Discussion
REBOA is indicated for traumatic life-threatening hemorrhage below the diaphragm in patients who present in hemorrhagic shock and are unresponsive or transiently responsive to resuscitation.10 Although REBOA offers a minimally invasive approach to aortic occlusion, there are technical challenges that accompany the procedure which have contributed to its limited use in practice. One of the limiting factors has been device profile, as procedure time and complications may increase with catheter size.11–16 It is intuitive that smaller access sheaths in coagulopathic trauma patients would be preferred from an access site bleeding complication standpoint and eliminating the need to upsize an initial low-profile sheath can speed up the overall procedure.
This first-in-human feasibility study demonstrates the safety and effectiveness of a novel 4 Fr REBOA device. Existing REBOA devices continue to require a 7 Fr sheath, which is a larger sheath profile than with most standard percutaneous endovascular products used by expert interventionalists (most often 5 to 6 Fr). By reducing the profile to 4 Fr, the aim was to decrease access site complications and simplify the procedure by eliminating the need to upsize an initial sheath. In addition to the reduction in profile, the COBRA-OS was also designed to be “fluoroscopy-free” (without the need to be tracked over a wire), have an atraumatic flexible tip for safe blind advancement in arteries, and have a stiff enough body to withstand aortic pressures during full aortic occlusion. Besides safety and effectiveness, this study also demonstrates that the device can be deployed very quickly in experienced hands, although under very controlled circumstances.
There are some key differences to be noted about the COBRA-OS compared with other REBOA devices besides the reduction in profile. Similar to other devices, but not all, it is not an over-the-wire device and instead is inserted directly through the empty 4 Fr sheath and advanced atraumatically into the aorta to either Zone 1 or Zone 3. The device does not have a built-in arterial line, contrary to some other devices, and therefore an alternative means to monitor blood pressure and confirm aortic occlusion must be used. The device is also only indicated for vessels up to 25 mm in diameter, with typical trauma patient proximal thoracic aortic diameters being approximately 23 mm.17 This was a conscious design feature to help prevent aortic and balloon rupture by setting the maximum volume of the compliant balloon at 13cc, equivalent to 25 mm. In addition, the COBRA-OS has only two markers on the shaft to indicate typical distances for Zone 1 (single black marker at 48 cm depth) and Zone 3 (three black markers at 28 cm depth) as suggested by Eliason et al for fixed REBOA length catheters,18 compared with other devices with either no markers or markers on the entire length of the device. It also has a unique offset ice-cream cone shaped balloon with a safety shoulder reservoir, compared with other elliptical or spherical shaped balloons, that was incorporated into the design to help prevent rupture of the balloon or aorta during inflation. The shape and design of the balloon also lends to its ability to achieve partial-REBOA on deflation if desired, which is not easily achieved by some other compliant REBOA balloon systems.19
The COBRA-OS can be used to improve the situations in which REBOA is currently being used. Depending on local institutional protocols for trauma patients, the COBRA-OS 4 Fr sheath can be placed in the femoral artery and used as a femoral arterial line to monitor blood pressure. Early femoral access when considering REBOA has been associated with a survival advantage.20 If REBOA is not required, the 4 Fr sheath can be removed and manual compression can be used for hemostasis. However, if REBOA is required, the COBRA-OS can be quickly deployed without the need to insert a separate stiff wire and upsize to a larger sheath, thus making the procedure simpler and less cumbersome, avoiding additional endovascular equipment which is not always readily available in trauma suites.
Apart from the advantages of reducing potential access site complications and increasing the speed of the procedure, a smaller profile access sheath and device traversing the iliac arteries and aorta has other benefits. Larger sheaths are known to be more obstructive in small and often tortuous iliac vessels. Trauma patients are frequently known to have vasospastic blood vessels and are often started on vasopressor medications which vasoconstrict their vasculature. Therefore, a 7 Fr sheath may be fully or partially occlusive, potentially promoting vessel thrombosis, especially if left in place when patients are transferred to postoperative care. It is unknown if a 4 Fr sheath will reduce vessel thrombosis if left in place postoperatively but the significantly lower profile makes this a possibility. The 4 Fr sheath may be used as an arterial line monitor during postoperative care and even as a conduit to a subsequent REBOA device placement if the patient becomes hemodynamically unstable again.
When considering applications other than trauma, a low-profile system may be equally advantageous. In patients with hypercoagulable postpartum hemorrhage who often have small vasospastic iliac vessels and aorta, the 4 Fr COBRA-OS may be the ideal Zone 3 aortic occlusion device to be placed and only deployed if necessary, decreasing the chance of vessel thrombosis and potential limb loss when using REBOA as a surgical adjunct.21 Furthermore, in patients presenting with severe trauma to non-level 1 trauma centers or in prehospital scenarios, the smaller and less obstructive 4 Fr sheath and COBRA-OS may potentially be placed prophylactically for patient transfer and REBOA only used if the patient becomes unstable.22 Finally, in pediatric REBOA scenarios, a low-profile system would be preferable due to the inherent smaller size of access vessels and aorta in this patient population.23
As described here, low-profile aortic occlusion balloons may be used to potentially improve the efficiency of NRP techniques during organ procurement. NRP is an evolving technique to improve the function of procured organs after controlled or uncontrolled DCD.24 Low-profile occlusion balloons placed percutaneously may enable less manipulation of the DCD organ donor during preparation prior to organ procurement. These devices may play an important role in the future of NRP techniques, but have yet to be studied extensively.
To our knowledge, this is the lowest profile aortic occlusion device ever reported25 and we think that the 4 Fr COBRA-OS represents a significant improvement in REBOA technology by lowering the profile without compromising aortic occlusion ability. Due to the lower profile, we expect adoption for REBOA to increase when this device becomes widely available, similar to when there was a transition from 12 Fr to 7 Fr devices. For perspective on device profile, a typical femoral arterial line is 18 gauge or 1.3 mm outer diameter (OD); the 4 Fr sheath used with the COBRA-OS is approximately 1.8 mm OD; and a typical 7 Fr sheath is approximately 3.1 mm OD. See figure 4 for demonstration of two COBRA-OS devices fitting through a 7 Fr sheath. Further studies and use of the COBRA-OS will help elucidate the benefits of this low profile REBOA device.
Figure 4Image of two COBRA-OS devices fitting through a 7 Fr sheath. COBRA-OS: Control of Bleeding, Resuscitation, Arterial Occlusion System; Fr, French.
There are a number of limitations with this study. The procedure was completed by a single expert general and vascular surgeon under controlled circumstances at a single center which raises the question of whether these results are repeatable in emergency trauma suite scenarios with users that are not as familiar with the device. In addition, the relatively small number of patients limits broad generalizations about the device in all patient populations and applications.