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The suprasternal notch as a landmark of chest compression depth in CPR
American Journal of Emergency Medicine xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation☆,☆☆ Tae Hu Kim, MD, Soo Hoon Lee, MD ⁎, Dong Hoon Kim, MD, PhD, Ryun Kyung Lee, MD, So Yeon Kim, MD, Changwoo Kang, MD, Jin Hee Jeong, MD, Seong Chun Kim, MD, Sang Bong Lee, MD Department of Emergency Medicine, Gyeongsang National University School of Medicine and Gyeongsang National University Hospital, Jinju, Republic of Korea
a r t i c l e
i n f o
Article history: Received 19 October 2015 Accepted 14 November 2015 Available online xxxx
a b s t r a c t Objective: This study was performed to determine a landmark for chest compression depth for adult cardiopulmonary resuscitation (CPR) using chest computed tomography and to evaluate the validity of the landmark. Methods: The external anteroposterior diameters (EAPDs) of each chest at the suprasternal notch (SN) and the lower half (LH) of the sternum were measured. We analyzed the differences in the EAPDs between the LH and the SN in each EAPD group in the LH of the sternum as follows: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We compared the differences in the EAPDs between the 2 points with 50 mm and the chest compression depth on simulated one-fourth external chest compressions for each EAPD group on the LH of the sternum. Results: The mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.91 mm. The differences in the EAPDs between the SN and the LH of the sternum with 50 mm did not indicate a significant difference. The mean one-fourth EAPD at the LH of the sternum was 5.50 ± 0.53 mm. There was not a significant difference in the residual chest depth on one-fourth simulated chest compression for each EAPD group on the LH of the sternum. Conclusions: The SN may have value as a functional landmark for chest compression depth in adult CPR. Our findings combined with the simulated one-fourth chest compressions were more consistent with the depth between 50 and 60 mm recommended by the 2015 CPR guidelines. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Survival outcomes for cardiac arrest patients are related to the implementation of the crucial 5 links in the chain of survival and the quality of the cardiopulmonary resuscitation (CPR) including the chest compression rate, depth, and complete chest recoil [1-3]. Chest compressions generate blood flow and facilitate the delivery of oxygen to the myocardium and brain by increasing the intrathoracic pressure and by directly compressing the heart. The 2015 International Liaison Committee on Resuscitation emphasized delivering high-quality chest compressions: ensuring chest compressions of adequate rate, ensuring chest compressions of adequate depth, allowing full chest recoil between compressions, minimizing interruptions in chest compressions, and avoiding excessive ventilation [4]. In the 2010 CPR guidelines, there is a little difference between the current compression depths recommended by the American Heart Association (AHA) and the European
☆ Competing interests: No authors have any competing interests to declare. ☆☆ Funding and all other required statements: No authors have any funding to declare. ⁎ Corresponding author at: Department of Emergency Medicine, Gyeongsang National University Hospital, Gangnam-ro 79, Jinju, Gyeongsangnam-do, Republic of Korea, 660702. Tel.: +82 55 750 8975; fax: +82 55 757 0514. E-mail address: [email protected] (S.H. Lee).
Resuscitation Council. However, there is no difference between the chest compression depths recommended in the current 2015 guidelines. Both the AHA and the European Resuscitation Council recommend a compression depth of “at least 5 cm but not to exceed 6 cm” as an excessive compression depth can be associated with fatal iatrogenic injuries [4,5]. Several studies have demonstrated that it is not easy or practical to achieve an adequate chest compression depth [3,6]. In addition, both professional and lay rescuers find it difficult to accurately estimate the chest compression depth recommended by CPR guidelines. A significant proportion of lay rescuers are likely to underestimate the target range of chest compressions on manikins. This inability to estimate distances could explain the failure to perform chest compression correctly [7]. Therefore, easy and quick recognition of the correct compression depth can lead to the high-quality CPR that is needed for survival and favorable neurologic outcome. The primary purposes of this study were to determine a landmark for chest compression depth for adult CPR using chest computed tomography (CT) and to evaluate the validity of the landmark on chest compression recommended by the current adult CPR guidelines and simulated chest compression. We hypothesized that the suprasternal notch (SN) could be a good landmark for the chest compression depth that is recommended by the current adult CPR guidelines.
http://dx.doi.org/10.1016/j.ajem.2015.11.026 0735-6757/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
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T.H. Kim et al. / American Journal of Emergency Medicine xxx (2015) xxx–xxx
sternum was defined as the midpoint of the lower sternum (ie, onequarter of the total sternal length from the xiphoid process in the midline sagittal view). A total of 293 consecutive retrospective chest CT scans that were available were reviewed and analyzed for each EAPD at the LH of the sternum in groups as follows: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We divided these into 4 groups at intervals of 20 mm, as mean EAPD at the LH of the sternum was 22.02 ± 2.11 mm. Using CT reconstruction, individual external chest depths at the SN and the LH of the sternums were measured. We calculated the differences in the EAPDs between the LH and the SN for each EAPD at the LH of the sternum: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We compared the difference in the EAPDs between the 2 points with 50 mm, the chest compression depth recommended in current adult CPR guidelines. A difference in the EAPDs between the 2 points of nearly 50 mm would indicate that the SN is suitable as a landmark for chest compression depth in adult CPR. The anteroposterior (AP) chest diameter at the LH of the sternum varies among adults with different body sizes in our previous study [8]. Therefore, we selected one-fourth of the EAPD as appropriate chest compression depth at the LH of the sternum because we believed that expressing the chest compression depth as a fraction of the depth of the chest would be better than an absolute measurement. We compared the differences in the EAPDs between the 2 points and the chest compression depth from simulated external chest compressions of one-fourth the AP chest depth for each EAPD at the LH of the sternum in the following groups: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. 2.3. Statistical analysis Fig. 1. An axial image at the SN level (A) and at the LH level of the sternum (B) from a CT scan and the method for calculating the chest external anteroposterior diameter and internal anteroposterior diameter.
2. Methods 2.1. Study setting Patients older than 18 years who underwent precontrast low-dose chest CT scans as a screening test for latent pulmonary diseases in the health care center of our hospital from September 1 to December 31, 2013, were enrolled in this study. Patients with severe thoracic deformities, such as funnel chest, pectus excavatum/carinatum, or chest hypoplasia, were excluded. The patients' demographic data including sex, age, height, and body weight were acquired from the final reports of the medical examinations. 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 of the CT images from the patients in this study were generated by 64-channel multidetector CT (Lightspeed VCT; General Electric Medical Systems, Milwaukee, WI). All of the imaging data were transferred to a dedicated workstation (Advantage Windows 4.3; GE Healthcare, Milwaukee, WI). The picture archiving and communication system that was used in this study to analyze the images, to perform 3-dimensional reconstructions, and to obtain direct measurements using an electronic cursor was an AGFA Impax 5.3 PACS workstation (Mortsel, Belgium). 2.2. Methods and measurements The external anteroposterior diameters (EAPDs) of the chests at the SN and the lower half (LH) of the sternum were measured as displayed in Fig. 1. Using an axial slice at the SN and the LH of the sternum, we calculated the external chest depth by measuring a line drawn perpendicularly from the skin anteriorly to the floor posteriorly. The LH of the
All of the continuous variables are presented as the mean ± SD. A 1sample t test was used to compare the difference in the EAPDs between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended in current adult CPR guidelines. One-way analyses of variances among groups and univariate linear regression analyses were used for comparisons of the differences in the EAPDs between the SN and the LH of the sternum in each EAPD groups at the LH level of the sternum. For all of the comparisons, a 2-sided P value of .05 was considered statistically significant. All of the analyses were performed using SPSS statistical software (version 21.0; IBM, Chicago, IL). 3. Results A total of 298 consecutive patients underwent precontrast low-dose chest CT scans during the study period. Five patients were excluded because of severe chest deformities. A total of 218 males and 75 females were included in the study. The unequal male to female ratios in the group were a result of an unequal sex distribution during this study period. The demographic data of the patients and the average EAPD measured at the SN and the LH of the sternum are displayed in the Table. The average EAPD measured at the SN and the difference in the EAPDs between the SN and the LH for each EAPD group at the LH of the sternum are presented in Fig. 2. The mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.91 mm. A 1-sample t test comparing the EAPD between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended in the current adult CPR guidelines, did not show a significant difference, although there were a statistically significant differences in both the average EAPD measured at the SN and the difference between the LH of the sternum and the SN for each EAPD on the LH of the sternum (EAPD at the SN: R2 = 0.822, P b .001, the difference between 2 points: R2 = 0.457, P b .001). The mean one-fourth EAPD at the LH of the sternum was 5.50 ± 0.53 mm. The mean residual chest depth as measured by the difference of EAPD between 2 points minus one-fourth EAPD was 0.34 ± 0.67 mm. Fig. 3 displays the residual chest depth as measured by the EAPD difference
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
T.H. Kim et al. / American Journal of Emergency Medicine xxx (2015) xxx–xxx
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Table Demographic data and internal and external chest depth by body mass index in study group Variables
Total
b20.00
20.00-21.99
22.00-23.99
≥24.00
P
n Sex, male, % Average age, mean ± SD (y) Average height, mean ± SD (cm) Average weight, mean ± SD (kg) Body mass index Mean EAPD at the LH of the sternum, mean ± SD (cm) One-fourth mean EAPD at the LH of the sternum, mean ± SD (cm) Mean EAPD at the SN, mean ± SD (cm)
293 218 46.09 ± 9.15 168.58 ± 8.61 68.87 ± 12.53 24.13 ± 3.44 22.02 ± 2.11 5.50 ± 0.53 17.27 ± 1.46
48 16 43.98 ± 9.96 162.38 ± 8.23 52.84 ± 6.50 20.02 ± 1.84 18.67 ± 1.06 4.67 ± 0.26 15.11 ± 0.83
94 68 47.24 ± 9.16 167.86 ± 8.80 64.08 ± 8.10 22.72 ± 2.18 21.09 ± 0.59 5.27 ± 0.15 16.73 ± 0.73
100 89 47.10 ± 9.47 170.00 ± 7.71 72.98 ± 6.96 25.26 ± 1.90 23.01 ± 0.58 5.75 ± 0.15 17.86 ± 0.65
51 45 43.98 ± 6.96 172.99 ± 6.78 84.73 ± 8.86 28.36 ± 3.00 24.94 ± 0.78 6.24 ± 0.20 19.15 ± 0.82
b.001 .043 b.001 b.001 b.001 b.001 b.001 b.001
between the 2 points minus either 50 mm or one-fourth of the EAPD for each EAPD at the LH of the sternum. There was not a significant difference in the residual chest depth as measured by the difference of EAPD between the 2 points minus one-fourth EAPD for each EAPD group at the LH of the sternum, although there was a significant difference the residual chest depth as measured by the difference of EAPD between the 2 points minus 50 mm for each EAPD group at the LH of the sternum. 4. Discussion The SN, also known as the jugular notch, is found at the superior border of the manubrium of the sternum, between the clavicular notches. It has been used as a landmark in central venous catheterization via the infraclavicular approach and in airway management including tracheal ultrasonography for the confirmation of endotracheal tube placement during CPR [9-11]. Recently, van Tudler et al [7] observed that only one-third of professional rescuers and lay rescuers made correct visual estimations on a horizontal axis. In addition, a significant proportion of lay rescuers are likely to underestimate the target range for chest compressions on a manikin, and one-third of the participants failed to reach the target compression depth, even in the professional health care group. A landmark that indicates the correct compression depth easily and quickly might improve the quality of CPR. The SN has several advantages as a landmark for chest compression depth. First, the SN can be found easily during chest compressions as it is a large, visible dip. Second, the SN does not move; it is relatively fixed superiorly at the thoracic inlet even when chest compressions are performed for cardiac arrest. Pickard et al [12] suggested that the sternum acts as a hinge that is relatively fixed superiorly at the thoracic inlet including the SN, moving predominantly at the bottom end during chest compression based on examinations of chest CT scans. Therefore, the SN may be worth using as a recognizable landmark of chest compression depth in adult CPR. An association has been observed between increased compression depth and survival and functional outcomes [13,14]. However, there have been also reports about iatrogenic injuries associated with chest compressions since CPR was introduced in the 1960s [15,16]. The iatrogenic injuries such as intrathoracic or intraabdominal laceration and
Fig. 2. The average EAPD measured at the SN and the difference between the SN and the LH for each EAPD at the LH of the sternum.
hemorrhage could be fatal [17,18]. An increased compression depth may be associated with a higher incidence of iatrogenic injuries. Regardless of the mechanism regarding forward blood flow during CPR, 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. Stiell et al [13] found a strong association between survival outcomes and increased compression depths, although a study of compression depth data in out-of-hospital cardiac arrest (OHCA) cases from May 2006 to June 2009 found a large number of suboptimal compression depths. Recently, they found that the highest survival rates were observed with a depth interval of 40.3 to 55.3 mm (peak, 45.6 mm) in a large study of OHCA patients. They suggested that the 2010 AHA CPR guideline target may be too high, although increased CPR compression depths are strongly associated with better survival rates [14]. In our study, the mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.53 mm. There was not a significant difference in the comparison of the EAPDs between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended currently in adult CPR guidelines. Therefore, these results suggest that the SN may have value as a functional landmark for chest compression depth in adult CPR, although actual chest compression and/or positive pressure ventilation might displace the location of intrathoracic structures in actual CPR; the CT images were not taken during real CPR situations. However, there have also been several studies that indicated chest compression greater than or equal to 50 mm improved early outcomes [19-21]. Adequate compressions increase the tolerance to delays of defibrillation, keep rhythms shockable, and increase first shock success, thus improving survival rates in cases of OHCA [22,23]. Recently, Vadeboncoeur et al [24] found that deeper chest compressions that followed the recommended depth of at least 50 mm from the 2010 AHA Guideline were associated with improved survival and functional outcome after OHCA. The mean value of one-fourth of the EAPD at the
Fig. 3. The residual chest depth of the difference in EAPDs between 2 points minus either 50 mm or one-fourth of the EAPD for each EAPD at the LH of the sternum.
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
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T.H. Kim et al. / American Journal of Emergency Medicine xxx (2015) xxx–xxx
LH of the sternum was 5.50 ± 0.53 mm in this study. The mean residual chest depth using the difference in the EAPDs between the 2 points minus one-fourth of the EAPD was 0.34 ± 0.67 mm. Regarding the simulated one-fourth chest compression that we thought as appropriate chest compression depth at the LH of the sternum, there was not a significant difference in the residual chest depth as measured by the difference in EAPDs between the 2 points minus one-fourth EAPD for each EAPD group at the LH of the sternum. Therefore, our findings combined with the simulated one-fourth chest compression were more consistent with the recommended depth between 50 and 60 mm from the 2015 CPR guidelines. Recent technological advances in real-time assistance and feedback for CPR allow for the detailed measurement of key chest compression parameters. Therefore, it has become more important to ensure the optimal chest compression depth recommended in the current CPR guidelines. In addition, standard parameters for chest compressions in adult CPR should generally be applied to cardiac arrest patients. This study might add more evidence to this field, as the quality of CPR could differ based on the body composition of the victim and the rescuer [25]. We believe that this study will have a positive impact on the current field of adult CPR by providing radiographic evidence for a landmark for chest compression depth.
5. Limitations There were some limitations in this study. First, the results may not be generalizable as this study is a retrospective, observational, and 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 alter the location of intrathoracic structures. We also did not account for potential soft tissue compressibility during 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. Different respiratory phases may affect the precise measurement of the length and the conformational changes of the intrathoracic structures. However, Pickard et al [12] found that inspiration made little difference in the results of their pilot work reviewing chest CT scans for the radiological assessment of the adult chest to assess the depth of chest compression. Fourth, there was a sex imbalance in the study group, and the mean age of the patients in this study is younger than the mean age of patients who experience OHCA. Although this is not a significant problem for the statistical analysis in this study, the sex imbalance and the younger age mean it cannot be considered representative of the whole adult population.
6. Conclusions The SN may have value as a functional landmark for chest compression depth in adult CPR. In addition, our findings combined with simulated one-fourth chest compressions were more consistent with the depth between 50 and 60 mm recommended in the 2015 CPR guidelines.
References [1] Wik L, Steen PA, Bircher NG. Quality of bystander cardiopulmonary resuscitation influences outcome after prehospital cardiac arrest. Resuscitation 1994;28(3):195–203. [2] Yannopoulos D, McKnite S, Aufderheide TP, Sigurdsson G, Pirrallo RG, Benditt D, et al. Effects of incomplete chest wall decompression during cardiopulmonary resuscitation on coronary and cerebral perfusion pressures in a porcine model of cardiac arrest. Resuscitation 2005;64(3):363–72. [3] Abella BS, Alvarado JP, Myklebust H, Edelson DP, Barry A, O'Hearn N, et al. Quality of cardiopulmonary resuscitation during in-hospital cardiac arrest. JAMA 2005;293(3):305–10. [4] Kleinman ME, Brennan EE, Goldberger ZD, Swor RA, Terry M, Bobrow BJ, et al. Part 5: adult basic life support and cardiopulmonary resuscitation quality: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2015;132(18 Suppl. 2):S414–35. [5] Perkins GD, Handley AJ, Koster RW, Castren M, Smyth MA, Olasveengen T, et al. European Resuscitation Council Guidelines for Resuscitation 2015: Section 2. Adult basic life support and automated external defibrillation. Resuscitation 2015;95:81–99. [6] Wik L, Kramer-Johansen J, Myklebust H, Sorebo H, Svensson L, Fellows B, et al. Quality of cardiopulmonary resuscitation during out-of-hospital cardiac arrest. JAMA 2005;293(3):299–304. [7] van Tulder R, Laggner R, Kienbacher C, Schmid B, Zajicek A, Haidvogel J, et al. The capability of professional- and lay-rescuers to estimate the chest compression-depth target: a short, randomized experiment. Resuscitation 2015;89:137–41. [8] Lee SH, Kim DH, Kang TS, Kang C, Jeong JH, Kim SC, et al. The uniform chest compression depth of 50 mm or greater recommended by current guidelines is not appropriate for all adults. The American journal of emergency medicine 2015;33(8): 1037–41. [9] Chou HC, Chong KM, Sim SS, Ma MH, Liu SH, Chen NC, et al. Real-time tracheal ultrasonography for confirmation of endotracheal tube placement during cardiopulmonary resuscitation. Resuscitation 2013;84(12):1708–12. [10] Kristensen MS. Ultrasonography in the management of the airway. Acta Anaesthesiol Scand 2011;55(10):1155–73. [11] Tessaro MO, Salant EP, Arroyo AC, Haines LE, Dickman E. Tracheal rapid ultrasound saline test (T.R.U.S.T.) for confirming correct endotracheal tube depth in children. Resuscitation 2015;89:8–12. [12] Pickard A, Darby M, Soar J. Radiological assessment of the adult chest: implications for chest compressions. Resuscitation 2006;71(3):387–90. [13] Stiell IG, Brown SP, Christenson J, Cheskes S, Nichol G, Powell J, et al. What is the role of chest compression depth during out-of-hospital cardiac arrest resuscitation? Crit Care Med 2012;40(4):1192–8. [14] Stiell IG, Brown SP, Nichol G, Cheskes S, Vaillancourt C, Callaway CW, et al. What is the optimal chest compression depth during out-of-hospital cardiac arrest resuscitation of adult patients? Circulation 2014;130(22):1962–70. [15] Buschmann CT, Tsokos M. Frequent and rare complications of resuscitation attempts. Intensive Care Med 2009;35(3):397–404. [16] 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. [17] Meron G, Kurkciyan I, Sterz F, Susani M, Domanovits H, Tobler K, et al. Cardiopulmonary resuscitation–associated major liver injury. Resuscitation 2007;75(3):445–53. [18] 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. [19] Babbs CF, Kemeny AE, Quan W, Freeman G. A new paradigm for human resuscitation research using intelligent devices. Resuscitation 2008;77(3):306–15. [20] Edelson DP, Abella BS, Kramer-Johansen J, Wik L, Myklebust H, Barry AM, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation 2006;71(2):137–45. [21] Kramer-Johansen J, Myklebust H, Wik L, Fellows B, Svensson L, Sorebo H, et al. Quality of out-of-hospital cardiopulmonary resuscitation with real time automated feedback: a prospective interventional study. Resuscitation 2006;71(3):283–92. [22] Swor RA, Jackson RE, Cynar M, Sadler E, Basse E, Boji B, et al. Bystander CPR, ventricular fibrillation, and survival in witnessed, unmonitored out-of-hospital cardiac arrest. Ann Emerg Med 1995;25(6):780–4. [23] Wik L, Hansen TB, Fylling F, Steen T, Vaagenes P, Auestad BH, et al. Delaying defibrillation to give basic cardiopulmonary resuscitation to patients with out-of-hospital ventricular fibrillation: a randomized trial. JAMA 2003;289(11):1389–95. [24] Vadeboncoeur T, Stolz U, Panchal A, Silver A, Venuti M, Tobin J, et al. Chest compression depth and survival in out-of-hospital cardiac arrest. Resuscitation 2014;85(2):182–8. [25] 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.
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
Original Contribution
The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation☆,☆☆ Tae Hu Kim, MD, Soo Hoon Lee, MD ⁎, Dong Hoon Kim, MD, PhD, Ryun Kyung Lee, MD, So Yeon Kim, MD, Changwoo Kang, MD, Jin Hee Jeong, MD, Seong Chun Kim, MD, Sang Bong Lee, MD Department of Emergency Medicine, Gyeongsang National University School of Medicine and Gyeongsang National University Hospital, Jinju, Republic of Korea
a r t i c l e
i n f o
Article history: Received 19 October 2015 Accepted 14 November 2015 Available online xxxx
a b s t r a c t Objective: This study was performed to determine a landmark for chest compression depth for adult cardiopulmonary resuscitation (CPR) using chest computed tomography and to evaluate the validity of the landmark. Methods: The external anteroposterior diameters (EAPDs) of each chest at the suprasternal notch (SN) and the lower half (LH) of the sternum were measured. We analyzed the differences in the EAPDs between the LH and the SN in each EAPD group in the LH of the sternum as follows: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We compared the differences in the EAPDs between the 2 points with 50 mm and the chest compression depth on simulated one-fourth external chest compressions for each EAPD group on the LH of the sternum. Results: The mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.91 mm. The differences in the EAPDs between the SN and the LH of the sternum with 50 mm did not indicate a significant difference. The mean one-fourth EAPD at the LH of the sternum was 5.50 ± 0.53 mm. There was not a significant difference in the residual chest depth on one-fourth simulated chest compression for each EAPD group on the LH of the sternum. Conclusions: The SN may have value as a functional landmark for chest compression depth in adult CPR. Our findings combined with the simulated one-fourth chest compressions were more consistent with the depth between 50 and 60 mm recommended by the 2015 CPR guidelines. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Survival outcomes for cardiac arrest patients are related to the implementation of the crucial 5 links in the chain of survival and the quality of the cardiopulmonary resuscitation (CPR) including the chest compression rate, depth, and complete chest recoil [1-3]. Chest compressions generate blood flow and facilitate the delivery of oxygen to the myocardium and brain by increasing the intrathoracic pressure and by directly compressing the heart. The 2015 International Liaison Committee on Resuscitation emphasized delivering high-quality chest compressions: ensuring chest compressions of adequate rate, ensuring chest compressions of adequate depth, allowing full chest recoil between compressions, minimizing interruptions in chest compressions, and avoiding excessive ventilation [4]. In the 2010 CPR guidelines, there is a little difference between the current compression depths recommended by the American Heart Association (AHA) and the European
☆ Competing interests: No authors have any competing interests to declare. ☆☆ Funding and all other required statements: No authors have any funding to declare. ⁎ Corresponding author at: Department of Emergency Medicine, Gyeongsang National University Hospital, Gangnam-ro 79, Jinju, Gyeongsangnam-do, Republic of Korea, 660702. Tel.: +82 55 750 8975; fax: +82 55 757 0514. E-mail address: [email protected] (S.H. Lee).
Resuscitation Council. However, there is no difference between the chest compression depths recommended in the current 2015 guidelines. Both the AHA and the European Resuscitation Council recommend a compression depth of “at least 5 cm but not to exceed 6 cm” as an excessive compression depth can be associated with fatal iatrogenic injuries [4,5]. Several studies have demonstrated that it is not easy or practical to achieve an adequate chest compression depth [3,6]. In addition, both professional and lay rescuers find it difficult to accurately estimate the chest compression depth recommended by CPR guidelines. A significant proportion of lay rescuers are likely to underestimate the target range of chest compressions on manikins. This inability to estimate distances could explain the failure to perform chest compression correctly [7]. Therefore, easy and quick recognition of the correct compression depth can lead to the high-quality CPR that is needed for survival and favorable neurologic outcome. The primary purposes of this study were to determine a landmark for chest compression depth for adult CPR using chest computed tomography (CT) and to evaluate the validity of the landmark on chest compression recommended by the current adult CPR guidelines and simulated chest compression. We hypothesized that the suprasternal notch (SN) could be a good landmark for the chest compression depth that is recommended by the current adult CPR guidelines.
http://dx.doi.org/10.1016/j.ajem.2015.11.026 0735-6757/© 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
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T.H. Kim et al. / American Journal of Emergency Medicine xxx (2015) xxx–xxx
sternum was defined as the midpoint of the lower sternum (ie, onequarter of the total sternal length from the xiphoid process in the midline sagittal view). A total of 293 consecutive retrospective chest CT scans that were available were reviewed and analyzed for each EAPD at the LH of the sternum in groups as follows: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We divided these into 4 groups at intervals of 20 mm, as mean EAPD at the LH of the sternum was 22.02 ± 2.11 mm. Using CT reconstruction, individual external chest depths at the SN and the LH of the sternums were measured. We calculated the differences in the EAPDs between the LH and the SN for each EAPD at the LH of the sternum: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. We compared the difference in the EAPDs between the 2 points with 50 mm, the chest compression depth recommended in current adult CPR guidelines. A difference in the EAPDs between the 2 points of nearly 50 mm would indicate that the SN is suitable as a landmark for chest compression depth in adult CPR. The anteroposterior (AP) chest diameter at the LH of the sternum varies among adults with different body sizes in our previous study [8]. Therefore, we selected one-fourth of the EAPD as appropriate chest compression depth at the LH of the sternum because we believed that expressing the chest compression depth as a fraction of the depth of the chest would be better than an absolute measurement. We compared the differences in the EAPDs between the 2 points and the chest compression depth from simulated external chest compressions of one-fourth the AP chest depth for each EAPD at the LH of the sternum in the following groups: less than 20.00, 20.00 to 21.99, 22.00 to 23.99, greater than or equal to 24.00. 2.3. Statistical analysis Fig. 1. An axial image at the SN level (A) and at the LH level of the sternum (B) from a CT scan and the method for calculating the chest external anteroposterior diameter and internal anteroposterior diameter.
2. Methods 2.1. Study setting Patients older than 18 years who underwent precontrast low-dose chest CT scans as a screening test for latent pulmonary diseases in the health care center of our hospital from September 1 to December 31, 2013, were enrolled in this study. Patients with severe thoracic deformities, such as funnel chest, pectus excavatum/carinatum, or chest hypoplasia, were excluded. The patients' demographic data including sex, age, height, and body weight were acquired from the final reports of the medical examinations. 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 of the CT images from the patients in this study were generated by 64-channel multidetector CT (Lightspeed VCT; General Electric Medical Systems, Milwaukee, WI). All of the imaging data were transferred to a dedicated workstation (Advantage Windows 4.3; GE Healthcare, Milwaukee, WI). The picture archiving and communication system that was used in this study to analyze the images, to perform 3-dimensional reconstructions, and to obtain direct measurements using an electronic cursor was an AGFA Impax 5.3 PACS workstation (Mortsel, Belgium). 2.2. Methods and measurements The external anteroposterior diameters (EAPDs) of the chests at the SN and the lower half (LH) of the sternum were measured as displayed in Fig. 1. Using an axial slice at the SN and the LH of the sternum, we calculated the external chest depth by measuring a line drawn perpendicularly from the skin anteriorly to the floor posteriorly. The LH of the
All of the continuous variables are presented as the mean ± SD. A 1sample t test was used to compare the difference in the EAPDs between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended in current adult CPR guidelines. One-way analyses of variances among groups and univariate linear regression analyses were used for comparisons of the differences in the EAPDs between the SN and the LH of the sternum in each EAPD groups at the LH level of the sternum. For all of the comparisons, a 2-sided P value of .05 was considered statistically significant. All of the analyses were performed using SPSS statistical software (version 21.0; IBM, Chicago, IL). 3. Results A total of 298 consecutive patients underwent precontrast low-dose chest CT scans during the study period. Five patients were excluded because of severe chest deformities. A total of 218 males and 75 females were included in the study. The unequal male to female ratios in the group were a result of an unequal sex distribution during this study period. The demographic data of the patients and the average EAPD measured at the SN and the LH of the sternum are displayed in the Table. The average EAPD measured at the SN and the difference in the EAPDs between the SN and the LH for each EAPD group at the LH of the sternum are presented in Fig. 2. The mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.91 mm. A 1-sample t test comparing the EAPD between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended in the current adult CPR guidelines, did not show a significant difference, although there were a statistically significant differences in both the average EAPD measured at the SN and the difference between the LH of the sternum and the SN for each EAPD on the LH of the sternum (EAPD at the SN: R2 = 0.822, P b .001, the difference between 2 points: R2 = 0.457, P b .001). The mean one-fourth EAPD at the LH of the sternum was 5.50 ± 0.53 mm. The mean residual chest depth as measured by the difference of EAPD between 2 points minus one-fourth EAPD was 0.34 ± 0.67 mm. Fig. 3 displays the residual chest depth as measured by the EAPD difference
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
T.H. Kim et al. / American Journal of Emergency Medicine xxx (2015) xxx–xxx
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Table Demographic data and internal and external chest depth by body mass index in study group Variables
Total
b20.00
20.00-21.99
22.00-23.99
≥24.00
P
n Sex, male, % Average age, mean ± SD (y) Average height, mean ± SD (cm) Average weight, mean ± SD (kg) Body mass index Mean EAPD at the LH of the sternum, mean ± SD (cm) One-fourth mean EAPD at the LH of the sternum, mean ± SD (cm) Mean EAPD at the SN, mean ± SD (cm)
293 218 46.09 ± 9.15 168.58 ± 8.61 68.87 ± 12.53 24.13 ± 3.44 22.02 ± 2.11 5.50 ± 0.53 17.27 ± 1.46
48 16 43.98 ± 9.96 162.38 ± 8.23 52.84 ± 6.50 20.02 ± 1.84 18.67 ± 1.06 4.67 ± 0.26 15.11 ± 0.83
94 68 47.24 ± 9.16 167.86 ± 8.80 64.08 ± 8.10 22.72 ± 2.18 21.09 ± 0.59 5.27 ± 0.15 16.73 ± 0.73
100 89 47.10 ± 9.47 170.00 ± 7.71 72.98 ± 6.96 25.26 ± 1.90 23.01 ± 0.58 5.75 ± 0.15 17.86 ± 0.65
51 45 43.98 ± 6.96 172.99 ± 6.78 84.73 ± 8.86 28.36 ± 3.00 24.94 ± 0.78 6.24 ± 0.20 19.15 ± 0.82
b.001 .043 b.001 b.001 b.001 b.001 b.001 b.001
between the 2 points minus either 50 mm or one-fourth of the EAPD for each EAPD at the LH of the sternum. There was not a significant difference in the residual chest depth as measured by the difference of EAPD between the 2 points minus one-fourth EAPD for each EAPD group at the LH of the sternum, although there was a significant difference the residual chest depth as measured by the difference of EAPD between the 2 points minus 50 mm for each EAPD group at the LH of the sternum. 4. Discussion The SN, also known as the jugular notch, is found at the superior border of the manubrium of the sternum, between the clavicular notches. It has been used as a landmark in central venous catheterization via the infraclavicular approach and in airway management including tracheal ultrasonography for the confirmation of endotracheal tube placement during CPR [9-11]. Recently, van Tudler et al [7] observed that only one-third of professional rescuers and lay rescuers made correct visual estimations on a horizontal axis. In addition, a significant proportion of lay rescuers are likely to underestimate the target range for chest compressions on a manikin, and one-third of the participants failed to reach the target compression depth, even in the professional health care group. A landmark that indicates the correct compression depth easily and quickly might improve the quality of CPR. The SN has several advantages as a landmark for chest compression depth. First, the SN can be found easily during chest compressions as it is a large, visible dip. Second, the SN does not move; it is relatively fixed superiorly at the thoracic inlet even when chest compressions are performed for cardiac arrest. Pickard et al [12] suggested that the sternum acts as a hinge that is relatively fixed superiorly at the thoracic inlet including the SN, moving predominantly at the bottom end during chest compression based on examinations of chest CT scans. Therefore, the SN may be worth using as a recognizable landmark of chest compression depth in adult CPR. An association has been observed between increased compression depth and survival and functional outcomes [13,14]. However, there have been also reports about iatrogenic injuries associated with chest compressions since CPR was introduced in the 1960s [15,16]. The iatrogenic injuries such as intrathoracic or intraabdominal laceration and
Fig. 2. The average EAPD measured at the SN and the difference between the SN and the LH for each EAPD at the LH of the sternum.
hemorrhage could be fatal [17,18]. An increased compression depth may be associated with a higher incidence of iatrogenic injuries. Regardless of the mechanism regarding forward blood flow during CPR, 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. Stiell et al [13] found a strong association between survival outcomes and increased compression depths, although a study of compression depth data in out-of-hospital cardiac arrest (OHCA) cases from May 2006 to June 2009 found a large number of suboptimal compression depths. Recently, they found that the highest survival rates were observed with a depth interval of 40.3 to 55.3 mm (peak, 45.6 mm) in a large study of OHCA patients. They suggested that the 2010 AHA CPR guideline target may be too high, although increased CPR compression depths are strongly associated with better survival rates [14]. In our study, the mean difference in the EAPDs between the SN and the LH was 5.16 ± 0.53 mm. There was not a significant difference in the comparison of the EAPDs between the SN and the LH of the sternum with 50 mm, the chest compression depth recommended currently in adult CPR guidelines. Therefore, these results suggest that the SN may have value as a functional landmark for chest compression depth in adult CPR, although actual chest compression and/or positive pressure ventilation might displace the location of intrathoracic structures in actual CPR; the CT images were not taken during real CPR situations. However, there have also been several studies that indicated chest compression greater than or equal to 50 mm improved early outcomes [19-21]. Adequate compressions increase the tolerance to delays of defibrillation, keep rhythms shockable, and increase first shock success, thus improving survival rates in cases of OHCA [22,23]. Recently, Vadeboncoeur et al [24] found that deeper chest compressions that followed the recommended depth of at least 50 mm from the 2010 AHA Guideline were associated with improved survival and functional outcome after OHCA. The mean value of one-fourth of the EAPD at the
Fig. 3. The residual chest depth of the difference in EAPDs between 2 points minus either 50 mm or one-fourth of the EAPD for each EAPD at the LH of the sternum.
Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026
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LH of the sternum was 5.50 ± 0.53 mm in this study. The mean residual chest depth using the difference in the EAPDs between the 2 points minus one-fourth of the EAPD was 0.34 ± 0.67 mm. Regarding the simulated one-fourth chest compression that we thought as appropriate chest compression depth at the LH of the sternum, there was not a significant difference in the residual chest depth as measured by the difference in EAPDs between the 2 points minus one-fourth EAPD for each EAPD group at the LH of the sternum. Therefore, our findings combined with the simulated one-fourth chest compression were more consistent with the recommended depth between 50 and 60 mm from the 2015 CPR guidelines. Recent technological advances in real-time assistance and feedback for CPR allow for the detailed measurement of key chest compression parameters. Therefore, it has become more important to ensure the optimal chest compression depth recommended in the current CPR guidelines. In addition, standard parameters for chest compressions in adult CPR should generally be applied to cardiac arrest patients. This study might add more evidence to this field, as the quality of CPR could differ based on the body composition of the victim and the rescuer [25]. We believe that this study will have a positive impact on the current field of adult CPR by providing radiographic evidence for a landmark for chest compression depth.
5. Limitations There were some limitations in this study. First, the results may not be generalizable as this study is a retrospective, observational, and 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 alter the location of intrathoracic structures. We also did not account for potential soft tissue compressibility during 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. Different respiratory phases may affect the precise measurement of the length and the conformational changes of the intrathoracic structures. However, Pickard et al [12] found that inspiration made little difference in the results of their pilot work reviewing chest CT scans for the radiological assessment of the adult chest to assess the depth of chest compression. Fourth, there was a sex imbalance in the study group, and the mean age of the patients in this study is younger than the mean age of patients who experience OHCA. Although this is not a significant problem for the statistical analysis in this study, the sex imbalance and the younger age mean it cannot be considered representative of the whole adult population.
6. Conclusions The SN may have value as a functional landmark for chest compression depth in adult CPR. In addition, our findings combined with simulated one-fourth chest compressions were more consistent with the depth between 50 and 60 mm recommended in the 2015 CPR guidelines.
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Please cite this article as: Kim TH, et al, The suprasternal notch as a landmark of chest compression depth in cardiopulmonary resuscitation, Am J Emerg Med (2015), http://dx.doi.org/10.1016/j.ajem.2015.11.026