What is the role of feeling for a pulse?
The assessment of a pulse is also controversial. This issue has previously been discussed in detail. It is reasonable for practitioners taught to feel a pulse to do so as part of the assessment for signs of life, but to limit the total time taken to 10 seconds.
Why is a single shock technique being advocated?
The default defibrillation technique is now to use a single shock technique rather than a salvo of up to three shocks. The main rationale for this approach is to minimise the interruptions to CPR, which have been shown to be associated with a rapidly decreasing diastolic blood pressure (and coronary perfusion pressure) and a decreased likelihood of successful defibrillation. The shock success for currently used defibrillators is actually very high for the initial shock, and the interruptions to CPR for the
second and third shocks in succession are thought in most circumstances to be more detrimental than the incremental success from these subsequent shocks.
For what specific circumstances is the three-shock strategy being retained?
Three Stacked Shocks were removed from the standard ALS algorithm as part of the 2010 CoSTR changes. It is now included under the special circumstances in resuscitation guideline.
Where a patient with a perfusing rhythm develops a shockable rhythm in a witnessed and monitored setting and the defibrillator is immediately available and they were previously well perfused and oxygentated pre-arrest then the use of 3 stacked shocks may be considered.
This situation is rare and may occur in the pre-hospital setting, emergency departments, critical care and coronary care units, and possibly also in the operating room. In these settings it may be appropriate to use a 3 stacked-shock technique, especially where there may be a relative contraindication to external cardiac compressions (e.g. after cardiac surgery).
The “3 stacked-shock sequence” can be optimized by immediate rhythm analysis and charging of the defibrillator. This sequence may be of benefit in scenarios where the time required for rhythm recognition and for recharging the defibrillator is short (ie:. <10 seconds). In these situations, such as in-hospital arrests, it would be expected to deliver the sequence of shocks (up to three) in no more than 30 seconds.
Why not assess for a rhythm and a pulse immediately after defibrillation?
The recommendation to immediately start CPR after a shock is based on the fact that the chance of developing a rhythm associated with an output in the first minute or so after defibrillation is extremely small. Starting CPR immediately after defibrillation, irrespective of the electrical success or otherwise, or the attempt at defibrillation, restores blood flow to the brain and heart and creates an environment more conducive to return of spontaneous circulation. A period of at least 1-2 minutes of good CPR appears to be able to increase the likelihood of success of the next attempt at defibrillation. Obviously there is no need for CPR to continue if signs of life return.
What is the exact protocol that should be followed for a persistent shockable rhythm?
The optimal sequence of events that should follow for a persistent shockable rhythm is not known. The sequence cannot be prescribed exactly but the general principles that should be followed are listed here.
- At all times, interruptions to compressions should be minimised.
- After an unsuccessful attempt at defibrillation a 2-minute period of CPR is recommended before the rhythm is reassessed.
- If when the rhythm is reassessed a shockable rhythm persists, repeat defibrillation (second shock).
- After the second attempt at defibrillation on recommencing chest compressions administer 1 mg adrenaline, continue CPR for 2 minutes and then reassess and repeat defibrillation if indicated (third shock).
- Adrenaline should subsequently be administered at a rate of 1 mg approximately every three minutes until Return of Spontaneous Circulation. For simplicity, adrenaline could be administered in alternate loops. A period of at least 1-2 minutes of good CPR is recommended after each dose of adrenaline to help circulate the drug.
- If the subsequent attempt at defibrillation is also unsuccessful, a 2-minute period of CPR is again recommended before the rhythm is reassessed.
- If VF is still present after the administration of adrenaline and one further shock, consider administration of an anti-arrhythmic before defibrillation (fourth shock).
- At any stage if a rhythm is present that should be associated with a pulse, then formal checking for signs of life (including a pulse check) should be performed. If there are no signs of life (including a pulse) then the non-shockable sequence should be followed.
What about the new devices that evaluate CPR quality or the VF waveform?
New devices that evaluate quality of CPR and the defibrillation waveform offer promise in the management of cardiac arrests, but at this stage they need further study before any recommendations can be made.
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