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FIREFIGHTER INCIDENT REHABILITATION: INTERPRETING HEART RATE RESPONSES Denise L. Smith, PhD, Jeannie M. Haller, MS, Ron Benedict, MS, Lori Moore-Merrell, PhD ABSTRACT The primary objective of this observational
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FIREFIGHTER INCIDENT REHABILITATION: INTERPRETING HEART RATE RESPONSES Denise L. Smith, PhD, Jeannie M. Haller, MS, Ron Benedict, MS, Lori Moore-Merrell, PhD ABSTRACT The primary objective of this observational study was to document the heart rate (HR) responses of firefighters during incident rehabilitation following firefighting activity in a high-rise building with a simulated fire on the 10th floor. Additionally, the study investigated potential factors, including firefighting workload, ambient temperature, firefighter movement, and individual characteristics, that may have affected HR during recovery. Firefighters (n = 198) were assigned to perform a simulation of fire suppression, search and rescue, or material support during one of six firefighting trials that involved different crew sizes and ascent modes, and were performed in different environmental conditions. After completing the simulated firefighting activity, firefighters reported to a rehabilitation area on the 8th floor. The rehabilitation area was staffed by firefighter/paramedics. HR was monitored continuously during simulated firefighting activity and a 15-minute rehabilitation period. Average HR during rehabilitation (HR mean ) was calculated and compared across trials. Simulated firefighting activity was performed in the summer in Virginia, USA, and ambient conditions varied among trials (mean ± SD: 31 ± 4 C; 46 ± 15% relative humidity; 32 ± 4 C heat index). Duration of simulated firefighting activity ranged from 12.0 to 20.3 minutes among trials (mean: 15.4 ± 5.2 minutes). Over all trials, mean peak HR during simulations was 173 ± 18 beats min 1. Mean HR over all trials at entry into rehabilitation was 149 ± 24 beats min 1. Following 15 minutes of recovery, mean HR over all trials Received November 12, 2014 from the the First Responder Health and Safety Laboratory, Department of Health and Exercise Sciences, Skidmore College, Saratoga Springs, New York (DLS, JMH), and the International Association of Fire Fighters, Washington, DC (RB, LMM). Revision received March 20, 2015; accepted for publication March 20, Funding for the parent study was provided through DHS/FEMA s Grant Program Directorate for FY 2010 and FY 2011 Assistance to Firefighters Grant Program Fire Prevention and Safety Grants [EMW-2010-FP-01276] and [EMW-2011-FP-00588]. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. The authors would like to formally thank the firefighters who participated in the high-rise drills and this study. We also gratefully acknowledge that Zephyr provided the physiological monitors that were used in this study. Address correspondence to Denise L. Smith, PhD, First Responder Health and Safety Laboratory, Department of Health and Exercise Sciences, Skidmore College, Saratoga Springs, NY 12866, USA. E- mail: doi: / was 126 ± 23 beats min 1. Exploratory analyses revealed that higher workload during firefighting (stair trials), higher ambient temperature ( 30 C), greater movement during rehabilitation ( 0.1 g-force), higher age ( 45 years), and higher BMI ( 30.0 kg m 2 ) were associated with higher HR responses during rehabilitation. During complex emergency operations, emergency medical service personnel will likely encounter considerable variability in HR responses upon initial evaluation and throughout rehabilitation. Following one bout of firefighting activity during a simulated fire scenario, HR decreased but remained elevated well above resting values following 15 minutes of rehabilitation. Based on current fire service recommendations, the majority of firefighters (88%) would not have been released from rehabilitation and eligible for reassignment after a 15-minute rehabilitation period following a brief bout of simulated firefighting activity. Key words: medical monitoring, cardiac strain, firefighting PREHOSPITAL EMERGENCY CARE 2015;Early Online:1 9 INTRODUCTION Firefighting involves strenuous physical activity while wearing heavy and insulating personal protective equipment (PPE) in extreme conditions. Even short bouts of firefighting have been reported to lead to near maximal heart rates (HR) and elevated core temperatures. 1 3 Additionally, studies have demonstrated that firefighting results in dehydration, 4 decreased plasma volume, 3 decreased stroke volume, 2 and a procoagulatory state. 5 7 Furthermore, increased arterial stiffness 8 and cardiac changes consistent with cardiac fatigue 9 have been documented following prolonged firefighting. Due to the physiological strain and the inherently dangerous nature of firefighting, several fire service organizations have recommended the use of incident rehabilitation to allow for recovery from operations and to ensure that members can safely continue with emergency operations. 10,11 In recognition of the importance of incident rehabilitation, the National Fire Protection Association (NFPA) published NFPA 1584: Standard on the Rehabilitation Process for Members During Emergency Operations and Training Exercises, 12 which calls for the implementation of rehabilitation operations whenever emergency operations or training exercises pose a safety or health risk to members. Incident scene rehabilitation has been defined as an intervention designed to mitigate the physical, physiological, and emotional stresses of firefighting to improve performance and decrease the likelihood of on-scene injury or death. 10,13 Rehabilitation includes 1 2 PREHOSPITAL EMERGENCY CARE 2015 EARLY ONLINE relief from climatic conditions, rest and recovery, active and/or passive cooling or warming as appropriate, rehydration, calorie and electrolyte replacement, medical monitoring by emergency medical services (EMS) personnel throughout rehabilitation, medical treatment in accordance with local protocol, member accountability, and release. 10,12 For medical monitoring, observation of visual signs and symptoms is considered the most reliable means of evaluation, whereas vital sign measurements are recommended for use in establishing a baseline and as indicators of health or safety concerns. 10,12 HR is the most easily measured vital sign and arguably the most reflective of cardiovascular strain and physical workload. 14,15 Hence, there is considerable interest in establishing guidelines or thresholds, especially for HR, upon which to base the need for medical treatment or release from rehabilitation. While some agencies provide a guideline of an HR less than 100 or 110 beats min 1 for release from rehabilitation, this guideline was not firmly established based on data from live-fire operations; rather it was based on allowing HR to return to near normal resting rates, which range from 60 to 100 beats min The ability to establish threshold levels based on vital signs is hampered by a lack of data on normal recovery and any data on abnormal recovery associated with adverse events. Several research studies have documented physiological responses during the application of various strategies to enhance recovery during rehabilitation following simulated firefighting activities. 5,16 22 In general, the tightly controlled conditions during rehabilitation in these studies were necessary to investigate the effects of different interventions; however, the conditions may not have reflected the true activity of firefighters in rehabilitation on the fireground. In fact, there is a lack of data available about recovery of HR following operations that mimic complex, large-scale fireground operations in which firefighters report to a rehabilitation area that is less controlled than what is provided in most research studies. Therefore, the purpose of this study was to document the HR responses of firefighters during incident rehabilitation following firefighting activity in a high-rise building with a simulated fire on the 10th floor on a summer day in the Mid- Atlantic region of the United States. Additionally, the study investigated the effect of different trials (deployments including different crew sizes [4-, 5-, or 6-person crews] and modes of ascent [stairs and elevator]), environmental conditions, and individual factors on HR responses. Participants METHODS Participants were career firefighters from the Washington, DC metropolitan area. Participants provided written informed consent after being provided with a detailed description of the study. The Skidmore College institutional review board approved this study. Experimental Procedures A large study that evaluated the effectiveness of crew size (3-, 4-, 5-, 6-person), ascent mode (stairs vs. elevator), and size of full alarm assignment (low vs. high) on time to complete simulated fire suppression activities was undertaken during the summer of The present study was conducted using six of the trials from the parent study. Selected trials included 4-, 5-, and 6-person crews and each mode of ascent: trial 1, 4- person stairs (ST); trial 2, 4-person elevator (EL); trial 3, 5-person ST; trial 4, 5-person EL; trial 5, 6-person ST; trial 6, 6-person EL. Although the parent study included 3-person crews, we did not include those trials in this analysis because 3-person crews were combined to form larger crews and thus did not provide unique data during recovery. The study was conducted in a vacant 13-story commercial building. The scenario consisted of a simulated fire on the 10th floor of the high-rise building with multiple fire engines and trucks initially deployed to perform fire suppression, search and rescue, and material support assignments. As reported elsewhere, 23,24 digital fire displays and water vapor smoke generators were used to simulate heavy fire and smoke, creating realistic visibility conditions but no thermal load. Props were constructed to model an open floor plan containing 96 cubicles on the 10th floor (fire floor) and four distinct areas with offices distributed throughout on the 11th floor. Sand-filled hose lines were used to approximate the weight and feel of a charged hose line to avoid potential water damage to the building. The scenario involved two victims: one located on the fire floor and a second located on the floor above the fire. A safety officer was assigned to the experiments to ensure compliance with relevant National Fire Protection Association standards. 25 Following a briefing that included an explanation of experimental procedures and orientation to the fireground props, firefighters donned their own personal protective equipment over their typical station uniform. The PPE was department-issued and consisted of turnout coat and pants, flash hood, gloves, boots, helmet, and selfcontained breathing apparatus. Engine crews received assignments typically associated with fire suppression activities and truck crews received assignments associated with search and rescue. Additionally, one truck crew was assigned to transport material from the lobby to the staging area on the 8th floor. Only firefighters who engaged in a simulation of fire suppression, search and rescue, or material support activities were included in this study. In all trials, participants completed only one bout of work. D. L. Smith et al. HEART RATE DURING FIREFIGHTER INCIDENT REHAB 3 Rehabilitation Area The rehabilitation area was established adjacent to the staging area on the 8th floor. Firefighter/paramedics with advanced life support certification established and managed the rehabilitation area. In all trials (stairs and elevator), firefighters took the stairs to the rehabilitation area after completing their assigned task or depleting their air supply. All firefighters used 45-minute air cylinders; however, crews were paged following 15 minutes of on air time to ensure no one ran out of air. The training protocol required a mandatory 15- minute rehabilitation period, which was more conservative than the minimum time (10 minutes) set forth in NFPA Within the rehabilitation area, firefighters received a physical assessment, rest, hydration, evaluation, treatment (if necessary), continual monitoring of their physical condition, transportation for additional evaluation (if necessary), and reassignment to staging (when appropriate). Firefighters were required to take off their helmets, hoods, turnout coats, and gloves. At the discretion of the individual firefighter, the turnout pants could be lowered to facilitate cooling. Additionally, firefighters were required to consume a minimum of one 12-oz (0.36 L) bottle of water before being sent to the staging area for possible reassignment. Firefighters were permitted to move around within the rehabilitation area to mimic realistic conditions. Once moved to staging, firefighters could replace their air cylinders and continue to rehabilitate while awaiting reassignment. In order to provide cooling, the rehabilitation area was cooled with two industrial-sized air conditioners and three portable air conditioning units with high-powered fans for greater air circulation. The rehabilitation area was cooled to 27 C, which was substantially cooler than the fire floor ( C) but still warmer than ideal conditions for evaporative cooling. Measurements Before the trial commenced, participants were fitted with a physiological status monitor (BioHarness 3, Zephyr Technology, Annapolis, MD) that was mounted on an adjustable, elastic strap worn around the chest. Following the trial, the physiological status monitor was removed and downloaded to a personal computer. Simulated firefighting activity was identified as beginning when the crew left the lobby to ascend to the staging area and terminating upon the completion of the assignment or relief by another crew. The highest HR during simulated firefighting activity was designated as the peak HR during the assignment. HR at the time the firefighter reported to rehabilitation was identified from the data file. HR and activity data were averaged over 1-minute intervals during the 15-minute rehabilitation period. The mean HR during rehab (HR mean ) was computed for each firefighter. Movement during rehabilitation was assessed using the activity measurement from the physiological status monitor, which reflects acceleration (expressed in g- force) computed from a three-dimensional accelerometer. Activity scores between 0.2 and 0.8 g-force reflect moderate activity (walk/jog). Height and body mass were self-reported. Environmental Conditions Trials took place on different days in June and July of 2012 between 0800 and 1200 hours. Ambient temperature and relative humidity at the time of the trials were recorded 26 and used to calculate heat indices. Analytical Methods Mean data were used to describe HR recovery over time in each trial. To determine if HR in recovery varied across trials, HR mean was compared among trials using a one-way (trial) ANOVA. When a significant F- ratio was obtained, a post hoc analysis with Bonferroni correction was used to identify differences. Potential factors that may account for differences among trials were subsequently investigated. For these analyses, HR data were stratified according to a single factor: firefighting workload (stairs or elevator), ambient temperature ( 30 Cor 30 C), movement during rehabilitation (activity 0.1 or 0.1 g-force), age ( 45 or 45 years of age), and body mass index (BMI; 25.0, , or 30.0 kg m 2 ). Comparisons of peak HR during work by stratified factors were made using independent t-tests for normally distributed data and nonparametric tests for non-normal distributions. Analyses were performed using SPSS version 21 (SPSS, Inc., Chicago, IL). Values are means ± SD unless indicated otherwise. Statistical significance was set at p RESULTS Table 1 presents descriptive characteristics of the 198 participants with viable HR data. On average, participants were 34.2 ± 7.8 years of age and had served 9.9 ± 7.4 years in the fire service. Six firefighters were women. During the trials, two firefighters were treated for dehydration and held in rehabilitation until all vital signs returned to normal range; otherwise, all firefighters completed rehabilitation and then participated in clean-up operations. Table 2 presents the ascent mode, crew size, and ambient conditions for the six trials. Ambient conditions varied considerably among trials, with 10 C ranges for temperature and heat index. Furthermore, the time needed to complete the assignments varied among trials (range: minutes; mean ± SD: 15.4 ± 5.2 minutes). 4 PREHOSPITAL EMERGENCY CARE 2015 EARLY ONLINE Variable TABLE 1. Descriptive characteristics of firefighters Mean + SD Age (yr) (n = 184) 34.2 ± 7.8 Height (cm) (n = 151) 179 ± 8 Body mass (kg) (n = 150) 89.0 ± 15.5 Body mass index (kg m 2 )(n = 150) 27.8 ± 4.8 Years of service (n = 151) 9.9 ± 7.4 N = 198 for heart rate data included in analyses; n s indicated for participants who self-reported descriptive characteristic (body mass index was calculated). Figure 1 depicts peak HR during the simulated firefighting activity (peak work) and the time course of recovery of HR during rehabilitation by trial. Upon entry in rehabilitation, HR averaged 149 ± 24 beats min 1 and ranged from 138 to 158 beats min 1 for the six trials. There was a significant effect of trial on HR mean during rehabilitation (p 0.001). HR mean was significantly lower in trials 1, 2, and 4 (127 ± 13, 128 ± 18, and 127 ± 18 beats min 1, respectively) compared with trials 3 and 5 (142 ± 18 and 143 ± 15 beats min 1, respectively). Although HR mean differed among trials, the pattern of HR responses in most trials was fairly consistent, with HR decreasing and then leveling off around minute 9 of recovery. On average, HR was 126 ± 23 beats min 1 (range: beats min 1 )after 15 minutes of recovery. Considering criteria recommended by fire service agencies to determine the disposition for personnel assigned to rehabilitation to parse the data, 10,12 23 of the 198 firefighters had an HR less than 100 beats min 1 and 93 firefighters had an HR less than or equal to 120 beats min 1 at minute 15. Although Figure 1 depicts the general tendency for HR to decrease over time in recovery, HR did not always decline continuously as would be expected in a seated recovery. Examination of the activity data revealed that firefighters did not necessarily remain seated during recovery (Figure 2). On average, activity decreased initially, reaching a minimum (0.09 ± 0.07 g- force) at minute 7. Figure 2 shows marked increases in activity in several trials in the last several minutes of the 15-minute rehabilitation period. Figure 3 displays the effect of differences in work, ambient temperature, movement during rehabilitation, and individual characteristics on HR responses during the six trials. HR was higher at peak work (p 0.001) and in the early phase of rehabilitation following the stair trials compared with the elevator trials; however, HR converged as time progressed (panel A). Stratification by temperature (panel B) indicated that higher ambient temperatures ( 30 Cvs. 30 C) were associated with higher ( 10 beats min 1 ) peak HR during work (p = 0.002) that persisted throughout the rehabilitation period. A comparison of more active and less active (during rehabilitation) firefighters showed that HR responses reached a lower level (110 vs. 126 beats min 1 ) in the less active group (panel C). On average, firefighters 45 years of age attained higher peak HR than older firefighters during work (p = 0.011) and HR responses in the younger group were slightly higher throughout rehabilitation (panel D).PeakHRduringworkdidnotdifferbyBMIclass (p = 0.744). During rehabilitation HR responses were similar during the first 7 minutes of rehabilitation, after which HR remained higher in obese firefighters (BMI 30.0 kg m 2 ) than nonobese firefighters (BMI 30.0 kg m 2 ) (panel E). DISCUSSION The aim of this study was to describe HR responses during emergency
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