Relationship of brain tissue Po₂ to outcome after severe head injury

Objective: To determine thresholds of brain tissue PO₂ (PbtO₂) that are critical for survival after severe head injury. Design: Prospective data collection. Setting: Neurosurgical intensive care unit of Ben Taub General Hospital, a comprehensive academic neurosurgical facility and Level I trauma center. Patients: Forty-three severely head-injured patients who were not obeying commands on presentation or whose condition deteriorated to this level shortly after admission. Interventions: lntracerebral placement of Licox (n = 39) or Paratrend (n = 4) PO₂ probes during craniotomy or in the intensive care unit. Measurements and Main Results: PbtO₂ monitoring continued for an average of 84.6 ± 41.8 hrs. The probes were calibrated before insertion according to the manufacturer's specifications. After removal, probes were tested in room air and in blood gas standard calibration solutions. PbtO₂ data were analyzed by comparing the average time that PbtO₂ was below the values of 20, 15, 10, 8, 6, 4, and 2 torr (2.7, 2.0, 1.3, 1.0, 0.8, 0.5, and 0.3 kPa, respectively) in patients who were living 3 mos after injury vs. those who died. A Tobit regression analysis using maximum likelihood methods was utilized. Both Licox and Paratrend probes functioned well in room air and in the Level I control. However, in the zero- oxygen solution, the Paratrend probes gave an average reading of 7.0 ± 1.4 torr (0.9 ± 0.2 kPa), compared with 0.3 ± 0.3 torr (0.04 ± 0.04 kPa) for the Licox probes. Conclusions: Analysis of the PbtO₂ monitoring data suggested that the likelihood of death increased with increasing duration of time at or below a PbtO₂ of 15 torr (2.0 kPa) or with the occurrence of any PbtO₂ values of ≤6 torr (≤0.8 kPa).