Position of probe determines prognostic information of brain tissue PO2 in severe traumatic brain injury

Abstract

Background: Monitoring brain tissue PO2 (PbtO2) is part of multimodality monitoring of patients with traumatic brain injury (TBI). However, PbtO2 measurement is a sampling of only a small area of tissue surrounding the sensor tip.

Objective: To examine the effect of catheter location on the relationship between PbtO2 and neurological outcome.

Methods: A total of 405 patients who had PbtO2 monitoring as part of standard management of severe traumatic brain injury were studied. The relationships between probe location and resulting PbtO2 and outcome were examined.

Results: When the probe was located in normal brain, PbtO2 averaged 30.8 ± 18.2 compared with 25.6 ± 14.8 mm Hg when placed in abnormal brain (P < .001). Factors related to neurological outcome in the best-fit logistic regression model were age, PbtO2 probe position, postresuscitation motor Glasgow Coma Scale score, and PbtO2 trend pattern. Although average PbtO2 was significantly related to outcome in univariate analyses, it was not significant in the final logistic model. However, the interaction between PbtO2 and probe position was statistically significant. When the PbtO2 probe was placed in abnormal brain, the average PbtO2 was higher in those with a favorable outcome, 28.8 ± 12.0 mm Hg, compared with those with an unfavorable outcome, 19.5 ± 13.7 mm Hg (P = .01). PbtO2 and outcome were not related when the probe was placed in normal-appearing brain.

Conclusion: These results suggest that the location of the PbtO2 probe determines the PbtO2 values and the relationship of PbtO2 to neurological outcome.

FIGURE 1

Algorithm for treatment of a low brain tissue PO₂ (PbtO₂) used throughout the study period. CT, computed tomography; Hgb, hemoglobin; ICP, intracranial pressure; MAP, mean arterial pressure; rCBF, regional cerebral blood flow.

FIGURE 2

Computed tomography scans illustrate typical appearance of the different catheter positions. The arrow identifies the brain tissue PO₂ (PbtO₂) probe in each case. Top left, the PbtO₂ probe in normal-appearing right frontal lobe in a patient with a diffuse brain injury. Top right, the PbtO₂ probe in brain after evacuation of a subdural hematoma. The probe was placed at the time of surgery in brain tissue. The brain appears normal but has been compressed by the subdural hematoma. Bottom left, a PbtO₂ probe in the left frontal lobe near a contusion. If the contusion expands, this tissue is likely to become involved or to be compressed. Bottom right, a PbtO₂ within a contusion in the right frontal lobe.

FIGURE 3

The position of the brain tissue PO₂ (PbtO₂) probe was significantly influenced by the type of computed tomography (CT) scan lesion (P < .001).

FIGURE 4

Trend graphs of brain tissue PO₂ (PbtO₂) over time (median ± interquartile range) for the different catheter positions. ICU, intensive care unit.

FIGURE 5

Results of logistic regression model for the relationship of average brain tissue PO₂ (PbtO₂) and neurological outcome. The chances for a favorable outcome are generally less in patients with poor admission neurological status (diamonds) than in patients with better admission neurological status (circles). The open symbols show the chances of favorable outcome significantly improving with increasing PbtO₂ when the probe is placed in abnormal tissue; the solid symbols show no significant relationship between outcome and PbtO₂ when the probe is placed in normal brain. GCS, Glasgow Coma Scale.