Defibrillator
- 1. Defibrillator Dr Sumanth Reddy Assistant professor in Anaesthesiology
- 2. Learning objectives Need for a Defibrillator? Physics behind how a defibrillator works. Types of defibrillator. Clinical uses of a defibrillator. Defibrillator maintenance policy and checklist.
- 3. Defibrillator Definition- Application of a preset electrical current across the myocardium to cause synchronous depolarization of the cardiac muscle with the aim of converting a dysrhythmia into normal sinus rhythm.
- 4. Brief history of defibrillator 1899 : Jean-louis prevost & Frederic batelli demonstrated that “small electrical shocks induce VF and larger shocks revert it” in dogs 1930 : Manual external defibrillator known today was designed by WILLIAM KOUWENHOVEN, an electrical engineer. 1947 : First human use was done by CLAUDE BECK, a surgeon, on a 14 year old boy getting operated for a congenital heart disease.
- 6. Need for a defibrillator “ Defibrillation” – Definitive treatment of life threatening cardiac arrhythmias – VENTRICULAR FIBRILLATION PULSELESS VENTRICULAR TACHYCARDIA Ventricular fibrillation- Irregular contraction of muscle fibres Ineffective pumping of blood from left ventricle Steep fall in Cardiac output
- 7. The longer the duration of fibrillation, the greater the deterioration of the myocardium, because a fibrillating heart consumes a very large amount of oxygen. Defibrillators deliver a brief electric shock to the heart, which enables the heart's natural pacemaker to regain control and establish a normal sinus rhythm .
- 8. One of the most crucial links in the “Chain of survival”(AHA) – EARLY DEFIBRILLATION
- 9. Physics behind Defibrillator 3 major components of a defibrillator : a) Power supply b) Capacitor c) Inductor
- 10. Power supply/ Voltage source Step-up transformers are transformers that increase voltage Allow the doctor to choose among different amounts of charge This output voltage is then fed to a capacitor, which stores the high voltage charge. As an additional energy source, many defibrillators also have internal rechargeable batteries.
- 11. Capacitors Capacitors store a large amount of energy in the form of electric charge This stored energy is released over a short period of time “Capacitance” describes a capacitor quantitatively C = Q/V A capacitor has 1 farad of capacitance if a potential difference of 1 volt is present across its plates, when they hold a charge of 1 coulomb. Capacitors typically have values of microfarads
- 12. Capacitors Capacitance is directly proportional to area and indirectly proportional to the distance between plates C = (Eo x A) / d
- 13. Inductors Coils of wire that produce a magnetic field when current flows through them, prolong the duration of current flow Inductors generate electricity that opposes the motion of current passing through it This opposition is called “inductance”. Inductors typically have values of microhenries (µH).
- 15. Types of defibrillators Manual external defibrillator Automated external defibrillator (AED) Implantable cardiac defibrillator (ICD)
- 16. Manual external defibrillator DC defibrillator Clinician decides what charge has to be set, depending on prior knowledge and experience Shock will be delivered through paddles applied to the patient’s chest. Found in hospitals & ambulances
- 17. Automated external defibrillator A unit based on computer technology and designed to analyze the heart rhythm itself, and then advise whether a shock is required or not. Designed to be used by lay persons, who require little training. Usually limited in the treatment of VF and VT rhythms. Usually take time ( around 5-10 secs) in diagnosing the rhythm Can be found in places like corporate and government offices, shopping centers, airports, restaurants, sports stadiums, schools and universities, community centers, fitness centers and health clubs.
- 19. Automated external defibrillator Require self-adhesive electrodes(pads) instead of handheld paddles The ECG signal acquired from self- adhesive electrodes usually contains less noise and has higher quality ⇒ allows faster and more accurate analysis of the ECG ⇒better shock decisions “Hands off” defibrillation - safer procedure for the operator, especially if the operator has little or no training
- 20. Implantable cardiac defibrillator An electronic device that constantly monitors heart rate and rhythm. When it detects a very fast, abnormal rhythm, it delivers energy to the heart muscle. This causes the heart to beat in a normal rhythm again. Used for cardioversion, defibrillation, anti-tachycardia pacing & bradycardia pacing. 2 parts : a)The leads b)The pulse generator
- 22. Defibrillator electrodes The electrodes for external defibrillation are metal discs about 3-5 cm in diameter (or rectangular flat paddles 5x10 cm ) and attached to highly insulated handle. The size of electrodes plays an important part in determining the chest wall impedance which influence the efficiency of defibrillation. The capacitor is discharged only when the electrodes make a good and firm contact with the chest of the patient.
- 24. Defibrillator electrodes For internal defibrillation when the chest is open, large spoon- shaped electrodes are used.
- 25. Defibrillator with synchronizer Used for termination of unstable ventricular tachycardia with pulse, atrial fibrillation and other arrhythmias In this device the ECG of the patient is fed to the defibrillator and the shock is given automatically at the right moment There is a period in the heart cycle in which the danger is least and defibrillation must take place during this period (this is called “Synchronized Cardio-version”) The function of the synchronizer circuit is to permit placement of discharge at the right point on the patient’s ECG ( avoided during the T wave and it is approximately 20 –30 ms after the peak of the R wave )
- 26. Defibrillator Wave forms Monophasic wave form : Energy is delivered through the patient’s chest in a “single direction” Biphasic wave form : Energy is delivered through the patient’s chest in two directions. Low-energy biphasic shocks may be as effective as higher-energy monophasic shocks
- 28. Energy levels for Defibrillation Defibrillation for Ventricular fibrillation and Pulseless ventricular tachycardia : Monophasic : 360 J Biphasic : 120-200 J If unknown – Use maximum available dose ( manufacturer recommended)
- 29. Synchronized Cardioversion Initial recommended doses: Narrow regular QRS complex tachycardia : 50-100J Narrow Irregular complex tachycardia : 120-200 J biphasic or 200 J monophasic Wide regular QRS complex tachycardia : 100 J Wide irregular QRS complex tachycardia : Defibrillation dose (NOT synchronized)
- 30. Energy levels for Defibrillation Pediatric defibrillation : 2J per Kg Defibrillation using INTERNAL PADS/PADDLES : Monophasic : 50 J maximum Biphasic : 5J, 10J, 20J, 30J, 50J (max)
- 31. Clinical indications Indications for Defibrillation : a) Ventricular fibrillation b) Pulseless Ventricular Tachycardia Indications for Cardioversion – a) Supraventricular Tachycardia (AVNRT/AVRT) b) Atrial fibrillation c) Atrial flutter d) Ventricular Tachycardia with pulse
- 32. Contra-indications Any arrhythmia with enhanced automaticity like Catecholamine induced tachycardia Digitalis toxicity induced arrhythmias Multi focal atrial tachycardia
- 33. Complications Most common- Harmless arhhythmias like atrial/ventricular premature beats. Serious complications : a) ventricular fibrillation b) Thrombo-embolisation c) Myocardial necrosis d) Myocardial stunning e) Pulmonary edema f) Painful skin burns
- 34. Defibrillator maintenance policy First, The daily test procedure - 30 J self-test : is a low energy test to check the charging circuits & the integrity of cables. Second, a weekly check - is carried out to test at higher energy level using ECG simulator. Third, the detailed half-yearly test procedure- should be performed by the biomedical department in a hospital
- 35. Daily low energy test Step 1 : Put the defibrillator on Battery mode and ensure machine is disconnected from the AC power supply . Turn the selector switch to ON and select Manual mode Select leads to PADDLES/PADS Step 2 : Ensure the universal cable is connected to the paddles Place paddles in paddle wells Step 3 : Select the ENERGY to 30 J Step 4 : Press the CHARGE button Step 5 : The unit charges to 30J, then the red LED charge indicator illuminates and the charge tone sounds
- 36. Step 6 : Ensure DEFIB 30J READY displays on screen Step 7 : Press and hold both paddles SHOCK buttons Step 8 : The unit discharges. The TEST OK message displays and the red LED turns off Step 9 : The above TEST OK message conforms that low energy circuits are in proper working condition
- 37. Weekly test: Defibrillator internal discharge test Repeat the steps from 1 to 9 Step 10 : Select ENERGY button to maximum energy level 200J displays Step 11 : The unit charges to 200J, then the red LED charge indicator illuminates and the charge tone sounds Step 12 : Ensure DEFIB 200J READY displays on screen Step 13 : Ensure the machine holds the charge for 50 seconds by giving a long continuous sound Step 14 : This confirms the unit is fully functional
- 38. References ACC/AHA Guidelines 2015 for adult advanced cardiac life support David J Williams, Fiona J Mc Gill. Physical principles of defibrillator, Anesthesia and intensive care medicine; 2003. LL Bossaert. Fibrillation and defibrillation of heart : British journal of anesthesia 1997 ;79:203-213 Kundra P, Vishnu Prasad PS, Padmavathi V, Siva T. Defibrillator maintenance policy. Indian J Anaesth 2015;59:685-7.