Page 400 - Feline Cardiology

420 Section O: Anesthesia in the Patient with Cardiac Disease

channel blockers such as diltiazem (0.02–0.1 mg/kg; ticularly if an abnormal respiratory pattern or tachypnea
begin low and repeat as needed) can also be adminis- is present. Pulse oximetry can sometimes be obtained by
tered intravenously. placing the probe on the ear, or on a toe web. Some cats
The treatment of ventricular arrhythmias is consid- require oxygen supplementation for a few hours after
ered necessary during anesthesia if they cause hypoten- anesthesia based on persistently low arterial oxygen
sion, are multifocal, or are malignant (e.g., R on T content on blood gas, persistent desaturation on pulse
phenomenon). Lidocaine at a low dose (0.5–1 mg/kg oximetry, or cyanosis. Continuous oxygen supplementa-
bolus, repeated if necessary up to 4 mg/kg) can be used tion can be achieved by placing the patient in an oxygen
in cats with normal cardiac function, but should be used cage, or, if such a cage is not available, in an induction
very cautiously in cats with cardiac disease, particularly box with a high oxygen flow.
during anesthesia, since it may result in a severe decrease
in cardiac output, presumably due to an effect on myo- PLANNING ANESTHESIA IN THE CARDIAC
cardial contractility. A study in normal cats anesthetized PATIENT WITHOUT AN ECHOCARDIOGRAM
with isoflurane showed that lidocaine dose-dependently
reduced cardiac output, despite also reducing require- Although an echocardiogram is an invaluable tool to
ments for isoflurane (Pypendop and Ilkiw 2005a,b). diagnose the presence and specific type and extent of
Alternatively, short-acting beta blockers like esmolol can cardiac disease, sometimes clients are unable to pursue
also be used. a thorough diagnostic workup prior to anesthesia.
Murmurs in cats are not definitive for presence of struc-
Anesthetic Management of Cats with tural heart disease; 69% of asymptomatic cats with
Shunting Defects murmurs in one study had no evidence of cardiomyopa-
Left-to-right cardiovascular shunts including ventricu- thy or cardiac disease (Paige et al. 2009). On the con-
lar septal defects or patent ductus arteriosus may lead to verse, absence of a murmur does not exclude presence
volume overload of the left ventricle and possibly left of heart disease; only 31% of asymptomatic cats with
heart failure. During anesthesia, shunting may be cardiomyopathy had murmurs in one study (Paige et al.
reduced by increasing pulmonary vascular resistance, 2009). As a precaution, an abnormal cardiac ausculta-
decreasing systemic vascular resistance, or both. Carbon tion including a murmur or gallop heart sound should
dioxide has been reported to cause systemic vasodilation raise suspicion of possible heart disease, and thoracic
and pulmonary vasoconstriction (Barer et al. 1967; Price radiographs should be taken if further diagnostic
1960), so mild-moderate permissive hypercapnia (e.g., workup with an echocardiogram is not possible.
PaCO 2 50–60 mm Hg) may be beneficial. Radiographic evidence of significant cardiomegaly and
Right-to-left shunting through ventricular septal pulmonary edema or pleural effusion demand treat-
defects or patent ductus arteriosus may be reduced by ment and further justify diagnostic workup with echo-
increasing systemic vascular resistance, and can be wors- cardiography, blood pressure, and a minimum data base,
ened with systemic hypotension. Baseline arterial blood and postponing or canceling (if elective) the anesthetic
gas analysis or pulse oximetry often reveals significant procedure.
hypoxemia prior to anesthesia. Titration of vasocon- If an echocardiogram is not possible but anesthesia is
strictors such as phenylephrine may result in improved deemed indispensable, the practitioner is forced to
predict the form of heart disease present in the cat,
Anesthesia (often in conjunction with pulmonic stenosis) are which is very difficult or impossible. Because cardiomy-
oxygenation. Shunting through a patent foramen ovale
opathies, and hypertrophic cardiomyopathy in particu-
usually unresponsive to modulation of arterial resis-
lar, are the most common heart diseases in cats, the
tance or other interventions.
practitioner may want to assume that this disease is
present. A generic “cardiac” anesthetic protocol can be
POSTOPERATIVE MONITORING AND RECOVERY
used in cats without significant arrhythmia or heart
Oxygen should be administered until extubation. If iat- failure if unspecified cardiac disease is suspected. This
rogenic fluid overload is suspected, thoracic radiographs anesthetic protocol is particularly adapted to moderate
should be taken prior to recovery, and treatment should hypertrophic cardiomyopathy, but it is unlikely to result
be instituted if indicated. After extubation, pulse rate, in severe complications if another form of mild cardiac
respiratory rate and pattern, and body temperature disease is present. Premedication includes an opioid and
should be monitored at least every 15 minutes until the avoidance of acepromazine and anticholinergics.
cat is totally recovered and deemed normal. The chest Induction may include propofol (4 mg/kg) and diaze-
should be ausculted bilaterally on a regular basis, par- pam (0.3 mg/kg), or etomidate (1–2 mg/kg) and diaze-