Systematic review and meta-analysis comparing ventilatory support in chemical, biological and radiological emergencies*

Objective: to compare the mean development time of the techniques of direct laryngoscopy and insertion of supraglottic devices; and to evaluate the success rate in the first attempt of these techniques, considering health professionals wearing specific personal protective equipment (waterproof overalls; gloves; boots; eye protection; mask). Method: meta-analysis with studies from LILACS, MEDLINE, CINAHL, Cochrane, Scopus and Web of Science. The keywords were the following: personal protective equipment; airway management; intubation; laryngeal masks. Results: in the “reduction of the time of the procedures” outcome, the general analysis of the supraglottic devices in comparison with the orotracheal tube initially presented high heterogeneity of the data (I2= 97%). Subgroup analysis had an impact on reducing heterogeneity among the data. The “laryngeal mask as a guide for orotracheal intubation” subgroup showed moderate heterogeneity (I2= 74%). The “2ndgeneration supraglottic devices” subgroup showed homogeneity (I2= 0%). All the meta-analyses favored supraglottic devices. In the “success in the first attempt” outcome, moderate homogeneity was found (I2= 52%), showing a higher proportion of correct answers for supraglottic devices. Conclusion: in the context of chemical, biological or radiological disaster, the insertion of the supraglottic device proved to be faster and more likely to be successful by health professionals. PROSPERO record (CRD42019136139).


Introduction
Several emergency situations are triggered by the malicious or accidental use of chemical, biological or radiological agents, which can result in respiratory failure for the victims. The terrorist attacks in Syria with the Sarin neurotoxic gas in 2013 and 2017 can be cited (1) . In Brazil, in 2013, in the city of Santa Maria -Rio Grande do Sul, there was an accidental fire in a nightclub, which generated the emission of hydrogen cyanide, a chemical agent that, at that time, was responsible for the increase in clinical cases of acute respiratory failure, which resulted in the drastic death of 242 people and respiratory distress in approximately 1,000 victims (2) .
As for the biological agents, in West Africa, the Ebola virus epidemic in 2014 triggered an international civicmilitary response that left several countries on alert. The epidemic claimed the lives of thousands (3)(4) . In 2015, in Brazil, the first suspected case of Ebola was reported, which mobilized the health sector and provided the opportunity for the preparation of health professionals in relation to the specific protective equipment they should wear, as well as transportation and adequate health care addressed to the person with the suspected condition. This initiative was justified by the pathophysiology of the disease itself, which stimulates an inflammatory response, followed by an immuno-suppressive phase, causing respiratory failure due to blood aspiration and septic shock (5)(6) .
In relation to the inadvertent use of radiological agents, in 1987, in Goiânia, a municipality belonging to the state of Goiás (Brazil), a relevant radiological accident with cesium-137 had worldwide repercussion from the rupture of a lead capsule of an abandoned radiotherapy device in a disabled clinic. The consequence was the monitoring of 112,000 citizens, health care for 249 irradiated or contaminated people and four deaths, in addition to the marks it left as the worst radiological disaster in the world that occurred outside nuclear plants (7) .
Faced with such situations, when considering that first aids often occur with the victim still contaminated by a chemical, biological or radiological agent, it is recommended that at least the health professional use level C personal protective equipment, which essentially consists of waterproof overalls, gloves, boots, eye protection, and mask (3,(8)(9)(10) .
In view of the dimension and severity that events of this nature can cause, it is necessary to provide adequate protection to the health professionals, especially to the nursing team, who must be able to fully exercise their craft to alleviate suffering and care for the people affected in a safe and fruitful way. Indeed, the procedures analyzed and the individual protection equipment indicated to the health professionals in these complex circumstances confirm the need to discuss better standards of response and risk management, as well as the importance of having effective health technologies in calamitous scenarios (11) .
Additionally, it is worth mentioning the authorization issued by the Federal Nursing Council (Brazil), through its Opinion No. 1/2015, for trained nurses to proceed with the insertion of supraglottic devices, in case of urgencies and emergencies. In this sense, in a scenario of emergencies and disasters involving chemical, biological or radiological agents, the autonomy of these professionals is reasserted in the management of the airways in assisting victims with respiratory failure (12) .
In face of the agents that cause respiratory failure, there are procedures, such as direct laryngoscopy and the insertion of supraglottic devices, for establishing a patent airway and, consequently, a reduced risk of death (13)(14) .
However, there are divergences among studies on the "reduction of time to perform the procedure" and "success in the first attempt of each applied technique" outcomes. As an example, there is a study that recommends direct laryngoscopy (15) , as well as a study recommending supraglottic devices  The search strategies were configured as follows:  The studies derived from the application of the strategies were selected by two independent reviewers and filtered by reading their titles and abstracts, with due registration on the studies' eligibility form.
After checking the lists, a Kappa coefficient of 0.74 was obtained, a satisfactory value that reflected the objectivity and clarity of the data to be collected (17) .

Disagreements regarding the inclusion of studies
were resolved in a consensus meeting. Subsequently, citations were exported to the EndNote online reference manager. All the studies from this first selection were analyzed in their full texts.
The data collected from each study were organized in a data extraction instrument containing the following: authors' names; title; country of origin; year and magazine of publication; study population and environment; types of ventilatory support devices; number of participants; mean time spent performing the technique; standard deviation; and success rate in the first attempt of each procedure.
According to the Cochrane collaboration tool, for assessing the risk of bias in randomized studies, each eligible study was classified as low, moderate, or high risk of bias (18) .
The meta-analysis was developed using the  Figure 1 shows the product of the search strategies used.

Results
In the sequence, Figure  the sealing ability in the larynx to withstand pressure ventilation; a composition that is difficult to deform in case of bites by the victim; and the creation of a gastric drainage route (13) .
It should be noted that there were studies that compared more than one supraglottic device with the orotracheal tube, which made meta-analyses and their recommendations more robust.
Rev. Latino-Am. Enfermagem 2020;28:e3347.    Using the Cochrane collaboration tool, the quality of each selected study was assessed. As shown in Figure 3, the following domains were evaluated: selection bias, performance bias, detection bias, attrition bias, and reporting bias (18) .
When considering that the final classification of the study should be based on the highest risk of bias found among the domains, selection bias stood out as the main criterion for attributing a moderate risk of bias. Three studies with a low risk of bias, six studies with a moderate risk of bias, and one study with a high risk of bias were identified.
It was prioritized that the study reported how the random sequence and allocation secrecy were generated. Low risk of performance and detection bias was attributed to studies due to textual evidence in the sources of information and explanation of the extra author acquired via e-mail. Low risk was attributed in relation to attrition bias, as there was no provision of incomplete data. Regarding reporting bias, a low risk of bias was attributed, since no trace of attempted data manipulation was identified.  In accident scenarios with multiple victims, with or without involvement of a chemical, biological or radiological agent, one of the objectives is to provide a prior airway for as many people as possible (24,30) . Therefore, the use of supraglottic devices by the health professionals with personal protective equipment in these scenarios has been systematically studied. In general, the results point to ease of use and rapid insertion (30-32) . In addition, less stringent training requirements for its use have been confirmed when compared to orotracheal intubation (30-31) .
Another aspect highlighted is related to the clinical conditions of seriously infected victims, who require advanced immediate life support, which includes the use of ventilatory support techniques, a priority to reduce mortality (33) . Even in these cases, orotracheal intubation is the gold standard to ensure the airway and prevent death (34) .
In the case of the evolution of 2 nd generation supraglottic devices, feasible improvements have made them more useful and applicable in different environments, like the pre-hospital, in-hospital emergency, and surgical environments (24) . There are currently a variety of 2 nd generation supraglottic devices, which have similar characteristics, such as anti-bite system, route for gastric emptying, better airway sealing, and structure to be a Borges IBS, Carvalho MR, Quintana MS, Oliveira AB ventilatory support route under high pressures. Such characteristics make supraglottic devices a technology that has been gaining space and importance in the daily care of the health professionals (13,24,32) . It can be inferred that the effectiveness and the performance among the 2 nd generation supraglottic devices of this systematic review reflected in the homogeneity of this subgroup.
In addition, emergency orotracheal intubation outside the operating room is associated with significant operational challenges, which include a higher incidence of difficult intubation due to environmental factors, possible lack of experience in laryngoscopy, rapid deterioration of clinical conditions, and risk of regurgitation (13) .
Paradoxically, despite all the selected studies, a study was retrieved, whose participants were emergency physicians with level C personal protective equipment, performing orotracheal intubation and the insertion of supraglottic devices in cadavers (15) . The results suggest orotracheal intubation as a faster technique, with statistically significant data (p = 0.02) and with a higher success rate in the first attempt (direct laryngoscopy = 58% and supraglottic device = 21%) (15) .
However, it is noteworthy that this study was eliminated from this systematic review because it did not present data with the respective standard deviation or means for calculating it, which made insertion in the meta-analysis unfeasible, in compliance with the provisions of the inclusion criteria. Thus, a high risk of attrition bias was identified due to the fact that it did not present the standard deviation in the study. It is worth mentioning that few participants in this study had previous experience with a supraglottic device, which meant that the researchers promoted a preliminary training, in which each participant performed the two procedures three times. These same participants had an Advanced Life Support Course, and reported having performed direct laryngoscopy at least 30 times in their career. In view of the above, after assessing the risk of bias by the highest degree identified in the domains, the general assessment of this study (15) was considered high risk, weakening the reliability of its results. This was the only study that was contrary to the favorable trend towards supraglottic devices.
Regarding the potential limitations of this study, it is emphasized that the systematic review evaluated different types of supraglottic devices, as well as it considered different methodologies, professional categories or areas of activity, which reflected in heterogeneity. However, the summary effect was strongly favorable to supraglottic devices, in all the meta-analyses.
Another limitation concerns the instruments on which the ventilatory support techniques were applied. As explained in Figure 2  Therefore, it should be considered that nine of the ten studies in this systematic review were carried out in a skills laboratory, that is, in a closed environment, with ideal brightness, controlled temperature and mannequins, which may not reflect reality (10,14,35) . In addition to the above, scholars in the field comment on the difficulty of developing research studies of this nature with human beings, in relation to the use of chemical warfare agents (14) .

Conclusion
The systematic review points to supraglottic devices as being faster to the detriment of orotracheal intubation,