In this study, we observed that surgical complications and adverse events were common after iMMM placement, in particular probe misplacement and small-volume intracranial hemorrhage. No infection related to iMMM was observed. The type of acute brain injury and the timing of placement were not associated with a higher occurrence of iMMM-related complications. Only a minority of these complications were associated with iMMM dysfunction.
The most investigated surgical complications related to iMMM are probe misplacement and intracranial hemorrhage. Placement of PbtO2 probes outside the white matter, within a lesion or within a ventricle may yield irrelevant brain oxygen measurement and would result in additional costs (i.e. for probe replacement and/or because of lack of an adequate monitoring tool to guide interventions). Misplacement rates ranged from 0% to 14.3% across different studies [2, 8, 10, 17, 18] and varied depending on the targeted area of the brain (i.e. higher when the target was a contusional then a healthy brain area). In our cohort, 13% of iMMM placement was associated with probe misplacement. Although this is quite higher than in most of previous reports, we investigated a heterogeneous cohort of patients with different forms of brain injury, while most of other studies focused on TBI patients. Future prospective studies evaluating with more accuracy the occurrence of iMMM-related complications should therefore include different forms of brain injury to better evaluate the potential role of the underlying disease in the occurrence of such complications.
Conversely, the occurrence of ICH was relatively low. In our series, where all patients underwent cerebral CT-scan after iMMM placement, tract and distal probe hemorrhages were evaluated by an independent radiologist who reviewed all postoperative imaging, including immediate post-placement but also delayed imaging studies. Moreover, only one case required surgical drainage (i.e. a compressive right parasagittal extradural hematoma). Dings et al. [8] described a similar occurrence of ICH due to placement of the PbtO2 probes close to the sagittal sinus, which should require a particular attention from physicians placing iMMM. Considering the variable occurrence of ICH due to iMMM placement reported in the literature, ranging from 0% to 40.5% [2, 8, 10, 17, 18], large multicentric registries are required to better describe the occurrence of such complication, its localization and size, the consequences on patients’ clinical status as well as related interventions.
We observed no infection related to the iMMM placement. In fact, infections due to this type of intraparenchymal monitoring appear to be rare: in the largest series available including 501 patients, only one infection was reported [2]. On the other hand, accidental dislodgment and probe breaking are usually reported, ranging from 5.9% to 7.4% and from 2.5% to 4.5%, respectively [2, 8, 10, 17, 18]. Whether these complications occur because of agitation or discomfort, during daily standard interventions (i.e. changes in bed positioning, physical therapy) or during transport (i.e. to perform brain imaging or other diagnostic/therapeutic procedures), it remains unclear from our retrospective data. Neuro-critical patients often require great manipulation and transportation which may make them vulnerable to these adverse events [10]. An interesting dynamic approach to adverse events was proposed by Foreman et al. [10], who quantified sudden stops of data recording as discontinuations, resulting either from dislodgement or unplugging by time tracking them as one-off events rather than only reporting their occurrence. During a median monitoring time of 97 hours, device discontinuation was noted in 25/43 (58%) patients and concerned the combined ICP/PbtO2 probe in 7 (16%) cases, with a total of 4% of the recorded data considered as unusable. They also found a significant association between discontinuation and the number of patient trips for procedures or imaging.
Finally, despite complications and technical malfunctioning, iMMM appears to be safe, as only one additional surgery with no subsequent short-term neurological sequelae was observed. Moreover, both hospital mortality rate and neurological outcome were similar between patients that experienced at least one complication when compared to others. However, 10 (8%) probes presenting a technical malfunction independently from other complications and, in some cases, this occurred within the first week of monitoring. The additional costs for probe replacement as well as the immediate loss of relevant monitoring data in these patients should also be further evaluated in larger cohorts, as it might be important information for centers who would decide to initiate placing iMMM in their routine practice.
This study has some limitations due to its monocentric retrospective design, which limit the generalization of the main findings. Also, we did not specifically investigate long-term effects of the reported complications. Moreover, the role of neurosurgeons’ skills was not considered into the analysis as iMMM placement was performed by rotating residents supervised by senior neurosurgeons with no main operator clearly identified into medical charts. Second, we used a triple lumen bolt device placed into the operating room and our findings do not apply to other possible solutions (i.e. double lumen bolts or subcutaneous tunelization without bolt) or setting (i.e. placement into the ICU and/or by a non-neurosurgeon). Third, the PbtO2 was the sole modality concerned by technical malfunction report, as being the only one used in clinical routine (i.e. microdialysis and iEEG data were only collected for research purposes).