86 Abstracts events. [1] Anti-coagulating patients with low molecular weight heparin however increases their risk of bleeding intra- and post- surgery. Deciding whether to anti-coagulate a patient pre-surgery involves weighing up their risk of bleeding vs their risk of throm- bus formation. [2] Objectives: We present a case of a crash call which resulted in multiple diagnoses. We explore the literature behind pre-operative anti-coagulation to try and prevent thrombotic events and their resulting delay to surgery. Methods: A 77-year-old woman with a T4aN2bM0 SCC of the right mandible attended a couple of days prior to major resection and reconstructive surgery for peg placement. Findings: A couple of hours following peg placement the patient became unresponsive on the head and neck ward and a crash call was put out by the nursing team. The patient had a systolic blood pressure of 50 mmHg, a respiratory rate of 4 bpm and a profound neck rash. The rest of the clinical examina- tion was normal. The patient was treated for anaphylaxis and the mast cell tryptase blood tests were sent off. The following morning a CTPA showed bilateral small volume PEs. A couple of weeks later the blood test results confirmed the diagnosis of anaphylaxis. Conclusion: Head and neck oncology patients have multiple risk factors for a wide range of acute diagnoses, and it is important during crash calls to consider multiple diagnoses. https://doi.org/10.1016/j.ijom.2019.03.259 Surgical management of osteoradionecrosis using three- dimensional isodose curve visualization: a multi center retrospective study M.J.H. Witjes * , H.H. Glas, S. Lai, S. Tribius, M. Heiland, R. Ashkan, I. ten Hove, J.L.N. Roodenburg, F.K.L. Spijkervet, J. Kraeima UMCG, Groningen, the Netherlands Background: Osteoradionecrosis (ORN) is defined as bone death, secondary to radiotherapy. There is a relation between the received radiation dose and ORN, with the risk increasing after a dose of > 60 Gy. In cases of class III mandibular ORN, a segmental resection can be indicated. Current practice is to completely remove the affected bone up to the point where the bone looks healthy and is bleeding. 3D planning and guided surgery based on imaging of the bone have not been reported so far. Objectives: The aim is to determine whether 3D visualization of radio therapy (RT) isodose distribution would be helpful for surgical decision making, concerning the optimal resection line of the bone in case of surgical management of ORN. Methods: This multi-center study describes a method whereby RT dose information is incorporated into a 3D model based on CT, for analysis of the areas at risk (>56 Gy). The method enables 3D visualization of each desired isodose, in relation to the 3D model of the affected bone. Findings: A total of 26 cases where included in the 3D analysis. For every case RT planning was projected onto the pre-op and post-op (after surgical resection of the ORN) CT images. The 50-, 56 and > 60 Gy isodoses where visualized and compared with the resection planes derived from the post-op CT. Conclusion: This study provides a decision supporting method visualizing the selected isodoses together with the 3D bone mod- els. At this point however, there is no strict relation between received RT dose and risk for ORN, related to the cut-off dose, and where to perform the resection in surgical management of ORN. https://doi.org/10.1016/j.ijom.2019.03.260 Jehovah’s witnesses and blood loss in head and neck surgery: a case report E. Yonis * , I. Hussain, K. Maharaj, R. James Norfolk and Norwich University Hospital, England, United Kingdom Background: In Head and Neck surgery, blood loss is a com- mon, routine risk discussed with patients. Some patients may object to having a blood transfusion due to their beliefs such as Jehovah’s Witnesses, who may refuse transfusion of blood-derived products. Current techniques in the management of blood loss may be acceptable to some Jehovah’s Witnesses and mandates careful peri-operative discussion. Objectives: We aim to highlight the importance and increase the awareness of the peri-operative management of Jehovah’s Wit- nesses, particularly where the patient is anemic pre-operatively and where high-risk surgery is planned. Methods: A 74-year-old Jehovah’s Witness patient presented with a mass arising from his right maxillary alveolar process invading the buccal mucosa. This was his third primary oral cav- ity squamous cell carcinoma; he had previously undergone left mandibular resection with neck dissection and reconstruction and a right hemiglossectomy including ipsilateral neck dissection and anterolateral thigh flap reconstruction. On this occasion he was diagnosed as T4 N0 M0 Squamous Cell Carcinoma of the right maxilla and was planned for Right Hemi-maxillectomy and recon- struction with Anterior Lateral Thigh flap. Findings: Prior to surgery he was noted to be anemic; despite intervention he remained anemic. This factor in conjunction with poor flap perforators, short pedicle length and limitations over hematological management, an intra-operative decision was taken to postpone reconstruction and temporarily obturate the surgical defect. Conclusion: Clear discussions are essential for the patient to understand risks of bleeding and alternatives to transfusion. Where patients have beliefs precluding transfusion, it is essential that surgeons respect their beliefs. https://doi.org/10.1016/j.ijom.2019.03.261 Conservative treatment of cervical chylous fistula following neck dissection in oral cancer patients L.J. Zhu * , S.Q. Wang, S. Jiang, Q.P. Wang, J. Li, Z.B. Chen Department of oral and maxillofacial surgery, Guangdong General Hospital & Guangdong Academy of Medical Sciences, Guangzhou, China Background: Cervical chylous fistula is an uncommon com- plication after neck dissection. Persistent chyle loss leads to electrolyte disturbance, hypovolemia, hypoalbuminemia, coagu- lopathy, immunosuppression, chylothorax, even wound infection and local skin breakdown. Both conservative and surgery treat- ment are effective way. Objectives: In this retrospective study, we showed our expe- riences on conservative treatment for cervical chylous fistula. Methods: From January 2017 to June 2018, all patients who received conservative treatment for neck chylous fistula after neck