Pleural
Fluid Sampling (or Thoracentesis)
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What is the
test?
Some infections and diseases cause fluid to
accumulate in the space between the lung and
the rib cage or between the lung and the diaphragm.
This collection of fluid is called a pleural
effusion. A pleural effusion might be detected
on a chest x-ray. Sampling this fluid is important
because it enables doctors to understand what
caused the fluid to collect and how to treat
the problem. The fluid can be sampled with a
needle.
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How
do I prepare for the test?
You will need to sign a consent form giving
your doctor permission to perform this test.
Some patients have this test done in a doctor's
office, while others are admitted to the hospital
for it. Generally your doctor will decide whether
you need to be in the hospital based on your
medical condition. A chest x-ray or an ultrasound
is done before the procedure.
Tell your doctor if you have ever had an allergic
reaction to lidocaine or the numbing medicine
used at the dentist's office. If you take aspirin,
nonsteroidal anti-inflammatory drugs, or other
medicines that affect blood clotting, talk with
your doctor. It may be necessary to stop or adjust
the dose of these medicines before your test.
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What
happens when the test is performed?
You wear a hospital gown and sit on a bed or
table leaning forward against some pillows. The
doctor listens to your lungs with a stethoscope
and may tap on your back to find out how much
fluid has collected.
Soap is used to disinfect an area of skin on
one side of your back. A small needle is used
to numb a patch of skin between two of your lower
ribs. The numbing medicine usually stings for
a second. A needle on an empty syringe is then
inserted into the fluid pocket. Usually this
pocket is around one inch below the skin surface.
You might feel some minor pressure as the needle
is inserted. Depending on the quantity of fluid
that the doctor plans to remove, either the syringe
itself is filled or soft plastic tubing is used
to remove fluid into a collection bag or jar.
While the doctor is attaching the tubing, he
or she might ask you to hum out loud. This humming
is for your safety: It prevents you from taking
a deep breath, which could expand your lung,
causing it to touch the needle.
It sometimes takes 15 minutes or longer to remove
the necessary amount of fluid. Most patients
feel no discomfort during this time, although
a few patients feel some chest pain at the end
of the procedure as their lung expands and touches
the chest wall. After the fluid is removed, a
bandage is placed on your back.
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What
risks are there from the test?
This procedure carries a few serious risks,
but most patients have no complications. If the
needle touches the lung it may create an air
leak, which is seen on the x-ray and might require
you to stay in the hospital for a few days. Some
patients with this complication need to have
a plastic tube (called a chest tube) inserted
between two ribs. The tube uses vacuum pressure
to keep the lung expanded until it has healed.
Other risks include bleeding into the fluid
space or infection. Rarely, if a large amount
of fluid is removed (more than one liter), the
rapid pressure changes in your lung as it fills
this space can cause some fluid to seep from
your bloodstream into your lungs. This is called
pulmonary edema. Let your doctor know if you
feel shortness of breath following the procedure.
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Must
I do anything special after the test is over?
You will need to have an x-ray taken after the
sampling is completed. Your breathing should feel
the same (or better) after the procedure.
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How
long is it before the result of the test is
known?
The fluid may be tested for a variety of things,
including infection and cancer. Cells in the
fluid will be examined. It may be several days
before full results are available.
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