Abstract

We hypothesized that the Monro–Kellie doctrine, a key principle in traumatic brain injury (TBI), also applies in traumatic spinal cord injury (TSCI). By analyzing 9986 h of intraspinal pressure (ISP) monitoring data from 79 TSCI patients, we show that concepts developed to quantify compensatory reserve in TBI may be analogously defined in TSCI, termed ISP pulse amplitude (sAMP), spinal compensatory reserve index (sRAP), and ISP waveform shape. As ISP increases beyond 15 mmHg, compensatory reserve becomes impaired (sAMP rises and sRAP becomes positive). As ISP increases beyond 20 mmHg, the morphology of the ISP waveform changes from three peaks (P1, P2, P3) with P1 dominant, to three peaks with P2 dominant, to a rounded signal. Key differences in TSCI, compared with TBI, are no plateau ISP waves, and no critical ISP beyond which sAMP decreases and sRAP becomes negative. Four factors were associated with increased spinal cord swelling or reduced spinal cord compliance: thoracic level of injury, no laminectomy, delayed surgery, and more severe injury. We also hypothesized that, as in TBI, the spinal cord maximally swells a few days after injury. Serial ultrasound scans of the injured spinal cords in 9 patients and plots of change from baseline in ISP, sAMP, and sRAP versus time in 79 patients revealed delayed maximal cord swelling within 5 days of surgery. We conclude that the spinal Monro–Kellie concept allows the spinal compensatory reserve to be quantified. Our data show that spinal compensatory reserve becomes exhausted as ISP increases above 15–20 mmHg and that there is delayed cord swelling after injury, which implies that adequate cord decompression confirmed during surgery by ultrasound may not persist postoperatively.