Before the start of the workshop, a pre-meeting survey about the incidences of CSF leaks and established surgical practices in dural closure procedures was sent to all 10 participating neurosurgeons. All participants answered the survey before the start of the meeting without being aware of other participants' answers. A consensus on a statement was assumed when ≥70% of participants responded similarly.

Hemopatch® Sealing Hemostat was developed and is distributed by Baxter Healthcare SA [8152 Glattpark (Opfikon), Switzerland] as a Class III medical device in many countries worldwide. It was first launched in October 2013 with a hemostasis indication. Sealing indications, including dural sealing, were added to the label in the fourth quarter of 2016.

Hemopatch® consists of a collagen patch that is coated with PEG. A detailed description of its composition, properties, and mode of action was published earlier (20). When the patch comes in contact with blood or other body fluids, the PEG coating on the non-marked, white side dissolves and starts to cross-link. The reactive PEG groups form covalent bonds with free amine groups on the tissue, e.g., amino acid residues, forming a hydrogel which firmly attaches the patch to the underlying tissue, sealing the defect. As sealing of a bleeding source with PEG hydrogel is independent of the patient’s coagulation status, the product works even in patients with a compromised coagulation status, as shown in preclinical and clinical studies (20–23). The non-coated side of the patch is marked with small blue squares to better distinguish it from the coated side (“blue to you”). These marks also provide orientation when smaller pieces of the patch need to be cut. Detailed recommendations for the optimal application of the PEG-coated collagen patch can be found in the Results section.

A live tissue surgery was performed on pigs under an animal experiment permission granted by the respective authority in Brandenburg (Landesamt für Arbeitsschutz, Verbraucherschutz und Gesundheit).

Two young adult pigs with an approximately 35–40 kg body weight were anesthetized by intramuscular injection of standard anesthetics. After 15 min, an ear vein access was placed, and 5 mg/kg propofol was injected for analgesia. The animals were then endotracheally intubated and mechanically ventilated. Balanced anesthesia was maintained with inhalation anesthesia. Throughout the procedure, the animals were monitored for heart rate, blood pressure, airway pressure, and body temperature and provided with anesthetics and analgesics as needed. Qualified veterinary staff were present throughout the procedure. After completion of all procedures, the animals were euthanized under deep anesthesia with a lethal dose of thiopental sodium and embutramide/mebezonium iodine/tetracaine hydrochloride (T61; Hoechst Marion Roussel, Brussels, Belgium). The established anesthesia management of pigs is described in greater detail elsewhere (24).

In the practical part, 10 neurosurgeons (AA, GB, DC, S-YC, ND, JF, PA, JR, JT, VY) used Hemopatch® as primary sealant in different challenging situations on the anesthetized live pigs to evaluate the best application techniques during a surgical skills training session. The animals were placed in a prone position, and for the cranial procedures, the head was shaved and sterilized, and the skin was opened. A midline parietal craniectomy was performed using a cranial drill. For the spinal procedures, the back was shaved and sterilized, and the skin along the midline was opened. Soft tissue surrounding the vertebrae was removed with an electrocautery knife. To expose the spinal cord, a laminectomy was performed. The surgeons tried to mimic typical intraoperative situations by creating defects, leading to bleeding or CSF leakage by using a scalpel and/or microhook. When feasible, bleeding grades were rated according to the VIBe scale before treatment (25). Based on the low number of defects and the difficulty to exactly reproduce defects, no statistical evaluation could be performed, but results were evaluated based on consensus among the surgeons regarding their observations.

In addition to the already marketed Hemopatch®, which is storable at room temperature for 6 months, a new “Hemopatch RT” configuration, provided as an R&D sample, with an extended shelf life of 36 months at room temperature (RT, based on a new packaging configuration), was tested by all neurosurgeons. The neurosurgeons were blinded to the configuration of the patch provided. The products were applied following the instructions for use (IFU). The target application area was dried from excess liquid using dry gauze. Patches were held in place with a dry gauze or sponge with appropriate compression for 2 min, before carefully removing the gauze and inspecting the application area for successful hemostasis or sealing. To facilitate the removal of the gauze in cases where it adhered to the patch, gentle irrigation with saline solution could be applied.

Concluding the workshop, a follow-up discussion was held, at which all 10 attending neurosurgeons discussed their experience with Hemopatch® from previous clinical use as well as the practical preclinical testing in the workshop. The results of the survey were discussed, and the suitability of the PEG-coated collagen patch for addressing challenging situations in neurosurgery was critically evaluated. Additionally, observations during the practical application of Hemopatch® and “Hemopatch RT” were discussed.

After completion of the workshop, the team of neurosurgeons discussed the results of the pre-meeting survey and their experiences during the workshop. The results of the survey, described above, were discussed, underlining the findings that for the closure of larger defects, many autologous and commercial materials can be used, based on the availability and preference of the surgeon, and that sealants and sealing patches can be used alone or in combination with dural substitutes to finally achieve watertight dural closure. Recommendations regarding the best use of Hemopatch® are summarized below.

Hemopatch® is licensed as a surgical sealant for procedures in which control of body fluids by conventional surgical techniques is either ineffective or impractical. Furthermore, it is not intended as a substitute for meticulous surgical techniques and the proper application of ligatures or other conventional procedures for sealing (26). Since its market introduction as a dural sealant in 2016, Hemopatch® has been therefore used as a watertight primary sealant for smaller CSF leaks or dural defects and as a secondary sealant on larger sutured dural defects in various neurosurgical procedures (9, 10, 12, 14, 15, 17). During the neurosurgical procedures performed in the workshop by the 10 neurosurgeons, the PEG-coated collagen patch was used only as a primary sealant to evaluate its efficacy in more exceptional circumstances. It was successfully used to control bleeding and CSF leakages in cranial and spinal scenarios. The efficacy of Hemopatch® as a dural sealant for cranial and spinal surgeries was already validated in four prospective, single-center studies (9, 12–14) and one prospective multicenter, single-arm observational study (17). Furthermore, it was evaluated for cranial approaches in a retrospective, single-center cohort study (15) and by Schebesch and Brawanski in supratentorial, infratentorial, and transsphenoidal approaches. The authors concluded in their retrospective clinical experience report that the use of the PEG-coated collagen patch for these approaches is safe and feasible (10). Based on the experts' discussion, there seem to be only minor differences in the use of Hemopatch® for cranial and spinal surgery. However, experts also mentioned that cranial surgeries usually require a suture for primary dural closure and dural patches should be used as a secondary sealant to achieve a watertight closure, while in spinal surgeries, it might be sufficient to use a sealing patch as a primary sealant. Similar results were obtained by Montano and colleagues (12) who mentioned that it is often not possible to close incidental spinal durotomies by suturing. In these cases, dural patches might be used as a primary sealant. Moreover, dural sealants have also been shown to reduce epidural fibrosis in spinal surgery (27, 28). Two fluid dural sealants proved to be safe and effective in reducing CSF leaks in over 90% of patients in a large prospective study with 250 patients (6).

Intentional durotomies, irrespective of whether spinal or cranial, are more likely to require suturing for primary closure, followed by a sealing patch as secondary sealant. Experts assume that suturing will become less common in the future. In a recent publication, researchers even used Hemopatch® as a dural substitute (29). As this application is outside the intended use by the manufacturer, the expert group recommended using it as a dural sealant only, as this is shown to be safe.

Experts also discussed which applications of Hemopatch® they see, in cases with a high risk of CSF leakage, and in which they prefer to use a dural sealant in combination with a dural substitute. The most relevant answers to these two questions were identical, suggesting that experts indeed use a dural substitute in combination with a dural sealant in situations that carry a high risk of a CSF leak. Some of the applications mentioned match the already published indications for the use of the PEG-coated collagen patch, such as posterior fossa (10, 13–15) and skull base surgeries (15).

In the survey, experts were also asked for patient profiles that are at high risk for the development of a CSF leak. More than one expert cited advanced age, obesity, postradiation therapy status, meningioma (especially with dural excision), or synovial cysts as risk factors for postoperative CSF leakage. Such risk factors are the subject of controversial debate in recent research. A few of these factors are shown to influence the CSF leakage rate in some but not all applications, while others do not (30–33). A recent study by Atchley and colleagues (34) developed a predictive model and clinical risk score for postoperative CSF-related complications after posterior fossa and posterolateral skull base surgeries and therefore applications that were also repeatedly mentioned by the experts. The authors based their highly specific risk score on the factors age, body mass index, dural repair technique, use of bone substitute, and duration of postoperative CSF diversion, suggesting that at least patients' age and weight might indeed influence the risk for the development of postoperative CSF leakage.

Overall, the group of experts confirmed that Hemopatch® is well-suited as a dural sealant when applied following the instructions.