What is a Bird's Nest inferior vena cava (IVC) filter?

Updated: Oct 31, 2020
  • Author: Gary P Siskin, MD; Chief Editor: Kyung J Cho, MD, FACR, FSIR  more...
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Answer

Bird's Nest filter

The Bird's Nest filter (BNF) was developed in 1982. This filter is constructed of a network of 4 biocompatible stainless steel wires (see the following image). Each wire is 25 cm long and 0.18 mm in diameter. The wires are preshaped with many nonmatching bends of a short radius and they are fixed at each end to V-shaped struts, the 2 legs of which are connected at an acute angle. A hook with a small loop stop minimizes the risk of IVC perforation at the end of each strut. The original designs called for 0.25-mm struts, but the later design (introduced in 1986) used 0.46-mm struts. This change increased the size of the loaded filter from an 8F to a 12F catheter system. The length of the introducer is 75 cm for the jugular approach and 40 cm for the femoral approach.

Bird's nest filter. Bird's nest filter.

When a Bird's Nest filter is deployed, one of the V-shaped paired struts is pushed gently to engage to the IVC wall. Originally, it was recommended that the catheter be withdrawn by 1-3 cm over the pusher wire after the hooks were fixed to the IVC; later, it was recommended that 2 or 3 twists of 360° be applied. The purpose of the twists is to prevent or reduce the chance of wire prolapse. The second pair of struts is then pushed into the IVC so that the junctions overlap by 1-2 cm. The handle of the pusher wire is turned counterclockwise 10-15 times to free it from the struts.

The Bird's Nest filter has a unique design. The final shape of the deployed filter varies owing to the flexibility of the long 0.18-mm wires. The maximum span of the V-shaped struts is 60 mm. Therefore, the Bird's Nest filter is suitable for placement in a megacava with a diameter greater than 28 mm, [19] and the FDA approved it for this use. Other filters are associated with a risk of migration if the IVC diameter is greater than 28 mm. The Bird's Nest filter has been placed successfully in patients with an IVC diameter as large as 42 mm, without filter migration.

In an experimental model, Korbin et al suggested that placement of a single Bird's Nest filter was preferred to bi-iliac placement of filters in cases of megacava. [20] Other investigators also demonstrated the clot-trapping efficacy of the BNF in various in vitro studies. [19, 21, 22, 23, 24]

Wire prolapse beyond the struts has been reported, but it does not affect the clot-trapping ability of the Bird's Nest filter. CT scan studies performed in patients with Bird's Nest filters demonstrated penetration of the caval wall in 83%. All of the patients were asymptomatic in the series reported by Wojtowycz et al. [25] The authors also reported that 8 patients (3%) in the series of 267 Bird's Nest filter insertions had thromboses at the access site.

Roehm et al reported a rate of 2.9% for IVC thrombosis in their series of 568 patients. [26] IVC thrombosis was reported to occur in as many as 17% of patients by Ferris et al, [27] in 7% by Thomas et al, [28] and in 4.7% by Nicholson et al. [29] Wojtowycz et al reported rates of 1% confirmed and 3% suspected recurrent PE, which is similar to the 2.7% rate reported by Roehm et al. Athanasoulis et al reported a 7% recurrent PE rate, 90% of which were fatal, in a series of 255 patients. [5]


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