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

Summary 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 (15×12 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.