BEST EVIDENCE TOPIC REPORTS Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary

A short cut review was carried out to establish whether biphasic defibrillatory shocks were superior to monophasic shocks in patients in ventricular fibrillation. Altogether 337 papers were found using the reported search, of which seven presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated. Clinical scenario An adult is brought into the emergency department following an out of hospital ventricular fibrillatory arrest. Ventricular fibrillation persists despite repeated shocks. You remember reading about biphasic defibrillation and wonder if it offers any advantages. Three part question In [an adult in ventricular fibrillation] is [external biphasic shock better than monophasic shock] at [achieving defibrillation]? Search strategy Medline 1966–06/03 using the OVID interface. Biphasic.mp AND (defib$.mp OR shock$.mp OR exp electric countershock) LIMIT to human AND English. Search outcome Altogether 337 papers were found of which seven related to out of hospital studies relevant to the original question. Comment(s) The studies shown in table 1 represent two independent groups of patients. The first two studies are a prospective randomised controlled trial (PRCT) and subsequent subgroup analysis of data from it. The last five studies represent ongoing investigation by a group of researchers with some overlap of patient groups between each study because of differing selection criteria and differing dates of study. The PRCT provides good evidence for the superiority of biphasic defibrillation over monophasic. Analysis of the data from this study gives an NNT of three for successful defibrillation with first shock, and an NNT of four for successful defibrillation within the first three shocks by biphasic compared with monophasic waveforms. These out of hospital studies follow on from extensive in hospital and animal studies showing the superiority of biphasic defibrillation. All the studies reported used the Heartstream Forerunner defibrillator with non-escalating 150 J shocks. This device uses an impedance compensating biphasic truncated exponential waveform. Laboratory and hospital based studies show the superiority of biphasic waveforms to be broadly applicable and not confined to this specific example of a biphasic waveform. Work is ongoing to refine which parameters of the waveform influence effectiveness. Evidence should be appraised for the effectiveness of the specific waveform used when selecting a defibrillator. Local considerations will determine when biphasic devices replace monophasic defibrillators. c CLINICAL BOTTOM LINE Biphasic defibrillation is currently the best treatment for adult VF and should be used when available. White RD. Early out-of-hospital experience with an impedance-compensating low-energy biphasic waveform automatic external defibrillator. J Interv Card Electrophysiol 1997;1:203–8. Poole JE, White RD, Kanz KG, et al. Low-energy impedance-compensating biphasic waveforms terminate ventricular fibrillation at high rates in victims of out-of-hospital cardiac arrest. LIFE investigators. J Cardiovasc Electrophysiol 1997;8:1373–85. Best evidence topic reports (BETs) summarise the evidence pertaining to particular clinical questions. They are not systematic reviews, but rather contain the best (highest level) evidence that can be practically obtained by busy practising clinicians. The search strategies used to find the best evidence are reported in detail in order to allow clinicians to update searches whenever necessary. The BETs published below were first reported at the Critical Appraisal Journal Club at the Manchester Royal Infirmary or placed on the BestBETs web site. Each BET has been constructed in the four stages that have been described elsewhere. The BETs shown here together with those published previously and those currently under construction can be seen at http://www.bestbets.org. Six BETs are included in this issue of the journal. c Biphasic or monophasic defibrillation for adult ventricular fibrillation c Ascorbate for alkali burns to the eye c Leucovorin (calcium folinate) in “antifreeze” poisoning c Vasopressin or adrenaline (epinephrine) in cardiac resuscitation c Is the central venous pressure reading equally reliable if the central line is inserted via the femoral vein c Oucher or CHEOPS for pain assessment in children K Mackway-Jones Emergency Department, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK; [email protected] 1 Carley SD, Mackway-Jones K, Jones A, et al. Moving towards evidence based emergency medicine: use of a structured critical appraisal journal club. J Accid Emerg Med 1998;15:220–2. 2 Mackway-Jones K, Carley SD, Morton RJ, et al. The best evidence topic report: A modified CAT for summarising the available evidence in emergency medicine. J Accid Emerg Med 1998;15:222–6. 3 Mackway-Jones K, Carley SD. bestbets.org: Odds on favourite for evidence in emergency medicine reaches the worldwide web. J Accid Emerg Med 2000;17:235–6. 464 www.emjonline.com group.bmj.com on July 8, 2017 Published by http://emj.bmj.com/ Downloaded from