Why do chest compressions aid delayed defibrillation?

Hemodynamic rescue and ECG stability during chest compressions using adenosine and lidocaine after 8-minute asphyxial hypoxia in the rat

INTRODUCTION

Sudden cardiac death generally arises from either ventricular fibrillation or asphyxial hypoxia. In an effort to translate the cardioprotective effects of adenosine and lidocaine (AL) from hemorrhagic shock to cardiopulmonary resuscitation, we examined the effect of AL on hemodynamics and electrocardiogram (ECG) stability in the rat model of asphyxial hypoxia.

METHODS

Male Sprague-Dawley rats were randomly assigned to 1 of 4 groups (n = 8): saline (SAL), adenosine (ADO), lidocaine (LIDO), and AL. Cardiac arrest (mean arterial pressure <10 mm Hg) was induced by clamping the ventilator line for 8 minutes. A 0.5-mL intravenous drug bolus was injected followed by chest compressions (300 min(-1)), which were repeated every 5 minutes for 1 hour.

RESULTS

Return of spontaneous circulation was achieved in 5 SAL (62.6%), 4 ADO (50%), 7 LIDO (87.5%), and 8 AL rats (100%) within 5 minutes but could not be sustained. During chest compressions, mean arterial pressure was consistently higher in the AL-treated rats compared with all groups (P < .05; 35-45 and 55 minutes) followed by the LIDO group and was lowest in the ADO and SAL groups (P < .05). Systolic pressure followed a similar pattern. In addition, diastolic pressure in the AL-treated rats was significantly higher from 25 to 60 minutes than LIDO and ADO alone or SAL, and heart rate was 30% to 40% lower. Improved ECG rhythm and R-R variability were apparent in AL-treated rats during early compressions and hands-off intervals.

CONCLUSIONS

We conclude that a small bolus of 0.9% NaCl AL improved hemodynamics with possible diastolic rescue and ECG stabilization during chest compressions compared with ADO, LIDO, or SAL controls.

Use of cardiocerebral resuscitation or AHA/ERC 2005 Guidelines is associated with improved survival from out-of-hospital cardiac arrest: a systematic review and meta-analysis

OBJECTIVE

To determine whether the use of cardiocerebral resuscitation (CCR) or AHA/ERC 2005 Resuscitation Guidelines improved patient outcomes from out-of-hospital cardiac arrest (OHCA) compared to older guidelines.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

MEDLINE, EMBASE, Web of Science and the Cochrane Library databases. We also hand-searched study references and consulted experts.

STUDY SELECTION

Design: randomised controlled trials and observational studies.

POPULATION

OHCA patients, age >17 years.

COMPARATORS

'Control' protocol versus 'Study' protocol. 'Control' protocol defined as AHA/ERC 2000 Guidelines for cardiopulmonary resuscitation (CPR). 'Study' protocol defined as AHA/ERC 2005 Guidelines for CPR, or a CCR protocol.

OUTCOME

Survival to hospital discharge.

QUALITY

High-quality or medium-quality studies, as measured by the Newcastle Ottawa Scale using predefined categories.

RESULTS

Twelve observational studies met inclusion criteria. All the three studies using CCR demonstrated significantly improved survival compared to use of AHA 2000 Guidelines, as did five of the nine studies using AHA/ERC 2005 Guidelines. Pooled data demonstrate that use of a CCR protocol has an unadjusted OR of 2.26 (95% CI 1.64 to 3.12) for survival to hospital discharge among all cardiac arrest patients. Among witnessed ventricular fibrillation/ventricular tachycardia (VF/VT) patients, CCR increased survival by an OR of 2.98 (95% CI 1.92 to 4.62). Studies using AHA/ERC 2005 Guidelines showed an overall trend towards increased survival, but significant heterogeneity existed among these studies.

CONCLUSIONS

We demonstrate an association with improved survival from OHCA when CCR protocols or AHA/ERC 2005 Guidelines are compared to use of older guidelines. In the subgroup of patients with witnessed VF/VT, there was a threefold increase in OHCA survival when CCR was used. CCR appears to be a promising resuscitation protocol for Emergency Medical Services providers in increasing survival from OHCA. Future research will need to be conducted to directly compare AHA/ERC 2010 Guidelines with the CCR approach.

Protocol C: a nonguidelines-compliant approach to improve survival of patients with out-of-hospital cardiac arrest

PURPOSE OF REVIEW

To describe a resuscitation protocol for out-of-hospital cardiac arrest designed for healthcare professionals that demands more from rescuers than does conventional cardiopulmonary resuscitation. It was introduced with the aim of improving survival that has remained disappointingly poor worldwide.

RECENT FINDINGS

Survival to hospital discharge, that could be measured accurately in one city, improved appreciably with the use of the novel protocol. The implications are discussed in relation to the scientific background and relevant literature.

SUMMARY

Uniform resuscitation protocols for lay and for professional use may not be appropriate. Only randomized trials can indicate the potential value of this challenge to conventional wisdom.

Resuscitation feedback and targeted education improves quality of pre-hospital resuscitation in Scotland

BACKGROUND

Out-of-hospital cardiac arrest (OHCA) is a leading cause of mortality and serious neurological morbidity in Europe. Recent studies have demonstrated the adverse physiological consequences of poor resuscitation technique and have shown that quality of cardiopulmonary resuscitation (CPR) is a critical determinant of outcome from OHCA. Telemetry of the defibrillator transthoracic impedance (TTI) trace can objectively measure quality of pre-hospital resuscitation. This study aims to analyse the impact of targeted resuscitation feedback and training on quality of pre-hospital resuscitation.

METHODS

Prospective, single centre, cohort study over 13 months (1st December 2009-31st December 2010). Baseline pre-hospital resuscitation data was gathered over a 3-month period. Modems (n=40) were fitted to defibrillators on ambulance vehicles. Following a resuscitation attempt, the event was sent via telemetry and the TTI trace analysed. Outcome measures were time spent performing chest compressions, compression rate, the interval required to deliver a defibrillator shock and use of automatic or manual cardiac rhythm analysis. Targeted resuscitation classes were introduced and all ambulance crews received feedback following a resuscitation attempt. Pre-hospital resuscitation quality pre and post intervention were compared.

RESULTS

111 resuscitation traces were analysed. Mean hands-on-chest time improved significantly following feedback and targeted resuscitation training (73.0% vs 79.3%, p=0.007). There was no significant change in compression rate during the study period. There was a significant reduction in median time-to-shock interval from 20.25s (IQR 15.50-25.50s) to 13.45 s (IQR 2.25-22.00 s) (p=0.006). Automatic rhythm recognition fell from 50% to 28.6% (p=0.03) following intervention.

CONCLUSION

Telemetry and analysis of the TTI trace following OHCA allows objective evaluation of the quality of pre-hospital resuscitation. Targeted resuscitation training and ambulance feedback improves the quality of pre-hospital resuscitation. Further studies are required to establish possible survival benefit from this technique.

Chest compressions before defibrillation for out-of-hospital cardiac arrest: a meta-analysis of randomized controlled clinical trials

BACKGROUND

Current 2005 guidelines for advanced cardiac life support strongly recommend immediate defibrillation for out-of-hospital cardiac arrest. However, findings from experimental and clinical studies have indicated a potential advantage of pretreatment with chest compression-only cardiopulmonary resuscitation (CPR) prior to defibrillation in improving outcomes. The aim of this meta-analysis is to evaluate the beneficial effect of chest compression-first versus defibrillation-first on survival in patients with out-of-hospital cardiac arrest.

METHODS

Main outcome measures were survival to hospital discharge (primary endpoint), return of spontaneous circulation (ROSC), neurologic outcome and long-term survival. Randomized, controlled clinical trials that were published between January 1, 1950, and June 19, 2010, were identified by a computerized search using SCOPUS, MEDLINE, BIOS, EMBASE, the Cochrane Central Register of Controlled Trials, International Pharmaceutical Abstracts database, and Web of Science and supplemented by conference proceedings. Random effects models were used to calculate pooled odds ratios (ORs). A subgroup analysis was conducted to explore the effects of response interval greater than 5 min on outcomes.

RESULTS

A total of four trials enrolling 1503 subjects were integrated into this analysis. No difference was found between chest compression-first versus defibrillation-first in the rate of return of spontaneous circulation (OR 1.01 [0.82-1.26]; P = 0.979), survival to hospital discharge (OR 1.10 [0.70-1.70]; P = 0.686) or favorable neurologic outcomes (OR 1.02 [0.31-3.38]; P = 0.979). For 1-year survival, however, the OR point estimates favored chest compression first (OR 1.38 [0.95-2.02]; P = 0.092) but the 95% CI crossed 1.0, suggesting insufficient estimate precision. Similarly, for cases with prolonged response times (> 5 min) point estimates pointed toward superiority of chest compression first (OR 1.45 [0.66-3.20]; P = 0.353), but the 95% CI again crossed 1.0.

CONCLUSIONS

Current evidence does not support the notion that chest compression first prior to defibrillation improves the outcome of patients in out-of-hospital cardiac arrest. It appears that both treatments are equivalent. However, subgroup analyses indicate that chest compression first may be beneficial for cardiac arrests with a prolonged response time.

Continued breathing followed by gasping or apnea in a swine model of ventricular fibrillation cardiac arrest

BACKGROUND

Continued breathing following ventricular fibrillation has here-to-fore not been described.

METHODS

We analyzed the spontaneous ventilatory activity during the first several minutes of ventricular fibrillation (VF) in our isoflurane anesthesized swine model of out-of-hospital cardiac arrest. The frequency and type of ventilatory activity was monitored by pneumotachometer and main stream infrared capnometer and analyzed in 61 swine during the first 3 to 6 minutes of untreated VF.

RESULTS

During the first minute of VF, the air flow pattern in all 61 swine was similar to those recorded during regular spontaneous breathing during anesthesia and was clearly different from the patterns of gasping. The average rate of continued breathing during the first minute of untreated VF was 10 breaths per minute. During the second minute of untreated VF, spontaneous breathing activity either stopped or became typical of gasping. During minutes 2 to 5 of untreated VF, most animals exhibited very slow spontaneous ventilatory activity with a pattern typical of gasping; and the pattern of gasping was crescendo-decrescendo, as has been previously reported. In the absence of therapy, all ventilatory activity stopped 6 minutes after VF cardiac arrest.

CONCLUSION

In our swine model of VF cardiac arrest, we documented that normal breathing continued for the first minute following cardiac arrest.

Transthoracic defibrillation potential gradients in a closed chest porcine model of prolonged spontaneous and electrically induced ventricular fibrillation

OBJECTIVE

The purpose of this study was to measure the local electrical field or potential gradient, measured with a catheter-based system, required to terminate long duration electrically or ischaemically induced ventricular fibrillation (VF). We hypothesized that prolonged ischaemic VF would be more difficult to terminate when compared to electrically induced VF of similar duration.

METHODS

Thirty anesthetized and instrumented swine were randomized to electrically induced VF or spontaneous, ischaemically induced VF, produced by balloon occlusion of the left anterior descending coronary artery. After 7 min of VF, chest compressions were initiated and rescue shocks were attempted 1 min later. The potential gradient for each shock was measured and the mean values required for defibrillation compared for the VF groups.

RESULTS

The number of shocks and the shock strength required for termination of VF were not significantly different for the groups. The potential gradient of the first successful defibrillating shock was significantly greater in the spontaneous, occlusion-induced VF group (12.80+/-2.82 V/cm vs 9.60+/-2.48 V/cm, p=0.002). The number of refibrillations was greater in the ischaemic group than in the non-ischaemic electrical group (6+/-4 vs 1+/-1, p<0.001). The number of animals requiring a shock at 360J was 2.5 times greater for the ischaemic group.

CONCLUSIONS

Defibrillation of prolonged VF produced by acute myocardial ischaemia requires a significantly greater potential gradient to terminate than prolonged VF induced by electrical stimulation of the right ventricular endocardium. The VF duration used in this study approximates that occurring in victims of out-of-hospital cardiac arrest. Our findings may be of clinical importance in the management of such patients.

The primacy of basics in advanced life support

PURPOSE OF REVIEW

The standards required for optimal effect of chest compressions and the degree to which most practice falls short of ideal have not been widely appreciated. This review highlights some of the important data now available and offers a haemodynamic explanation that broadens current concepts.

RECENT FINDINGS

New techniques have permitted a detailed examination of how compressions are performed in practice. The implications of recent experimental work adds a new imperative to the need for improvement.

SUMMARY

In addition to highlighting the need for improved training and audit, the greater understanding of mechanisms in resuscitation suggest that guidelines for management of adult cardiac arrest of presumed cardiac origin need further revision and simplification.

Development of the probability of return of spontaneous circulation in intervals without chest compressions during out-of-hospital cardiac arrest: an observational study

BACKGROUND

One of the factors that limits survival from out-of-hospital cardiac arrest is the interruption of chest compressions. During ventricular fibrillation and tachycardia the electrocardiogram reflects the probability of return of spontaneous circulation associated with defibrillation. We have used this in the current study to quantify in detail the effects of interrupting chest compressions.

METHODS

From an electrocardiogram database we identified all intervals without chest compressions that followed an interval with compressions, and where the patients had ventricular fibrillation or tachycardia. By calculating the mean-slope (a predictor of the return of spontaneous circulation) of the electrocardiogram for each 2-second window, and using a linear mixed-effects statistical model, we quantified the decline of mean-slope with time. Further, a mapping from mean-slope to probability of return of spontaneous circulation was obtained from a second dataset and using this we were able to estimate the expected development of the probability of return of spontaneous circulation for cases at different levels.

RESULTS

From 911 intervals without chest compressions, 5138 analysis windows were identified. The results show that cases with the probability of return of spontaneous circulation values 0.35, 0.1 and 0.05, 3 seconds into an interval in the mean will have probability of return of spontaneous circulation values 0.26 (0.24-0.29), 0.077 (0.070-0.085) and 0.040(0.036-0.045), respectively, 27 seconds into the interval (95% confidence intervals in parenthesis).

CONCLUSION

During pre-shock pauses in chest compressions mean probability of return of spontaneous circulation decreases in a steady manner for cases at all initial levels. Regardless of initial level there is a relative decrease in the probability of return of spontaneous circulation of about 23% from 3 to 27 seconds into such a pause.

Advanced life support update

INTRODUCTION

Cardiac arrest is a common emergency in acute hospitals. The Resuscitation Council (UK) Advanced Life Support Guidelines provide a systematic approach to cardiac arrest recognition, treatment and aftercare. This review provides an update on the current treatment guidelines and identifies areas where these may be strengthened.

METHODS

The evidence informing the 2005 Resuscitation Guidelines is reviewed. New evidence since the publication of the guidelines was identified by searching Medline (December 2005-December 2008) with the term heart arrest or advanced life support.

RESULTS

Opportunities for strengthening the chain of survival exist for each link. These include better recognition of critically ill patients at risk of cardiac arrest, improved quality of cardiopulmonary resuscitation, defibrillation strategies, which minimize pre- and post-shock pauses and development of post-resuscitation care bundles.

CONCLUSION

Emerging evidence suggests opportunities where Resuscitation Guidelines could be strengthened by focusing on specific aspects of the chain of survival.