Advice to delay giving a second heart shock to patients with cardiac arrest in hospital is not associated with improved survival, according to US researchers.
US national guidelines were revised in 2005 to recommend deferring a second defibrillation attempt to allow time for chest compressions.
However, study authors said data on the effect of the guideline changes on survival for patients with cardiac arrest in hospital were lacking.
They used data from a national registry to examine trends in the time interval between first and second defibrillation attempts among 2,733 patients undergoing cardiac arrest in 172 hospitals.
In line with the guidelines, the proportion of patients with a deferred second defibrillation attempt doubled from about 25% in 2004 to slightly more than 50% in 2012.
However, deferred second defibrillation was not found to be associated with improved survival.
Writing in the British Medical Journal, the authors said the findings raised questions about the specific benefit of deferred second defibrillation attempts for patients in hospital.
Meanwhile, a second study in the BMJ found early administration of adrenaline – within two minutes after the first defibrillation – was associated with poorer outcomes in hospital patients with cardiac arrest and a shockable rhythm.
Researchers looked at data on almost 3,000 patients with cardiac arrest at more than 300 US hospitals.
In a comment piece in the same journal, UK experts from Warwick Medical School said the results from the two studies should inform practice.
Meanwhile, Dr Carl Gwinnutt, president of the UK’s Resuscitation Council, noted that its current UK guidelines, published in October 2015, differed from those in the US.
The UK guidance recommend that, where a patient suffers a witnessed and monitored arrest, for example in a critical care area, three shocks are given in quick succession – referred to as “stacked shocks”. In other situations, the guidelines advocate that between the first and second shocks there should be a two-minute period of chest compressions.
Dr Gwinnutt also highlighted that there might be other explanations for the US study findings.
Defib timing in resuscitation guidelines questioned
For example, a greater proportion of patients in the shock delay group had sepsis, which is associated with a very poor outcome from cardiac arrest, and more were also being cared for in wards where they were not on heart monitors, which may have delayed the start of resuscitation.
He added: “There is evidence that outcome is worse in those patients where there is a prolonged delay between stopping chest compressions and delivering the shock, and this may have been a further factor influencing the findings.
“Consequently, the current guidelines issued by the Resuscitation Council (UK) advocate two minutes of high quality chest compressions between the first and second shocks with an interruption to chest compressions of less than five seconds whilst the shock is delivered,” he said.