Nitrous oxide depresses the H-reflex in children with cerebral palsy.
Hoffmann's reflex or H-reflex (HR) is an electrically elicited reflex that measures excitability of motoneurons and shares some physiologic properties with the deep tendon reflex. Children with tendon hyperreflexia due to cerebral palsy usually have higher amplitude HRs. Nitrous oxide (N2O) depresses the HR in patients with normal spinal reflexes, although the effect of N2O in conditions with hyperreflexia such as cerebral palsy is not known. We propose to determine the effect of N2O on the amplitude of the HR under general anesthesia in children with hyperreflexia due to cerebral palsy. We studied eight children undergoing selective dorsal rhizotomy (SDR) for the relief of spasticity. The maximum amplitudes of the HR (HRmax) and direct motor response (MRmax) were routinely evoked under the following anesthetic conditions: 1) sufentanil and 66% N2O/33% oxygen; and 2) sufentanil and 100% oxygen. The HRmax amplitude was significantly lower when N2O was part of the inspired gas mixture. The differences between the no N2O and the 66% N2O groups were significant. The MRmax did not change significantly. Abnormal spinal reflexes seen in spastic diplegia can be abolished by inhaled N2O. This finding also suggests that N2O-induced depression of spinal reflexes should be a consideration during physiologic monitoring of the spinal cord under general anesthesia.
Soriano
S G
SG
Department of Anesthesia, Children's Hospital, Boston, MA 02115.
Logigian
E L
EL
Scott
R M
RM
Prahl
P A
PA
Madsen
J R
JR
D002547:Cerebral Palsy / Q000503:physiopathology*; D002675:Child, Preschool; D003864:Depression, Chemical; D005260:Female; D006181:H-Reflex / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D009128:Muscle Spasticity / Q000209:etiology / Q000601:surgery; D009609:Nitrous Oxide / Q000494:pharmacology*; D012021:Reflex, Abnormal / Q000187:drug effects* / Q000502:physiology
D009609:Nitrous Oxide