Cardiac arrest (CA) is still a major public health problem around the world. It might contribute to more than 800,000 victims in western industrialized society and 540,000 in developing China annually with limited survival rate [
Although scene rapid defibrillation had been feasible with the aid of automatic external defibrillator (AED) and public access defibrillation (PAD), the quality of chest compression is still a critical determinant in preshock interval. Based on investigation data on animal and human, sufficient blood flow of vital organs produced by optimal cardiopulmonary resuscitation (CPR) was supposed to hold promise to the successful defibrillation following ventricular fibrillation (VF) and survival discharged with intact neurological behavior [
The data stated that shallow compression depth, inappropriate rate, incomplete thoracic recoil, and unnecessary compression interruption usually lead to the failure on establishment of spontaneous circulation [
This prospective, randomized, single center and controlled experiment was designed to simulate the suboptimal bystander CPR and investigate its consequence. Experiments were performed in an established swine model of electrically induced cardiac arrest in Laboratory Animal Center of Sun Yat-sen University (Guangzhou, China). All animals received humane care and the experiments were conducted after approval of the Animal Ethics Committee, Sun Yat-sen University. The protocol was performed according to institutional guidelines.
Fourteen male Yorkshire pigs, weighting
For the measurement of aortic pressure, a 6F fluid-filled angiographic catheter (model 070, Cordis Corporation, Miami Lakes, FL, USA) was advanced from the surgically exposed right femoral artery into the thoracic aorta. For measurements of right atrial pressure and pulmonary arterial pressure, a 7F pentalumen thermodilution-tipped catheter (model 131HF7, Swan-Ganz TD, Edwards Life sciences, CA, USA) was advanced from the surgically exposed right femoral vein and flow directed into the pulmonary artery. For inducing VF, a 5-Fr pacing catheter (Cordis Corporation, Miami Lakes, FL, USA) was advanced from the right jugular vein into the right ventricle until an endocardial electrocardiogram confirmed endocardial contact via a multi parameter monitor (78352C, HP Corporation, Palo Alto, CA, USA). The hard gel type of adult defibrillation/pacing pads (stat-padz, Zoll Medical Corporation, Chelmsford, MA, USA) was applied with an anterior to lateral placement. An accelerometer-based handheld CPR device (CPR-D-padz, Zoll Medical Corporation, Chelmsford, MA, USA) was placed on the surface of the animal’s chest just above the heart and underneath the rescuer’s hands during chest compression. Cardiac output was measured by the thermodilution technique with the aid of a cardiac output computer (Baxter COM-2TM, Edwards Division, Santa Ana, CA, USA) after a bolus injection into the right atrium of 5 mL cold saline solution, which had been maintained at a temperature between 0°C and 2°C. Aortic blood gases were measured with the aid of a handheld blood analyzer (model CG4+ Cartridge, Abbott i-STAT System, Princeton, NJ, USA). Respiratory frequency was adjusted to maintain PetCO2 between 35 mmHg and 40 mmHg before inducing cardiac arrest and when mechanical ventilation was resumed after resuscitation.
After collection of baseline data, cardiac arrest was induced with a 2 mA alternating current delivered to the endocardium of the right ventricle. After VF had been successfully induced, mechanical ventilation was discontinued and cardiac arrest was untreated for a total of 6 mins. Animals were then randomized to one of the following two groups: good CPR, where manual chest compression was performed by an emergency medical doctor at a rate of 100 per min and a depth comparable to 25% of the anterior posterior diameter of the chest, which represented approximately 50 mm; poor CPR, where chest compression was operated by another emergency medical doctor at the same rate, but the chest was compressed to 70% of the depth of good CPR group, which was equivalent to approximately 17% of the anterior posterior diameter of 35 mm [
Catheters were removed after 1 hr of postresuscitation monitoring, and the animals were euthanized by injection of 150 mg/kg intravenous pentobarbital.
Baseline measurements were obtained, including ECG, the aortic pressure, right atrial pressure, cardiac output, and blood gas analysis. The ECG, pressure measurements and acceleration signals were continuously measured and recorded through a data acquisition system supported by Windaq hardware/software (Dataq Instruments Inc., Akron, OH, USA) at a sample rate of 300 Hz. The coronary perfusion pressure (CPP) was digitally computed from the differences in time-coincident diastolic aortic and right atrial pressures. The compression rate and depth were calculated from the double integration of acceleration signals recorded from accelerometer by MATLAB7.0 (The Math Works, Inc., Natick, MA, USA).
Data are presented as mean ± standard deviation (SD). Differences in compression depth and CPP between the two groups were analyzed by two-tailed Student’s
Baseline measurements did not differ significantly between the two groups before inducing cardiac arrest (Table
Baseline characteristics.
G-CPR ( |
P-CPR ( |
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Right atrium pressure (mmHg) |
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Heart rate (bpm) |
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Cardiac output (L/min) |
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Blood-gas analysis | |||
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pH |
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PaO2 (mmHg) |
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Lactate (mmol/L) |
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Based on analysis of variance test as appropriate. Values are expressed as mean ± SD.
During initial 2 mins of CPR, the measured compression depth was ranged from 19.00 to 38.50 mm in poor CPR group and between 35.20 and 57.00 mm in good CPR group. As shown in Figure
Comparison of compression depth values between the two groups during initial 2 mins of cardiopulmonary resuscitation.
Comparison of coronary perfusion pressure (CPP) values between the two groups during initial 2 mins of cardiopulmonary resuscitation.
In poor CPR group, the measured compression depth of the first 4 mins of CPR significantly increased after is being changed to good quality compression for the last 6 mins of CPR (
The characteristics of compression depth and coronary perfusion pressure (CPP) in poor CPR group during the entire 10 mins of cardiopulmonary resuscitation procedure. PC = chest compression.
The defibrillation success rate for the first shock was higher in the good CPR group than in the poor CPR group, but a statistical significance was not achieved (100% versus 71.43%,
All of the 7 animals had ROSC after high quality compressions, while only 2 of the animals had ROSC with 4 mins of low quality compressions (100% versus 28.57%,
Our present study demonstrated that initial 4 mins of low quality compression followed by high quality of CPR compromised the outcomes significantly compared with good CPR from the beginning. Additionally, we also found that coronary flow produced by subsequent optimal chest compression could not provide a favorable outcome to those who experienced a low quality of CPR.
Base on previous studies and the current guideline, early and immediate bystander CPR was of importance in treating arrest patients before paramedic arrived, and if it is available, it may improve outcome on survival and neurological function. However, initiation of CPR for a bystander was still hesitating and the quality of this CPR was rarely satisfying. In a perspective observational trial by Kitamura and his team [
For chest compression, the fact that CPP was a positive associated with compression depth had been well documented. Sufficient compression depth may bring better blood perfusion to cardiomyodium and produce optimistic resuscitation outcome in animal model of prolonged VF and CPP of ≥15 mmHg in the period of chest compression was considered as an essential condition with the purpose of subsequently successful electrical shock and return of spontaneous circulation [
The other explanation of deteriorative CPP in following optimal compression might be partially contributed to the decreasing compliance of chest. After 4 mins of low quality of compression, the thoracic elasticity decreased. Then incomplete recoil of chest wall and subsequently decreased CPP and myocardial blood flow even only 10–20% leaning attended in CPR.
Rapid defibrillation has been recommended as a critical and primary treatment for cardiac arrest with initial shockable rhythm as VF or pulseless ventricular tachycardia (VT) [
The finding of this study indicated that there was no statistic difference of the first shock success in both groups. However, 5 animals in poor CPR group failed to return perfused rhythm and functional arterial pressure which finally lead to the significant difference with subsequent final ROSC. For a cardiac arrest porcine model, 6 mins of untreated VF was not long enough to guarantee the difference. A canine model of 5 mins of VF demonstrated that immediate defibrillation without preshock CPR brought none of animals ROSC (0/10), but resulted in 30% successful defibrillation (3/10) [
It is well known that, with every minute without CPR following sudden cardiac arrest, the probability of survival reduces by 7%–10% per minute [
We realized that there were some limitations in this study. Firstly, we did not compare the poor CPR group with prolonged (10 mins) untreated VF animals to evaluate if the initial poor rescue action might result in worse outcomes. We need deeply investigation to answer this question. Secondly, the healthy swine model is not always indicated a real condition of patients in clinical setting. People in VF usually suffered from coronary artery occlusion or asphyxia; besides, the successful resuscitation are not usually benefited from only CPR and counter shock if suspected coronary artery was not under revascularization. After all, despite these limitations existed, the facts that the suboptimal CPR impaired CPP was confirmed, and if it occurs, even a delayed optimal CPR may fail to improve the limited survival opportunities.
In this porcine model of prolonged cardiac arrest, even four minutes of initial poor quality of CPR compromises the survival outcome.
The authors declare no conflict of interests.
This study was supported in part by National Nature Science Foundation of China (NSFC 81000823 and 31070884), a Foundation Grant for Yat-sen Young Investigator. Lei Zhang and Heng Li contributed equally to this work, and Yongqin Li and Tao Yu contributed equally and were cocorresponding authors.