Our experience of using Dexmedetomidine-Propofol sedation in patients undergoing treatment planning Magnetic resonance imaging scan for Deep brain stimulator insertion surgery during Covid 19 pandemic

ABSTRACT

Introduction: Patients undergoing Deep brain stimulator (DBS) insertion require a high-resolution MRI for treatment planning prior to DBS surgery. This group of patients has movement disorders therefore traditionally the planning MRI is done under General anaesthesia to ensure patient immobility and to obtain good quality MRI images. Providing sedation/anaesthesia for MRI procedure during COVID-19 pandemic was challenging. When we restarted elective surgery during Covid-19 pandemic we were worried about aerosol generating procedures, therefore we looked at the feasibility of using Dexmedetomidine-Propofol sedation for treatment planning MRI as an alternative to General anaesthesia to prevent aerosol generating procedure. Method(s) We conducted retrospective review of anaesthetic records of all patients who underwent MRI under sedation for DBS planning from August 2020 to July 2021. We collected the data on patient demographics, Indication & target site for DBS, duration of sedation, complications during the scan, cardiovascular side effects like hypotension and bradycardia during scan, quality of image, duration of PACU stay and post scan complications. The quality of MRI imaging was assessed by the neurosurgeon who did the treatment planning. Sedation protocol sedation was commenced with Propofol target controlled infusion (TCI) using Schneider model with effector site concentration (Cet) of 2 to 3 and Dexmedetomidine bolus dose of 1 microgram per kilogram was infused over 10 minutes. All the patients were induced to a Ramsay Sedation Scale of at least 5 or 6. Sedation was maintained with Dexmedetomidine infusion at 0.5 mcg/kg/hr and Propofol TCI (Schneider model Cet of 2 mcg/mL). Result(s) During our study period 15 patients underwent MRI under sedation with Propofol-Dexmedetomidine for DBS treatment planning. Of this 7 were males and 8 were females. Age range was from 39 to 75 years. The target site was Subthalamic nucleus in 9 patients, Thalamic nuclei in 4 patients and Globus pallidus internus in 2 patients. Duration of sedation ranged from 40 minutes to 100 minutes with a median of 45 minutes. 2 patients developed movement artefacts during scanning and were converted to GA, 3 patients developed hypotension (20% reduction from pre-induction blood pressure) requiring treatment with ephedrine. Five patients had sinus bradycardia (20% reduction from pre-induction heart rate) but did not require treatment. The qualities of images were classified as good in 11 patients and acceptable in 2 patients by the neurosurgeon involved in treatment planning. None of the patients needed repeat MRI scanning. Patient's stay in PACU ranged from 20-50 minutes with a mean of 26.5 minutes. Discussion(s) Dexmedetomidine-Propofol sedation has been widely used for sedation to perform MRI scans in paediatric patients, its use in adult patients is not well documented in the literature. Propofol enables smooth induction of sedation and rapid recovery however it may cause hypotension, decreased respiratory drive and upper airway obstruction. Dexmedetomidine has been used as a single sedative agent for MRI however its onset of action is slow and when used as a sole sedative agent large dose of dexmedetomidine is required and this may contribute to delayed recovery after sedation. Propofol-Dexmedetomidine combination has synergistic effects and is advantageous. Propofol can induce sedation smoothly, Dexmedetomidine can reduce dose required for sedation and suppression of motor response in healthy subjects (1). Combination of Dexmedetomidine- Propofol infusion reduced total Propofol dose and decreased the incidence of airway complications in a paediatric study (2). During our study period 2 patients sedation were converted to General anaesthesia, both patients had raised BMI and had laboured breathing under sedation causing transmitted head movement, therefore patient selection is important for successful scan under sedation. Propofol-Dexmedetomidine sedation can be used safely for treatment planning MRI in selective movement disorder patients.