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Reperfusion injury protection during Basic Life Support improves circulation and survival outcomes in a porcine model of prolonged cardiac arrest
Resuscitation 105 (2016) 29–35
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Experimental paper
Reperfusion injury protection during Basic Life Support improves circulation and survival outcomes in a porcine model of prolonged cardiac arrest Guillaume Debaty a,b,∗ , Keith Lurie c , Anja Metzger c , Michael Lick c , Jason A. Bartos a , Jennifer N. Rees a , Scott McKnite a , Laura Puertas c , Paul Pepe d , Raymond Fowler d , Demetris Yannopoulos a a
Department of Medicine-Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA University Grenoble Alps/CNRS/CHU de Grenoble/TIMC-IMAG UMR 5525, Grenoble, France c Department of Emergency Medicine, Hennepin County Medical Center, University of Minnesota, Minneapolis, MN, USA d University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-8579, USA b
a r t i c l e
i n f o
Article history: Received 27 November 2015 Received in revised form 3 April 2016 Accepted 2 May 2016 Keywords: Cardiac arrest Cardiopulmonary resuscitation Basic life support Ischemic postconditioning Active compression decompression Impedance threshold device
a b s t r a c t Objective: Ischemic postconditioning (PC) using three intentional pauses at the start of cardiopulmonary resuscitation (CPR) improves outcomes after cardiac arrest in pigs when epinephrine (epi) is used before defibrillation. We hypothesized PC, performed during basic life support (BLS) in the absence of epinephrine, would reduce reperfusion injury and enhance 24 h functional recovery. Design: Prospective animal investigation. Setting: Animal laboratory Subjects: Female farm pigs (n = 46, 39 ± 1 kg). Interventions: Protocol A: After 12 min of ventricular fibrillation (VF), 28 pigs were randomized to four groups: (A) Standard CPR (SCPR), (B) active compression-decompression CPR with an impedance threshold device (ACD-ITD), (C) SCPR + PC (SCPR + PC) and (D) ACD-ITD CPR + PC. Protocol B: After 15 min of VF, 18 pigs were randomized to ACD-ITD CPR or ACD-ITD + PC. The BLS duration was 2.75 min in Protocol A and 5 min in Protocol B. Following BLS, up to three shocks were delivered. Without return of spontaneous circulation (ROSC), CPR was resumed and epi (0.5 mg) and defibrillation delivered. The primary end point was survival without major adverse events. Hemodynamic parameters and left ventricular ejection fraction (LVEF) were also measured. Data are presented as mean ± SEM. Measurements and Main Results: Protocol A: ACD-ITD + PC (group D) improved coronary perfusion pressure after 3 min of BLS versus the three other groups (28 ± 6, 35 ± 7, 23 ± 5 and 47 ± 7 for groups A, B, C, D respectively, p = 0.05). There were no significant differences in 24 h survival between groups. Protocol B: LVEF 4 h post ROSC was significantly higher with ACD-ITD + PC vs ACD-ITD alone (52.5 ± 3% vs. 37.5 ± 6.6%, p = 0.045). Survival rates were significantly higher with ACD-ITD + PC vs. ACD-ITD alone (p = 0.027). Conclusions: BLS using ACD-ITD + PC reduced post resuscitation cardiac dysfunction and improved functional recovery after prolonged untreated VF in pigs. Protocol number: 12-11. © 2016 Elsevier Ireland Ltd. All rights reserved.
Introduction Despite years of research to improve survival after out-ofhospital cardiac arrest (OHCA), survival with good neurologic
∗ Corresponding author at: SAMU 38, Pôle Urgences Médecine Aigue CHU de Grenoble, CS 10217, 38043 Grenoble Cedex 09, France. E-mail address: [email protected] (G. Debaty). http://dx.doi.org/10.1016/j.resuscitation.2016.05.008 0300-9572/© 2016 Elsevier Ireland Ltd. All rights reserved.
outcome remains poor.1 Recently, new investigations have examined the relationship between outcomes and the method by which blood flow is reintroduced to the body after a prolonged period of ischemia. In many clinical scenarios, the reperfusion process itself can cause injury. Reperfusion injury is proportional to the duration of ischemia and the way blood flow is reintroduced after prolonged ischemia. Reperfusion injury can cause up to 50% of the total damage induced by myocardial infarction in animal models2–4 .
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There are multiple ways to reduce reperfusion injury: most involve modulation of this process with drugs that affect the reperfusion injury salvage kinase (RISK) pathway or mitochondrial permeability transition pore, or both.4 Re-introduction of blood flow with “controlled pauses” is a non-pharmacological means to protect the myocardium and the brain from ischemia reperfusion injury in clinical scenarios of regional ischemia during ST elevation myocardial infarction and stroke.4–6 This concept is called “ischemic post-conditioning” (PC).7 PC using three intentional 20 s pauses at the initiation of CPR improves hemodynamics and neurologically intact survival after prolonged ventricular fibrillation in porcine models of cardiac arrest.8,9 In previous studies with PC, epinephrine was always used before the first defibrillation attempt. The aim of the study was to assess if PC used during the Basic Life Support (BLS) phase of CPR would provide better cerebral and myocardial protection against reperfusion injury and facilitate functional recovery after prolonged untreated VF compared to CPR alone. Methods This study was approved by the Institutional Animal Care Committee of the Minneapolis Medical Research Foundation of Hennepin County Medical Center. All animal care was compliant with the National Research Council’s 1996 Guidelines for the Care and Use of Laboratory Animals (protocol number: 12-11). All studies were performed by a qualified, experienced research team in Yorkshire female farm bred pigs weighing 39 ± 1 kg. A certified and licensed veterinarian assured the protocols were performed in accordance with the National Research Council’s Guidelines. Preparatory phase The aseptic surgical preparation, anesthesia, data monitoring and recording procedures used in this study have been previously described.10,11 Animals were fasted overnight. Intramuscular ketamine (10 mL of 100 mg mL-1 ) was used for sedation followed by inhaled isoflurane (0.8–1.2%). Pigs were intubated with a size 7.0 endotracheal tube then ventilated with room air, using an anesthesia machine (Narkomed, Telford, Pennsylvania), with a tidal volume of 10 ml kg-1 and a respiratory rate adjusted to continually maintain a PaCO2 of 40 mmHg and PaO2 of 80 mmHg (blood oxygen saturation > 95%). Normothermia was maintained with a warming blanket (Bair Hugger, Augustine Medical, Eden Prairie, Minnesota). Central aortic blood pressure was recorded continuously with a Millar catheter (Mikro-Tip Transducer, Millar Instruments, Houston, TX, USA) placed in the descending thoracic aorta. A second Millar catheter was inserted in the right atrium via the right external jugular vein. An ultrasound flow probe (Transonic 420 series multichannel, Transonic Systems, Ithaca, New York) was placed in the left common carotid artery to quantify carotid blood flow (ml min-1 ). Animals received an intravenous heparin bolus (100 units kg-1 ). Arterial blood gases (Gem 3000, Instrumentation Laboratory) were obtained at baseline, 15, 30, 60 and 4 h after return of spontaneous circulation (ROSC). Electrocardiograms were continuously recorded. Hemodynamic data were continuously monitored and recorded (BIOPAC MP 150, BIOPAC Systems, Inc., CA, USA). Coronary perfusion pressure (CPP) was calculated as the difference between aortic and right atrial pressures during the decompression phase. End tidal carbon dioxide (ETCO2 ), tidal volume, minute ventilation, and blood oxygen saturation were continuously measured (COSMO Plus, Novametrix Medical Systems, Wallingford, Connecticut). ROSC was defined using the Utstein guidelines for uniform reporting in animal research as maintenance of systolic pressure of ≥60 mm Hg for ≥10 consecutive minutes.12
Experimental protocol Following the surgical preparation VF was induced by delivering direct intra-cardiac current via a temporary pacing wire. STD-CPR and ACD-CPR were performed with a pneumatically driven automatic piston device (Pneumatic Compression Controller, Ambu International, Glostrup, Denmark) as previously described.13 During STD-CPR, uninterrupted chest compressions were performed at a rate of 100 compressions/min, with a 50% duty cycle and a compression depth of 25% of the anteroposterior chest diameter. After each compression, the chest wall was allowed to fully recoil passively. With ACD-CPR, after each compression, the chest was actively pulled upwards with a suction cup attached to the skin with a decompression force of ∼20 lbs.13,14 Concurrently with ACD-CPR, an impedance threshold device (ITD, ResQPOD TM, Advanced Circulatory Systems, Roseville, MN, USA) with a resistance of 16 mmHg was attached to the endotracheal tube. After the period of intentional pauses, when positive pressure breaths were delivered only during the pauses, asynchronous positive pressure ventilations were delivered with room air (FiO2 of 0.21) with a manual resuscitator bag. The tidal volume was maintained at ∼10 mL kg-1 and the respiratory rate was 10 breaths min-1 . Protocol A Following 12 min of untreated ventricular fibrillation, 28 pigs were randomized to receive CPR during the BLS period as follows: 1) 2) 3) 4)
Group A: Standard CPR (SCPR) Group B: ACD-ITD CPR Group C: SCPR plus PC (SCPR-PC) Group D: ACD-ITD CPR plus PC (ACD-ITD + PC)
PC groups initially received 20 s of CPR (SCPR or ACD-ITD) without positive pressure breaths followed by a 20 s pause of compressions followed by another 20 s of CPR and the cycle was repeated for a total of three pauses. Three positive pressure breaths were delivered during each pause, with each breath delivered over 1 s and 6 s between each breath. After 2.75 min of BLS, the first defibrillation effort was delivered with 275-J biphasic shocks. If ROSC was not achieved, defibrillation was delivered every 2 min thereafter during CPR. Epinephrine was administered in all animals without ROSC as a 0.5 mg (∼15 g kg-1 ) bolus at 4 min together with 25 mg of amiodarone. In addition, during this Advanced Life Support (ALS) phase we used an active form of the intrathoracic pressure regulation therapy rather than the ITD, which generated a continuous negative intrathoracic pressure of -9 mmHg between each positive pressure breath.15,16 All animals received oxygen at 4 l min-1 rate during ALS. Protocol B The two groups with the best survival results in Protocol A were selected. After 15 min of untreated VF, 18 pigs were randomized to receive BLS augmented with ACD-ITD CPR or ACD-ITD CPR plus controlled pauses (Fig. 1). Controlled pauses, ventilations, and the CPR method were performed as in Protocol A. Unlike Protocol A, the BLS period in Protocol B was 5 min in duration, after which the first defibrillation shock was delivered. If ROSC was not achieved, defibrillation shocks were delivered every 2 min thereafter during CPR. Epinephrine was administered in all groups in a 0.5 mg (∼15 g kg-1 ) bolus at 6 min together with 25 mg of amiodarone. Similar to Protocol A, an active form of the ITD that provided continuous negative intrathoracic pressure was used during the ALS phase.
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Fig. 1. ACD-ITD-PC and ACD-ITD CPR alone protocol with associated hemodynamic tracings. ACD-ITD: active compression decompression with impedance threshold device CPR, PC: ischemic post-conditioning, ROSC: Return of spontaneous circulation.
Resuscitation efforts were continued until ROSC was achieved or a total of 10 min of CPR was provided. Post-ROSC care After ROSC, animals were mechanically ventilated and maintained under general anesthesia with isoflurane. Supplemental oxygen was added only if arterial saturation was lower than 90% with a SaO2 target between 90 and 94%. Animals that had a stable post-ROSC rhythm but were hypotensive (mean arterial pressure < 50 mmHg) received increments of 0.1–0.2 mg intravenous epinephrine every 5 min until the mean arterial pressure rose above 50 mmHg. If the arterial blood pH was lower than 7.2 then 50–100 mEq of NaHCO3 were given intravenously. Therapeutic hypothermia was induced and sustained between 32 and 34 ◦ C
using intravenous cold saline (1000 ml) and external cooling. The carotid flow probe and venous and arterial catheters were removed during this time. Controlled rewarming (0.5 ◦ C h-1 ) to normothermia was performed at that point using a blanket and a heating lamp. The total duration of hypothermia was about 12 h. Once rewarmed animals were weaned off the ventilator and extubated. Survivors received nonsteroidal anti-inflammatory medication, as previously described, and had free access to water and food.17 They were returned to their cages and were observed for the first 4 h for signs of clinical deterioration. Based upon predetermined stopping criteria determined by protocol in collaboration with the Animal Care Committee and the on-site, independent, boardcertified veterinarian, animals were euthanized if they had epileptic seizure activity that could not be terminated with a single dose of
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Table 1 Hemodynamics parameters and outcomes in protocol A. Group of CPR
Measure
Baseline
BLS 1 min
BLS 1.5 min
Group A: SCPR n=7
SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2
101 ± 6 69 ± 5 3±2 66 ± 7 235 ± 20 40 ± 1 107 ± 6 76 ± 6 1±1 75 ± 6 264 ± 29 41 ± 1 105 ± 6 73 ± 5 0±1 73 ± 5 269 ± 34 42 ± 1 109 ± 7 79 ± 6 2±1 77 ± 5 239 ± 14 40 ± 2
45 ± 7 22 ± 5 4±1 18 ± 5 60 ± 10£ 26 ± 3# 52 ± 7 21 ± 1 3±1 18 ± 2 45 ± 5£ 35 ± 4 41 ± 7 20 ± 3 6±1 14 ± 3 58 ± 12£ 27 ± 2 53 ± 5 24 ± 5 4±1 21 ± 4 90 ± 8*,#,§ 30 ± 4
55 ± 9 25 ± 5 4±2 21 ± 5 46 ± 9£ 27 ± 3# 78 ± 14§ 32 ± 2 4±2 28 ± 3 39 ± 6£ 44 ± 5*§,£ 30 ± 5# 25 ± 7 5±1 20 ± 7 50 ± 12£ 31 ± 3# 58 ± 15 35 ± 5 2±0 34 ± 6 80 ± 10*,#,§ 33 ± 4#
Group B: ACD-ITD n=7
Group C: SCPR-PC n=7
Group D: ACD-ITD-PC n=7
BLS 2.5 min 80 ± 11 33 ± 6 5±2 28 ± 6£ 27 ± 8£ 30 ± 3# 97 ± 8§ 41 ± 7 5±1 35 ± 7 42 ± 8 45 ± 4* 60 ± 11#,£ 29 ± 5 6±1 23 ± 5£ 32 ± 6 35 ± 4 92 ± 10§ 50 ± 7 3±1 47 ± 7*,§ 48 ± 6* 36 ± 5
ALS 1.5 min
ROSC 1 hour
# shocks
ROSC at BLS
ROSC BLS+ ALS
24-hour Survival
121 ± 10 56 ± 8 6±2 50 ± 6 38 ± 10 43 ± 4 117 ± 8 57 ± 3 11 ± 3 46 ± 6 37 ± 10 42 ± 2 96 ± 14 48 ± 8 10 ± 1 38 ± 7 24 ± 5 41 ± 6 110 ± 13 65 ± 10 8±2 57 ± 9 45 ± 20 41 ± 3
79 ± 4# 44 ± 3# 1±1 43 ± 3 169 ± 19 44 ± 2 106 ± 9* 64 ± 6* 4±2 60 ± 6 201 ± 25 45 ± 2 89 ± 9 55 ± 5 1±1 50 ± 7 181 ± 8 46 ± 2 88 ± 5 55 ± 6 0±2 54 ± 5 151 ± 17 45 ± 3
4.7 ± 0.7
0 (0%)
7 (100%)
6 (86%)
4.3 ± 0.9
3 (43%)
7 (100%)
7 (100%)
4 ± 0.6
1 (14%)
6 (86%)
5
3.7 ± 0.3
3 (43%)
7 (100%)
7 (100%)
SCPR: Standard CPR; ACD-ITD: active compression decompression with impedance threshold device CPR, PC: post conditioning. SBP and DBP: Systolic and diastolic blood pressure; RA: right atrial pressure, CPP: Coronary perfusion pressure; CBF: Carotid blood flow; ROSC: Return of spontaneous circulation. Values are shown as mean ± SEM. All pressures are in mm Hg and all flows in ml min-1 . *denotes p < 0.05 compare to STD, # denotes p < 0.05 compare to ACD-ITD, § denotes p < 0.05 compare to STD-PC, £ denotes p < 0.05 compare to ACD-ITD-PC.
midazolam (25 mg) intramuscular or if they developed cardiorespiratory distress. Neurologic assessment Twenty-four hours after ROSC, the same veterinarian, blinded to the study intervention, assessed the pigs’ neurologic function based on a cerebral performance category (CPC) scoring system modified for pigs.17 The following scoring system was used: 1 = normal; 2 = slightly disabled; 3 = severely disabled but conscious; 4 = vegetative state; a five was given to animals that died in the lab due to unachievable ROSC or died in the cage following ROSC.17 The Swine Neurologic Deficit Score (NDS) was also used to evaluate the level of consciousness, respiratory pattern, cranial nerve function, motor and sensory function, and behavior evaluation, in 24 h survival animals.18 Echocardiographic evaluation of left ventricular function A transthoracic echocardiogram was obtained on all survivors 1, 4 and 24 h post ROSC.19 Ejection fraction was assessed using Simpson’s method of volumetric analysis by an independent clinical echocardiographer blinded to the treatments.20 Arterial blood was collected at baseline and from all survivors 4 h and 24 h post-ROSC. Statistical analysis Data are expressed as mean ± standard error of mean (SEM). The primary end point was survival without major adverse outcomes at 24 h. Major adverse outcomes were defined by the protocol and included pigs which did not have a ROSC after resuscitation or were intentionally euthanized according to the study protocol and as a result of the veterinarian’s evaluation of the animals in a blinded manner, for reasons due to coma, refractory seizures or cardiorespiratory distress before the 24 h point after ROSC. The chi-square
test or Fisher exact test was used for comparison of proportions. A single-factor ANOVA was used to determine statistical significance of differences in means of continuous variables between groups in Protocol A and a two-tailed unpaired t-test or Mann-Whitney non parametric test was used in Protocol B. Kaplan–Meier major adverse outcomes curves were compared between the intervention groups in Protocol B with the use of the log-rank test. P-value less than 0.05 was considered statistically significant. Statistical analysis was performed using SPSS 21 (IBM Corporation, Armonk, NY, USA).
Results Protocol A All animals were included in this analysis. There were no significant baseline differences between treatment groups (Table 1). ACD-ITD-PC (group D) provided significantly higher CPP and CBF after 3 min of BLS compared with the three other groups (Table 1), whereas SCPR-PC did not improve CPP, CBF or ETCO2 during BLS vs. SCPR alone. ROSC after completion of BLS was achieved in 0, 3, 1, and 3 pigs in groups A, B, C, and D, respectively (p = 0.22). There was no significant difference in 24 h survival between groups. CPC scores at 24 h are represented in Fig. 2. NDS score at 24 h in survivor was 6.3 ± 3.7 in group A, 1.0 ± 0.6 in group B, 23.0 ± 16.6 in group C and 2.8 ± 0.9 in group D (p = 0.27).
Protocol B Nine animals were included in the ACD-ITD group while eight were included in the ACD-ITD-PC group. One animal from the ACD-ITD-PC group was excluded because of respiratory and hemodynamic instability during the preparatory phase. There were no significant baseline differences between treatment groups (Table 2).
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Table 2 Hemodynamics parameters and outcomes in protocol B. Group of CPR
Measure
Baseline
BLS 2 min
BLS 4 min
BLS 5 min
ALS 6 min
ROSC 1 h
# shocks
ROSC at BLS
ROSC at BLS+ ALS
24-hour Survival
Group A ACD-ITD-PC n=8
SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2
104 ± 6 69 ± 4 2±1 79 ± 5 259 ± 35 39 ± 1 103 ± 8 69 ± 6 2 ± 0,4 79 ± 7 214 ± 35 40 ± 1
46 ± 5 20 ± 2 3±1 17 ± 2 63 ± 12 29 ± 2* 59 ± 5 23 ± 2 2±1 21 ± 2 31 ± 6 38 ± 2
74 ± 7 31 ± 2* 5±1 26 ± 2* 38 ± 6 39 ± 3 69 ± 4 24 ± 2 4±1 20 ± 1 43 ± 8 42 ± 3
68 ± 5 29 ± 2 5±1 24 ± 1* 54 ± 11 41 ± 3 67 ± 3 23 ± 2 4±1 19 ± 1 42 ± 7 41 ± 2
87 ± 12 46 ± 6 10 ± 2 41 ± 6* 23 ± 15 35 ± 6 88 ± 10 36 ± 1 9±2 27 ± 2 17 ± 3 28 ± 5
85 ± 3 49 ± 2 1±1 58 ± 3 164 ± 42 45 ± 2 87 ± 6 55 ± 6 2,3 ± 1,2 64 ± 7 151 ± 22 43 ± 2
4±1
5 (63%)
8 (100%)#
3 (38%)&
6±2
2 (22%)
5 (56%)
1 (11%)
Group B ACD-ITD n=9
STD: Standard CPR; ACD-ITD: active compression decompression with impedance threshold device CPR, PC: post conditioning; SBP and DBP: Systolic and diastolic blood pressure; RA: right atrial pressure, CPP: Coronary perfusion pressure; CBF: Carotid blood flow; ROSC: Return of spontaneous circulation. Values are shown as mean ± SEM. All pressures are in mm Hg and all flows in ml min-1 . *p < 0.05 compared to ACD-ITD group. # p = 0.053 compared to ACD-ITD group. & p = 0.027 compared to ACD-ITD (log-rank test comparison).
Fig. 2. Cerebral performance category score at 24 h in Protocol A. Group A: Standard CPR group, group B: active compression decompression with impedance threshold device (ACD-ITD), Group C: Standard CPR plus PC group (SCPRPC), Group D: ACD-ITD-PC group
CPP increased over time in the ACD-ITD-PC group during the first 3 min of CPR. CPP became significantly higher in the ACDITD-PC group compared with ACD-ITD alone only after 4 min of CPR. ETCO2 was significantly lower during the first 3 min of CPR in the ACD-ITD-PC group compared with ACD-ITD (p = 0.01 at 3 min)
and reached similar level after 4 min (Table 2 and Fig. 3). ROSC at 5 min (BLS phase) was achieved in five animals in the ACDITD-PC group compared with two animals in the ACD-ITD group (p = 0.15). After the ALS phase, ROSC was achieved in eight animals in the ACD-ITD-PC group vs. five animals in the ACD-ITD group (p = 0.053). The ACD-ITD-PC group trended toward to require less epinephrine to achieve ROSC compared to ACD-ITD alone (0.3 ± 0.1 vs. 0.7 ± 0.4, p = 0.06). There were no significant differences in the number of shocks or the dose of amiodarone needed to achieve or to maintain a sinus rhythm with ACD-ITD-PC versus ACD-ITD alone (7 ± 2 vs. 9 ± 2 and 34 ± 5 mg vs. 31 ± 4 mg, p = 0.51 and 0.52, respectively). A significant increase in survival was demonstrated with ACDITD-PC compared with ACD-ITD (Log-rank comparison, p = 0.027) (Fig. 4). There were three survivors after 24 h in the ACD-ITD-PC and their CPC scores were 2, 3, and 4 versus one survivor in the ACD + ITD group with a CPC score of 4. The NDS scores at 24 h in survivors were 29.3 ± 8.4 compared with 43 in the sole ACD-ITD survivor. Left ventricular Function. Among survivors, LVEF was higher 15 min after ROSC but did not reach significance with ACD-ITDPC versus ACD-ITD (51 ± 4% vs. 39 ± 10%, p = 0.19). Four hours after ROSC, LVEF was significantly higher with ACD-ITD-PC vs. ACD-ITD alone (52.5 ± 3% vs. 37.5 ± 6.6%, p = 0.045).
Fig. 3. Coronary perfusion pressure and ETCO2 over time in Protocol B. ACD-ITD: active compression decompression with impedance threshold device CPR, PC: ischemic post-conditioning
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by others.29,30 Together they suggest a common mechanism of myocardial protection that can be rapidly and easily delivered.
Limitations
Fig. 4. Kaplan–Meier curve of survival after start of CPR in Protocol B. The data demonstrate a significant increase in survival at 24 h with ACD-ITD-PC compared with ACD-ITD (Log-rank comparison, p = 0.027). ACD-CPR, active compression decompression cardiopulmonary resuscitation; PC, ischemic post-conditioning.
Discussion This study demonstrates, for the first time, the successful application of PC during the BLS phase of resuscitation in an animal model. PC in combination of ACD-ITD significantly improved coronary perfusion pressure, preserved cardiac ejection fraction and enhanced survival rates. In previous studies, the benefits of PC with regard to increased CPP and survival were observed in combination with epinephrine injected during the last of three sequential intentional pauses.7–9 In the current study, the beneficial effects of the combined use of PC and ACD-ITD were observed without use of epinephrine. These findings provide proof of the clinical concept that PC could be of value if provided by first responders in the setting of prolonged untreated cardiac arrest. The protective mechanism of PC during CPR is not well understood. Reperfusion with three intentional 20 s pauses at the start of CPR may limit reperfusion injury by slowing the normalization of intracellular pH and calcium, thereby reducing production of reactive oxygen species, preventing opening of the mitochondrial permeability transition pore, and preventing activation of the pro-apoptotic calcium-sensitive protease.21–25 Improved myocardial function has been observed when PC was used in the setting of myocardial infarction and cardiac arrest.7,8,26 Improved neurologic function has also been observed with the use of PC in the setting of ischemic stroke27 and global ischemia such as that experienced during cardiac arrest.7,8,28,29 Recently, PC combined with ACD CPR, ITD, sevoflurane, and poloxamer 188 improved cardiac and neurologic function after 17 min of untreated cardiac arrest in pigs.9 In the current study, 2.75 min of BLS may not have been long enough to overcome the potential negative hemodynamic effects of three intentional 20 s pauses used to mitigate the potential harm associated with reflow after prolonged ischemia. By contrast, 5 min of BLS with three intentional 20 s pauses at the start of CPR to provide PC was sufficient to demonstrate a hemodynamic (Fig. 3) and survival benefit (Fig. 4). As demonstrated by the results of Protocol A, the combination of ACD + ITD was needed to provide greater circulation during CPR whereas use of conventional SCPR, even with PC, provided inferior results. One of the important results of the current study is the absence of cardiac dysfunction in the PC group after 15 min of untreated VF. These findings are consistent with work from our prior cardiac arrest studies and studies of acute myocardial infarction
The optimal duration of ischemic time and/or BLS CPR duration remain unclear. We were unable to demonstrate a significant survival benefit with 12 min of untreated VF and 2.75 min of CPR, but we did observe the hypothesized survival benefit with 5 min of BLS CPR. Though the protective biochemical mechanisms underlying these observations is currently unknown, we speculate based upon the results from Protocols A and B that in order to observe a clinically meaningful PC effect without epinephrine that at least 5 min of CPR is needed to overcome the absolute hypoperfusion associated with three 20 s pauses. Similarly, the optimal duration and number of pauses for PC is unknown. It is possible that the current 30:2 compression: ventilation ratio recommended by ILCOR for BLS confers some PC.31 This is suggested by the benefit of 30:2 versus continuous chest compressions (CCC) in a recent clinical trial where the per protocol analysis demonstrated superior results in patients with 30:2 in terms of survival to hospital discharge and favorable neurological function.32 Further work is needed to determine the optimal duration and number of pauses needed to provide PC during CPR. Some confounding factors may have also affected the results of the study. First isoflurane has been described to have a protective effect on reperfusion injuries. The same dosage was administrated in all study groups but it remains unclear if the effects of PC on reperfusion injury observed in our study could have been affected with this additional protective effect. Second, prolongation of the untreated VF times may have also contributed to our ability to observe a statistically significant survival advantage with PC in Protocol B. Third, all survivors were treated with hypothermia. It is currently unknown whether hypothermia is required together with the PC to provide the observed reperfusion protection. Further study is underway to examine the potential synergy between these two protective strategies. Importantly, the study was not powered a priori to demonstrate improved neurologically-favorable survival outcomes with the study intervention. This study has provided an anticipated effect size for future studies. Further studies are needed to determine if there are any untoward effects of providing BLS CPR with intentional pauses as described herein with shorter untreated VF times. It is noteworthy, however, that in the present study there were no observed adverse effects of using only 2.75 min of BLS CPR with PC provided with three intentional pauses.
Conclusion After a prolonged untreated cardiac arrest in pigs use of PC with a simple strategy comprised of three 20 s compression pauses during the start of the BLS CPR phase delivered with ACD CPR and an ITD without initial use of epinephrine reduced post-resuscitation cardiac dysfunction and increased the likelihood of survival up to 24 h.
Conflict of interest Keith G. Lurie is the inventor of the active compression decompression and impedance threshold devices and the intrathoracic pressure regulator used in this study. He is consultant for Zoll Medical. Anja Metzger is an employee of Zoll Medical. The others authors do not have any conflict of interest.
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Acknowledgments This study was funded by NIH grants: NIH 1R43HL110517 and NHLBI R01 HL123227-02 (PI: Yannopoulos). Guillaume Debaty received a grant from the Region Rhône-Alpes (France) and from the Société Franc¸aise de Medecine d’Urgence (SFMU) for a post-doctoral fellowship. References 1. Field JM, Hazinski MF, Sayre MR, et al. Part 1: executive summary: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122:S640–56. 2. Eltzschig HK, Eckle T. Ischemia and reperfusion–from mechanism to translation. Nat Med 2011;17:1391–401. 3. Zhao ZQ, Corvera JS, Halkos ME, et al. Inhibition of myocardial injury by ischemic postconditioning during reperfusion: comparison with ischemic preconditioning. Am J Physiol Heart Circ Physiol 2003;285:H579–88. 4. Yellon DM, Hausenloy DJ. Myocardial reperfusion injury. N Engl J Med 2007;357:1121–35. 5. Garcia S, Henry TD, Wang YL, et al. Long-term follow-up of patients undergoing postconditioning during ST-elevation myocardial infarction. J Cardiovasc Transl Res 2011;4:92–8. 6. Ovize M, Baxter GF, Di Lisa F, et al. Postconditioning and protection from reperfusion injury: where do we stand? Position paper from the Working Group of Cellular Biology of the Heart of the European Society of Cardiology. Cardiovasc Res 2010;87:406–23. 7. Yannopoulos D, Segal N, McKnite S, Aufderheide TP, Lurie KG. Controlled pauses at the initiation of sodium nitroprusside-enhanced cardiopulmonary resuscitation facilitate neurological and cardiac recovery after 15 mins of untreated ventricular fibrillation. Crit Care Med 2012;40:1562–9. 8. Segal N, Matsuura T, Caldwell E, et al. Ischemic postconditioning at the initiation of cardiopulmonary resuscitation facilitates functional cardiac and cerebral recovery after prolonged untreated ventricular fibrillation. Resuscitation 2012;83:1397–403. 9. Bartos JA, Matsuura TR, Sarraf M, et al. Bundled postconditioning therapies improve hemodynamics and neurologic recovery after 17min of untreated cardiac arrest. Resuscitation 2015;87:7–13. 10. Metzger AK, Herman M, McKnite S, Tang W, Yannopoulos D. Improved cerebral perfusion pressures and 24-hr neurological survival in a porcine model of cardiac arrest with active compression-decompression cardiopulmonary resuscitation and augmentation of negative intrathoracic pressure. Crit Care Med 2012;40:1851–6. 11. Lurie KG, Yannopoulos D, McKnite SH, et al. Comparison of a 10-breathsper-minute versus a 2-breaths-per-minute strategy during cardiopulmonary resuscitation in a porcine model of cardiac arrest. Respir Care 2008;53:862–70. 12. Idris AH, Becker LB, Ornato JP, et al. Utstein-style guidelines for uniform reporting of laboratory CPR research. A statement for healthcare professionals from a Task Force of the American Heart Association, the American College of Emergency Physicians, the American College of Cardiology, the European Resuscitation Council, the Heart and Stroke Foundation of Canada, the Institute of Critical Care Medicine, the Safar Center for Resuscitation Research, and the Society for Academic Emergency Medicine. Resuscitation 1996;33:69–84. 13. Lurie KG, Coffeen P, Shultz J, McKnite S, Detloff B, Mulligan K. Improving active compression-decompression cardiopulmonary resuscitation with an inspiratory impedance valve. Circulation 1995;91:1629–32.
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14. Lindner KH, Pfenninger EG, Lurie KG, Schurmann W, Lindner IM, Ahnefeld FW. Effects of active compression-decompression resuscitation on myocardial and cerebral blood flow in pigs. Circulation 1993;88:1254–63. 15. Debaty G, Metzger A, Rees J, et al. Enhanced perfusion during advanced life support improves survival with favorable neurologic function in a porcine model of refractory cardiac arrest. Crit Care Med 2015;43:1087–95. 16. Yannopoulos D, Nadkarni VM, McKnite SH, et al. Intrathoracic pressure regulator during continuous-chest-compression advanced cardiac resuscitation improves vital organ perfusion pressures in a porcine model of cardiac arrest. Circulation 2005;112:803–11. 17. Yannopoulos D, Matsuura T, Schultz J, Rudser K, Halperin HR, Lurie KG. Sodium nitroprusside enhanced cardiopulmonary resuscitation improves survival with good neurological function in a porcine model of prolonged cardiac arrest. Crit Care Med 2011;39:1269–74. 18. Bircher N, Safar P. Cerebral preservation during cardiopulmonary resuscitation. Crit Care Med 1985;13:185–90. 19. Marino BS, Yannopoulos D, Sigurdsson G, et al. Spontaneous breathing through an inspiratory impedance threshold device augments cardiac index and stroke volume index in a pediatric porcine model of hemorrhagic hypovolemia. Crit Care Med 2004;32:S398–405. 20. Quinones MA, Waggoner AD, Reduto LA, et al. A new, simplified and accurate method for determining ejection fraction with two-dimensional echocardiography. Circulation 1981;64:744–53. 21. Argaud L, Gateau-Roesch O, Muntean D, et al. Specific inhibition of the mitochondrial permeability transition prevents lethal reperfusion injury. J Mol Cell Cardiol 2005;38:367–74. 22. Argaud L, Gateau-Roesch O, Raisky O, Loufouat J, Robert D, Ovize M. Postconditioning inhibits mitochondrial permeability transition. Circulation 2005;111:194–7. 23. Halestrap AP, Clarke SJ, Javadov SA. Mitochondrial permeability transition pore opening during myocardial reperfusion–a target for cardioprotection. Cardiovasc Res 2004;61:372–85. 24. Weiss JN, Korge P, Honda HM, Ping P. Role of the mitochondrial permeability transition in myocardial disease. Circ Res 2003;93:292–301. 25. Bartos JA, Debaty G, Matsuura T, Yannopoulos D. Post-conditioning to improve cardiopulmonary resuscitation. Curr Opin Crit Care 2014;20:242–9. 26. Cour M, Gomez L, Mewton N, Ovize M, Argaud L. Postconditioning: from the bench to bedside. J Cardiovasc Pharmacol Ther 2011;16:117–30. 27. Zhao H. Ischemic postconditioning as a novel avenue to protect against brain injury after stroke. J Cereb Blood Flow Metab 2009;29:873–85. 28. Wang JY, Shen J, Gao Q, et al. Ischemic postconditioning protects against global cerebral ischemia/reperfusion-induced injury in rats. Stroke 2008;39: 983–90. 29. Yannopoulos D, Segal N, Matsuura T, et al. Ischemic post-conditioning and vasodilator therapy during standard cardiopulmonary resuscitation to reduce cardiac and brain injury after prolonged untreated ventricular fibrillation. Resuscitation 2013;84:1143–9. 30. Shinohara G, Morita K, Nagahori R, et al. Ischemic postconditioning promotes left ventricular functional recovery after cardioplegic arrest in an in vivo piglet model of global ischemia reperfusion injury on cardiopulmonary bypass. J Thorac Cardiovasc Surg 2011;142:926–32. 31. Perkins GD, Handley AJ, Koster RW, et al. European Resuscitation Council Guidelines for Resuscitation 2015: Section 2. Adult basic life support and automated external defibrillation. Resuscitation 2015;95:81–99. 32. Nichol G, Leroux B, Wang H, et al. Trial of continuous or interrupted chest compressions during CPR. N Engl J Med 2015;373:2203–14.
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Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Experimental paper
Reperfusion injury protection during Basic Life Support improves circulation and survival outcomes in a porcine model of prolonged cardiac arrest Guillaume Debaty a,b,∗ , Keith Lurie c , Anja Metzger c , Michael Lick c , Jason A. Bartos a , Jennifer N. Rees a , Scott McKnite a , Laura Puertas c , Paul Pepe d , Raymond Fowler d , Demetris Yannopoulos a a
Department of Medicine-Cardiovascular Division, University of Minnesota, Minneapolis, MN, USA University Grenoble Alps/CNRS/CHU de Grenoble/TIMC-IMAG UMR 5525, Grenoble, France c Department of Emergency Medicine, Hennepin County Medical Center, University of Minnesota, Minneapolis, MN, USA d University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-8579, USA b
a r t i c l e
i n f o
Article history: Received 27 November 2015 Received in revised form 3 April 2016 Accepted 2 May 2016 Keywords: Cardiac arrest Cardiopulmonary resuscitation Basic life support Ischemic postconditioning Active compression decompression Impedance threshold device
a b s t r a c t Objective: Ischemic postconditioning (PC) using three intentional pauses at the start of cardiopulmonary resuscitation (CPR) improves outcomes after cardiac arrest in pigs when epinephrine (epi) is used before defibrillation. We hypothesized PC, performed during basic life support (BLS) in the absence of epinephrine, would reduce reperfusion injury and enhance 24 h functional recovery. Design: Prospective animal investigation. Setting: Animal laboratory Subjects: Female farm pigs (n = 46, 39 ± 1 kg). Interventions: Protocol A: After 12 min of ventricular fibrillation (VF), 28 pigs were randomized to four groups: (A) Standard CPR (SCPR), (B) active compression-decompression CPR with an impedance threshold device (ACD-ITD), (C) SCPR + PC (SCPR + PC) and (D) ACD-ITD CPR + PC. Protocol B: After 15 min of VF, 18 pigs were randomized to ACD-ITD CPR or ACD-ITD + PC. The BLS duration was 2.75 min in Protocol A and 5 min in Protocol B. Following BLS, up to three shocks were delivered. Without return of spontaneous circulation (ROSC), CPR was resumed and epi (0.5 mg) and defibrillation delivered. The primary end point was survival without major adverse events. Hemodynamic parameters and left ventricular ejection fraction (LVEF) were also measured. Data are presented as mean ± SEM. Measurements and Main Results: Protocol A: ACD-ITD + PC (group D) improved coronary perfusion pressure after 3 min of BLS versus the three other groups (28 ± 6, 35 ± 7, 23 ± 5 and 47 ± 7 for groups A, B, C, D respectively, p = 0.05). There were no significant differences in 24 h survival between groups. Protocol B: LVEF 4 h post ROSC was significantly higher with ACD-ITD + PC vs ACD-ITD alone (52.5 ± 3% vs. 37.5 ± 6.6%, p = 0.045). Survival rates were significantly higher with ACD-ITD + PC vs. ACD-ITD alone (p = 0.027). Conclusions: BLS using ACD-ITD + PC reduced post resuscitation cardiac dysfunction and improved functional recovery after prolonged untreated VF in pigs. Protocol number: 12-11. © 2016 Elsevier Ireland Ltd. All rights reserved.
Introduction Despite years of research to improve survival after out-ofhospital cardiac arrest (OHCA), survival with good neurologic
∗ Corresponding author at: SAMU 38, Pôle Urgences Médecine Aigue CHU de Grenoble, CS 10217, 38043 Grenoble Cedex 09, France. E-mail address: [email protected] (G. Debaty). http://dx.doi.org/10.1016/j.resuscitation.2016.05.008 0300-9572/© 2016 Elsevier Ireland Ltd. All rights reserved.
outcome remains poor.1 Recently, new investigations have examined the relationship between outcomes and the method by which blood flow is reintroduced to the body after a prolonged period of ischemia. In many clinical scenarios, the reperfusion process itself can cause injury. Reperfusion injury is proportional to the duration of ischemia and the way blood flow is reintroduced after prolonged ischemia. Reperfusion injury can cause up to 50% of the total damage induced by myocardial infarction in animal models2–4 .
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There are multiple ways to reduce reperfusion injury: most involve modulation of this process with drugs that affect the reperfusion injury salvage kinase (RISK) pathway or mitochondrial permeability transition pore, or both.4 Re-introduction of blood flow with “controlled pauses” is a non-pharmacological means to protect the myocardium and the brain from ischemia reperfusion injury in clinical scenarios of regional ischemia during ST elevation myocardial infarction and stroke.4–6 This concept is called “ischemic post-conditioning” (PC).7 PC using three intentional 20 s pauses at the initiation of CPR improves hemodynamics and neurologically intact survival after prolonged ventricular fibrillation in porcine models of cardiac arrest.8,9 In previous studies with PC, epinephrine was always used before the first defibrillation attempt. The aim of the study was to assess if PC used during the Basic Life Support (BLS) phase of CPR would provide better cerebral and myocardial protection against reperfusion injury and facilitate functional recovery after prolonged untreated VF compared to CPR alone. Methods This study was approved by the Institutional Animal Care Committee of the Minneapolis Medical Research Foundation of Hennepin County Medical Center. All animal care was compliant with the National Research Council’s 1996 Guidelines for the Care and Use of Laboratory Animals (protocol number: 12-11). All studies were performed by a qualified, experienced research team in Yorkshire female farm bred pigs weighing 39 ± 1 kg. A certified and licensed veterinarian assured the protocols were performed in accordance with the National Research Council’s Guidelines. Preparatory phase The aseptic surgical preparation, anesthesia, data monitoring and recording procedures used in this study have been previously described.10,11 Animals were fasted overnight. Intramuscular ketamine (10 mL of 100 mg mL-1 ) was used for sedation followed by inhaled isoflurane (0.8–1.2%). Pigs were intubated with a size 7.0 endotracheal tube then ventilated with room air, using an anesthesia machine (Narkomed, Telford, Pennsylvania), with a tidal volume of 10 ml kg-1 and a respiratory rate adjusted to continually maintain a PaCO2 of 40 mmHg and PaO2 of 80 mmHg (blood oxygen saturation > 95%). Normothermia was maintained with a warming blanket (Bair Hugger, Augustine Medical, Eden Prairie, Minnesota). Central aortic blood pressure was recorded continuously with a Millar catheter (Mikro-Tip Transducer, Millar Instruments, Houston, TX, USA) placed in the descending thoracic aorta. A second Millar catheter was inserted in the right atrium via the right external jugular vein. An ultrasound flow probe (Transonic 420 series multichannel, Transonic Systems, Ithaca, New York) was placed in the left common carotid artery to quantify carotid blood flow (ml min-1 ). Animals received an intravenous heparin bolus (100 units kg-1 ). Arterial blood gases (Gem 3000, Instrumentation Laboratory) were obtained at baseline, 15, 30, 60 and 4 h after return of spontaneous circulation (ROSC). Electrocardiograms were continuously recorded. Hemodynamic data were continuously monitored and recorded (BIOPAC MP 150, BIOPAC Systems, Inc., CA, USA). Coronary perfusion pressure (CPP) was calculated as the difference between aortic and right atrial pressures during the decompression phase. End tidal carbon dioxide (ETCO2 ), tidal volume, minute ventilation, and blood oxygen saturation were continuously measured (COSMO Plus, Novametrix Medical Systems, Wallingford, Connecticut). ROSC was defined using the Utstein guidelines for uniform reporting in animal research as maintenance of systolic pressure of ≥60 mm Hg for ≥10 consecutive minutes.12
Experimental protocol Following the surgical preparation VF was induced by delivering direct intra-cardiac current via a temporary pacing wire. STD-CPR and ACD-CPR were performed with a pneumatically driven automatic piston device (Pneumatic Compression Controller, Ambu International, Glostrup, Denmark) as previously described.13 During STD-CPR, uninterrupted chest compressions were performed at a rate of 100 compressions/min, with a 50% duty cycle and a compression depth of 25% of the anteroposterior chest diameter. After each compression, the chest wall was allowed to fully recoil passively. With ACD-CPR, after each compression, the chest was actively pulled upwards with a suction cup attached to the skin with a decompression force of ∼20 lbs.13,14 Concurrently with ACD-CPR, an impedance threshold device (ITD, ResQPOD TM, Advanced Circulatory Systems, Roseville, MN, USA) with a resistance of 16 mmHg was attached to the endotracheal tube. After the period of intentional pauses, when positive pressure breaths were delivered only during the pauses, asynchronous positive pressure ventilations were delivered with room air (FiO2 of 0.21) with a manual resuscitator bag. The tidal volume was maintained at ∼10 mL kg-1 and the respiratory rate was 10 breaths min-1 . Protocol A Following 12 min of untreated ventricular fibrillation, 28 pigs were randomized to receive CPR during the BLS period as follows: 1) 2) 3) 4)
Group A: Standard CPR (SCPR) Group B: ACD-ITD CPR Group C: SCPR plus PC (SCPR-PC) Group D: ACD-ITD CPR plus PC (ACD-ITD + PC)
PC groups initially received 20 s of CPR (SCPR or ACD-ITD) without positive pressure breaths followed by a 20 s pause of compressions followed by another 20 s of CPR and the cycle was repeated for a total of three pauses. Three positive pressure breaths were delivered during each pause, with each breath delivered over 1 s and 6 s between each breath. After 2.75 min of BLS, the first defibrillation effort was delivered with 275-J biphasic shocks. If ROSC was not achieved, defibrillation was delivered every 2 min thereafter during CPR. Epinephrine was administered in all animals without ROSC as a 0.5 mg (∼15 g kg-1 ) bolus at 4 min together with 25 mg of amiodarone. In addition, during this Advanced Life Support (ALS) phase we used an active form of the intrathoracic pressure regulation therapy rather than the ITD, which generated a continuous negative intrathoracic pressure of -9 mmHg between each positive pressure breath.15,16 All animals received oxygen at 4 l min-1 rate during ALS. Protocol B The two groups with the best survival results in Protocol A were selected. After 15 min of untreated VF, 18 pigs were randomized to receive BLS augmented with ACD-ITD CPR or ACD-ITD CPR plus controlled pauses (Fig. 1). Controlled pauses, ventilations, and the CPR method were performed as in Protocol A. Unlike Protocol A, the BLS period in Protocol B was 5 min in duration, after which the first defibrillation shock was delivered. If ROSC was not achieved, defibrillation shocks were delivered every 2 min thereafter during CPR. Epinephrine was administered in all groups in a 0.5 mg (∼15 g kg-1 ) bolus at 6 min together with 25 mg of amiodarone. Similar to Protocol A, an active form of the ITD that provided continuous negative intrathoracic pressure was used during the ALS phase.
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Fig. 1. ACD-ITD-PC and ACD-ITD CPR alone protocol with associated hemodynamic tracings. ACD-ITD: active compression decompression with impedance threshold device CPR, PC: ischemic post-conditioning, ROSC: Return of spontaneous circulation.
Resuscitation efforts were continued until ROSC was achieved or a total of 10 min of CPR was provided. Post-ROSC care After ROSC, animals were mechanically ventilated and maintained under general anesthesia with isoflurane. Supplemental oxygen was added only if arterial saturation was lower than 90% with a SaO2 target between 90 and 94%. Animals that had a stable post-ROSC rhythm but were hypotensive (mean arterial pressure < 50 mmHg) received increments of 0.1–0.2 mg intravenous epinephrine every 5 min until the mean arterial pressure rose above 50 mmHg. If the arterial blood pH was lower than 7.2 then 50–100 mEq of NaHCO3 were given intravenously. Therapeutic hypothermia was induced and sustained between 32 and 34 ◦ C
using intravenous cold saline (1000 ml) and external cooling. The carotid flow probe and venous and arterial catheters were removed during this time. Controlled rewarming (0.5 ◦ C h-1 ) to normothermia was performed at that point using a blanket and a heating lamp. The total duration of hypothermia was about 12 h. Once rewarmed animals were weaned off the ventilator and extubated. Survivors received nonsteroidal anti-inflammatory medication, as previously described, and had free access to water and food.17 They were returned to their cages and were observed for the first 4 h for signs of clinical deterioration. Based upon predetermined stopping criteria determined by protocol in collaboration with the Animal Care Committee and the on-site, independent, boardcertified veterinarian, animals were euthanized if they had epileptic seizure activity that could not be terminated with a single dose of
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Table 1 Hemodynamics parameters and outcomes in protocol A. Group of CPR
Measure
Baseline
BLS 1 min
BLS 1.5 min
Group A: SCPR n=7
SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2
101 ± 6 69 ± 5 3±2 66 ± 7 235 ± 20 40 ± 1 107 ± 6 76 ± 6 1±1 75 ± 6 264 ± 29 41 ± 1 105 ± 6 73 ± 5 0±1 73 ± 5 269 ± 34 42 ± 1 109 ± 7 79 ± 6 2±1 77 ± 5 239 ± 14 40 ± 2
45 ± 7 22 ± 5 4±1 18 ± 5 60 ± 10£ 26 ± 3# 52 ± 7 21 ± 1 3±1 18 ± 2 45 ± 5£ 35 ± 4 41 ± 7 20 ± 3 6±1 14 ± 3 58 ± 12£ 27 ± 2 53 ± 5 24 ± 5 4±1 21 ± 4 90 ± 8*,#,§ 30 ± 4
55 ± 9 25 ± 5 4±2 21 ± 5 46 ± 9£ 27 ± 3# 78 ± 14§ 32 ± 2 4±2 28 ± 3 39 ± 6£ 44 ± 5*§,£ 30 ± 5# 25 ± 7 5±1 20 ± 7 50 ± 12£ 31 ± 3# 58 ± 15 35 ± 5 2±0 34 ± 6 80 ± 10*,#,§ 33 ± 4#
Group B: ACD-ITD n=7
Group C: SCPR-PC n=7
Group D: ACD-ITD-PC n=7
BLS 2.5 min 80 ± 11 33 ± 6 5±2 28 ± 6£ 27 ± 8£ 30 ± 3# 97 ± 8§ 41 ± 7 5±1 35 ± 7 42 ± 8 45 ± 4* 60 ± 11#,£ 29 ± 5 6±1 23 ± 5£ 32 ± 6 35 ± 4 92 ± 10§ 50 ± 7 3±1 47 ± 7*,§ 48 ± 6* 36 ± 5
ALS 1.5 min
ROSC 1 hour
# shocks
ROSC at BLS
ROSC BLS+ ALS
24-hour Survival
121 ± 10 56 ± 8 6±2 50 ± 6 38 ± 10 43 ± 4 117 ± 8 57 ± 3 11 ± 3 46 ± 6 37 ± 10 42 ± 2 96 ± 14 48 ± 8 10 ± 1 38 ± 7 24 ± 5 41 ± 6 110 ± 13 65 ± 10 8±2 57 ± 9 45 ± 20 41 ± 3
79 ± 4# 44 ± 3# 1±1 43 ± 3 169 ± 19 44 ± 2 106 ± 9* 64 ± 6* 4±2 60 ± 6 201 ± 25 45 ± 2 89 ± 9 55 ± 5 1±1 50 ± 7 181 ± 8 46 ± 2 88 ± 5 55 ± 6 0±2 54 ± 5 151 ± 17 45 ± 3
4.7 ± 0.7
0 (0%)
7 (100%)
6 (86%)
4.3 ± 0.9
3 (43%)
7 (100%)
7 (100%)
4 ± 0.6
1 (14%)
6 (86%)
5
3.7 ± 0.3
3 (43%)
7 (100%)
7 (100%)
SCPR: Standard CPR; ACD-ITD: active compression decompression with impedance threshold device CPR, PC: post conditioning. SBP and DBP: Systolic and diastolic blood pressure; RA: right atrial pressure, CPP: Coronary perfusion pressure; CBF: Carotid blood flow; ROSC: Return of spontaneous circulation. Values are shown as mean ± SEM. All pressures are in mm Hg and all flows in ml min-1 . *denotes p < 0.05 compare to STD, # denotes p < 0.05 compare to ACD-ITD, § denotes p < 0.05 compare to STD-PC, £ denotes p < 0.05 compare to ACD-ITD-PC.
midazolam (25 mg) intramuscular or if they developed cardiorespiratory distress. Neurologic assessment Twenty-four hours after ROSC, the same veterinarian, blinded to the study intervention, assessed the pigs’ neurologic function based on a cerebral performance category (CPC) scoring system modified for pigs.17 The following scoring system was used: 1 = normal; 2 = slightly disabled; 3 = severely disabled but conscious; 4 = vegetative state; a five was given to animals that died in the lab due to unachievable ROSC or died in the cage following ROSC.17 The Swine Neurologic Deficit Score (NDS) was also used to evaluate the level of consciousness, respiratory pattern, cranial nerve function, motor and sensory function, and behavior evaluation, in 24 h survival animals.18 Echocardiographic evaluation of left ventricular function A transthoracic echocardiogram was obtained on all survivors 1, 4 and 24 h post ROSC.19 Ejection fraction was assessed using Simpson’s method of volumetric analysis by an independent clinical echocardiographer blinded to the treatments.20 Arterial blood was collected at baseline and from all survivors 4 h and 24 h post-ROSC. Statistical analysis Data are expressed as mean ± standard error of mean (SEM). The primary end point was survival without major adverse outcomes at 24 h. Major adverse outcomes were defined by the protocol and included pigs which did not have a ROSC after resuscitation or were intentionally euthanized according to the study protocol and as a result of the veterinarian’s evaluation of the animals in a blinded manner, for reasons due to coma, refractory seizures or cardiorespiratory distress before the 24 h point after ROSC. The chi-square
test or Fisher exact test was used for comparison of proportions. A single-factor ANOVA was used to determine statistical significance of differences in means of continuous variables between groups in Protocol A and a two-tailed unpaired t-test or Mann-Whitney non parametric test was used in Protocol B. Kaplan–Meier major adverse outcomes curves were compared between the intervention groups in Protocol B with the use of the log-rank test. P-value less than 0.05 was considered statistically significant. Statistical analysis was performed using SPSS 21 (IBM Corporation, Armonk, NY, USA).
Results Protocol A All animals were included in this analysis. There were no significant baseline differences between treatment groups (Table 1). ACD-ITD-PC (group D) provided significantly higher CPP and CBF after 3 min of BLS compared with the three other groups (Table 1), whereas SCPR-PC did not improve CPP, CBF or ETCO2 during BLS vs. SCPR alone. ROSC after completion of BLS was achieved in 0, 3, 1, and 3 pigs in groups A, B, C, and D, respectively (p = 0.22). There was no significant difference in 24 h survival between groups. CPC scores at 24 h are represented in Fig. 2. NDS score at 24 h in survivor was 6.3 ± 3.7 in group A, 1.0 ± 0.6 in group B, 23.0 ± 16.6 in group C and 2.8 ± 0.9 in group D (p = 0.27).
Protocol B Nine animals were included in the ACD-ITD group while eight were included in the ACD-ITD-PC group. One animal from the ACD-ITD-PC group was excluded because of respiratory and hemodynamic instability during the preparatory phase. There were no significant baseline differences between treatment groups (Table 2).
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Table 2 Hemodynamics parameters and outcomes in protocol B. Group of CPR
Measure
Baseline
BLS 2 min
BLS 4 min
BLS 5 min
ALS 6 min
ROSC 1 h
# shocks
ROSC at BLS
ROSC at BLS+ ALS
24-hour Survival
Group A ACD-ITD-PC n=8
SBP DBP RA CPP CBF ETCO2 SBP DBP RA CPP CBF ETCO2
104 ± 6 69 ± 4 2±1 79 ± 5 259 ± 35 39 ± 1 103 ± 8 69 ± 6 2 ± 0,4 79 ± 7 214 ± 35 40 ± 1
46 ± 5 20 ± 2 3±1 17 ± 2 63 ± 12 29 ± 2* 59 ± 5 23 ± 2 2±1 21 ± 2 31 ± 6 38 ± 2
74 ± 7 31 ± 2* 5±1 26 ± 2* 38 ± 6 39 ± 3 69 ± 4 24 ± 2 4±1 20 ± 1 43 ± 8 42 ± 3
68 ± 5 29 ± 2 5±1 24 ± 1* 54 ± 11 41 ± 3 67 ± 3 23 ± 2 4±1 19 ± 1 42 ± 7 41 ± 2
87 ± 12 46 ± 6 10 ± 2 41 ± 6* 23 ± 15 35 ± 6 88 ± 10 36 ± 1 9±2 27 ± 2 17 ± 3 28 ± 5
85 ± 3 49 ± 2 1±1 58 ± 3 164 ± 42 45 ± 2 87 ± 6 55 ± 6 2,3 ± 1,2 64 ± 7 151 ± 22 43 ± 2
4±1
5 (63%)
8 (100%)#
3 (38%)&
6±2
2 (22%)
5 (56%)
1 (11%)
Group B ACD-ITD n=9
STD: Standard CPR; ACD-ITD: active compression decompression with impedance threshold device CPR, PC: post conditioning; SBP and DBP: Systolic and diastolic blood pressure; RA: right atrial pressure, CPP: Coronary perfusion pressure; CBF: Carotid blood flow; ROSC: Return of spontaneous circulation. Values are shown as mean ± SEM. All pressures are in mm Hg and all flows in ml min-1 . *p < 0.05 compared to ACD-ITD group. # p = 0.053 compared to ACD-ITD group. & p = 0.027 compared to ACD-ITD (log-rank test comparison).
Fig. 2. Cerebral performance category score at 24 h in Protocol A. Group A: Standard CPR group, group B: active compression decompression with impedance threshold device (ACD-ITD), Group C: Standard CPR plus PC group (SCPRPC), Group D: ACD-ITD-PC group
CPP increased over time in the ACD-ITD-PC group during the first 3 min of CPR. CPP became significantly higher in the ACDITD-PC group compared with ACD-ITD alone only after 4 min of CPR. ETCO2 was significantly lower during the first 3 min of CPR in the ACD-ITD-PC group compared with ACD-ITD (p = 0.01 at 3 min)
and reached similar level after 4 min (Table 2 and Fig. 3). ROSC at 5 min (BLS phase) was achieved in five animals in the ACDITD-PC group compared with two animals in the ACD-ITD group (p = 0.15). After the ALS phase, ROSC was achieved in eight animals in the ACD-ITD-PC group vs. five animals in the ACD-ITD group (p = 0.053). The ACD-ITD-PC group trended toward to require less epinephrine to achieve ROSC compared to ACD-ITD alone (0.3 ± 0.1 vs. 0.7 ± 0.4, p = 0.06). There were no significant differences in the number of shocks or the dose of amiodarone needed to achieve or to maintain a sinus rhythm with ACD-ITD-PC versus ACD-ITD alone (7 ± 2 vs. 9 ± 2 and 34 ± 5 mg vs. 31 ± 4 mg, p = 0.51 and 0.52, respectively). A significant increase in survival was demonstrated with ACDITD-PC compared with ACD-ITD (Log-rank comparison, p = 0.027) (Fig. 4). There were three survivors after 24 h in the ACD-ITD-PC and their CPC scores were 2, 3, and 4 versus one survivor in the ACD + ITD group with a CPC score of 4. The NDS scores at 24 h in survivors were 29.3 ± 8.4 compared with 43 in the sole ACD-ITD survivor. Left ventricular Function. Among survivors, LVEF was higher 15 min after ROSC but did not reach significance with ACD-ITDPC versus ACD-ITD (51 ± 4% vs. 39 ± 10%, p = 0.19). Four hours after ROSC, LVEF was significantly higher with ACD-ITD-PC vs. ACD-ITD alone (52.5 ± 3% vs. 37.5 ± 6.6%, p = 0.045).
Fig. 3. Coronary perfusion pressure and ETCO2 over time in Protocol B. ACD-ITD: active compression decompression with impedance threshold device CPR, PC: ischemic post-conditioning
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by others.29,30 Together they suggest a common mechanism of myocardial protection that can be rapidly and easily delivered.
Limitations
Fig. 4. Kaplan–Meier curve of survival after start of CPR in Protocol B. The data demonstrate a significant increase in survival at 24 h with ACD-ITD-PC compared with ACD-ITD (Log-rank comparison, p = 0.027). ACD-CPR, active compression decompression cardiopulmonary resuscitation; PC, ischemic post-conditioning.
Discussion This study demonstrates, for the first time, the successful application of PC during the BLS phase of resuscitation in an animal model. PC in combination of ACD-ITD significantly improved coronary perfusion pressure, preserved cardiac ejection fraction and enhanced survival rates. In previous studies, the benefits of PC with regard to increased CPP and survival were observed in combination with epinephrine injected during the last of three sequential intentional pauses.7–9 In the current study, the beneficial effects of the combined use of PC and ACD-ITD were observed without use of epinephrine. These findings provide proof of the clinical concept that PC could be of value if provided by first responders in the setting of prolonged untreated cardiac arrest. The protective mechanism of PC during CPR is not well understood. Reperfusion with three intentional 20 s pauses at the start of CPR may limit reperfusion injury by slowing the normalization of intracellular pH and calcium, thereby reducing production of reactive oxygen species, preventing opening of the mitochondrial permeability transition pore, and preventing activation of the pro-apoptotic calcium-sensitive protease.21–25 Improved myocardial function has been observed when PC was used in the setting of myocardial infarction and cardiac arrest.7,8,26 Improved neurologic function has also been observed with the use of PC in the setting of ischemic stroke27 and global ischemia such as that experienced during cardiac arrest.7,8,28,29 Recently, PC combined with ACD CPR, ITD, sevoflurane, and poloxamer 188 improved cardiac and neurologic function after 17 min of untreated cardiac arrest in pigs.9 In the current study, 2.75 min of BLS may not have been long enough to overcome the potential negative hemodynamic effects of three intentional 20 s pauses used to mitigate the potential harm associated with reflow after prolonged ischemia. By contrast, 5 min of BLS with three intentional 20 s pauses at the start of CPR to provide PC was sufficient to demonstrate a hemodynamic (Fig. 3) and survival benefit (Fig. 4). As demonstrated by the results of Protocol A, the combination of ACD + ITD was needed to provide greater circulation during CPR whereas use of conventional SCPR, even with PC, provided inferior results. One of the important results of the current study is the absence of cardiac dysfunction in the PC group after 15 min of untreated VF. These findings are consistent with work from our prior cardiac arrest studies and studies of acute myocardial infarction
The optimal duration of ischemic time and/or BLS CPR duration remain unclear. We were unable to demonstrate a significant survival benefit with 12 min of untreated VF and 2.75 min of CPR, but we did observe the hypothesized survival benefit with 5 min of BLS CPR. Though the protective biochemical mechanisms underlying these observations is currently unknown, we speculate based upon the results from Protocols A and B that in order to observe a clinically meaningful PC effect without epinephrine that at least 5 min of CPR is needed to overcome the absolute hypoperfusion associated with three 20 s pauses. Similarly, the optimal duration and number of pauses for PC is unknown. It is possible that the current 30:2 compression: ventilation ratio recommended by ILCOR for BLS confers some PC.31 This is suggested by the benefit of 30:2 versus continuous chest compressions (CCC) in a recent clinical trial where the per protocol analysis demonstrated superior results in patients with 30:2 in terms of survival to hospital discharge and favorable neurological function.32 Further work is needed to determine the optimal duration and number of pauses needed to provide PC during CPR. Some confounding factors may have also affected the results of the study. First isoflurane has been described to have a protective effect on reperfusion injuries. The same dosage was administrated in all study groups but it remains unclear if the effects of PC on reperfusion injury observed in our study could have been affected with this additional protective effect. Second, prolongation of the untreated VF times may have also contributed to our ability to observe a statistically significant survival advantage with PC in Protocol B. Third, all survivors were treated with hypothermia. It is currently unknown whether hypothermia is required together with the PC to provide the observed reperfusion protection. Further study is underway to examine the potential synergy between these two protective strategies. Importantly, the study was not powered a priori to demonstrate improved neurologically-favorable survival outcomes with the study intervention. This study has provided an anticipated effect size for future studies. Further studies are needed to determine if there are any untoward effects of providing BLS CPR with intentional pauses as described herein with shorter untreated VF times. It is noteworthy, however, that in the present study there were no observed adverse effects of using only 2.75 min of BLS CPR with PC provided with three intentional pauses.
Conclusion After a prolonged untreated cardiac arrest in pigs use of PC with a simple strategy comprised of three 20 s compression pauses during the start of the BLS CPR phase delivered with ACD CPR and an ITD without initial use of epinephrine reduced post-resuscitation cardiac dysfunction and increased the likelihood of survival up to 24 h.
Conflict of interest Keith G. Lurie is the inventor of the active compression decompression and impedance threshold devices and the intrathoracic pressure regulator used in this study. He is consultant for Zoll Medical. Anja Metzger is an employee of Zoll Medical. The others authors do not have any conflict of interest.
G. Debaty et al. / Resuscitation 105 (2016) 29–35
Acknowledgments This study was funded by NIH grants: NIH 1R43HL110517 and NHLBI R01 HL123227-02 (PI: Yannopoulos). Guillaume Debaty received a grant from the Region Rhône-Alpes (France) and from the Société Franc¸aise de Medecine d’Urgence (SFMU) for a post-doctoral fellowship. References 1. Field JM, Hazinski MF, Sayre MR, et al. Part 1: executive summary: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2010;122:S640–56. 2. Eltzschig HK, Eckle T. Ischemia and reperfusion–from mechanism to translation. Nat Med 2011;17:1391–401. 3. Zhao ZQ, Corvera JS, Halkos ME, et al. Inhibition of myocardial injury by ischemic postconditioning during reperfusion: comparison with ischemic preconditioning. Am J Physiol Heart Circ Physiol 2003;285:H579–88. 4. Yellon DM, Hausenloy DJ. Myocardial reperfusion injury. N Engl J Med 2007;357:1121–35. 5. Garcia S, Henry TD, Wang YL, et al. Long-term follow-up of patients undergoing postconditioning during ST-elevation myocardial infarction. J Cardiovasc Transl Res 2011;4:92–8. 6. Ovize M, Baxter GF, Di Lisa F, et al. Postconditioning and protection from reperfusion injury: where do we stand? Position paper from the Working Group of Cellular Biology of the Heart of the European Society of Cardiology. Cardiovasc Res 2010;87:406–23. 7. Yannopoulos D, Segal N, McKnite S, Aufderheide TP, Lurie KG. Controlled pauses at the initiation of sodium nitroprusside-enhanced cardiopulmonary resuscitation facilitate neurological and cardiac recovery after 15 mins of untreated ventricular fibrillation. Crit Care Med 2012;40:1562–9. 8. Segal N, Matsuura T, Caldwell E, et al. Ischemic postconditioning at the initiation of cardiopulmonary resuscitation facilitates functional cardiac and cerebral recovery after prolonged untreated ventricular fibrillation. Resuscitation 2012;83:1397–403. 9. Bartos JA, Matsuura TR, Sarraf M, et al. Bundled postconditioning therapies improve hemodynamics and neurologic recovery after 17min of untreated cardiac arrest. Resuscitation 2015;87:7–13. 10. Metzger AK, Herman M, McKnite S, Tang W, Yannopoulos D. Improved cerebral perfusion pressures and 24-hr neurological survival in a porcine model of cardiac arrest with active compression-decompression cardiopulmonary resuscitation and augmentation of negative intrathoracic pressure. Crit Care Med 2012;40:1851–6. 11. Lurie KG, Yannopoulos D, McKnite SH, et al. Comparison of a 10-breathsper-minute versus a 2-breaths-per-minute strategy during cardiopulmonary resuscitation in a porcine model of cardiac arrest. Respir Care 2008;53:862–70. 12. Idris AH, Becker LB, Ornato JP, et al. Utstein-style guidelines for uniform reporting of laboratory CPR research. A statement for healthcare professionals from a Task Force of the American Heart Association, the American College of Emergency Physicians, the American College of Cardiology, the European Resuscitation Council, the Heart and Stroke Foundation of Canada, the Institute of Critical Care Medicine, the Safar Center for Resuscitation Research, and the Society for Academic Emergency Medicine. Resuscitation 1996;33:69–84. 13. Lurie KG, Coffeen P, Shultz J, McKnite S, Detloff B, Mulligan K. Improving active compression-decompression cardiopulmonary resuscitation with an inspiratory impedance valve. Circulation 1995;91:1629–32.
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