Effects of decreasing inspiratory times during simulated bag-valve-mask ventilation

During CPR, an inspiratory time of 2 s is recommended when the airway is unprotected; indicating that approximately 30% of the resuscitation attempt is spent on ventilation, but not on chest compressions. Since survival rates may not decrease when ventilation levels are relatively low, and uninterrupted chest compressions with a constant rate of approximately 100/min have been shown to be lifesaving, it may be beneficial to cut down the time spent on ventilation, and instead, increase the time for chest compressions. In an established bench model of a simulated unprotected airway, we evaluated if inspiratory time can be decreased from 2 to 1 s at different lower oesophageal sphincter pressure (LOSP) levels during ventilation with a bag-valve-mask device. In comparison with an inspiratory time of 2 s, 1 s resulted in significantly (p < 0.001) higher peak airway pressure and peak inspiratory flow rate, while lung tidal volumes at all LOSP levels were clinically comparable. Neither ventilation strategy produced stomach inflation at 20 cmH2O LOSP, and 1 s versus 2 s inspiratory time did not produce significantly higher (mean +/- S.D.) stomach inflation at 15 (8 +/-9 ml versus 0 +/- 0 ml; p < 0.01) and 10 cmH2O LOSP (69 +/- 20 ml versus 34 +/- 18 ml; p < 0.001), and significantly lower stomach inflation at 5 cmH2O LOSP (219 +/- 16 ml versus 308 +/- 21 ml; p < 0.001) per breath. Total cumulative stomach inflation volume over constantly decreasing LOSP levels with an inspiratory time of 2 s versus 1 s was higher (6820 ml versus 5920 ml). In conclusion, in this model of a simulated unprotected airway, a reduction of inspiratory time from 2 to 1 s resulted in a significant increase of peak airway pressure and peak inspiratory flow rate, while lung tidal volumes remained clinically comparable (up to approximately 15% difference), but statistically different due to the precise measurements. Theoretically, this may increase the time available for, and consequently the actual number of, chest compressions during CPR by approximately 25% without risking an excessive increase in stomach inflation.     

Effects of decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation

Reducing inspiratory flow rate and peak airway pressure may be important in order to minimise the risk of stomach inflation when ventilating an unprotected airway with positive pressure ventilation. This study was designed to yield enough power to determine whether employing an inspiratory gas flow limiting bag-valve device (SMART BAG, O-Two Medical Technologies Inc., Ontario, Canada) would also decrease the likelihood of stomach inflation in an established bench model of a simulated unintubated respiratory arrest patient. The bench model consists of a training lung (lung compliance, 50 ml/cm H2O; airway resistance, 4 cm H2O/l/s) and a valve simulating lower oesophageal sphincter opening at a pressure of 19 cm H(2)O. One hundred and ninety-one emergency medicine physicians were requested to ventilate the manikin utilising a standard single-person technique for 1 min (respiratory rate, 12/min; Vt, 500 ml) with both a standard adult bag-valve-mask and the SMART BAG. The volunteers were blinded to the experimental design of the model until completion of the experimental protocol. The SMART BAG versus standard bag-valve-mask resulted in significantly (P < 0.001) lower (mean +/- S.D.) mean airway pressure (14 +/- 2 cm H2O versus 16 +/- 3 cm H2O), respiratory rates (13 +/- 3 breaths per min versus 14 +/- 4 breaths per min), incidence of stomach inflation (4.2% versus 38.7%) and median stomach inflation volumes (351 [range, 18-1211 ml] versus 1426 [20-5882 ml]); lung tidal volumes (538 +/- 97 ml versus 533 +/- 97 ml) were comparable. Inspiratory to expiratory ratios were significantly (P < 0.001) increased (1.7 +/- 0.5 versus 1.5 +/- 0.6). In conclusion, the SMART BAG reduced inspiratory flow, mean airway pressure and both the incidence and actual volume of stomach inflation compared with a standard bag-valve-mask device while maintaining delivered lung tidal volumes and increasing the inspiratory to expiratory ratio.     

Arterial blood gases during basic life support of human cardiac arrest victims

BACKGROUND: Ventilation with tidal volumes sufficient to raise the victim's chest is an integral part of guidelines for lay-rescuer basic life support, but optimal tidal volume, frequency and ratio to chest compressions are not known. METHODS: Adults with non-traumatic, out-of-hospital cardiac arrest, who were not successfully resuscitated following advanced life support by the staff of a physician-manned ambulance, were included. Advanced life support comprised tracheal intubation and mechanical ventilation with tidal volume of 700 ml and 100% oxygen, 12 times per min. An arterial blood sample was drawn at the end of the resuscitation attempt and analysed on the scene. After the victim was declared dead, basic life support was initiated with chest compressions and mouth-to-mask or mouth-to-tracheal tube ventilation (15:2), with volumes sufficient to make the chest rise. The tracheal tube was equipped with an impedance valve to avoid passive ventilation secondary to chest compressions. Arterial blood samples were drawn after 7-8 min of basic life support and analysed on the scene. RESULTS: Six men and two women, median (range) age 72 (32-86) years, were included in the study. Four of these received mouth-to-mask ventilation and four mouth-to-tracheal tube ventilation. Mean (S.D.) arterial blood carbon dioxide and oxygen tension during advanced life support were 6.4 (1.4)kPa and 22 (15)kPa, respectively. Similar values during basic life support were 9.6 (1.9)kPa and 8.5 (1.6)kPa, respectively, with no differences between the ventilation methods. CONCLUSION: Ventilation during basic life support performed according to international guidelines (2000) resulted in arterial hypercapnia and hypoxia.     

Prevention of deterioration of ventricular fibrillation by basic life support during out-of-hospital cardiac arrest

Survival of cardiac arrest is improved by basic life support (BLS). This study investigated the relationship between ventricular fibrillation (VF) characteristics and survival. In a 2-year prospective study out-of-hospital witnessed non-traumatic cardiac arrests were observed. The probabilities of recording VF, asystole or other rhythms in relation to BLS and the time to the rhythm recording were analyzed with logistic regression. Amplitude and baseline crossings of VF were related to survival, using linear regression analysis.In 873 patients, the probability to record VF decreased per minute (OR 0.92, 95%CI 0.89-0.95) and of asystole increased (OR 1.13, 95%CI 1.09-1.18) as time from collapse elapsed. BLS reduced these trends significantly for VF (OR 0.97, 95%CI 0.94-0.99) and asystole (OR 1.09, 95%CI 1.05-1.13). This effect was not observed for other rhythms. The amplitude of VF decreased in time; significantly less for patients who received BLS than for those who did not (p=0.009). Survival significantly decreased with lower amplitude of VF (OR 0.23 per mV, 95%CI 0.07-0.79) and with less baseline crossings (OR 0.80 per baseline crossings per second, 95%CI 0.71-0.91). Our study demonstrated that BLS and VF as initial rhythm, considered being "baseline" predictors in survival models, were proved not independent of each other. The decrease of VF amplitude and increase in prevalence of asystole is slowed significantly by BLS. Predicting survival from VF amplitude and baseline crossings alone is limited.     

不同潮气量机械通气对肺损伤的影响及其针对性护理

目的 研究不同潮气量机械通气对肺损伤的影响,探讨机械通气时的针对性护理措施.方法 将24只健康SD大鼠随机分为对照组（n=8）、小潮气量通气组（n=8,VT=8 ml/kg）和大潮气量通气组（n=8,VT=40ml/kg）.通气时间均为4 h.检测肺组织总蛋白、肺湿干重比（W/D）、白细胞计数和中性粒细胞髓过氧化物酶（MPO）含量以及肿瘤坏死因子α（TNF-α）蛋白和mRNA的含量.结果与对照组比较,大潮气量通气组肺组织总蛋白、W/D、白细胞计数和MPO含量以及TNF-α蛋白和mRNA含量均显著增加（P〈0.05）,而小潮气量通气组上述指标的变化无统计学意义（P〉0.05）.结论 大潮气量机械通气可导致呼吸机所致肺损伤,临床上应加强对机械通气患者的护理防护.     

Can better basic and advanced cardiac life support improve outcome from cardiac arrest?

The effect of basic and advanced cardiac life support (BLS and ACLS) on long-term survival is dependent upon both the response time and the quality of intervention. Retention research using the results of classroom testing as indirect indicators has shown that performance of BLS and ACLS skills is poor. This suggests that BLS and ACLS courses do not teach the knowledge and skills well, the information is too difficult to retain, testing procedures are faulty, and/or the performance standards are unrealistic. To maximize the likelihood of successful resuscitation from cardiac arrest, we propose the following: (a) simplify the BLS procedures; (b) simplify the BLS and ACLS curricula; (c) simplify teaching strategies; (d) simplify testing based on what steps are required to sustain life; (e) define objective criteria for knowledge acquisition and skill performance; (f) base refresher training on diagnosed deficiencies and evaluate innovative ways to improve retention; (g) develop a resuscitation record to provide accurate documentation of patient status, dysrhythmias, therapy, and responses to therapy; (h) develop a process evaluation tool to evaluate individual and group performances during actual resuscitation; and (i) form an international consortium of BLS and ACLS investigators.     

Effects of endothelin-1 on resuscitation rate during cardiac arrest

OBJECTIVES: Endothelin-1 (ET-1) is a potent peripheral and coronary artery vasoconstrictor and has been shown to improve coronary perfusion pressure (CPP) during cardiac arrest. The effect of ET-1 on return of spontaneous circulation (ROSC) following cardiac arrest has not been studied. Our hypothesis was that ET-1 does not improve ROSC from cardiac arrest when compared to placebo. METHODS: A total of 11 immature swine were used in this laboratory study. Animals were randomized to receive 300 microg ET-1 and standard dose epinephrine (SDE) or placebo and SDE during arrest. After a 10-min period of no-flow ventricular fibrillation (VF), CPR was performed for 3 min followed by ET-1/SDE or placebo/SDE administration. Following drug administration, standard ACLS was followed with SDE given every 3 min. Aortic pressure was monitored during resuscitation. ROSC was defined as any perfusing rhythm with a systolic pressure greater than 60 mmHg for 60 s. Animals received post-ROSC care as needed for 2 h post-ROSC. CPP and ROSC were analyzed using repeated measures ANOVA and Fischer's exact test respectively. P<0.05 was considered significant. RESULTS: Pre-arrest variables and CPP prior to ET-1 administration were not different between groups. Following ET-1 administration, CPP was significantly increased at all time points in ET-1/SDE versus placebo/SDE animals. ROSC was achieved in 1/5 (20%) ET-1/SDE versus 1/6 (16.7%) placebo/SDE animals (P>0.05). The resuscitated ET-1/SDE animal survived 6.5 min compared to 120 min for the resuscitated placebo/SDE animal. CONCLUSIONS: In our study, ET-1 administration during cardiac arrest increases CPP but does not improve ROSC.     

Out-of-hospital extra-corporeal life support implantation during refractory cardiac arrest in a half-marathon runner

For patients who present with an out-of-hospital refractory cardiac arrest, in-hospital extracorporeal life-support (ECLS) initiation represents an alternative therapy which allows significant survival. We describe here the first case of out-of-hospital ECLS implantation in a patient presenting with a refractory cardiac arrest during a road race. ECLS was initiated within the MICU ambulance 60 min after cardiac arrest and enabled restoration of cardiac output to 4.5 l min⁻¹. Coronarography revealed a severe isolated stenosis of the right coronary artery, which was treated by angioplasty. The cardiogenic shock resolved progressively, enabling ECLS weaning within 48 h, while renal, hepatic, and respiratory functions recovered simultaneously.     

Physiological effects of reduced tidal volume at constant minute ventilation and inspiratory flow rate in acute respiratory distress syndrome

Objective To assess the effect of changes in tidal volume (V _T) with a constant inspiratory flow and minute ventilation on gas exchange and oxygen transport in acute respiratory distress syndrome (ARDS).Design A crossover study of threeV _T in two study groups, using patients as their own controls.Setting: A medical-surgical intensive care unit in a tertiary care center.Patients Eight patients with ARDS and seven postoperative cardiac surgery patients with uncomplicated recoveries were studied during volume-controlled mechanical ventilation.Interventions During controlled mechanical ventilation, patients were first ventilated with aV _T of 9–11 ml/kg.V _T was then increased to 12–14 ml/kg (+25%) for 30 min and subsequently decreased to 6–8 ml/kg (–25%) for 30 min by adjusting the respiratory rate (RR) while the inspiratory flow rate, , and inspiratory duty cycle (T_L/T_TOT) were kept constant. At the end, patients were ventilated with the baseline settings for another 30 min.Measurements and results V _E, carbon dioxide production and oxygen consumption were measured continuously with a gas exchange monitor, and cardiac output and arterial and mixed venous blood samples were taken at the end of each 30-min period to assess CO₂ removal and oxygen transport. Alveolar minute ventilation and the deadspace to tidal volume ratio (V _D/V _T) were calculated from the Bohr equation. Despite large changes inV _T, arterial oxygenation (P _aO₂) and oxygen transport were unchanged throughout the study. WhenV _T was increased, physiologicalV _D increased from 448±34 ml to 559±46 ml (mean±SE) in ARDS (P<0.001) and from 281±22 ml to 357±35 ml in CABG (P<0.05). With the smallV _T,V _D decreased to 357±22 ml in ARDS (P<0.01), and to 234±24 ml in CABG (P<0.05). In ARDS,V _D/V _T decreased from 0.57±0.03 to 0.55±0.03 (P<0.05) with the largeV _T, and increased to 0.60±0.03 (P<0.01), whenV _T was reduced. In CABG,V _D/V _T did not change significantly. ARDS patients had a higherP _aCO₂ than cardiac patients (P<0.001), and only minor changes inP _aCO₂ were observed (for ARDS and CABG respectively, baseline 5.9±0.3 kPa and 4.1±0.1 kPa, largeV _T 5.7±0.3 kPa and 4.1±0.2 kPa, smallV _T 6.2±0.3 kPa and 4.2±0.2 kPa;P<0.05).Conclusions Tidal volumes can be reduced to 6–8 ml/kg in ARDS patients without compromising oxygen transport, while adequate CO₂ elimination can be maintained.     

Cardiopulmonary effect of various inspiratory flow profiles during controlled mechanical ventilation in a porcine lung model

We studied the influence of inspiratory flow (VI) patterns on gas exchange and hemodynamics after metacholine inhalation challenge (MIC) in seven swine mechanically ventilated with a constant, sinusoidal, accelerating, and decelerating flow pattern. Blood gas and expired CO2 tensions, pulmonary mechanics, and hemodynamics were measured during each pattern. Flow pattern sequence was randomized and MIC was repeated at 30 to 45-min intervals. MIC reliably reduced PaO2, and increased PaCO2 and peak tracheal pressure (PT). There was no significant difference in gas exchange or hemodynamics between various VI curves. Insufflation with an accelerated VI manifested a significantly higher PT than any other pattern. We conclude that no VI contour studied offers a unique advantage for gas exchange after MIC in swine. However, since accelerated gas flow generates significantly higher PT values, it is not recommended in the presence of significant airway resistance.     

Extracorporeal life support during cardiac arrest and cardiogenic shock: a systematic review and meta-analysis

Purpose

Veno-arterial extracorporeal life support (ECLS) is increasingly used in patients during cardiac arrest and cardiogenic shock, to support both cardiac and pulmonary function. We performed a systematic review and meta-analysis of cohort studies comparing mortality in patients treated with and without ECLS support in the setting of refractory cardiac arrest and cardiogenic shock complicating acute myocardial infarction.

Methods

We systematically searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and the publisher subset of PubMed updated to December 2015. Thirteen studies were included of which nine included cardiac arrest patients (n = 3098) and four included patients with cardiogenic shock after acute myocardial infarction (n = 235). Data were pooled by a Mantel-Haenzel random effects model and heterogeneity was examined by the I ² statistic.

Results

In cardiac arrest, the use of ECLS was associated with an absolute increase of 30 days survival of 13 % compared with patients in which ECLS was not used [95 % CI 6–20 %; p < 0.001; number needed to treat (NNT) 7.7] and a higher rate of favourable neurological outcome at 30 days (absolute risk difference 14 %; 95 % CI 7–20 %; p < 0.0001; NNT 7.1). Propensity matched analysis, including 5 studies and 438 patients (219 in both groups), showed similar results. In cardiogenic shock, ECLS showed a 33 % higher 30-day survival compared with IABP (95 % CI, 14–52 %; p < 0.001; NNT 13) but no difference when compared with TandemHeart/Impella (?3 %; 95 % CI ?21 to 14 %; p = 0.70; NNH 33).

Conclusions

In cardiac arrest, the use of ECLS was associated with an increased survival rate as well as an increase in favourable neurological outcome. In the setting of cardiogenic shock there was an increased survival with ECLS compared with IABP.

     

Effect of inspiratory time and flow settings during assist-control ventilation

The effect of the settings of inspiratory time and inspiratory flow during assist-control ventilation on the response of a patient's respiratory controller has been the subject of intense research during the last few years. An increase in inspiratory flow or a decrease in tidal volume delivered by the ventilator is associated with prompt increases in respiratory frequency. The changes occur before any change in arterial blood gases can take place. These responses occur both during wakefulness and sleep and in health and disease states. Whether the responses are the result of Hering-Breuer reflex activity or they arise in flow-sensitive receptors remains to be defined. Important clinical implications of the respiratory rate response to changes in ventilatory settings include effects on carbon dioxide, intrinsic positive end-expiratory pressure, and, possibly, on the instability of the respiratory rate in the transition between wakefulness and sleep.     

Mild hypothermia during advanced life support: a preliminary study in out-of-hospital cardiac arrest

Introduction  

Induction of mild hypothermia after cardiac arrest may confer neuroprotection. We assessed the feasibility, safety and effectiveness of therapeutic infusion of 2 l of normal saline at 4°C before return of spontaneous circulation during cardiopulmonary resuscitation after out of hospital cardiac arrest.     

Increased initial flow rate reduces inspiratory work of breathing during pressure support ventilation in patients with exacerbation of chronic obstructive pulmonary disease

Objective To investigate whether the level of initial flow rate alters the work of breathing in chronic obstructive pulmonary disease (COPD) patients ventilated in pressure support ventilation (PSV).Design Prospective study.Settings Medical ICU in University hospital.Patients Eleven intubated COPD patients.Methods We modulated the initial flow rate in order to achieve seven different sequences. In each sequence, the plateau pressure was reached within a predetermined time: 0.1, 0.25, 0.50, 0.75, 1, 1.25 or 1.50 s. The more rapidly the pressure plateau was achieved, the higher was the initial flow rate. In each patient, the pressure support level was an invariable parameter. The order of the seven sequences for each patient was determined randomly.Measurements and results Ten minutes after application of each initial flow rate, we measured the following parameters: inspiratory work of breathing, electromyogram (EMG) of the diaphragm (EMGdi), breathing pattern, and intrinsic positive end-expiratory pressure (PEEPi). Comparison between the means for each sequence and each variable measured was performed by two-way analysis of variance with internal comparisons between sequences by Duncan's test. The reduction of the initial flow rate induced a progressive increase in the values of the work of breathing, EMGdi, and mouth occlusion pressure (P 0.1). In contrast, the reduction of the initial flow rate did not induce any significant change in tidal volume, respiratory frequency or PEEPi.Conclusion As the objective of PSV is to reduce the work of breathing, it seems logical to use the highest initial flow rate to induce the lowest possible work of breathing in COPD ventilated patients.     

CPREzy: an evaluation during simulated cardiac arrest on a hospital bed

CPREzy is a new adjunct designed to improve the application of manual external chest compressions (ECC) during cardiopulmonary resuscitation (CPR). The aim of this study was to determine the effect of using the CPREzy device compared to standard CPR during the simulated resuscitation of a patient on a hospital bed. Twenty medical student volunteers were randomised using a cross over trial design to perform 3 min of continuous ECC using CPREzy and standard CPR. There was a significant improvement in ECC depth with CPREzy compared to standard CPR 42.9 (4.4) mm versus 34.2 (7.6): mm, P = 0.001; 95% CI d.f. 4.4-12.9 mm. This translated to a reduction in the percentage of shallow compressions (<38 mm) with CPREzy 16 (23)% compared to standard CPR 59 (44)%, P = 0.003. There was a small increase in the percentage of compression regarded excessive (>51 mm): CPREzy 6.5 (19)% versus standard CPR 0 (0.1)%. P = 0.012). There was no difference in compression rate or duty cycle between techniques. Equal numbers of participants (40% in each group) performed one of more incorrectly placed chest compression. However the total number of incorrect compressions was higher for the CPREzy group (26% versus 3.9% standard CPR, P < 0.001). This was due to a higher number of low compressions (26% of total compressions for CPREzy versus 1% for standard CPR, P < 0.001). In conclusion, CPREzy was associated with significant improvements in ECC performance. Further animal and clinical studies are required to validate this finding in vivo and to see if it translates to an improvement in outcome in human victims of cardiac arrest.     

Haemodynamic effects of mental stress during cardiac arrest simulation testing on advanced life support courses

We investigated the haemodynamic response to the mental stress induced by being evaluated as a team leader in simulated advanced life support (ALS) scenarios. METHODS: Healthcare providers participating as candidates to ALS courses were monitored while acting as team leaders in a cardiac arrest testing scenario (CASTest). Heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured before, during and after the CASTest. The correlation between the haemodynamic responses and sex, age, body mass index (BMI) and marks on course multiple choice questions (MCQs) were studied using multiple linear regression. RESULTS: Eighty-eight subjects (46 women, 42 men, mean age 34.9+/-6.8 years) were enrolled. Mean HR, SBP and DBP increased significantly during the CASTest and reached a peak after a phase of the scenario which included an unsuccessful defibrillation. Ten minutes after the CASTest, HR, SBP and DBP were still significantly higher than their respective baseline values. A significant positive correlation was found between the DBP and SBP response during the scenario and the BMI, and between the DBP response and the candidates' age. The haemodynamic stress response was neither correlated with the candidates' marks in the course MCQ nor with their instructor potential (IP). CONCLUSION: During the testing scenario the ALS candidates showed a significant haemodynamic response to mental stress, which depended mainly on their age and BMI rather than on their knowledge and skills.     

Effects of a mandatory basic life support training programme on the no-flow fraction during in-hospital cardiac resuscitation: An observational study

Aim of the study

Many hospitals have basic life support (BLS) training programmes, but the effects on the quality of chest compressions are unclear. This study aimed to evaluate the no-flow fraction (NFF) during BLS provided by standard care nursing teams over a five-year observation period during which annual participation in the BLS training was mandatory.

Methods

All healthcare professionals working at Dresden University Hospital were instructed in BLS and automated external defibrillator (AED) use according to the current European Resuscitation Council guidelines on an annual basis. After each cardiac arrest occurring on a standard care ward, AED data were analyzed. The time without chest compressions during the period without spontaneous circulation (i.e., the no-flow fraction) was calculated using thoracic impedance data.

Results

For each year of the study period (2008–2012), a total of 1454, 1466, 1487, 1432, and 1388 health care professionals, respectively, participated in the training. The median no-flow fraction decreased significantly from 0.55 [0.42; 0.57] (median [25‰; 75‰]) in 2008 to 0.3 [0.28; 0.35] in 2012. Following revision of the BLS curriculum after publication of the 2010 guidelines, cardiac arrest was associated with a higher proportion of patients achieving ROSC (72% vs. 48%, P = 0.025) but not a higher survival rate to hospital discharge (35% vs. 19%, P = 0.073).

Conclusion

The NFF during in-hospital cardiac resuscitation decreased after establishment of a mandatory annual BLS training for healthcare professionals. Following publication of the 2010 guidelines, more patients achieved ROSC after in-hospital cardiac arrest.     

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.