Page 102 - Small Animal Internal Medicine, 6th Edition

74 PART I Cardiovascular System Disorders

pulmonary edema in animals with chronic heart failure. is usually done at each recheck visit. Electrolyte imbalance
Even before the initial onset of CHF, when the patient still (especially hypokalemia or hyperkalemia, hypomagnesemia,
VetBooks.ir has stage B disease, the authors recommend that clients and sometimes hyponatremia) can occur from the use of
diuretics, ACEIs, and salt restriction. Poor appetite as well as
assess the RRR to become comfortable with the technique
and to establish the animal’s baseline RRR (see Box 3.2).
sium supplements should not be used without documenting
RRRs for normal animals in the home environment usually loop diuretics can promote hypokalemia; however, potas-
are 30 breaths/min or less. A persistent increase (of ≥ 20%) hypokalemia, especially when an ACEI and spironolactone
above the patient’s normal baseline RRR often is the earliest are prescribed. Serum magnesium concentration does not
sign of decompensating heart failure. RRRs above 40 breaths/ accurately reflect total body stores; however, supplementa-
min typically accompany clinical pulmonary edema. This is tion may be especially beneficial in animals that develop
because pulmonary edema increases lung stiffness; faster, ventricular arrhythmias while receiving furosemide and
more shallow respirations reduce the work of ventilating digoxin. Hyponatremia in patients with severe CHF results
stiffer lungs. It is more difficult to monitor heart rate without from an inability to excrete free water (dilutional hyponatre-
disturbing the animal’s rest or sleep. However, in cases where mia) rather than from a total body sodium deficit. It can be
this can be done, a persistent increase in resting heart rate difficult to correct and is considered a poor prognostic sign.
usually accompanies the heightened sympathetic tone of In some cases, reducing the furosemide and/or other diuretic
decompensating CHF. dose, cautiously adding/increasing an arteriolar vasodilator
In addition to home monitoring, periodic recheck exami- (to improve renal perfusion), or increasing inotropic support
nations are important because complications often develop. (with higher pimobendan dose or addition of another ino-
+
The time frame for recheck visits may vary from a few days trope) might improve serum Na concentration. However,
to every 4 months or so, depending on heart disease severity vigilant monitoring is necessary to avoid worsened conges-
and patient stability. All medications and their dosage sched- tion, hypotension, and other potential adverse effects.
ules should be reviewed at each visit. Ask the owner about Many factors can exacerbate the signs of heart failure,
the patient’s RRR, diet, appetite level, activity and stamina, including physical exertion, infection, anemia, exogenous
whether there are any problems with administering the med- fluid administration (excess volume or sodium load), high-
ications or if refills are needed, and any other concerns. salt diet or dietary indiscretion, erratic administration of
A thorough physical examination (see Chapter 1) is medication, inappropriate medication dosage for the level of
important at each evaluation. Depending on the patient’s disease, development of cardiac arrhythmias, environmental
status, additional clinical tests might include blood pressure stress (such as heat, humidity, cold, smoke), development or
measurement, thoracic radiographs, serum biochemistry worsening of concurrent extracardiac disease, and progres-
analyses, resting or ambulatory ECG recording, an echocar- sion of underlying heart disease (including ruptured chordae
diogram, or other tests. Measurement of serum electrolyte tendineae, secondary pulmonary hypertension and right
and creatinine or blood urea nitrogen (BUN) concentrations heart failure, and LA tear). Repeated episodes of acute,
decompensated congestive failure that sometimes require
hospitalization and intensive diuresis are relatively common
BOX 3.2 in patients with chronic progressive heart failure.
Owner Instructions for Monitoring Resting STRATEGIES FOR RECURRENT
Respiratory Rate OR REFRACTORY CONGESTIVE
HEART FAILURE
While your pet is quietly sleeping (or almost sleeping) and
without touching or disturbing him/her, count the number It is important to confirm that the standard stage C heart
of breaths taken during a period of 15 seconds. (You can failure therapies are being appropriately administered to
usually determine this by watching the chest move in and patients that develop recurrent, decompensated CHF. For
out.) dogs, especially those with chronic MR or DCM, this involves
Multiply this number by 4 to obtain the breaths per furosemide (at approximately 2 mg/kg q12 or 8 h), com-
minute. bined with pimobendan (at 0.2-0.3 mg/kg q12h) and an
Keep track of this number by recording it in a calendar or ACEI (usually enalapril or benazepril, at 0.5 mg/kg q12h);
logbook, or with a respiratory rate monitoring phone app. spironolactone (2 mg/kg q24h) usually is included here as
Most dogs and cats with normal lungs have an RRR of well. Recurrent episodes of CHF often respond initially to an
<30 breaths/min; some are <20/min. increased dose of furosemide and/or pimobendan (to q8h
Once you have determined your pet’s normal baseline ±increased dosage, see following text). Renal function and
RRR, continue to monitor the RRR periodically.
If this number becomes persistently increased by more electrolytes should be assessed; ultimately, increases in furo-
than 20% above his/her normal baseline (and especially semide dosage are limited mainly by kidney function. If the
if the RRR increases >40 breaths/min), this may be an early ACEI has been dosed only once daily, it is increased to every
indicator of congestion (fluid) in the lungs and you should 12 hours, unless this is not tolerated. If spironolactone is not
contact your veterinarian. already being administered, it should be added. Arrhythmias
commonly develop in animals with advanced heart failure