Cardiac Arrest Occurring in High-Rise Buildings: A Scoping Review

Out-of-hospital cardiac arrests (OHCAs) occurring in high-rise buildings are a challenge to Emergency Medical Services (EMS). Contemporary EMS guidelines lack specific recommendations for systems and practitioners regarding the approach to these patients. This scoping review aimed to map the body of literature pertaining to OHCAs in high-rise settings in order to clarify concepts and understanding and to identify knowledge gaps. Databases were searched from inception through to 6 May 2021 including OVID Medline, PubMed, Embase, CINAHL, and Scopus. Twenty-three articles were reviewed, comprising 8 manikin trials, 14 observational studies, and 1 mathematical modelling study. High-rise settings commonly have lower availability of bystanders and automatic external defibrillators (AEDs), while height constraints often lead to delays in EMS interventions and suboptimal cardiopulmonary resuscitation (CPR), scene access, and extrication. Four studies found return of spontaneous circulation (ROSC) rates to be significantly poorer, while seven studies found rates of survival-to-hospital discharge (n = 3) and neurologically favourable survival (n = 4) to be significantly lower in multistorey settings. Mechanical chest compression devices, transfer sheets, and strategic defibrillator placement were suggested as approaches to high-rise OHCA management. A shift to maximising on-scene treatment time, along with bundling novel prehospital interventions, could ameliorate some of these difficulties and improve clinical outcomes for patients.


Introduction
Emergencies occurring in high-rise buildings are becoming increasingly prevalent due to rapid urbanisation globally and they present significant challenges to prehospital emergency care. This is especially true for out-of-hospital cardiac arrest (OHCA), which is the most time-sensitive medical emergency. OHCA has generally poor survival rates [1], but favourable clinical outcomes are possible if essential care processes are rendered in a rapid and seamless manner, as exemplified by the "chain of survival" model [2]. Previous literature has consistently shown that prehospital interventions confer greater survival impact in OHCA relative to advanced hospital-based interventions, and the benefits of the latter are confined to those who receive timely prehospital interventions [3]. Thus, optimising the efficiency and effectiveness of emergency medical services (EMS) in providing resuscitative care, along with the public response to OHCA occurring in high-rise buildings, is of paramount clinical and scientific interest.
Real-world data from several regions have shown poorer clinical outcomes among OHCAs occurring in high-rise locations [4][5][6]. A study from Singapore went on to demonstrate a dose-response effect in the highly urbanised Southeast Asian city, with survival being lower with incremental floors above the ground [7]. The reasons for this effect are unclear, but the findings of delayed access to patients, increased transport times, and reduced rate of bystander cardiopulmonary resuscitation (CPR) shown in several studies suggest that disruption in the chain of survival (particularly early CPR) is part of the causal pathway [4][5][6]. In densely populated areas where large proportions of the population reside in high-rise residential buildings, EMS crews frequently encounter scene access and stretcher transport difficulties due to narrow corridors and enclosed elevators [5,8]. Rapid urbanisation and densification, which are happening at an increasing pace [9,10], further complicate this issue of vertical access and care delivery for EMS systems.
However, contemporary guidelines for resuscitation and EMS protocols lack specific recommendations for EMS systems and practitioners regarding their approach to patients in cardiac arrest in high-rise buildings. Furthermore, definitions and standards on the classification of high-rise buildings used in the literature are heterogenous, ranging from 3-storey apartment buildings without elevators [11] to those with more than 30 storeys and with elevator access to every floor [12].
This scoping review therefore aimed to map the body of literature pertaining to OHCAs occurring in high-rise settings in order to clarify concepts and current understanding, as well as to identify knowledge gaps. The themes investigated were the extent of the problem, outcomes and prognosis, unique challenges, and potential solutions.

Materials and Methods
This scoping review protocol was guided by recommendations from Arksey and O'Malley's framework and the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) [13,14] As the study designs and definition of high-rise differed across contexts with no clear indication of homogeneity in the literature, a scoping review, instead of a systematic review, was chosen to give an overarching perspective of the challenges, prognoses, unique approaches, and solutions in caring for OHCA occurring in high-rise settings.

Search Strategy
In consultation with a medical information specialist, a search strategy was developed employing various combinations of the keywords ((out-of-hospital cardiac arrest OR out of hospital cardiac arrest OR OHCA) AND (high-rise OR high rise OR height* OR vertical* OR skyscraper* OR tall OR elevator* OR stair*)). Five bibliographical databases were searched from database inception through to 6 May 2021: OVID Medline, PubMed, Embase, Cumulative Index to Nursing and Allied Health Literature (CINAHL), and Scopus. Abstracts were screened using Covidence (Melbourne, Victoria, Australia) by three independent researchers (M.X.H., A.F.W.H. and Q.X.N.). Full texts were obtained for all articles of interest and their reference lists were manually searched to identify additional relevant papers. Subject content experts were consulted to identify additional relevant articles. Conflicts were resolved by discussion and consensus amongst the study team (M.X.H., A.F.W.H. and Q.X.N.).

Selection Criteria
Articles were considered eligible for inclusion if they reported on OHCAs in a highrise building (in order to encompass all relevant papers despite heterogeneity of definitions, we adopted an inclusive definition of any building with individual floors located above ground). All study designs (case reports, case series, randomised controlled trials, and observational cohort studies) were included in the initial search. Subsequently, studies were excluded if they did not present primary data, did not have an accompanying English translation, or had no specific description of the type of high-rise components (i.e., floor levels, staircases, elevators) within the location of arrest. Abstracts with reported data but no full text available were referenced accordingly and their corresponding documents used as the full text.

Data Extraction
Relevant quantitative and qualitative data were extracted by two authors (M.X.H. and Y.A.N.) and cross-checked by a third author (A.F.W.H. or Q.X.N.). Categorical variables were presented as percentages while continuous variables were presented as mean and standard deviation (SD), or median and interquartile range (IQR). The data included several outcomes of interest, namely survival to discharge, neurologically intact survival at discharge, return of spontaneous circulation (ROSC), CPR quality measures (compression rate and depth), and operational time intervals between the EMS crew's arrival to and departure from the scene. A favourable neurological outcome was defined as a cerebral performance category (CPC) score of 1 or 2.

Geographical Distribution of Studies
As shown in Figure 2, studies reporting on high-rise OHCA were mostly found in densely populated and metropolitan regions such as South Korea (n = 7), Taiwan (n = 3), Singapore (n = 2), and Japan (n = 1). Apart from these 13 Asian studies, the remaining studies originated from Europe (n = 4) and North America (n = 6).

Unique Challenges of High-Rise Settings
High-rise OHCA poses a myriad of challenges to EMS personnel and first responders alike due to the vertical height. Most evident are the obstacles to scene access and egress. Travelling vertically within a building involves an additional layer of transport via an elevator or staircase. Certain floors may not have elevator access and occasionally the elevator may be too small for the stretcher [24]. Multiple elevator stops in a building with high human traffic interfere with EMS crew response as EMS responders are generally unable to override the elevator's mechanism to bypass floors and provide them with the necessary priority [6]. These barriers result in both time delays [18][19][20]26] and difficulty in maintaining CPR quality during transfer to the ambulance [11,21].   Elevator-based AED vs. lobby-based AED Arrest floor I = 0 vs. arrest floor I = 0.
Average response distance was shorter for elevator-based AED if the number of floors exceeded 3 4 of the ratio of ground-floor OHCA risk to above-ground floor risk plus 0.5. If not, a lobby-based AED had a shorter response distance. If the risk of OHCA was equal for each floor, an elevator-based AED would have a shorter average response distance.
Cardiac arrests in a tall building may experience faster response from an elevator-based AED, whereas a building with much higher risk on the ground floor compared to any above-ground floor would be better off with a lobby-based AED.  The call-to-scene time was a median of 7 min, which was shorter on a high floor for events in both homes and public places. Call-to-patient time for home events was significantly longer on a high floor (a median of 9 min).
Nature of setting (home vs. public) affects EMS response times to OHCA in high-rise buildings. Patient's prognosis is more likely to be affected by the structure and use of the building, rather than the floor height where the CA event occurred. Survival to hospital discharge: Significantly lower for patients residing on the third floor and above (2.6%) as compared to below the third floor (4.2%), p = 0.002 Time interval between arrival and patient contact:Significantly greater for higher floors compared with lower floors (4.9 ± 2.6 vs. 3.0 ± 2.0, p = 0.01) Use of AED: No significant differences although the rate of use was very low regardless of floor level (0.3% for lower floors and 0.4% for higher floors) OHCA on high floors had lower rates of survival to hospital discharge, and no survivors above the 25th floor. This is likely due to longer intervals from arrival of 911 responder to patient contact, and lower rates of initial shockable rhythm for high floor patients. The more deprived an area was, the longer EMS response times were due to the higher prevalence of EMS access constraints. There was significantly higher CPR quality when a reducible stretcher was used with mCPR during vertical transport in a high-rise building, specifically for nonflow fraction and proportion of adequate chest compression depth and rate.   Singapore A high-rise building was taken to be one that crew had to ascend at least one flight of stairs i.e., 2nd storey and higher. Ground-level building did not involve any stair climbing.
Prospective cohort study (n = 150 ambulance runs) Arrival-to-patient contact delay    OHCAs occurring in high-rise buildings also have a lower chance of being witnessed by a bystander who is able and willing to perform basic life support, as highlighted by Lee et al. (2018), who reported a common lack of trained bystanders in high-rise settings [27]. Compounding this problem is the limited access to defibrillators, which are most often located on the ground floor of high-rise buildings [31]. The additional time needed to fetch the equipment and reach the patient via the elevator is also proportional to the number of elevator stops encountered along the way [6].
A total of seven studies reported an adverse impact of vertically higher locations of arrest on EMS time intervals. With respect to the time between EMS arrival on-scene and arrival at patient's side, also known as T4 and T5, Silverman et al., Park [4,5,8,18,26]. Furthermore, the studies by Lateef and Park found that this finding remained applicable to the time interval between leaving the patient's location and the commencement of the ambulance's journey to the hospital, known as T6 and T7, respectively [8,26]. In Heidet et al.'s Parisian study, it was found that the number of floors in a patient's residence significantly affected EMS response times [22]. This was particularly prevalent in the most deprived areas of the precinct with more multistorey dwellings.
Conway et al. was the only study in this review that measured the time interval between arrival at-scene and prehospital defibrillation, termed curb-to-defib interval [19]. It was reported that tall buildings and buildings with larger volumes had significantly greater curb-to-defib intervals as compared to shorter buildings and those with smaller volumes.
There were seven studies, all manikin trials, which suggested that higher floors compromised CPR quality. Bekgoz et al. and Chen et al. reported poorer CPR quality (measured in terms of lower chest compression fractions) with manual compared to mechanical chest compressions when manual compressions were administered to the manikins during transport from the third to first floor [11,15]. Drinhaus et al. similarly reported a significantly lower proportion of good-quality compressions with adequate rate when manual compressions were performed en-route via a lift, turntable ladder, or staircase [21]. When a standard stretcher was used in Kim et al.'s 2016 study, there was a significantly smaller proportion of compression with adequate depth and rate when the manikins were transported from the sixth to first floor [24]. Conversely, Chi et al. found no significant differences in chest compression fraction between manual and mechanical CPR groups when manikins were transported from the thirteenth to first floor [17].

Prognosis and Outcomes
Given the aforementioned challenges, studies have reported congruent findings on the negative impact of high-rise settings on EMS time intervals, CPR quality, and the clinical outcomes of OHCA, namely survival and ROSC.
Three studies reported congruent findings of a negative impact of higher floor number on survival to hospital discharge. Drennan et al. found that patients living three floors and higher above ground had a significantly lower unadjusted survival-to-hospital discharge of 2.6% as compared to those who lived below the third floor (4.2%) [20]. Similarly, Lian et al. reported that the unadjusted rates of survival to hospital discharge declined from 2.7% for patients residing on the second floor to 0.7% for patients on the sixth floor [7]. This difference remained significant after adjustment for confounders. Sinden et al. similarly reported lower rates of survival to hospital discharge in OHCA patients when EMS arrival at scene to patient's side was delayed [29].
Four studies reported similar findings of the negative impact of higher floors on neurologically intact survival measured at hospital discharge or at 1 month. Kobayashi et al. and Sohn et al. both reported significantly lower unadjusted rates of neurologically intact survival for OHCA patients living 3 floors or higher above ground [25,30]. Choi et al. found that patients residing on a high floor of 3 storeys or more had significantly lower unadjusted rates of neurologically intact survival compared to if the OHCA took place in a public area [18]. Interestingly, if the arrest occurred at home, favourable neurological outcomes were more likely in patients residing on higher floors. Sinden et al. similarly reported lower unadjusted rates of neurologically intact survival for patients subjected to longer EMS arrival times [29].
Five studies reported on the outcomes of prehospital ROSC in their results. Chi et al., Kobayashi et al., and Sohn et al. showed a consistent detrimental effect of higher floors on patient ROSC [16,25,30]. These three studies reported a significantly lower rate of prehospital ROSC for patients living on the third floor and higher, compared to lower floors. In particular, the study by Chi et al. reported an odds ratio of 0.40 (95% CI 0.17-0.98) for ROSC in a vertical OHCA location. Heidet et al. reported that ROSC rates were significantly poorer only for the most deprived areas in a densely populated Parisian precinct, with 33% of buildings being multistorey residential blocks [22]. Contrarily, Choi et al. reported anomalous findings of a significantly higher rate of ROSC for residential OHCAs occurring at higher floors of three storeys and above as compared to lower floors [18]. The study was located in South Korea and defined residential areas as apartments, condominiums, and townhouses. All analyses were unadjusted for potential confounders.

Approaches and Solutions
Given the poorer outcomes of OHCA patients from high-rise settings and poorer quality of prehospital interventions, some studies have attempted to look at solutions to address these issues. Six manikin trials compared the use of mechanical CPR (mCPR) with manual compressions during scenario-based resuscitative procedures in high-rise settings [11,12,15,21,23,28]. Four of these trials reported positive findings for mCPR where its use led to higher chest compression fractions and greater proportions of guidelinecompliant chest compression rate and depth [11,12,15,21].
Jorgens et al. was the only trial that compared four different mCPR devices through a multistage route and found that the need for correction of pressure points was the lowest with the use of LUCAS-2 [23]. Finally, only one manikin trial reported the use of an active compression decompression (ACD) device and compared this with load-distributing band mCPR in an elevator setting [28]. It was reported that the use of LUCAS-2 mCPR compressions with the ACD had the lowest percentage change in compression depth and was recommended in elevator settings, which necessitate changes of stretcher positioning.
In terms of introducing specific equipment for procedural transport, two studies reported logistical interventions that improved CPR quality. Kim et al.'s 2016 study employed the use of a reducible stretcher that accommodated a hinged position during transport. CPR in the reducible stretcher group was found to have a significantly higher proportion of good compressions with adequate depth and rate as compared to the standard stretcher group [24].
Alternatively, Chi et al. employed the use of a transfer sheet in their 2020 study. Instead of placing the manikin on a stretcher before entering the elevator, the manikin was lifted with a transfer sheet and placed directly onto the elevator floor. It was reported that this led to significantly better compressions in terms of adequate depth and rate, and significantly shorter time intervals between moving the patient from the scene into the elevator [17].
Moreover, the strategic placement of defibrillators can contribute to a reduction in time to first defibrillation, as reported in Lee et al.'s 2018 study were AED placements in high-rise buildings increased willingness of inhabitants to perform CPR and utilise a defibrillator [27].
Of particular interest is Chan's 2017 study that developed a mathematical model of a high-rise building equipped with floors, one elevator, and one AED. Based on theoretical calculations, placing AEDs in elevators would benefit buildings only if they were sufficiently tall. If the OHCA risk on the ground floor were higher, such as in buildings with busier street level traffic or underground walkways, a lobby-based AED would be more beneficial [6].

Discussion
Across the included studies, it is apparent that high-rise settings pose significant challenges to EMS response to OHCA cases, resulting in poorer clinical outcomes for patients. This, however, does not change the fact that high-rise buildings are commonplace in many urbanised cities. Prehospital EMS systems could consider addressing the following gaps in the delivery of care for high-rise OHCA patients.
Firstly, protocols to override elevator systems in emergency situations can mitigate delays to scene access. In 2012, a patent was issued on a method of operating elevators during emergency situations [32]. This involved elevator cars being recalled to the ground floor and temporarily taken out of service till the arrival of emergency medical personnel, who can use a unique key and travel to designated floors within the building to attend to casualties or evacuate residents. Delays to extrication can likewise be reduced with specific equipment such as transfer sheets and stretchers which can accommodate tight spaces, as reported in the manikin trials [17,24], although the actual deployment of these equipment for real-life situations remains to be elucidated.
Secondly, there is value for EMS crews to maximise treatment opportunities, especially during times where patient movement is minimal and where procedural transfers are not yet necessary. The time-critical urgency of OHCAs coupled with the constant reminders for EMS crew to rapidly transport patients to secondary or tertiary care facilities could at times be an albatross that distracts EMS personnel from providing quality and vital ALS treatment on-scene.
Lengthening on-scene time allows EMS services operating in highly urbanised environments to implement novel, bundled interventions and team-led high-performance CPR. Ambulance services in well-developed EMS systems, such as that of Victoria, Australia, have formalised a delay in mechanical CPR during the crucial early stages of resuscitation. This underlines the importance of staying on-scene for the delivery of optimal basic and advanced life support to achieve ROSC [33]. Liao et al.'s 2019 manikin trial reported the use of an ACD together with a LUCAS-2 mechanical CPR device, which led to better CPR quality in the elevator. This bundling of interventions has been found to significantly improve cerebral perfusion pressure in porcine studies of cardiac arrest [34], while other interventions such as head-up CPR and an impedance threshold device (ITD) have also been reported as effective solutions as part of an optimal bundle of OHCA management [35][36][37]. While these have yielded promising findings in porcine models, the transferability of such interventions to real-world OHCA patients in a dynamic prehospital environment remains to be elucidated.
Thirdly, timely CPR may be better achieved with improved public education programmes, especially for family members of at-risk patients (e.g., chronic heart failure). Given that bystander and lay rescuer involvement have been highlighted as a potential issue in high-rise settings, systemic, nationwide strategies that leverage technology to bring trained rescuers closer to OHCA victims are promising steps forward in tackling the challenge of high-rise OHCAs. In Singapore, the myResponder application is used to notify trained responders of cardiac arrest cases within a 400 m radius and the location of the nearest defibrillator. The responder may be located on a different floor in the same high-rise building, but would still be able to respond swiftly [38]. This concept of training members of the public and utilising them as prehospital manpower is a promising approach, and is practised in a similar fashion in London with the GoodSAM application [39] and also echoed by the European Resuscitation Council in their statement on teaching CPR to children in schools [40].
The prudent deployment of trained first responders in high-rise buildings in the form of fire or cardiac arrest wardens could also augment early access to OHCA victims. Defibrillators could also be issued to first responders who are constantly on the move, such as train drivers or drivers of hired cars and taxis. A recent collaboration between the Singapore Civil Defence Force and the Singaporean private car hire company Grab equipped private hire drivers with AEDs as part of the AED-on-Wheels programme [41].
This allows drivers to respond swiftly to any location when notified of an incident within their radius.
Fourthly, the concept of energy ratings for buildings can perhaps be extended to health ratings in the context of prehospital measures such as presence of AEDs, cardiac arrest wardens, and trained responders as a percentage of the resident population. This evaluation of a building's safety can be applied to residential and nonresidential spaces and shed light on the areas that need more robust AED deployment and bystander training.
Lastly, given that contemporary EMS response time data have been mainly centred on call-to-curb intervals which lack data on building height, floor levels, and elevator or AED availability, there could be value in the creation of prehospital datasets that are unique to high-rise settings. Variables such as the number of storeys and even the type of residential unit could be recorded as part of ambulance case records and transferred to registry data. This information could furnish valuable insight into space constraints and the difficulties impeding the smooth execution of team resuscitative procedures due to certain factors such as the lack of a 360 degree access and overview of the patient.
As an extension to unique prehospital OHCA datasets, a linkage of OHCA data registries with other data repositories such as socioeconomic data or urban density data could prove useful in the analysis and evaluation of OHCA resuscitative performance. Heidet et al.'s 2020 study successfully retrieved census data on socioeconomic status stratified by geographical areas, and linked that with a validated calculation of the degree of deprivation associated with each of these areas [22]. If such linkage of data is replicated in more EMS systems worldwide, the findings could provide important insight to the unique but less-reported-on barriers EMS systems face in different geographical contexts and demographic groups, hence informing policy changes and improvements.

Limitations
The findings of this scoping review are limited by retrospective observational evidence and manikin-dominated trial designs. Compared to manikins, compression depth and rate inevitably differs in accuracy when measured on human patients of varying body weight and height. Secondly, while the variable of EMS time intervals has been quantified and analysed in a number of studies, other reported barriers of high-rise settings have been primarily studied in a qualitative manner. Further randomised, controlled trials (RCTs) with human subjects should be conducted to ascertain the efficacy of proposed strategies as well as the impact of high-rise buildings on OHCA clinical outcomes.

Conclusions
High-rise OHCAs are a challenge for prehospital EMS crew and care systems due to often ineluctable delays in scene access and egress and inherent space constraints. A focus on maximising on-scene treatment time, along with bundling novel prehospital interventions, could ameliorate some of these difficulties and improve patient outcomes.

Data Availability Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.