Ultrasound Guidance (US)
Ultrasound is one of the key tools for guidance during drain placement. This method provides the physician with real-time imaging (real-time). The main advantage lies in the excellent visualization of superficial structures, as well as parenchymal organs and fluid collections. Ultrasound allows for detailed monitoring of the needle or catheter advancing toward the target, regardless of the scanning plane's tilt angle.
This method is especially important in pediatric practice because it completely eliminates ionizing radiation, minimizing the radiation dose to the child. In addition, the ultrasound machine is mobile, allowing life-saving procedures to be performed directly at the bedside (bedside) without transporting a critically ill patient to the radiology department.
The main indications for ultrasound are solid-organ abscesses (solid-organ abscesses) and large fluid collections in the abdominal cavity. However, the method has strict limitations. Ultrasound waves cannot penetrate gas media; therefore, the presence of gas inside an abscess makes guidance difficult. Visualization is also sharply impaired by adjacent bowel loops, which carries a high risk of iatrogenic injury during puncture.
Features of US drainage technique and combined approach
To successfully perform the procedure under ultrasound guidance, strict technical rules must be followed. The most important one is that the needle or drainage catheter must remain constantly and strictly in the imaging plane (in the plane of imaging). For the instrument to be clearly displayed on the monitor, its insertion angle is crucial. The optimal angle between the needle and the ultrasound probe surface (needle-probe angle) is 55 to 60 degrees . It is at this inclination that maximum ultrasound beam reflection is achieved, guaranteeing the best visibility of the instrument.
In complex cases, a combined approach is used, uniting ultrasound and fluoroscopy (fluoroscopy).
- First stage (US): used for puncture and initial placement of the drainage catheter into a large or partially visualized collection.
- Second stage (Fluoroscopy): necessary for further safe manipulation and precise catheter positioning.
This approach is particularly relevant when using the Seldinger technique (Seldinger technique). Fluoroscopic control at this stage is critically important as it reduces the risk of losing access to the lesion and prevents kinking the guidewire (kinking the guidewire).
CT guidance and CT fluoroscopy
When a pathological fluid collection is poorly visualized using ultrasound, computed tomography becomes the method of choice. CT-guided fluoroscopy (CT-guided fluoroscopy) provides the highest anatomical detail regardless of overlying structures. The physician receives an image with excellent spatial resolution, making the procedure precise and reducing its duration.
There are two main techniques for performing interventions under CT guidance:
- Real-time mode (Real-time): Scanning is performed continuously during instrument advancement. The physician holds the needle or catheter using a special clamp (clamp).
- Quick-check method (Quick-check): This is the most commonly used technique. Scanning to visualize the needle tip is performed strictly after each step of instrument advancement.
Clinical case: pleural effusion drainage
To better understand the capabilities of bedside ultrasound, let us consider a clinical case of draining a symptomatic pleural effusion in a 45-year-old man diagnosed with invasive follicular thyroid carcinoma.
- The baseline chest radiograph reveals a massive left-sided effusion, a large space-occupying lesion in the upper right mediastinum, and right-sided hilar adenopathy.
- Bedside ultrasound visualizes a large simple effusion on the left and reveals nodular metastatic pleural involvement.
- The follow-up ultrasound sonogram after the procedure clearly shows the catheter in the correct position.
- The final chest radiograph confirms a good initial response to drainage: positive dynamics are noted as a reduction in fluid volume.
Briefly: answers to topical questions
What are the absolute and relative contraindications to image-guided percutaneous drainage?
Contraindications to percutaneous drainage depend on the localization of the pathological process and the patient's hemostatic status.
- Hepatic hydrothorax (hepatic hydrothorax) is an absolute contraindication to chest drain placement.
- Abscesses in the setting of colitis are contraindicated for percutaneous access due to the high risk of fistula formation.
- Uncorrected coagulopathy (uncorrected coagulopathy) is a general contraindication; any clotting disorders must be corrected prior to the procedure.
- Lack of safe access prevents the safe advancement of the needle to the pathological lesion.
What types of drainage catheters are used for percutaneous abscess drainage?
During CT-guided percutaneous drainage, the catheter is usually placed using the tandem-trocar technique or the Seldinger technique. For the tandem-trocar technique, 8–16 F catheters are used. Needle aspiration is preferred for draining prostate abscesses; in cases of thick pus and difficult aspiration, a pigtail catheter is placed, which is removed after complete drainage of the cavity.
What complications can occur during percutaneous drainage of abdominal fluid collections?
The following complications are possible during percutaneous drainage of abdominal fluid collections:
- Iatrogenic bowel injury — the risk increases when bowel loops lie adjacent to the puncture zone.
- Fistula formation — a risk in percutaneous drainage of abscesses in the setting of colitis, especially Crohn's disease.
- Catheter obstruction — can occur due to blockage by dense necrotic detritus or tissue sequesters.
- Hemorrhage — a potential complication of invasive interventions.
To choose the method, remember the rule of mediums: ultrasound excels at visualizing fluids and parenchyma, but is "blinded" by gas and bowel loops. If ultrasound fails, CT comes to the rescue.
Class and exam questions
Why should the needle be held at a 55–60 degree angle during ultrasound?
This angle of inclination relative to the transducer ensures maximum reflection of ultrasound waves from the instrument, making it clearly visible on the monitor.
Why combine ultrasound and fluoroscopy?
Ultrasound helps to accurately puncture the lesion, while fluoroscopy allows the guidewire and catheter to be safely advanced using the Seldinger technique, avoiding loss of access and kinking.
What is the core idea of the CT quick-check method?
The physician advances the needle to a predetermined distance without radiation, and then performs a quick scan to confirm the position of the instrument tip after the manipulation.
What else to study on this topic
- Seldinger technique in drainage
- Prevention of guidewire kinking (kinking the guidewire)
- US signs of simple pleural effusion and metastatic pleural involvement
- Special clamps (clamp) for real-time CT fluoroscopy
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