Electrical countershock

23.14 Electrical countershock



Ronald A. Dieckmann, Conor Deasy



Background


When a child’s heart deteriorates into ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), there is usually a severe systemic insult, such as profound hypoxia, ischaemia, acidosis, electrocution, or myocarditis. Sometimes the child has a congenital heart defect such as idiopathic hypertrophic subaortic stenosis or long QT syndrome. Any detectable ventricular rhythm, even fibrillation, suggests that there is still some perfusion of the heart – therefore VF or pulseless VT is a survivable presenting rhythm. This is in distinction to the clinical circumstances with asystole or bradyasystole, the most common paediatric cardiopulmonary arrest rhythms. In these rhythm presentations, the degree of hypoxia is usually so severe that treatment of any kind is less to work. Ventricular dysrhythmias represent approximately 5–10% of presenting paediatric cardiopulmonary arrest rhythms. SVT represents <1%. Resuscitation from such pulseless rhythms also includes ventilation, oxygenation, and effective chest compressions.


Electrical countershock for tachydysrhythmias is a common life-saving procedure in adult emergency cardiac care and is the most effective treatment for sudden cardiac arrest from ventricular dysrhythmias in all age groups. The concept behind electrical countershock is that if a properly delivered electrical dose is applied to the heart in a magnitude that does not damage the myocardium, all electrical activity will be momentarily ablated through depolarisation, and the intrinsic pacemaker of the heart will resume rhythm control (automaticity). When the child is pulseless and has a ventricular dysrhythmia the most effective treatment is immediate electrical asynchronised countershock (defibrillation) performed as quickly as possible with the appropriate technique. In contrast, if a child has a pulse, and the rhythm is either SVT or VT, use synchronised countershock.


Electrical countershock is frequently effective in children with ventricular dysrhythmias but it will not provide benefit in asystole, bradyasystole or pulseless electrical activity (PEA). Essential treatments for VF, such as cardiopulmonary resuscitation (CPR), improved gas exchange, correction of acidosis and vasopressor support of perfusion may change the type of VF from fine, low amplitude VF to coarse, high amplitude VF. Coarse, high amplitude VF is more responsive to electrical countershock than fine, low amplitude VF. After electrical countershock for a ventricular dysrhythmia, administer amiodarone to reduce recurrence. In addition, in children with torsades de pointes VT, give magnesium.


In certain clinical scenarios, other interventions in addition to countershock may also improve survival, e.g. fluids for hypovolaemia, potassium-lowering treatment for hyperkalaemia, calcium for hypocalcaemia, pericardiocentesis for pericardial tamponade and needle thoracostomy for tension pneumothorax.



Indications for asynchronous countershock (defibrillation)



• VF.

• Pulseless VT.


Indications for synchronous countershock



• SVT with shock and pulse but no vascular access rapidly available.

• VT with shock and pulse present.

• Atrial fibrillation or atrial flutter with shock.

• Stable VT or SVT in collaboration with specialist.


Contraindications


Conscious patient with good perfusion.



Equipment



Standard defibrillator (monophasic or biphasic).

Automated external defibrillator (AED).

Newer models feature lower power outputs to deliver lower energy countershocks.


Standard preparation



Open airway. Look listen and feel for no more than 10 seconds. If the child is not breathing or is not breathing normally then deliver 5 rescue breaths. Take no more than 10 seconds to assess for signs of life or a pulse. If there are no signs of life, no pulse, or a pulse rate less than 60 beats per minute commence chest compressions.

If child is pulseless, begin closed chest compressions without delay, delivering 100 chest compressions per minute. For lone rescuers with victims of all ages the chest compression to ventilation rate is 30:2. For health-care providers performing 2-rescuer CPR for infants and children: 15:2 (and 3:1 for neonates).

Turn on the defibrillator but do not activate the synchronised mode.

Select the proper paddles size. Use the 8-cm adult paddles if these will fit on the chest wall; otherwise, use the 4.5-cm paediatric paddles. Self-adhesive electrode pads are simpler, safer and more efficient than the conventional paddles when defibrillating or cardioverting. Paediatric pads are usually recommended for any child under 10–15 kg.

Prep paddles with electrode jelly, paste, or saline-soaked gauze pads, or use self-adhesive defibrillator pads. Do not let jelly or paste from one site touch the other and form an ‘electrical bridge’ between sites, which could result in ineffective defibrillation or skin burns.

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Sep 7, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Electrical countershock

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