Relevance of ICP and ptiO2 for indication and timing of decompressive craniectomy in patients with malignant brain edema

BACKGROUND

The exact effects of decompressive craniectomy on intracranial pressure (ICP) and cerebral tissue oxygenation (ptiO2) are still unclear. Therefore, we have monitored ICP and ptiO2 intra-operatively and correlated these values to different operative steps during craniectomy.

METHODS

ICP and ptiO2 values have been monitored both, simultaneously and continuously, in 15 patients with cerebral edema due to posttraumatic or postischemic brain swelling. Indications for craniectomy were an increase in ICP above 25 mmHg or a decrease in ptiO2 below 10 mmHg resistant to conservative treatment (e.g. mannitol, hyperventilation, adequate arterial blood oxygenation, etc.). In all cases, we performed a fronto-temporo-parietal craniectomy (15 x 12 cm) and dura enlargement with galea-periosteum. During craniectomy, monitoring of ICP and ptiO2 in the affected hemisphere was continued. Values were recorded and correlated with the different operative steps.

FINDINGS

We performed craniectomy according to our treatment protocol in 5 patients. Prior to surgery, mean ICP values were 25.6 mmHg (range: 23-29 mmHg), mean ptiO2 values were 5.9 mmHg (range: 2.4-9.5 mmHg), and mean CPP values were 66 mmHg (range: 60-70 mmHg). After removing the bone flap, ICP values dropped to physiological values (mean: 7.4 mmHg), whereas ptiO2 values increased only slightly (mean: 11 mmHg). Opening of the dura resulted in a further decrease of ICP (mean 4.8 mmHg) and an increase of ptiO2 to normal limits (mean: 18.8 mmHg). After skin closure, mean ICP was 6.8 mmHg and mean ptiO2 was 21.7 mmHg, respectively. We found a significant decrease of ICP after craniectomy (p<0.042) and after dura enlargement (p<0.039) as well as a statistically significant increase in ptiO2 after craniectomy (p<0.043) and after dura enlargement (p<0.041).

CONCLUSION

As a large bone flap in decompressive craniectomy is essential for adequate ICP reduction, the results of the presented cases suggest that dura enlargement is the crucial step to restore adequate brain tissue oxygenation and that ptiO2 monitoring could be an important tool for timing craniectomy in the future.

Comparative use of magnetic resonance imaging and electrophysiologic investigation for the prognosis of head injury

BACKGROUND

To compare magnetic resonance imaging (MRI) and electrophysiologic investigation as prognostic methods in acute head injury.

METHODS

Fifty-seven patients suffering moderate to mild (Glasgow Coma Scale score > 8) or severe (Glasgow Coma Scale score < 8) head injury were included. Both groups were analyzed as a total and separately for outcome as assessed by Glasgow Outcome Score. Two outcome groups were separated (Glasgow Outcome Score 1-3: unfavorable vs. Glasgow Outcome Score 4-5: favorable). MRI scans (T1-, T2-, T2*-sequences; transverse, coronal, and sagittal slices) were obtained 1 to 39 days after trauma (mean, 14 days). Electrophysiologic investigations consisted of median nerve-evoked somatosensory responses to assess corticosubcortical function and brain stem auditory-evoked potentials and brain stem reflexes for brain stem function. Recordings were performed 24 to 72 hours after trauma and repeated every 3 to 5 days.

RESULTS

Evaluation of all patients revealed a prognostic significance of MRI lesions within the corpus callosum, the basal ganglia, the hippocampus, the midbrain, and the pons. In the severe head injury subgroup, significance was limited to lesions within the corpus callosum, the basal ganglia, and the midbrain. Among the electrophysiologic findings, dysfunction of the corticosubcortical region as well as of the midbrain were linked to an unfavorable outcome. In severe head injury, prognostic significance was restricted to bilateral corticosubcortical dysfunction. A statistical test for diagnostic convergence of both methods indicated a distinct convergence only for lesions of the midbrain and the pons.

CONCLUSION

MRI scans performed early after head injury provide several indicators for unfavorable outcome. Electrophysiologic investigations add to this prognostic evidence. Both methods have comparably high specificity. However, because of the higher density of prognostic information obtained, MRI seems superior to electrophysiologic testing.