Susceptibility of Motor-Evoked Potentials to Varying Targeted Blood Levels of Dexmedetomidine

Susceptibility of Motor-Evoked Potentials to Varying Targeted Blood Levels of Dexmedetomidine

Reduction of the spinal cord injuries during scoliosis surgery is a major goal of the anesthesia and surgical team. Despite improvement in scoliosis surgery over the years, the development of neurological deficits remains the most feared complication of spine surgery. During scoliosis surgery it is very important to monitor the spinal cord to detect spinal cord injury with surgical manipulation. Continuous or intermittent intraoperative electrophysiological monitoring (neuron-monitoring) is used routinely during these procedures to provide the surgeon with information concerning the integrity of neurological structures at risk. All neuron-monitoring modalities are affected by the anesthetic regimen used. Of the various intravenous anesthetic drugs, the combination of propofol, remifentanil and dexmedetomidine appear to impact neuron-monitoring the least. The current anesthetic practice is to use the three drugs in combination at doses that do not depress the signals but there is no data relating targeted dexmedetomidine and propofol blood levels to neuron-monitoring signals. The lack of data results in wide variability in dosing with consequent variability in patient response.

Hypothesis: Clinically relevant blood levels of dexmedetomidine will affect the amplitude of transcranial motor-evoked potentials (TcMEP) either independently or by interaction with propofol in a dose dependent manner.

Inclusion Criteria:

• Subjects must be 10 to 25 years of age
• Diagnosis of idiopathic scoliosis is established
• Subject's legal authorized representative has given written, informed consent to participate in the study and, where appropriate, the subject has given assent to participate
• American society of Anesthesiology physical status one/two
• Patients scheduled for posterior spinal fusion only

Exclusion Criteria:

• • Patients with neuromuscular scoliosis and patients with motor or sensory deficit in the lower extremities

  • Patients with allergy to, or contraindication for the drugs or techniques used in the study
  • Morbid obesity (Body mass index higher than 40)
  • History of malignant hyperthermia
  • Patient with severe cardiopulmonary disease (pulmonary hypertension, cardiomyopathy, mechanical ventilation)