Page 450 - Clinical Small Animal Internal Medicine

418 Section 5 Critical Care Medicine

choreographing the steps to be taken. The use of mild The most effective medication to achieve consistent,
VetBooks.ir sedatives can facilitate catheter placement in this situa- rapid vasodilation is nitroprusside, which acts by increas-
ing nitric oxide (a powerful arterial dilator) primarily at
tion. Administration of butorphanol (0.1–0.3 mg/kg) is
generally safe and is unlikely to have an untoward effect
found hypotension, the use of nitroprusside should be
on cardiac performance. The use of diuretics is not the level of the arterioles. Due to the potential for pro-
expected to improve clinical signs in animals with pulmo- reserved for patients with confirmed congestive heart
nary hypertension, tamponade, or tachycardia‐induced failure and systolic or valvular dysfunction. When used,
cardiogenic shock but is also not likely to result in acute nitroprusside is most effective as a constant rate infusion
decompensation. (CRI) with doses starting at 1 μg/kg/min. As with dobu-
Medications that increase cardiac contractility (posi- tamine, nitroprusside dose should be uptitrated until the
tive inotropes) should be considered in animals that have desired effect is achieved or a maximum dose of 10 μg/
documented systolic dysfunction. It must be remem- kg/min is reached. Patients being treated with nitroprus-
bered that positive inotropes not only increase cardiac side should have their blood pressure monitored very
contractility but also increase myocardial oxygen con- closely. Ideally, blood pressure is checked every 10–15
sumption. Dobutamine, an injectable beta‐adrenergic minutes until the target pressure (mean arterial pressure
agonist, can be administered as a constant rate infusion [MAP] 70 mmHg, systemic arterial pressure [SAP]
to treat systolic failure. For dogs with strongly suspected 90 mmHg) is achieved. Mean arterial pressures less than
or confirmed systolic dysfunction, dobutamine can be 60 mmHg or systolic pressures less than 90 mmHg should
started at a rate of 2.5 μg/kg/min. The dose is uptitrated be avoided due to the potential for additional organ
every five minutes until systolic function improves or to injury. An early sign of hypotension in patients on nitro-
a maximum rate of 20 μg/kg/min. In certain clinical situ- prusside is vomiting and if this occurs the patient should
ations, systolic dysfunction cannot be confirmed due to have blood pressure checked immediately and the CRI
the patient’s condition or unavailability of echocardiog- rate adjusted accordingly. Fortunately, nitroprusside has
raphy. In this situation, the clinician will rely on signal- a very short half‐life so discontinuation of a CRI should
ment and results of other diagnostic tests to determine if result in rapid recovery of blood pressure. Inadvertent,
systolic dysfunction is likely. abrupt cessation of nitroprusside should be avoided due
Systolic dysfunction in cats can be difficult to confirm to the risk of rebound hypertension.
due to their rather tenuous condition when in cardio- The use of nitroglycerine paste has been advocated in
genic shock, therefore inotropic support should be the past. There is not good evidence to support its rou-
considered in any cat presenting with heart failure and tine use and dosing of transdermal medications can be
bradycardia. The dose of dobutamine for cats ranges notoriously difficult, especially in low cardiac output
from 1 to 5 μg/kg/min and should again be uptitrated states where absorption and perfusion are likely to be
to effect. In some instances, it may be possible to impaired.
use pimobendan to improve cardiac contractility. Sildenafil citrate is a phosphodiesterase V inhibitor that
Pimobendan is a phosphodiesterase III inhibitor and a has been shown to be useful for the treatment of pulmo-
calcium sensitizer that increases inotropy while reducing nary hypertension in dogs. While the use of sildenafil is
vascular tone, making it an attractive treatment option well documented for management of chronic pulmonary
for many causes of cardiogenic shock. Unfortunately, hypertension, the benefits in the acute setting are less
pimobendan is only available as an oral medication in the clear. Sildenafil has a rapid onset of action so administra-
United States, limiting its use in emergency situations. tion in a crisis would be expected to result in at least some
Administering oral medications to patients in shock improvement in pulmonary pressure. Clinically, this
should be avoided due to the stress associated with pilling appears to be the case. As with pimobendan, however,
and concerns about absorption of the drug from the sildenafil is currently most widely available as an oral
underperfused gastrointestinal tract. An injectable form medication and its administration needs to be carefully
of pimobendan has recently been approved for use in considered prior to dosing. An injectable form of sildena-
Europe with a labeled dose of 0.15 mg/kg. fil is approved for use in human patients with pulmonary
As mentioned earlier, the use of vasoactive medications hypertension but there are no descriptions of clinical use
in cardiogenic shock is rare. Almost never,will a patient in veterinary medicine. When given, the recommended
with cardiogenic shock benefit from an increase in vascu- dose of sildenafil for management of pulmonary hyper-
lar tone alone. The same cannot be said for decreasing tension is 1–2 mg/kg PO TID.
vascular tone, however. Patients that are likely to benefit Treatment of acute pericardial tamponade involves
from afterload reduction include those with rupture of a immediate pericardiocentesis. Although the possibility
first‐order chorda tendina or dilated cardiomyopathy – in of continued, uncontrolled hemorrhage exists, the mor-
other words, patients with forward heart failure. bidity and possible mortality associated with tamponade