EDITOR:
A 49-yr-old male patient was scheduled for clipping of a giant right middle cerebral artery (MCA) aneurysm. He presented with Grade IV subarachnoid haemorrhage (SAH) and large intracerebral haemorrhage. Upon admission, the patient’s Glasgow Coma Scale score was 8 (E2V2M4) with left-sided hemiplegia. The patient was transferred to the operating room, sedated and intubated. Two 18-G peripheral intravenous lines and a left radial arterial line were placed. In addition to the routine standard monitors, electroencephalograph (EEG) electrodes were placed over the midline and left cerebral hemisphere. Two near-infrared spectroscopy (NIRS) sensors (model INVOS-4100; Somanetics Corporation, Troy, MI, USA) were applied, one on either side of the forehead. The sensors were covered with adhesive cover to shield them from ambient light. Baseline rSO2 recordings from both sides were 71–73%. Baseline systemic temperature was 37.0°C.
General anaesthesia was maintained with sevoflurane (0.5% MAC (minimum alveolar concentration)), oxygen/air (40–60%) and remifentanil (0.15 μg kg−1 min−1). Mechanical ventilation was adjusted to maintain a PCO2 in the 30–35 mmHg range.
Following right fronto-temporal craniotomy, right femoral artery to right carotid artery (FA–CA) extracorporeal hypothermic bypass was instituted. After 40 min of cooling and right brain surface temperature of 23°C, a temporary clip was placed on the right MCA. Systemic temperature was 37.3°C. Shortly after temporary clip application, the right rSO2 recordings were in the range of 55–60%. After 26 min of temporary clip application, right rSO2 readings dropped below 50% on two separate occasions 5 min apart each episode lasted for 3 min. Left-sided rSO2 recordings remained unchanged and EEG recording from midline and left hemisphere did not show any changes suggestive of ischaemia. In response to the episodes of cerebral desaturation, the neurosurgeon was informed and the temporary clip position was adjusted. Propofol infusion (3–5 mg kg−1 h−1) was started to reduce cerebral metabolic rate and titrated until EEG burst suppression was achieved. Right cerebral oxygen saturation readings returned to baseline values after 5 min of temporary clip adjustment (Fig. 1). Total temporary clipping time was 67 min and 54 s and the total duration of surgery was 12 h and 15 min.
Figure 1 Time course of changes in cerebral oxygen saturation. Point A: correspond to temporary clip application, areas B&C: represent periods of desaturation, Point D: correspond to temporary clip adjustment.
Postoperatively, the patient was transferred to the ICU on mechanical ventilation. The patient was extubated 3 days following surgery and discharged from ICU on day 4. He was awake, obeying commands. His preoperative left-sided hemiplegia did not change. There was no new neurological deficit and postoperative cerebral angiography did not reveal any evidence of new infarction or haemorrhage.
Discussion
Intraoperative cerebral ischaemic complications may be due to improper temporary or permanent clip application, prolonged temporary clipping time, retraction injury and cerebral vasospasm. With respect to intraoperative neuromonitoring, in addition to EEG, NIRS was used to monitor cerebral oxygen saturation during periods of potentially compromised cerebral blood flow (in this case, prolonged temporary parent artery occlusion of 67 min).
Several investigators have reported the use of NIRS during carotid endarterectomy and found rSO2 recordings less than 50% is indicative of cerebral ischaemia [Reference Samra, Dy, Welch, Dorje, Zelenock and Stanley1,Reference Hirofumi, Otone and Hiroshi2]. However, the efficacy and clinical outcome associated with the use of NIRS during cerebral aneurysm surgery has not yet been established. In this case report, the patient developed two episodes of right rSO2 desaturation (<50%) which were not detected clinically or by EEG. This could have resulted in significant cerebral ischaemia.
NIRS can provide a useful feedback to the anaesthesiologist and neurosurgeon that could allow early detection of cerebral ischaemia and thus early intervention. In this case report, in response to the episodes of cerebral desaturation and after discussion with the surgeon, the potential cerebral protection of propofol was considered [Reference Ergun, Akdemir, Sen, Tasci and Ergungor3,Reference Engelhard, Werner and Eberspacher4].
The findings of this report are consistent with earlier studies showing the clinical utility of multimodal neuromonitoring in the prevention of uncommon but possibly catastrophic cerebral ischaemia [Reference De Georgia and Deogaonkar5]. This modality is relatively new in neurosurgery and appears to be a promising technology that could support clinical decisions regarding detection of cerebral ischaemia. Since limited data are available, more research is needed to establish its clinical efficacy and justify its routine use in neurosurgery.
