Ali Movahedi, Seyed Reza Mirhafez, PhD, Hamidreza Behnam-Voshani, Hamidreza Reihani, MD, Ali Kavosi, Gordon A. Ferns, DSc, MD, and Javad Malekzadeh

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1 ORIGINAL CONTRIBUTION A Comparison of the Effect of Interposed Abdominal Compression Cardiopulmonary Resuscitation and Standard Cardiopulmonary Resuscitation Methods on End-tidal CO 2 and the Return of Spontaneous Circulation Following Cardiac Arrest: A Clinical Trial Ali Movahedi, Seyed Reza Mirhafez, PhD, Hamidreza Behnam-Voshani, Hamidreza Reihani, MD, Ali Kavosi, Gordon A. Ferns, DSc, MD, and Javad Malekzadeh Abstract Objectives: Sudden cardiac arrest is a major cause of death in the adult population of developed countries, with only 10% 15% of cardiopulmonary resuscitations (CPRs) being successful. We aimed to compare the effects of interposed abdominal compression CPR (IAC-CPR) with standard CPR (STD-CPR) methods on end-tidal CO 2 (ETCO 2 ) and the return of spontaneous circulation (ROSC) following cardiac arrest in a hospital setting. Methods: After cardiac arrest was confirmed in a patient at Mashhad Ghaem Hospital, 80 cases were randomly assigned to one of the two methods of resuscitation, either IAC-CPR or STD-CPR, respectively. The inclusion criteria for the study were nontraumatic cardiac arrest, in patients between the age of 18 and 85 years, and the presence of endotracheal tube. Exclusion criteria were abdominal surgery in the past 2 weeks, active gastrointestinal bleeding, pulmonary embolism, and suspected pregnancy. Results: There was a significant difference between the two groups in ETCO 2 (p < 0.003), but there was no significant difference as far as the ROSC (p > 0.50). Conclusion: The increase in the ETCO 2 during IAC-CPR is an indicator of the increase in cardiac output following the use of this method of CPR. ACADEMIC EMERGENCY MEDICINE 2016;23: by the Society for Academic Emergency Medicine Sudden cardiac arrest is a leading cause of death in the adult population of developed countries 1 with an annual prevalence of more than 400,000 in the United States alone 2. Although cardiopulmonary resuscitation (CPR) is extensively used, the survival rate after CPR is low. 3 From 2000 to 2008, a total of 64,339 patients in 435 hospitals in the United States experienced cardiac arrest; only 10% 15% of in-hospital CPR attempts and only 3% of out-of-hospital CPR attempts were successful. 4 In a study conducted in Iran, the From the Department of Anesthesia and Operating Room Nursing, Neyshabur University of Medical Sciences (AM, AK), Neyshabur, Iran; the Department of Intensive Care Nursing, School of Nursing & Midwifery, Mashhad University of Medical Sciences (AM), Mashhad, Iran; the Department of Basic Medical Sciences, Neyshabur University of Medical Sciences (SRM), Neyshabur, Iran; the Department of Pediatrics, School of Nursing & Midwifery, Mashhad University of Medical Sciences (HBV), Mashhad, Iran; the Department of Emergency Medicine, School of Medicine, Mashhad University of Medical Sciences (HR), Mashhad, Iran; the Division of Medical Education, Brighton & Sussex Medical School (GAF), Sussex, UK; and the Department of Medical Emergencies, School of Nursing & Midwifery, Mashhad University of Medical Sciences (JM), Mashhad, Iran. Received August 16, 2015; revision received October 28, 2015; accepted November 17, This study was supported by Vice Chancellor for Research of Mashhad University of Medical Sciences, Mashhad, Iran The authors have no potential conflicts to disclose. Supervising Editor: Brian J. O Neil, MD. Address for correspondence and reprints: Javad Malekzadeh; Malekzadehj@mums.ac.ir. 448 ISSN by the Society for Academic Emergency Medicine 448 PII ISSN doi: /acem.12903

2 ACADEMIC EMERGENCY MEDICINE April 2016, Vol. 23, No mortality rate following CPR was also reported to be more than 90%, while the discharge rate was less than 7%. 5 Discharge rates of these patients from the hospital and their overall survival rates from cardiopulmonary arrest are poor. 6 The quality of CPR, as assessed by effective cardiac output, is often low 7 and less than desirable. 8 The cardiac output derived following optimally performed CPR is >30% of the normal cardiac output, 9 and coronary blood flow during CPR is often less than 35% of the normal coronary blood flow. 10 These findings may be caused by the initial delay in CPR, the older age of patients receiving CPR, and severe preexisting underlying disease. So it is perhaps necessary to consider more effective methods for CPR. Interposed abdominal compression CPR (IAC-CPR) is perhaps one of these methods. In 1967 Harris et al. 11 conducted abdominal compression during CPR on six animals. Harris found that abdominal compression could increase carotid blood flow, but led to liver injury in two of the six animals. In their study on 30 swine, Xavier et al. 12 found that IAC-CPR produced more aortic diastolic and right atrial diastolic pressure than standard CPR (STD-CPR; p < 0.05). No difference was seen between the two groups concerning CPR-produced trauma and survival rate. Some years ago, Ralston et al. 13 assessed IAC-CPR, a three-rescuer technique that includes conventional chest compression combined with intermittent abdominal compression, where one rescuer compresses the abdomen, one compresses the chest, and the third provides ventilation. The rescuer who is responsible for abdominal compressions compresses the abdomen in the beginning of the relaxation phase of chest compression, at a site midway between xiphoid and umbilicus. Hand position, depth, rhythm, and rate of abdominal compressions are similar to those of chest compressions and the required force is similar to that needed for palpating the abdominal aorta. An endotracheal tube must be placed in patient trachea, before or shortly after the start of IAC-CPR. IAC-CPR can increase diastolic aortic pressure, coronary perfusion, and venous return and can improve blood flow to other vital organs. 14 Rhythmic compression of abdomen can increase venous return and cardiac output, thereby enhancing CPR results. Certain clinical studies have proved that IAC-CPR is a more useful technique than STD-CPR in cardiopulmonary arrest patients. 10,12,15 Although there are some studies that found no clinical significant difference between these methods. 16 A comprehensive evidencebased review demonstrated that IAC-CPR had clinical benefit in humans, in 10 of 12 small- to medium-sized clinical studies. 17 The American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care indicates that IAC-CPR is a useful method in CPR if sufficient trained personnel are available. 13 The standard of evidence for the use of IAC-CPR is categorized as Class IIb 13 meaning that though not strongly recommended, IAC-CPR has more positive points than drawbacks, hence further research is necessary. Research Hypotheses IAC-CPR can increase end-tidal CO 2 (ETCO 2 ) during resuscitation and improve the return of spontaneous circulation (ROSC) and 24-hour survival in cardiopulmonary arrest patients. METHODS Study Setting and Population Samples were selected from Ghaem Hospital in Mashhad, northeastern Iran, and randomly assigned to either STD-CPR or IAC-CPR. Randomization of patients was achieved using computer-generated random numbers. Patients were considered eligible for the study if they suffered from a nontraumatic cardiac arrest in the surgical or medical or emergency departments (EDs) of the hospital, were between the age of 18 and 85 years, and had an endotracheal tube. The following exclusion criteria were used: a history of an abdominal aortic aneurysm, a history of coagulopathy, significant ascites, abdominal surgery in past 2 weeks, active gastrointestinal bleeding, pulmonary embolism, suspected pregnancy, and ROSC before the arrival of the CPR team. Study Protocol All patients underwent resuscitation using the 2010 American Heart Association advanced cardiac life support protocol. Chest compressions were performed at a rate of 100 compressions per minute at a depth of 5 cm and ventilation rate was 8 10/min. Cardiac arrest was confirmed by a physician and endotracheal intubation was performed as soon as possible. A code (99) was announced when a cardiac arrest happened and the cardiac arrest team was notified by pocket beeper. The cardiac arrest team included two nurses and an anesthesiology nurse and a third-year internal medicine resident. They were trained in the technique of IAC-CPR. The IAC-CPR group received STD-CPR plus IAC-CPR and the STD-CPR group received STD-CPR only. In patients who received IAC-CPR, abdominal compression was performed with open hands, fused together in center of abdomen between the xiphoid and the umbilicus during the relaxation phase of chest compression. Depth, rhythm, and rate of abdominal compressions were similar to chest compressions and force on the abdomen was maintained until the beginning of next chest compression. Ventilation was performed using a bag-valve-mask apparatus attached to the endotracheal tube at a rate of 8 10 breaths/min. Oxygen was delivered at 100% FiO 2 in both groups. During CPR, the patients received 1 mg of epinephrine every 5 minutes and other medications were administered intravenously according to 2010 American Heart Association advanced life support guideline. CPR was continued until confirming of ROSC or presence of one of the indications for ending CPR. Post-ROSC systolic and diastolic pressures and heart rate were measured, in patients who had successful CPR. For evaluation of complications of IAC-CPR, patients were followed for 24 hours and the presence of abdominal pain, tenderness in abdomen, and need for

3 450 Movahedi et al. INTERPOSED ABDOMINAL COMPRESSION CPR abdominal surgery after CPR were assessed in these patients. A 24-hour survival was assessed in all patients included in the study. Ethical Approval The 2010 American Heart Association Guideline for Cardiopulmonary mentions that IAC-CPR is a useful method in CPR if sufficient trained personnel are available. 14 The study was approved by Ethics Committee of the Mashhad University of Medical sciences. The Iranian Registry of Clinical Trials (IRCT) code of our study is IRCT N1. Data Collection Demographic and clinical information of patients at the time of cardiac arrest was recorded. The initial arrest rhythm was documented as the first rhythm seen at the start of CPR. Blood pressure was measured with a cuff that attached to a monitor. ETCO 2 was monitored continuously and recorded with a capnograph (side stream, model Comdeck). ETCO 2 values were recorded every 2 minutes and reported in mmhg. ROSC was defined as the presence of a palpable femoral arterial pulse and a systolic blood pressure above 80 mmhg for longer than 3 minutes. Patients followed for 24-hour after resuscitation for evaluation of complications of CPR, include abdominal pain, presence of tenderness in abdomen or need for abdominal surgery after CPR. ETCO 2 and ROSC were primary outcomes and 24-hour survival and complications of CPR were secondary outcomes of this study. Data Analysis We used SPSS Statistics for Windows version 16 (IBM Corp., Armonk, NY) for data analysis. Resuscitation outcomes, ETCO 2, ROSC, and 24-hour survival for both groups were compared. Continuous variables were analyzed by Student s two-tailed t-test and Mann-Whitney U-test for normally and nonnormally distributed variables, respectively. Values were expressed as mean s- tandard deviation (SD) for normally distributed variables and median (interquartile range) for nonnormally distributed variables. To examine the association of the following prearrest and during arrest variables (such as age, sex, length of hospitalization, the actual arrest time prior to CPR, length of CPR, initial arrest rhythm, presence or absence of hypertension, myocardial infarction, cancer, chronic obstructive pulmonary disease, ischemic heart disease, renal failure, pneumonia, hepatitis, pulmonary edema, cerebral vascular accident [CVA], and diabetes mellitus) on ETCO 2, ROSC, 24-hour survival, and other resuscitation outcomes, we used two-way analysis of variance, chi-square test, Fisher s exact test, and Pearson and Spearman correlation test. To examine associations between ETCO 2 and IAC- CPR in the presence of confounding factors including age, sex, and CVA that differed between the groups, multivariate analysis model was used. The correlation analysis was assessed using Pearson correlation analysis. Differences were considered as significant when the p-values were RESULTS Demographic data and clinical diagnoses in the two groups are summarized in Table 1. Eighty cardiac arrest victims (42 women and 38 men) during the period of January to February 2014 were studied. They were randomized to receive IAC-CPR or STD-CPR and followed for 24 hours. The mean SD age of the patients was years (range = years) and there was a significant difference in the mean SD age of two groups ( years in STD-CPR group vs years in IAC-CPR group, p < 0.02). Sex distribution was not different between the two groups (p > 0.82). Length of hospitalization was not significantly different between the two groups. There was no significant difference in the estimated time from arrest to starting CPR between two groups and it was under 5 minutes in 91.2% of patients. Time from beginning CPR to endotracheal intubation in the STD-CPR group was minutes and in IAC-CPR was minutes (p > 0.57). There was no significant difference in duration of resuscitation process, between the two groups ( minutes in STD-CPR group vs minutes in IAC-CPR group, p = 1.00). The most common clinical comorbidities in the study groups were hypertension, diabetes, and CVA (Table 1). CVA in IAC-CPR group was significantly more prevalent than in the STD-CPR group (p < 0.02). A total of 62.6% of all resuscitation attempts were performed in the EDs and 37.4% of resuscitations were performed on general medical and surgical wards or coronary care unit. There was no significant difference in location of arrest between the two groups (EDs 60% in STD-CPR group vs. 65% in IAC-CPR group). Initial rhythm was not significantly different between the two groups (p > 0.31). Only in one patient in the STD-CPR group was the initial rhythm ventricular fibrillation, and in other patients, asystole was the initial finding. There was no significant difference in initial ETCO 2 between the two groups (9.5 ( ) mm Hg in STD- CPR group vs ( ) mm Hg in IAC-CPR group, p > 0.21), but the increase in ETCO 2 during CPR in the IAC-CPR was significantly more than for the STD-CPR group ( mm Hg vs mm Hg, p < 0.03). An increase in ETCO 2 during CPR was seen in both groups. Increasing in ETCO 2 in IAC-CPR group was more than for the STD-CPR group ( mm Hg increase in ETCO 2 of patients during IAC-CPR vs mm Hg during STD-CPR, p > 0.001). Return of spontaneous circulation in the IAC-CPR group was not significantly higher than for the STD- CPR group (60% vs. 52.5%, p > 0.50, odds ratio = 1.35, 95% confidence interval [CI] = ). Survival at 24 hours was equal in both groups (37.5%, p = 1.00). For evaluating the complications of CPR we assessed patients at 24 hours after CPR for clinical evidence of abdominal trauma, including abdominal pain, presence of tenderness in abdomen, and the need for abdominal surgery during the postresuscitation period. We found no evidence of abdominal trauma in patients who survived. We examined the relation between amount of ETCO 2 and ROSC. As shown in Table 2, we found that in

4 ACADEMIC EMERGENCY MEDICINE April 2016, Vol. 23, No Table 1 Demographic and Clinical Characteristic Data in Two Groups STD-CPR (n = 40) IAC-CPR (n = 40) p-value Sex Female 22 (55) 20 (50) >0.82 Male 18 (45) 20 (50) Age (yr) <0.02 Length of hospitalization (days) 1.0 ( ) 4.0 ( ) >0.34 Time prior to CPR (min) 1.0 ( ) 1.0 ( ) >0.34 Time to intubation (min) 2.0 ( ) 2.0 ( ) >0.57 Duration of CPR (min) 12.5 ( ) 15.0 ( ) 1.00 Hypertension 9 (22.5) 13 (32.5) >0.32 Cancer 6 (15) 6 (15) 1.00 MI 2 (5) 1 (2.5) >0.55 COPD 4 (10) 1 (2.5) >0.36 IHD 5 (12.5) 7 (17.5) >0.53 Renal failure 0 (0) 2 (5) >0.49 Pneumonia 1 (2.5) 1 (2.5) 1.00 Hepatitis 1 (2.5) 1 (2.5) 1.00 Pulmonary edema 2 (5) 3 (7.5) >0.64 Asthma 0 (0) 3 (7.5) >0.24 CVA 5 (12.5) 14 (35) <0.02 Diabetes 7 (17.5) 13 (32.5) >0.12 Post-ROSC sbp (mm Hg) ( ) ( ) (>0.91) Post-ROSC dbp (mm Hg) 60.0 ( ) 60.0 ( ) (>0.25) Post-ROSC heart rate (beats/min) (>0.54) Values are expressed as number (%). For normally and nonnormally distributed variables, values are expressed as mean SD and median (interquartile range), respectively. the Student t-test and Mann-Whitney U-test were used to compare the demographic and clinical characteristics in normally and nonnormally distributed variables, respectively. For categorical data chisquare and Fisher s exact test were used. Time to intubation = time from beginning of CPR to endotracheal intubation; time prior to CPR = the actual arrest time prior to CPR. COPD = chronic obstructive pulmonary disease; CVA = cerebral vascular accident; dbp = diastolic blood pressure; IAC- CPR = interposed abdominal compression-cardiopulmonary resuscitation; IHD = ischemic heart disease; MI = myocardial infarction; ROSC = return of spontaneous circulation; sbp = systolic blood pressure; STD-CPR = standard CPR. Table 2 Relation Between Amount of ETCO 2 and ROSC ROSC in IAC-CPR ROSC in STD-CPR ROSC in All Patients ETCO 2 (mm Hg) Neg Pos p-value Neg Pos p-value Neg Pos p-value <10 2 (12.5) 3 (12.5) 4 (21.1) 3 (14.3) 6 (17.4) 6 (13.3) (56.2) 6 (25.0) 10 (52.6) 12 (57.1) 19 (54.2) 18 (40.2) (18.8) 8 (33.3) 4 (21.1) 5 (23.8) 7 (20.2) 13 (28.8) (6.2) 6 (25.0) (5.3) 0 (0.0) (5.6) 6 (13.4) (6.2) 6 (25.0) 0 (0.0) 0 (0.0) 1 (2.8) 6 (13.4) >50 1 (6.2) 1 (4.2) 0 (0.0) 1 (4.8) 1 (2.8) 2 (4.4) Total 16 (100) 24 (100) 19 (100) 21 (100) 35 (100) 45 (100) Data are presented as number (%). Fisher s exact test was used. ETCO 2 = end-tidal CO 2 ; IAC-CPR = interposed abdominal compression-cardiopulmonary resuscitation; ROSC = return of spontaneous circulation; STD-CPR = standard CPR. patients with higher levels of ETCO 2, ROSC was more likely, but the distribution of negative and positive ROSC in ETCO 2 categories in the IAC-CPR and STD- CPR groups and total subjects was not statistically different (all p > 0.05). We examined prearrest variables for their effect on ETCO 2, ROSC, and 24-hour survival. There was an association between ETCO 2 with age (p < 0.02) and the method of CPR (p < 0.001). Age of patients in the IAC- CPR group was significantly higher than for the STD-CPR group. A total of 62.6% of patients who had ROSC survived for 24 hours. Survival at 24 hours in female patients was 54.8% and in male patients it was 18.4% (p < 0.001). There was no association between age and ROSC, age and 24-hour survival, presence of CVA and ROSC, or presence of CVA and 24-hour survival (all p > 0.05). We also examined other prearrest variables for their effect on ROSC and 24-hour survival (all p > 0.05). Only in patients who had history of CPR were ROSC and 24-hour survival significantly less than

5 452 Movahedi et al. INTERPOSED ABDOMINAL COMPRESSION CPR Table 3 Adjusted Association of ETCO 2 and CPR Methods in Present of Age, Sex, and CVA by Linear Regression Model b (95% CI) p-value IAC-CPR 6.10 (0.50 to 11.70) Sex (female) 3.09 ( 2.36 to 8.54) Age (yr) 0.15 ( 0.33 to 0.02) CVA (yes) 3.61 ( 2.91 to 10.14) Variables in the model were analyzed as enter method. b = regression coefficient; CVA = central venous accident; ETCO 2 = end-tidal CO 2 ; IAC-CPR = interposed abdominal compression-cardiopulmonary resuscitation. in patients who underwent CPR for the first time. Survival at 24 hours in patients who received CPR for the first time was 46.4%, 28.6% in patients who received CPR for the second time, and 0.0% in patients who received CPR for third and fourth time (p < 0.04), but there was no significant difference between the two groups in this variable. Pearson and Spearman correlation analysis between all the prearrest variables and ETCO 2 showed no significant correlation between variables (all p > 0.05). Multivariate Analysis To assess the effect of CPR method on ETCO 2, multivariate analysis was undertaken using linear regression model in the presence of age, sex, and CVA. As illustrated in Table 3, CPR method remained statistically significant independent predictors of ETCO 2 (p = 0.033) after correction for age, sex, and CVA. The ETCO 2 during CPR in the IAC-CPR group was mm Hg higher than for the STD-CPR group after controlling for age, sex, and CVA. DISCUSSION Outcomes of in-hospital CPRs are very poor, especially in elderly patients and in patients with asystole or with EMD initial arrest rhythm. 10 Capnometry monitoring during CPR is a beneficial process that guides the therapy and helps positively affect the chest compressions. Animal and adult studies have shown a strong correlation between ETCO 2 and cardiac output during CPR. 18 We found that IAC-CPR can increase ETCO 2 during CPR and improve cardiac output even after correcting for confounder factors. Babbs et al. 19 in their study recognized that myocardial perfusion increased during abdominal compression. Ward et al. 15 and Hoekstra et al. 20 demonstrated that ETCO 2 increased by 70% in patients who received IAC-CPR. Sack et al. 10 also showed that ETCO 2 in IAC-CPR group was higher than that in the STD-CPR group, a difference that was not statistically significant (p > 0.05). Xanthos et al. 21 showed that insofar as ETCO 2 during CPR, no difference existed between the IAC-CPR and STD-CPR group. In this study, ROSC was higher in patients who received IAC-CPR than in those were treated by STD- CPR. Furthermore, the IAC-CPR group was significantly older than STD-CPR group. Also, the length of hospitalization and most of the clinical diagnosis such as hypertension, CVA, and diabetes was higher in the IAC-CPR group than in STD-CPR group, which could be the reason why ROSC was not significantly different between the two groups. Babbs et al. 22 showed that abdominal counter pulsation improves blood flow during otherwise STD-CPR in animal models and in electronic models of the circulation. Hoekstra et al. 20 demonstrated that compared with STD-CPR, IAC-CPR improves total and vital organ oxygen delivery through enhanced venous return and perfusion pressures. Wenzel et al. 23 in their study on pigs showed that compared with STD-CPR, abdominal compression-decompression CPR increased significantly hemodynamic variables and vital organ blood. Sack et al. 10 recognized a significant difference between the two groups concerning ROSC (49% in IAC-CPR group vs. 28% in STD-CPR group (p < 0.01)). In their study on pigs, Xavier et al. 12 found no significant difference in ROSC between IAC-CPR and STD-CPR. In the study of Mateer et al. 16 ROSC in IAC-CPR and STD- CPR groups was 34 and 30%, respectively, a difference that is not significant. Xavier et al. 12 found no significant difference between IAC-CPR and STD-CPR regarding survival rate in the swine models (90% vs. 70%). Concerning vital signs after resuscitation in this study, no significant difference was found between the two groups. Unlike STD-CPR, IAC-CPR did not involve any increase in the blood pressure. Berryman et al. 9 indicated that in IAC-CPR systolic blood pressure and mean arterial pressure were significantly greater than those in STD-CPR (p < 0.05). In this study, for patients who had ROSC, the blood pressure was measured only at the end of the CPR. The 24-hour survival in both groups was 37.5%. Numerous factors can affect 24-hour survival rate, including age that was significantly more in IAC-CPR group than in STD-CPR group, the length of hospitalization or clinical diagnosis, and so on. Xavier et al. 12 found no significant difference between IAC-CPR and STD-CPR in pigs. Also, Ward et al. 15 observed no difference between the two groups as far as 24-hour survival. Sack et al. 10 demonstrated that a significant difference existed between their two groups regarding the 24-hour survival (33% in IAC-CPR group vs. 13% in STD-CPR group, p < 0.009). In this study, as in other studies (Sack et al., 10 Ralston et al., 13 and Mateer et al. 16 ), we found no abdominal trauma following the use of IAC-CPR. Sex was not statistically different between the two groups; however, there were more females in the STD- CPR group than in the IAC-CPR group. The 24-hour survival in females was significantly greater than for males, while sex differences did not exist in the study of Sack et al. 10 and Mateer et al. 16 There are several possible mechanisms through which IAC-CPR can enhance ROSC during resuscitation. Twenty percent of the blood volume is in the abdominal compartments. Accordingly, the rhythmic compression of abdomen during CPR can increase venous return and cardiac preload. Coronary perfusion occurs in diastole. Thus, abdominal compressions during the diastolic phase of chest compression can

6 ACADEMIC EMERGENCY MEDICINE April 2016, Vol. 23, No increase diastolic pressure and blood flow to the heart. In our study, the primary objective was to determine whether or not IAC-CPR can improve resuscitation outcomes in cardiac arrest patients. Also we found an increase in ETCO 2 during IAC-CPR. IAC-CPR is an easily applied manual technique in the treatment of cardiac arrest 10 and can be considered during in-hospital resuscitation when sufficiently trained personnel are available (Class IIb). 14 No complications were reported in the adults. 14 LIMITATIONS This study had limited scopes and objectives. Cardiac arrest patients have various comorbidities and are usually complicated, which can affect the CPR outcomes. We compared some of these potential confounding factors and their effect on CPR outcomes between two groups. Cardiac arrests usually go unnoticed even in hospitals. We were not able to estimate the actual arrest time prior to CPR, a fact that influenced the results. Instead, we trusted the hospital personnel on the start time of the cardiac arrest. We do not measure minute ventilation of patients during CPR because of using the bag-valve-mask apparatus. Chest compressions (as possible determinants of resuscitation outcome) were not standardized; there may have been differences in the rate and force of chest compression between the rescuers. Using mechanical devices (e.g., thumper) for CPR prevented us from initiating CPR in a timely manner. No neurologic assessment was made at 24 hours. CONCLUSIONS We found that interposed abdominal compression cardiopulmonary resuscitation can increase end-tidal CO 2 during cardiopulmonary resuscitation. End-tidal CO 2 is a noninvasive monitoring with a relationship with cardiac output during cardiopulmonary resuscitation. This method may be considered for in-hospital resuscitations. In this study interposed abdominal compression cardiopulmonary resuscitation, which was compared with standard cardiopulmonary resuscitation, did not significantly increase return of spontaneous circulation, but we think more research is required. We found no complications associated with the use of interposed abdominal compression cardiopulmonary resuscitation. Discharge from hospital and neurologic assessment of interposed abdominal compression cardiopulmonary resuscitation requires further investigations. The authors acknowledge the personnel of CPR team, nursing personnel and residents of Ghaem s Hospital, and everyone whose cooperation made this study possible. We thank to Kazem Ahmadi, MSc, for his generous help and collaboration. References 1. Ornato JP, Peberdy MA. Cardiopulmonary resuscitation. Berlin: Springer Science & Business Media, Huikuri HV, Castellanos A, Myerburg RJ. Sudden death due to cardiac arrhythmias. 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7 454 Movahedi et al. INTERPOSED ABDOMINAL COMPRESSION CPR 20. Hoekstra OS, van Lambalgen AA, Groeneveld A, van den Bos GC, Thijs LG. Abdominal compressions increase vital organ perfusion during CPR in dogs: relation with efficacy of thoracic compressions. Ann Emerg Med 1995;25: Xanthos T, Bassiakou E, Dontas I, et al. Abdominal compressions do not achieve similar survival rates compared with chest compressions: an experimental study. Am J Emerg Med 2011;29: Babbs CF. Abdominal counterpulsation in cardiopulmonary resuscitation: animal models and theoretical considerations. Am J Emerg Med 1985;3: Wenzel V, Lindner KH, Prengel AW, Strohmenger HU. Effect of phased chest and abdominal compression-decompression cardiopulmonary resuscitation on myocardial and cerebral blood flow in pigs. Crit Care Med 2000;28: