Suprasegmental neurophysiological monitoring with H reflex and TcMEP in spinal surgery. Transient loss due to hypotension. A case report

OBJECTIVE: H-reflex is a well known neurophysiological test used to evaluate sensory afferent and motor efferent impulses of S1 root. Despite its simplicity and feasibility, it is not used very often in the operating room. METHODS: We report the case of a 16-year-old male patient who undergoes a surgical correction for a severe paralytic scoliosis (160°). On account of previous deficits, intraoperative neurophysiological monitoring was achieved through TcMEP and H-reflex. RESULTS: Intraoperative neurophysiological monitoring (IONM) showed a transient and simultaneous loss of bilateral TcMEP and H-reflex, coinciding with an abrupt hypotension during pedicle screw placement. After having dismissed mechanical injury and after increasing blood pressure, TcMEP and H-reflex were equivalent to those at baseline. CONCLUSIONS: The H-reflex is a classic neurophysiological test not used very frequently in the operating room. It is a feasible and reliable technique that can be helpful during spine surgery IONM, especially in patients with preexisting neurological deficits. Although simultaneous TcMEP and H-reflex monitoring has been previously described, to our knowledge, this is the first recorded case of a decline in both associated with abrupt hypotension.