can head position improve surgical field during ear surgery?

Conditions: Intra-operative Bleeding

Summary: middle ear surgeries utilizes microscope in a narrow field. they are better performed under controlled hypotension, to minimize bleeding and improve surgical field visualization and hence improve results.head-up or anti-trendelenburg position influences intraoperative bleeding by generating regional ischaemia in sites elevated above the level of the heart. also by augmenting the effect of vasodilators through pooling of blood in dilated veins.

after obtaining local ethical committee approval and written informed consent from the patients, 225 adult patients, scheduled for elective middle ear surgery in ain shams university hospitals will be enrolled in this randomized, prospective controlled study. after applying basic monitors (ecg, pulse oximetry, non-invasive blood pressure monitoring and capnography), all patients will be premedicated with midazolam 0.02 mg.kg -1 iv and ranitidine 50 mg iv, 15 min. prior to surgery. all patients will receive dexmedetomidine 1mcg. kg-1 loading dose over 10 min just before induction, followed by continuous infusion of 0.4 mcg.kg-1hr-1. rate of infusion will be adjusted to maintain map 20% below baseline. dexmedetomidine infusion will be stopped after graft insertion. total dexmedetomidine consumption will be recorded. in the operating room and after 5 min preoxygenation, general anesthesia will be conducted using the same protocol for all patients: fentanyl 1 μg.kg-1, propofol 1.5-2 mg.kg -1 titrated to loss of verbal response, atracurium 0.5 mg. kg-1 to facilitate endotracheal intubation. anaesthesia will be maintained using isoflurane 1 % in oxygen and air mixture 1:1 and atracurium 0.1 mg. kg-1 every 20 mim. positive pressure ventilation will be set to maintain normocapnia. patients will be randomly and evenly assigned to one of three groups, 75 patients each. group i (control): patients will be positioned supine. group ii: patients will be positioned 10° anti-trendelenburg position. group iii: patients will be positioned 20° anti-trendelenburg position. randomization will be done using computer generated list. the anaesthesia nurse recording the data is blinded to the study groups. at the end of surgery, isoflurane will be discontinued and residual neuromuscular blockade will be reversed. recovery time will be recorded (defined as: the time from discontinuation of volatile anaesthetic till the patient is able to respond to verbal command). patients will then be transferred to pacu. during surgery, if the surgeon found it difficult to complete the surgery in the anti-trendelenburg (groups ii and iii), surgery will be continued in the supine position. patients will still be calculated in the pre-assigned group with recording of such event, and assuming surgeon satisfaction to be 5 in these patients.

Eligibility criteria:
inclusion criteria: * asa i-ii exclusion criteria: * patients with uncontrolled hypertension, coronary artery disease or on beta blockers. * cerebrovascular insufficiency. * anaemia. * end stage renal failure. * liver cirrhosis. * patients with coagulopathy or receiving drugs influencing blood coagulation. * pregnancy. * known sensitivity to any of the study drugs. * patients' refusal to participate in the study.