Download Paracentesis: You Want Me to Put the Needle Where?

Paracentesis: You Want Me to Put the Needle Where?
Ladan Mohammad-Zadeh, DVM, DACVECC
DoveLewis Annual Conference Speaker NOtes
Paracentesis can be an important diagnostic and therapeutic tool in veterinary medicine.
It is a technique that can be used both in an emergency and non-emergent setting with
basic tools. This lecture will cover the basics of thoracocentesis, abdominocentesis and
pericardiocentesis. For any paracentesis you want to be familiar with some standard
questions. What are the indications and contraindications for the procedure? What are
the anatomical landmarks to perform the procedure? What tools will you need to perform
the procedure? What are complications of the procedure? How much should you be able
to diagnose on a fluid sample?
Thoracocentesis
Causes:
 Major causes of pleural effusion: Neoplasia, pyothorax, chylothorax, hemothorax,
heart failure transudate
 Less common causes: hypoalbuminemia related effusion, pancreatitis related,
vasculitis, severe pneumonia related, trauma related, diaphragmatic hernia, lung
lobe torsion – these etiologies typically result in smaller quantity effusions that
will resolve once the underlying disease process is addressed.
 Major causes of pneumothorax: Intrinsic causes (bulla, bleb, inflammatory disease
causing alveolar rupture such as severe pneumonia or neoplasia, asthma) and
Extrinsic causes ( iatrogenic, trauma)
Indications
 Therapeutic: to relieve excessive fluid or air accumulation
 Diagnostic: to obtain sample for analysis. Plain red top and purple top are ideal for
sample submission
 It is common to do both therapeutic and diagnostic in the same procedure.
Contraindications
Active coagulopathy (platelet dysfunction or DIC), actively moving patient that makes
risk of complications higher. The caveat is that these things can be addressed and should
be addressed if an immediate therapeutic centesis is necessary.
Anatomical Landmarks
ICS 7-9 is the best place to start to perform a blind thoracocentesis. If you are using
ultrasound to help guide you to fluid pockets, then you may venture outside these
landmarks. In general, entering at the costochondral junction is best for fluid and slightly
more dorsal for air. However if the patient is in lateral recumbency, tap for air at the
highest point of the chest. Remember the intercostal vessels follow the caudal border of
2013 DoveLewis Annual Conference
Page 1
the ribs, thus entering the thorax just cranial to the rib is the best way to avoid these
vessels.
Necessary Tools
The basic items needed are a needled apparatus, +/- extension set, +/- three way
stopcock, syringe and collection bucket and sterile tubes (if collecting fluid). The gauge
and length of the needle will vary greatly depending on the size of the patient. You may
get a lot of help in determining the thickness of the chest wall by measuring it on a VD
radiograph. In general ¾ - 1 inch needle, 22-20 gauge works well for most non-obese cats
and similar sized dogs. For medium sized dogs the needle should be at least 1 inch long
and 20-18 ga and for large dogs, 1.5 in and 18 ga. Remember large dogs can have large
amounts of fluid or air, thus consider using a 16ga or even 14 ga needle. Plain needles or
butterflys work well, but the advantage of using a catheter is the ability to remove the
stylet to reduce the risk of iatrogenic trauma. Use a three way stopcock if you anticipate
more than one syringe full of fluid or air will be collected. Don’t forget to have collection
tubes and a large collection bucket if you anticipate a large amount of fluid will be
aspirated.
Procedure
Shave a region 2-3 rib spaces cranial and caudal to where you intend to enter the thorax.
For large dogs, you can use a local lidocaine block to instill a bleb under the skin and into
the intercostal muscle, especially if you are using a large gauge catheter. Locate the rib
and enter the chest just cranial to the rib as the intercostal vessel lies caudal to the rib.
Try to avoid entering the thorax with an open ended needle/catheter to lessen the
chance of introducing air into the pleural space. Gently pull back on the syringe to collect
fluid or air. You may gently redirect the needle or catheter if you get negative pressure. It
is possible you may need to remove the needle and try again at a rib space cranial or
caudal to the original site. You can also try going a little more dorsally or ventrally.
Pocketed pleural fluid can be very difficult to completely remove. The expectation is to
remove most of the fluid, not all of the fluid. Post tap radiographs can be helpful in
determining how much fluid remains.
Complications of the Procedure
Iatrogenic complication during thoracocentesis can be kept to a minimum if you stick to
the correct anatomical landmarks and the shortest needle length for the patient. However
complications can still arise and include lung laceration and resultant pneumothorax and
lacerating the intercostal vessel. When aspirating fluid it is tempting to pull back on the
syringe as hard as you can to get the most negative pressure and get a faster aspiration
of fluid. However creating excessive negative pressure in the chest may result in rupture
of fragile alveoli. Thus it is safest to not apply more than 5ml of negative pressure while
aspirating fluid from the thoracic cavity. If a complication does happen, DON’T PANIC!
Iatrogenic pneumothorax is possible and may result in needing a follow up tap, but
uncommonly does it progress beyond this.
Abdominocentesis
Causes of ascites
Too numerous to list! A short list would include liver failure, heart failure, septic
abdomen, neoplasia, hemoabdomen, uroabdomen, pancreatitis related. Any inflammatory
disease in the abdomen can result in small amounts of peritoneal effusion.
Indication for Abdominocentesis
2013 DoveLewis Annual Conference
Page 2
It is usually being done for diagnostic purposes thus a small amount is being removed.
But liver failure and heart failure patients may accumulate enough to create respiratory
compromise or general discomfort and require large amounts of the effusion to be
removed.
Contraindications
Similar to thoracocentesis, however since abdominocentesis is generally a quick
diagnostic tap instead of a prolonged therapeutic procedure, even the presence of a
coagulopathy may not stop you from performing a quick abdominal tap. The presence of
a large space occupying mass or GDV could make a blind abdominocentesis more risky,
thus the use of an ultrasound to find a fluid pocket is advised to help reduce the risk of
lacerating a malpositioned spleen, liver or inadvertently aspirating a mass or bowel.
Anatomical Landmarks
For a blind abdominocentesis a four quadrant tap using the umbilicus as a center point is
often recommended with the patient in lateral recumbency. Also a single blind tap at the
level of the umbilicus is another method. Alternatively if you have an ultrasound machine,
you can go where the fluid pocket is.
Necessary Tools
For a simple diagnostic abdominocentesis, the basic items needed are a needled
apparatus and a syringe. If you are performing a therapeutic centesis then you will
additionally need an extension set, three way stopcock, collection bucket and sterile
tubes. The gauge and length of the needle will vary greatly depending on the size of the
patient. A ¾ inch to 1 inch butterfly or regular needle works well in cats and small dogs
while a minimum of 1.5 in is usually needed in larger dogs.
Pericardiocentesis
Causes of Pericardial Effusion
Idiopathic, neoplasia (hemangiosarcoma, chemodectoma, lymphoma), coagulopathy, atrial
rupture, fungal disease. Cats have a slightly more expanded list that includes the
aforementioned along with CHF and FIP. In fact non-neoplastic causes for pericardial
effusion are more common than neoplastic causes in cats.
Indications
Pericardial fluid visualized on ultrasound examination that is resulting in circulatory
compromise. Tamponade is an automatic indication of performing a pericardiocentesis.
Tamponade occurs when pericardial space pressure exceeds right atrial pressure
resulting in collapse or buckling of the right atrium. This can usually be seen on
ultrasound. Clinical signs of pericardial effusion may be subtle such as lethargy and
coughing or severe such as hypotension, tachycardia, pale MM and collapse. Chronic
pericardial effusion may result in right sided heart failure signs such as ascites or left
sided heart failure signs such as pulmonary edema.
Contraindications
Active coagulopathy or an actively moving patient, both of which can be addressed prior
to centesis.
Anatomical Landmarks
2013 DoveLewis Annual Conference
Page 3
ICS 6 dorsal to the sternum or better to use an US to guide you. Sternal or lateral
recumbency is acceptable. Entering from the right side is safest to avoid lacerating the
great vessels.
Necessary Tools
Over the needle catheter, gauge and length varies with the patient. 20ga catheter works
well for cats and small dogs. Large 16ga or 14 ga intracaths are necessary for large breed
dogs. No. 11 blade, extension set, three way stop cock, syringe, collection buckets and
tubes, lidocaine, EKG.
Procedure
Clip a large area from ICS 4 to 8. Infuse lidocaine at ICS 6 just dorsal to the sternum as a
bleb under the skin but also insert the needle into the intercostal muscle and continue to
infuse as the needle is coming out of the muscle creating a “tunnel” of lidocaine. Be
careful to limit the lidocaine dose to 2mg/kg for a dog and < 0.5mg/kg for a cat as more
lidocaine may be needed during the procedure. Take a No. 11 blade and make a small
incision in the skin over the bleb. This may not be necessary in a small dog or cat. Enter
at the level of the lidocaine bleb and advance the catheter until a flash is seen in the hub.
Remove the stylet and attach the hub to the extension set/three way stopcock. Place the
first of the fluid that is obtained in a plain red top tube and observe for clotting. Cavitary
blood is defibrinated and usually will not clot. Remove the fluid until you get negative
pressure. You may recheck with the US to see how much effusion remains. Even if you
only remove a small quantity of effusion you may notice a dramatic improvement in
cardiac output parameters such as MM color, BP and HR.
Complications
The most common complication that occurs during pericardiocentesis is ventricular
arrhythmias. The closer you get to the wall of the ventricle the more likely this is to occur.
This is why it is very important to have an EKG on the patient at all times when doing
this procedure. A few VPCs may not require treatment, but a sudden aggressive run of
ventricular tachycardia will require lidocaine for conversion (2mg/kg dog, 0.5mg/kg cat).
Ventricular wall tear or entering into the ventricle can occur but is not common. You will
know this may have happened by confirming the blood in the tube is clotting or by seeing
aggressive arrhythmias.
Interpreting the Fluid
Most of us don’t claim to be clinical pathologists but there is a lot of information you can
obtain from a fluid sample before you send it out for cytology. First examine the fluid
color and turbidity. Most fluids will have some pink color to it, even if it is benign, noninfectious in nature. But completely see through, straw colored fluid is certainly less likely
to have any cells in it. Just because a fluid may be hemorrhagic doesn’t mean it is
hemorrhage. Spin the fluid in a hematocrit tube and obtain a PCV on it. Comparing it to
the peripheral PCV will be helpful in determining if it does in fact represent hemorrhage.
Now that you have a tube that has a spun fluid sample, you can take the opportunity to
get a refractometry total protein level on the fluid. Knowing if it is low, moderate or high
in protein can help you rule certain diseases in or out. Smell the fluid (yuck!). If it smells
like pus, it probably is . Here is a table below of fluid classification based on protein
level.
Fluid Type
2013 DoveLewis Annual Conference
Characteristics
Page 4
Pure transudate
Modified transudate
Exudate
TP < 2.5 g/dL, Total Nucleated cell count < 1500
TP 2.5 – 7.5, TNCC 1000 to 7000
TP > 3.0 g/dL, TNCC > 7000
On cytological examination, the only things I concern myself with are 1) the subjective
cellularity of the sample, 2) the predominant WBC type, and 3) the presence or absence of
intracellular bacteria. These three things can be very helpful in starting to get a handle
on the disease process in your patient. I don’t try to be a pathologist and look for
neoplastic cells, but I will comment on any very large cells that I see. Cancer is generally
not a surgical emergency unless it is causing a septic process, hemorrhagic process, or
obstructive process. The hemorrhagic and obstructive processes are easier to diagnose,
but the septic process can also be ruled in or out simply by looking at the fluid. There
should not be any bacteria in a thoracic or abdominal fluid sample. If you see intracellular
bacteria, that is an indication for surgical intervention. If you see extracellular bacteria,
you should consider the possibility of stain contamination or stain precipitate on the slide.
If you see rare extracellular bacteria then you could wait for the cytology results if the
patient is stable to wait and isn’t showing signs of sepsis. Here are some general
guidelines for what you might see with certain conditions.
Fluid type
Protein
Cellular characteristics
Septic fluid (abd or thorax)
TP > 3.0
Neoplastic
TP >2.5
CHF
Chlyothorax
TP <2.0
TP < 2.0
Non-neoplastic
inflammatory,
pancreatitis, etc.
FIP
TP
variable
Mostly neutrophilic inflammation with
intracellular bacteria
Mixed inflammation, neutrophils and
macrophages, reactive mesothelial cells and
lymphoblasts. May see large unidentifiable
neoplastic cells with hi N:C ratio and multiple
nuclei
Usually acellular or few small lymphocytes
May see many small lymphocytes, uniform in
size
Mixed inflammation with RBC and neutrophils,
macrophages, reactive mesothelial cells and
lymphocytes or blasts,
Usually acellular and viscous
2013 DoveLewis Annual Conference
TP > 3.0
Page 5