Page 683 - ACCCN's Critical Care Nursing

660 S P E C I A LT Y P R A C T I C E I N C R I T I C A L C A R E

Defibrillation After checking for a pulse, the AED requires only four
While CPR has been associated with improved survival steps to operate: turn power on, place self-adhesive elec-
to discharge from hospital, it cannot be substituted for trodes on a victim’s chest, rhythm analysis follows (hands-
the definitive treatment of early defibrillation. It is thought off period), then (if advised by the machine) press the
that CPR will supply sufficient oxygen to the brain and shock button. The AED will automatically interpret
heart until defibrillation is available. Ultimately, despite the cardiac rhythm and if VF/VT is present, will advise the
the most effective CPR, the single-most important cause operator to provide a shock. This ‘hands-off’ period may
of decreased prognosis in pulseless VT/VF cardiac arrests result in significant interruptions to chest compressions
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is a delay in electrical defibrillation. 3 and adversely impact patient survival. The combined
preshock and the postshock pause ideally should be less
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Praecordial thump than 5 seconds. This can be achieved by continuing
compressions while the defibrillator is charging and
A praecordial thump is a single, sharp blow delivered resuming chest compressions immediately after the deliv-
with a clenched fist to the midsternum of a victim’s chest ery of the shock. Biphasic AEDs are safe, easy to use and
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from a height of 25–30 cm above the sternum. The are effective for detecting and classifying arrhythmias
mechanical energy generated by the praecordial thump (sensitivity 100%, specificity 97%). FAEDs are pro-
may generate a few joules, and therefore if applied within grammed to assess the rhythm, charge the defibrillator
the first few seconds of onset of a shockable rhythm, but and deliver shocks without user intervention.
it has a very low success rate at converting VF/VT to a
perfusing rhythm. 50,51 Because of the very low success rate Successful defibrillation and survival to discharge is
and the brief period for application, delivery of the thump inversely related to the time from onset of ventricular
must not delay accessing help or a defibrillator. Only situ- fibrillation to defibrillation. For every minute that passes,
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ations where the VF arrest is witnessed and monitored the probability of survival decreases 5–10%, so resusci-
and a defibrillator is not immediately on hand (i.e. criti- tation bodies place great emphasis on early defibrillation.
cal care environments) would the delivery of the praeco- To facilitate early defibrillation, ILCOR endorses the
rdial thump be appropriate. 20 concept of non-medical individuals being authorised,
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educated and encouraged to use defibrillators. This
Electrical defibrillation public access to early defibrillation has seen the place-
ment of defibrillators on aircraft, in casinos and cricket
Defibrillation is the passage of a current of electricity grounds, with non-medical personnel such as police,
through a fibrillating heart to simultaneously depolarise flight attendants, security guards, family members and
the mass of myocardial cells and allow them to repolarise even children successfully initiating early defibrilla-
uniformly to an organised electrical activity. There are tion. 57,58 The effectiveness of training non-traditional out-
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two defibrillator modes for delivery of electrical energy: of-hospital first responders to use the AED has improved
monophasic and biphasic waveforms. Monophasic defi- survival to discharge rates. Similarly, in-hospital cardiac
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brillators are no longer manufactured, however they are arrests also occur in any area, and all healthcare workers
still available in clinical settings. Monophasic defibrilla- should be capable of initiating early defibrillation. The
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tors operate by the current travelling in one direction ARC notes that while BLS does not have to include the
from one paddle through the heart to the opposite use of adjunctive equipment, the use of AEDs by persons
paddle. 52,53 In comparison, the biphasic defibrillator’s with education in their use is supported and should be
current travels in one direction through the heart for a taught. Figure 24.3 outlines the integration of defibrilla-
predetermined time, then reverses. tion with BLS.

Practice tip
Practice tip
Effective BLS can slow the loss of amplitude and waveform of
VF. Interruptions to effective CPR should be kept to a minimum. Remember, when using a monophasic defibrillator for AF car-
dioversion, the use of hand-held paddles is preferable to the
use of self adhesive pads. 59
There are two types of external defibrillators: the manual
external defibrillator (MED), and the automatic external
defibrillator (AED). The AED can be either fully auto- For 90% of people in VF, return of a perfusing rhythm
matic (FAED) or semiautomatic (SAED). The MED will occur after a single shock. However it is rare that a
requires the user to be able to immediately and accurately pulse will be palpable with the perfusing rhythm, hence
recognise arrhythmias and make the decision whether to the immediate resumption of chest compressions in the
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initiate defibrillation or not. In comparison, the AED postshock period is supported. Failure to successfully
automatically detects and interprets the rhythm without convert VF after the single-shock strategy may indicate the
relying on the user’s recognition of arrhythmias. AEDs need for a period of effective CPR (30 : 2) for 2 min and
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can be operated in both manual and semiautomatic rhythm reanalysis, then shock if indicated. A single
mode. When using an AED, the user determines whether shock strategy is now recommended for all patients in
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the person is unresponsive, not breathing and pulseless. cardiac arrest requiring defibrillation for VF or pulseless