A comparative study, between intra-operative low dose ketamine and dexmedetomidine, as anesthetic adjuvant in lumbar spine instrumentation surgery for post-operative analgesia requirement

PROTOCOL:-  A computer generated randomisation scheme isto be used to randomise patients into one of the 3 treatment regimens: racemicketamine/K-group (0.5mg/kg bolus followed by 250µg/kg/hr infusion),dexmedetomidine/D-group (1µg/kg bolus followed by 0.5µg/kg/hr infusion) or theplacebo/ P-group. Principal investigator/ anesthesia provider, patient andnursing staff will be blinded to the treatment assignment during the entirehospital stay. An opaque sealed- envelope method will be used for allocation ofthe patients to different groups.

A standard anesthesia induction and maintenanceprotocol will be followed. The sevoflurane vapourizer will be weighed prior tostarting of induction and weight recorded in grams or volume consumed measured if available on ventilator. After shifting the patientto OT standard monitors like electrocardiograph, pulse oximeter andnon-invasive blood pressure will be connected and an intravenous (IV) line willbe established.

After preoxygenation for 2 min, anesthesia will beinduced with fentanyl 2µg/kg, propofol 2-3 mg/kg and tracheal intubation willbe facilitated with rocuronium 1mg/kg. Anesthesia will be maintained usingoxygen-air mixture in 40:60 ratio with fresh gas flow @1.5L/min. Muscle relaxation will be maintained withrocuronium 0.25mg/kg bolus every 40 minute and analgesia with fentanyl 1µg/kg asand when required. A bispectral index (BIS. A 2000: Aspect medical system) willbe used with target BIS between 40-50 by titration of sevoflurane. Additionalmonitors after intubation will consist of end tidal carbon dioxide (ETCO2),invasive blood pressure/IBP, central venous pressure (CVP), anesthetic agent,airway pressure and nasopharyngeal temperature.

Once the patient is made prone the study drug(bolus) will be administered over 10 minutes using the syringe pump (TERUMO)with 10ml syringe (i.e. 60ml/hr for 10 min). Patients in low dose ketaminegroup will receive 0.5mg/kg bolus while those in dexmedetomidine group willreceive 0.5µg/kg. For placebo group 0.9% normal saline will be used. Heart rate(HR), blood pressure (BP) and oxygen saturation will be noted during the startand end of bolus infusion. A constant infusion rate of 10ml/hr will be startedprior to skin incision which would deliver at the rate of 0.5µg/kg/hr fordexmedetomidine and 250µg/kg/hr for ketamine by varying the drug concentrationin a 50ml syringe. The study drug infusions will be prepared by ananaesthesiologist based on the weight of the patient pre-operatively withrandom drug selection who will be a co-investigator of the trial but notinvolved in the management of the patient. The prepared syringe will belabelled as “study drug†with serial number. BP will be targeted to keep within20% of baseline values with hypotension defined as 20% drop from baseline valueand hypertension defined as 20% rise from baseline value for more than 1 minute.

Hypotensionwillbe treated with:-

1)Increase of intravenous fluid, and/or

2. Bolusdoses of phenylephrine 0.5µg/kg

3. Fornon responsive cases intravenous infusion of vasopressor will be used.

Hypertensionwill be treated with:-

1)  Bolus dose of propofol 0.5mg/kg if BIS ismore than 50.

2. If BISranges between 40-50, then fentanyl bolus of 0.5µg/kg will be given. Intraoperatively,bradycardia was defined as HR < 60/min accompanied with hemodynamicinstability or a HR <40/min with or without hemodynamic instability while tachycardiaas a 20% increase from baseline in HR.

Bradycardiawillbe treated with:-

1. 0.6mg atropine intravenous bolus and repeated asrequired.

2. For non responders dopamine (2-10 µg/kg infusion)or adrenaline (2-10µg/min infusion) may be used.

Number of episodes of bradycardia, hypotension andhypertension is noted. End tidal sevoflurane concentration will be decreased by50% at start of skin closure and turned off after making the patient supine.The study drug infusion will be stopped at closure of muscle layer. After turning the patient supine residual neuromuscular blockade will bereversed with neostigmine (50µg/kg) and glycopyrollate (8-10µg/kg). The patientwill be extubated on meeting the extubation criteria and time is noted.Emergence agitation if any is noted and scored based on Riker sedationagitation scale (SAS).

HR, BP, ETCO2 and SPO2 are tobe recorded at 0min, 5min, 15 min and every 15 min starting from pronepositioning till end of skin closure. Apart from demographic data,hemodynamics, total dose of fentanyl, propofol, phenylephrine used, duration ofsurgery (from skin incision to skin closure), blood loss, recovery time (timefrom stopping of sevoflurane to time of extubation) will be noted.

The patient will beshifted to ICU where IV-patient controlled analgesia (IV-PCA) will be started (bolusdose of 1µg/kg of fentanyl, lockout interval of 10 minute with no basalinfusion). Fentanyl consumption via IV-PCA will be evaluated for 24 hours aftersurgery. The pain will be quantified with a 100mm visual analog scale (VAS).Pain scores will be recorded at rest and with movement at 1, 6, 12 and 24 hrafter surgery. Adverseevents such as sedation, headache, nausea/vomiting and hallucination/dreamswill be recorded. For moderate to severe nausea or vomiting 4mg ondansetronwill be administered.

STUDY HYPOTHESIS:- We believe that using adjuvants like ketamine and dexmedetomidine in the intraoperative period in lumbar instrumentation surgery (which are painful procedures even in the post operative period due to major tissue handling/damage) decrease the post operative analgesic/narcotic requirements (primary aim) and also decreases intraoperative analgesic and/or anesthetic requirement leading to better recovery profile( secondary aim).