Dexmedetomidine-saves the day.

Sir,

A 67-year-old morbidly obese (Wt.-94 kgs, Ht.-145 cm, Body Mass Index (BMI) of 44.7/m2) patient with a traumatic spine, presented to our institute for magnetic resonance imaging (MRI) of the lumbar spine. She had an anxiety disorder, a history of snoring at night, was a hypertensive on regular treatment. She had short neck, a Mallampati score of III. An unsuccessful attempt to get an MRI scan of the patient in another hospital was explained to us.

On request to move to the MRI suite which was seven floors down, she refused to cooperate for the procedure. Discussion with the orthopaedic surgeon and the radiologist clarified that the MRI was essential for the diagnosis. The relatives were explained about the plan of action and a special consent was obtained.

An IV access was secured and portable monitoring was setup. A bolus of dexmedetomidine 0.5 mcg/kg was administered over 10 minutes. The patient calmed down after the bolus, obeyed commands and co-operated. She shifted to the trolley on instructions and was started on a continuous infusion of 0.4 mcg/kg/hr using a dial-a-flow as it is MRI compatible. Continuous positive airway pressure (CPAP) was instituted using a Boussignac CPAP system (VYGON Laboratories Pharmaceutiques, France) and the patient was transferred to the MRI suite with an anesthesiologist. Emergency airway management equipment were carried along during the transfer, End-tidalCO2 (EtCO2) was monitored continuously in view of respiratory obstruction. In the MRI suite, the monitors were changed to the MRI compatible ones. The transfer to the MRI gantry did not awaken her, Ramsay sedation score being 4. The procedure took 45 minutes. Heart rate dropped from 96/min to 64/min, no drop in blood pressure or respiratory depression was observed. The infusion of dexmedetomidine was stopped 10 minutes before the anticipated end of the procedure and the patient was shifted back to the room. The entire exercise took over 1 hour and 40 minutes. On assessment, patient was awake, responding to verbal commands and had no recall of the events.

Multiple factors like obesity, a potentially difficult airway, anxiety and the logistics of transferring an unconscious patient to the MRI suite while maintaining a patent airway and avoiding respiratory depression were the key challenges. Airway compromise is of grave concern in an obese patient who is remotely located in the MRI gantry and is receiving sedation and anaesthesia.

Dexmedetomidine is a selective alpha-2 (α2) agonist in use since 1999.[1] It has 7-8 times more selectivity to α2 receptors than clonidine, producing sedation, anxiolysis and sympatholysis and possess some analgesic properties without any respiratory depression. Dexmedetomodine has been used safely intraoperatively in obese patients with and without narcotics.[2] These properties can be very useful as a sedating agent in high risk patients prone to respiratory depression with potentially difficult airways.[3] Obese patients may be sensitive to the respiratory depressant effect of opioid analgesic drugs and more likely to require postoperative ventilation to avoid hypoxic episodes.

Dexmedetomidine has been used effectively for MRI in paediatric patients.[3] It has been used intraoperatively as the sole sedative agent in a patient receiving regional anaesthesia. Prophylactic use of CPAP in obese patients can reduce upper airway obstruction, increase functional residual capacity, and improve lung compliance, ventilation and oxygenation, especially with use of sedatives. The Boussignac CPAP system consists of a silicon mask which is applied to the patient's face and the CPAP device with a virtual valve is connected to the mask.[4] High flow through many capillaries at an angle of 45° creates a virtual diaphragm and generates positive pressure in the patient's airway. The pressure generated depends on the gas flow.[4] It can be used in the MRI suite in obese patients receiving sedation and anaesthesia because of its simple design. Dexmedetomidine is finding its way into every segment of anaesthesia practice, the above mentioned incident is a testimony.[5]