Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest.

INTRODUCTION: Little is known about the impact of tidal volumes delivered by emergency medical services (EMS) to adult patients with out-of-hospital cardiac arrest (OHCA). A large urban EMS system changed from standard adult ventilation bags to small adult bags. We hypothesized that the incidence of return of spontaneous circulation (ROSC) at the end of EMS care would increase after this change. METHODS: We performed a retrospective analysis evaluating adults treated with advanced airway placement for nontraumatic OHCA between January 1, 2015 and December 31, 2021. We compared rates of ROSC, ventilation rate, and mean end tidal carbon dioxide (ETCO2) by minute before and after the smaller ventilation bag implementation using linear and logistic regression. RESULTS: Of the 1,994 patients included, 1,331 (67%) were treated with a small adult bag. ROSC at the end of EMS care was lower in the small bag cohort than the large bag cohort, 33% vs 40% (p = 0.003). After adjustment, small bag use was associated with lower odds of ROSC at the end of EMS care [OR 0.74, 95% CI 0.61 - 0.91]. Ventilation rates did not differ between cohorts. ETCO2 values were lower in the large bag cohort (33.2 ± 17.2 mmHg vs. 36.9 ± 19.2 mmHg, p < 0.01). CONCLUSION: Use of a small adult bag during OHCA was associated with lower odds of ROSC at the end of EMS care. The effects on acid base status, hemodynamics, and delivered minute ventilation remain unclear and warrant additional study.

Metronome use improves achievement of a target compression rate in out-of-hospital cardiac arrest: A retrospective analysis.

Aim: The aim of this study was to evaluate chest compression rates (CCR) with and without the use of a metronome during treatment of out-of-hospital cardiac arrest (OHCA). Methods: We performed a retrospective cohort investigation of non-traumatic OHCA cases treated by Seattle Fire Department from January 1, 2013, to December 31, 2019. The exposure was a metronome running during CPR at a rate of 110 beats per minute. The primary outcome was the median CCR for all periods of CPR with a metronome compared to periods without a metronome. Results: We included 2,132 OHCA cases with 32,776 minutes of CPR data; 15,667 (48%) minutes had no metronome use, and 17,109 (52%) minutes had a metronome used. Without a metronome, the median CCR was 112.8 per minute with an interquartile range of 108.4 - 119.1, and 27% of minutes were above 120 or less than 100. With a metronome, the median CCR was 110.5 per minute with an interquartile range of 110.0-112.0, and less than 4% of minutes were above 120 or less than 100. The compression rate was 109, 110, or 111 in 62% of minutes with a metronome compared to 18% of minutes with no metronome. Conclusion: The use of a metronome during CPR resulted in increased compliance to a predetermined compression rate. Metronomes are a simple tool that improves achievement of a target compression rate with little variance from that target.

Increase in end-tidal carbon dioxide after defibrillation predicts sustained return of spontaneous circulation during out-of-hospital cardiac arrest.

INTRODUCTION: Guidelines recommend monitoring end-tidal carbon dioxide (ETCO2) during out-of-hospital cardiac arrest (OHCA), though its prognostic value is poorly understood. This study investigated the relationship between ETCO2 and return of spontaneous circulation (ROSC) after defibrillation in intubated non-traumatic OHCA patients. METHODS: This retrospective, observational cohort analysis included adult OHCA patients who received a defibrillation shock during treatment by an urban EMS agency from 2015 to 2021. Peak ETCO2 values were determined for the 90-second periods before and after the first defibrillation in an intubated patient (shock of interest [SOI]). Values were analyzed for association between the change in ETCO2 from pre- to post-shock and the presence of ROSC on the subsequent pulse check. RESULTS: Of 518 eligible patients, mean age was 61, 72% were male, 50% had a bystander-witnessed arrest, and 62% had at least one episode of ROSC. The most common arrest etiology was medical (92%). Among all patients, peak ETCO2 during resuscitation prior to SOI was 36.8 mmHg (18.6). ETCO2 increased in patients who achieved ROSC immediately after SOI (from 38.3 to 47.6 mmHg; +9.3 CI: 6.5, 12.1); patients with sustained ROSC experienced the greatest increase in ETCO2 after SOI (from 37.8 to 48.2 mmHg; +10.4 CI: 7.2, 13.6), while ETCO2 in patients who did not achieve ROSC after SOI rose (from 36.4 to 37.8 mmHg; +1.4 CI: -0.1, 2.8). CONCLUSIONS: ETCO2 rises after defibrillation in most patients during cardiac arrest. Patients with sustained ROSC experience larger rises, though the majority experience rises of less than 10 mmHg.

Optimizing Physiology During Prehospital Airway Management: An NAEMSP Position Statement and Resource Document.

Airway management is a critical component of resuscitation but also carries the potential to disrupt perfusion, oxygenation, and ventilation as a consequence of airway insertion efforts, the use of medications, and the conversion to positive-pressure ventilation. NAEMSP recommends:Airway management should be approached as an organized system of care, incorporating principles of teamwork and operational awareness.EMS clinicians should prevent or correct hypoxemia and hypotension prior to advanced airway insertion attempts.Continuous physiological monitoring must be used during airway management to guide the timing of, limit the duration of, and inform decision making during advanced airway insertion attempts.Initial and ongoing confirmation of advanced airway placement must be performed using waveform capnography. Airway devices must be secured using a reliable method.Perfusion, oxygenation, and ventilation should be optimized before, during, and after advanced airway insertion.To mitigate aspiration after advanced airway insertion, EMS clinicians should consider placing a patient in a semi-upright position.When appropriate, patients undergoing advanced airway placement should receive suitable pharmacologic anxiolysis, amnesia, and analgesia. In select cases, the use of neuromuscular blocking agents may be appropriate.

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.

Evaluation of Physiologic Alterations during Prehospital Paramedic-Performed Rapid Sequence Intubation.

OBJECTIVE: Physiologic alterations during rapid sequence intubation (RSI) have been studied in several emergency airway management settings, but few data exist to describe physiologic alterations during prehospital RSI performed by ground-based paramedics. To address this evidence gap and provide guidance for future quality improvement initiatives in our EMS system, we collected electronic monitoring data to evaluate peri-intubation vital signs changes occurring during prehospital RSI. METHODS: Electronic patient monitor data files from cases in which paramedic RSI was attempted were prospectively collected over a 15-month study period to supplement the standard EMS patient care documentation. Cases were analyzed to identify peri-intubation changes in oxygen saturation, heart rate, and blood pressure. RESULTS: Data from 134 RSI cases were available for analysis. Paramedic-assigned prehospital diagnostic impression categories included neurologic (42%), respiratory (26%), toxicologic (22%), trauma (9%), and cardiac (1%). The overall intubation success rate (95%) and first-attempt success rate (82%) did not differ across diagnostic impression categories. Peri-intubation desaturation (SpO2 decrease to below 90%) occurred in 43% of cases, and 70% of desaturation episodes occurred on first-attempt success. The incidence of desaturation varied among patient categories, with a respiratory diagnostic impression associated with more frequent, more severe, and more prolonged desaturations, as well as a higher incidence of accompanying cardiovascular instability. Bradycardia (HR decrease to below 60 bpm) occurred in 13% of cases, and 60% of bradycardia episodes occurred on first-attempt success. Hypotension (systolic blood pressure decrease to below 90 mmHg) occurred in 7% of cases, and 63% of hypotension episodes occurred on first-attempt success. Peri-intubation cardiac arrest occurred in 2 cases, one of which was on first-attempt success. Only 11% of desaturations and no instances of bradycardia were reflected in the standard EMS patient care documentation. CONCLUSIONS: In this study, the majority of peri-intubation physiologic alterations occurred on first-attempt success, highlighting that first-attempt success is an incomplete and potentially deceptive measure of intubation quality. Supplementing the standard patient care documentation with electronic monitoring data can identify unrecognized physiologic instability during prehospital RSI and provide valuable guidance for quality improvement interventions.

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.

A quality improvement initiative to optimize use of a mechanical chest compression device within a high-performance CPR approach to out-of-hospital cardiac arrest resuscitation.

BACKGROUND: Minimizing the chest compression pause associated with application of a mechanical CPR device is a key component of optimal integration into the overall resuscitation process. As part of a multi-agency implementation project, Anchorage Fire Department deployed LUCAS CPR devices on BLS and ALS fire apparatus for initiation early in resuscitation efforts. A 2012 report identified the pause interval for device application as a key opportunity for quality improvement (QI). In early 2013 we began a QI initiative to reduce device application time interval and optimize the overall CPR process. To assess QI initiative effectiveness, we compared key CPR process metrics from before to during and after its implementation. METHODS: We included all cases of EMS-treated out-of-hospital cardiac arrest during 2012 and 2013 in which a mechanical CPR device was used and the defibrillator electronic record was available. Continuous ECG and impedance data were analyzed to measure chest compression fraction, duration of the pause from last manual to first mechanical compression, and duration of the longest overall pause in the resuscitation effort. RESULTS: Compared to cases from 2012 (n = 61), median duration of the pause prior to first mechanical compression for cases from 2013 (n = 71) decreased from 21 (15, 31) to 7 (4, 12)s (p < 0.001), while median chest compression fraction increased from 0.90 (0.88, 0.93) to 0.95 (0.93, 0.96) (p < 0.001). Median duration of the longest pause decreased from 25 (20, 35) to 13 (10, 20)s (p < 0.001), while the proportion of cases where the longest pause was for mechanical CPR application decreased from 74% to 31% (p < 0.001). CONCLUSIONS: Our QI initiative substantially reduced the duration of the pause prior to first mechanical compression. Combined with the simultaneous significant increase in compression fraction and significant decrease in duration of the longest pause, this finding strongly suggests a large improvement in mechanical CPR device application efficiency within an overall high-performance CPR process.

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.

BIPHASIC Trial: a randomized comparison of fixed lower versus escalating higher energy levels for defibrillation in out-of-hospital cardiac arrest.

BACKGROUND: There is little clear evidence as to the optimal energy levels for initial and subsequent shocks in biphasic waveform defibrillation. The present study compared fixed lower- and escalating higher-energy regimens for out-of-hospital cardiac arrest. METHODS AND RESULTS: The Randomized Controlled Trial to Compare Fixed Versus Escalating Energy Regimens for Biphasic Waveform Defibrillation (BIPHASIC Trial) was a multicenter, randomized controlled trial of 221 out-of-hospital cardiac arrest patients who received > or = 1 shock given by biphasic automated external defibrillator devices that were randomly programmed to provide, blindly, fixed lower-energy (150-150-150 J) or escalating higher-energy (200-300-360 J) regimens. Patient mean age was 66.0 years; 79.6% were male. The cardiac arrest was witnessed in 63.8%; a bystander performed cardiopulmonary resuscitation in 23.5%; and initial rhythm was ventricular fibrillation/ventricular tachycardia in 92.3%. The fixed lower- and escalating higher-energy regimen cases were similar for the 106 multishock patients and for all 221 patients. In the primary analysis in multishock patients, conversion rates differed significantly (fixed lower, 24.7%, versus escalating higher, 36.6%; P=0.035; absolute difference, 11.9%; 95% CI, 1.2 to 24.4). Ventricular fibrillation termination rates also were significantly different between groups (71.2% versus 82.5%; P=0.027; absolute difference, 11.3%; 95% CI, 1.6 to 20.9). For the secondary analysis of first shock success, conversion rates were similar between the fixed lower and escalating higher study groups (38.4% versus 36.7%; P=0.92), as were ventricular fibrillation termination rates (86.8% versus 88.8%; P=0.81). There were no distinguishable differences between regimens for survival outcomes or adverse effects. CONCLUSIONS: This is the first randomized trial to compare fixed lower and escalating higher biphasic energy regimens in out-of-hospital cardiac arrest, and it demonstrated higher rates of ventricular fibrillation conversion and termination with an escalating higher-energy regimen for patients requiring multiple shocks. These results suggest that patients in ventricular fibrillation benefit from higher biphasic energy levels if multiple defibrillation shocks are required.

A percutaneous catheter-based system for the measurement of potential gradients applicable to the study of transthoracic defibrillation.

BACKGROUND: The local electric (E) field or potential gradient produced by a shock reliably predicts VF termination. In this study we evaluated a multiple electrode, catheter-based device for closed-chest 3D measurements of E field from transthoracic defibrillation shocks. METHODS: Catheters with multiple electrodes on the tip were placed in intracardiac locations in anesthetized swine. An empirically derived calibration matrix and custom microprocessor was used to transform simultaneously measured voltages into orthogonal E field vector components. E fields produced in six intracardiac locations by 30 and 300 J shocks were compared in eight animals. Correlations were determined for measured current and E field at various shock strengths at two different transthoracic impedances in five additional animals. VF was induced in 12 animals and E field measured during defibrillation attempts. RESULTS: The E field measurements resulting for 30 J transthoracic shocks were not significantly different among different intracardiac sites. At 300 J, however, significant differences were observed between sites with the greatest intensities recorded in the coronary sinus and right ventricle. Within animals, the variability of the measurement at each site was small, ranging from 2.8 +/- 1.6% to 5.7 +/- 4.5%. Significant correlations (P < 0.001) between measured E field and peak current were observed at native impedance (34 +/- 4 Omega, r = 0.81) and at adjusted impedance (76 +/- 4 Omega, r = 0.78) with transthoracic shocks of 200, 300, and 360 J. In VF studies, the probability of defibrillation was closely fit by a sigmoidal dose response curve in the coronary sinus E field with an approximate threshold of 4.7 V/cm with 50% defibrillation success at 9.3 V/cm. CONCLUSIONS: The measured intracardiac E field variability within animals and at a specific site was small, exhibiting a median value of 5.1%, contrasted to median variabilities across animals of 5-11% suggesting the capacity of this measurement system to provide subject specific information on the distribution of E fields. The measured E field magnitudes across animals in the coronary sinus were linearly correlated with applied shock current with a very strong linear relation to effective shock voltage observed in vitro in a saline tank. When evaluated as a predictor of shock success, the observed values were consistent with previously reported critical fields. This technique may be of value in evaluating waveforms for transthoracic defibrillation as well as electrode size, placement, and composition.

Management of cervical weakness based on the measurement of cervical resistance index.

OBJECTIVE: To assess the value of measuring cervical resistance index (CRI) as an aid to selecting patients with a history of spontaneous mid-trimester miscarriage for cervical cerclage in subsequent pregnancies. STUDY DESIGN: An observational study of 175 patients with a history of one or more spontaneous mid-trimester losses and 123 non-pregnant women who had CRI measurements performed while undergoing routine gynaecological surgery. Those women whose CRI indicated an incompetent cervix were recommended for cervical cerclage in future pregnancies while women with a normal CRI were recommended for conservative management without cerclage. RESULTS: The median CRI in the 123 control women was 38.26 N while the median CRI in the study group was 17.00 N. In 62 of the 175 study women (35%) the CRI findings were at variance with the history of previous mid-trimester loss; 30 (16.6%) were deemed competent on CRI whereas the history suggested incompetence and 32 (18.4%) were incompetent on CRI while the history suggested that the cervix should be competent. The 175 study women had had 486 previous pregnancies with a successful outcome in 27.4% of the pregnancies. Ninety-four patients have now had 148 pregnancies with a successful outcome in 75.8% of the pregnancies. CONCLUSIONS: Non-pregnant women with a history of spontaneous mid-trimester miscarriage have a significantly lower cervical resistance index than parous women who have not suffered mid-trimester loss. In 35% of patients the CRI was at variance with the history of the previous loss. CRI may be a useful technique to aid the diagnosis of cervical weakness allowing a rational selection for treatment with prophylactic cervical cerclage.

Definition of successful defibrillation.

OBJECTIVES: The definition of defibrillation shock "success" endorsed by the International Liaison Committee on Resuscitation since the publication of Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiac Care has been removal of ventricular fibrillation at 5 secs after shock delivery. Although this success criterion provides a direct assessment of the primary task of a shock, it may not be the only clinically useful measure of shock outcome. We evaluated a different defibrillation success criterion to determine whether it could provide additional insight into the relative performance of different defibrillation shocks. DESIGN: A randomized study comparing monophasic and biphasic waveform shocks is reported with return of organized rhythm as the primary outcome measure of defibrillation success. PATIENTS: A total of 120 patients with out-of-hospital ventricular fibrillation as the first recorded rhythm were treated with defibrillation with automated external defibrillators. MEASUREMENTS AND MAIN RESULTS: Return of organized rhythm (two QRS complexes, <5 secs apart, <60 secs after defibrillation) was achieved in 31 monophasic shock (45%) and 35 biphasic shock (69%) patients (relative risk, 1.53, 95% confidence interval, 1.11-2.10). Logistic regression analysis revealed that shock waveform was the strongest independent predictor of return of organized rhythm (odds ratio, 4.0; 95% confidence interval, 1.67-10.0). Defibrillation success with the conventional International Liaison Committee on Resuscitation criterion was very high (91% and 98%, respectively) and not significantly different between groups. CONCLUSIONS: Return of organized rhythm proved to be a more sensitive measure of relative defibrillation shock performance than the conventional shock success criterion. Inclusion of return of organized rhythm as an end point in future clinical research could help discern more subtle defibrillation shock effects and contribute to further optimization of defibrillation technology.

Better outcome after pediatric defibrillation dosage than adult dosage in a swine model of pediatric ventricular fibrillation.

OBJECTIVES: This study was designed to compare outcome after adult defibrillation dosing versus pediatric dosing in a piglet model of prolonged prehospital ventricular fibrillation (VF). BACKGROUND: Weight-based 2 to 4 J/kg monophasic defibrillation dosing is recommended for children in VF, but impractical for automated external defibrillator (AED) use. Present AEDs can only provide adult shock doses or newly developed attenuated adult doses intended for children. A single escalating energy sequence (50/75/86 J) of attenuated adult-dose biphasic shocks (pediatric dosing) is at least as effective as escalating monophasic weight-based dosing for prolonged VF in piglets, but this approach has not been compared to standard adult biphasic dosing. METHODS: Following 7 min of untreated VF, piglets weighing 13 to 26 kg (19 +/- 1 kg) received either biphasic 50/75/86 J (pediatric dose) or biphasic 200/300/360 J (adult dose) therapies during simulated prehospital life support. RESULTS: Return of spontaneous circulation was attained in 15 of 16 pediatric-dose piglets and 14 of 16 adult-dose piglets. Four hours postresuscitation, pediatric dosing resulted in fewer elevations of cardiac troponin T (0 of 12 piglets vs. 6 of 11 piglets, p = 0.005) and less depression of left ventricular ejection fraction (p < 0.05). Most importantly, more piglets survived to 24 h with good neurologic scores after pediatric shocks than adult shocks (13 of 16 piglets vs. 4 of 16 piglets, p = 0.004). CONCLUSIONS: In this model, pediatric shocks resulted in superior outcome compared with adult shocks. These data suggest that adult defibrillation dosing may be harmful to pediatric patients with VF and support the use of attenuating electrodes with adult biphasic AEDs to defibrillate children.

Intracardiac voltage gradients during transthoracic defibrillation: implications for postshock myocardial injury.

UNLABELLED: In-vitro studies indicate that the electric-field intensity, or voltage gradient (VG), generated by a defibrillation shock is a determinant of defibrillation success as well as potential shock-induced cardiac injury. It is not clear how common descriptors of shock dose, e.g., joules (J), relate to VGs. OBJECTIVES: To assess the relationships between shock energy descriptors and VG. METHODS: One monophasic and three biphasic waveforms were compared using transthoracic shocks and standard electrodes in five swine. VG measurements via intracavitary multielectrode-tipped catheters were compared with delivered energy and peak current. Shock variables were recorded at native transthoracic impedance and an adjusted impedance approximating that of typical humans. RESULTS: For shocks at the same energy setting, peak current and VGs varied widely among the four defibrillators. At simulated human impedance (75 Omega), shocks at each device's maximum energy setting produced similar VGs among the three biphasic defibrillators, despite different delivered energies. For both native impedance (35 Omega) and at 75 Omega, VG correlated with peak current (r = 0.81 and 0.77, respectively) but not energy setting (r = 0.61, 0.52) or delivered energy (r = 0.58, 0.56). At the maximum energy setting of each device, maximum recorded VGs for both monophasic (33 V/cm) and biphasic (24 V/cm) defibrillators were less than those reported to cause myocardial injury (>60 to 80 V/cm). CONCLUSIONS: Energy descriptors correlate poorly to actual shock intensities. When compared with reported VG thresholds of myocardial injury, this study suggests that risk of injury from critically strong VGs is low for all of these defibrillators and equivalent among tested biphasic waveforms.

Efficacy of lower-energy biphasic shocks for transthoracic defibrillation: a follow-up clinical study.

OBJECTIVE: This clinical study prospectively evaluated the first-shock defibrillation efficacy of 150-joule impedance-compensated, 200-microF biphasic truncated exponential (BTE) shocks in patients with electrically-induced ventricular fibrillation (VF), and compared it with a historical control group treated with 200-J monophasic damped sine (MDS) shocks. METHODS: Ventricular tachyarrhythmias were induced in patients undergoing electrophysiologic (EP) testing for ventricular arrhythmias or testing of an implantable cardioverter-defibrillator (ICD). A 150-J shock was delivered as the primary therapy to terminate induced arrhythmias in the EP group, and as a "rescue" shock when a single ICD shock failed to terminate the arrhythmias in the ICD group. RESULTS: Ninety-six patients received study shocks. The preshock rhythm was classified as VF in 77 patients and as ventricular tachycardia (VT) in 19 patients. First-shock success rates for VF and VT were 75 out of 77 (97.4%) and 19 out of 19 (100%) for the 150-J BTE compared with the historical control rates of 61 out of 68 (89.7%) and 29 out of 31 (94%) for 200-J MDS. The first-shock success rate for VF treated with 150-J BTE was technically equivalent to that of 200-J MDS (p=0.001). The transthoracic impedance did not vary between groups, yet the peak current delivered by the 150-J BTE shock was about 50% lower. CONCLUSIONS: This study demonstrated that 150-J shocks of this impedance-compensated, 200-microF BTE waveform provided very high efficacy for defibrillation of short duration, electrically-induced VF. These lower-energy biphasic shocks had a success rate equivalent to that of 200-J MDS shocks, and they provided this efficacy while exposing patients to much less current than the monophasic shocks.