Recovery of arterial blood pressure after chest compressions pauses in patients with out-of-hospital cardiac arrest.

BACKGROUND AND AIMS: Chest compressions generating good perfusion during cardiopulmonary resuscitation (CPR) in cardiac arrest patients are critical for positive patient outcomes. Conventional wisdom advises minimizing compression pauses because several compressions are required to recover arterial blood pressure (ABP) back to pre-pause values. Our study examines how compression pauses influence ABP recovery post-pause in out-of-hospital cardiac arrest. METHODS: We analyzed data from a subset of a prospective, randomized LUCAS 2 Active Decompression trial. Patients were treated by an anesthesiologist-staffed rapid response car program in Oslo, Norway (2015-2017) with mechanical chest compressions using the LUCAS device at 102 compressions/min. Patients with an ABP signal during CPR and at least one compression pause >2 sec were included. Arterial cannulation, compression pauses, and ECG during the pause were verified by physician review of patient records and physiological signals. Pauses were excluded if return of spontaneous circulation occurred during the pause (pressure pulses associated with ECG complexes). Compression, mean, and decompression ABP for 10 compressions before/after each pause and the mean ABP during the pause were measured with custom MATLAB code. The relationship between pause duration and ABP recovery was investigated using linear regression. RESULTS: We included 56 patients with a total of 271 pauses (pause duration: median = 11 sec, Q1 = 7 sec, Q3 =18 sec). Mean ABP dropped from 53 ± 10 mmHg for the last pre-pause compression to 33 ± 7 mmHg during the pause. Compression and mean ABP recovered to >90% of pre-pause pressure within 2 compressions, or 1.7 sec. Pause duration did not affect the recovery of ABP post-pause (R2: 0.05, 0.03, 0.01 for compression, mean, and decompression ABP, respectively). CONCLUSIONS: ABP generated by mechanical CPR recovered quickly after pauses. Recovery of ABP after a pause was independent of pause duration.

Automated external defibrillator electrode size and termination of ventricular fibrillation in out-of-hospital cardiac arrest.

Smaller electrodes allow more options for design of automated external defibrillator (AED) user interfaces. However, previous studies employing monophasic-waveform defibrillators found that smaller electrode sizes have lower defibrillation shock success rates. We hypothesize that, for impedance-compensated, biphasic truncated exponential (BTE) shocks, smaller electrodes increase transthoracic impedance (TTI) but do not adversely affect defibrillation success rates. METHODS AND RESULTS: In this prospective before-and-after clinical study, Amsterdam police and firefighters used AEDs with BTE waveforms: an AED with larger electrodes in 2016-2017 (113 cm2), and an AED with smaller electrodes in 2017-2020 (65 cm2). We analyzed 157 and 178 patient cases with an initial shockable rhythm where the larger and smaller electrodes were used, respectively. A single 200-J shock terminated ventricular fibrillation (VF) in 86% of patients treated with large electrodes and 89% of patients treated with smaller electrodes. Small electrodes had a non-inferior first shock defibrillation success rate compared to large electrodes, with a difference of 3% (95% CI: -3% -9%) with the lower confidence limit remaining above the defined non-inferiority threshold. TTI was significantly higher for the smaller electrodes (median: 100 Ω) compared to the larger electrodes (median: 88 Ω) (p < 0.001). CONCLUSIONS: For AEDs with impedance-compensating BTE waveforms, TTI was higher for smaller electrodes than the large electrode electrodes. Overall defibrillation shock success for AEDs with smaller electrodes was non-inferior to the AEDs with larger electrodes.

Out-of-hospital resuscitation of a 3 month old boy presenting with recurrent ventricular fibrillation cardiac arrest: a case report.

A 3 month old boy, with no known health conditions, suffered a sudden collapse at home. On first EMS arrival, ventricular fibrillation (VF) cardiac arrest was identified and resuscitation following UK national guidelines was initiated. He remained in cardiac arrest for over 25 min, during which he received 10 defibrillation shocks, each effective, but with VF reoccurring within a few seconds of each of the first 9. A return of spontaneous circulation (ROSC) was achieved after the 10th shock. The resuscitation was conducted fully in his home, with the early involvement of Advanced Paramedic Practitioners specialising in critical care (APP- CC). Throughout his resuscitation, there remained a strong focus on delivering quality resuscitation in situ, rather than a 'load and go' approach that would have resulted in very early conveyance to hospital with on-going CPR.The patient was subsequently discharged home and is making an excellent recovery. The arrest was later determined to have been caused by a primary arrhythmia as a result of a previously unidentified non-obstructive variant hypertrophic cardiomyopathy.We present data downloaded from the defibrillator used during the resuscitation that illustrates clearly the recurrent nature of his fibrillation.

Alternating fast and slow chest compression rates during CPR improved hemodynamics.

INTRODUCTION: Mechanical chest compression devices allow for variation in chest compression (CCs) characteristics from moment to moment, enabling therapy that is not feasible for manual CCs. Effects of varying compressions over time have not been studied. In a randomized trial in an experimental model of prolonged cardiac arrest, we compared time-varying CPR (TVCPR), alternating between 100 and 200 compressions per minute (cpm) every 6 s, to guidelines CPR (Control). METHODS: Ventricular fibrillation (VF) was electrically induced in 20 anesthetized pigs (28.4-45.8 kg). Following 10 min of untreated VF, cardiopulmonary resuscitation (CPR) began, randomized to TVCPR or Control. Rate of return of spontaneous circulation (ROSC), 4-h survival, and hemodynamics during the first 5 min of CPR were compared between groups. Moment-to-moment hemodynamic effects of changing the CC rate were analyzed. RESULTS: TVCPR improved the proportion of ROSC over time compared to Control (p < 0.05) but ROSC (9/10 vs. 5/10) and 4-h survival (8/10 vs 5/10) did not differ significantly between groups. During CPR, coronary and cerebral perfusion pressures and femoral artery pressure did not differ between groups; however, end-tidal CO2 and mixed venous O2 saturation were higher, and pulmonary artery pressure was lower (p < 0.05) for TVCPR than Control. During TVCPR, switching to 100 cpm increased coronary perfusion pressure (p < 0.05), and switching to 200 cpm increased cerebral perfusion pressure (p < 0.05). CONCLUSIONS: Time-varying CPR significantly improved indicators of net forward blood flow and proportion of ROSC over time without negatively impacting perfusion pressures. Alternating CC rate alternates between perfusion pressures favoring the brain and those favoring the heart. Time-varying CPR represents a new avenue of research for optimizing CPR. INSTITUTIONAL PROTOCOL NUMBER: University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 140406860.

Analyzing the heart rhythm during chest compressions: Performance and clinical value of a new AED algorithm.

PURPOSE: Automated external defibrillators (AED) prompt the rescuer to stop chest compressions (CC) for ECG analysis during out-of-hospital cardiac arrest (OHCA). We assessed the diagnostic accuracy and clinical benefit of a new AED algorithm (cprINSIGHT), which analyzes ECG and impedance signals during CC, allowing rhythm analysis with ongoing chest compressions. METHODS: Amsterdam Police and Fire Fighters used a conventional AED in 2016-2017 (control) and an AED with cprINSIGHT in 2018-2019 (intervention). In the intervention AED, cprINSIGHT was activated after the first (conventional) analysis. This algorithm classified the rhythm as "shockable" (S) and "non-shockable" (NS), or "pause needed". Sensitivity for S, specificity for NS with 90% lower confidence limit (LCL), chest compression fractions (CCF) and pre-shock pause were compared between control and intervention cases accounting for multiple observations per patient. RESULTS: Data from 465 control and 425 intervention cases were analyzed. cprINSIGHT reached a decision during CC in 70% of analyses. Sensitivity of the intervention AED was 96%, (LCL 93%) and specificity was 98% (LCL 97%), both not significantly different from control. Intervention cases had a shorter median pre-shock pause compared to control cases (8 s vs 22 s, p < 0.001) and higher median CCF (86% vs 80%, P < 0.001). CONCLUSION: AEDs with cprINSIGHT analyzed the ECG during chest compressions in 70% of analyses with 96% sensitivity and 98% specificity when it made a S or a NS decision. Compared to conventional AEDs, cprINSIGHT leads to a significantly shorter pre-shock pause and a significant increase in CCF.

Metrics of mechanical chest compression device use in out-of-hospital cardiac arrest.

OBJECTIVE: The quality of cardiopulmonary resuscitation (CPR) affects outcomes from cardiac arrest, yet manual CPR is difficult to administer. Although mechanical CPR (mCPR) devices offer high quality CPR, only limited data describe their deployment, their interaction with standard manual CPR (sCPR), and the consequent effects on chest compression continuity and patient outcomes. We sought to describe the interaction between sCPR and mCPR and the impact of the sCPR-mCPR transition upon outcomes in adult out-of-hospital cardiac arrest (OHCA). METHODS: We analyzed all adult ventricular fibrillation OHCA treated by the Anchorage Fire Department (AFD) during calendar year 2016. AFD protocols include the immediate initiation of sCPR upon rescuer arrival and transition to mCPR, guided by patient status. We compared CPR timing, performance, and outcomes between those receiving sCPR only and those receiving sCPR transitioning to mCPR (sCPR + mCPR). RESULTS: All 19 sCPR-only patients achieved return of spontaneous circulation (ROSC) after a median of 3.3 (interquartile range 2.2-5.1) minutes. Among 30 patients remaining pulseless after sCPR (median 6.9 [5.3-11.0] minutes), transition to mCPR occurred with a median chest compression interruption of 7 (5-13) seconds. Twenty-one of 30 sCPR + mCPR patients achieved ROSC after a median of 11.2 (5.7-23.8) additional minutes of mCPR. Survival differed between groups: sCPR only 14/19 (74%) versus sCPR + mCPR 13/30 (43%), P = 0.045. CONCLUSION: In this series, transition to mCPR occurred in patients unresponsive to initial sCPR with only brief interruptions in chest compressions. Assessment of mCPR must consider the interactions with sCPR.

An investigation of inter-shock timing and electrode placement for double-sequential defibrillation.

BACKGROUND: Double-Sequential Defibrillation (DSD) is the near-simultaneous use of two defibrillators to treat refractory VF. We hypothesized that (1) risk of DSD-associated defibrillator damage depends on shock vector and (2) the efficacy of DSD depends on inter-shock time. METHODS: Part 1: risk of defibrillator damage was assessed in three anaesthetized pigs by applying two sets of defibrillation electrodes in six different configurations (near-orthogonal or near-parallel vectors). Ten 360J shocks were delivered from one set of pads and peak voltage was measured across the second set. Part 2: the dependence of DSD efficacy on inter-shock time was assessed in ten anaesthetized pigs. Electrodes were applied in lateral-lateral (LL) and anterior-posterior positions. Control (LL Stacked Shocks; one vector, two shocks ∼10 s apart) and DSD therapies (Overlapping, 10 ms, 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms apart) were tested in a block randomized design treating electrically-induced VF (n = ∼89 VF episodes/therapy). Shock energies were selected to achieve 25% shock success for a single LL shock. RESULTS: Part 1: peak voltage delivered was 1833 ± 48 V (mean ± 95%CI). Peak voltage exposure was, on average, 10-fold higher for parallel than orthogonal vectors (p < 0.0001). Part 2: DSD efficacy compared to Stacked LL shocks was higher for Overlapping, 10 ms, and 100 ms (p < 0.05); lower at 50 ms (p < 0.05); and not different at 200 ms or longer inter-shock times. CONCLUSION: Risk of DSD-associated defibrillator damage can be mitigated by using near-orthogonal shock vectors. DSD efficacy is highly dependent on the inter-shock time and can be better, worse, or no different than stacked shocks from a single vector. INSTITUTIONAL PROTOCOL NUMBER: University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 06860.

Minor Variations in Electrode Pad Placement Impact Defibrillation Success.

Defibrillation is essential for resuscitating patients with ventricular fibrillation (VF), but shocks often fail to defibrillate. We hypothesized that small variations in pad placement affect shock success, and that defibrillation waveform and shock dose could compensate for suboptimal pad placement. In 10 swine experiments, electrode pads were attached at 3 adjacent anterolateral positions, less than 3 centimeters apart. At each position, 24 episodes of VF were induced and shocked, 8 episodes for each of 3 defibrillation therapies. This resulted in 9 tested combinations of pad position and defibrillation therapy, with 80 episodes of VF for each combination. An episode consisted of 15 seconds of untreated VF, followed by a first shock and, if necessary, a repeat shock. Episodes were separated by four minutes of recovery. Both electrode pad position and therapy order were randomized by experiment. Primary outcome was defined as successful VF termination after the first shock; secondary outcome was the cumulative success of the first and second shocks. First shock efficacy varied widely across the 9 tested combinations of pad position and defibrillation therapy, ranging from 11.3% to 86.3%. When grouped by therapy, first shock efficacy varied significantly between the 3 pad positions: 38.3%, 48.3%, 36.7% (p = 0.02, ANOVA), and, when grouped by pad position, it varied significantly between therapies: 15.0%, 32.5%, 75.8% (p < 0.001, ANOVA). Cumulative 2-shock success varied significantly with therapy (p < 0.001, ANOVA) but not with pad position (p = 0.30, ANOVA). The lowest first shock success was at one position in 6 of 10 animals, at another position in 4 of 10 animals, and never at the third position. Small variations in pad placement can significantly affect defibrillation shock efficacy. However, anatomical variation between individuals and the challenging conditions of real-world resuscitations make optimal pad placement impractical. Suboptimal pad placement can be overcome with defibrillation waveform and shock dose.

Association Between Chest Compression Interruptions and Clinical Outcomes of Ventricular Fibrillation Out-of-Hospital Cardiac Arrest.

BACKGROUND: Minimizing pauses in chest compressions during cardiopulmonary resuscitation is a focus of current guidelines. Prior analyses found that prolonged pauses for defibrillation (perishock pauses) are associated with worse survival. We analyzed resuscitations to characterize the association between pauses for all reasons and both ventricular fibrillation termination and patient survival. METHODS AND RESULTS: In 319 patients with ventricular tachycardia/fibrillation out-of-hospital cardiac arrest, we analyzed recordings from all defibrillators used during resuscitation and measured durations of all cardiopulmonary resuscitation pauses. Median durations were 32 seconds (25th and 75th percentile, 22 and 52 seconds) for the longest pause for any reason, 23 seconds (25th and 75th percentile, 14 and 34 seconds) for the longest perishock pause, and 24 seconds (25th and 75th percentile, 11 and 38 seconds) for the longest nonshock pause. Multivariable regression models showed lower odds for survival per 5-second increase in the longest overall pause (odds ratio, 0.89; 95% confidence interval, 0.83-0.95), longest perishock pause (odds ratio, 0.85; 95% confidence interval, 0.77-0.93), and longest nonshock pause (odds ratio, 0.83; 95% confidence interval, 0.75-0.91). In 36% of cases, the longest pause was a nonshock pause; this subgroup had lower survival than the group in whom the longest pause was a perishock pause (27% versus 44%, respectively; P<0.01) despite a higher chest compression fraction. Preshock pauses were 8 seconds (25th and 75th percentile, 4 and 17 seconds) for shocks that terminated ventricular fibrillation and 7 seconds (25th and 75th percentile, 4 and 13 seconds) for shocks that did not (P=0.18). CONCLUSIONS: Prolonged pauses have a negative association with survival not explained by chest compression fraction or decreased ventricular fibrillation termination rate. Ventricular fibrillation termination was not the mechanism linking pause duration and survival. Strategies shortening the longest pauses may improve outcome.

Mechanical chest compressions improved aspects of CPR in the LINC trial.

AIM: We studied resuscitation process metrics in patients with out-of-hospital cardiac arrest enrolled in a randomized trial comparing one protocol designed to best use a mechanical CPR device, with another based on the 2005 European Resuscitation Council guidelines for manual CPR. METHODS: We analyzed clinical data, ECG signals, and transthoracic impedance signals for a subset of the patients in the LUCAS in Cardiac Arrest (LINC) trial, including 124 patients randomized to mechanical and 82 to manual CPR. Chest compression fraction (CCF) was defined as the fraction of time during cardiac arrest that chest compressions were administered. RESULTS: Patients in the mechanical CPR group had a higher CCF than those in the manual CPR group [0.84 (0.78, 0.91) vs. 0.79 (0.70, 0.86), p < 0.001]. The median duration of their pauses for defibrillation was also shorter [0 s (0, 6.0) vs. 10.0 s (7.0, 14.3), p < 0.001]. Compressions were interrupted for a median of 36.0 s to apply the compression device. There was no difference between groups in duration of the longest pause in compressions [32.5s vs. 26.0 s, p = 0.24], number of compressions received per minute [86.5 vs. 88.3, p = 0.47], defibrillation success rate [73.2% vs. 81.0%, p = 0.15], or refibrillation rate [74% vs. 77%, p = 0.79]. CONCLUSIONS: A protocol using mechanical chest compression devices reduced interruptions in chest compressions, and enabled defibrillation during ongoing compressions, without adversely affecting other resuscitation process metrics. Future emphasis on optimizing device deployment may be beneficial.

Will medical examination gloves protect rescuers from defibrillation voltages during hands-on defibrillation?

BACKGROUND: Continuing compressions during a defibrillation shock has been proposed as a method of reducing pauses in cardiopulmonary resuscitation (CPR) but the safety of this procedure is unproven. The medical examination gloves worn by rescuers play an important role in protecting the rescuer yet the electrical characteristics of these gloves are unknown. This study examined the response of medical examination gloves to defibrillation voltages. METHODS: Part 1 of this study measured voltage-current curves for a small sample (8) of gloves. Part 2 tested more gloves (460) to determine the voltage required to produce a specific amount of current flow. Gloves were tested at two current levels: 0.1 mA and 10 mA. Testing included four glove materials (chloroprene, latex, nitrile, and vinyl) in a single layer and double-gloved. RESULTS: All gloves tested in part 1 allowed little current to flow (<1 mA) as the voltage was increased until breakdown occurred, at which point current flow increased precipitously. In part 2, 118 of 260 (45%) single gloves and 93 of 120 (77%) double gloves allowed at least 0.1 mA of current flow at voltages within the external defibrillation voltage range. Also, 6 of 80 (7.5%) single gloves and 5 of 80 (6.2%) double gloves allowed over 10 mA. CONCLUSIONS: Few of the gloves tested limited the current to levels proven to be safe. A lack of sensation during hands-on defibrillation does not guarantee that a safety margin exists. As such, we encourage rescuers to minimize rather than eliminate the pause in compressions for defibrillation.

Assessment of CPR interruptions from transthoracic impedance during use of the LUCAS™ mechanical chest compression system.

BACKGROUND: Quality of cardiopulmonary resuscitation (CPR) is a key determinant of outcome following out-of-hospital cardiac arrest (OHCA). Recent evidence shows manual chest compressions are typically too shallow, interruptions are frequent and prolonged, and incomplete release between compressions is common. Mechanical chest compression systems have been developed as adjuncts for CPR but interruption of CPR during their use is not well documented. AIM: Analyze interruptions of CPR during application and use of the LUCAS™ chest compression system. METHODS: 54 LUCAS 1 devices operated on compressed air, deployed in 3 major US emergency medical services systems, were used to treat patients with OHCA. Electrocardiogram and transthoracic impedance data from defibrillator/monitors were analyzed to evaluate timing of CPR. Separately, providers estimated their CPR interruption time during application of LUCAS, for comparison to measured application time. RESULTS: In the 32 cases analyzed, compressions were paused a median of 32.5s (IQR 25-61) to apply LUCAS. Providers' estimates correlated poorly with measured pause length; pauses were often more than twice as long as estimated. The average device compression rate was 104/min (SD 4) and the average compression fraction (percent of time compressions were occurring) during mechanical CPR was 0.88 (SD 0.09). CONCLUSIONS: Interruptions in chest compressions to apply LUCAS can be <20s but are often much longer, and users do not perceive pause time accurately. Therefore, we recommend better training on application technique, and implementation of systems using impedance data to give users objective feedback on their mechanical chest compression device use.

Time in recurrent ventricular fibrillation and survival after out-of-hospital cardiac arrest.

BACKGROUND: Current resuscitation guidelines (2005 guidelines [G2005]) accelerate ventricular fibrillation (VF) recurrence. We investigated whether patients resuscitated under G2005 spend more time in VF and have better survival rates than patients treated under the 2000 guidelines (G2000). METHODS AND RESULTS: We analyzed continuous ECG recordings of out-of-hospital cardiac arrests prospectively collected from January 2006 to January 2008. Patients treated according to G2000 (n=282) or G2005 (n=240) with VF as initial rhythm were included. We measured the total time a patient was in recurrent VF (the sum of all intervals from each onset of recurrent VF to each next successful shock) and the time a patient was in initial VF (time interval from rescuer arrival to first effective shock). The primary outcome measure was neurologically intact survival to discharge. The median time in recurrent VF was 2.7 minutes (quartile 1 to 3, 0.4 to 9.0 minutes) under G2000 versus 4.0 minutes (quartile 1 to 3, 0.2 to 11.6 minutes) under G2005 (P=0.03). Median time in initial VF was 2.7 minutes (quartile 1 to 3, 1.7 to 4.3 minutes) versus 3.9 minutes (quartile 1 to 3, 2.3 to 6.5 minutes), respectively (P<0.001). Increased time in recurrent VF was significantly associated with decreased neurologically intact survival in both G2000 use (odds ratio, 0.92; 95% confidence interval, 0.87 to 0.97; P=0.001) and G2005 use (odds ratio, 0.94; 95% confidence interval, 0.90 to 0.99; P=0.02). Neurologically intact survival decreased significantly with increasing time in initial VF under G2000 (odds ratio, 0.86; 95% confidence interval, 0.74 to 0.99; P=0.04). This observation was nonexistent in patients treated under G2005. Neurologically intact survival was 29% (82 of 282) under G2000 versus 27% (65 of 240) under G2005 (P=0.61). CONCLUSIONS: With G2005, the time in recurrent VF remains associated with worse outcome. Studies of immediate defibrillation for recurrent VF are warranted.

DEFI 2005: a randomized controlled trial of the effect of automated external defibrillator cardiopulmonary resuscitation protocol on outcome from out-of-hospital cardiac arrest.

BACKGROUND: Using automated external defibrillators (AEDs) that implement the Guidelines 2000 resuscitation protocol constrains administration of cardiopulmonary resuscitation (CPR) to <50% of AED connection time. We tested a different AED protocol aimed at increasing the CPR administered to patients with out-of-hospital cardiac arrest. METHODS AND RESULTS: In a randomized controlled trial, patients with out-of-hospital cardiac arrest requiring defibrillation were treated with 1 of 2 AED protocols. In the control protocol, based on Guidelines 2000, sequences of up to 3 stacked countershocks were delivered, with rhythm analyses initially and after the first and second shocks. The study protocol featured 1 minute of CPR before the first shock, shorter CPR interruptions before and after each shock, and no stacked shocks. The primary end point was survival to hospital admission. Of 5107 out-of-hospital cardiac arrest patients connected to an AED, 1238 required defibrillation, and 845 were included in the final analysis. Study patients (n=421) had shorter preshock pauses (9 versus 19 seconds; P<0.001), had shorter postshock pauses (11 versus 33 seconds; P<0.001), and received more CPR (61% versus 48%; P<0.001) and fewer shocks (2.5 versus 2.9; P<0.001) than control patients (n=424). Similar proportions survived to hospital admission (43.2% versus 42.7%; P=0.87), survived to hospital discharge (13.3% versus 10.6%; P=0.19), achieved return of spontaneous circulation before physician arrival (47.0% versus 48.6%; P=0.65), and survived to 1 year (P=0.77). CONCLUSIONS: Following prompts from AEDs programmed with a protocol similar to Guidelines 2005, firefighters shortened pauses in CPR and improved overall hands-on time, but survival to hospital admission of patients with ventricular fibrillation out-of-hospital cardiac arrest did not improve. Clinical Trial Registration- http://www.clinicaltrials.gov. Unique identifier: NCT00139542.

Defibrillation probability and impedance change between shocks during resuscitation from out-of-hospital cardiac arrest.

OBJECTIVE: Technical data now gathered by automated external defibrillators (AEDs) allows closer evaluation of the behavior of defibrillation shocks administered during out-of-hospital cardiac arrest. We analyzed technical data from a large case series to evaluate the change in transthoracic impedance between shocks, and to assess the heterogeneity of the probability of successful defibrillation across the population. METHODS: We analyzed a series of consecutive cases where AEDs delivered shocks to treat ventricular fibrillation (VF) during out-of-hospital cardiac arrest. Impedance measurements and VF termination efficacy were extracted from electronic records downloaded from biphasic AEDs deployed in three EMS systems. All patients received 200J first shocks; second shocks were 200J or 300J, depending on local protocols. Results presented are median (25th, 75th percentiles). RESULTS: Of 863 cases with defibrillation shocks, 467 contained multiple shocks because the first shock failed to terminate VF (n=61) or VF recurred (n=406). Defibrillation efficacy of subsequent shocks was significantly lower in patients that failed to defibrillate on first shock than in patients that did defibrillate on first shock (162/234=69% vs. 955/1027=93%; p<0.0001). The failed VF terminations were distributed heterogeneously across the population; 5% of patients accounted for 71% of failed shocks. Shock impedance decreased by 1% [0%, 4%] and peak current increased by 1% [0%, 4%] between 200J first and 200J second shocks. Shock impedance decreased 4% [2%, 6%] and current increased 27% [25%, 29%] between 200J first and 300J second shocks. In all 499 pairs of same-energy consecutive shocks, impedance changed by less than 1% in 226 (45%), increased >1% in 124 (25%) and decreased >1% in 149 (30%). CONCLUSIONS: Impedance change between consecutive shocks is minimal and inconsistent. Therefore, to increase current of a subsequent shock requires an increase of the energy setting. Distribution of failed shocks is far from random. First shock defibrillation failure is often predictive of low efficacy for subsequent shocks.

Effect of timing and duration of a single chest compression pause on short-term survival following prolonged ventricular fibrillation.

BACKGROUND: Pauses during chest compressions are thought to have a detrimental effect on resuscitation outcome. The Guidelines 2005 have recently eliminated the post-defibrillation pause. Previous animal studies have shown that multiple pauses of increasing duration decrease resuscitation success. We investigated the effect of varying the characteristics of a single pause near defibrillation on resuscitation outcome. METHODS: Part A: 48 swine were anesthetized, fibrillated for 7min and randomized. Chest compressions were initiated for 90s followed by defibrillation and then resumption of chest compressions. Four groups were studied-G2000: 40s pause beginning 20s before, and ending 20s after defibrillation, A1: a 20s pause just before defibrillation, A2: a 20s pause ending 30s prior to defibrillation, and group A3: a 10s pause ending 30s prior to defibrillation. Part B: 12 swine (Group B) were studied with a protocol identical to Part A but with no pause in chest compressions. Primary endpoint was survival to 4h. RESULTS: The survival rate was significantly higher for groups A1, A2, A3, and B (5/12, 7/12, 5/12, and 5/12 survived) than for the G2000 group (0/12, p<0.05). Survival did not differ significantly among groups A1, A2, A3, and B. CONCLUSIONS: These results suggest that the Guidelines 2005 recommendation to omit the post-shock pulse check and immediately resume chest compressions may be an important resuscitation protocol change. However, these results also suggest that clinical maneuvers further altering a single pre-shock chest compression pause provide no additional benefit.

Recurrent ventricular fibrillation during advanced life support care of patients with prehospital cardiac arrest.

AIM OF THE STUDY: The response of recurrent episodes of ventricular fibrillation (VF) to defibrillation shocks has not been systematically studied. We analyzed outcomes from countershocks delivered for VF during advanced life support (ALS) care of patients with out-of-hospital cardiac arrest. METHODS: Cohort of patients with prehospital cardiac arrest presenting with VF, treated by ALS ambulance staff following ERC Guidelines 2000. Biphasic defibrillators provided shocks increasing from 200 to 360J. Recorded signals were analyzed to determine, for each shock, if VF was terminated and if a sustained organized rhythm was restored within 60s. RESULTS: In 465 of the 467 patients enrolled, the initial VF episode was terminated within three shocks: 92%, 61%, and 83% responded to 200J first, 200J second and 360J third shocks, respectively. VF recurred in 48% of patients within 2min of the first episode, and in 74% sometime during prehospital care. In the 175 patients experiencing five or more VF episodes, single shock VF termination dropped from the first to the fifth episode (90-80%, p<0.001) without change in transthoracic impedance, yet the proportion returning to organized rhythms increased (11-42%, p<0.0001). CONCLUSIONS: Repeated refibrillation is common in patients with VF cardiac arrest. The likelihood of countershocks to terminate VF declines for repeated episodes of VF, yet shocks that terminate these episodes result increasingly in a sustained organized rhythm.

Attenuating the defibrillation dosage decreases postresuscitation myocardial dysfunction in a swine model of pediatric ventricular fibrillation.

OBJECTIVE: The optimal biphasic defibrillation dose for children is unknown. Postresuscitation myocardial dysfunction is common and may be worsened by higher defibrillation doses. Adult-dose automated external defibrillators are commonly available; pediatric doses can be delivered by attenuating the adult defibrillation dose through a pediatric pads/cable system. The objective was to investigate whether unattenuated (adult) dose biphasic defibrillation results in greater postresuscitation myocardial dysfunction and damage than attenuated (pediatric) defibrillation. DESIGN: Laboratory animal experiment. SETTING: University animal laboratory. SUBJECTS: Domestic swine weighing 19 +/- 3.6 kg. INTERVENTIONS: Fifty-two piglets were randomized to receive biphasic defibrillation using either adult-dose shocks of 200, 300, and 360 J or pediatric-dose shocks of approximately 50, 75, and 85 J after 7 mins of untreated ventricular fibrillation. Contrast left ventriculograms were obtained at baseline and then at 1, 2, 3, and 4 hrs postresuscitation. Postresuscitation left ventricular ejection fraction and cardiac troponins were evaluated. MEASUREMENTS AND MAIN RESULTS: By design, piglets in the adult-dose group received shocks with more energy (261 +/- 65 J vs. 72 +/- 12 J, p < .001) and higher peak current (37 +/- 8 A vs. 13 +/- 2 A, p < .001) at the largest defibrillation dose needed. In both groups, left ventricular ejection fraction was reduced significantly at 1, 2, and 4 hrs from baseline and improved during the 4 hrs postresuscitation. The decrease in left ventricular ejection fraction from baseline was greater after adult-dose defibrillation. Plasma cardiac troponin levels were elevated 4 hrs postresuscitation in 11 of 19 adult-dose piglets vs. four of 20 pediatric-dose piglets (p = .02). CONCLUSIONS: Unattenuated adult-dose defibrillation results in a greater frequency of myocardial damage and worse postresuscitation myocardial function than pediatric doses in a swine model of prolonged out-of-hospital pediatric ventricular fibrillation cardiac arrest. These data support the use of pediatric attenuating electrodes with adult biphasic automated external defibrillators to defibrillate children.