Page 451 - Clinical Small Animal Internal Medicine

42 Cardiogenic Shock 419

cannot be tolerated. If complete drainage is not achieved, shock as a result of toxin ingestion. For dogs with ECG‐
VetBooks.ir serial attempts can be made but may not be necessary. confirmed sinus tachycardia (with a rate >180 bpm), the
administration of beta‐blockers should be considered
Because the pericardial sac is essentially an enclosed
sphere, the removal of even a small amount of fluid will
absence of congestive heart failure has been confirmed.
exponentially decrease the pressure within the sac. once other causes of shock have been ruled out and the
Observation of the pericardial space with ultrasound (if Due to the need to urgently address cardiogenic shock,
available) following every attempt at pericardiocentesis injectable, ultra‐short‐acting beta‐blockers should be
should be made. Often, the pericardium is lacerated dur- used as first‐line treatment with oral formulations
ing the attempt and although only a small amount of reserved for patients that have stabilized. Esmolol admin-
fluid is retrieved, tamponade has been relieved and peri- istered as a bolus of 0.2–0.5 mg/kg followed by a CRI of
cardial fluid has been drained into the thoracic cavity 50–200 μg/kg/min is preferred. If bradycardia develops,
where it is better tolerated. In cases where hemorrhage the CRI rate should be slowed or discontinued. Diltiazem
cannot be controlled or multiple attempts at percutane- (5–20 μg/kg/min) can also be used and may be more
ous pericardiocentesis are unsuccessful, emergency effective at managing nonsinus SVT. Because of their
thoracotomy may be required although this should only negative inotropic effects, the use of beta‐blockers and
be attempted as a last resort when death is believed to be calcium channel blockers should be avoided in patients
imminent or cardiac arrest has already occurred. with congestive heart failure.
Treatment of tachyarrhythmias can be achieved Some cardiac rhythms are amenable to electrical car-
through one of two mechanisms: conversion of the dioversion using a debrillator (atrial fibrillation, parox-
rhythm to a normal sinus rhythm or control of the rate of ysmal ventricular tachycardia). When used to perform
ventricular contractions. Administration of antiarrhyth- cardioversion, the energy delivered is generally much
mic medications can be used in an emergency setting to lower (0.5–1 J/kg) than for defibrillation and the timing
treat patients with cardiogenic shock from tachyarrhyth- of energy delivery must be synchronized with the R‐
mias in an attempt to achieve either of these endpoints. wave of the ECG. The synchronization function on the
Due to the urgency inherent in this condition, injectable defibrillator should be activated and the energy dosage
antiarrhythmics are always preferred to oral formula- should be selected. Once the synchronization function
tions. Lidocaine or procainamide are considered first‐ has correctly identified the R‐waves, defibrillation can
line therapies for the treatment of ventricular tachycardia. be performed as usual. If the defibrillator is not equipped
Control of ventricular tachycardia begins with a 2 mg/kg with a synchronization feature then electrical cardiover-
slow bolus of lidocaine. If no response is seen, a second sion should not be attempted as inappropriately timed
dose of lidocaine can be administered. Occasionally, delivery of the shock can result in ventricular fibrilla-
rhythms that are refractory to lidocaine will respond to tion. Heavy opioid sedation or anesthesia should be
procainamide so if the rhythm has not improved with used if electrical cardioversion is going to be attempted
lidocaine, a dose of procainamide 5–15 mg/kg slow IV on a conscious patient to minimize discomfort associ-
can be attempted. ated with the procedure (see description for transcuta-
Amiodarone has recently been incorporated into the neous pacing).
human CPR guidelines developed by the American Treatment of cardiogenic shock due to complete (third
Heart Association for use during cardiopulmonary arrest degree) AV block consists of temporary or permanent
as a treatment for pulseless ventricular tachycardia and placement of a pacemaker. Temporary transcutaneous
ventricular fibrillation refractory to electrical defibrilla- pacing can be used in emergency situations and requires
tion. Amiodarone has been used as an oral medication in little advanced training to be effective. Most modern
veterinary medicine to treat many different arrhythmias, defibrillators are capable of performing temporary trans-
including atrial fibrillation and ventricular tachycardia. cutaneous pacing while temporary transvenous pacing
The use of injectable amiodarone is reported in veteri- may require the use of a pacemaker programmer or pur-
nary patients but has been associated with development pose‐made generator. Transcutaneous pacing is an
of anaphylactic or anaphylactoid reactions. Due to these uncomfortable experience at best and requires general
potential adverse effects, it should be considered as a anesthesia. To perform transcutaneous pacing, the
second‐choice option for management of acute, life‐ patient is prepared while awake. The fur is clipped over
threatening tachyarrhythmias. If amiodarone is going to the heart on both sides of the chest at the level of the
be used, the recommended starting dose is 5–10 mg/kg costochondral junction. The temporary pacing pads are
as a slow IV bolus to effect and the amiodarone should placed and plugged into the defibrillator base unit. Once
be diluted prior to administration. the patient is instrumented, a rapid‐sequence anesthetic
Occasionally, dogs will present with supraventricular induction (IV bolus premed followed immediately by IV
tachycardia (SVT) or sinus tachycardia causing cardiogenic bolus of induction agent) is performed and temporary