812
P A R T 9
Drugs acting on the renal system
CRITICAL THINKING SCENARIO
Using frusemide (Lasix) in heart failure
THE SITUATION
M.R. is a 68-year-old woman with rheumatic mitral valve
heart disease. She has refused any surgical intervention and
has developed progressively worsening heart failure (HF).
Recently frusemide (
Lasix
), 40 mg/day PO, was prescribed
for her along with digoxin. After 10 days with the new
prescription, M.R. calls to tell you that she is allergic to the
new medicine and cannot take it anymore. She reports
extensive ankle swelling and difficulty breathing. You refer
her to a cardiologist for immediate review.
CRITICAL THINKING
Think about the physiology of mitral valve disease and the
progression of HF in this person. How does frusemide
work in the body?
What additional activities will be important to help maintain
some balance in this person’s cardiac status?
What is the nature of M.R.’s reported allergy and what other
options could be tried?
DISCUSSION
Over time, an incompetent mitral valve leads to an
enlarged and overworked left ventricle as the backup of
blood “waiting to be pumped” continues to progress.
Drug therapy for a person with this disorder is usually
aimed at decreasing the workload of the heart as much
as possible to maintain cardiac output. Digoxin increases
the contractility of the heart muscle, which should lead
to better perfusion of the kidneys. Frusemide—a loop
diuretic—acts on the loop of Henle to block the
reabsorption of sodium and water, and lead to a diuresis,
which decreases the volume of blood the heart needs to
pump and makes the blood that is pumped more efficient.
This blood then has an oncotic pull to move fluid from
the tissue into circulation, where it can be acted on by the
kidney, leading to further diuresis.
M.R. should be encouraged to maintain fluid intake
and to engage in activity as much as possible but to
take frequent rest periods. Her potassium level should
be monitored regularly (this is especially important
because she is also taking digoxin, which is very sensitive
to potassium levels), her oedematous limbs should be
elevated periodically during the day, and she should
monitor her sodium intake.
When M.R. was questioned about her reported
allergy, it was discovered that her “allergic reaction” was
actually increased urination (a therapeutic effect). M.R.
needs to learn about the actions of the drug. She also
needs information about the timing of administration
so that the resultant diuresis will not interfere with rest
or with her daily activities. HF is a progressive, incurable
disease, so education is a very important part of the overall
management regimen.
CARE GUIDE FOR M.R.: DIURETIC AGENTS
Assessment: History and examination
Assess M.R.’s health history, including allergies to diuretics,
fluid or electrolyte disturbances, gout, glucose
tolerance abnormalities, liver disease, systemic lupus
erythematosus, pregnancy and breastfeeding.
Focus the physical examination on the following areas:
Neurological: orientation, reflexes, strength
Skin: colour, texture, oedema
Cardiovascular: blood pressure, pulse, cardiac auscultation
Gastrointestinal: liver evaluation
Genitourinary: urinary output
Laboratory tests: haematology; serum electrolytes, glucose,
uric acid; liver function tests
Implementation
Obtain daily weight and monitor urine output.
Provide comfort and safety measures: sugarless lozenges,
mouth care, safety precautions, skin care, nutrition.
Administer the drug with food early in the day.
Provide support and reassurance to deal with drug effects
and lifestyle changes.
Provide teaching regarding drug name, dosage, side effects,
precautions, warnings to report, daily weighing and
recording dietary changes as needed.
Evaluation
Evaluate drug effects: urinary output, weight changes,
status of oedema, blood pressure changes.
Monitor for adverse effects: hypotension, hypokalaemia,
hyperkalaemia, hypocalcaemia, hypercalcaemia,
hyperglycaemia, increased uric acid levels.
Monitor for drug–drug interactions as indicated.
Evaluate the effectiveness of the teaching program and
comfort and safety measures.
TEACHING FOR M.R.
• A diuretic, or “water pill”, such as frusemide (
Lasix
) will
help to reduce the amount of fluid that is in your body by
causing the kidneys to pass larger amounts of water and
salt into your urine. By removing this fluid, the diuretic
helps to decrease the work of the heart, lower blood
pressure, and get rid of oedema or swelling in your tissues.
• This drug can be taken with food, which may eliminate
possible stomach upset. When taking a diuretic, you
