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Nitrous oxide depresses the H-reflex in children with cerebral palsy

S G Soriano1, E L Logigian, R M Scott

  • 1Department of Anesthesia, Children's Hospital, Boston, MA 02115.

Anesthesia and Analgesia
|February 1, 1995
PubMed

Insights

Nitrous oxide (N2O) significantly reduces the Hoffmann reflex (HR) amplitude in children with cerebral palsy. This anesthetic gas can abolish abnormal spinal reflexes, impacting neuromonitoring during surgery.

Area of Science:

  • Neuroscience
  • Anesthesiology
  • Pediatric Neurology

Background:

  • The Hoffmann reflex (HR) measures motoneuron excitability and shares properties with deep tendon reflexes.
  • Children with cerebral palsy often exhibit hyperreflexia and elevated HR amplitudes.
  • Nitrous oxide (N2O) is known to depress normal spinal reflexes, but its effect on hyperreflexia in cerebral palsy is unknown.

Purpose of the Study:

  • To investigate the impact of N2O on the amplitude of the HR in children with cerebral palsy under general anesthesia.
  • To determine if N2O affects spinal reflexes in the context of hyperreflexia associated with cerebral palsy.

Main Methods:

  • Eight children undergoing selective dorsal rhizotomy (SDR) for spasticity were studied.
  • Maximum HR (HRmax) and direct motor response (MRmax) amplitudes were measured under two anesthetic conditions: sufentanil with 66% N2O/33% oxygen, and sufentanil with 100% oxygen.
  • Statistical analysis was performed to compare HRmax and MRmax between the N2O and no-N2O groups.

Main Results:

  • The HRmax amplitude was significantly lower when N2O was included in the inspired gas mixture.
  • The reduction in HRmax amplitude with N2O was statistically significant compared to the group without N2O.
  • No significant changes were observed in the MRmax amplitude between the anesthetic conditions.

Conclusions:

  • Inhaled N2O can effectively abolish abnormal spinal reflexes observed in spastic diplegia.
  • The findings suggest that N2O-induced depression of spinal reflexes must be considered during intraoperative spinal cord monitoring.
  • N2O's effect on spinal reflexes has implications for interpreting physiological monitoring in pediatric patients with neurological conditions.

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