- Email: [email protected]
Quality of external closed-chest compressions in a tertiary pediatric setting: Missing the mark
Resuscitation 81 (2010) 718–723
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Simulation and education
Quality of external closed-chest compressions in a tertiary pediatric setting: Missing the mark夽 Justin T. Hamrick ∗ , Brock Fisher, Kenneth B. Quinto, Jennifer Foley University of California San Diego (UCSD), Rady’s Children’s Hospital, 3020 Children’s Way, MC-5065 San Diego, CA 92123-4282, United States
a r t i c l e
i n f o
Article history: Received 6 June 2009 Received in revised form 10 January 2010 Accepted 18 January 2010 Keywords: Closed-chest compressions CPR Pediatric Compression rate Compression depth
a b s t r a c t Introduction: Recent adult reports have demonstrated sub-optimal performance of basic cardiopulmonary resuscitation (CPR) skills in advanced training scenarios and real life arrest situations. We studied the adequacy of chest compressions performed by advanced trained pediatric providers in code scenarios. Methods: We designed a prospective observational study of pediatric providers performing external closed-chest compressions on a child mannequin that is designed to assess adequacy based on depth and rate of chest compressions. The study was conducted from 2008 to 2009 in which 42 subjects were screened and enrolled for participation. Each subject underwent a basic life support scenario that included two minutes of uninterrupted external closed-chest compressions that were assessed for adequacy based on depth and rate. Results: For 42 subjects, 168 total 30-s time segments were available for analysis. Chest compressions were performed at a median rate of 110 (interquartile range (IQR) of 75–145) compressions per minute (cpm). No significant decay in rate of chest compressions was noted over the two-minute evaluation. Chest compression depth was adequate in 9.4% of total delivered chest compressions. No statistical significance was found on the job exposure to CPR and delivery of effective chest compressions. Conclusion: Advanced training of pediatric providers does not ensure adequate delivery of chest compressions. Rate standards and adequate depth of chest compressions are infrequently achieved and both may need more emphasis in CPR training and attention during resuscitations. © 2010 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Cardiac arrest occurs in up to four percent of pediatric patients admitted to the intensive care unit.1–3 The frequency of inhospital arrests is greater than 100-fold more frequent than out-of-hospital arrests, prioritizing a need for staff well trained in effective delivery of cardiopulmonary resuscitation.4,5 In pediatric patients, rapid and effective CPR is associated with return of spontaneous circulation and neurologically intact survival.6,7 Outcomes depend not only on timing, but also on the effectiveness of closed-chest compressions.6–10 The “2005 American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care” emphasize the importance of minimally interrupted, effective closed-chest compressions.11 Recent changes to the guidelines have included the use of 100 compressions per minute for all non-infant resuscitations and the “push hard and fast” mantra for all closed-chest compressions.11 The
夽 “A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.01.029”. ∗ Corresponding author. E-mail address: [email protected] (J.T. Hamrick). 0300-9572/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2010.01.029
most recent AHA guidelines recommend that the chest be compressed a minimum of one-third the total depth of the thoracic cavity in the pediatric patient and a minimum of 4–5 cm in the adult patient.11 Even though most cardiac arrests in children are caused by asphyxia, effective closed-chest compressions remain a cornerstone of resuscitation. The quality of closed-chest compressions remains paramount in pediatric arrests in which neurologically intact survival rates of greater than 70% are possible.5 The ultimate goal of closed-chest compressions is to provide adequate coronary perfusion pressure and maintain cerebral blood flow. Multiple animal and human studies have demonstrated that blood flow increases with increasing compression depth during closedchest compressions.12–17 However, despite revised guidelines11 and requirements for advanced training for health care providers, the performance of basic CPR remains poor. Recent adult studies show that the quality of CPR is inconsistent and often does not meet published guideline recommendations, even when performed by well-trained hospital staff.18,19 Although recent adult literature reports less than one-half of chest compressions are less than the adequate depth, adequacy of chest compressions in pediatric setting is not as well studied.19,20 A recent adult study has reported up to 97% of all delivered chest compressions were too
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
719
Fig. 1. Mannequin setup. A and B demonstrate mannequin setup for scenario while C and D demonstrate placement of pressure sensitive device below sternal plate.
shallow in an adult mannequin model.21 Our study is designed to evaluate the adherence to the 2005 guidelines defining effective closed-chest compressions in a pediatric intensive care setting. Current AHA recommendations define a rate of 100 compressions per minute and a minimum depth of one-third the anterior–posterior depth of the chest for adequate chest compressions. The study was performed in a tertiary pediatric intensive care unit from 2008 to 2009. 2. Materials and methods 2.1. Ethics approval This study was approved by the University of California, San Diego, Human Research Protections Program. Written informed consent was obtained from all participants. 2.2. Study design This study is a prospective observational study. Our evaluation of closed-chest compressions utilized a novel pediatric mannequin designed for our study to record rate and depth of individual chest compressions. We adapted a standard three-year-old Kyle mannequin® (Simulaids, NY, USA) with a standard arterial line pressure monitor system placing a 250 ml saline bag underneath the chest flap directly below the sternal plate centered at two centimeters (cm) below the nipple line (Fig. 1). Having the saline bag in this positioned allowed the force of the chest compressions to be translated into an arterial type waveform. The bag was then connected to an arterial monitor device and the individual pres-
sures and rates of compression were recorded. This novel model used a base model of the Kyle manikin (by Simulaids, NY, USA). This model is designed by the manufacturer to have the characteristics of a three-year-old for performance of basic life support. Our additions to the original manikin did not change the compliance of the chest wall as designed by the original manufacturer (data not shown). The study was conducted in a standard pediatric ICU room on an ICU bed with the addition of a CPR backboard placed prior to evaluation of the subject. A standard CPR backboard was placed below the mannequin prior to each scenario. The mannequin and pressure bag system were standardized prior to each evaluation so that a known pressure recording of the arterial tracing approximated the minimum depth of one-third of the anterior–posterior diameter of the mannequin chest wall (minimum defined by the 2005 AHA guidelines).11 This minimum depth of compression was less than the adult minimum defined as 4 cm compression depth.11 Our study subjects consisted of pediatric nurses, residents and respiratory therapists certified in Pediatric Advanced Life Support (PALS). Closed-chest compressions were performed for a total of two minutes during each scenario.
2.3. Cardiac arrest scenario Each subject was presented with a clinical scenario of an inhospital arrest. The scenario consisted of a three-year-old male who was admitted to the pediatric intensive care unit and developed a full cardiopulmonary arrest. Each subject was asked to perform a series of basic life support skills consisting of a two breath bag-mask ventilation, pulse check and a two-minute cycle of uninterrupted closed-chest compressions on the study mannequin.
720
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
Table 1 Subject demographics. Percentage (%)
Cumulative percentage (%)
Most recent level of CPR training ATLS/ACLS PALS/APLS BLS
14 62 24
14 76 100
Time since last CPR certification Less than 1 month 2–4 months 5–7 months 8–11 months 12–24 months
7 14 24 12 43
7 21 45 57 100
Job title RT RN/BLN MD
21 74 5
21 95 100 Fig. 2. Chest compressions rates per 30-s time segment.
Subjects were informed that the airway was secured in order that compressions could remain uninterrupted. Hand placement was visually inspected by evaluator and verbally redirected if improperly placed. Subjects were instructed to perform all actions just as they would in a real life situation. Subjects were blinded to the measuring system of chest compressions and had no feedback on adequacy of chest compressions. Upon completion of the scenario, subjects were asked to complete a short post evaluation survey concerning the study. 2.4. Data collection Data was collected during 42 scenarios. Each two-minute dataset was divided into four 30-s segments for analysis. Pressure monitor recordings were analyzed for compression depth against a known standardized minimum pressure. Compression rates were also recorded and analyzed. 2.5. Statistical analysis The two minutes of chest compressions was separated into four consecutive 30-s segments for purposes of analysis. Data was collected and stored in Excel (Microsoft, NV, USA) and analyzed by SAS for Microsoft (SAS, USA). We set statistical significance at an alpha value of 0.05.
of the chest was significantly lower than the adequacy of chest compressions deemed effective by rate. The average percentage of effective chest compressions based on minimal depth was 9.4% (Table 2). There was no significant decline in the percentage of effective chest compressions based on depth across the two-minute data collection. No statistical significance was noted for effective chest compressions based on level of most recent training. Subjects certified less than 12 months prior to evaluation performed poorer in delivery of adequate depth chest compressions than those certified greater than 12 months prior to evaluation. Median effective chest compressions were 0.5 ± 12.3 per two minutes and 45.8 ± 77.6 per two minutes respectively (p = 0.014). No statistical difference was noted between subjects based on exposure to code situations when comparing number of effective compressions per 2 min (p value = 0.31). There was a statistical difference between registered nurses and respiratory therapists when comparing total number of effective compressions per two minutes (p value = 0.002) Median number of effective compressions per two minutes for RNs is 5.5 ± 20.3 compressions per two minutes. Median number of effective compressions per two minutes for respiratory therapists is 71.2 ± 93.8 compressions per two minutes. No statistical significance was noted between other groups. Fig. 3 summarizes these findings. 3.3. Perception
3. Results During a study period of approximately 20 months, 42 subjects were screened for eligibility and 42 subjects were enrolled. Data was collected from 42 two-minute scenarios and then separated into 30-s segments for analysis. This yielded 168 total data blocks for analysis. Basic subject characteristics are presented in Table 1.
Study subjects were uniformly unable to detect inadequate chest compressions when self-evaluating their chest compressions
3.1. Compression rate The median compression rate for the scenarios was 110 with 46.4% falling in the target range of 90–120 cpm. The median number of chest compressions per 30-s segment did not decline significantly over the two-minute study period (105–113 cpm). Table 2 and Fig. 2 summarize the compression rates for the data segments analyzed. 3.2. Compression depth The adequacy of chest compressions as defined by an appropriate minimum depth of one-third of the anterior–posterior diameter
Fig. 3. Percentage of effective chest compressions per 30-s time segment.
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
721
Table 2 Compression results. Time segmenta
Total compressions per minute (CPM)b Target = 100
P value
Shallowc compressions per minute (CPM)b Target = 0
P value
Shallowc compressions (%) Target = 0
1 2 3 4
105 (73–137) 113 (77–149) 110 (72–148) 111 (69–153)
0.42 0.16 0.12 0.06
96 (48–144) 106 (64–148) 105 (61–149) 109 (68–150)
<0.001 <0.001 <0.001 <0.001
85.1 90.6 93.8 93.0
a b c
Time segments represent 30-s intervals. Compressions reported as median (interquartile range). Shallow compressions defined as less than one-third of the depth of the chest wall per 2005 American Heart Association Guidelines.
on the post scenario survey (correlation coefficient = 0.19 with p value = 0.23). No statistical difference was found between those who felt their compression quality decreased and those who felt their compression quality did not decrease when comparing number of effective compressions over the two-minute data collection (p value = 0.8). Less than 20% of subjects rated their performance of chest compressions as poor on a graded scale. Fifty-seven percent of subjects stated that they would have done less forceful or no different chest compressions if done on a live patient (Table 3). 4. Discussion The institution of the recent AHA 2005 Guidelines emphasizes the importance of uninterrupted effective chest compressions. One of the main goals of the pediatric AHA 2005 Guidelines is to provide adequate depth and rate closed-chest compressions while minimizing interruptions. Multiple animal and human studies have shown effective, uninterrupted chest compressions to be a primary determinant in successful defibrillation and return of spontaneous circulation.9,10,16,22–26 A recent publication has demonstrated inadequate depth in greater than one-fifth of total chest compressions delivered during the resuscitation of older children and adolescents.27 The delivery of effective chest compressions involves several factors: namely rate, depth, adequate recoil and correct hand placement. The adequacy of rate in animal studies has been shown to be approximately 90–120 cpm. The current AHA guidelines reflect this
Table 3 Post evaluation survey results. Percentage (%) Self rating of chest compressions (1(poor)–10(excellent) scale) <3 0 3 2.38 4 2.38 5 7.14 6 7.14 7 21.43 8 28.57 9 14.29 10 16.67
Cumulative percentage (%) 0 2.38 4.76 11.90 19.05 40.48 69.05 83.33 100.00
Self perceived decay of compressions Yes 59.52 No 35.71 Not sure 4.76 On the job exposure to code situations Never 2.38 Rarely 21.43 Sometimes 40.48 Often 35.71
2.38 23.81 64.29 100.00
Self perceived force if done on a live patient Less forceful 11.90 No difference 45.24 More forceful 42.86
11.90 57.14 100.00
animal data. The chest compressions are not only to be done at an appropriate rate, but also must be done according to proper depth and allowing complete recoil of the chest. This ensures not only adequate forward flow upon direct compression of the heart, but also allows for an adequate preload prior to the next compression.28 Animal studies have shown that increasing compression depth is associated with improved cardiac output and therefore increased myocardial and cerebral perfusion.12,13,29 The delivery of closed-chest compressions results in phasic blood flow. There are two theories on the mechanism of how this occurs. The direct compression method states that upon direct compression of the ventricles between the sternum and thoracic spine a pressure gradient is established. In the case of the left ventricle this gradient causes closing of the mitral valve, opening of the aortic valve and blood is ejection forward into the aorta. The left ventricle then fills during complete recoil of the sternum.30–32 The thoracic pump theory states that closed-chest compressions create changes in intrathoracic pressure promoting blood flow out of and into the thoracic cavity.33 Debate still remains on the exact mechanism of blood flow during chest compressions and one study suggests that the mechanism may be patient dependent.34 Although debate about the mechanism persists, it is evident that forward flow into the aorta and pulmonary artery occurs during active compression of the sternum and that retrograde flow occurs during complete decompression.35 The subjects in this study adequately reflected a standard composition of a tertiary pediatric intensive care unit with all of subjects being PALS certified and most having advanced training in the previous 12 months (Table 1). All of the subjects were PALS certified within the last 24 months. However, some subjects had additional training that was more recent than the pediatric training. While all subjects were PALS trained, it cannot be ignored that many subjects had non-pediatric courses as their most recent training. Over 92% of subjects reported the intensive care unit as their primary assigned work location with >75% of subjects rating their on the job code exposure as more than rare. The findings of this study suggest that the quality of CPR even in highly trained personnel with remains sub-optimal. Our study suggests that the target rate of chest compressions is infrequently achieved during pediatric resuscitations and there is no significant decay in delivered rate over the recommended two-minute compression cycle. This is in support of recent adult data that shows rates are often sub-optimal. In a recent article by Abella et al. compression rates were <80 compressions per minute (cpm) in about one-third of the data analyzed.36 A recent pediatric study has shown basic life support skills to be poor in a training model20 but few recent pediatric studies have looked specifically at chest compression adequacy over time. Our study demonstrated an almost uniform inadequacy in compression depth. This is consistent with recent data from adult reports. Abella et al. reported that one-third of closed-chest compressions delivered to a cohort of adult arrest scenarios were too shallow.19 A more recent observational study by Perkins et al. reported that 97% of chest compressions were too shallow dur-
722
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
ing advanced life support training scenarios.21 This finding of our study was in stark contrast to adequacy defined by rate, which was achieved by most subjects. Our study could not demonstrate a significant correlation between subject characteristics and the delivery of effective chest compressions. The statistical difference demonstrated in time since last certification and delivery of chest compressions most likely represents the characteristics of the minority of subjects who performed adequate depth chest compressions. This same phenomenon most likely explains the difference in performance of registered nurses versus respiratory therapists. A larger study is needed to adequately characterize the subjects who consistently perform chest compressions adequately. Subjects were unable to self-evaluate the inadequacy of delivered chest compressions. While a minority of subjects reported that they would have performed more forceful compressions if done in a real life situation, most report that they would have done compressions no differently or even less forceful. This suggests that subjects not only were unable to deliver adequate depth chest compressions but also were unable to identify adequate compressions in this simulation model. The subjects had no feedback during the scenario. While this may not reflect the situation of a real code, it allowed for an isolated evaluation of chest compression delivery. This does point out the need for emphasis of the leader’s role in assurance of adequate chest compression delivery. While the study demonstrated that the subjects were not able to adequately judge the chest compressions they delivered, it does support an absolute need for an independent check of chest compression depth in the form of the code leader. An additional study would be needed to tell if the leader role would be able to impact the adequacy of chest compressions by feedback and recognition of inadequate chest compressions. The study was designed to accurately reflect real life pediatric cardiac arrests, but there are several limitations to this design. Our study did not quantify complete recoil of the chest compressions, which has been demonstrated in a recent study to be inadequate in pediatric resuscitations.27 The current model may be adapted to measure this in a future study. Based on feedback from subjects on the post evaluation survey, our study seemed to limit the mannequin biases in all simulation models but could not completely eliminate it. 5. Conclusion The findings of this study suggest that the quality of CPR even in highly trained personnel with CPR experience remains sub-optimal. Similar to recent adult reports, pediatric chest compressions infrequently achieve adequate rates and almost uniformly are inadequate in depth. This suggests an even more vigilant emphasis on delivery and identification of adequate depth chest compressions at proper rates may be needed. Conflicts of interest None. Acknowledgements The authors would like to thank the entire Rady’s Children’s Hospital staff for their cooperation. A special thanks to Matt Schiel and Bradley Peterson who provided essential help in this study. References 1. Slonim Anthony D, Patel Kantilal M, Ruttimann Urs E, Pollack Murray M. Cardiopulmonary resuscitation in pediatric intensive care units. Crit Care Med 1997;25:1951–5.
2. Suominen P, Olkkola KT, Voipio V, Korpela R, Palo R, Rasanen J. Utstein style reporting of in-hospital paediatric cardiopulmonary resuscitation. Resuscitation 2000;45:17–25. 3. Parra David A, Totapally Bala R, Zahn Evan, et al. Outcome of cardiopulmonary resuscitation in a pediatric cardiac intensive care unit. Crit Care Med 2000;28:3296–300. 4. Morris MC, Nadkarni VM. Pediatric cardiopulmonary-cerebral resuscitation: an overview and future directions. Crit Care Clin 2003;19:337–64. 5. Meaney Peter A, Nadkarni Vinay M, Cook Francis E, et al. Higher survival rates among younger patients after pediatric intensive care unit cardiac arrests. Pediatrics 2006;118:2424–33. 6. Wik L, Steen PA, Bircher NG. Quality of bystander cardiopulmonary resuscitation influences outcome after prehospital cardiac arrest. Resuscitation 1994;28:195–203. 7. Gallagher EJ, Lombardi G, Gennis P. Effectiveness of bystander cardiopulmonary resuscitation and survival following out-of-hospital cardiac arrest. JAMA 1995;274:1922–5. 8. Van Hoeyweghen Raf J, Bossaert Leo L, Mullie Arsene, et al. Quality and efficiency of bystander CPR. Belgian Cerebral Resuscitation Study Group. Resuscitation 1993;26:47–52. 9. Kern Karl B, Hilwig Ronald W, Berg Robert A, Sanders Arthur B, Ewy Gordon A. Importance of continuous chest compressions during cardiopulmonary resuscitation: improved outcome during a simulated single lay-rescuer scenario. Circulation 2002;105:645–9. 10. Yu Ting, Weil Max Harry, Tang Wanchun, et al. Adverse outcomes of interrupted precordial compression during automated defibrillation. Circulation 2002;106:368–72. 11. 2005 American Heart Association (AHA) guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiovascular care (ECC) of pediatric and neonatal patients: pediatric basic life support. Pediatrics 2006; 117(5):e9891004. 12. Babbs CF, Voorhees WD, Fitzgerald KR, Holmes HR, Geddes LA. Relationship of blood pressure and flow during CPR to chest compression amplitude: evidence for an effective compression threshold. Ann Emerg Med 1983;12:527–32. 13. Bellamy RF, DeGuzman LR, Pedersen DC. Coronary blood flow during cardiopulmonary resuscitation in swine. Circulation 1984;69:174–80. 14. Feneley MP, Maier GW, Kern KB, et al. The influence of manual chest compression rate on hemodynamic support during cardiac arrest: high-impulse cardiopulmonary resuscitation. Circulation 1986;74:IV51–9. 15. Maier GW, Tyson Jr GS, Olsen CO, et al. The physiology of external cardiac massage: high-impulse cardiopulmonary resuscitation. Circulation 1984;70:86–101. 16. Ornato Joseph P, Levine Ronald L, Young Denise S, Racht Edward M, Garnett A Randy, Gonzalez Edgar R. The effect of applied chest compression force on systemic arterial pressure and end-tidal carbon dioxide concentration during CPR in human beings. Ann Emerg Med 1989;18:732–7. 17. Wolfe JA, Maier GW, Newton Jr JR, et al. Physiologic determinants of coronary blood flow during external cardiac massage. J Thorac Cardiovasc Surg 1988;95:523–32. 18. Aufderheide Tom P, Pirrallo Ronald G, Yannopoulos Demetris, et al. Incomplete chest wall decompression: a clinical evaluation of CPR performance by trained laypersons and an assessment of alternative manual chest compressiondecompression techniques. Resuscitation 2006;71:341–51. 19. Abella Benjamin S, Alvarado Jason P, Myklebust Helge, et al. Quality of cardiopulmonary resuscitation during in-hospital cardiac arrest. JAMA 2005;293:305–10. 20. Arshid M, Lo TY, Reynolds F. Quality of cardio-pulmonary resuscitation (CPR) during paediatric resuscitation training: time to stop the blind leading the blind. Resuscitation 2009;80:558–60. 21. Perkins Gavin D, Boyle William, Bridgestock Hannah, et al. Quality of CPR during advanced resuscitation training. Resuscitation 2008;77:69–74. 22. Ristagno Giuseppe, Tang Wanchun, Chang Yun-Te, et al. The quality of chest compressions during cardiopulmonary resuscitation overrides importance of timing of defibrillation. Chest 2007;132:70–5. 23. Steen Stig, Liao Qiuming, Pierre Leif, Paskevicius Audrius, Sjoberg Trygve. The critical importance of minimal delay between chest compressions and subsequent defibrillation: a haemodynamic explanation. Resuscitation 2003;58:249–58. 24. Weil Max Harry, Bisera Jose, Trevino Robert P, Rackow Eric C. Cardiac output and end-tidal carbon dioxide. Crit Care Med 1985;13:907–9. 25. Sato Yoji, Weil Max Harry, Sun Shijie, et al. Adverse effects of interrupting precordial compression during cardiopulmonary resuscitation. Crit Care Med 1997;25:733–6. 26. Eftestol T, Sunde K, Steen PA. Effects of interrupting precordial compressions on the calculated probability of defibrillation success during out-of-hospital cardiac arrest. Circulation 2002;105:2270–3. 27. Sutton Robert M, Niles Dana, Nysaether Jon, et al. Quantitative analysis of CPR quality during in-hospital resuscitation of older children and adolescents. Pediatrics 2009;124:494–9. 28. Lurie Keith G, Mulligan Katherine A, McKnite Scott, Detloff Barry, Lindstrom Paul, Lindner Karl H. Optimizing standard cardiopulmonary resuscitation with an inspiratory impedance threshold valve. Chest 1998;113:1084–90. 29. Edelson Dana P, Abella Benjamin S, Kramer-Johansen Jo, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation 2006;71:137–45. 30. Kouwenhoven WB, Jude JR, Knickerbocker GG. Closed-chest cardiac massage. JAMA 1960;173:1064–7.
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723 31. Rodarte JR. Mechanisms of blood flow during cardiopulmonary resuscitation. Mayo Clin Proc 1991;66:436–8. 32. Redberg RF, Tucker KJ, Cohen TJ, Dutton JP, Callaham ML, Schiller NB. Physiology of blood flow during cardiopulmonary resuscitation. A transesophageal echocardiographic study. Circulation 1993;88:534–42. 33. Werner JA, Greene HL, Janko CL, Cobb LA. Visualization of cardiac valve motion in man during external chest compression using two-dimensional echocardiography. Implications regarding the mechanism of blood flow. Circulation 1981;63:1417–21.
723
34. Ma Matthew Huei-Ming, Hwang Juey-Jen, Lai Ling-Ping, et al. Transesophageal echocardiographic assessment of mitral valve position and pulmonary venous flow during cardiopulmonary resuscitation in humans. Circulation 1995;92:854–61. 35. Andreka P, Frenneaux MP. Haemodynamics of cardiac arrest and resuscitation. Curr Opin Crit Care 2006;12:198–203. 36. Abella Benjamin S, Sandbo Nathan, Vassilatos Peter, et al. Chest compression rates during cardiopulmonary resuscitation are suboptimal: a prospective study during in-hospital cardiac arrest. Circulation 2005;111:428–34.
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Simulation and education
Quality of external closed-chest compressions in a tertiary pediatric setting: Missing the mark夽 Justin T. Hamrick ∗ , Brock Fisher, Kenneth B. Quinto, Jennifer Foley University of California San Diego (UCSD), Rady’s Children’s Hospital, 3020 Children’s Way, MC-5065 San Diego, CA 92123-4282, United States
a r t i c l e
i n f o
Article history: Received 6 June 2009 Received in revised form 10 January 2010 Accepted 18 January 2010 Keywords: Closed-chest compressions CPR Pediatric Compression rate Compression depth
a b s t r a c t Introduction: Recent adult reports have demonstrated sub-optimal performance of basic cardiopulmonary resuscitation (CPR) skills in advanced training scenarios and real life arrest situations. We studied the adequacy of chest compressions performed by advanced trained pediatric providers in code scenarios. Methods: We designed a prospective observational study of pediatric providers performing external closed-chest compressions on a child mannequin that is designed to assess adequacy based on depth and rate of chest compressions. The study was conducted from 2008 to 2009 in which 42 subjects were screened and enrolled for participation. Each subject underwent a basic life support scenario that included two minutes of uninterrupted external closed-chest compressions that were assessed for adequacy based on depth and rate. Results: For 42 subjects, 168 total 30-s time segments were available for analysis. Chest compressions were performed at a median rate of 110 (interquartile range (IQR) of 75–145) compressions per minute (cpm). No significant decay in rate of chest compressions was noted over the two-minute evaluation. Chest compression depth was adequate in 9.4% of total delivered chest compressions. No statistical significance was found on the job exposure to CPR and delivery of effective chest compressions. Conclusion: Advanced training of pediatric providers does not ensure adequate delivery of chest compressions. Rate standards and adequate depth of chest compressions are infrequently achieved and both may need more emphasis in CPR training and attention during resuscitations. © 2010 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Cardiac arrest occurs in up to four percent of pediatric patients admitted to the intensive care unit.1–3 The frequency of inhospital arrests is greater than 100-fold more frequent than out-of-hospital arrests, prioritizing a need for staff well trained in effective delivery of cardiopulmonary resuscitation.4,5 In pediatric patients, rapid and effective CPR is associated with return of spontaneous circulation and neurologically intact survival.6,7 Outcomes depend not only on timing, but also on the effectiveness of closed-chest compressions.6–10 The “2005 American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care” emphasize the importance of minimally interrupted, effective closed-chest compressions.11 Recent changes to the guidelines have included the use of 100 compressions per minute for all non-infant resuscitations and the “push hard and fast” mantra for all closed-chest compressions.11 The
夽 “A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.01.029”. ∗ Corresponding author. E-mail address: [email protected] (J.T. Hamrick). 0300-9572/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2010.01.029
most recent AHA guidelines recommend that the chest be compressed a minimum of one-third the total depth of the thoracic cavity in the pediatric patient and a minimum of 4–5 cm in the adult patient.11 Even though most cardiac arrests in children are caused by asphyxia, effective closed-chest compressions remain a cornerstone of resuscitation. The quality of closed-chest compressions remains paramount in pediatric arrests in which neurologically intact survival rates of greater than 70% are possible.5 The ultimate goal of closed-chest compressions is to provide adequate coronary perfusion pressure and maintain cerebral blood flow. Multiple animal and human studies have demonstrated that blood flow increases with increasing compression depth during closedchest compressions.12–17 However, despite revised guidelines11 and requirements for advanced training for health care providers, the performance of basic CPR remains poor. Recent adult studies show that the quality of CPR is inconsistent and often does not meet published guideline recommendations, even when performed by well-trained hospital staff.18,19 Although recent adult literature reports less than one-half of chest compressions are less than the adequate depth, adequacy of chest compressions in pediatric setting is not as well studied.19,20 A recent adult study has reported up to 97% of all delivered chest compressions were too
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
719
Fig. 1. Mannequin setup. A and B demonstrate mannequin setup for scenario while C and D demonstrate placement of pressure sensitive device below sternal plate.
shallow in an adult mannequin model.21 Our study is designed to evaluate the adherence to the 2005 guidelines defining effective closed-chest compressions in a pediatric intensive care setting. Current AHA recommendations define a rate of 100 compressions per minute and a minimum depth of one-third the anterior–posterior depth of the chest for adequate chest compressions. The study was performed in a tertiary pediatric intensive care unit from 2008 to 2009. 2. Materials and methods 2.1. Ethics approval This study was approved by the University of California, San Diego, Human Research Protections Program. Written informed consent was obtained from all participants. 2.2. Study design This study is a prospective observational study. Our evaluation of closed-chest compressions utilized a novel pediatric mannequin designed for our study to record rate and depth of individual chest compressions. We adapted a standard three-year-old Kyle mannequin® (Simulaids, NY, USA) with a standard arterial line pressure monitor system placing a 250 ml saline bag underneath the chest flap directly below the sternal plate centered at two centimeters (cm) below the nipple line (Fig. 1). Having the saline bag in this positioned allowed the force of the chest compressions to be translated into an arterial type waveform. The bag was then connected to an arterial monitor device and the individual pres-
sures and rates of compression were recorded. This novel model used a base model of the Kyle manikin (by Simulaids, NY, USA). This model is designed by the manufacturer to have the characteristics of a three-year-old for performance of basic life support. Our additions to the original manikin did not change the compliance of the chest wall as designed by the original manufacturer (data not shown). The study was conducted in a standard pediatric ICU room on an ICU bed with the addition of a CPR backboard placed prior to evaluation of the subject. A standard CPR backboard was placed below the mannequin prior to each scenario. The mannequin and pressure bag system were standardized prior to each evaluation so that a known pressure recording of the arterial tracing approximated the minimum depth of one-third of the anterior–posterior diameter of the mannequin chest wall (minimum defined by the 2005 AHA guidelines).11 This minimum depth of compression was less than the adult minimum defined as 4 cm compression depth.11 Our study subjects consisted of pediatric nurses, residents and respiratory therapists certified in Pediatric Advanced Life Support (PALS). Closed-chest compressions were performed for a total of two minutes during each scenario.
2.3. Cardiac arrest scenario Each subject was presented with a clinical scenario of an inhospital arrest. The scenario consisted of a three-year-old male who was admitted to the pediatric intensive care unit and developed a full cardiopulmonary arrest. Each subject was asked to perform a series of basic life support skills consisting of a two breath bag-mask ventilation, pulse check and a two-minute cycle of uninterrupted closed-chest compressions on the study mannequin.
720
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
Table 1 Subject demographics. Percentage (%)
Cumulative percentage (%)
Most recent level of CPR training ATLS/ACLS PALS/APLS BLS
14 62 24
14 76 100
Time since last CPR certification Less than 1 month 2–4 months 5–7 months 8–11 months 12–24 months
7 14 24 12 43
7 21 45 57 100
Job title RT RN/BLN MD
21 74 5
21 95 100 Fig. 2. Chest compressions rates per 30-s time segment.
Subjects were informed that the airway was secured in order that compressions could remain uninterrupted. Hand placement was visually inspected by evaluator and verbally redirected if improperly placed. Subjects were instructed to perform all actions just as they would in a real life situation. Subjects were blinded to the measuring system of chest compressions and had no feedback on adequacy of chest compressions. Upon completion of the scenario, subjects were asked to complete a short post evaluation survey concerning the study. 2.4. Data collection Data was collected during 42 scenarios. Each two-minute dataset was divided into four 30-s segments for analysis. Pressure monitor recordings were analyzed for compression depth against a known standardized minimum pressure. Compression rates were also recorded and analyzed. 2.5. Statistical analysis The two minutes of chest compressions was separated into four consecutive 30-s segments for purposes of analysis. Data was collected and stored in Excel (Microsoft, NV, USA) and analyzed by SAS for Microsoft (SAS, USA). We set statistical significance at an alpha value of 0.05.
of the chest was significantly lower than the adequacy of chest compressions deemed effective by rate. The average percentage of effective chest compressions based on minimal depth was 9.4% (Table 2). There was no significant decline in the percentage of effective chest compressions based on depth across the two-minute data collection. No statistical significance was noted for effective chest compressions based on level of most recent training. Subjects certified less than 12 months prior to evaluation performed poorer in delivery of adequate depth chest compressions than those certified greater than 12 months prior to evaluation. Median effective chest compressions were 0.5 ± 12.3 per two minutes and 45.8 ± 77.6 per two minutes respectively (p = 0.014). No statistical difference was noted between subjects based on exposure to code situations when comparing number of effective compressions per 2 min (p value = 0.31). There was a statistical difference between registered nurses and respiratory therapists when comparing total number of effective compressions per two minutes (p value = 0.002) Median number of effective compressions per two minutes for RNs is 5.5 ± 20.3 compressions per two minutes. Median number of effective compressions per two minutes for respiratory therapists is 71.2 ± 93.8 compressions per two minutes. No statistical significance was noted between other groups. Fig. 3 summarizes these findings. 3.3. Perception
3. Results During a study period of approximately 20 months, 42 subjects were screened for eligibility and 42 subjects were enrolled. Data was collected from 42 two-minute scenarios and then separated into 30-s segments for analysis. This yielded 168 total data blocks for analysis. Basic subject characteristics are presented in Table 1.
Study subjects were uniformly unable to detect inadequate chest compressions when self-evaluating their chest compressions
3.1. Compression rate The median compression rate for the scenarios was 110 with 46.4% falling in the target range of 90–120 cpm. The median number of chest compressions per 30-s segment did not decline significantly over the two-minute study period (105–113 cpm). Table 2 and Fig. 2 summarize the compression rates for the data segments analyzed. 3.2. Compression depth The adequacy of chest compressions as defined by an appropriate minimum depth of one-third of the anterior–posterior diameter
Fig. 3. Percentage of effective chest compressions per 30-s time segment.
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
721
Table 2 Compression results. Time segmenta
Total compressions per minute (CPM)b Target = 100
P value
Shallowc compressions per minute (CPM)b Target = 0
P value
Shallowc compressions (%) Target = 0
1 2 3 4
105 (73–137) 113 (77–149) 110 (72–148) 111 (69–153)
0.42 0.16 0.12 0.06
96 (48–144) 106 (64–148) 105 (61–149) 109 (68–150)
<0.001 <0.001 <0.001 <0.001
85.1 90.6 93.8 93.0
a b c
Time segments represent 30-s intervals. Compressions reported as median (interquartile range). Shallow compressions defined as less than one-third of the depth of the chest wall per 2005 American Heart Association Guidelines.
on the post scenario survey (correlation coefficient = 0.19 with p value = 0.23). No statistical difference was found between those who felt their compression quality decreased and those who felt their compression quality did not decrease when comparing number of effective compressions over the two-minute data collection (p value = 0.8). Less than 20% of subjects rated their performance of chest compressions as poor on a graded scale. Fifty-seven percent of subjects stated that they would have done less forceful or no different chest compressions if done on a live patient (Table 3). 4. Discussion The institution of the recent AHA 2005 Guidelines emphasizes the importance of uninterrupted effective chest compressions. One of the main goals of the pediatric AHA 2005 Guidelines is to provide adequate depth and rate closed-chest compressions while minimizing interruptions. Multiple animal and human studies have shown effective, uninterrupted chest compressions to be a primary determinant in successful defibrillation and return of spontaneous circulation.9,10,16,22–26 A recent publication has demonstrated inadequate depth in greater than one-fifth of total chest compressions delivered during the resuscitation of older children and adolescents.27 The delivery of effective chest compressions involves several factors: namely rate, depth, adequate recoil and correct hand placement. The adequacy of rate in animal studies has been shown to be approximately 90–120 cpm. The current AHA guidelines reflect this
Table 3 Post evaluation survey results. Percentage (%) Self rating of chest compressions (1(poor)–10(excellent) scale) <3 0 3 2.38 4 2.38 5 7.14 6 7.14 7 21.43 8 28.57 9 14.29 10 16.67
Cumulative percentage (%) 0 2.38 4.76 11.90 19.05 40.48 69.05 83.33 100.00
Self perceived decay of compressions Yes 59.52 No 35.71 Not sure 4.76 On the job exposure to code situations Never 2.38 Rarely 21.43 Sometimes 40.48 Often 35.71
2.38 23.81 64.29 100.00
Self perceived force if done on a live patient Less forceful 11.90 No difference 45.24 More forceful 42.86
11.90 57.14 100.00
animal data. The chest compressions are not only to be done at an appropriate rate, but also must be done according to proper depth and allowing complete recoil of the chest. This ensures not only adequate forward flow upon direct compression of the heart, but also allows for an adequate preload prior to the next compression.28 Animal studies have shown that increasing compression depth is associated with improved cardiac output and therefore increased myocardial and cerebral perfusion.12,13,29 The delivery of closed-chest compressions results in phasic blood flow. There are two theories on the mechanism of how this occurs. The direct compression method states that upon direct compression of the ventricles between the sternum and thoracic spine a pressure gradient is established. In the case of the left ventricle this gradient causes closing of the mitral valve, opening of the aortic valve and blood is ejection forward into the aorta. The left ventricle then fills during complete recoil of the sternum.30–32 The thoracic pump theory states that closed-chest compressions create changes in intrathoracic pressure promoting blood flow out of and into the thoracic cavity.33 Debate still remains on the exact mechanism of blood flow during chest compressions and one study suggests that the mechanism may be patient dependent.34 Although debate about the mechanism persists, it is evident that forward flow into the aorta and pulmonary artery occurs during active compression of the sternum and that retrograde flow occurs during complete decompression.35 The subjects in this study adequately reflected a standard composition of a tertiary pediatric intensive care unit with all of subjects being PALS certified and most having advanced training in the previous 12 months (Table 1). All of the subjects were PALS certified within the last 24 months. However, some subjects had additional training that was more recent than the pediatric training. While all subjects were PALS trained, it cannot be ignored that many subjects had non-pediatric courses as their most recent training. Over 92% of subjects reported the intensive care unit as their primary assigned work location with >75% of subjects rating their on the job code exposure as more than rare. The findings of this study suggest that the quality of CPR even in highly trained personnel with remains sub-optimal. Our study suggests that the target rate of chest compressions is infrequently achieved during pediatric resuscitations and there is no significant decay in delivered rate over the recommended two-minute compression cycle. This is in support of recent adult data that shows rates are often sub-optimal. In a recent article by Abella et al. compression rates were <80 compressions per minute (cpm) in about one-third of the data analyzed.36 A recent pediatric study has shown basic life support skills to be poor in a training model20 but few recent pediatric studies have looked specifically at chest compression adequacy over time. Our study demonstrated an almost uniform inadequacy in compression depth. This is consistent with recent data from adult reports. Abella et al. reported that one-third of closed-chest compressions delivered to a cohort of adult arrest scenarios were too shallow.19 A more recent observational study by Perkins et al. reported that 97% of chest compressions were too shallow dur-
722
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723
ing advanced life support training scenarios.21 This finding of our study was in stark contrast to adequacy defined by rate, which was achieved by most subjects. Our study could not demonstrate a significant correlation between subject characteristics and the delivery of effective chest compressions. The statistical difference demonstrated in time since last certification and delivery of chest compressions most likely represents the characteristics of the minority of subjects who performed adequate depth chest compressions. This same phenomenon most likely explains the difference in performance of registered nurses versus respiratory therapists. A larger study is needed to adequately characterize the subjects who consistently perform chest compressions adequately. Subjects were unable to self-evaluate the inadequacy of delivered chest compressions. While a minority of subjects reported that they would have performed more forceful compressions if done in a real life situation, most report that they would have done compressions no differently or even less forceful. This suggests that subjects not only were unable to deliver adequate depth chest compressions but also were unable to identify adequate compressions in this simulation model. The subjects had no feedback during the scenario. While this may not reflect the situation of a real code, it allowed for an isolated evaluation of chest compression delivery. This does point out the need for emphasis of the leader’s role in assurance of adequate chest compression delivery. While the study demonstrated that the subjects were not able to adequately judge the chest compressions they delivered, it does support an absolute need for an independent check of chest compression depth in the form of the code leader. An additional study would be needed to tell if the leader role would be able to impact the adequacy of chest compressions by feedback and recognition of inadequate chest compressions. The study was designed to accurately reflect real life pediatric cardiac arrests, but there are several limitations to this design. Our study did not quantify complete recoil of the chest compressions, which has been demonstrated in a recent study to be inadequate in pediatric resuscitations.27 The current model may be adapted to measure this in a future study. Based on feedback from subjects on the post evaluation survey, our study seemed to limit the mannequin biases in all simulation models but could not completely eliminate it. 5. Conclusion The findings of this study suggest that the quality of CPR even in highly trained personnel with CPR experience remains sub-optimal. Similar to recent adult reports, pediatric chest compressions infrequently achieve adequate rates and almost uniformly are inadequate in depth. This suggests an even more vigilant emphasis on delivery and identification of adequate depth chest compressions at proper rates may be needed. Conflicts of interest None. Acknowledgements The authors would like to thank the entire Rady’s Children’s Hospital staff for their cooperation. A special thanks to Matt Schiel and Bradley Peterson who provided essential help in this study. References 1. Slonim Anthony D, Patel Kantilal M, Ruttimann Urs E, Pollack Murray M. Cardiopulmonary resuscitation in pediatric intensive care units. Crit Care Med 1997;25:1951–5.
2. Suominen P, Olkkola KT, Voipio V, Korpela R, Palo R, Rasanen J. Utstein style reporting of in-hospital paediatric cardiopulmonary resuscitation. Resuscitation 2000;45:17–25. 3. Parra David A, Totapally Bala R, Zahn Evan, et al. Outcome of cardiopulmonary resuscitation in a pediatric cardiac intensive care unit. Crit Care Med 2000;28:3296–300. 4. Morris MC, Nadkarni VM. Pediatric cardiopulmonary-cerebral resuscitation: an overview and future directions. Crit Care Clin 2003;19:337–64. 5. Meaney Peter A, Nadkarni Vinay M, Cook Francis E, et al. Higher survival rates among younger patients after pediatric intensive care unit cardiac arrests. Pediatrics 2006;118:2424–33. 6. Wik L, Steen PA, Bircher NG. Quality of bystander cardiopulmonary resuscitation influences outcome after prehospital cardiac arrest. Resuscitation 1994;28:195–203. 7. Gallagher EJ, Lombardi G, Gennis P. Effectiveness of bystander cardiopulmonary resuscitation and survival following out-of-hospital cardiac arrest. JAMA 1995;274:1922–5. 8. Van Hoeyweghen Raf J, Bossaert Leo L, Mullie Arsene, et al. Quality and efficiency of bystander CPR. Belgian Cerebral Resuscitation Study Group. Resuscitation 1993;26:47–52. 9. Kern Karl B, Hilwig Ronald W, Berg Robert A, Sanders Arthur B, Ewy Gordon A. Importance of continuous chest compressions during cardiopulmonary resuscitation: improved outcome during a simulated single lay-rescuer scenario. Circulation 2002;105:645–9. 10. Yu Ting, Weil Max Harry, Tang Wanchun, et al. Adverse outcomes of interrupted precordial compression during automated defibrillation. Circulation 2002;106:368–72. 11. 2005 American Heart Association (AHA) guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiovascular care (ECC) of pediatric and neonatal patients: pediatric basic life support. Pediatrics 2006; 117(5):e9891004. 12. Babbs CF, Voorhees WD, Fitzgerald KR, Holmes HR, Geddes LA. Relationship of blood pressure and flow during CPR to chest compression amplitude: evidence for an effective compression threshold. Ann Emerg Med 1983;12:527–32. 13. Bellamy RF, DeGuzman LR, Pedersen DC. Coronary blood flow during cardiopulmonary resuscitation in swine. Circulation 1984;69:174–80. 14. Feneley MP, Maier GW, Kern KB, et al. The influence of manual chest compression rate on hemodynamic support during cardiac arrest: high-impulse cardiopulmonary resuscitation. Circulation 1986;74:IV51–9. 15. Maier GW, Tyson Jr GS, Olsen CO, et al. The physiology of external cardiac massage: high-impulse cardiopulmonary resuscitation. Circulation 1984;70:86–101. 16. Ornato Joseph P, Levine Ronald L, Young Denise S, Racht Edward M, Garnett A Randy, Gonzalez Edgar R. The effect of applied chest compression force on systemic arterial pressure and end-tidal carbon dioxide concentration during CPR in human beings. Ann Emerg Med 1989;18:732–7. 17. Wolfe JA, Maier GW, Newton Jr JR, et al. Physiologic determinants of coronary blood flow during external cardiac massage. J Thorac Cardiovasc Surg 1988;95:523–32. 18. Aufderheide Tom P, Pirrallo Ronald G, Yannopoulos Demetris, et al. Incomplete chest wall decompression: a clinical evaluation of CPR performance by trained laypersons and an assessment of alternative manual chest compressiondecompression techniques. Resuscitation 2006;71:341–51. 19. Abella Benjamin S, Alvarado Jason P, Myklebust Helge, et al. Quality of cardiopulmonary resuscitation during in-hospital cardiac arrest. JAMA 2005;293:305–10. 20. Arshid M, Lo TY, Reynolds F. Quality of cardio-pulmonary resuscitation (CPR) during paediatric resuscitation training: time to stop the blind leading the blind. Resuscitation 2009;80:558–60. 21. Perkins Gavin D, Boyle William, Bridgestock Hannah, et al. Quality of CPR during advanced resuscitation training. Resuscitation 2008;77:69–74. 22. Ristagno Giuseppe, Tang Wanchun, Chang Yun-Te, et al. The quality of chest compressions during cardiopulmonary resuscitation overrides importance of timing of defibrillation. Chest 2007;132:70–5. 23. Steen Stig, Liao Qiuming, Pierre Leif, Paskevicius Audrius, Sjoberg Trygve. The critical importance of minimal delay between chest compressions and subsequent defibrillation: a haemodynamic explanation. Resuscitation 2003;58:249–58. 24. Weil Max Harry, Bisera Jose, Trevino Robert P, Rackow Eric C. Cardiac output and end-tidal carbon dioxide. Crit Care Med 1985;13:907–9. 25. Sato Yoji, Weil Max Harry, Sun Shijie, et al. Adverse effects of interrupting precordial compression during cardiopulmonary resuscitation. Crit Care Med 1997;25:733–6. 26. Eftestol T, Sunde K, Steen PA. Effects of interrupting precordial compressions on the calculated probability of defibrillation success during out-of-hospital cardiac arrest. Circulation 2002;105:2270–3. 27. Sutton Robert M, Niles Dana, Nysaether Jon, et al. Quantitative analysis of CPR quality during in-hospital resuscitation of older children and adolescents. Pediatrics 2009;124:494–9. 28. Lurie Keith G, Mulligan Katherine A, McKnite Scott, Detloff Barry, Lindstrom Paul, Lindner Karl H. Optimizing standard cardiopulmonary resuscitation with an inspiratory impedance threshold valve. Chest 1998;113:1084–90. 29. Edelson Dana P, Abella Benjamin S, Kramer-Johansen Jo, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation 2006;71:137–45. 30. Kouwenhoven WB, Jude JR, Knickerbocker GG. Closed-chest cardiac massage. JAMA 1960;173:1064–7.
J.T. Hamrick et al. / Resuscitation 81 (2010) 718–723 31. Rodarte JR. Mechanisms of blood flow during cardiopulmonary resuscitation. Mayo Clin Proc 1991;66:436–8. 32. Redberg RF, Tucker KJ, Cohen TJ, Dutton JP, Callaham ML, Schiller NB. Physiology of blood flow during cardiopulmonary resuscitation. A transesophageal echocardiographic study. Circulation 1993;88:534–42. 33. Werner JA, Greene HL, Janko CL, Cobb LA. Visualization of cardiac valve motion in man during external chest compression using two-dimensional echocardiography. Implications regarding the mechanism of blood flow. Circulation 1981;63:1417–21.
723
34. Ma Matthew Huei-Ming, Hwang Juey-Jen, Lai Ling-Ping, et al. Transesophageal echocardiographic assessment of mitral valve position and pulmonary venous flow during cardiopulmonary resuscitation in humans. Circulation 1995;92:854–61. 35. Andreka P, Frenneaux MP. Haemodynamics of cardiac arrest and resuscitation. Curr Opin Crit Care 2006;12:198–203. 36. Abella Benjamin S, Sandbo Nathan, Vassilatos Peter, et al. Chest compression rates during cardiopulmonary resuscitation are suboptimal: a prospective study during in-hospital cardiac arrest. Circulation 2005;111:428–34.