Processed EEG-based Bispectral Index (BIS) Monitor to Diagnose the Rapid Change in Intracranial Pressure during Endoscopic Third Ventriculostomy

Sir, A thirty-year-old woman was admitted with the features of raised intracranial pressure (ICP). MRI-brain (contrast) revealed a third ventricular mass (1.7 cm) with epicenter in the pineal gland with mass effect and hydrocephalus. She was planned for an endoscopic third ventriculostomy (ETV) and biopsy. After placing the standard monitors, induction and intubation were carried out using standard anesthesia drugs. Total intravenous anesthesia (TIVA) with the propofol using target-controlled infusion (TCI 2.5 μg/ml–3 μg/ml) was titrated to the Bispectral index (BIS) 40–50. Through the right frontal burr hole, the neuroendoscope was introduced and was irrigated with Ringer’s lactate solution. There was a transient increase in heart rate from 72 to 140/min; the BIS dropped from 35 to 0 within 10-15 sec of neuroendoscope insertion, along with a sharp rise in mean arterial pressure from 95 mmHg to 125 mmHg [Figure 1]. It was notified to the surgeon, the neuroendoscope was removed, and the lateral ventricle was decompressed with a ventriculoperitoneal (VP) shunt needle. The BIS improved from 0 to 10–30 over a minute and reached baseline at the end of 2 min. Then, the neuroendoscope was reintroduced, and an ETV and biopsy were done. At the end of the procedure, the patient woke-up without delay, and the post-extubating GCS was 15. Post-procedure Computed Tomography (CT) of the brain revealed mild pneumoventricle with a reduction in hydrocephalus. Biopsy was reported as pineal neoplasm. Written informed consent was taken to publish this letter to the editor.Figure 1: Shows the heart rate, BP (systolic, diastolic, mean), and the BIS changes at the time of Ringer’s lactate irrigation through the neuroendoscopeETV has gained popularity for the treatment of non-communicating hydrocephalus despite its high morbidity (0%–31.2%) and mortality (0.28%–1.28%).[1] During ETV, a rapid increase in ICP, occurs due to the rapid flushing of irrigating fluid or kinking/obstruction of an outflow tube. Cardiovascular changes, such as tachycardia and hypertension, followed by bradycardia, hypertension, and asystole, are reported due to hypothalamic stimulation/injury and raised ICP, causing decreased cerebral blood flow, thereby cerebral perfusion. Van Aken J et al.[2] looked at the cardiovascular changes during ETV (retrospective study of 88 cases) and have shown that tachycardia and hypertension, followed by bradycardia and hypertension, and then asystole is the sequence of events that occurred because of increased ICP. They have concluded that beat-to-beat arterial blood pressure monitoring provides a reliable early warning sign of raised ICP. Buxton et al.[3] have shown that simultaneous hypertension and tachycardia during endoscopy correlate with cerebral perfusion pressure (CPP) of <30 mmHg (specificity-77%), and premature, full-term neonates, older adults are vulnerable to cerebral ischemia during ETV. Also, many other investigators have shown that both tachycardia and bradycardia, along with hypertension, are the essential components of Cushing’s reflex. Waiting for the classic features of Cushing’s reflex, such as bradycardia and hypertension, could lead to severe morbidity and mortality during ETV. Measuring the pressure at the fluid outlet of neuroendoscope, intraparenchymal and epidural are some reported methods to measure the ICP. The pressure inside the neuroendoscope does not correlate with the systemic changes associated with raised ICP. Hence, it is not reliable to assess the acute increase in ICP.[4] Transcranial Doppler (TCD) showed transient cerebral circulatory arrest waveform pattern during rapid irrigation due to acute elevation of ICP.[5] However, its routine application during ETV is not practiced widely. Electroencephalography (EEG) is very sensitive in detecting cerebral blood flow changes.[6] Processed EEG-based depth of anesthesia (DOA) monitors, such as BIS, Entropy, and SedLine are Masimo used to detect cerebral ischemia during cranial, vascular, and cardiac surgeries.[6,7] However, its utilization as a cerebral ischemia monitor during ETV has not been reported. ETV is often performed under sevoflurane maintenance in many centers, keeping the minimum alveolar concentration (MAC) at 0.8–1 with mild hyperventilation. Hence, the DOA monitors are not used routinely. This case signifies the importance of CPP monitoring by any means, direct ICP monitoring or indirect monitoring such as EEG, processed EEG (BIS, entropy, SedLine Masimo), or TCD for the early detection of low CPP to prevent morbidity and mortality. Vigilant monitoring, rapid detection of low CPP, effective communication, and quick decompression of the lateral ventricle helped to prevent morbidity in our case. Prospective studies are warranted to see whether DOA monitors can detect the ICP and, thereby, the CPP changes during ETV. Author’s contributions All authors have made material contributions to handling the case and the article’s intellectual content. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.