American Journal of Emergency Medicine 33 (2015) 1037–1041
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
The uniform chest compression depth of 50 mm or greater recommended by current guidelines is not appropriate for all adults☆ Soo Hoon Lee, MD ⁎, Dong Hoon Kim, MD, PhD, Tae-Sin Kang, MD, Changwoo Kang, MD, Jin Hee Jeong, MD, Seong Chun Kim, MD, Dong Seob Kim, MD Department of Emergency Medicine, Gyeongsang National University Hospital, Jinju, Gyeongsangnam-Do, Republic of Korea
a r t i c l e
i n f o
Article history: Received 16 February 2015 Received in revised form 13 April 2015 Accepted 22 April 2015
a b s t r a c t Objective: This study was conducted to evaluate the appropriateness of the chest compression (CC) depth recommended in the current guidelines and simulated external CCs, and to characterize the optimal CC depth for an adult by body mass index (BMI). Methods: Adult patients who underwent chest computed tomography as a screening test for latent pulmonary diseases in the health care center were enrolled in this study. We calculated the internal anteroposterior (AP) diameter (IAPD) and external AP diameter (EAPD) of the chest across BMIs (b18.50, 18.50-24.99, 25.00-29.99, and ≥30.00 kg/m2) for simulated CC depth. We also calculated the residual chest depths less than 20 mm for simulated CC depth. Results: There was a statistically significant difference in the chest EAPD and IAPD measured at the lower half of the sternum for each BMI groups (EAPD: R2 = 0.638, P b .001; IAPD: R2 = 0.297, P b .001). For one-half external AP CC, 100% of the patients, regardless of BMI, had a calculated residual internal chest depth less than 20 mm. For one-fourth external AP CC, no patients had a calculated residual internal chest depth less than 20 mm. For onethird external AP CC, only 6.48% of the patients had a calculated residual internal chest depth less than 20 mm. Conclusions: It is not appropriate that the current CC depth (≥50 mm), expressed only as absolute measurement without a fraction of the depth of the chest, is applied uniformly in all adults. In addition, in terms of safety and efficacy, simulated CC targeting approximately between one-third and one-fourth EAPD CC depth might be appropriate. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Survival to hospital discharge for patients with out-of-hospital cardiac arrest varies widely between communities, with survival rates ranging from 3.3% to 45% [1,2]. This variation in survival outcomes among communities can be attributed to differences in the implementation of the 5 links in the chain of survival or the cardiopulmonary resuscitation (CPR) quality, including chest compression rate, depth, and complete chest recoil [3–5]. The 2010 International Liaison Committee on Resuscitation emphasized delivering high-quality chest compressions: push hard and fast to a depth of at least 2 in. or 5 cm at a rate of at least 100 compressions per minute, allowing for full chest recoil after each compression and minimizing interruptions in chest compressions [6]. Chest compressions generate blood flow and oxygen delivery to the myocardium and brain by increasing intrathoracic pressure and directly compressing the heart. To provide these effective chest compressions, the rescuers should push hard and push fast. The anteroposterior (AP) chest diameter by body size in adults varies from individual to individual. Therefore, there is a question of whether it ☆ Conflicts of interest: No authors have any conflicts of interest. ⁎ Corresponding author at: Department of Emergency Medicine, Gyeongsang National University Hospital, Gangnam-Ro 79, Jinju, Gyeongsangnam-Do 660-702, Republic of Korea. Tel.: +82 55 750 8975; fax: +82 55 757 0514. E-mail address: [email protected] (S.H. Lee). http://dx.doi.org/10.1016/j.ajem.2015.04.034 0735-6757/© 2015 Elsevier Inc. All rights reserved.
is appropriate that the chest compression depth of 50 mm or greater recommended by current guidelines be applied uniformly in all adults. The primary purposes of this study were to evaluate the appropriateness of chest compression depth recommended by the current adult CPR guidelines and to characterize the optimal chest compression depths of adults with various body mass indexes (BMIs) using chest computed tomography (CT). The secondary objective was to calculate and estimate residual internal chest depths if simulated external chest compressions of onehalf, one-third, and one-fourth AP chest depth were delivered. We hypothesized that CT reconstruction estimates of chest diameter by BMI spectrum would demonstrate that simulated chest compression targeting approximately one-third or one-fourth the external AP chest compression depth might be more appropriate than the chest compression depth of 50 mm or greater recommended by the current guidelines.
2. Methods 2.1. Setting Patients older than 18 years who underwent precontrast low-dose chest CT as a screening test for latent pulmonary diseases in the health care center of our hospital from September 1 to December 31, 2013,
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S.H. Lee et al. / American Journal of Emergency Medicine 33 (2015) 1037–1041
were enrolled in this study. Patients with severe thorax deformity, such as funnel chest, pectus excavatum/carinatum, or chest hypoplasia, were excluded. Demographic data including sex, age, height, and body weight of the patients were acquired from the final reports of the medical examination. The study was approved by the institutional review board of our hospital. Just before the CT scanning, the patients were requested to hold their breath at the half inspiration point. All CT images from patients included in this study were generated by 64 channel multidetector CT (Lightspeed VCT; General Electric Medical Systems, Milwaukee, WI). All of the patient imaging data were transferred to a dedicated workstation (Advantage Windows 4.3; GE Health Care). The picture archiving and communication system that was used to analyze the images in this study, to perform 3-dimensional reconstruction, and to take direct measurements by an electronic cursor was AGFA Impax 5.3 picture archiving and communication system workstations (Mortsel, Belgium). Two hundred ninety-three consecutive retrospective chest CT scans that were available were reviewed and analyzed for each BMI: b 18.50, 18.50-24.99, 25.00-29.99, and ≥30.00 kg/m 2. Using CT reconstruction, individual internal and external chest depths were measured and residual internal depth resulting from several simulated chest compression depths was calculated. We examined the percentages of patients who would have less than 20 mm of residual chest depth during a simulated 50-mm, one-half, one-third, and one-fourth external AP chest depth compression. We selected 20-mm residual chest depth as a cutoff by previous studies about normal right and left ventricular wall thickness [7–9], because we believed that 20-mm residual chest depth would still have the potential to injure the intrathoracic structures and may not actually be achievable because of the presence of the thickness of the myocardium.
proposed chest compression was calculated for one-half (50%), onethird (33%), and one-fourth (25%) the measured external chest depth. The residual internal chest depth after simulated chest compression was calculated as the internal chest depth from the chest CT scan minus the depth of the proposed chest compression (assuming that the full depth of the chest compression would be transmitted to the internal structures). We calculated the proportion of patients with a measured residual chest depths less than 20 mm residual chest depth across BMIs for both the calculated compression depths and adult recommendations (≥50 mm). A value of 20 mm would indicate that no remaining internal chest depth would be available during the simulated chest compression, and a negative value would suggest that it would be impossible to compress to that particular target depth because there would not be enough available internal chest depth to accommodate the chest compression. A positive value would reflect the remaining available internal chest depth after a simulated chest compression.
2.2. Analysis
A total of 298 consecutive patients underwent precontrast low-dose chest CT during the study period. Five patients were excluded because of severe chest deformity. A total of 218 men and 75 women were included in this study. The unequal male-to-female ratios in the group were a result of an unequal gender distribution during this study period. The demographic data of the patients enrolled in this study are shown in Table. The study populations have similar BMI distribution, including body weights and heights, for the Korean population [10,11]. The average EAPD and IAPD depths of chest compression measured at the lower half of the sternum for each BMI group are listed in Table and Fig. 2. There was a statistically significant difference in the chest EAPD and IAPD measured at the lower half of the sternum for each BMI group (EAPD: R2 = 0.638, P b .001; IAPD: R2 = 0.297, P b .001). Fig. 3 displays the ratio of a 50-mm, one-fourth, one-third, and one-half AP external chest depth to internal chest depth minus 20 mm in each simulated chest compression group. Fig. 4 displays residual internal chest depth minus 20 mm during simulated 50-mm, one-fourth, one-third, and one-half AP external chest depth compressions. As with the measured internal chest depths, the residual internal chest depth measurements available for compression also increased with BMI (P b .001). Fig. 5 displays the percentage of patients in each BMI group with less than 20 mm of residual internal chest depth during a 5-cm, one-fourth, one-third, and one-half AP external chest depth compression. For onehalf external AP chest compression, all patients, regardless of BMI, had a calculated residual internal chest depth less than 20 mm. For onefourth external AP chest compression, no patients had a calculated residual internal chest depth less than 20 mm. For one-third external AP chest compression, only 6.48% (19 of 293) of the patients had a calculated residual internal chest depth less than 20 mm.
The internal AP diameter (IAPD) and external AP diameter (EAPD) of the chest were measured as demonstrated in Fig. 1. By using an axial slice at the lower half level of the sternum, the typical chest compression location recommended by the current guidelines, we calculated the external chest depth by measuring a line drawn perpendicularly from the skin anteriorly to the skin posteriorly. The lower half of the sternum was defined as the midpoint of the lower sternum (ie, one quarter of the total sternal length from the xiphoid process in the midline sagittal view). In addition, we calculated the internal depth available by measuring a line drawn perpendicularly from the posterior sternum to the anterior vertebral body at the lower half level of the sternum. The depth of a
2.3. Statistical analysis All of the continuous values are presented as the mean and SD. The 1-way analyses of variance among groups and univariate linear regression analyses were used for comparisons of the average depth of chest compression of one-half, one-third, and one-fourth the measured external chest depth, as well as IAPD and EAPD at the midpoint of the lower half of the sternum, by BMI. For all of the comparisons, a 2-sided P value of .05 was considered statistically significant. All analyses were performed using SPSS statistical software (version 21.0; IBM, Chicago, IL). 3. Results
4. Discussion
Fig. 1. Computed tomographic scan demonstrating axial image at the midsternal level and method for calculating chest EAPD and IAPD.
In this study, the chest compression depth of 50 mm or greater recommended by the current guidelines was not appropriate in the ratio of EAPD and IAPD based on each BMI, and the ratio of a 50-mm, one-
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Table Demographic data and internal and external chest depth by BMI in study group Variables
Total
b18.5
18.50-24.99
25.00-29.99
≥30.00
P
No. Sex, male (%) Age (y), mean ± SD Height (m), mean ± SD Weight (kg), mean ± SD EAPD (cm), mean ± SD IAPD (cm), mean ± SD
293 218 46.09 ± 9.15 168.58 ± 8.61 68.87 ± 12.53 22.00 ± 2.13 10.79 ± 1.48
15 7 50.47 ± 15.19 164.07 ± 8.81 48.18 ± 5.65 18.52 ± 1.56 8.87 ± 1.44
168 121 45.52 ± 8.49 168.64 ± 8.83 64.24 ± 9.07 21.22 ± 1.65 10.42 ± 1.36
93 78 47.19 ± 9.27 169.25 ± 8.17 76.60 ± 8.53 23.35 ± 1.37 11.55 ± 1.16
17 12 41.88 ± 5.49 168.37 ± 8.14 90.57 ± 9.25 25.32 ± 1.12 12.09 ± 1.06
.028 .195 b.001 b.001 b.001
fourth, one-third, and one-half AP external chest depth to internal chest depth, minus 20 mm was simulated in each chest compression group. Also, in terms of safety and efficacy, simulated chest compression targeting approximately one-third or one-fourth EAPD chest compression depth by calculating and estimating residual internal chest depths in simulated external chest compressions might be more appropriate than the chest compression depth of 50 mm or greater recommended by current guidelines. The chest compression depths suggested by the guidelines have increased over time. According to the latest CPR guideline, the adult sternum should be depressed at least 2 in. (5 cm) in adult resuscitation. To provide these effective chest compressions, the rescuers should push hard and push fast. Several studies demonstrated that deeper chest compression of 50 mm or greater recommended by the 2010 American Heart Association and European Resuscitation Council Guidelines are associated with improved short-term outcomes [12,13]. The optimal compression depths for adults should be based on anatomical realities and hemodynamic measurements. The 2010 guidelines recommended a compression depth of at least one-third of the chest AP dimension or approximately 4 cm (1.5 in.) in infants and 5 cm (2 in.) in children during pediatric resuscitation. The chest compression depth was expressed as both a fraction of the depth of the chest and an absolute measurement [14,15]. However, in the 2010 guideline of adult resuscitation, it was expressed as only an absolute measurement, without a fraction of the depth of the chest. In this study, the average EAPD and IAPD depths of the chest measured at the lower half of the
sternum increased significantly with each BMI group. The ratio of chest compression of 50 mm or greater recommended by the 2010 current guidelines for the EAPD and IAPD depths of chest decreased with BMI. This result indicates that chest compression depth should increase with BMI to maintain the persistent ratio of chest compression depth to AP diameter of the chest. There are 2 major theories (cardiac pump theory and thoracic pump theory) regarding forward blood flow during CPR [12,13,16,17]. Recently, the aortic pump theory, that is, that direct chest compression is predominantly directed at the aorta during adult resuscitation, was introduced by the analysis of CT images [18–20]. However, the mechanism of forward blood flow during CPR remains controversial, and there have been many debates on the role of the heart during CPR. Regardless of the mechanism, optimal chest compression depths should not only achieve optimal cardiac output with maximal coronary and cerebral perfusion but also not increase unwanted complications by injury of the intrathoracic structures underlying the compression point of the sternum. To achieve this optimal cardiac output, the residual internal chest depth should as small as possible without being a negative. Maier et al [21] addressed that direct cardiac compression appeared to be the major determinant of stroke volume during manual external cardiac massage, and manual chest compressions of high velocity, moderate force, and brief duration at a rate of 120/min seemed to optimize systemic and coronary blood flow. In other words, to maximize cardiac stroke volume and coronary blood flow, manual massage should be performed with high-rate brief duration compressions using only moderate force. They suggested that the mechanism of this finding is unknown but may relate to obstructive compression of the left ventricular outflow tract, because the ventricular to aortic pressure gradient increased. In fact, Hwang et al [22] observed a significant narrowing of the left ventricular outflow tract or the aorta in all 34 of the adult arrest patients they studied, with the degree of compression at the area of maximal compression ranging from 19% to 83% (mean ± SD, 49% ± 19%). According to Maier et al [23], potentially injurious high compression force did not seem necessary, and when only moderate force was used, visceral damage was not observed in neither animal nor human studies that they conducted over a 5-year period. In their study of
Fig. 2. The correlation of chest EAPD and IAPD measured at the lower half of the sternum with each BMI group.
Fig. 3. The ratio of a 50-mm, one-fourth, one-third, and one-half AP external chest depth to internal chest depth minus 20 mm in each BMI group.
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Fig. 4. Residual internal chest depth during simulated 50-mm, one-fourth, one-third, and one-half AP external chest depth compressions.
high-impulse CPR in patients, they found that patients commonly regain consciousness using compression rates of 120 to 150/min. Even when chest compressions were performed with the dogs in the lateral position, which allows maximal compression directly over the left ventricle, they found that only moderate force was needed for optimal blood flow rather than a deep compression, which as we also suggested here, has the potential to cause injury to the intrathoracic structures. Fig. 4 shows the residual internal chest depth during simulated 50 mm, one-fourth, one-third, and one-half AP external chest depth compressions. This result suggests that during one-third EAPD chest compression depth, the residual internal chest depth would be the least with positive definiteness among the simulated chest compression depths. Babbs and colleagues [24], in addition to their mathematical study of optimal chest compression frequency vs body size (neonate to adult), they addressed pump mechanisms and briefly addressed compression depth. They conducted an analysis of CT images of neonates (Online Supplement 4) in which AP internal and external chest depth, heart depth, and noncardiac thoracic tissue depth were measured. They found that with 33% compression depth, one quarter of patients would experience maximal or overcompression of the mediastinum, thereby completely flattening the heart within the anatomic space available between the sternum and the spine. If compression depth were increased further to 50% of chest diameter, there would be overcompression of the heart in nearly all neonates. We selected 20-mm residual chest depth as a cutoff by previous studies on left and right ventricle wall thickness. We believed that less than 20 mm residual chest depth would possibly to injure intrathoracic structures adjacent to heart and may not actually be achievable because of the presence of the thickness of the ventricle. There have been reports about iatrogenic injuries associated with chest compressions since CPR was introduced in the 1960s [25,26]. The iatrogenic injuries such as intrathoracic or intra-abdominal laceration and hemorrhage could be fatal [27,28]. An increased compression depth may be associated with a
higher incidence of iatrogenic injuries. Regardless of the mechanism, optimal chest compression depths should not only achieve optimal cardiac output with maximal coronary and cerebral perfusion but also not increase unwanted complications by injury of the intrathoracic structures underlying the compression point of the sternum. In this study, the percentages of patients who would have less than 20 mm of residual chest depth during a simulated 50-mm, one-fourth EAPD, one-third EAPD, and one-half EAPD chest depth compression are displayed in Fig. 5. These results indicate that during a simulated 50-mm, onefourth, one-third, and one-half EAPD chest compression, 0.68% of 50 mm, 0.00% of one-fourth EAPD, 6.48% of one-third EAPD, and 100% of one-half EAPD group would have less than 20 mm of residual internal chest depth. The chest compression depth of one-half EAPD may not be theoretically attainable or safe for all adults. During a one-half chest depth compression, all patients in every BMI group would theoretically have no residual internal depth in the thorax. This may actually be impossible to achieve; however, if achievable, it could potentially harm the structures being compressed. These findings also suggest that a one-fourth EAPD chest compression for every BMI group might be a safe alternative to the chest compression depth recommended in the current adult CPR guidelines. Standard parameters for chest compressions in adult resuscitation should generally apply to the wide range and spectrum of chest wall characteristics of patients. The quality of CPR could be different considering the body contour of victim and the rescuer, and this study might add more evidence to this field [29]. With the growing field of CPR real-time assist and feedback technologies, it has become more important to ensure that the chest compression depth recommended in the current CPR guidelines is both safe and attainable in the adult population. We believe that this study will have a positive impact on the current field of adult resuscitation by providing radiographic evidence for chest compression depth.
5. Limitations There were some limitations to this study. First, the results may not be generalizable because this study is a retrospective, observational, and a single-center study. Second, the CT images were not taken during real CPR situations. In real CPR, actual chest compression and/or positive pressure ventilation might displace the location of intrathoracic structures. We also did not account for potential soft tissue compressibility during our calculated external chest compressions when we performed our calculations. A real-time approach during actual resuscitation is needed to explore the dynamic complexity. Third, the CT scans of this study were acquired while patients held their breath at the half inspiration point. The different respiratory phases may affect the precise measurement of the length and the conformational changes of intrathoracic structures. Fourth, the number of female patients is much smaller than that of male patients, and the mean age of the patients in this study is younger than the mean age of patients with out-of-hospital cardiac arrest in Korea. Although this presents no significant problem in the statistical analysis of this study, 75 female patients and the age of 46.09 ± 9.15 years cannot be thought to represent the whole population of Korean adults.
6. Conclusions
Fig. 5. The percentage of patients in each BMI group with less than 20 mm of residual internal chest depth during a 50-mm, one-fourth, one-third, and one-half AP external chest depth compression.
It is not appropriate that the current chest compression depth (≥50 mm) expressed as an absolute measurement without a fraction of the depth of the chest is applied uniformly in all adults. In addition, in terms of safety and efficacy, simulated chest compression targeting approximately between one-third and one-fourth EAPD chest compression depth based on calculating and estimating residual internal chest depths in simulated external chest compression might be more appropriate than the chest compression depth of 50 mm or greater recommended by the current guidelines.
S.H. Lee et al. / American Journal of Emergency Medicine 33 (2015) 1037–1041
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[15] Braga MS, Dominguez TE, Pollock AN, Niles D, Meyer A, Myklebust H, et al. Estimation of optimal CPR chest compression depth in children by using computer tomography. Pediatrics 2009;124(1):e69–74. [16] Feneley MP, Maier GW, Gaynor JW, Gall SA, Kisslo JA, Davis JW, et al. Sequence of mitral valve motion and transmitral blood flow during manual cardiopulmonary resuscitation in dogs. Circulation 1987;76(2):363–75. [17] Halperin HR, Tsitlik JE, Beyar R, Chandra N, Guerci AD. Intrathoracic pressure fluctuations move blood during CPR: comparison of hemodynamic data with predictions from a mathematical model. Ann Biomed Eng 1987;15(3-4): 385–403. [18] Rottenberg EM. The need for a leftward shift in the flow-depth relationship during cardiopulmonary resuscitation. Resuscitation 2007;72(3):350–2. [19] Pickard A, Darby M, Soar J. Radiological assessment of the adult chest: implications for chest compressions. Resuscitation 2006;71(3):387–90. [20] Rottenberg EM. The critical need for further research and development of abdominal compressions cardiopulmonary resuscitation. Am J Emerg Med 2014;32(8):931–4. [21] Maier GW, Tyson Jr GS, Olsen CO, Kernstein KH, Davis JW, Conn EH, et al. The physiology of external cardiac massage: high-impulse cardiopulmonary resuscitation. Circulation 1984;70(1):86–101. [22] Hwang SO, Zhao PG, Choi HJ, Park KH, Cha KC, Park SM, et al. Compression of the left ventricular outflow tract during cardiopulmonary resuscitation. Acad Emerg Med 2009;16(10):928–33. [23] Maier GW, Newton Jr JR, Wolfe JA, Tyson Jr GS, Olsen CO, Glower DD, et al. The influence of manual chest compression rate on hemodynamic support during cardiac arrest: high-impulse cardiopulmonary resuscitation. Circulation 1986;74(6 Pt 2): IV51–9. [24] Babbs CF, Meyer A, Nadkarni V. Neonatal CPR: room at the top—a mathematical study of optimal chest compression frequency versus body size. Resuscitation 2009;80(11):1280–4. [25] Buschmann CT, Tsokos M. Frequent and rare complications of resuscitation attempts. Intensive Care Med 2009;35(3):397–404. [26] Kim EY, Yang HJ, Sung YM, Cho SH, Kim JH, Kim HS, et al. Multidetector CT findings of skeletal chest injuries secondary to cardiopulmonary resuscitation. Resuscitation 2011;82(10):1285–8. [27] Meron G, Kurkciyan I, Sterz F. Cardiopulmonary resuscitation–associated major liver injury. Resuscitation 2007;75(3):445–53. [28] Kouzu H, Hase M, Kokubu N, Nishida J, Kawamukai M, Usami Y, et al. Delayed visceral bleeding from liver injury after cardiopulmonary resuscitation. J Emerg Med 2012; 43(4):e245–8. [29] Lee CJ, Chung TN, Bae J, Kim EC, Choi SW, Kim OJ. 50% duty cycle may be inappropriate to achieve a sufficient chest compression depth when cardiopulmonary resuscitation is performed by female or light rescuers. Clin Exp Emerg Med 2015;2(1):9–15.
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
The uniform chest compression depth of 50 mm or greater recommended by current guidelines is not appropriate for all adults☆ Soo Hoon Lee, MD ⁎, Dong Hoon Kim, MD, PhD, Tae-Sin Kang, MD, Changwoo Kang, MD, Jin Hee Jeong, MD, Seong Chun Kim, MD, Dong Seob Kim, MD Department of Emergency Medicine, Gyeongsang National University Hospital, Jinju, Gyeongsangnam-Do, Republic of Korea
a r t i c l e
i n f o
Article history: Received 16 February 2015 Received in revised form 13 April 2015 Accepted 22 April 2015
a b s t r a c t Objective: This study was conducted to evaluate the appropriateness of the chest compression (CC) depth recommended in the current guidelines and simulated external CCs, and to characterize the optimal CC depth for an adult by body mass index (BMI). Methods: Adult patients who underwent chest computed tomography as a screening test for latent pulmonary diseases in the health care center were enrolled in this study. We calculated the internal anteroposterior (AP) diameter (IAPD) and external AP diameter (EAPD) of the chest across BMIs (b18.50, 18.50-24.99, 25.00-29.99, and ≥30.00 kg/m2) for simulated CC depth. We also calculated the residual chest depths less than 20 mm for simulated CC depth. Results: There was a statistically significant difference in the chest EAPD and IAPD measured at the lower half of the sternum for each BMI groups (EAPD: R2 = 0.638, P b .001; IAPD: R2 = 0.297, P b .001). For one-half external AP CC, 100% of the patients, regardless of BMI, had a calculated residual internal chest depth less than 20 mm. For one-fourth external AP CC, no patients had a calculated residual internal chest depth less than 20 mm. For onethird external AP CC, only 6.48% of the patients had a calculated residual internal chest depth less than 20 mm. Conclusions: It is not appropriate that the current CC depth (≥50 mm), expressed only as absolute measurement without a fraction of the depth of the chest, is applied uniformly in all adults. In addition, in terms of safety and efficacy, simulated CC targeting approximately between one-third and one-fourth EAPD CC depth might be appropriate. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Survival to hospital discharge for patients with out-of-hospital cardiac arrest varies widely between communities, with survival rates ranging from 3.3% to 45% [1,2]. This variation in survival outcomes among communities can be attributed to differences in the implementation of the 5 links in the chain of survival or the cardiopulmonary resuscitation (CPR) quality, including chest compression rate, depth, and complete chest recoil [3–5]. The 2010 International Liaison Committee on Resuscitation emphasized delivering high-quality chest compressions: push hard and fast to a depth of at least 2 in. or 5 cm at a rate of at least 100 compressions per minute, allowing for full chest recoil after each compression and minimizing interruptions in chest compressions [6]. Chest compressions generate blood flow and oxygen delivery to the myocardium and brain by increasing intrathoracic pressure and directly compressing the heart. To provide these effective chest compressions, the rescuers should push hard and push fast. The anteroposterior (AP) chest diameter by body size in adults varies from individual to individual. Therefore, there is a question of whether it ☆ Conflicts of interest: No authors have any conflicts of interest. ⁎ Corresponding author at: Department of Emergency Medicine, Gyeongsang National University Hospital, Gangnam-Ro 79, Jinju, Gyeongsangnam-Do 660-702, Republic of Korea. Tel.: +82 55 750 8975; fax: +82 55 757 0514. E-mail address: [email protected] (S.H. Lee). http://dx.doi.org/10.1016/j.ajem.2015.04.034 0735-6757/© 2015 Elsevier Inc. All rights reserved.
is appropriate that the chest compression depth of 50 mm or greater recommended by current guidelines be applied uniformly in all adults. The primary purposes of this study were to evaluate the appropriateness of chest compression depth recommended by the current adult CPR guidelines and to characterize the optimal chest compression depths of adults with various body mass indexes (BMIs) using chest computed tomography (CT). The secondary objective was to calculate and estimate residual internal chest depths if simulated external chest compressions of onehalf, one-third, and one-fourth AP chest depth were delivered. We hypothesized that CT reconstruction estimates of chest diameter by BMI spectrum would demonstrate that simulated chest compression targeting approximately one-third or one-fourth the external AP chest compression depth might be more appropriate than the chest compression depth of 50 mm or greater recommended by the current guidelines.
2. Methods 2.1. Setting Patients older than 18 years who underwent precontrast low-dose chest CT as a screening test for latent pulmonary diseases in the health care center of our hospital from September 1 to December 31, 2013,
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S.H. Lee et al. / American Journal of Emergency Medicine 33 (2015) 1037–1041
were enrolled in this study. Patients with severe thorax deformity, such as funnel chest, pectus excavatum/carinatum, or chest hypoplasia, were excluded. Demographic data including sex, age, height, and body weight of the patients were acquired from the final reports of the medical examination. The study was approved by the institutional review board of our hospital. Just before the CT scanning, the patients were requested to hold their breath at the half inspiration point. All CT images from patients included in this study were generated by 64 channel multidetector CT (Lightspeed VCT; General Electric Medical Systems, Milwaukee, WI). All of the patient imaging data were transferred to a dedicated workstation (Advantage Windows 4.3; GE Health Care). The picture archiving and communication system that was used to analyze the images in this study, to perform 3-dimensional reconstruction, and to take direct measurements by an electronic cursor was AGFA Impax 5.3 picture archiving and communication system workstations (Mortsel, Belgium). Two hundred ninety-three consecutive retrospective chest CT scans that were available were reviewed and analyzed for each BMI: b 18.50, 18.50-24.99, 25.00-29.99, and ≥30.00 kg/m 2. Using CT reconstruction, individual internal and external chest depths were measured and residual internal depth resulting from several simulated chest compression depths was calculated. We examined the percentages of patients who would have less than 20 mm of residual chest depth during a simulated 50-mm, one-half, one-third, and one-fourth external AP chest depth compression. We selected 20-mm residual chest depth as a cutoff by previous studies about normal right and left ventricular wall thickness [7–9], because we believed that 20-mm residual chest depth would still have the potential to injure the intrathoracic structures and may not actually be achievable because of the presence of the thickness of the myocardium.
proposed chest compression was calculated for one-half (50%), onethird (33%), and one-fourth (25%) the measured external chest depth. The residual internal chest depth after simulated chest compression was calculated as the internal chest depth from the chest CT scan minus the depth of the proposed chest compression (assuming that the full depth of the chest compression would be transmitted to the internal structures). We calculated the proportion of patients with a measured residual chest depths less than 20 mm residual chest depth across BMIs for both the calculated compression depths and adult recommendations (≥50 mm). A value of 20 mm would indicate that no remaining internal chest depth would be available during the simulated chest compression, and a negative value would suggest that it would be impossible to compress to that particular target depth because there would not be enough available internal chest depth to accommodate the chest compression. A positive value would reflect the remaining available internal chest depth after a simulated chest compression.
2.2. Analysis
A total of 298 consecutive patients underwent precontrast low-dose chest CT during the study period. Five patients were excluded because of severe chest deformity. A total of 218 men and 75 women were included in this study. The unequal male-to-female ratios in the group were a result of an unequal gender distribution during this study period. The demographic data of the patients enrolled in this study are shown in Table. The study populations have similar BMI distribution, including body weights and heights, for the Korean population [10,11]. The average EAPD and IAPD depths of chest compression measured at the lower half of the sternum for each BMI group are listed in Table and Fig. 2. There was a statistically significant difference in the chest EAPD and IAPD measured at the lower half of the sternum for each BMI group (EAPD: R2 = 0.638, P b .001; IAPD: R2 = 0.297, P b .001). Fig. 3 displays the ratio of a 50-mm, one-fourth, one-third, and one-half AP external chest depth to internal chest depth minus 20 mm in each simulated chest compression group. Fig. 4 displays residual internal chest depth minus 20 mm during simulated 50-mm, one-fourth, one-third, and one-half AP external chest depth compressions. As with the measured internal chest depths, the residual internal chest depth measurements available for compression also increased with BMI (P b .001). Fig. 5 displays the percentage of patients in each BMI group with less than 20 mm of residual internal chest depth during a 5-cm, one-fourth, one-third, and one-half AP external chest depth compression. For onehalf external AP chest compression, all patients, regardless of BMI, had a calculated residual internal chest depth less than 20 mm. For onefourth external AP chest compression, no patients had a calculated residual internal chest depth less than 20 mm. For one-third external AP chest compression, only 6.48% (19 of 293) of the patients had a calculated residual internal chest depth less than 20 mm.
The internal AP diameter (IAPD) and external AP diameter (EAPD) of the chest were measured as demonstrated in Fig. 1. By using an axial slice at the lower half level of the sternum, the typical chest compression location recommended by the current guidelines, we calculated the external chest depth by measuring a line drawn perpendicularly from the skin anteriorly to the skin posteriorly. The lower half of the sternum was defined as the midpoint of the lower sternum (ie, one quarter of the total sternal length from the xiphoid process in the midline sagittal view). In addition, we calculated the internal depth available by measuring a line drawn perpendicularly from the posterior sternum to the anterior vertebral body at the lower half level of the sternum. The depth of a
2.3. Statistical analysis All of the continuous values are presented as the mean and SD. The 1-way analyses of variance among groups and univariate linear regression analyses were used for comparisons of the average depth of chest compression of one-half, one-third, and one-fourth the measured external chest depth, as well as IAPD and EAPD at the midpoint of the lower half of the sternum, by BMI. For all of the comparisons, a 2-sided P value of .05 was considered statistically significant. All analyses were performed using SPSS statistical software (version 21.0; IBM, Chicago, IL). 3. Results
4. Discussion
Fig. 1. Computed tomographic scan demonstrating axial image at the midsternal level and method for calculating chest EAPD and IAPD.
In this study, the chest compression depth of 50 mm or greater recommended by the current guidelines was not appropriate in the ratio of EAPD and IAPD based on each BMI, and the ratio of a 50-mm, one-
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Table Demographic data and internal and external chest depth by BMI in study group Variables
Total
b18.5
18.50-24.99
25.00-29.99
≥30.00
P
No. Sex, male (%) Age (y), mean ± SD Height (m), mean ± SD Weight (kg), mean ± SD EAPD (cm), mean ± SD IAPD (cm), mean ± SD
293 218 46.09 ± 9.15 168.58 ± 8.61 68.87 ± 12.53 22.00 ± 2.13 10.79 ± 1.48
15 7 50.47 ± 15.19 164.07 ± 8.81 48.18 ± 5.65 18.52 ± 1.56 8.87 ± 1.44
168 121 45.52 ± 8.49 168.64 ± 8.83 64.24 ± 9.07 21.22 ± 1.65 10.42 ± 1.36
93 78 47.19 ± 9.27 169.25 ± 8.17 76.60 ± 8.53 23.35 ± 1.37 11.55 ± 1.16
17 12 41.88 ± 5.49 168.37 ± 8.14 90.57 ± 9.25 25.32 ± 1.12 12.09 ± 1.06
.028 .195 b.001 b.001 b.001
fourth, one-third, and one-half AP external chest depth to internal chest depth, minus 20 mm was simulated in each chest compression group. Also, in terms of safety and efficacy, simulated chest compression targeting approximately one-third or one-fourth EAPD chest compression depth by calculating and estimating residual internal chest depths in simulated external chest compressions might be more appropriate than the chest compression depth of 50 mm or greater recommended by current guidelines. The chest compression depths suggested by the guidelines have increased over time. According to the latest CPR guideline, the adult sternum should be depressed at least 2 in. (5 cm) in adult resuscitation. To provide these effective chest compressions, the rescuers should push hard and push fast. Several studies demonstrated that deeper chest compression of 50 mm or greater recommended by the 2010 American Heart Association and European Resuscitation Council Guidelines are associated with improved short-term outcomes [12,13]. The optimal compression depths for adults should be based on anatomical realities and hemodynamic measurements. The 2010 guidelines recommended a compression depth of at least one-third of the chest AP dimension or approximately 4 cm (1.5 in.) in infants and 5 cm (2 in.) in children during pediatric resuscitation. The chest compression depth was expressed as both a fraction of the depth of the chest and an absolute measurement [14,15]. However, in the 2010 guideline of adult resuscitation, it was expressed as only an absolute measurement, without a fraction of the depth of the chest. In this study, the average EAPD and IAPD depths of the chest measured at the lower half of the
sternum increased significantly with each BMI group. The ratio of chest compression of 50 mm or greater recommended by the 2010 current guidelines for the EAPD and IAPD depths of chest decreased with BMI. This result indicates that chest compression depth should increase with BMI to maintain the persistent ratio of chest compression depth to AP diameter of the chest. There are 2 major theories (cardiac pump theory and thoracic pump theory) regarding forward blood flow during CPR [12,13,16,17]. Recently, the aortic pump theory, that is, that direct chest compression is predominantly directed at the aorta during adult resuscitation, was introduced by the analysis of CT images [18–20]. However, the mechanism of forward blood flow during CPR remains controversial, and there have been many debates on the role of the heart during CPR. Regardless of the mechanism, optimal chest compression depths should not only achieve optimal cardiac output with maximal coronary and cerebral perfusion but also not increase unwanted complications by injury of the intrathoracic structures underlying the compression point of the sternum. To achieve this optimal cardiac output, the residual internal chest depth should as small as possible without being a negative. Maier et al [21] addressed that direct cardiac compression appeared to be the major determinant of stroke volume during manual external cardiac massage, and manual chest compressions of high velocity, moderate force, and brief duration at a rate of 120/min seemed to optimize systemic and coronary blood flow. In other words, to maximize cardiac stroke volume and coronary blood flow, manual massage should be performed with high-rate brief duration compressions using only moderate force. They suggested that the mechanism of this finding is unknown but may relate to obstructive compression of the left ventricular outflow tract, because the ventricular to aortic pressure gradient increased. In fact, Hwang et al [22] observed a significant narrowing of the left ventricular outflow tract or the aorta in all 34 of the adult arrest patients they studied, with the degree of compression at the area of maximal compression ranging from 19% to 83% (mean ± SD, 49% ± 19%). According to Maier et al [23], potentially injurious high compression force did not seem necessary, and when only moderate force was used, visceral damage was not observed in neither animal nor human studies that they conducted over a 5-year period. In their study of
Fig. 2. The correlation of chest EAPD and IAPD measured at the lower half of the sternum with each BMI group.
Fig. 3. The ratio of a 50-mm, one-fourth, one-third, and one-half AP external chest depth to internal chest depth minus 20 mm in each BMI group.
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Fig. 4. Residual internal chest depth during simulated 50-mm, one-fourth, one-third, and one-half AP external chest depth compressions.
high-impulse CPR in patients, they found that patients commonly regain consciousness using compression rates of 120 to 150/min. Even when chest compressions were performed with the dogs in the lateral position, which allows maximal compression directly over the left ventricle, they found that only moderate force was needed for optimal blood flow rather than a deep compression, which as we also suggested here, has the potential to cause injury to the intrathoracic structures. Fig. 4 shows the residual internal chest depth during simulated 50 mm, one-fourth, one-third, and one-half AP external chest depth compressions. This result suggests that during one-third EAPD chest compression depth, the residual internal chest depth would be the least with positive definiteness among the simulated chest compression depths. Babbs and colleagues [24], in addition to their mathematical study of optimal chest compression frequency vs body size (neonate to adult), they addressed pump mechanisms and briefly addressed compression depth. They conducted an analysis of CT images of neonates (Online Supplement 4) in which AP internal and external chest depth, heart depth, and noncardiac thoracic tissue depth were measured. They found that with 33% compression depth, one quarter of patients would experience maximal or overcompression of the mediastinum, thereby completely flattening the heart within the anatomic space available between the sternum and the spine. If compression depth were increased further to 50% of chest diameter, there would be overcompression of the heart in nearly all neonates. We selected 20-mm residual chest depth as a cutoff by previous studies on left and right ventricle wall thickness. We believed that less than 20 mm residual chest depth would possibly to injure intrathoracic structures adjacent to heart and may not actually be achievable because of the presence of the thickness of the ventricle. There have been reports about iatrogenic injuries associated with chest compressions since CPR was introduced in the 1960s [25,26]. The iatrogenic injuries such as intrathoracic or intra-abdominal laceration and hemorrhage could be fatal [27,28]. An increased compression depth may be associated with a
higher incidence of iatrogenic injuries. Regardless of the mechanism, optimal chest compression depths should not only achieve optimal cardiac output with maximal coronary and cerebral perfusion but also not increase unwanted complications by injury of the intrathoracic structures underlying the compression point of the sternum. In this study, the percentages of patients who would have less than 20 mm of residual chest depth during a simulated 50-mm, one-fourth EAPD, one-third EAPD, and one-half EAPD chest depth compression are displayed in Fig. 5. These results indicate that during a simulated 50-mm, onefourth, one-third, and one-half EAPD chest compression, 0.68% of 50 mm, 0.00% of one-fourth EAPD, 6.48% of one-third EAPD, and 100% of one-half EAPD group would have less than 20 mm of residual internal chest depth. The chest compression depth of one-half EAPD may not be theoretically attainable or safe for all adults. During a one-half chest depth compression, all patients in every BMI group would theoretically have no residual internal depth in the thorax. This may actually be impossible to achieve; however, if achievable, it could potentially harm the structures being compressed. These findings also suggest that a one-fourth EAPD chest compression for every BMI group might be a safe alternative to the chest compression depth recommended in the current adult CPR guidelines. Standard parameters for chest compressions in adult resuscitation should generally apply to the wide range and spectrum of chest wall characteristics of patients. The quality of CPR could be different considering the body contour of victim and the rescuer, and this study might add more evidence to this field [29]. With the growing field of CPR real-time assist and feedback technologies, it has become more important to ensure that the chest compression depth recommended in the current CPR guidelines is both safe and attainable in the adult population. We believe that this study will have a positive impact on the current field of adult resuscitation by providing radiographic evidence for chest compression depth.
5. Limitations There were some limitations to this study. First, the results may not be generalizable because this study is a retrospective, observational, and a single-center study. Second, the CT images were not taken during real CPR situations. In real CPR, actual chest compression and/or positive pressure ventilation might displace the location of intrathoracic structures. We also did not account for potential soft tissue compressibility during our calculated external chest compressions when we performed our calculations. A real-time approach during actual resuscitation is needed to explore the dynamic complexity. Third, the CT scans of this study were acquired while patients held their breath at the half inspiration point. The different respiratory phases may affect the precise measurement of the length and the conformational changes of intrathoracic structures. Fourth, the number of female patients is much smaller than that of male patients, and the mean age of the patients in this study is younger than the mean age of patients with out-of-hospital cardiac arrest in Korea. Although this presents no significant problem in the statistical analysis of this study, 75 female patients and the age of 46.09 ± 9.15 years cannot be thought to represent the whole population of Korean adults.
6. Conclusions
Fig. 5. The percentage of patients in each BMI group with less than 20 mm of residual internal chest depth during a 50-mm, one-fourth, one-third, and one-half AP external chest depth compression.
It is not appropriate that the current chest compression depth (≥50 mm) expressed as an absolute measurement without a fraction of the depth of the chest is applied uniformly in all adults. In addition, in terms of safety and efficacy, simulated chest compression targeting approximately between one-third and one-fourth EAPD chest compression depth based on calculating and estimating residual internal chest depths in simulated external chest compression might be more appropriate than the chest compression depth of 50 mm or greater recommended by the current guidelines.
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