Our study shows that use of AB impedes airway management, with risks for patients in terms of intubation outcome and in terms of potential harm; as a further remark, the use of AB seems to superimpose infection risks for HCWs with evidence of increased cognitive and physical workload.
COVID-19 represents an unprecedented challenge for healthcare system organization and facilities  with significant efforts and tasks for HCWs exposed to high-infection risk given the nature of the pathogen agent [18,19,20]. Data from the international and multicentric intubateCOVID-study indicate that 1 in 10 HCWs taking care of airway management develops SARS-CoV-2 infection , not underestimating physical and mental health issues due to increased workload . Implications of such phenomena on endurance, performance, and safety of airway management teams are of paramount importance, either during a pandemic event and during endemic/silent phases, given the potential long-term effects in terms of fatigue, burnout, and risk of death [23, 24]. The use of PPE and of AB is a further load to be considered, especially during airway management, and to our knowledge, this is one of the first reports of clinical data on the performance and impact of barrier enclosure systems on airway management.
A recent review  suggests that barrier enclosures may impede airway management, limit hands-on time if help is needed, and may complicate the use of some airway devices, such as tracheal introducers  or advanced airway manipulation as for one-lung ventilation procedures . Simulation studies suggest longer intubation times with barrier enclosure systems, with a first pass success rate of 75% when using first-generation AB , and these data were supported also by a recent systematic review .
Our data indicate that when the AB was used (90% of intubations), the first-pass intubation success rate was 70%. In 22.2% of cases, and the AB was removed because of multiple intubation attempts, with documented traumatic complications during airway management. This observation is in line with experimental studies and experts’ hypothesis as from relevant literature , supporting the evidence that use of AB has a significant interference with ergonomics of airway management, and it may add extra cognitive and operational tasks to operators which are already under heavy psychological and physical pressure. We did not record the intubation time, but our data suggest that airway management was prolonged and complicated by the use of AB in many cases, including a reported incidence of 46.2% for Cormack-Lehane grade 3 laryngeal view; of notice, given the limited availability and lack of experience, a videolaryngoscope was not used for any intubation.
This finding may represent a bias, given that acquisition of line of sight with standard laryngoscope may be hindered by the optical and physical interface represented by the AB wall. Also, the need for intubation out of operatory room but in medical wards may have added difficulty to airway management, and this could be considered a biasing factor in AB evaluation.
As a subjective data, 66.6% of physicians participating the study reported significant airway management limitations.
Our study also raises concerns for patients and HCWs’ safety: the AB migrated during airway management in 91.66% of cases, which may have multiple implications: first, the box movement may complicate or compromise airway management attempts. Secondly, should the box move or fall from the bed, it may hit hurt the patient or the attending physician; last but not least, the box dislodgment may compromise the infection-control principle, if any.
Interestingly, 83.3% of the providers reported physical contact with the box walls, with 33.3% suggesting the use of larger access ports. As reported in Begley’s simulation study , this contact may also result in PPE damage with increased infection risk.
Perception of increased difficulty in airway management and risks for patients and HCWs was a common concern: In 10% of cases, the intubation team decided not to use the AB prior to the procedure either for comfort or patient’s size or perceived risk of difficult intubation during pre-procedural evaluation.
The AB’s perceived protection was somewhat controversial: 83.3% of surveyed providers reported feeling safe with the device, whereas in 92% of cases some kind of discomfort was reported, and only 75% of participants recommended the use of barrier enclosure systems when filling the post-procedural report.
Our study was underpowered to detect infection risks or incidence in HCWs, and it was not designed for such an endpoint. Nevertheless, at the end of the study, 25% of the intubation team members had a SARS-CoV-2-positive PCR nasal swab test, verisimilarly related to a clinical exposure.
We may not exclude that an infection route was some aerosolization associated with the use of AB. As elegantly demonstrated in recent simulation studies, these devices may effectively stop the large droplets but they may not stop aerosols, with particles escaping through access ports via Bernoulli effect  or upon removal (“secondary aerosolization”) [16, 30].
Concerns about safety and performance, and overall effects on airway management success, prompted the FDA to revoke the permit of AB in August 2020, so that barrier enclosures without the possibility of additional negative pressure are no longer recommended .
Recent studies also highlight that any not fully enclosed AB may redirect aerosol toward the laryngoscopist, indicating that only an aerosol evacuation system may reduce aerosols inside the box, which should never substitute, but complementary to certified PPE [32, 33].
Interestingly, recent evidence suggests that extubation may be even more critical in terms of aerosol generation and consequential infective risks ; the use of AB or barrier enclosures may be even more challenging during extubation [16, 35], with poorly cooperative if not combative patients and with few medications to counteract extubation associated phenomena (coughing, nausea, vomiting, etc.). Operator’s discomfort, the risk of AB damage or patients’ injury was also largely perceived during extubation phase, and in all cases when AB was removed or not used during initial airway management, it was not used a priori for extubation.
With 2.5% of all COVID-19-diagnosed Mexican patients requiring endotracheal intubation and invasive mechanical ventilation and a global 73.7% mortality , Mexico was heavily hit by the pandemic , paying the price of one of the highest levels of infected HCWs globally.
46,013 (22.08%) of young (30––54 years old) Mexican HCWs developed a SARS-CoV-2 infection. The majority of them were not hospitalized, but between the 693 in critical condition, 234 required endotracheal intubation, with a case fatality rate of 1.48% (683/46 013) within HCWs compared with a global 15.26% [38, 39]. A report from the Amnesty International indicated that Mexico had the world highest number of deaths between HCWs (1320), followed by USA (1077 deaths) and UK (677 deaths) .
PPE per se do not protect, unless users are not well trained in their use, in donning and doffing procedures and only if PPE are part of a wider strategy and preparedness , including protocols, logistics, and availability of well trained and specialized physicians [17, 36] with an educated and consolidated teamwork approach . The use of barrier enclosure systems in countries like Mexico may reflect the need to achieve some means of protection when conventional and certified PPEs are lacking . Nevertheless, our clinical data confirm that barrier enclosure systems add complexity to airway management; they may represent a risk for patients’ safety, they may expose HCWs to a higher risk of infection when used as surrogates or substitutes of conventional PPE, and they may finally provide a false sense of safety thus resulting in lower attention and perception of lower personal protection needed, not considering the risk of PPE damage because of contact or impingement with the AB.
Our study has limitations as follows: first, it is a retrospective study conducted during the pandemic surge, and some data may have been missed or misreported. The survey responses were subjective, but we believe they may reflect quite objectively the clinical reality and HCWs feelings.
We did not collect intubation duration data, nor could we carefully analyze data of HCWs infection rates, because of the study’s design, with a control arm missing.
On the other hand, to our knowledge, this is one of the first clinical studies evaluating the use of AB in airway management in a series of 40 COVID-19 patients.