Determination of TOF Test Threshold for Obtaining Reliable Pedicle Screw Stimulation Test During Lumbar Spine Surgery
Condition: Neuromuscular Blockade
Study type: Observational

Summary: 
      During lumbar spine fusion surgery intraoperative neurophysiological monitoring is in routine
      use for prevention of possible nerve injuries during placement of screw into pedicle. Pedicle
      screw stimulation test is performed to assess if screw placement is encroaching on the nerve
      roots. Relative distance between the pedicle screw and the neighbouring root can be estimated
      by the intensity of the current required to activate the root and appropriate muscle. A
      properly placed screw can be distinguished from those perforating the pedicle wall by its
      higher minimum level of electrical current needed to elicit a muscle response. The minimum
      level is deemed as threshold. This test is based on compound muscle action potential (CMAP)
      and use of neuromuscular blocking agents (NMBA) should be avoided because of possible cause
      of false negative results of screw stimulation test. Neuromuscular blocking agents, which are
      in routine use during anesthesia, will have effect on muscle action potential. When NMBA are
      used current stimulus will depolarize the same number of axons and the associated muscle
      response will be present but of lower amplitude because some percentage of motor fibers will
      be blocked by activity of NMBA. At this point, stronger stimulus is needed to recruit
      additional axons/muscle fibers , and hence, the measured threshold is elevated.

      Train of four (TOF) test is method used to determine level of neuromuscular blockade, by
      stimulation of peripheral nerve and following induced muscle contractions. Interpretation of
      muscle contractions may be by subjective (visual) or objective (quantitative) method.
      Quantitative TOF test may be used prior screw stimulation test by calculating T4/T1 ratio and
      obtaining quantitative value which shows level of neuromuscular blockade. Residual
      neuromuscular blockade may be present before screw stimulation test, and effect on accuracy
      of this test in this situation was not clearly investigated in recent studies.

      The purpose of this study would be to determine changes of screw stimulation thresholds under
      different range of neuromuscular blockade.Therefore, acceptable neuromuscular blockade
      threshold (determined by TOF test) acceptable for obtaining reliable screw stimulation test
      should be determined. Screw stimulation test may be performed when neuromuscular blockade is
      absent and compared to repeated screw stimulation test when neuromuscular blockade is
      present. Different levels of neuromuscular blockade may provide different results on screw
      stimulation test, so if difference is statistically significant, induced neuromuscular
      blockade level may be set as threshold value, acceptable for obtaining reliable testing
      results.
    


Intervention name(s): Rocuronium Bromide, Cisatracurium Besylate
Intervention type(s): Drug
Intervention description(s): Both Rocuronium Bromide and Cisatracurium Besylate are administered intravenously following induction of anesthesia initially by bolus, and subsequently re-bolused or administered in continuous infusion as clinically indicated to maintain muscle relaxation. Initial doses of Rocuronium range from 0.45 to 1.2 mg/kg IV, and doses for continuous infusion range from 0.01-0.012 mg/kg/min IV. Initial doses of Cisatracurium range from 0.15 to 0.2 mg/kg, and doses for continuous infusion range from 0.5 to 3 µg/kg/min. Following recovery and baseline screw stimulation at TOF >0.9, the dosing regimen for this study will rely on restarting a continuous infusion, and adjusting the infusion until the desired TOF ratios are reached. Following screw stimulations and data collection, the infusion will be terminated, and neuromuscular blockade allowed to recover.
Other intervention name(s): Zemurone, Nimbex
Intervention MeSH terms: Bromides; Rocuronium; Cisatracurium
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Subjects undergoing elective lumbar spine fusion surgery