This study will compare three different doses of perineural dexmedetomidine 0.67 mcg/kg, 1 mcg/kg, and 1.33 mcg/kg as adjuvants to local anesthetics for ultrasound-guided infraclavicular brachial plexus blocks (ICBs). Our research hypothesis is that 1.33 mcg/kg will provide a 15%-longer duration than 1mcg/kg, which in turn will provide a 15%-longer duration than 0.67 mcg/kg. Since analgesic duration and sensory duration can be influenced by intake of pain medications and surgical trauma to small cutaneous nerves, respectively, we will select motor block duration as the main outcome to better target the action of dexmedetomidine on the brachial plexus.
With the approval of Ethics Committee of the McGill University Health Centre, a total of 69 patients undergoing upper extremity surgery (elbow and below) will be recruited. Recruitment will be carried out by an investigator not involved in patient care one day before surgery All ICBs will be supervised by the coauthors and conducted preoperatively in an induction room. After skin disinfection and draping, the ICB will be performed with a previously described technique. In each group, a proven 90% effective volume of 35 mL of local anesthetic solution will be injected. As LA solution, it will be used a mixture of lidocaine 1.0%-bupivacaine 0.25% with epinephrine 5 µ/mL plus PN 2 mg dexamethasone. The injectate will be slowly injected through the block needle. Patients will be randomized to receive the study drug, PN dexmedetomidine 0.67 mcg/kg or PN dexmedetomidine 1 mcg/kg, or PN dexmedetomidine 1.33 mcg/kg mixed with the above-mentioned LA solution. A research assistant (licensed anesthesiologist) will prepare the local anesthetic solutions and will add the study drug following the randomization order. The operator, patient, and investigator assessing the block will be blinded to group allocation. The primary outcome will be the duration of the motor block (defined as the temporal interval between the end of LA injection through the block needle and the return of movement to the hand and fingers) for patients with successful ICBs. Patients will be provided with a data sheet and asked to record the time at which motor function returns. An investigator blinded to group allocation will collect this data sheet in person (inpatients) or by phone (outpatients) on postoperative day 1.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
SUPPORTIVE_CARE
Masking
QUADRUPLE
Enrollment
69
Perineural dexmedetomidine 0.67 mcg/kg will be added to the local anesthetic used to block the cords of the brachial plexus with an infraclavicular approach.
Perineural dexmedetomidine 1 mcg/kg will be added to the local anesthetic used to block the cords of the brachial plexus with an infraclavicular approach.
Perineural dexmedetomidine 1.33 mcg/kg will be added to the local anesthetic used to block the cords of the brachial plexus with an infraclavicular approach.
McGill University Health Centre
Montreal, Quebec, Canada
RECRUITINGMotor block duration
The elapsed period in minutes between the ending time of the local anesthetic injection and the time of return of hand and fingers movement
Time frame: 24-48 hours after block
Sensory block duration
The elapsed period in minutes between the ending time of the local anesthetic injection and the time of the return of hand and fingers sensation
Time frame: 24-48 hours after block
Analgesic block duration
The elapsed period in minutes between the ending time of the local anesthetic injection and the time of the first sensation of pain in the surgical area
Time frame: 24-48 hours after block
Block performance time
Sum of: 1- the acquisition time of the ultrasonographic image. and 2- the time to perform the block itself (from the skin anesthesia to the end of local anesthetic injection)
Time frame: 1 hour before surgery
Intensity of pain during block procedure
Evaluated with the Numeric Rating Scale for Pain. This scale is graduated from 0 to 10 points. A 0-point score represents the absence of pain, and a 10-points score represents the worst imaginable pain. Patients will be asked to rate their pain verbally with this scale. The blinded assessor will register the score reported.
Time frame: 1 hour before surgery
Block onset time
Time required to reach a minimal sensorimotor composite score of 14 points out of a maximum of 16 points. The sensorimotor score is described in outcome 7.
Time frame: 1 hour before surgery
Sensory and motor block score
The sensorimotor block will be assessed every 5 minutes until 30 minutes after the end of local anesthetic injection using a 16-point composite score evaluating sensory and motor block of musculocutaneous, medium, radial, and ulnar nerves. Sensation will be assessed with ice in each nerve territory with a 0 to 2 point scale. 0= no block, patients can feel cold; 1= analgesic block, the patient can feel touch but not cold; 2= anesthetic block, the patient cannot feel cold or touch. The motor function will be assessed for each nerve with a 0 to 2 points scale where 0= no motor block; 1= paresis; 2= paralysis. Successful blocks at 30 minutes correlate with a final score ( sum of all individual sensory and motor scores) of at least 14 points out of 16.
Time frame: 30 minutes after the ending time of local anesthetic injection
Incidence of complete block
Percentage of blocks with a minimal sensorimotor composite score of 14 points out of a maximum of 16 points at 30 minutes after the injection
Time frame: 30 minutes after the ending time of local anesthetic injection
Incidence of surgical anesthesia
Ability to proceed with surgery without the need for intravenous narcotics, general anesthesia, rescue blocks or local anesthesia infiltration by the surgeon
Time frame: 30-60 minutes after the ending time of local anesthetic injection
Incidence of nerve block side effects
Determined by the presence of paresthesia, local anesthetic systemic toxicity, vascular puncture, Horner syndrome, hoarseness, or pneumothorax after the block.
Time frame: 0 minutes after skin disinfection to 30 minutes after the nerve block
Respiratory depression
Presence of low respiratory rates (lower than 8 breaths per minute) or persistent oxygen requirements (pulse oximetry lower than 90% without supplementary oxygen). The respiratory rate and pulse oximetry are continuously measured intra- and post-operatively (in the post-anesthetic care unit) as a standard of care with a multiparameter monitor. Alarms are set to alert when predetermined levels are reached
Time frame: 30 minutes after the nerve block to 2 hours after surgery
Bradycardia
Defined as a heart rate lower than 50 beats per minute. The heart rate is continuously measured intra- and post-operatively (in the post-anesthetic care unit) as a standard of care with a multiparameter monitor. Alarms are set to alert when predetermined levels are reached
Time frame: 30 minutes after the nerve block to 2 hours after surgery
Hypotension
Mean arterial pressure lower than 60 mmHg. The blood pressure is measured intra- and post-operatively (in the post-anesthetic care unit) as a standard of care with a multiparameter monitor. Alarms are set to alert when predetermined levels are reached
Time frame: 30 minutes after the nerve block to 2 hours after surgery
Postoperative persistent sedation
Persistent sedation after surgery using Ramsay sedation scale. The scale has 6 points from 1 to 6. A higher score represents a more sedated patient. 1= anxious, agitated or restless; 2= co-operative, oriented and tranquil; 3= responds to command only; 4= brisk response to light pain or loud auditory stimulus; 5= sluggish response to light pain or loud auditory stimulus; 6= no response.
Time frame: 2 hours after surgery
Persistent neurologic deficit
Presence of persistent sensory or motor postoperative deficit. The patients will be contacted by telephone and inquired about any sensory or motor deficit in the operated extremity.
Time frame: 7 days after surgery
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