The Effect of Intra Operative Dexmedetomidine in Prevention of Early Postoperative Atrial Fibrillation

This a randomized control trial is designed to include (350) patients ASA physical status II patients ranging from(18) to(70)years old scheduled for thoracic non cardiac surgeries

Patients meeting the inclusion criteria will be randomly assigned to receive either :

Group I : dexmedetomidine: (n=175) dexmedetomidine will be administered as a bolus dose, before the surgical incision with 1mcg/kg iv over 10 minutes followed by infusion rate of 0.5 μg/kg per h and stopped at the end of operation.

GroupII: normal saline placebo:(n=175) similar bolus and infusion volumes of normal saline will be administered as dexmedetomidine group

Anesthesia management

Preoperative procedures:

Full history and investigation will be taken in the form of CBC, blood sugar ,liver function tests. Kidney function tests ,electrolytes and coagulation profile Preoperative awake supine trans thoracic echocardiograms will be performed before operation using a 2.5/2.0- MHz transducer for imaging and Doppler echocardiography. Preoperative 12-leads will be performed to all patients. On arrival of the patient to the operating theatre and before induction of anesthesia, all standard monitors will be applied, including heart rate (HR), ECG, oxygen saturation (SpO2), end-tidal CO2, arterial blood pressure (systolic, diastolic, and MAP), and temperature, arterial catheter will be inserted in the radial artery for continuous blood pressure monitoring and frequent blood gas analysis. Initial readings of all these monitors will be taken and recorded before starting any drug infusion. After securing IV access by 20G cannula, all patients will be premedicated with 0.05mg/kg midazolam for anxiety, antibiotic 50mg/kg.

Intraoperative procedures:

Induction of general anesthesia will be done by fentanyl 2ug/kg/ iv, 2mg \kg propofol, and 0.5mg\kg atracurium to facilitate endotracheal intubation. Anesthesia maintenance will be achieved with endotracheal tube with suitable size, 1.2 minimum alveolar concentration of isoflurane, volume controlled mode ventilation, respiratory rate will be adjusted according to Et CO2 to range between 35-40 mmHg, a tidal volume of 6-8 ml/kg and mixture of gases in proportion 50% oxygen and 50% air, with PEEP 5 cm H2O and0.1 mg\kg atracurium every 30 min.10mg morphine intravenous will be given after induction and intubation.

Intervention Dexmedetomidine will be administered as a bolus dose, before the surgical incision with 1mcg/kg iv in 100 ml saline solution over 10 minutes followed by infusion rate of 0.5 μg/kg per h infusion via syringe pump during surgery and stopped at the end of operation. Similar bolus and infusion volumes of normal saline will be administered in the Control group (placebo) However, anaesthesiologists will be permitted to reduce dose of the study drug as necessary to preserve haemodynamic stability(systolic blood pressure decrease more than 20% from the baseline or\ and heart rate less than 60 ). with occurence of bradycardia and \or hypotension it will be managed by the attending anesthesiologist according to standard institutional guidelines and drug infusion rate will be decreased to the half. if bradycardia or hypotension persisted, drug infusion will be unblinded, stopped and reported as a serious side effect occured with drug infusion .By the end of surgery, anaesthesia will be discontinued ,patient will be reversed by neostigmine 0.05mg\kg and atropine0.02mg\kg, extubation will be done and patient will be transferred to post anaesthesia care unit (PACU).

Postoperative

1. Postoperative analgesia will be started with continuous infusion of 30 mg morphine associated with 180 mg ketorolac in 250 ml of normal saline at 5 ml /h and paracetamol infusion 1 g every 6 h. Additional bolus dose of 0.04mg/kg if vas exceed or equal 4 and it will be repeated if pain exist every 6 hours. All patients will be continuously monitored by 5-leads ECG and pulse oximeter(oxygen saturation) .12-leads ECG will be performed in occurence of tachycardia or arrythmia for the first 72 hours. Diagnoses of atrial fibrillation in the cardiac ICU will be made by clinicians who will be masked to group allocation. Atrial fibrillation will be defined by: clinician diagnosis; documented arrhythmia lasting at least 5 min ( supraventricular tachyarrhythmia characterized by uncoordinated atrial activation .Electrocardiographic findings include the replacement of the normal consistent p waves with oscillatory or fibrillatory waves of different sizes amplitudes and timing with narrow QRS complex unless other conduction abnormalities exist ( e.g. bundle branch block , accessory pathways). The ventricular response is often rapid and between 90 and 170 beats per minute and it will be documented by 12- lead ECG.
2. Post operative haemodynamic will be assessed (heart rate , ,systolic and diastolic blood pressure every 2 hours or with the occurrence of dysrhythmia)
3. Serial cardiac enzymes concentration (CK MB , Troponin ) will be measured every 6 h to rule out myocardial infarction.