What is pinch off syndrome (POS)?

POS is a mechanical complication that can occur in cases where the catheter of the implanted port has been located in the subclavian vein, between the first rib and the clavicle.
The anatomy of the area explains this syndrome: the costoclavicular space is triangular in shape, with a vertex in the medial portion. The subclavian vein leaves the chest through the widest portion of this space in its middle and lateral thirds.
The implantation of a central venous catheter in the medial third of the costoclavicular space can produce the compression of the catheter between the clavicle forceps and the first rib.

This incidence occurs on average six months after port implantation (estimated to affect 0.1-1 % of catheters), but in some cases it occurs up to 60 months later. In fact, once the port is no longer required, it must be removed immediately to avoid POS. Chest x-rays should be taken at any sign or symptom that makes one suspect the presence of POS in order to confirm the diagnosis and establish timely treatment.

In cases of embolization, 93.5% are removed by a percutaneous procedure and only about 2.3% require surgical treatment with thoracotomy. In the remaining 4.2%, the fragments are preserved in the vascular bed.
The most common sites for embolization of catheter fragments are :

• the pulmonary artery (35%) 
• right atrium (27.6%) –
• right ventricle (22%) –
• superior vena cava or peripheral veins (15.4%)

POS symptoms

Symptoms that may lead to the suspicion of a spontaneous fracture are:

• pain in the upper anterior pectoral region or shoulder 
• difficulty or pain during aspiration or infusion 
• radiological catheter stenosis • history of difficult implantation

The first symptoms related to catheter compression and transection are:

• intermittent resistance to the passage of solutions with a better infusion while raising the arm (lift)
• variable haemodynamic status in patients with inotropes due to variable drug passage
• edema in the anterior region of the chest near the catheter insertion site or frequent ventricular extrasystoles in case of catheter embolization to the heart

Complications include arrhythmias, endocarditis, perforated right ventricleand  pulmonary embolism. The suspected pinch off is confirmed by an x-ray.

Pinch Off Syndrome was first described in 1990 by Hinke et al. who specified the following scale of signs:

• grade 0, no catheter deformation
• grade 1, without catheter deformation, but with deviation
• grade 2, deformation of the light as the catheter passes under the collarbone (true pinch-off sign)
• grade 3, transection of the catheter between the clavicle and the first rib accompanied by embolization of the distal catheter

The treatment of POS is the removal of the catheter by surgery, which should occur as soon as possible. As for the removal of the distal fragment of the embolized catheter to the right heart chamber or pulmonary arteries, it is recommended that this should be done to avoid serious complications. The method of choice for fragment removal is percutaneously through the femoral vein with a loop catheter. When this option is not successful, it can be attempted through a percutaneous access through the internal jugular vein, leaving as a last option the surgical approach through a median sternotomy.

How to prevent pinch off syndrome

It is important to emphasize that the catheter should not be implanted in the subclavian vein in a forced upper limb position (stretching) because this transitory increase in the costoclavicular angle is reduced when the limb is returned to a neutral position, producing a state of permanent compression of the catheter. The weight of the shoulder will further narrow the angle between the first rib and the clavicle and produce greater compression on the catheter when the patient is in an upright position. The technique of catheter insertion can reduce the incidence of pinch off. The ideal location for subclavian insertion is lateral to the midclavian line, placing the catheter within the vein where the angle between the first rib and the clavicle is wide.

Another option for prophylaxis is to use the jugular access to insert the catheter, this way the occurrence of the POS is impossible.
Recently, some authors have proposed the insertion of the subclavian catheter with supraclavicular approach, since it has shown better results, the rate of complications is much lower and it is well accepted by patients.

In summary, the measures-(guidelines) to be followed to avoid pinch off would be:

• Cannulation in the lateral part of the mid-clavicular line during subclavian venous access, with assessment of the supraclavicular access as an alternative
• Perform the procedure accurately, avoiding forced positions of the upper limb 
• Watching patients closely 
• Remove the venous port immediately when it is no longer needed