If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Rapid response teams mobilize resources to patients experiencing acute deterioration. Failed airway management results in death or anoxic brain injury. A codified, systems-based approach to bring personnel and equipment to the bedside for multidisciplinary airway assessment and rescue was reflected in the initial implementation of an airway rapid response (ARR) team.
A retrospective review of records of 117 ARR events in a 40-month period (August 2011–November 2014) was undertaken at the Hospital of the University of Pennsylvania, a 789-bed, academic, urban, tertiary care, Level 1 trauma center.
Of the 117 ARR events, 60 (51.3%) were called in the ICU, and 43 (36.8%) in the general ward. A definitive airway was secured in all patients for whom airway management was attempted. A new surgical airway was performed in five of the patients. Seven patients went to the operating room for airway management. Nine patients died or had care withdrawn shortly after the ARR.
Difficult airway emergencies represent a small but critical element of airway rescue scenarios. Before the implementation of the ARR system, the process to bring the right team, equipment, expertise, and consensus on the right actions to critical airway emergencies was ad hoc. ARR activation, which brings multidisciplinary airway consultation, expert skills, and advanced airway equipment to the bedside, contributed to definitive airway management for surgical and nonsurgical airways. Performance of a bedside emergency surgical airway was uncommon. The ARR system represents a significant enhancement of the “anesthesia stat” system that typifies the airway emergency system at many institutions.
Rapid response teams (RRTs) have been introduced in many institutions to mobilize appropriate resources to patients experiencing acute deterioration. The effectiveness of these systems in acute care settings has been the subject of multiple reviews and editorials.
for which there is limited time for triaging and assessment. Such focused RRTs are intended to directly assemble multidisciplinary clinician expertise and advanced equipment targeted to a specific subset of emergent conditions.
Emergent intubation is associated with increased risk and morbidity and is a common component of rapid response scenarios.
Respiratory compromise can occur very rapidly with little margin for error or delay. Failed airway management is catastrophic and ultimately results in death or unrecoverable anoxic brain injury. A codified, systems-based approach that can rapidly bring necessary personnel and equipment to the bedside for both multidisciplinary assessment and rescue may limit morbidity in these scenarios.
The literature is sparse regarding optimization of systems approaches to out-of–operating room (OR) airway emergencies. A report by Mark et al. on a difficult airway response team (DART) in a large academic medical center highlighted operational aspects of implementation and demonstrated the value of the DART for airway rescue.
In this article, we present our 40-month experience with an airway rapid response (ARR) team in a large academic trauma center. A subanalysis of the data set, specifically involving tracheostomy as a trigger for airway emergencies, was reported elsewhere.
We herein introduce the rationale for the ARR team as a component of a high-reliability emergency airway system, present our approach to implementation, and discuss both limitations and considerations for iterative improvement.
Setting and Ethics
The Hospital of the University of Pennsylvania (HUP) is the main teaching hospital of the University of Pennsylvania Health System (Philadelphia). It is an adult, 789-bed facility that includes a general surgical ICU (24 beds), a cardiothoracic surgery ICU (32 beds), a cardiac ICU (8 beds), a mixed neurology/neurosurgical ICU (22 beds), and a medical ICU (24 beds). For the duration of this study, HUP was a Level 1 trauma center staffed by a 24-hour in-house attending traumatologist, attending anesthesiologist, and anesthesiology house staff. Overnight in-house ICU coverage was typically provided by a fellow with attending backup. Overnight otorhinolaryngology–head and neck surgery (ORL-HNS) coverage was provided by an in-house resident who covered two adjacent facilities, with home backup by senior house staff, fellows, and attending physicians. Regular daytime ICUs were staffed by in-house attending anesthesiologists, surgical intensivists, or medical intensivists, depending on the unit.
The study was reviewed and approved by the Institutional Review Board of the Hospital of the University of Pennsylvania.
Emergency Airway System Structure and Airway Rapid Response System Development
When a patient requires urgent intubation, the primary team calls the operator and requests an “anesthesia stat” page. The page brings a rapid response nurse coordinator, anesthesiologist, pharmacist, a respiratory therapist, and x-ray technician to the bedside. With the exception of emergency medicine physicians, to promote the goal of reducing variation in care at our institution, nonanesthesiologists do not routinely perform emergent intubation. Respiratory therapists are not trained or credentialed to perform intubations in our institution. The anesthesia stat system is highly reliable for routine emergencies but is not optimized for the special, high-risk circumstances of the difficult intubation, failed intubation, or emergency involving an existing surgical airway. Such situations benefit from combined multidisciplinary airway expertise beyond that of the anesthesiologist. Since 2006, the emergency airway system at our institution has undergone several safety-focused improvement iterations based on critical event review involving failed airway management. This led to the creation of a difficult airway identification (DAID) bracelet and the ARR system. We describe the implementation and structure of the DAID and ARR systems in the following sections. A key feature is the distinction between anesthesia stat and ARR activation calls, in which we consider the ARR to represent an upgrade in acuity. Details of these two pathways are shown in Figure 1.
Difficult Airway ID System
A DAID bracelet system was implemented at HUP in 2006 along the lines of a model described by Berkow et al.
An anesthesiologist, emergency medicine physician, or ORL-HNS surgeon may designate a patient to be a difficult airway on the basis of either documented difficulty with mask ventilation or intubation or anticipated difficulty due to factors such as history of laryngeal radiation, airway tumor, tracheal stenosis or stent, or congenital malformation of the airway. Any clinician can request a formal anesthesiology airway consult for difficult airway assessment, but only patients scheduled for a procedure or undergoing airway management are typically screened. The DAID is entered into all electronic health record (EHR) systems and subsequently appears as a highlighted header in the record. A difficult airway wristband is placed on the patient while he or she is in the hospital or procedure area, and an information sheet describing the reasons for difficult airway and known failed and successful approaches to intubation is printed. A copy of this sheet resides in the patient chart and on the wall at bedside.
ARR System Development
The ARR system was designed after quality improvement review of several emergency airway cases revealed that ad hoc processes contributed to delays in assembling the surgical team and tracheostomy equipment after failed emergency intubation outside the OR. The review evidenced the need for a “hardwired” approach, with defined activation criteria for emergency surgical airway scenarios that would include immediate access to clinical staff with surgical airway expertise, the equipment necessary for a surgical airway at any time, and rapid mobilization of OR resources if necessary. A leadership group of anesthesiologists, surgeons, and nurses worked with the Clinical Emergencies Committee to develop the system. The trauma surgeon was selected as the primary surgeon (instead of ORL-HNS) because of the continuous (24-hour) in-house presence of an attending trauma physician. In addition to the trauma surgeon, daytime ORL-HNS coverage for airway emergencies includes faculty and senior house staff. Off-hours ORL-HNS support is provided by a house officer with attending backup from home. The hospital was engaged to purchase the surgical airway equipment for code carts in the hospital. Respiratory therapy was equipped with portable, battery-powered fiberoptic bronchoscopes to be brought to ARR emergencies. A set of criteria for activation was developed, an activation poster was distributed, and education was provided by individual clinical units and departments (Figure 2).
Any member of the clinical team can activate the ARR by calling the operator and requesting an “airway rapid response.” Staff members are trained to bypass anesthesia stat and directly activate the ARR for any airway emergency that meets the criteria included in Figure 2. The ARR system was designed to direct trauma surgical expertise to all airways that could be complicated rather than to only provide surgical rescue after failed intubation. In addition, the anesthesia stat could be upgraded to ARR at any time by any member of the clinical team if the anesthesiologist was struggling to oxygenate the patient or if the intubation proved unexpectedly challenging.
The overhead ARR call brings to the bedside the following resources: an anesthesiology attending, an anesthesia resident (postgraduate year 3 or higher), a trauma surgery attending, an ORL-HNS resident (and an attending if available), a rapid response nursing coordinator, a pharmacist, a respiratory therapist (who brings a battery-operated flexible fiberoptic bronchoscope), nursing staff (who bring a code cart equipped with a surgical airway tray), and a radiology technician (who brings a portable x-ray machine). Originally, the anesthesiologist brought a videolaryngoscope tower from the perioperative area to all ARR events. Beginning in August 2014, as a process improvement based on utilization patterns of videolaryngoscopy for emergency intubations, a handheld portable videolaryngoscope became a standard part of the equipment, which the responding anesthesiology resident carried in an airway bag (which would contain other routinely used advanced airway rescue equipment). The responding team performs a joint patient assessment in conjunction with the primary team; the teams may elect to intubate the patient, perform a bedside needle or surgical cricothyroidotomy or tracheostomy, recannulate an existing tracheostomy, or mobilize the patient to the OR for the airway procedure. The activation pathways and options for management are depicted in the flow diagram (Figure 1).
Each unit has a unit-based clinical leadership (UBCL) team, which introduced the ARR system to clinical units throughout the hospital; descriptive flyers were posted in all units and online. Trauma surgery, ORL-HNS, and anesthesia departments educated their own staff. The anesthesiology department conducted a series of in situ multidisciplinary simulation exercises to both educate staff regarding the ARR system and to rehearse and test the fidelity of the system. All anesthesia house staff were taken through a simulated “can't intubate / can't ventilate” scenario in the simulation lab, with the scenario that activation of the ARR system and performance of a bedside surgical airway were both necessary for successful resuscitation. Ongoing training occurs via in-situ simulation and refreshers delivered by the Clinical Emergencies Committee, the Department of Anesthesiology, and the UBCL team.
We reviewed operator call logs for notation of ARR activation during the 40-month period of August 2011 through November 2014. Date and room number from the call records were cross-referenced with RRT data sheets and inpatient hospital room logs to identify patients. All available documentation regarding the event and a recent history and physical exam were reviewed for each patient. Data obtained from the patient record included patient age, gender, body mass index (BMI), admission diagnosis, date, time and location of event, presence of an in situ airway immediately prior to the ARR, and attempted and successful airway management techniques. Anesthesia stat totals for 2012 were calculated from operator call records; and the total number of medical and surgical rapid response calls, in 2013, was tallied from a database of surgical and medical databases (not available before 2013).
Activations, Indications, Outcomes
For the 40-month period (August 2011–November 2014), 124 activations of the ARR system were identified, of which 117 contained patient information for review. The other 7 activations were excluded from analysis for the following reasons: call related to simulation exercise (2 cases), canceled call (2), and unable to link the call to a patient record (3). Of the remaining 117 activations, several patients were associated with multiple different ARR calls during the same admission, reducing the number of unique patients to 108.
Patient and Event Characteristics for Emergency Airway Calls
To provide a frame of reference for the proportion of emergency calls that involved the ARR, we tabulated call totals from available operator logs for selected years. In 2012 there were 503 emergency airway calls—472 anesthesia stat (93.8%) and 31 ARR (6.2%). In 2013 there was a total of 2,205 rapid response and anesthesia stat calls, including 40 ARR (1.8%). Selected patient and event characteristics are summarized in Table 1 and Table 2.
Table 1Characteristics of Patients on Whom ARR Was Called
The 108 patients, identified as stated, were admitted with a primary medical diagnosis (80 [74.1%]), primary surgical diagnosis (23 [21.3%]), or recent trauma event (5 [4.6%]). Locations of ARR activations were the ICU (60 [51.3%]), general ward (43 [36.8%]), PACU (6 [5.1%]), emergency department (3), radiology (3), dialysis unit (1), and ENT (ear, nose, and throat) clinic (1). ARR events occurred off-hours (between 5:30 p.m. and 7:00 a.m.) 57.3% (n = 67) of the time. Thirty (27.8%) of the 108 patients had an in situ airway (tracheostomy , laryngectomy , or endotracheal tube ) that became dislodged, became ineffective for ventilation, or evidenced bleeding leading to the ARR. The majority (17 [56.7%]) of these 30 patients were managed by recannulation of the tracheostomy. Tracheostomy emergencies (for example, decannulation, bleeding, mucus plugging) were led by the surgical team (trauma + ENT) with anesthesiology support. A small subset of the 108 patients (15 [13.9%]) had documented difficult airway status prior to the event. A definitive airway was secured in all patients on whom the ARR was activated except in those for whom intubation was determined to be unnecessary (n = 5). In 80 (74.1%) of the 108 patients, airway management consisted of intubation at the bedside. The anesthesiologist intubated with a standard laryngoscope (n = 28) or videolaryngoscope, (n = 33), or—working as a team—the anesthesiologist and otolaryngologist intubated with a fiberoptic scope (n = 19).
Intubation at the bedside was unsuccessful in a small subset (n = 9) of the 108 patients. The interventions in these patients included bedside surgical airway or transport to the OR for airway management. We examined the clinical circumstances of each of these cases in an effort to identify elements of the system that were successful as well as opportunities for optimization.Table 3 presents clinical and contextual details of these 9 patients with the associated outcomes—a new bedside surgical airway, emergent OR airway management, anoxic brain injury, death, or withdrawal of care.
Table 3Summary of Major Events (New or Revised Surgical Airway, Death, Anoxia) for 9 Patients for Whom Bedside Intubation Was Unsuccessful
ESLD awaiting transplant
Massive oral bleeding, respiratory arrest
Cricothyroidotomy by intensivist, could not be resuscitated, bleeding
CLL with severe myelodysplasia
Sudden onset respiratory distress
Failed fiberoptic intubation, trach by ENT, unable to resuscitate, 2° intraabdominal process
Pelvic mass myeloproliferative disorder
Difficult intubation 2° edema; ruptured pilot balloon, cricothyroidotomy by Trauma
In 5 of the 108 patients (4.6%), a new bedside surgical airway was performed by ENT or trauma surgery. A total of 7 other patients (6.5%) went directly to the OR for management, 3 of whom required no airway management after clinical assessment.
There is limited literature characterizing the nature of surgical airway emergencies and systems for reliable rescue. Berkow et al. demonstrated a reduction of emergency surgical airways from 6.5 to 2.2 per year after introduction of a comprehensive difficult airway program at a large academic medical center.
Available studies confirm that airway emergencies requiring a surgical airway are infrequent but associated with high potential for morbidity. These situations justify the immediate availability of expert teams and specialized equipment in an academic trauma setting. The American Society of Anesthesiologists Difficult Airway Guidelines emphasize the importance of early consideration of invasive airway techniques, which include calling for help and preparing equipment early.
Moreover, as we reported, ARR events commonly occurred during off-hours (57.3%) when an ad hoc system of phone calls and pages to locate expert consultants and obtain critical rescue equipment such as a fiberoptic scope, scalpel, or tracheostomy tray is neither feasible nor reliable.
Anesthesiologists in the United States rarely perform surgical airway access, and maintenance of skills is challenging. Nonphysician providers are often quite uncomfortable with surgical airways. In fact, we have found that surgical house staff, particularly those outside the ORL-HNS department, are uncomfortable with cricothyroidotomy techniques. The early presence of trauma and ORL-HNS surgeons facilitated collaborative, interdisciplinary assessment and planning. In seven cases, as we reported, these discussions resulted in patients being mobilized directly to the OR for airway interventions that might otherwise have resulted in failed intubation efforts. Those procedures were uniformly successful with minimal morbidity. Although the anesthesiologists intubated the majority of ARR patients, fiberoptic intubation of the difficult airway may have been facilitated by multispecialty expertise. Moreover, the preparedness for immediate conversion to surgical airway if intubation attempts fail represents an important aspect of high-reliability airway management. Similarly, the capacity to rapidly escalate care of the “at-risk” airway to minimize catastrophic sequelae is a relevant systems consideration. Our experience with the ARR and review of individual cases revealed the need to consider approaches to improve the system to enhance reliability and specially target particularly vulnerable populations, as we discuss in the following section.
Our review of the 124 activations of the ARR system reveals that even with excellent preparedness, emergent bedside surgical airways were associated with high morbidity despite achieving definitive airway access. The 5 bedside surgical airway patients fell into one of two categories: severe preexisting disease (particularly coagulopathy) and cervical spine (C-spine) disease with recent surgical fusion. Few interventions are likely to improve surgical airway management of a coagulopathic patient, but airway complications in C-spine patients may be preventable.
The specifics of the spine cases (Table 3, Patients 4 and 5) warrant further discussion for contrast in management. Patient 4 experienced an airway emergency after anterior cervical disk fusion. The surgery and anesthesia teams were assembled at the bedside quickly through the ARR system. Attempted fiberoptic intubation failed but was converted immediately to a surgical airway without anoxic brain injury. This case demonstrates the critical importance of the “golden minutes” of airway rescue. Anticipation, preparation, and early activation of a hardwired system according to defined criteria may make a critical difference. In contrast, Patient 5, who also had C-spine disease, suffered anoxic brain injury after failed intubation. A delay in activation of the ARR system resulted from a serial escalation of emergency teams—that is, rapid response, then anesthesia stat, then ARR. This very situation wastes the golden minutes and was a primary driver for the creation of the ARR system. Education on ARR and early activation was incorporated as a standard teaching in the Clinical Emergencies Committee orientation curriculum, which educates the rapid response nurse coordinators and first responder house staff.
High-Risk Extubation Protocol
The presence of multiple C-spine surgical patients in the surgical airway group has caused us to carefully consider risk reduction efforts for such patients. The ARR for Patient 4 occurred in the ICU within one hour of extubation. To address this, we have implemented a high-risk extubation and reintubation planning protocol. Intubated patients who meet high risk-criteria, which include C-spine immobilization, now have a red “high risk extubation” label placed on the endotracheal tube. The anesthesia team documents formal extubation and emergent reintubation plans for these patients, and an Extubation Risk Card with this information remains with the patient on transport and until discharge, A series of warning banners has been built into the EHR to alert clinicians to the high-risk extubation status, to trigger review of the extubation plan prior to extubation, and to require manual override if an extubation order is entered without documentation of a formal extubation plan. We believe that this process represents a systems-based practice benefit of highlighting the airway risks of C-spine patients to all care team members and promoting communication and awareness between services on airway-related concerns.
Rapid Notification and Review Process
Before our current effort, we had no formal structure for reporting, reviewing, and discussing ARR events or other airway-related safety issues. An Airway Safety Committee was formed shortly before this study began to serve as a central sounding board for hospitalwide airway issues. The committee, jointly chaired by ENT Surgery and Anesthesiology, maintains representation by all clinical and ancillary support departments involved in airway management. Recognizing the need for better real-time review of ARR, the committee implemented an e-mail alert system. The co-chair of the Airway Safety Committee is notified within 24 hours of any ARR activation. The events are briefly reviewed with the care teams involved to identify any systems-based issues that would benefit from intensive review or process improvement. In addition, we are working on a process to collect more detailed information on these events electronically in real time using REDCap (Research Electronic Data Capture) to facilitate additional analysis for subsequent optimization.
To date, this event review process has identified the importance of defined leadership at ARR events. For example, if the ARR is activated to support an emergency department clinician experienced in airway management, does the arriving airway team take over management or provide consultation and collaboratively manage the airway? Similarly, if the decision is made to proceed with a delicate fiberoptic intubation during an ARR and the ORL-HNS and anesthesia team members are both experienced in the technique, who should lead the procedure? Given the inherent variability of each situation, we continue to reinforce through team discussion and in situ simulation training the importance leadership designation, situational awareness, and closed-loop communication throughout an emergency response. In situ simulations of ARR events were conducted in selected high-risk areas that included the medical intensive care unit, the inpatient and outpatient postanesthesia care units (PACUs), and the cardiac electrophysiology suite. In situ simulation for staff training was reported to be highly effective by a group at Boston Medical Center during implementation of its Emergency Airway Response Team.
These simulation sessions have provided guidance for process optimization, systems learning, and understanding of team dynamics. In addition, multidisciplinary airway safety Grand Rounds have been instituted for case-based discussion and systems improvement. These learning sessions are organized by the Airway Safety Committee and include clinical area nurse managers, perioperative nursing teams, ORL-HNS, anesthesia providers, respiratory therapy, pulmonary medicine, and trauma surgery.
The ARR cohort had 23 patients with a tracheostomy in situ, and 6 patients required immediate operative intervention in the OR for new tracheostomy or tracheostomy revision. For many tracheostomy patients, orotracheal intubation will be difficult or impossible. Rescue via the stoma by surgical intervention and recannulation is the only viable alternative. We believe that having surgical expertise and equipment at the bedside throughout the airway management of tracheostomy patients is an important element of the ARR system. We conducted a separate in-depth analysis of these tracheostomy-related ARR events.
As a result of our findings, we have implemented bedside tracheostomy information cards that contain patient-specific tracheostomy details and emergency rescue algorithms and are receiving very positive feedback from all members of our multidisciplinary team.
After initial deployment of bedside cards for open tracheostomy procedures, we added specific cards for percutaneous tracheostomy and laryngectomy, for which nuanced airway differences may affect assessment and rescue. Respiratory therapists and emergency responders are now routinely referencing these cards during tracheostomy-related airway emergencies. In view of their response, affiliated hospitals have expressed interest in implementation, but we have not yet been able to measure direct clinical impact.
The study is limited by being retrospective in nature and by the lack of data from a preimplementation comparison group regarding outcomes. The total number of airway events that met ARR criteria may be underestimated by our study. Compliance with triggering the ARR in patients who meet criteria is not universal in our institution, which highlights a common obstacle to system change. Continued education about the resources and algorithms for airway emergencies is ongoing. Introduction of portable videolaryngoscopy in the latter part of the study, and increased training regarding the ARR system, airway safety Grand Rounds case discussions, and the Airway Safety Committee review process, may also have changed practice during the 40-month study period. Pilot initiatives at the end of the study period in 2014 involving extubation of high-risk C-spine surgical patients may have affected the rate of events over time and their characteristics.
The data were collected at an academic medical center with clinical house staff, trauma surgery expertise, 24-hour multispeciality in-house coverage, and deep technological resources for airway support. Clearly, this resource model is not generalizable to other institutions with different clinical staffing structures and technical support. Still, we believe that our experience may be useful to institutions seeking to better understand exposure to critical airway events, potential gaps in emergency airway rescue, and potential strategies to make their local system more robust. Other institutions will likely identify relevant elements of our system that they can adapt or adopt to meet local needs, with the recognition that successful management of critical airway emergencies requires broad diagnostic and technical skills that are best achieved by multidisciplinary expertise.
We continue to seek opportunities to refine our ARR system, which may include earlier activation, increased use of bridging techniques for oxygenation and ventilation prior to team arrival, measurement and reduction of the time from activation to established airway, and defined leadership frameworks during events.
in the perioperative environment by training anesthesiologists and surgeons, and in the RRT area, the nursing coordinators and clinical leadership of the Clinical Emergencies Committee. We will be expanding TeamSTEPPS training to the clinical emergencies response group and selected high-acuity wards in July 2017. We are optimistic that the principles of leadership, communication, and mutual support that are central to TeamSTEPPS will enhance the team dynamics in this critical interdisciplinary emergencies.
Emergency airway rescue systems must address a wide range of clinical scenarios that include difficult intubation, unplanned extubation, and tracheostomy decannulation, which represent a significant component of airway emergencies. The ARR system described represents a significant enhancement of the anesthesia stat system that typifies the airway emergency system at many institutions. A codified difficult airway rescue system with established criteria for activation and multidisciplinary participation addresses a gap in the management of difficult airways, failed intubation, and tracheostomy emergencies and successfully addressed our problem of ad hoc assembly of the right resources at the right time.
Acknowledgments. The authors acknowledge Eric Greenblatt, MD, and David S. Smith, MD, PhD, for their original work in designing and implementing the difficult airway identification and airway rapid response systems. The authors also thank all members of the Airway Safety Committee for their contributions to the implementation of the study and to efforts to improve the system. The authors are particularly grateful to Stacie Neefe, BSN, RN; Melissa Spahr, BSN, RN, CCRN; and Leah Davis, BSN, RN, CEN, and their colleagues for assistance in obtaining records and tracking airway rapid response activations.
Conflicts of Interest. All authors report no conflicts of interest.
Rapid-response systems as a patient safety strategy: a systematic review.
Joshua H. Atkins, MD, PhD, is Associate Professor, Department of Anesthesiology and Critical Care and Department of Otorhinolaryngology–Head and Neck Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia.
Christopher H. Rassekh, MD, is Associate Professor, Department of Otorhinolaryngology–Head and Neck Surgery, Perelman School of Medicine.
Ara A. Chalian, MD, is Professor, Department of Otorhinolaryngology–Head and Neck Surgery, and Patient Safety Officer, Perelman School of Medicine.
Jing Zhao, MD, formerly Visiting Scholar, Department of Anesthesiology and Critical Care, Perelman School of Medicine, and Professor and Vice Chair, Department of Anesthesiology, Peking Union Medical College Hospital, Beijing, is Chair, Department of Anesthesiology, China-Japan Friendship Hospital, Beijing, and Adjunct Associate Professor, Department of Anesthesiology and Critical Care, Perelman School of Medicine.