Phased chest and abdominal compression-decompression. A new option for cardiopulmonary resuscitation

A proof-of-concept study evaluating cardiac compression techniques for cardiopulmonary resuscitation in laying hens (Gallus gallus)

OBJECTIVE

To determine in adult chickens which of 3 CPR techniques, sternal compressions (SC), SC with interposed caudal coelomic compressions (ICCC), or lateral compressions (LC), results in the highest mean systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) as measured directly from the carotid artery.

DESIGN

Prospective, nonblinded, experimental crossover study.

SETTING

University teaching hospital laboratory.

ANIMALS

Ten retired laying hens.

INTERVENTIONS

Birds were sedated, anesthetized, and placed in dorsal recumbency. A carotid artery catheter was placed to directly measure arterial pressure. Ventricular fibrillation was induced with direct cardiac stimulation using a 9-Volt battery. Each bird then received 2 minutes of the 3 different cardiac compression techniques in a random order by 3 different compressors, with the compressor order also randomized. Birds were subsequently administered IV epinephrine, and transthoracic defibrillation was attempted. At the end of experimentation, each bird was euthanized, and simple gross necropsies were performed. Linear mixed models followed by pairwise paired t-tests were performed to evaluate differences in pressures generated by each technique.

MEASUREMENTS AND MAIN RESULTS

The primary study outcomes were SAP, DAP, and MAP over 2 minutes of compressions for each compression technique. Pressures from ICCC (SAP: 27.6 ± 5.3 mm Hg, DAP: 18.7 ± 5.2 mm Hg, MAP: 21.7 ± 5.2 mm Hg) were significantly higher than those from LC (SAP: 18.9 ± 5.4 mm Hg, DAP: 11.6 ± 4.1 mm Hg, MAP: 14.1 ± 4.5 mm Hg). Pressures from SC (SAP: 24.5 ± 6.4 mm Hg, DAP: 15.2 ± 4.3 mm Hg, MAP: 18.3 ± 5.0 mm Hg) were not significantly different from ICCC or LC.

CONCLUSIONS

External compressions can generate detectable increases in arterial pressure in chickens with ventricular fibrillation. SC with ICCC generated significantly higher arterial pressures than LC. SC alone generated blood pressures that were not significantly different from those generated by SC with ICCC or LC.

Comparison of continuous compression with regular ventilations versus 30:2 compressions-ventilations strategy during mechanical cardiopulmonary resuscitation in a porcine model of cardiac arrest

Background

A compression-ventilation (C:V) ratio of 30:2 is recommended for adult cardiopulmonary resuscitation (CPR) by the current American Heart Association (AHA) guidelines. However, continuous chest compression (CCC) is an alternative strategy for CPR that minimizes interruption especially when an advanced airway exists. In this study, we investigated the effects of 30:2 mechanical CPR when compared with CCC in combination with regular ventilation in a porcine model.

Methods

Sixteen male domestic pigs weighing 39±2 kg were utilized. Ventricular fibrillation was induced and untreated for 7 min. The animals were then randomly assigned to receive CCC combined with regular ventilation (CCC group) or 30:2 CPR (VC group). Mechanical chest compression was implemented with a miniaturized mechanical chest compressor. At the same time of beginning of precordial compression, the animals were mechanically ventilated at a rate of 10 breaths-per-minute in the CCC group or with a 30:2 C:V ratio in the VC group. Defibrillation was delivered by a single 150 J shock after 5 min of CPR. If failed to resuscitation, CPR was resumed for 2 min before the next shock. The protocol was stopped if successful resuscitation or at a total of 15 min. The resuscitated animals were observed for 72 h.

Results

Coronary perfusion pressure, end-tidal carbon dioxide and carotid blood flow in the VC group were similar to those achieved in the CCC group during CPR. No significant differences were observed in arterial blood gas parameters between two groups at baseline, VF 6 min, CPR 4 min and 30, 120 and 360 min post-resuscitation. Although extravascular lung water index of both groups significantly increased after resuscitation, no distinct difference was found between CCC and VC groups. All animals were successfully resuscitated and survived for 72 h with favorable neurologic outcomes in both groups. However, obviously more numbers of rib fracture were observed in CCC animals in comparison with VC animals.

Conclusions

There was no difference in hemodynamic efficacy and gas exchange during and after resuscitation, therefore identical 72 h survival with intact neurologic function was observed in both VC and CCC groups. However, the incidence of rib fracture increases during the mechanical CPR strategy of CCC combined with regular ventilations.

Clinical evaluation of active abdominal lifting and compression CPR in patients with cardiac arrest

BACKGROUND

Chest compression is a standard recommendation during cardiopulmonary resuscitation (CPR). However, chest compression cannot be effectively applied under certain situations, such as chest wall deformity, rib fracture, or hemopneumothorax. An alternative method, abdominal compression, was reported to achieve better resuscitation outcomes in these patients.

MATERIALS AND METHODS

A prospective study was performed in adult patients with cardiac arrest and anticipated ineffective chest compression (thoracic trauma, chest deformity, rib fracture, and hemopneumothorax). Active abdominal lifting and compression cardiopulmonary resuscitation was used. Primary outcome was success rate of restoration of spontaneous circulation (ROSC). Secondary outcomes included heart rate (HR), mean arterial pressure (MAP), pulse oximetry saturation (SpO₂), arterial blood pH value, arterial oxygen pressure (PaO₂), and arterial carbon dioxide tension (PaCO₂), which were measured during the periods of pre-CPR, CPR, and 30min post-ROSC.

RESULTS

A total of 35 patients were enrolled into the study. Five of them had ROSC (14.3%), which was statistically significantly higher than that (0%) reported in the 2015 Advanced Cardiovascular Life Support manual. HR, MAP, and SpO₂ during CPR were also statistically significantly higher during CPR when compared to the period of pre-CPR period (HR 58 versus 0 beats/min, P<0.01; MAP 25 versus 0mm Hg, P<0.01; SpO₂ 0.68 versus 0.48%, P<0.01). In post-ROSC period, HR was statistically significantly higher than that during pre-CPR period (121 versus 0 best/min, P<0.01).

CONCLUSIONS

Active abdominal lifting and compression cardiopulmonary resuscitation could reach better resuscitation outcomes in certain cardiac arrest patients.

Not Bad: Passive Leg Raising in Cardiopulmonary Resuscitation-A New Modeling Study

Aim: To evaluate, using a simulated haemodynamic circulation model, whether passive leg raising (PLR) is able to improve the effect during cardiopulmonary resuscitation (CPR); to expose the possible reasons why PLR works or not. Materials and Methods: We adapted a circulatory model for CPR with PLR. First we compared cardiac output (CO), coronary perfusion pressure (CPP), blood flow to heart (Q_heart), and blood flow to neck and brain (Q_head) of standard chest compression-only CPR with and without PLR; second we simulated the effects of PLR in different situations, by varying the thoracic pump factor (TPF) from 0 to 1; third we simulated the effects when the legs are lifted to the different heights. Finally, we compared our results with those obtained from a published clinical study. Results: According to the simulation model, (1) When TPF is in the interval (0,1), CPP, CO, Q_heart, and Q_head are improved with PLR, among them with half-thoracic/half-cardiac pump effect (TPF is 0.5), CPP, CO, Q_head, and Q_heart increase the most (by 14, 14, 15, and 17%). (2) When TPF is 1 (pure thoracic pump, with an emphysema or extremely thick thorax), PLR has almost no effect on CPP, CO, and Q_heart (-1, 2, and 0%), whereas Q_head is increased by 9%; (3) Regardless of whether there is a cardiac or thoracic pump effect, PLR is able to increase Q_head by 9-15%. (4) When the legs are lifted to 30° to the ground, the volume transferred from legs to upper body is 36% of the initial volume in legs; when the legs are lifted to 45°, the volume transferred is 43%; when the legs are lifted to 60°, the volume transferred is 47%; when the legs are lifted to 90°, the volume transferred is 50%. Conclusion: Generally PLR is able to achieve improved cerebral perfusion and coronary perfusion. In some extreme situations, it has no effect on cardiac output and coronary perfusion, but still improves cerebral perfusion. PLR could be a beneficial supplement to CPR, and it is not necessary to lift the legs too high above the ground.

Remote Postconditioning Alone and Combined with Hypothermia Improved Postresuscitation Cardiac and Neurological Outcomes in Swine

Objective. Previously, we demonstrated that remote ischemic postconditioning (RIpostC) improved postresuscitation myocardial and cerebral functions in rat. Here, we investigated the effects of RIpostC alone and combined with therapeutic hypothermia (TH) on cardiac and neurological outcomes after CPR in swine. Methods. Twenty-one pigs were subjected to 10 mins of VF and then 5 mins of CPR. The animals were randomized to receive RIpostC alone, or its combination with TH, or sham control. RIpostC was induced by 4 cycles of limb ischemia followed by reperfusion. TH was implemented by surface cooling to reach a temperature of 32–34°C. Results. During 72 hrs after resuscitation, lower level of cardiac troponin I and greater stroke volume and global ejection fraction were observed in animals that received RIpostC when compared to the control. RIpostC also decreased serum levels of neuron-specific enolase and S100B and increased neurologic alertness score after resuscitation. The combination of RIpostC and TH resulted in greater improvement in cardiac and neurological outcomes than RIpostC alone. Conclusion. RIpostC was conducive to improving postresuscitation myocardial and cerebral functions and reducing their organ injuries. Its combination with TH further enhanced its protective effects.

Standard versus Abdominal Lifting and Compression CPR

Background. This study compared outcomes of abdominal lifting and compression cardiopulmonary resuscitation (ALP-CPR) with standard CPR (STD-CPR). Materials and Methods. Patients with cardiac arrest seen from April to December 2014 were randomized to receive standard CPR or ALP-CPR performed with a novel abdominal lifting/compression device. The primary outcome was return of spontaneous circulation (ROSC). Results. Patients were randomized to receive ALP-CPR (n = 40) and STD-CPR (n = 43), and the groups had similar baseline characteristics. After CPR, 9 (22.5%) and 7 (16.3%) patients in the ALP-CPR and STD-CPR groups, respectively, obtained ROSC. At 60 minutes after ROSC, 7 (77.8%) and 2 (28.6%) patients, respectively, in the ALP-CPR and STD-CPR groups survived (P = 0.049). Patients in the ALP-CPR group had a significantly higher heart rate and lower mean arterial pressure (MAP) than those in the STD-CPR group (heart rate: 106.8 versus 79.0, P < 0.001; MAP: 60.0 versus 67.3 mm Hg, P = 0.003). The posttreatment PCO₂ was significantly lower in ALP-CPR group than in STD-CPR group (52.33 versus 58.81, P = 0.009). PO₂ was significantly increased after ALP-CPR (45.15 to 60.68, P < 0.001), but it was not changed after STD-CPR. PO₂ after CPR was significantly higher in the ALP-CPR group (60.68 versus 44.47, P < 0.001). There were no differences between genders and for patients who are > 65 or ≤ 65 years of age. Conclusions. The abdominal lifting and compression cardiopulmonary resuscitation device used in this study is associated with a higher survival rate after ROSC than standard CPR.

Combination of chest compressions and interposed abdominal compressions in a swine model of ventricular fibrillation

PURPOSE

The aim of this study was to investigate the effects of the combination of chest compressions and interposed abdominal compressions (IAC-CPR) in a swine model of ventricular fibrillation (VF).

METHODS

Twenty healthy female Landrace-Large White pigs were the study subjects. At the end of the eighth minute of VF, animals in the control group (Group A) received chest compressions at a rate of 100/min, while animals in the experimental group received chest compressions and simultaneous interposed abdominal compressions (CC-IAC - Group B), both at a rate of 100/min. The primary end point of the experiment was return of spontaneous circulation (ROSC). Secondary outcomes were 48-h survival rate and 48-h neurologic outcome.

RESULTS

Six animals (60%) from Group A and 9 animals (90%) from Group B achieved ROSC (P=.121). There was a statistically significant difference in systolic aortic pressure, mean aortic pressure, right atrial pressures, and end-tidal carbon dioxide (ETCO2) between the two groups during the first cycle of CPR, while during the second cycle, diastolic aortic pressure was significantly higher in Group B. Coronary perfusion pressure (CPP) values in group B were significantly higher compared with those in Group A during the first and second cycle of CPR. Neurologic examination was statistically significantly better in Group B (75.00±10.00 vs. 90.00±10.00, P=.037).

CONCLUSION

ROSC did not differ statistically significant in the IAC-CPR compared to the CPR group only, while CPP was significantly higher in IAC-CPR-treated animals.

Interposed Abdominal Compression CPR for an Out-of-Hospital Cardiac Arrest Victim Failing Traditional CPR

Interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) is an alternative technique to traditional cardiopulmonary resuscitation (CPR) that can improve perfusion and lead to restoration of circulation in patients with chest wall deformity either acquired through vigorous CPR or co-morbidity such as chronic obstructive pulmonary disease. We report a case of out-of-hospital cardiac arrest where IAC-CPR allowed for restoration of spontaneous circulation and eventual full neurologic recovery when traditional CPR was failing to generate adequate pulses with chest compression alone.

Infusion of 4°C normal saline can improve the neurological outcome in a porcine model of cardiac arrest

BACKGROUND

This study sought to investigate induction of therapeutic hypothermia using ice-cold intravenous fluid after cardiopulmonary resuscitation (CPR). The effects on temperature, hemodynamics, cognitive performance and the accompanying neurohistopathological changes, and apoptosis were assessed.

METHODS

Fourteen piglets had 4 minutes of untreated ventricular fibrillation, followed by CPR. The animals in which spontaneous circulation was restored were randomly assigned to two groups: the hypothermia group (n = 7) was given an infusion of 4°C cold normal saline solution 30 mL/kg at an infusion rate of 1.33 mL/kg/min, followed by 10 mL/kg/h to 4 hours after restoration of spontaneous circulation; the control group (n = 7) was given the same infusion at room temperature. Variables were measured repeatedly until 4 hours after restoration of spontaneous circulation. Neurocognitive performance was evaluated 24 hours after CPR. Then animals were killed and the brains were removed for histopathology at 24 hours after restoration of spontaneous circulation. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling method was used for apoptosis evaluation.

RESULTS

Compared with the control group, the core temperature of the hypothermia group was significantly decreased (p < 0.01). The cerebral performance categories at 24 hours after restoration of spontaneous circulation in the hypothermia group were better than that in the control group (p < 0.05). The percentage of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells in the cortex and dentate gyrus of the hippocampus were significantly reduced in the hypothermia group compared with the control group at 24 hours after restoration of spontaneous circulation. By observation of transmission electron microscopy, the neuron damages were significantly reduced in hypothermia group.

CONCLUSION

4°C normal saline solution is a safe and effective method to reduce brain damages and prevent apoptotic cell death after cardiac arrest.

Pharmacological postconditioning with sevoflurane after cardiopulmonary resuscitation reduces myocardial dysfunction

Introduction

In this study, we sought to examine whether pharmacological postconditioning with sevoflurane (SEVO) is neuro- and cardioprotective in a pig model of cardiopulmonary resuscitation.

Methods

Twenty-two pigs were subjected to cardiac arrest. After 8 minutes of ventricular fibrillation and 2 minutes of basic life support, advanced cardiac life support was started. After successful return of spontaneous circulation (N = 16), animals were randomized to either (1) propofol (CONTROL) anesthesia or (2) SEVO anesthesia for 4 hours. Neurological function was assessed 24 hours after return of spontaneous circulation. The effects on myocardial and cerebral damage, especially on inflammation, apoptosis and tissue remodeling, were studied using cellular and molecular approaches.

Results

Animals treated with SEVO had lower peak troponin T levels (median [IQR]) (CONTROL vs SEVO = 0.31 pg/mL [0.2 to 0.65] vs 0.14 pg/mL [0.09 to 0.25]; P < 0.05) and improved left ventricular systolic and diastolic function compared to the CONTROL group (P < 0.05). SEVO was associated with a reduction in myocardial IL-1β protein concentrations (0.16 pg/μg total protein [0.14 to 0.17] vs 0.12 pg/μg total protein [0.11 to 0.14]; P < 0.01), a reduction in apoptosis (increased procaspase-3 protein levels (0.94 arbitrary units [0.86 to 1.04] vs 1.18 arbitrary units [1.03 to 1.28]; P < 0.05), increased hypoxia-inducible factor (HIF)-1α protein expression (P < 0.05) and increased activity of matrix metalloproteinase 9 (P < 0.05). SEVO did not, however, affect neurological deficit score or cerebral cellular and molecular pathways.

Conclusions

SEVO reduced myocardial damage and dysfunction after cardiopulmonary resuscitation in the early postresuscitation period. The reduction was associated with a reduced rate of myocardial proinflammatory cytokine expression, apoptosis, increased HIF-1α expression and increased activity of matrix metalloproteinase 9. Early administration of SEVO may not, however, improve neurological recovery.

Neurological outcome after experimental lung injury

We examined the influences of acute lung injury and hypoxia on neurological outcome. Functional performance was assessed using a neurocognitive test and a neurologic deficit score (NDS) five days before. On experimental day, mechanically ventilated pigs were randomized to hypoxia only (HO group, n=5) or to acute lung injury (ALI group, n=5). Hemodynamics, respiratory mechanics, systemic cytokines and further physiologic variables were obtained at baseline, at the time of ALI, 2, 4 and 8h thereafter. Subsequently, injured lungs were recruited and animals weaned from the ventilator. Neurocognitive testing was re-examined for five days. Then, brains were harvested for neurohistopathology. After the experiment, neurocognitive performance was significantly worsened and the NDS increased in the ALI group. Histopathology revealed no significant differences. Oxygenation was comparable between groups although significantly higher inspiratory pressures occured after ALI. Cytokines showed a trend towards higher levels after ALI. Neurocognitive compromise after ALI seems due to a more pronounced inflammatory response and complex mechanical ventilation.

Transthoracic application of electrical cardiopulmonary resuscitation for treatment of cardiac arrest

OBJECTIVE

Observational studies have shown that muscular stimulation contracting the thoracic cage may produce coronary perfusion pressures equal to manual chest compressions. This study examined electrical cardiopulmonary resuscitation for coronary perfusion pressures during ventricular fibrillation in a porcine model of cardiac arrest.

DESIGN

Prospective randomized controlled study.

SETTING

University affiliated research institute.

SUBJECTS

Domestic male pigs.

INTERVENTIONS

In seven domestic male pigs (40 +/- 2 kg), ventricular fibrillation was induced electrically and untreated for 10 secs. For each ventricular fibrillation episode, one of 16 electrical cardiopulmonary resuscitation stimulation protocols (pulse trains) or manual chest compression was applied. Each compression protocol was applied for 20 secs, followed by a defibrillation shock. The experimental procedure was performed across one or more randomized complete blocks. The electrical cardiopulmonary resuscitation pulse trains were defined by four two-level factors: pulse width (0.15 and 7.5 msec), pulse period (15 and 30 msec), train width (50 and 200 msec), and train rate (60 or 120 compressions per min). Pulse trains comprised two groups, based on pulse width (skeletal-based, 0.15 msec; cardiac-based, 7.5 msec).

MEASUREMENTS AND MAIN RESULTS

Train width was the significant design parameter for producing efficacious levels of coronary perfusion pressures for the skeletal-based electrical cardiopulmonary resuscitation pulse trains (p = 0.02). Both train width and train rate were significant design parameters for producing efficacious levels of coronary perfusion pressures for the cardiac-based electrical cardiopulmonary resuscitation pulse trains (p < 0.001, p = 0.5, respectively). Optimal skeletal-based and cardiac-based electrical cardiopulmonary resuscitation pulse trains were significantly better than ventricular fibrillation (p = 0.01, p = 0.01, respectively) and equivalent to manual chest compression (p = 0.2, p = 0.7, respectively) for sufficient coronary perfusion pressure levels.

CONCLUSIONS

Optimal skeletal-based and cardiac-based electrical cardiopulmonary resuscitation pulse train parameters generated levels of coronary perfusion pressure significantly greater than ventricular fibrillation and comparable with manual chest compression over a short interval of untreated cardiac arrest.

Intra-arrest rapid head cooling improves postresuscitation myocardial function in comparison with delayed postresuscitation surface cooling

OBJECTIVE

To compare resuscitation outcomes and myocardial function among intra-arrest head cooling, delayed surface cooling, and uncooled controls.

DESIGN

Prospective animal study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Twenty-four male domestic pigs.

INTERVENTIONS

Ventricular fibrillation remained untreated for 10 mins after which animals were assigned into three groups: 1) intra-arrest head cooling, 2) postresuscitation surface cooling, and 3) uncooled controls. Head cooling by evaporative perfluorochemical began coincident with the start of cardiopulmonary resuscitation and continued for a total of 4 hrs. Surface cooling using a cooling blanket began at 2 hrs after return of spontaneous circulation and continued for 8 hrs. Control animals were treated identically with the exception for cooling.

MEASUREMENTS AND MAIN RESULTS

Return of spontaneous circulation was achieved in eight of eight head-cooled animals, in seven of eight surface-cooled animals, and in seven of eight of controls. Myocardial functions measured by transthoracic echocardiography were significantly better in the head-cooled animals than in surface-cooled and controls. All head-cooled animals survived for more than 96 hrs. This contrasted with six of eight survivors after surface cooling, and only two of eight among controls.

CONCLUSIONS

Both intra-arrest head cooling and delayed surface cooling improved postresuscitation myocardial dysfunction. The beneficial effects were greatest with head cooling initiated with cardiopulmonary resuscitation.

Defibrillation delivered during the upstroke phase of manual chest compression improves shock success

OBJECTIVE

The current standard of manual chest compression during cardiopulmonary resuscitation requires pauses for rhythm analysis and shock delivery. However, interruptions of chest compression greatly decrease the likelihood of successful defibrillations, and significantly better outcomes are reported if this interruption is avoided. We therefore undertook a prospective randomized controlled animal study in an electrically induced ventricular fibrillation pig model to assess the effects of timing of defibrillation on the manual chest compression cycle on the defibrillation threshold.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Yorkshire-X domestic pigs (Sus scrofa).

INTERVENTIONS

In eight domestic male pigs weighing between 24 and 31 kg, ventricular fibrillation was electrically induced and untreated for 10 secs. Manual chest compression was then performed and continued for 25 secs with the protection of an isolation blanket. The depth and frequency of chest compressions were guided by a cardiopulmonary resuscitation prompter. Animals were randomized to receive a biphasic electrical shock in five different compression phases with a predetermined energy setting. A control phase was chosen at a constant 2 secs after discontinued chest compression. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 mins, the sequence was repeated for a total of 60 test shocks for each animal.

MEASUREMENTS AND MAIN RESULTS

No difference in coronary perfusion pressure before delivering of the shock was observed among the six study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of manual chest compression.

CONCLUSION

Defibrillation efficacy is maximal when electrical shock is delivered during the upstroke phase of manual chest compression.

Intra-arrest selective brain cooling improves success of resuscitation in a porcine model of prolonged cardiac arrest

AIMS OF STUDY

We have previously demonstrated that early intra-nasal cooling improved post-resuscitation neurological outcomes. The present study utilizing a porcine model of prolonged cardiac arrest investigated the effects of intra-nasal cooling initiated at the start of cardiopulmonary resuscitation (CPR) on resuscitation success. Our hypothesis was that rapid nasal cooling initiated during "low-flow" improves return of spontaneous resuscitation (ROSC).

METHODS

In 16 domestic male pigs weighing 40+/-3 kg, VF was electrically induced and untreated for 15 min. Animals were randomized to either head cooling or control. CPR was initiated and continued for 5 min before defibrillation was attempted. Coincident with starting CPR, the hypothermic group was cooled with a RhinoChill device which produces evaporative cooling in the nasal cavity of pigs. No cooling was administrated to control animals. If ROSC was not achieved after defibrillation, CPR was resumed for 1 min prior to the next defibrillation attempt until either successful resuscitation or for a total of 15 min.

MAIN RESULTS

Seven of eight animals in the hypothermic group (87.5%) and two of eight animals in control group (25%) (p=0.04) were successfully resuscitated. At ROSC, brain temperature was increased from baseline by 0.3 degrees C in the control group, and decreased by 0.1 degrees C in the hypothermic animals. Pulmonary artery temperature was above baseline in both groups.

CONCLUSION

Intra-nasal cooling initiated at the start of CPR significantly improves the success of resuscitation in a porcine model of prolonged cardiac arrest. This may have occurred by preventing brain hyperthermia.

The abdominal circulatory pump

Blood in the splanchnic vasculature can be transferred to the extremities. We quantified such blood shifts in normal subjects by measuring trunk volume by optoelectronic plethysmography, simultaneously with changes in body volume by whole body plethysmography during contractions of the diaphragm and abdominal muscles. Trunk volume changes with blood shifts, but body volume does not so that the blood volume shifted between trunk and extremities (Vbs) is the difference between changes in trunk and body volume. This is so because both trunk and body volume change identically with breathing and gas expansion or compression. During tidal breathing Vbs was 50–75 ml with an ejection fraction of 4–6% and an output of 750–1500 ml/min. Step increases in abdominal pressure resulted in rapid emptying presumably from the liver with a time constant of 0.61±0.1SE sec. followed by slower flow from non-hepatic viscera. The filling time constant was 0.57±0.09SE sec. Splanchnic emptying shifted up to 650 ml blood. With emptying, the increased hepatic vein flow increases the blood pressure at its entry into the inferior vena cava (IVC) and abolishes the pressure gradient producing flow between the femoral vein and the IVC inducing blood pooling in the legs. The findings are important for exercise because the larger the Vbs the greater the perfusion of locomotor muscles. During asystolic cardiac arrest we calculate that appropriate timing of abdominal compression could produce an output of 6 L/min. so that the abdominal circulatory pump might act as an auxiliary heart.

Miniaturization of a Chest Compressor for Cardiopulmonary Resuscitation

A miniaturized chest compressor (MCC®) for cardiopulmonary resuscitation (CPR) was designed to serve as a compact portable device to overcome limitations of manual chest compression and of currently marketed mechanical devices. We sought to especially address constraints of size and weight of current devices, together with the need for ease of application and consistent compressions with appropriate force and depth. We further intended that the device allows for ease of evacuation and transport through small spaces. These objectives are responsive to the increasingly recognized requirements for uninterrupted chest compression including that which results from operator fatigue during manual compressions. Utilizing a garment applied to the torso, the device incorporated a telescopic piston for chest compression. The compressor was pneumatically powered so as to avoid the added weight and potential electrical adversity of power delivered by batteries. Pneumatic power was supplied by the same compressed air or oxygen tank, which is routinely carried by professional emergency medical rescuers. The MCC® was tested on a porcine model during cardiac arrest and resuscitation with comparisons to the current industry standard, the Michigan Thumper®. Arterial, carotid, and coronary perfusion pressures, together with end-tidal carbon dioxide as a surrogate for cardiac output, were measured. The MCC® threshold levels of pressure, flow, and end-tidal PCO2 are achieved, which were predictive of successful defibrillation with restoration of spontaneous circulation. We conclude that the MCC® is as effective as that of the established industry standard, the Michigan Thumper®, with the potential advantage of portability and facile application, especially for out-of-hospital resuscitation.

The use of mice and rats as animal models for cardiopulmonary resuscitation research

Cardiopulmonary resuscitation (CPR) after the induction of cardiac arrest (CA) has been studied in mice and rats. The anatomical and physiological parameters of the cardiopulmonary system of these two species have been defined during experimental studies and are comparable with those of humans. Moreover, these animal models are more ethical to establish and are easier to manipulate, when compared with larger experimental animals. Accordingly, the effects of successful CPR on the function of vital organs, such as the brain, have been investigated because damage to these vital organs is of concern in CA survivors. Furthermore, the efficacy of several drugs, such as adrenaline (epinephrine), vasopressin and nitroglycerin, has been evaluated for use in CA in these small animal models. The purpose of these studies is not only to increase the rate of survival of CA victims, but also to improve their quality of life by reducing damage to their vital organs after CA and during CPR.

Safety, feasibility, and hemodynamic and blood flow effects of active compression-decompression of thorax and abdomen in patients with cardiac arrest

OBJECTIVE

During closed chest compression for cardiac arrest, any increase in coronary perfusion pressure accounts for a proportional increase in myocardial blood flow and therefore the resuscitability of the patient. The objectives of this study were to evaluate the safety, feasibility, and hemodynamic effects of phased chest and abdominal compression-decompression and to compare it with mechanical chest compression during cardiopulmonary resuscitation.

DESIGN

In this prospective, single-center, phase II study, we compared patients treated with the Datascope Lifestick Resuscitator with patients who had been treated with mechanical precordial compression.

SETTING

Emergency department of a tertiary care university hospital.

PATIENTS

We included 31 patients with cardiac arrest who had received cardiopulmonary resuscitation in the emergency department.

INTERVENTIONS

The Lifestick device was used in 20 patients. In 11 patients, mechanical chest compression with the Thumper device was used as a control intervention.

MEASUREMENTS AND MAIN RESULTS

We evaluated the safety, feasibility, and hemodynamic effects of both interventions and observed, with the help of echocardiography, the mechanisms through which blood flow was generated. We found no significant difference between the use of the Lifestick device and standard chest compression with the Thumper device in resuscitations. Most operators regarded the Lifestick as a feasible alternative to the Thumper. We could observe a mean increase in coronary perfusion pressure of 9.33 mm Hg (interquartile range, 1.96-14.36; p = .08) and an increase of end-tidal CO2 of 10 mm Hg (interquartile range, 5-16; p = .003) (1333Pa [interquartile range, 665-2133]) during resuscitation with the Lifestick compared with using the Thumper.

CONCLUSION

In this preliminary study, resuscitation with the Lifestick was found to be safe and feasible. The design of the study and small number of patients included in it limit the conclusions about the hemodynamic effects of the Lifestick.

A new cardiopulmonary resuscitation method using only rhythmic abdominal compression

This article introduces 2 new cardiopulmonary resuscitation (CPR) concepts: (1) the use of only rhythmic abdominal compression (OAC) to produce blood flow during CPR with ventricular fibrillation and (2) a new way of describing coronary perfusion effectiveness, namely, the area between the aortic and right atrial pressure curves, summed over 1 minute, the units being millimeters of mercury per second. We call this unit the coronary perfusion index (CPI). True mean coronary perfusion pressure is CPI/60. We also relate CPI during CPR with ventricular fibrillation to the CPI for the normally beating heart in the same animal, obtained before each experiment. This 11-pig (25-35 kg) study compares the CPI for standard chest-compression CPR and that obtained with OAC-CPR. The coronary perfusion ratio for OAC-CPR compared with standard chest-compression CPR was 1.6 +/- 0.73 (P = .024). In other words, OAC-CPR produced 60% more coronary perfusion than standard chest-compression CPR, with no damage to visceral organs.

Spontaneous gasping produces carotid blood flow during untreated cardiac arrest

OBJECTIVES

Coincident with "agonal" gasping during cardiac arrest, there are prominent increases in stroke volumes even in the absence of chest compression. In the present study, we tested the hypothesis that gasps also increase carotid blood flow (CBF) during untreated cardiac arrest.

MATERIALS AND METHODS

The tracheas of nine domestic male pigs, weighing 39+/-2kg, were intubated and animals were ventilated mechanically. Ventricular fibrillation (VF) was induced electrically and untreated for 5min. Coincident with the onset of VF, mechanical ventilation was discontinued. The right femoral artery and vein were cannulated. Intrathoracic pressure (ITP) was measured with the aid of a balloon tipped catheter advanced into the esophagus for a distance of 35cm. A transonic flowprobe was placed around the right common carotid artery for measurement of CBF.

RESULTS

Gasps increased in frequency during the first 4min of untreated VF together with increases in CBF. The CBF produced by gasping averaged 220+/-102mL/min, which represented approximately 59% of a pre-cardiac arrest CBF. Significant increases in CBF were highly correlated with the decreases in ITP during the inspiratory phase of the gaspings (r=0.78) and with the increases in aortic pressure during the expiratory phase of the gaspings (r=0.76).

CONCLUSIONS

Spontaneous gasps produce significant increases in CBF during untreated cardiac arrest. The present study therefore confirmed beneficial effects of gasping during cardiac arrest.

Drug administration in animal studies of cardiac arrest does not reflect human clinical experience

INTRODUCTION

To date, there is no evidence showing a benefit from any advanced cardiac life support (ACLS) medication in out-of-hospital cardiac arrest (OOHCA), despite animal data to the contrary. One explanation may be a difference in the time to first drug administration. Our previous work has shown the mean time to first drug administration in clinical trials is 19.4min. We hypothesized that the average time to drug administration in large animal experiments occurs earlier than in OOHCA clinical trials.

METHODS

We conducted a literature review between 1990 and 2006 in MEDLINE using the following MeSH headings: swine, dogs, resuscitation, heart arrest, EMS, EMT, ambulance, ventricular fibrillation, drug therapy, epinephrine, vasopressin, amiodarone, lidocaine, magnesium, and sodium bicarbonate. We reviewed the abstracts of 331 studies and 197 full manuscripts. Exclusion criteria included: non-peer reviewed, all without primary animal data, and traumatic models. From these, we identified 119 papers that contained unique information on time to medication administration. The data are reported as mean, ranges, and 95% confidence intervals. Mean time to first drug administration in animal laboratory studies and clinical trials was compared with a t-test. Regression analysis was performed to determine if time to drug predicted ROSC.

RESULTS

Mean time to first drug administration in 2378 animals was 9.5min (range 3.0-28.0; 95% CI around mean 2.78, 16.22). This is less than the time reported in clinical trials (19.4min, p<0.001). Time to drug predicted ROSC (odds ratio 0.844; 95% CI 0.738, 0.966).

CONCLUSION

Shorter drug delivery time in animal models of cardiac arrest may be one reason for the failure of animal studies to translate successfully into the clinical arena.

Vital organ blood flow with the impedance threshold device

OBJECTIVE

The purpose of this study is to review cardiopulmonary resuscitation hemodynamics and vital organ blood flow in animal models with the use of the impedance threshold device (ITD) and to correlate these findings with the results of human clinical trials.

RESULTS

Animal studies have demonstrated near normalization of cerebral blood flow and an increase between 50% and 100% in cardiac blood flow with use of the ITD. Coincident coronary perfusion pressure is significantly increased with the ITD. Results of human clinical trials generally reflect the data seen in animal models, with near normal blood pressure during active compression-decompression cardiopulmonary resuscitation and the ITD, near doubling of blood pressure with standard cardiopulmonary resuscitation plus the ITD, and significantly increased short-term survival rates.

CONCLUSIONS

Improved vital organ perfusion with ITD use during cardiopulmonary resuscitation is an important advance in resuscitation. Incorporation of the ITD into protocols that improve other aspects of the care of patients during cardiac arrest and after successful resuscitation should result in further benefit from the ITD.

A comparison of electrically induced cardiac arrest with cardiac arrest produced by coronary occlusion

OBJECTIVE

The present study was undertaken to compare an animal model of electrically induced VF with ischemically induced VF. In a preponderance of models of cardiac arrest and resuscitation in intact animals, ventricular fibrillation (VF) is induced by an alternating current delivered directly to the epicardium or endocardium. Yet, the applicability of such animal models has been challenged for it is not an electrical current alone but rather a current generated in the ischemic myocardium that triggers VF. Accordingly, a potentially more clinically relevant model was investigated in which spontaneous VF followed acute myocardial ischemia.

METHODS

Twenty anesthetized pigs were randomized to either electrical fibrillation or myocardial ischemia following transient occlusion of the left anterior descending (LAD) coronary artery.

RESULTS

VF was untreated for 7 min in both models after which mechanical ventilation and precordial compression were begun. Defibrillation was attempted after 5 min of CPR in both groups. VF appeared within 5.7+/-2.0 min of LAD occlusion.

CONCLUSIONS

A significant increase in the number of post-resuscitation premature ventricular beats and recurrent VF followed ROSC and a significantly greater number of shocks was required for restoration of spontaneous circulation (ROSC) after LAD occlusion. Nevertheless, early post-resuscitation myocardial dysfunction, neurological recovery and 72 h survival were indistinguishable between the two models.

Cardiopulmonary resuscitation in prone position: a simplified method for outpatients

BACKGROUND

The efficacy of cardiopulmonary resuscitation (CPR) is vital for saving lives of victims with sudden cardiac arrest. In 1960, Kuowenhoven and colleagues proposed the method that has become standard for CPR. Despite vast input of resources for public education and training of this procedure, its success rate outside hospitals remains poor to dismal. During CPR, restoration of respiration is as important as circulation. But opening the airway and giving effective mouth-to-mouth respiration is difficult for lay people to learn. Furthermore, most bystanders are reluctant to do mouth-to-mouth respiration because of the risk of infection. Therefore, the general population needs a more simplified CPR method for outpatients. The practice of CPR in the prone position, first proposed by McNeil in 1989, has not been adopted, despite the fact that it meets the desirable requirements of ideal resuscitation: simultaneous restoration of circulation and respiration with a very simple maneuver.

METHODS

Part 1 (circulation test): Eleven patients who expired in the intensive care unit (ICU), with arterial lines attached, received standard pre-cordial cardiac massage, and the generated blood pressure (BP) was recorded. They were then turned to the prone position, with the head turned to one side. We compressed the patient's thoracic spine with the same force used in standard CPR (rhythm of approximately 60 per minute each time when the back bounces back), and the BP was also recorded. Part 2 (ventilation test): Ten healthy volunteers (5 doctors and 5 nurses) were enlisted for respiratory assessment during compression on the back. With the nose clipped and spontaneous breathing held, the volunteer's exhaled tidal volume upon compression was measured with a spirometer.

RESULTS

Standard external cardiac massage of the cadavers generated BPs of 55 +/- 20/13 +/- 7 mmHg; however, external compression on the back of the cadavers generated higher BP of 79 +/- 20/17 +/- 10 mmHg (p = 0.028, Wilcoxon signed-rank analysis). External compression on the back of the volunteers generated mean tidal volumes of 399 +/- 110 mL.

CONCLUSION

Our study revealed that prone CPR provides good respiratory and circulatory support at the same time. It is easy to perform and it may be a good alternative way for bystanders to perform CPR in public surroundings. We recommend that more investigators do further studies on this topic.

Design of near-optimal waveforms for chest and abdominal compression and decompression in CPR using computer-simulated evolution

OBJECTIVE

To discover design principles underlying the optimal waveforms for external chest and abdominal compression and decompression during cardiac arrest and cardiopulmonary resuscitation (CPR).

METHOD

A 14-compartment mathematical model of the human cardiopulmonary system is used to test successive generations of randomly mutated external compression waveforms during cardiac arrest and resuscitation. Mutated waveforms that produced superior mean perfusion pressure became parents for the next generation. Selection was based upon either systemic perfusion pressure (SPP = thoracic aortic minus right atrial pressure) or upon coronary perfusion pressure (CPP = thoracic aortic pressure minus myocardial wall pressure). After simulations of 64,414 individual CPR episodes, 40 highly evolved waveforms were characterized in terms of frequency, duty cycle, and phase. A simple, practical compression technique was then designed by combining evolved features with a constant rate of 80 min(-1) and duty cycle of 50%.

RESULTS

All ultimate surviving waveforms included reciprocal compression and decompression of the chest and the abdomen to the maximum allowable extent. The evolved waveforms produced 1.5-3 times the mean perfusion pressure of standard CPR and greater perfusion pressure than other forms of modified CPR reported heretofore, including active compression-decompression (ACD)+ITV and interposed abdominal compression (IAC)-CPR. When SPP was maximized by evolution, the chest compression/abdominal decompression phase was near 70% of cycle time. When CPP was maximized, the abdominal compression/chest decompression phase was near 30% of cycle time. Near-maximal SPP/CPP of 60/21 mmHg (forward flow 3.8 L/min) occurred at a compromise compression frequency of 80 min(-1) and duty cycle for chest compression of 50%.

CONCLUSIONS

Optimized waveforms for thoraco-abdominal compression and decompression include previously discovered features of active decompression and interposed abdominal compression. These waveforms can be used by manual (Lifestick-like) and mechanical (vest-like) devices to achieve short periods of near normal blood perfusion non-invasively during cardiac arrest.

Cardiopulmonary resuscitation in patients with a Nuss bar--a case report and review of the literature

Pectus excavatum (PE) is a common chest wall deformity that may produce a variety of physiological and psychological effects in children and adolescents. In addition, some of these patients have associated cardiac diseases (ie, mitral valve prolapse and Marfan syndrome). Recently, a minimally invasive surgical repair of PE that requires sternal bar placement has become increasingly frequent to enhance patients' cardiopulmonary functioning as well as their self-esteem. However, despite this innovative technique, it is possible for such patients to have a cardiac arrest while their sternal bar is in place. Whether the presence of a metal bar on the underside of their sternum may hinder resuscitative chest compressions (cardiopulmonary resuscitation) is an issue that concerns us, our patients, and their families; the answer requires further investigation. We present a 21-year-old man with PE who underwent a minimally invasive pectus repair but had a fatal cardiac event before bar removal. Paramedics conducting cardiopulmonary resuscitation on the patient later reported that they were unable to deliver effective cardiac compressions and that the sternal bar may have contributed to this.

Increases in Both Buccal and Sublingual Partial Pressure of Carbon Dioxide Reflect Decreases of Tissue Blood Flows in a Porcine Model During Hemorrhagic Shock

BACKGROUND

Earlier studies had demonstrated that gastric partial pressure of carbon dioxide (PCO2) of the gastric wall is an early indication of perfusion failure. Because hypercarbia is a general phenomenon of perfusion failure, this study investigated whether sublingual and buccal mucosal tissue PCO2 also serve as a sensitive indicator of systemic blood flow during hemorrhagic shock.

METHODS AND RESULTS

Hemorrhagic shock was induced in five male domestic pigs. Buccal and sublingual PCO2 increased from 60 to 129 mm Hg (p < 0.01) in parallel with average decreases in cardiac output to 44% (from 6.1 to 2.8 L/minute; p < 0.01), and mean arterial pressure to 47% (from 115 to 57 mm Hg; p < 0.01), over the 2-hour interval of shock. According to colored microspheres used for measurements, buccal mucosal flow decreased to 35% (from 6.3 to 2.2 mL/minute/100 g; p < 0.01) in close parallel with sublingual blood flow, which decreased to 34% (from 7.2 to 2.5 mL/minute/100 g; p < 0.01). Liver flow decreased to 56% (from 152 to 85 mL/minute/100 g;p < 0.01), and renal flow to 47% (from 272 to 128 mL/minute/100 g;p < 0.01) of baseline values. The procedure yielded to overall comparable volume exchanges in different animals. After reinfusion of shed blood, buccal PCO2, like sublingual PCO2, was restored to approximately baseline values (respectively, from 56 to 71 mm Hg and from 60 to 71 mm Hg; p = not significant), together with arterial pressure, cardiac output, and end-tidal CO2 (EtCO2) (respectively, from 115 to 115 mm Hg, from 6.1 to 6.3 L/minute, and from 35 to 39 mm Hg; p = not significant), but there was delayed reversal of lactic acidosis (from 0.7 to 2.5 mmol/L;p < 0.01). In five unbled control animals, no significant changes were observed over the same interval.

CONCLUSION

The current study extends the rationale for noninvasive measurements to both buccal and sublingual mucosa for diagnosis and quantitation of hemorrhagic shock severity.

Miniaturized chest compressor

BACKGROUND

Current American Heart Association guidelines call for continuous manual chest compressions for cardiopulmonary resuscitation. Chest compressions maintain critical levels of forward blood flow, including blood flow to the myocardium during cardiac arrest, to allow for successful resuscitation. The demand on rescuers is to ensure that compression is consistent, with appropriate force and depth, often under difficult conditions of rescue, evacuation, and transport. It is also of great moment that fatigue of the rescuer adversely affects outcomes. This evaluation was to compare two pneumatically driven devices, the Michigan Thumper (Michigan Instruments, Grand Rapids, MI), as an industrial standard, and the miniaturized chest compressor.

METHODS

On a porcine model of cardiopulmonary resuscitation, alternating current fibrillation was induced for 7 mins, followed by 5 mins of chest compression. Arterial and right atrial pressures and end-tidal CO2 were measured. Coronary perfusion pressure was calculated as the difference between compression end-diastolic arterial pressure and right atrial pressure.

RESULTS

Threshold levels of coronary perfusion pressure (>15 mm Hg) and end-tidal CO2 (>10 mm Hg) for successful defibrillation were maintained with the miniaturized chest compressor. Consistently greater coronary perfusion pressure and end-tidal CO2 values were achieved with the miniaturized chest compressor in comparison with the Thumper.

CONCLUSION

The miniaturized chest compressor has the important potential advantage of minimal weight and, therefore, portability, without any reduction in effectiveness. To the contrary, it is potentially more effective than the much larger and heavier industry standard for maintaining circulation.

Evaluation of an impedance threshold device in patients receiving active compression–decompression cardiopulmonary resuscitation for out of hospital cardiac arrest

AIMS

The purpose of this multicentre clinical randomized controlled blinded prospective trial was to determine whether an inspiratory impedance threshold device (ITD), when used in combination with active compression-decompression (ACD) cardiopulmonary resuscitation (CPR), would improve survival rates in patients with out-of-hospital cardiac arrest.

METHODS AND RESULTS

Patients were randomized to receive either a sham (n = 200) or an active impedance threshold device (n = 200) during advanced cardiac life support performed with active compression-decompression cardiopulmonary resuscitation. The primary endpoint of this study was 24 h survival. The 24 h survival rates were 44/200 (22%) with the sham valve and 64/200 (32%) with the active valve (P = 0.02). The number of patients who had a return of spontaneous circulation (ROSC), intensive care unit (ICU) admission, and hospital discharge rates was 77 (39%), 57 (29%), and 8 (4%) in the sham valve group versus 96 (48%) (P = 0.05), 79 (40%) (P = 0.02), and 10 (5%) (P = 0.6) in the active valve group. Six out of ten survivors in the active valve group and 1/8 survivors in the sham group had normal neurological function at hospital discharge (P = 0.1).

CONCLUSION

The use of an impedance valve in patients receiving active compression-decompression cardiopulmonary resuscitation for out-of-hospital cardiac arrest significantly improved 24 h survival rates.

The effects of biphasic waveform design on post-resuscitation myocardial function

OBJECTIVES

This study examined the effects of biphasic truncated exponential waveform design on survival and post-resuscitation myocardial function after prolonged ventricular fibrillation (VF).

BACKGROUND

Biphasic waveforms are more effective than monophasic waveforms for successful defibrillation, but optimization of energy and current levels to minimize post-resuscitation myocardial dysfunction has been largely unexplored. We examined a low-capacitance waveform typical of low-energy application (low-energy biphasic truncated exponential [BTEL]; 100 microF, < or =200 J) and a high-capacitance waveform typical of high-energy application (high-energy biphasic truncated exponential [BTEH]; 200 microF, > or =200 J).

METHODS

Four groups of anesthetized 40- to 45-kg pigs were investigated. After 7 min of electrically induced VF, a 15-min resuscitation attempt was made using sequences of up to three defibrillation shocks followed by 1 min of cardiopulmonary resuscitation. Animals were randomized to BTEL at 150 J or 200 J or to BTEH at 200 J or 360 J.

RESULTS

Resuscitation was unsuccessful in three of the five animals treated with BTEH at 200 J. All other attempts were successful. Significant therapy effects were observed for survival (p = 0.035), left ventricular ejection fraction (p < 0.001), stroke volume (p < 0.001), fractional area change (p < 0.001), cardiac output (p = 0.044), and mean aortic pressure (p < 0.001). Hemodynamic outcomes were negatively associated with energy and average current but positively associated with peak current. Peak current was the only significant predictor of survival (p < 0.001).

CONCLUSIONS

Maximum survival and minimum myocardial dysfunction were observed with the low-capacitance 150-J waveform, which delivered higher peak current while minimizing energy and average current.

Interposed abdominal compression CPR: a comprehensive evidence based review

Interposed abdominal compression (IAC)-CPR includes all steps of standard external CPR with the addition of manual mid-abdominal compressions in counterpoint to the rhythm of chest compressions. IAC-CPR can increase blood flow during CPR about 2-fold compared with standard CPR without IAC, as shown by six of six studies in computer models and 19 of 20 studies in various animal models. The addition of IAC has clinical benefit in humans, as indicated in 10 of 12 small to medium sized clinical studies. The technique increases the frequency of immediate return of spontaneous circulation for in-hospital resuscitations from roughly 25 to 50%. Improved survival to discharge is also likely on the basis of two small in-hospital trials. Possible harm from abdominal compression is minimal on the basis of 426 humans, 151 dogs and 14 pigs that received IAC in published reports. The complexity of performing IAC is similar to that of opening the airway and is less than that of other basic life support maneuvers. The aggregate evidence suggests that IAC-CPR is a safe and effective means to increase organ perfusion and survival, when performed by professionally trained responders in a hospital and when initiated early in the resuscitation protocol. Cost and logistical considerations discourage use of IAC-CPR outside of hospitals.

Fixed-energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation

OBJECTIVE

For adults, 150-J fixed-energy, impedance-compensating biphasic truncated exponential (ICBTE) shocks are now effectively used in automated defibrillators. However, the high energy levels delivered by adult automated defibrillators preclude their use for pediatric patients. Accordingly, we investigated a method by which adult automated defibrillators may be adapted to deliver a 50-J ICBTE shock for pediatric defibrillation.

DESIGN

Prospective, randomized study.

SETTING

A university-affiliated research institution.

SUBJECT

Domestic piglets.

INTERVENTIONS

We initially investigated four groups of anesthetized mechanically ventilated piglets weighing 3.8, 7.5, 15, and 25 kg. Ventricular fibrillation was induced with an AC current delivered to the right ventricular endocardium. After 7 mins of untreated ventricular fibrillation, a conventional manual defibrillator was used to deliver up to three 50-J ICBTE shocks. If ventricular fibrillation was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored, or for a total of 15 mins. In a second set of experiments, we evaluated a 150-J biphasic adult automated defibrillator that was operated in conjunction with energy-reducing electrodes such as to deliver 50-J shocks. The same resuscitation protocol was then exercised on piglets weighing 3.7, 13.5, and 24.2 kg.

MEASUREMENTS AND MAIN RESULTS

All animals were successfully resuscitated. Postresuscitation hemodynamic and myocardial function quickly returned to baseline values in both experimental groups, and all animals survived.

CONCLUSION

An adaptation of a 150-J biphasic adult automated defibrillator in which energy-reducing electrodes delivered 50-J shocks successfully resuscitated animals ranging from 3.7 to 25 kg without compromise of postresuscitation myocardial function or survival.

Mechanical devices for cardiopulmonary resuscitation: an update

Despite the promise and universal use of the Kouwenhoven technique for closed chest cardiac massage, this method has been shown repeatedly to suffer from lack of clinical efficacy. Although the Kouwenhoven technique can clearly save lives, the inherent inefficiency of this approach and the challenges related to teaching and retaining the skills needed to perform the technique correctly have limited its overall effectiveness. This has prompted the development of newer lifesaving CPR techniques and devices. Some of the advances, such as the vest approach, active compression-decompression, and the impedance threshold valve, offer a benefit when compared with the Kouwenhoven technique. It is clear, however, that challenges related to implementation of these newer approaches will determine their ultimate utility. It is not sufficient to have a better technique or device available. Challenges to implementation of the newer approaches include overcoming the inertia of a universal mindset on the already-familiar Kouwenhoven technique and creating a cost-effective justification for change. Each year, approximately 10 million people in the United States are trained in the Kouwenhoven technique. Americans spend nearly $500,000,000 annually on this form of CPR training and retraining. Given the less than 5% survival rate for the 300,000 patients who experience out-of-hospital cardiac arrest each year in the United States, the prudence of this societal investment when compared with other ways health care dollars are spent should be questioned. It is hoped that this mismatch between costs and benefits will be recognized and will lead to the adoption of more effective means to resuscitate patients.

Cardiopulmonary resuscitation in the mouse

We sought to develop a model of cardiac arrest and resuscitation on mice that would be comparable to that of large mammals and would allow for more fundamental investigations on cardiopulmonary arrest and cardiac resuscitation. A model of cardiopulmonary resuscitation previously developed by our group on rats was adapted to anesthetized, mechanically ventilated adult male Institute of Cancer Research mice that weighed 46 +/- 3 g. The trachea was intubated through the mouth, and end-tidal PCO(2) (PET(CO(2))) was measured with a microcapnometer. Catheters were advanced into the aorta and into the right atrium, and coronary perfusion pressure (CPP) was computed. A 1.5-mA alternating current was delivered to the right ventricular endocardium, which produced ventricular fibrillation or a pulseless rhythm. Precordial compression was begun 4 min later. Ten sequential studies were performed, during which five animals were successfully resuscitated and five failed resuscitation efforts. Successful resuscitation was contingent on the restoration of threshold levels of CPP and PET(CO(2)) during chest compression. As in rats, swine, and human patients, threshold levels of mean aortic pressure, CPP, and PET(CO(2)) were critical determinates of resuscitability in this murine model of threshold level of cardiac arrest and resuscitation.

Optimum compression to ventilation ratios in CPR under realistic, practical conditions: a physiological and mathematical analysis

OBJECTIVE

To develop and evaluate a practical formula for the optimum ratio of compressions to ventilations in cardiopulmonary resuscitation (CPR). The optimum value of a variable is that for which a desired result is maximized. Here the desired result is assumed to be either oxygen delivery to peripheral tissues or a combination of oxygen delivery and waste product removal.

METHOD

Equations describing oxygen delivery and blood flow during CPR as functions of the number of compressions and the number of ventilations delivered over time were developed from principles of classical physiology. These equations were solved explicitly in terms of the compression/ventilation ratio and evaluated for a wide range of conditions using Monte Carlo simulations.

RESULTS

As the compression to ventilation ratio was increased from 0 to 50 or more, both oxygen delivery and the combination of oxygen delivery with blood flow increased to maximum values and then gradually declined. For variables typical of standard CPR as taught and specified in international guidelines, maximum values occurred at compression/ventilation ratios near 30:2. For variables typical of actual lay rescuer performance in the field, maximal values occurred at compression/ventilation ratios near 60:2.

CONCLUSION

Current guidelines overestimate the need for ventilation during standard CPR by two to four-fold. Blood flow and oxygen delivery to the periphery can be improved by eliminating interruptions of chest compression for these unnecessary ventilations.

Alternative cardiopulmonary resuscitation devices

Cardiac arrest survival rates remain low despite increased access to advanced cardiac life support. Survival from cardiac arrest is, at least in part, related to the perfusion pressures and blood flow achieved during cardiopulmonary resuscitation (CPR). A number of alternative CPR devices have been developed that aim to improve the perfusion pressures and/or blood flow achieved during CPR. Active compression-decompression CPR devices are by far the most studied alternative CPR devices, but the results have been inconsistent and conflicting. A number of other devices, including the inspiratory impedance threshold valve, minimally invasive direct cardiac massage, phased chest and abdominal compression-decompression CPR, and vest CPR, are all capable of improving perfusion pressures and/or blood flow compared with standard external chest compressions. However, no convincing human outcome data has been produced yet for any of these devices. Although an interesting area of research, none of the alternative CPR devices convincingly improve long-term patient outcomes.