Defibrillation Flashcards
Every minute which passes between cardiac arrest and defibrillation mortality increases by approx what?
10% (3-4% if CPR is given)
Every 5 second increase in the pre-shock pause does what to the chances of a successful defibrillation?
Almost halves the chances of a successful defibrillation
Define what defibrillation is
This is the passage of an electrical current of sufficient magnitude across the myocardium to depolarise a critical mass of cardiac muscle simultaneously, enabling the natural pacemaker cells to resume control.
What does successful defibrillation depend on ?
Sufficient current being delivered to the myocardium
What is the delivered current when defibrillating someone influenced by?
Transthoracic impedance (electrical resistance) & electrode position
When defibrillating someone a lot of current is diverted along non-cardiac pathways, how much current actually reaches the heart?
Approx 4%
What type of defibrillators can compensate for transthoracic impendence
Biphasic defibrillators can measure transthoracic impedence and adjust the energy needed for the shock
If a patient has a transdermal patch on their chest in the way of defibrillator pads what should you do ?
Remove the pad and dry the skin or if this will delay defibrillation then alternate defib pad positioning.
If a patient has a very hairy chest what should you do to the defib pad position?
Bi-axillary defib pad position
What is the standard defib pad positoning ?
1st pad - right of the upper sterum under right clavicle
2nd pad - left mid-axillary position.
Does it matter which way around the defib pads are placed?
No
What are the 3 main alternate acceptable defib pad positions?
- Antero-posterior = one atnerior over left precordium and the other on the back just inferior to left scapulae
- Postero-lateral = one in left mid-axillary line and other on the back just inferior to right scapula
- Bi-axillary = each pad on the lateral chest walls (axillae) both left and right
What should you do with defib pad positoning and why if someone has a ICD or PPM?
Place the electrode 10-15cm away from the device or use alternative pad positoning e.g. antero-posterior
Is a period of CRP (2-3min) recommened before the first rhythm analysis in a cardiac arrest ?
No - if you can analysis the rhythm then do it as soon as +/- shock if appropriate
Recall - do you continue chest compressions whilst the defibrillator is charging if deemed a shockable rhythm?
Yes
Recap these points
What is the range of energy levels and accepted strategy which can be used for shock attempts?
Range 120-360J
Any energy level within this range is acceptable for the initial shock, followed by a fixed or escalating strategy upto the max output of the defibrillator
If the defibrillator is capable of an increase in energy and the inital shock was unsuccessful what is generally the accepted approach?
Escalating shock energy
Prior to shock delivery, when ensuring everyone is clear of the patient what might people forget to not touch?
The patients trolley or IV infusions (indirect contact).
Do the latex gloves routinely used by healthcare professionals provide sufficient protection from electrical currents ?
No
What should be done with oxygen prior to shock delivery and why?
Take any O2 mask or nasal cannulae and place 1m away
Leave a ventilation bag connected to a tracheal tube or SGA as this will not cause any increase in O2 conc near defib pads (even if 15L/min).
This is due to a theoretical risk of fire in an O2 rich atmosphere but there have been no reports of this with self-adhesive pads.
What are the main advantages and disadvantages of manual defibrillators ?
Advantages:
* Enable operator to diagnose rhythm and deliver shock without having to wait for rhythm analysis. Thus minimising interuptions in chest compressions.
* Can delivery synchronised shocks and external pacing facilities
Disadvantages:
* Operator has to be skilled in ECG recognition
What energy setting should you select for the inital shock?
120-150J
Go over summary for shockable rhythm defib sequence
When wanting to cardiovert someone with an atrial or ventricular tachyarrythmia what must be done and why ?
The shock must be synchronised with the R-wave (ventricular depolarisation) avoiding ventricular depolarisation and the risk of putting someone into VF.
Do you need to synchronise for VF/pVT?
No
What should patients be given if you are going to carry out synchronised cardioversion?
Anaethetised or sedated.
If attempted synchronised cardioversion fails what should you do ?
Choose another lead &/or adjust the amplitude prior to re-trying
In a peri-arrest patient with VT if failed then give an unsynchronised shock to avoid delay in restoring NSR.
For implanted electronic devices (PPM, ICD, Implantable loop recorders and neurostimulators) what is there a risk to all of them when delivering a shock?
Damage, this should not matter though and interograte them to see if working normally after resus attempt.
What is done to minimse the risk of damage to implanted electronic devices when delivery a shock?
Apply pads approx. 10cm away from device and use any of the alternative electrode positions if required
ICD’s when they sense a shockable rhythm will fire uprto 8 shocks and may continue to do so if there is even a brief cessation of the tachycarrythmia. This can cause pain and distress, what should you do to deactivate an ICD in this scenario?
Use a ring magnet placed over the ICD.
If someone has an ICD but it has failed to terminate an arrhytmia resulting in cardiac arrest what should be done ?
Normal ALS protocol and manual defibrillation if appropriate.
For internal defibrillation i.e. during cardiac surgery what shock energy is required if cardiac arrest occurs?
- Bisphasic - 10-20J
- Monophasic 20-40J (max 50J).
