Comparison of complications secondary to cardiopulmonary resuscitation between out-of-hospital cardiac arrest and in-hospital cardiac arrest

Objective: The aim of this study was to assess whether there was a significant difference in the complications of cardiopulmonary resuscitation (CPR) between out-of-hospital cardiac arrest (OHCA) and in-hospital cardiac arrest (IHCA) survivors using multidetector computed tomography (MDCT). Subjects and methods: We performed a retrospective analysis of prospective registry data. We enrolled both OHCA and IHCA patients who underwent successful CPR. We classified chest injuries secondary to chest compression into rib fractures, sternum fractures, and uncommon complications such as lung contusions and extrathoracic complications. We compared these complications according to CPR locations. We also analysed risk factors for CPR complications using multiple regression analysis and classification and regression tree analysis. Results: During the study period, a total of 148 patients were included in the primary analysis. Rib fractures were detected more in OHCA survivors than in IHCA survivors (74 patients (83.2%) vs. 37 patients (62.7%), p = 0.05), and frequency of multiple rib fractures was higher in OHCA survivors than IHCA survivors (69 patients (77.5%) vs. 34 patients (57.6%), p = 0.01). Although other complications were not significantly different between the groups, there was a trend for OHCA survivors to sustain more serious and direct high-energy related complications. Older age, longer CPR, and OHCA were significantly associated with incidence of rib fractures, multiple rib fractures, and number of rib fractures. Conclusions: Rib fractures were more likely to occur in OHCA survivors, and serious complications tended to occur more often in OHCA compared to IHCA survivors.


LIST OF FIGURES
. CPR-related injuries before and after the change in the Subjects and methods: We performed a retrospective analysis of prospective registry data. We enrolled both OHCA and IHCA patients who underwent successful CPR. We classified chest injuries secondary to chest compression into rib fractures, sternum fractures, and uncommon complications such as lung contusions and extrathoracic complications. We compared these complications according to CPR locations. We also analysed risk factors for CPR complications using multiple regression analysis and classification and regression tree analysis.
Although other complications were not significantly different between the groups, there was a trend for OHCA survivors to sustain more serious and direct high-energy related complications. Older age, longer CPR, and OHCA were significantly associated with incidence of rib fractures, multiple rib fractures, and number of rib fractures.
Conclusions: Rib fractures were more likely to occur in OHCA survivors, and serious complications tended to occur more often in OHCA compared to IHCA survivors. Chest compression during cardiopulmonary resuscitation (CPR) may cause unintended complications consisting mainly of chest injuries. The most common complications are rib fractures and sternum fractures. [1][2][3][4] The incidence of rib fractures is 12.9-96.6%, and most often involves the second and sixth ribs along the mid clavicular line. 3 The incidence of sternum fractures is 1.3-43.3%. 1,2,4 Other complications, which are relatively rare but clinically significant, include fractures of clavicles, scapulae, and the vertebral column, flail chest, subcutaneous emphysema, pulmonary oedema,pulmonary haematoma, pneumothorax, haemothorax, lung laceration, pneumomediastinum, cardiac contusion/rupture, pericarditis, liver laceration, and bowel injury. 4 The incidence of these complications varies widely depending on the diagnostic approach. 1,2 Up to now, CPR quality during ambulance transport has not been maintained for various reasons. As the speed of ambulances has increased, excessive depth and the average rate of chest compressions have increased. 5 In a previous study, a high chest compression rate with a wide variability was reported during ambulance transport. 6 Changes in acceleration resulting in jerk force occur frequently during transport, which may throw ambulance personnel off balance. 7 Off-balance personnel may directly affect CPR hands-off time as well as the rescuer's posture during CPR.
If the rescuer is off balance, he/she cannot maintain the correct hand position, and may unavoidably compress the incorrect position on the victim's chest. Therefore, the CPR conducted out-of-hospital, especially during ambulance transport, may lead to more complications than that conducted in-hospital. To our knowledge, there is no study comparing the differences in complications of CPR between out-of-hospital cardiac arrest (OHCA) and in-hospital cardiac arrest (IHCA) survivors. In most prior studies pertaining to complications of CPR, chest injuries through autopsies or by means of chest radiographs were evaluated. 1,2 However, these methods have limitations in clinical practice.
Autopsies cannot be used for survivors after CPR. Chest X-rays can show a large haemothorax or pneumothorax, but some injuries, such as a smaller haemothorax, occult pneumothorax, lung contusion, sternum fracture, or minor rib fracture, could be missed. 8,9 Therefore, in studies utilizing chest X-rays, complications may be underestimated. Multidetector computed tomography (MDCT) enables thinner sections with greater speed, and allows for higher quality axial images and multiplanarreconstructions. [9][10][11] Given the increasing utilization of MDCT in the trauma setting, MDCT has become a useful diagnostic tool with high diagnostic accuracy. [8][9][10][11] Recently, studies using MDCT for detecting chest injuries secondary to CPR have been published. [12][13][14] Hence, the aim of this study was to assess whether there was a significant difference in the complications of CPR between OHCA and IHCA survivors using MDCT. We hypothesised that complications are more likely to arise in OHCA survivors because of the difficulty of CPR during ambulance transport.

Study design and participants
We performed a retrospective analysis of prospective registry data to compare complications of CPR between OHCA and IHCA survivors using chest MDCT.
We enrolled both OHCA and IHCA patients who underwent successful CPR in the emergency departments of two academic tertiary care centres from January 2009 to May 2014. We excluded patients under the age of 18, those who did not undergo chest MDCT within 48 h after return of spontaneous circulation (ROSC), and those with cardiac arrest following a trauma. We also excluded patients who underwent CPR in another hospital before being transferred to our institutions. Each hospital's Institutional Review Board approved this study protocol.

Study protocol
One investigator collected data through a retrospective review of medical records. Variables that were recorded included: age, gender, cause of arrest, witnessed or unwitnessed arrest, location of the arrest, whether bystander CPR was provided, and initial rhythm and duration of CPR. In our two institutions,

Data analysis
The statistical analysis was performed using SAS (version9.2, SAS Inc., Cary, NC, USA) and R package (version 3.0.3,http://www.R-project.org-package: party). The categorical variables were described as frequencies (%), and continuous variables were described as mean ± standard deviation. We used independent t-test for comparison of continuous variables and Fisher's exact test for categorical variables. The generalized estimating equation was used to analyse differences in CPR complications such as level of fractured ribs and location of fractured ribs between OHCA and IHCA survivors because these variables allowed multiple checks. Variables with a p < 0.05 from the univariate analyses, and clinically significant variables such as age and gender, were selected as potential risk factors for CPR complications. These variables were assessed with multiple logistic regression or multiple linear regression.
The classification and regression tree (CART) analysis was performed to determine interaction patterns for subjects with and without rib fractures, and to determine cut-off points for these parameters. The parameters that were identified as being significant by multivariate analysis were included in the CART analyses. Statistical significance was defined as p < 0.05. III. RESULTS

Study population
During the study period, a total of 2153 patients were enrolled. Most patients (n = 1214; 56.4%) were excluded because CPR was not successful. Among the 939 patients with ROSC, we excluded 56patients under the age of 18, 24 patients with cardiac arrest following a trauma, and 711 patients that did not undergo chest CT within 48 h. Finally, 148 patients were included in the primary analysis ( Figure 1). All patients in our study were resuscitated manually in the hospital and EMS. Of the 148 patients, 89 were categorized as OHCA (60.1%) and 59 were categorized as IHCA (39.8%).Among the 89 OHCA patients, 1 case had only out-of-hospital CPR without in-hospital CPR, because ROSC was achieved during ambulance transport. Demographic characteristics and clinical findings are summarised in Table 1. There were no significant differences in age, gender, cause of arrest, and initial rhythm between OHCA and IHCA survivors. The mean CPR time of OHCA was longer than that of IHCA survivors (28.6 ± 12.4 min vs. 7.9 ± 5.6 min, p < 0.001). In OHCA survivors, out-of-hospital CPR time was 17.6 ± 9.1 min and in-hospital CPR time was 11.0 ± 7.3 min.

Risk factors for CPR complications
We divided the groups according to whether the patients had a specific complication, such as rib fracture, or not, and performed univariate analysis to find the risk factors. Multiple logistic regression or multiple linear regression analyses were conducted using the variables in which p < 0.05 after the univariate analysis. Clinically important variables such as age and gender were also included in the multiple logistic regression or multiple linear regression analyses. CPR time and arrest location were highly interrelated with each other, so taking into consideration the multi collinearity between the two variables, we generated models one by one including one of the two variables. The results of the multivariate analyses are shown in Table 3. Older age, OHCA and longer CPR were significantly associated with incidence of rib fracture, multiple rib fractures, number of rib fractures, rib fracture combined with sternum fracture, and rib fracture combined with sternum fracture and serious complications. There were no differences in rib fractures, sternum fractures, and serious complications before and after the change in the 2010 CPR guidelines (Table 4).  CART analysis consisted of three basic steps based on two variables (age and arrest location ( Figure 3A), and age and CPR time ( Figure 3B)) for a total of four nodes. With a combination of two variables, we classified the risk of rib fracture. If the patient was under 41 years of age, the probability of rib fracture was relatively low (21.05% patient rate, "Node 2").On the other hand, if the patient's age was over 41 years with a CPR time over 10 min, the highest risk of rib fracture was 93.1% patient rate ("Node 7"). For patients over 41 years with a CPR time under10 min, the risk of rib fracture was divided at the age of 66 years(<66 yrs, 27.78% patient rate ("Node 5") vs >66 yrs, 87.5% patient rate ("Node 6")). As an example, a 60-year-old man with OHCA, is applicable to "Node 7" in Figure 3A and Exhibits 92.21% patient rate for risk of rib fracture. A 60-year-old man who underwent CPR for 15 min, is applicable to "Node 7" in Figure 3B and Exhibits 93.1%patient rate for risk of rib fracture.
In rib fractures combined with sternum fractures or rib and sternum fractures

IV. DISCUSSION
This was the first retrospective study to demonstrate that com-plications are more likely to occur in OHCA survivors than in IHCA survivors. In this study, there was a higher incidence of rib fractures, multiple rib fractures, and a higher numbers of rib fractures in OHCA survivors than in IHCA survivors.
Although there were no statistically significant differences because of the small number of complications, there was a trend for OHCA survivors to sustain more serious complications than IHCA survivors. Also, there were 2 cases of vertebral fractures and 2 cases of scapular fractures in the OHCA survivors. Scapular and vertebral fractures are very uncommon, and are usually associated with direct high-energy trauma. 5,16 Therefore, these results suggest that more physical force was applied to the OHCA survivors. A previous study showed that as the speed of ambulances increases, chest compressions with excessive depth, as well as the rate of chest compressions, increase. 5 Increased ambulance speed also causes an increase in high frequency acceleration of chest compressions which suggests the possibility of unnecessary application of force. 5 Another study reported that variability in chest compression rate and depth during transport was significantly greater than that occurring at the scene. 17 Therefore, CPR during transport could lead to unnecessary deeper and faster chest compressions resulting in more damage to the chest wall, including rib fractures, and higher force injuries such as scapular or vertebral fractures. First rib and 9 to 11th rib fractures happened more frequently in OHCA survivors than in IHCA survivors in our study.
Lateral portions of the ribs were more frequently fractured in OHCA patients.
Theas findings may be difficult to maintain the correct hand position for high quality CPR in OHCA than in IHCA (Figure 2). injuries. In a previous study, only 11.5% of patients who underwent bystander CPR suffered from minor injuries thought to be related to bystander CPR. 19 Another study, concerning frequency and severity of injury related to chest compressions in bystander CPR, also reported very low incidence of complications; 12% of patients experienced discomfort, and only 2% of patients had a fracture. 20