## 2 Materials and Methods
### The Lean Operational Algorithm  
Lean healthcare is a \"tools-based approach\". The algorithm is built on lean tools and techniques implementation [8].  
The Lean model applied for the management of the SARS-CoV-2 pandemic outbreak encompassed the implementation of standard work, with the aim of optimizing clinical practice and being able to implement the quality of care. Everyone has to follow the standard work to grant the highest quality of treatment for both the patients and the hospital until a more appropriate approach is found. In that case, it becomes the new standard of care.  
Firstly, a pre-triage internal protocol was defined (Standard work). Patients were screened outdoors for fever, respiratory, and gastrointestinal symptoms to determine the most appropriate route to take in ED. Patients with SARS-CoV-2 symptoms were directly transported to the COVID-19 Hospital facility hospital, where they underwent our first-level screening in a designated isolation area. A well-trained, fully personal protective equipment (PPE)-dressed nurse conducted the nasopharyngeal swab, pulse oximetry, took vital signs, and performed a rapid physical examination. Suspected cases were triagedin a specific isolated area to assign an appropriate priority code. Particular attention was paid to peripheral oxygen saturation (SpO\({}_{2}\)%): Patients with a SpO\({}_{2}\) < 90% (or < 86% if chronic obstructive pulmonary disease--COPD patients) were immediately assigned a code 1 or 2 and placed in a high-intensity treatment area; subjects with a SpO\({}_{2}\) > 94% were assigned a code 3 or higher and placed in a less-intensive treatment area. The gray zone was represented by suspected patients showing a 90% < SpO\({}_{2}\) < 94% (ore 86% < SpO\({}_{2}\) < 90% if COPD). Those patients were administered low-flow oxygen (4 liter/min) with a nasal cannula in order to evaluate any improvement in SpO\({}_{2}\). Patients with no or poor improvement in peripheral oxygenation were assigned with a code 1 or 2 and placed in the above-mentioned isolated area. Furthermore, all patients received a prompt full medical evaluation, chest ultrasound (US), laboratory blood tests, and supplementary oxygen and medical treatment if required (Figure 1).  
In the emergency setting, where time is vital and the rate of patient inflow is high, the risk of potentially making a mistake is greater. In the Lean methodology, human error can lead to a process failure. Based on this assumption, lean adopts simple tools to decrease the error rate (Poka Yoke). Inside the isolation area, a whiteboard was placed for the visual check (visual management) of all patients in order to always have the necessary information for the correct management of the patients available (Figure 2). Additionally, symbols were drawn on the floor to make the paths to follow clear and reduce the possibility of infection as well as logistical errors. In addition, hospital statistics and data reports were created and reviewed daily to improve the standards of care.  
Figure 1: Lean operational algorithm used during the COVID-19 outbreak.  
Lean has two primary goals, namely the identification and elimination of inefficient processes (i.e., waste elimination such as waiting, movement, overprocessing), and the integration of co-workers' feedback (multidisciplinarity and engagement). Of great importance was the feeling of being part of a united group. Health workers were involved in all levels without neglecting anyone's opinion. Weekly multidisciplinary meetings were held to share and improve logistics, clinical, and relational management leading to a constant increase in efficiency and safety. Figure 3 summarizes the Lean approach to COVID-19 in the ED.  
The overall data of patients managed at the ED in the timeframe February 21-May 28 2020 have been retrospectively analyzed.