Influence of induced hypotension and spinal distraction on feline spinal somatosensory evoked potentials

Spinal cord injury may occur during surgical correction of spinal deformity, which is performed frequently under hypotensive anaesthesia. We have investigated the interaction between pharmacologically induced hypotension and distraction on feline spinal cord function. Twelve anaesthetized cats were subjected to hypotension (mean arterial pressure (MAP) 60 mm Hg) using a mixture of sodium nitroprusside and trimetaphan (1:5). No significant changes were observed in somatosensory evoked potentials recorded at T11. In six cats distraction was applied at L2-3 in 2.5-mm increments up to 1 cm, while MAP was maintained at 100 mm Hg (normotensive group). The remaining cats were subjected to the same distraction procedure at an MAP of 60 mm Hg (hypotensive group). In the hypotensive group, a reduction in amplitude of evoked response occurred at significantly less distraction than in the normotensive group. These data indicate that the feline spinal cord is more sensitive to spinal distraction under hypotensive conditions.