Diuretics
Aside from oxygen supplementation, furosemide is one of the most important therapies for treating patients with CHF and cardiogenic
pulmonary edema.18-21 Furosemide can be administered as a bolus (4 to 8 mg/kg intravenously or intramuscularly) or as a constant-rate infusion
(0.66 to 1 mg/kg/hr intravenously) to promote diuresis and decrease pulmonary vascular overload and pulmonary edema. Subcutaneous
administration and absorption of furosemide in patients with CHF is not dependable, given the degree of peripheral vasoconstriction,
and, thus, is contraindicated. The goal of diuretic treatment is to repeat the therapy every 30 to 60 minutes until the patient's
body weight has decreased by 5% to 7%. Loss of body weight typically corresponds with improvement of the patient's respiratory
rate and effort as the pulmonary edema resolves. Once the patient's respiratory rate and effort have normalized, oral furosemide
can be started. Repeated doses of furosemide can cause marked hypokalemia and metabolic alkalosis, particularly in cats, so
potassium supplementation may be required in some patients.
Intravenous fluids: A cautionary note
Unless other drugs need to be administered by constant-rate infusion, the administration of intravenous supplemental fluids
is contraindicated in patients with acute fulminant CHF. If intravenous fluids are necessary, a low-sodium fluid such as lactated
Ringer's solution (130 mEq sodium/L), dextrose 5% in water, or half-strength (0.45%) saline solution should be considered
at the lowest rate possible for drug administration.
Nitric oxide donors
Nitric oxide donors should be given as a primary initial therapy in any patient with fulminant CHF.22 Nitric oxide donors dilate the pulmonary and systemic vasculature, thereby reducing pulmonary vascular pressures. Nitroglycerine
paste (0.25 in for patients < 10 kg [22 lb], 0.5 in for patients 10 to 20 kg [22 to 44 lb], 1 in for patients > 20 kg [44
lb] every eight hours) is absorbed readily across the skin and can be placed on the lateral body wall or the inner ear pinnae.
If cardiac output is poor and the extremities, including the ear pinnae, are cool to the touch, nitroglycerine absorption
may be poor. The axillary region or lateral thoracic wall would be a better site in these patients. Rotate the site at each
treatment to improve absorption.
In a patient with refractory pulmonary edema not responding to traditional diuretic therapy, consider sodium nitroprusside,
as long as the patient is not hypotensive. Sodium nitroprusside is a balanced arteriolar and venous dilator that decreases
both pulmonary and systemic vascular resistance.23 The drug is administered as a constant-rate infusion (2 to 10 μg/kg/min intravenously, gradually increased to effect). Because
of sodium nitroprusside's potent hypotensive effects, closely monitor arterial blood pressure throughout the infusion to reduce
the risk of inducing organ hypoperfusion. When using sodium nitroprusside, start with the lowest dose possible (2 μg/kg/min),
and gradually increase the dose to effect, checking blood pressures every five to 10 minutes. If the patient's blood pressure
does not increase within 15 to 20 minutes, increase the dose in increments of 0.5 to 1 μg/kg/min to effect. Cyanide toxicosis
has been suggested as a potential side effect with the use of nitroprusside for longer than 48 hours.
Morphine
Morphine is an opioid agonist that can be used in patients with CHF. In dogs, low-dose (0.025 to 0.05 mg/kg intravenously
every six to eight hours) morphine dilates the splanchnic vasculature and increases venous capacitance, allowing fluid drainage
from the pulmonary parenchyma.24 Morphine also allows slower, deeper respirations and decreases anxiety in patients with CHF.
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