Ultrasound guided percutaneous drainage is one form of image guided procedure, allowing minimally invasive treatment of collections that are accessible by ultrasound study.
It has several advantages and disadvantages over CT, which include:
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Advantages
is a dynamic study, allowing greater precision to control needle insertion
does not expose patients to ionizing radiation
does not require as wide a range of staff, compared to CT-guided procedures
Disadvantages
deeper targets may not be as well-visualized on ultrasound (e.g. retroperitoneal nodes)
bowel gas may obscure visualization
attenuation of the sound beam on larger patients
Indications
Indications for percutaneous drainage are broad: essentially any abnormal fluid collection in the patient which can be accessible. Examples include:
complicated diverticular abscess
Crohn's disease related abscess
complicated appendicitis with appendicular abscess
tuboovarian abscess
post-surgical fluid collections
hepatic abscess (e.g. amoebic or post-operative)
renal abscess or retroperitoneal abscess
splenic abscess
Contraindications
The only common contraindications are:
biopsy target is not accessible
patient has a bleeding diathesis
Procedure
Laboratory parameters for a safe procedure
Interventional procedures like percutaneous drainage require special attention to coagulation indices. There are widely divergent opinions about the safe values of these indices for percutaneous biopsies. The values suggested below were considered based on a literature review.
Complete blood count: platelet count > 50000/mm3 (Some institutions determine other values between 50000-100000/mm3) 1
Coagulation profile:
international normalized ratio (INR) ≤1.5 1
normal prothrombin time (PT), partial thromboplastin time (PTT)
Some studies show that having a normal INR or prothrombin time is no reassurance that the patient will not bleed after the procedure 2.
Pre-procedure evaluation
Review other diagnostic studies first to clarify the collection that is requested to be drained. An ultrasound study should be done prior to the procedure to decide the access angle and check the relationship of the collection to adjacent structures. In general, the shortest possible route is preferred, as long as it does not traverse other structures.
Technique
Ultrasound guided percutaneous drainage may be performed with a single or multiple stage technique.
In the single stage technique, the fluid collection is entered directly with a catheter, typically either 8F or 12F in size.
The multiple step technique utilizes the modified Seldinger technique, whereby the abscess is entered with an introducer needle, through which a stiff wire is passed. The track is then expanded with a dilator or serial dilators, before the catheter is passed over the wire to gain the final position within the abscess. A locking drain is typically used to ensure a secure position.
The catheter is then connected to a vaccum drainage system (for peritoneal or retroperitoneal space collections) or external drainage bags (for draining urinary, digestive and biliary tracts).
Post-procedure care
The patient's basic vital signs should be monitored for 4 hours post procedure (pulse, blood pressure, SpO2), or as long as deemed necessary.
The patient should remain in bed for 2 hours. After this period, mobilization and oral intake are permitted.
The entry site should be reviewed on a daily basis. If output from the collection ceases, it may mean that the collection is no longer present or that the drain is clogged. Re-imaging and/or flushing the drain should be considered before removing the drainage catheter.
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