mucous membrane of the respiratory tract was cleared of soot on the 1 st and 2 nd days after injury in most patients (92.3% and 88%, respectively). With AB of the 3 rd degree, the period of cleansing the mucous membrane from soot in the first 2 days was only 64.1%, and in 1/3 of patients (35.9%) -4 days or more.

THE DISCUSSION OF THE RESULTS
The chemical factor plays an important role in the pathogenesis of damage to the mucous membrane of TBT. In a fire in an enclosed space, the resulting combustion products are diverse and are always individual in chemical composition. Getting into the lumen of the trachea and bronchi, combustion products interact with the secretion of TBT and form acids and alkalis, which damage the mucous membrane [1,2]. Soot is carbon deposit, and soot by itself does not damage the mucous membrane of the respiratory tract, but it can be a carrier of chemically active compounds, which effect leads to an increase in the extent and depth of damage [11,15].
As our studies have shown, the determination of the depth of damage to the mucous membrane of the respiratory tract in the 1 st day after the injury is difficult due to the tightly fixed deposition of soot. According to various authors, foci of fixed soot on the surface of the mucous membrane in patients with AB can be sustained for up to 6-7 days [11,16]. It is not always possible to remove soot completely during the primary sanitation bronchoscopy, which can lead to diagnostic errors. The optimized technique of sanitation bronchoscopy made it possible to achieve the removal of soot in the shortest possible time and thereby increased the efficiency of primary endoscopic diagnostics of the severity of AB in IT from 57.3% (G.A. Mayorov, 2005) to 74.9%.
The effectiveness of the primary diagnosis of the severity of airway burns in patients with inhalation trauma depends on the results of sanitation bronchoscopy. Only with complete cleansing of the mucous membrane from soot the diagnosis of the degree of airway burn may be confirmed.