Page 401 - Clinical Small Animal Internal Medicine

37 Cardiopulmonary Resuscitation 369

potential complications associated with over‐ or under- normal electrical function does not necessarily correlate
VetBooks.ir correction, the management of electrolyte derangements with return of normal mechanical function of the heart
(i.e., PEA). It is therefore recommended that a single
during CPA should be reserved for animals with con-
firmed rather than assumed disturbances.
resumption of chest compressions for a full two‐minute
Recently, the use of an impedance threshold device defibrillation attempt be made followed by immediate
(ITD) intended to increase cardiac output during CPR cycle prior to ECG evaluation. This improves coronary
has been described in canine patients and results appear blood flow to the myocardium, making successful defi-
promising. Unfortunately, the use of an ITD is limited to brillation with resumption of mechanical activity more
patients greater than 10 kg. likely.
Performing defibrillation begins with selecting appro-
priately sized paddles. Most defibrillators come equipped
Defibrillation with standard‐sized adult paddles, which are suitable for
most patients larger than 15 kg. Smaller pediatric pad-
The purpose of defibrillation is to depolarize as many dles are usually available as a clip‐on attachment and
cardiac myocytes as possible, making them temporarily should be used for smaller dogs and cats to ensure
refractory, allowing the native pace‐making cells to focused delivery of the shock through the heart.
resume organized electrical conduction. Electrical defi- Defibrillator paste or contact gel is generously applied to
brillation should only be attempted on rhythms that are the paddles. The animal is typically placed in dorsal
potentially responsive to it. Of the four arrest rhythms, recumbency and the defibrillator paddles are placed on
only two are responsive to electrical defibrillation: ven- either side of the thorax at the level of the costochondral
tricular fibrillation (most significant in veterinary medi- junction with the heart centered between the paddles.
cine) and pulseless ventricular tachycardia. Any attempts The patient is firmly grasped between the paddles and is
at converting nonresponsive rhythms will not result in maintained in dorsal recumbency by the person deliver-
return of spontaneous circulation and will only need- ing the defibrillation. Once the patient is positioned,
lessly expose team members to accidental defibrillation depressing the charge button on the paddles or on the
and increase time spent without compressions. base unit charges the defibrillator. To maintain safety, the
There are two types of defibrillators commonly used in patient should be positioned prior to charging the pad-
veterinary medicine. Monophasic defibrillators function dles to lessen the likelihood of accidental discharge.
by passing a single electrical current from one electrode Once the defibrillator is charged, the provider should
through the heart to a receiving electrode. Biphasic defi- ensure that no one is in contact with the patient or metal
brillators pass a current from one electrode to the other; tabletop. Verbal commands to “CLEAR” the patient are
the current then reverses direction and is passed back to effective. Once all rescue providers are clear of the
the original electrode. This technology allows effective patient, the shock is delivered by depressing the shock
defibrillation to be performed using less energy than delivery buttons on the paddles or defibrillator base unit.
monophasic defibrillation, resulting in less myocardial Animals with thick undercoats that inhibit paddle con-
injury. If available, biphasic defibrillation is preferred. tact should be rapidly clipped at the intended paddle
Being familiar with the type of defibrillator in the practice locations prior to defibrillation attempts. The use of
is important due to the difference in energy selection, alcohol to improve paddle contact should be strictly
with monophasic defibrillator doses beginning at 4–6 J/ avoided due to the risk of fire.
kg and biphasic defibrillator doses beginning at 2–4 J/kg. Alternative defibrillation techniques involve the use of
If defibrillation is not successful following the first defibrillation pads attached directly to the patient and
attempt, the dose delivered can be increased by 50% for left in place while connected to the defibrillator base
subsequent defibrillation attempts. unit. The pads are placed on the chest in the same loca-
Historically, it was recommended to administer three tion as the paddles. If pads are used then clipping of the
stacked defibrillation attempts (discharges in rapid suc- hair is mandatory to ensure good contact between the
cession) prior to resuming chest compressions. The pads and the patient. The advantage to the use of pads is
advent of biphasic defibrillators and the recognition that that no rescue providers have to be in contact with the
delays in resumption of chest compressions can have a patient and patient positioning is minimally interrupted.
negative effect on outcome have made this recommen- The disadvantage is the necessity of clipping the hair that
dation obsolete. It should be remembered that successful results in longer time without chest compressions. The
defibrillation means that fibrillation has been stopped, use of a posterior paddle assembly, a flat paddle replace-
not that ROSC has been achieved. Successful defibrilla- ment resembling a spatula, may be the best method for
tion therefore can result in asystole or an electrocardio- delivering defibrillation in veterinary patients. The pad-
graphically normal rhythm. However, resumption of dle assembly is coated with paste or gel, as a normal