The Association Between the Duration of Chest Compression and Thoracic Injuries in Patients With Non-Traumatic Out-of-Hospital Cardiac Arrest

Abstract

Background: Current guidelines emphasize the indispensability of high-quality chest compression for improving survival in patients who experience out-of-hospital cardiac arrest (OHCA). However, chest compression can cause thoracic injuries that may contribute to poor prognosis; therefore, the purpose of this study is to identify the predictors of thoracic injuries and evaluate the association between thoracic injuries and prognosis.

Methods and Results: Between June 2017 to July 2019, Utstein-style data on 384 consecutive adult patients who experienced non-traumatic OHCA and who were transferred to our hospital (Aso Iizuka Hospital) were collected. Each patient underwent a full-body computed tomography scan. Two-hundred and thirty-four patients (76%) had thoracic injuries (Group-T). The duration of chest compression was significantly longer in Group-T than in patients without thoracic injuries (Group-N; 43 vs. 32 min, respectively, P<0.001). Multivariate analysis revealed that older age and longer chest compression duration were predictors of thoracic injuries (odds ratios 1.03 and 1.07, respectively, P≤0.005). Among patients who achieved return of spontaneous circulation, Kaplan-Meier curves showed a significantly higher cumulative survival rate in Group-N than in Group-T at the 30-day follow up (log-rank test P=0.009).

Conclusions: Older age and longer chest compression duration were independent predictors of thoracic injuries due to chest compression in patients who experienced non-traumatic OHCA. Moreover, the presence of thoracic injuries was associated with worse short-term prognosis.

Although high-quality chest compression is one of the most important components of cardiopulmonary resuscitation (CPR),¹ traumatic injuries due to CPR have been reported.^2,3 The 2015 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations (ILCOR/CoSTR) guidelines changed the former recommendation of a compression depth of >5 cm (2 inches) to limit of 6 cm^4,5 because excessive compression depth during CPR was found to be associated with a higher incidence of lethal thoracic injuries.^6,7 In addition, it is also reported that longer chest compression duration increases the likelihood of thoracic injuries.^8,9 Thoracic injuries due to CPR may lead to the poor prognosis of OHCA patients. Patients who experience a return of spontaneous circulation (ROSC) are at increased risk of bleeding due to therapeutic hypothermia, anticoagulation for mechanical circulatory support, and coagulopathy caused by ischemia or reperfusion injury secondary to cardiac arrest.^10,11 The presence of flail chest or pneumothorax is also very important information when ventilator management is required. However, there have been limited data available to investigate risk factors for iatrogenic thoracic injuries due to CPR and the relationship between their incidence and clinical prognosis.

In the field of trauma management, computed tomography (CT) scans can be useful for detecting various traumatic injuries in the emergency department. The aim of the present study was to use CT scans to identify the incidence and predictors of CPR-related thoracic injuries and the relationship between these injuries and prognosis.

Methods

This study was approved by the Aso Iizuka Hospital Ethics Committee (No. 21014) and was conducted in accordance with the ethical standards of the Declaration of Helsinki. The datasets generated or analyzed during the current study are available from the corresponding author on reasonable request.

Study Design and Participants

We retrospectively collected Utstein-style data on patients who experienced non-traumatic OHCA between June 2017 and July 2019 and who were transferred to Aso Iizuka Hospital, a tertiary emergency critical care medical center. We excluded patients who were aged <18 years, had committed suicide, had suspected rupture of a thoracic aortic aneurysm or aortic dissection, or were missing data on either CT scans or chest compression duration. CPR was performed in accordance with the 2015 ILCOR/CoSTR guidelines.

Study Protocol

We retrospectively collected information on factors potentially related to prognosis from medical records. Data included age, gender, presence or absence of witnessed cardiac arrest, presence or absence of bystander CPR, initial recorded cardiac rhythm, interval from call to CPR initiation by an emergency medical service (EMS), duration of chest compression, initial laboratory tests, prehospital management, management after hospital arrival, and prognosis. The onset time of chest compression was defined as the time when chest compression was initiated by EMS personnel or medical staff. ROSC was defined as the absence of chest compression for more than 20 min.¹² Favorable neurological outcome at 30 days was defined by a Cerebral Performance Category score (CPC) of 1 or 2.

CT scans using a 64-detector row clinical scanner system (LightSpeed VCT VISION; GE Healthcare) were performed in almost all patients (98%), in keeping with our hospital protocol for evaluating the cause of OHCA. CT scans were performed after obtaining ROSC or during CPR if the patient did not obtain ROSC. The parameters of the CT examinations were as follows: 120 kVp, 120–320 mAs (adjusted based on patients’ body size), 0.6-s rotation time, 5-mm slice thickness, and 5-mm intervals. Thoracic injuries due to chest compression were defined as rib fracture, sternal fracture, hemorrhagic pleural effusion, pneumothorax, retrosternal bleeding, mediastinal hematoma, and mediastinal emphysema. Rib fractures were categorized as follows: displaced fracture; non-displaced fracture, as indicated by a thin, sharp, low-attenuation line through the cortices and matrix; buckle fracture, in which only the outer cortex, and not the inner cortex, is disrupted; and segmental rib fracture, which is characterized by 2 separate fractures of the same rib.¹³ Sternal fracture was defined as any CT changes similar to those seen with a rib fracture. Radiological findings were interpreted by at least 2 of the following: a board-certified radiologist, a board-certified emergency physician who was also certified as a trauma specialist by the Japanese Association for Surgery of Trauma, and a cardiologist who had attended a training course that awarded trauma specialist certification. Each evaluator assessed the radiological findings without seeing the clinical findings, and the analysis was blinded. In case of disagreement, the opinion of the third evaluator was adopted. Regarding CT scan evaluation of hemorrhage, a CT value of 30 HU was used as the cut-off.^14,15

Statistical Analysis

Statistical analyses were performed with JMP (version 14.0; SAS institute, Cary, NC, USA). Categorical data are reported as proportions, and comparisons were made with the chi-squared test or Fisher’s exact test. Continuous data are expressed as medians with interquartile ranges, and comparisons were made with the Wilcoxon rank sum test. Cut-off values for chest compression duration and age were determined based on receiver-operating characteristic (ROC) curve analysis using the Youden index. The analyzed variables consisted of those showing a significant difference (P<0.05) in univariate analysis, previously identified predictors, and predictors considered to be important based on clinical considerations. These variables matched what remained in the stepwise approach. We incorporated these variables into a multivariate model and performed multiple regression analysis.

For survival analysis, the Kaplan-Meier method was used to create survival curves, and the survival rates of patients with and without thoracic injuries were compared using the log-rank test and Wilcoxon rank sum test. Survival of ≥30 days was censored, and the Cox proportional hazards model was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between thoracic injuries and survival. Differences were regarded as statistically significant at P<0.05.

Results

During the study period, 384 consecutive patients who experienced OHCA were identified. A total of 306 patients were assessed after 78 were excluded for the following reasons: suicide (n=19), aortic dissection (n=40), aortic aneurysm rupture (n=9), lack of CT evaluation (n=6), and unknown chest compression duration (n=4) (Figure 1). Thoracic injuries associated with chest compression were detected in 234 patients (76%). Rib fractures were the most common injury, accounting for 75% of the total, and more than half were bilateral. Hemorrhagic pleural effusion and pneumothorax were each observed in ~10% of patients (Table 1).

Figure 1.

Study flow chart. CT, computed tomography; OHCA, out-of-hospital cardiac arrest.

Table 1. Thoracic Injuries Associated With CPR

Complication	Number of patients (N=234)
Rib fracture	231 (75)
Side of fracture
Bilateral	159 (68)
Right	49 (21)
Left	26 (11)
Sternal fracture	41 (13)
Retrosternal bleeding	15 (5)
Hemorrhagic pleural effusion	39 (13)
Pneumothorax	32 (10)
Mediastinal hematoma	16 (5)
Mediastinal emphysema	12 (4)

Data are presented as n (%). CPR, cardiopulmonary resuscitation.

Of the 306 patients, 171 (56%) were male, with a median age of 81 years. OHCA had a cardiac etiology in 244 (80%) patients. One-hundred and fifty-two (50%) patients had received bystander CPR, which was performed by medical staff in 61 (20%) patients and by family members in 81 (26%) patients. We compared cardiac arrest-related data between patients with and without thoracic injuries (Group-T and Group-N, respectively). Patients in Group-T were significantly older and had a significantly longer chest compression duration than those in Group-N (81 [71–89] vs. 77 [68–85] years, respectively, P=0.01; 43 [32–54] vs. 32 [19–39] min, respectively, P<0.001; Table 2). On hospital arrival, levels of serum potassium, troponin I, and lactate were significant higher in Group-T than in Group-N (6.7 [5.1–8.9] vs. 5.3 [4–7.2] mmol/L, respectively, P=0.002; 0.19 [0.05–1.07] vs. 0.11 [0.03–0.73] μg/L, respectively, P=0.03; 11.5 [8.7–14.5] vs. 9.5 [6.9–12.9] mmol/L, respectively, P=0.01; Table 2). In contrast, there were no significant differences between the 2 groups in the rate of witnessed cardiac arrest, rate of bystander CPR, initial recorded rhythm, or prehospital management by EMS. ROC curve analysis identified a chest compression duration of 35 min and an age of 87 years as the optimal cut-offs for predicting thoracic injuries (areas under the curves, 0.73 and 0.60, respectively; Figure 2). A comparison of thoracic injuries according to duration of chest compression and age are shown in Supplementary Tables 1 and 2. Multivariate logistic regression analysis by the stepwise selection method revealed that duration of chest compression (odds ratio [OR], 1.07; 95% CI, 1.04–1.09; P<0.001) and age (OR, 1.03; 95% CI, 1.01–1.05; P=0.005) were predictors of thoracic injuries (Table 3).

Table 2. Comparison of Clinical Profiles Between Patients With and Without Thoracic Injuries

	Group-T (N=234)	Group-N (N=72)	Missing	P value
Age (years)	81 [71–89]	77 [68–85]	0	0.01
Male	127 (54)	44 (61)	0	0.31
Cause of cardiac arrest				0.25
Cardiac etiology	190 (81)	54 (75)	0
Non-cardiac etiology	44 (19)	18 (25)	0
Witnessed cardiac arrest	85 (36)	32 (44)	0	0.22
Bystander CPR	122 (52)	30 (42)	0	0.12
Medical staff	49 (21)	12 (17)
Family	67 (29)	14 (19)
Others	6 (3)	4 (6)
Initially recorded rhythm				0.41
Ventricular fibrillation	20 (9)	7 (10)	0
Pulseless ventricular tachycardia	2 (1)	1 (1)	0
Pulseless electrical activity	56 (24)	23 (32)	0
Asystole	155 (66)	39 (54)	0
Interval from call to EMS to CPR (min)	9 [7–11]	9 [7–12]	0	0.46
Duration of chest compression (min)	43 [32–54]	32 [19–39]	0	<0.001
Laboratory tests at hospital arrival
Hemoglobin, g/L	113 [96–129]	115 [93–135]	23	0.79
Serum potassium, mmol/L	6.7 [5.1–8.9]	5.3 [4–7.2]	23	0.002
Troponin I, μg/L	0.19 [0.05–1.07]	0.11 [0.03–0.73]	54	0.03
pH	6.9 [6.7–7.0]	6.9 [6.8–7.1]	5	0.01
Serum bicarbonate, mmol//L	16.1 [12.3–20.4]	17.6 [14.3–22.3]	6	0.07
Lactate, mmol/L	11.5 [8.7–14.5]	9.5 [6.9–12.9]	7	0.01
Prehospital management by EMS
Supraglottic airway device	59 (25)	18 (25)	0	0.97
Adrenaline	96 (41)	32 (44)	0	0.61
Defibrillation	29 (12)	11 (15)	0	0.53
Management after hospital arrival
Intubation	199 (85)	62 (86)	0	0.82
Adrenaline	217 (93)	59 (82)	0	0.007
Amiodarone	15 (6)	3 (4)	0	0.58
Defibrillation	26 (11)	3 (4)	0	0.11
Coronary angiography	6 (3)	8 (11)	0	0.002
Primary coronary intervention	3 (1)	2 (3)	0	0.34
IABP use	3 (1)	2 (3)	0	0.34
VA-ECMO use	5 (2)	2 (3)	0	0.67
Target temperature management	16 (7)	16 (22)	0	<0.001
Prognosis
Return of spontaneous circulation	48 (21)	35 (49)	0	<0.001
24-h survival	17 (7)	24 (33)	0	<0.001
30-day survival	9 (4)	13 (18)	0	<0.001
30-day favorable neurologic outcome	3 (1)	5 (7)	0	0.02
Survival to hospital discharge	6 (3)	12 (17)	0	<0.001

Data are presented as n (%) or medians with interquartile ranges. Group-T, patients with thoracic injuries; Group-N, patients without thoracic injuries. CPR, cardiopulmonary resuscitation; EMS, emergency medical services; IABP, intra-aortic balloon pumping; VA-ECMO, venoarterial extracorporeal membranous oxygenation.

Figure 2.

ROC curve analysis to determine the optimal cut-offs for predicting thoracic injuries. (A) Duration of chest compression; (B) Age. AUC, area under the curve; ROC, receiver-operating characteristic.

Table 3. Multivariate Logistic Regression Analysis of Risk Factors for Thoracic Injuries

	Univariate			Multivariate (n=306)			Stepwise (n=306)
	OR	95% CI	P value	OR	95% CI	P value	OR	95% CI	P value
Age (years)	1.02	1.00–1.04	0.02	1.03	1.01–1.05	0.007	1.03	1.01–1.05	0.005
Male, n (%)	0.76	0.44–1.29	0.31	1.06	0.57–1.97	0.86	–
Witnessed cardiac arrest, n (%)	0.71	0.42–1.22	0.22	0.88	0.47–1.66	0.7	–
Bystander CPR, n (%)	1.53	0.89–2.60	0.12	1.22	0.66–2.25	0.53	–
Initial recorded rhythm, shockable, n (%)	0.76	0.34–1.73	0.52	0.73	0.27–2.00	0.54	–
Intubation, n (%)	0.92	0.43–1.96	0.82	0.78	0.32–1.91	0.58	–
Administration of adrenaline during CPR, n (%)	1.55	0.57–4.22	0.41	0.39	0.10–1.53	0.16	0.43	0.13–1.41	0.15
Interval from call to EMS to CPR (min)	0.99	0.94–1.05	0.85	1.02	0.96–1.09	0.43	–
Duration of chest compression (min)	1.06	1.04–1.08	<0.001	1.07	1.04–1.09	<0.001	1.07	1.04–1.09	<0.001

CI, confidence interval; CPR, cardiopulmonary resuscitation; EMS, emergency medical services; OR, odds ratio.

Regarding prognosis, ROSC, 30-day favorable neurologic outcome, survival to hospital discharge, and 24-h and 30-day survival were better in Group-N than in Group-T (P<0.05). Figure 3 shows the Kaplan-Meier curves for cumulative survival in the 2 groups. Survival of ≥30 days was censored. The cumulative survival rate was significantly higher in Group-N than in Group-T (HR, 1.96; 95% CI, 1.17–3.40; P=0.01; log-rank test P=0.009, Wilcoxon test P=0.006; Figure 3).

Figure 3.

Survival analysis. The Kaplan-Meier plot shows the cumulative survival rates in patients with and without thoracic injuries (Group-T and Group-N, respectively). Survival of ≥30 days was censored. The cumulative survival rate is significantly higher in Group-N than in Group-T.

Discussion

This single-center, retrospective cohort study evaluated CPR-related thoracic injuries diagnosed by CT scan in patients with non-traumatic OHCA. The main findings were as follows: (1) patients with thoracic injuries were significantly older and had a significantly longer chest compression duration than patients without thoracic injuries; (2) in multivariate logistic regression analysis, age and chest compression duration were independent predictors of thoracic injuries; and (3) among patients with ROSC, 30-day mortality was higher in those with thoracic injuries than in those without.

Study Strengths

There are 4 main strengths of our study. First, in contrast with previous studies, CPR was performed in accordance with the recent 2015 ILCOR/CoSTR guidelines. Second, the start of chest compression duration was defined as the time of CPR initiation by EMS personnel or medical staff because we could not accurately determine the initiation time and quality of CPR performed by bystanders. Third, CT scans were performed in almost all patients diagnosed with OHCA. Fourth, this is the first study to reveal an association between short-term prognosis and thoracic injuries related to CPR.

Association Between Chest Compression and Thoracic Injuries

The ILCOR/CoSTR guidelines recommended a compression depth of 40–50 mm in 2005, ≥50 mm in 2010, and 50–60 mm in 2015.^4,5,16 These changes were made as it was discovered that an excessive compression depth is associated with a higher incidence of thoracic injuries.

Hellevuo et al analyzed CPR-related injuries by autopsy and CT scan, and showed that a deeper compression depth was correlated with an increased frequency of thoracic injuries (depths of <5 cm, 5–6 cm, and >6 cm were associated with injury frequencies of 28%, 27%, and 49%, respectively, P=0.06).⁶ Beom et al found that the incidence of rib fractures analyzed by CT scan was 62.8% from 2006 to 2010 and 78.9% from 2011 to 2015, indicating a significant increase.⁷ Stiell et al reported that the optimal compression depth was 45.6 mm (40.3–55.3 mm), and that the survival rate decreased at greater compression depths.¹⁷

However, the association between chest compression and thoracic injuries has not been fully investigated since the 2015 guidelines were issued. Our study evaluated the incidence of complications arising from chest compression performed according to the 2015 guidelines.

Usefulness of CT Scans for Detecting Thoracic Injuries Due to Chest Compression

Early recognition of thoracic injuries is crucial in the management of resuscitated patients. The usefulness of detecting blunt trauma by CT scan has been established, and it is recommended to perform CT scans when evaluating thoracic injuries.

Seung et al showed that age, total chest compression duration, and OHCA were predictors of CT-evaluated thoracic injuries in patients who experienced OHCA or in-hospital cardiac arrest (IHCA).⁸ However, chest compression was performed according to the 2005 or 2010 guidelines. It has been pointed out that the quality of CPR in moving ambulances differs from that in hospitals, and OHCA and IHCA cases should be evaluated separately.^8,18,19 In addition, the study by Seung et al only evaluated successfully resuscitated cases, and excluded 700 of 939 cases because CT scans were not performed. Takayama et al revealed that age and out-of-hospital chest compression duration were predictors of CT-evaluated thoracic injuries in patients who experienced OHCA;⁹ however, the chest compression in the Takayama et al study was performed according to the 2010 guidelines. In addition, 117 of 600 cases were excluded because CT scans were not performed. In a multicenter study, Kashiwagi et al found that age and total chest compression duration were predictors of CT-evaluated thoracic injuries in patients who experienced OHCA;²⁰ however, chest compression was performed according to the 2005 or 2010 guidelines. Further, the authors evaluated thoracic injuries by post-mortem or post-resuscitation CT scans, and the only thoracic injuries assessed were rib fractures.

In our study, CT scans were performed in almost all patients who experienced OHCA. The predictors of thoracic injuries identified in our study were not significantly inconsistent with those found in previous studies.

Association Between CPR-Related Thoracic Injuries and Prognosis

In the present study, we revealed that the cumulative survival rate was significantly lower in patients with thoracic injuries than in those without. This result suggests that thoracic injuries themselves may be lethal or that the duration of cardiac arrest had other effects such as brain damage and multiple organ failure that contributed to mortality.

Study Limitations

Our study has several limitations. First, it is a single-center, retrospective study. Second, the quality of chest compressions could not be evaluated. In particular, we could not evaluate the depth of chest compression, which is known to be associated with thoracic injuries. In our study, however, the onset of chest compression duration was defined as the time of CPR initiation by EMS personnel or medical staff, rather than by bystanders. This should increase the accuracy of our analysis of thoracic injuries. It is known that the 30-day survival and neurological prognosis of patients with OHCA are better when CPR is performed by responders who are trained rather than by those who are untrained.^21,22 Although we could not evaluate the quality of chest compression performed by EMS personnel and medical staff, we decided that it was most likely superior to that performed by untrained bystanders. Third, we could not determine the number of cases in which CPR was performed using mechanical chest compression devices, or their association with thoracic injuries. We do know that mechanical CPR was performed in 121 (40%) patients (113 patients, LUCAS [Jolife AB, Sweden]; 5 patients, Clover 3000 [Koken Medical Company, Japan]; 3 patients, [unknown device]) and that manual CPR was performed in 13 (4%) patients, but the type of CPR performed in the remaining 172 (56%) patients is unknown. Finally, thoracic injuries may not have been accurately evaluated, because this study did not include autopsy cases. In particular, we could not identify the incidence or predictive factors of flail chest or massive bleeding requiring surgical or interventional hemostasis. In addition, the number of contrast-enhanced CT examinations was low (21 cases), and the evaluation of bleeding may have been insufficient.

Conclusions

Older age and longer chest compression duration are predictors of thoracic injuries in patients with non-traumatic OHCA. Thoracic injuries are associated with worse short-term prognosis.

Disclosures

All authors have no conflicts of interest to declare.

Sources of Funding

This study received no specific funding.

IRB Information

This study was approved by the Aso Iizuka Hospital Ethics Committee (No. 21014).

Supplementary Files

Please find supplementary file(s);

http://dx.doi.org/10.1253/circj.CJ-22-0193

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