Rescuer Fatigue: Standard versus Continuous Chest-Compression Cardiopulmonary Resuscitation

Rescuer Fatigue: Standard versus Continuous Chest-Compression Cardiopulmonary Resuscitation Joseph W. Heidenreich, MD, Robert A. Berg, MD, Travis A. Higdon, MD, Gordon A. Ewy, MD, Karl B. Kern, MD, Arthur B. Sanders, MD Abstract Objectives: Continuous chest-compression cardiopulmonary resuscitation (CCC-CPR) has been advocated as an alternative to standard CPR (STD-CPR). Studies have shown that CCC-CPR delivers substantially more chest compressions per minute and is easier to remember and perform than STD-CPR. One concern regarding CCC-CPR is that the rescuer may fatigue and be unable to maintain adequate compression rate or depth throughout an average emergency medical services response time. The specific aim of this study was to compare the effects of fatigue on the performance of CCC-CPR and STD-CPR on a manikin model. Methods: This was a prospective, randomized crossover study involving 53 medical students performing CCC-CPR and STD-CPR on a manikin model. Students were randomized to their initial CPR group and then performed the other type of CPR after a period of at least two days. Students were evaluated on their performance of 9 minutes of CPR for each method. The primary endpoint was the number of adequate chest compressions (at least 38 mm of compression depth) delivered per minute during each of the 9 minutes. The secondary endpoints were total compressions, compression rate, and the number of breaks taken for rest. The students performance was evaluated on the basis of Skillreporter Resusci Anne (Laerdal, Wappingers Falls, NY) recordings. Primary and secondary endpoints were analyzed by using the generalized linear mixed model for counting data. Results: In the first 2 minutes, participants delivered significantly more adequate compressions per minute with CCC-CPR than STD-CPR, (47 vs. 32, p = 0.004 in the 1st minute and 39 vs. 29, p = 0.04 in the 2nd minute). For minutes 3 through 9, the differences in number of adequate compressions between groups were not significant. Evaluating the 9 minutes of CPR as a whole, there were significantly more adequate compressions in CCC-CPR vs. STD-CPR (p = 0.0003). Although the number of adequate compressions per minute declined over time in both groups, the rate of decline was significantly greater in CCC-CPR compared with STD-CPR (p = 0.0003). The mean number of total compressions delivered in the first minute was significantly greater with CCC-CPR than STD-CPR (105 per minute vs. 58 per minute, p < 0.001) and did not change over 9 minutes in either group. There were no differences in compression rates or number of breaks between groups. Conclusions: CCC-CPR resulted in more adequate compressions per minute than STD-CPR for the first 2 minutes of CPR. However, the difference diminished after 3 minutes, presumably as a result of greater rescuer fatigue with CCC-CPR. Overall, CCC-CPR resulted in more total compressions per minute than STD-CPR during the entire 9 minutes of resuscitation. ACADEMIC EMERGENCY MEDICINE 2006; 13:1020 1026 ª 2006 by the Society for Academic Emergency Medicine Keywords: cardiopulmonary resuscitation (CPR), basic life support (BLS), resuscitation From the Department of Pediatrics (RAB), Steele Memorial Research Center, and Department of Medicine, Section of Cardiology (GAE, KBK) and Department of Emergency Medicine (ABS), Sarver Heart Center, University of Arizona, Tucson, AZ; Scott & White Department of Emergency Medicine, Texas A&M College of Medicine (JWH), Temple, TX; and Department of Anesthesia, University of Florida (TAH), Gainesville, FL. Received February 26, 2006; revisions received June 7, 2006, and June 18, 2006; accepted June 21, 2006. Presented at the American College of Emergency Physicians Scientific Assembly, Washington, DC, September 27, 2005. Address for correspondence and reprints: Joseph W. Heidenreich, MD, Department of Emergency Medicine, Scott & White Hospital, 2401 South 31st Street, Temple, TX 76508. Fax: 254-724-1044; e-mail: phojesco@yahoo.com. 1020 ISSN 1069-6563 PII ISSN 1069-6563583 ª 2006 by the Society for Academic Emergency Medicine doi: 10.1197/j.aem.2006.06.049

ACAD EMERG MED October 2006, Vol. 13, No. 10 www.aemj.org 1021 Bystander cardiopulmonary resuscitation (CPR) clearly improves survival for victims of cardiac arrest, drowning, and respiratory arrest. 1 5 With more than 250,000 sudden cardiac arrests every year, the majority of which occur out of hospital, bystander CPR has the potential to improve survival. There is no doubt that a need exists to encourage the public to participate in bystander CPR. Recently, continuous chest-compression CPR (CCC- CPR) has been advocated as an alternative to standard CPR (STD-CPR). 6 8 Studies have shown that CCC-CPR delivers substantially more chest compressions per minute and is easier to remember and perform than STD-CPR. 9 12 Animal and clinical investigations show that CCC-CPR is at least as good as STD-CPR in terms of survival and neurologic outcome. 13 20 CCC-CPR also encourages bystander intervention because it negates the reticence of potential rescuers regarding mouthto-mouth contact. One concern regarding CCC-CPR is that as a result of fatigue, the rescuer may not be able to maintain adequate compression rate or depth throughout an average emergency medical services (EMS) response time. Several experimental studies have compared how rescuers perform CCC-CPR versus STD-CPR on a manikin model, but none adequately have addressed the issue of rescuer fatigue. 9 12,17 20 The specific aim of this study was to compare the effects of fatigue as measured by compression depth, rate, and pauses for rest, on the performance of CCC-CPR vs. STD-CPR on a manikin model. METHODS Study Design This study was a prospective, randomized crossover study. This design was chosen to show differences in the performance of two different types of CPR by using each subject as his or her own control. This study was approved by our university s institutional review board, and written informed consent was obtained from each participant. Study Setting and Population First- and second-year medical students were recruited via a class presentation to participate in a study comparing rescuer fatigue for two different types of CPR. They were told that they would each need to perform two different types of CPR on a manikin for 9 minutes, with each trial separated by a minimum of two days. Each subject received $50 for participation in the experiment. Subjects were enrolled on a first-come, first-served basis. Study Protocol Each of the students was randomized by coin toss to either CCC-CPR or STD-CPR first and was scheduled for two sessions that were two, three, or four days apart. Students performing STD-CPR were told simply that they needed to perform 15:2 single-rescuer CPR (15 compressions at a rate of 100 per minute, followed by two mouth-to-mouth rescue breaths), repeated for 9 minutes. Students performing CCC-CPR were told to deliver chest compressions at a rate of 100 per minute for a period of 9 minutes. No demonstration was given. All students were told that if they were too tired to continue, they could stop and rest until they felt they could resume CPR. They were allowed to take as many breaks as they needed during the 9 minutes. A break was considered any pause in compressions and ventilations that lasted 5 seconds or more. All students were told that they need not check for pulse or breathing at any time during the simulation for either type of CPR. Face shields were placed on each manikin for STD-CPR. No clock in the room was visible, and students were not told how much time remained at any point during the simulations. Each student also completed a brief form requesting demographic information, including age and gender as well as prior CPR experience including classroom, teaching, and clinical exposure. Observations of resuscitation simulations were recorded by using Recording Resusci Anne manikins (Laerdal, Wappingers Falls, NY). The full recording capabilities of the Resusci Anne manikins were enabled to include quantitative and qualitative data on both chest compressions and rescue breaths. Specifically, manikins reported compression depth, frequency, and placement, as well as ventilation volume and frequency. In addition to summary information, the manikins produced realtime analog data strips showing all compressions and ventilations for each simulated resuscitation. Measures The primary endpoint was the number of adequate compressions delivered per minute. An adequate compression was considered to be any compression achieving 38 mm or more of compression depth, as reported by the Skillreporter Resusci Anne manikin. Aspects such as incomplete release, bad positioning, and excessive compression depth were not evaluated. Secondary endpoints included total number of compressions delivered per minute, compression rate, and number and length of breaks taken to rest. The term total compressions per minute refers to the exact number of compressions delivered in a 1-minute period, and compression rate refers to the number of compressions that was delivered in an uninterrupted 15-compression span or, if there were no pauses for ventilation for the entire minute, then this was the exact number of compressions that was delivered in a 1-minute period. Thus, an individual performing STD-CPR at the American Heart Association (AHA) recommended compression rate of 100 per minute, but with significant interruptions for ventilations, might achieve only 50 60 total compressions per minute. Any pause of 5 seconds or more, during which neither compressions nor rescue breaths were attempted, was considered a break for rest. Ventilations delivered during STD-CPR also were recorded as either adequate (tidal volume of >700 ml) or inadequate (tidal volume of <700 ml). Data Analysis Statistical analysis of the data was performed by using SAS 8.2 software (SAS Institute, Cary, NC). Initial data analysis demonstrated a Poisson distribution; therefore, comparisons between CPR methods and selected individual time points were made by using paired generalized linear mixed (GLIMMIX) model for count data. Also, the GLIMMIX procedure was used to examine how the

1022 Heidenreich et al. RESCUER FATIGUE: STANDARD VS. CCC-CPR difference between CCC-CPR and STD-CPR changed over time. For evaluating whether the number of adequate compressions per minute declined at a greater rate in STD-CPR than in CCC-CPR, a delta value was used for each participant at each minute. RESULTS Table 1 Demographic Characteristics of Participants Characteristic Data Gender Male 23 (43) Female 30 (57) Age, yr SD (range) 27 6 (19w54) BLS instructor? Yes 10 (19) No 42 (79) N/A 1 (2) Number of CPR classes taken 1 10 (19) 2 17 (32) 2 3 1 (2) 3 7 (13) 3 4 1 (2) 4 9 (17) >5 7 (13) N/A 1 (2) Performed CPR before? Yes 7 (13) No 46 (87) Data are n (%) unless otherwise indicated. BLS = basic life support; N/A = data missing. Figure 1. Adequate compressions per minute for minutes 1to9. Fifty-seven medical students agreed to participate and provided informed consent before their participation in the project. Of the 57 students involved in the testing, data from 4 students were excluded from the final analysis because they did not return for their second session. Therefore, data from 53 students were obtained. Demographic data on the study participants are shown in Table 1. Figure 1 shows the mean number of adequate compressions for each group in each of the 9 minutes. The mean number of adequate compressions was significantly greater in CCC-CPR than in STD-CPR in the first 2 minutes (1st minute: 48 vs. 33, p = 0.006; and 2nd minute: 41 vs. 30, p = 0.04). By the 3rd minute of CPR, the difference no longer was significant, and in the 9th minute, the absolute number of effective compressions was higher in the STD-CPR group, although this difference was not statistically significant. The number of adequate compressions per minute trended down over time in both CCC-CPR (p < 0.0001) and STD-CPR (p = 0.0002). The delta adequate compressions, or CCC-CPR adequate compressions minus STD-CPR adequate compressions, also trended down over time (p = 0.0001), indicating that adequate compressions declined over time more rapidly in CCC-CPR than in STD-CPR. Overall, there were more adequate compressions delivered during CCC-CPR than in STD-CPR (p < 0.0001). Figure 2 shows the compression rate (the rate of at least 15 consecutively performed compressions) for minutes 1 through 9. The compression rate for CCC-CPR ranged from 103 to 108 compressions per minute and did not change over time. The compression rate for STD-CPR ranged from 113 to 117 compressions per minute and also did not change over time. The difference in compression rate between CCC-CPR and STD-CPR was not significant at any time point. Figure 3 shows the mean total compressions delivered per minute, including adequate and inadequate compressions, during each minute of CCC-CPR and STD-CPR. The number of mean total compressions per minute in CCC-CPR ranged from 106 to 109 and did not change over time. The mean total compressions per minute in STD-CPR ranged from 53 to 55 and did not change over time. The average pause for ventilation in STD-CPR was 9.2 seconds (SEM 0.4 sec) during the first minute, and this value did not change significantly over 9 Figure 2. Mean compression rates for minutes 1 to 9 for continuous chest-compression (CCC) cardiopulmonary resuscitation vs. standard (STD) cardiopulmonary resuscitation.

ACAD EMERG MED October 2006, Vol. 13, No. 10 www.aemj.org 1023 Figure 3. Total compressions per minute for minutes 1 to 9 for continuous chest-compression (CCC) cardiopulmonary resuscitation vs. standard (STD) cardiopulmonary resuscitation. minutes, whereas there were no pauses for ventilation during CCC-CPR. The average number of adequate ventilations (ventilations delivering at least 700 ml of air) delivered per minute in the 1st minute of STD-CPR was 0.4 (0.1), and this did not change significantly over time. Only four of the participants paused to rest during performance of CCC-CPR, and no participant paused to rest while performing STD-CPR. The average pause for rest was 6.9 seconds in duration, and the average number of pauses for each of the four students was two. A multivariate analysis of the number of adequate compressions showed that there was no significant change in the number of adequate compressions when considering age, the number of breaks, and number of CPR classes taken in the past. Male gender and being a basic life support (BLS) instructor resulted in statistically more adequate compressions per minute being delivered (p = 0.0042 and p = 0.0372). Also, those participants performing CCC-CPR on their first day of testing tended to achieve a higher number of adequate compressions per minute than did those performing CCC-CPR on their second day of testing. The same was true for STD-CPR (p = 0.0032). DISCUSSION This study demonstrates the effect of fatigue on CCC- CPR vs. STD-CPR in a relatively young, healthy population. The number of adequate compressions in both groups declines over time; however, this decline is more prominent in CCC-CPR, presumably as a result of greater fatigue. The number of adequate compressions per minute was greater in CCC-CPR than STD-CPR for the first 2 minutes, as well as in the entire 9-minute resuscitation as a whole. The total number of compressions per minute was significantly higher in CCC-CPR than STD-CPR during every minute of the simulated resuscitation. There never was any difference in compression rate between the two groups, nor did compression rate ever decline over time in either group. Therefore, although fatigue affects the number of adequate compressions delivered over time more in CCC-CPR than STD-CPR, more overall adequate and total compressions still were delivered during CCC-CPR than in STD-CPR in this 9-minute simulated resuscitation. Fatigue is manifested in this group of relatively young, healthy medical students by a decrease in force of compression rather than in a decline in the number of compressions. Originally described more than 40 years ago, 21 closedchest CPR clearly improves survival and neurological outcome for victims of cardiac arrest. 2 5 Recently, CCC- CPR has been advocated as an alternative to standard, basic CPR. 6,7 Current AHA BLS guidelines state that CCC-CPR is an acceptable alternative if the rescuer is unable or unwilling to perform mouth-to-mouth ventilation. 3 However, CCC-CPR heretofore has not been advocated, encouraged, or taught. The rationale behind CCC-CPR is multifold. STD-CPR is difficult to learn and remember, and skill retention is universally dismal. Substantial concerns regarding mouth-to-mouth contact exist among lay public and health care providers alike, which decrease the likelihood of timely intervention for cardiac arrest. Pauses for rescue breathing are substantial and result in far fewer chest compressions than recommended by AHA guidelines. According to a recent International Liaison Committee on Resuscitation advisory statement, Both skills acquisition and skills retention have been shown to be poor after conventional training in CPR for laypersons..the necessary psychomotor skills for current courses are complex and demanding. 22 This statement is substantiated by studies that show CPR retention rates to be poor among lay public and students and not to be much better in health care students and professionals. 2,23 34 These studies often cite CPR complexity as a cause. 23 25 Experts in the field have stated that simplicity should be a key element in any innovations in CPR. 22,25,26 CCC-CPR offers a variation of CPR that is easier to both remember and perform. 9,10,22,24,35 A second rationale for CCC-CPR is the well-documented concerns regarding mouth-to-mouth contact that also cause significant barriers in the performance of CPR. Reluctance to perform mouth-to-mouth ventilation is well documented among the lay public as well as among health care professionals. 9,35 39 This hesitancy to perform CPR presumably translates into delayed intervention and, hence, decreased survival. One recent study shows that although 42% of cardiac arrests are witnessed, only 15% receive bystander CPR. 4 CCC-CPR has been advocated as a strategy to increase the number of patients in cardiac arrest who receive bystander CPR. 39,40 A third reason for advocating CCC-CPR is the recent documentation of significant pauses in chest compressions for rescue breathing. Recent human studies have shown that laypersons pause 14 to 16 seconds for each pair of ventilations. 11,12 Such pauses substantially reduce the number of chest compressions provided during CPR and, hence, reduce myocardial blood flow. 41 The pauses for ventilation in STD-CPR also have been shown periodically to decrease coronary-perfusion pressure. 41 A recent animal study taking into account these lengthy pauses has demonstrated markedly improved survival in CCC-CPR vs. STD-CPR, 42 whereas other animal

1024 Heidenreich et al. RESCUER FATIGUE: STANDARD VS. CCC-CPR studies assuming only a minimal pause for rescue breathing have shown similar survival and neurological outcomes in the two groups. 13 16,24,43 Our study shows that medical students took an average of more than 9 seconds each time that they attempted the two mouth-to-mouth breaths. Most of these attempts were inadequate, resulting in delivery of only 0.4 breaths per minute. The time lost in attempting mouth-to-mouth breathing compromises the number of chest compressions delivered by approximately one half, whereas very few meaningful breaths actually are accomplished. Clinical data, including one prospective dispatcher-assisted CPR study, also have shown no difference in survival between CCC-CPR and STD-CPR. 18 20 Consequently, dispatcherassisted CCC-CPR is becoming the standard of care for witnessed sudden-collapse cardiac arrest. 5,7,20,44 One criticism, however, of CCC-CPR is that it may be more physically demanding and therefore may result in fewer adequately performed chest compressions than originally postulated. Several studies comparing performance of CPR in medical students and firefighters have shown a substantially greater number of correctly delivered compressions in CCC-CPR, compared with STD-CPR, in the first 2 minutes of simulated resuscitation. 9,10 EMS response times vary greatly but generally are longer than 2 minutes. 5,8,45 Therefore, rescuers who are willing and able to perform CPR may be required to continue it for 5 to 10 minutes or longer. It is known that in STD-CPR, chest-compression quality declines over time, 46 but to our knowledge, to date, no study has adequately compared the effects of fatigue or of prolonged rescue efforts on CCC-CPR vs. STD-CPR. The current study shows that over 9 minutes of simulated resuscitation, there is a significant decline in both CCC-CPR and STD-CPR, as measured by adequate compressions per minute, presumably because of fatigue. The largest drop in mean number of adequate compressions per minute came in the first 2 to 3 minutes of simulated resuscitation; thereafter, the number of adequate compressions per minute appeared to level off (Figure 1). This observation is helpful when considering the most effective way that two or more rescuers could assist each other in a resuscitation effort and supports recent AHA recommendations that rescuers alternate in delivering 2 minutes, or 200 continuous chest compressions each, thus maximizing the percentage of adequate compressions. 3 One advantage of CCC is its simplicity. Additional potential rescuers who observe its performance, even for a brief period, can thereafter copy what they saw with relative ease. This strategy could be recommended for both in-hospital and out-of-hospital cardiac arrests. Further studies are needed to investigate this type of alternating rescuer CCC-CPR. LIMITATIONS This study has a number of inherent limitations. It is important to note that a compression graded as adequate by Resusci Anne may not correlate with what is clinically effective. Until recently there have been relatively few clinical studies comparing outcome differences in wellperformed vs. poorly performed CPR, and those studies used subjective criteria, such as compressions sufficient to create a palpable pulse. 19,47,48 Several recent clinical studies, however, have carefully collected prospective data on compression depth and rate for both in- and out-of-hospital resuscitations. 49 51 Although one of those studies showed a correlation between compression rate and successful resuscitation, no correlation between compression depth and successful resuscitation or eventual hospital discharge was found, although these studies were not powered or designed to demonstrate such differences. Of note, animal studies also have shown a survival benefit to increased total compressions per minute during CPR. 52,53 Thus, even though the number of adequate chest compressions, as defined in this study, deteriorated early in CCC-CPR, the total number of chest compressions was consistently twice as high in CCC-CPR vs. STD-CPR, and it is unknown which of these factors most impacts successful resuscitation. CPR on a manikin model does not perfectly resemble clinical CPR and does not take into account issues such as chest-wall molding and physiologic differences among patients. Such chest molding may mean that less force is required to maintain adequate compression depth as time goes on. In addition, rescuers may not perform the same CPR during manikin simulation as during an actual emergency scenario. This population had a mean age of 27 years and a strong medical background, whereas those most likely to have the opportunity to perform bystander CPR may be much older and less experienced in medicine. The effect of fatigue on an elder population would likely be significantly greater. The Hawthorne effect may have impacted the results of this study, because participants certainly were aware that their performance was being observed and recorded. Finally, we note that we have shown deterioration in adequate chest compressions after 2 minutes of CCC-CPR and speculate that this is a result of fatigue. It is possible that there were other unknown factors that played a role in the deterioration of adequate chest compressions and that might be discovered in future investigations. CONCLUSIONS In summary, this study compared the performance by medical students of CCC-CPR and STD-CPR in a simulated single-rescuer scenario. CCC-CPR resulted in more adequate compressions and more total compressions per minute than did STD-CPR during 9 minutes of simulated resuscitation because of the pauses for ventilation during STD-CPR. CCC-CPR resulted in a significantly statistically higher number of adequate compressions per minute than did STD-CPR for the first 2 minutes of CPR. However, the differences diminished after 3 minutes, presumably as a result of greater rescuer fatigue with CCC-CPR. More research needs to be performed to evaluate the effects of fatigue in other and older populations, as well as in a scenario in which rescuers alternate chest compressions every 2 to 3 minutes. References 1. Statement by the Ad Hoc Committee on Cardiopulmonary Resuscitation of the Division of Medical Sciences, National Academy of Sciences National

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