Recent advancements in the practice of neuroanaesthesia and neurocritical care: An update

ABSTRACT

The practice of neuroanaesthesia has expanded significantly in recent years to keep up with various challenges posed in the perioperative care of patients for neurosurgical, interventional, neuroradiological, and diagnostic procedures. Technological advancements in neuroscience include the intraoperative use of computed tomography scans and angiograms for vascular neurosurgery, magnetic resonance imaging, neuronavigation, expansion of minimally invasive neurosurgery, neuroendoscopy, stereotaxy, radiosurgery, the performance of increasingly complex procedures, advancements in neurocritical care, etc. Recent advancements in neuroanaesthesia that can meet these challenges include the resurgence of ketamine, opioid-free anaesthesia, total intravenous anaesthesia, techniques to facilitate intraoperative neuromonitoring, awake neurosurgical and spine surgeries, etc. The current review provides an update on the recent advancements in neuroanaesthesia and neurocritical care.

INTRODUCTION

Significant technical advancements in diagnostic and interventional neurosciences have occurred in the last decade. Neuroanaesthesia and neurocritical care specialities have tried to incorporate these emerging advancements to facilitate patient management and to improve outcomes. We searched the literature on Google Scholar, Embase, MEDLINE, and PubMed using a word search pertaining to the recent practices in neuroanaesthesia and neurocritical care across the common neurological and neurosurgical indications for sedation, anaesthesia, and critical care services. Based on this research, we reviewed the recent advancements that have witnessed translation into clinical practice in neuroanaesthesia and neurocritical care.

A) NEWER ADVANCEMENTS IN NEUROANAESTHESIA

The resurgence of ketamine in neuroanaesthesia

The use of ketamine is on an increasing trend due to better understanding of its effect in improving cerebral perfusion pressure and reducing intracranial pressure (ICP).[1,2] The role of ketamine during thrombolytic therapy in acute ischaemic stroke is under evaluation for its utility in amelioration of cerebral infarction at a dose of 0.15 mg/kg intravenous (IV) bolus (maximum 15 mg) followed by an IV infusion of 0.15 mg/kg over 60 minutes (maximum 15 mg).[3]

Studies are exploring the utility of ketamine in patients with aneurysmal subarachnoid haemorrhage in sub-anaesthetic doses. Ketamine has been proposed to act as a neuroprotectant through analgesic, anti-inflammatory, sympathomimetic, anti-seizure, and sedative actions, thereby reducing cerebral ischaemia.[4] The role of ketamine in preventing delayed cerebral ischaemia through the suppression of cortical spreading depolarisations is also under evaluation.[5]

The anti-seizure property of this N-methyl-D-aspartate (NMDA) receptor antagonist qualifies its use in the management of super-refractory status epilepticus in adult[6] and paediatric patients at a dose of 1–3 mg/kg/h.[7] Patients with treatment-resistant depression have benefitted from rescue therapy with sub-anaesthetic doses of ketamine and its use is promising in electroconvulsive therapy.[8] Evaluation of the safety and efficacy of the use of ketamine for sedation, induction, and anaesthetic maintenance shows promising results post-traumatic brain injury.[9]

Dexmedetomidine as a sole analgesic for opioid-free anaesthesia

“Opioid-free” anaesthesia is a recent concept that is being explored in neurosurgical procedures to overcome opioid-induced side effects. Dexmedetomidine, an alpha-2 agonist, is a well-established agent for cooperative sedation in areas in neurosurgery and neuroradiology where periprocedural neurological testing is needed. It is further gaining importance as an effective adjunct and opioid alternative, with postoperative pain rescue analgesic requirements similar to the routine opioid regimen. The current opioid-based neuroanaesthesia regimens will give way to non-opioid-based perioperative management in neurosurgical patients in the future.[10]

Transient flow arrest for neurovascular procedures

Transient cardiac and cerebral flow arrest attenuates cerebral perfusion pressure across the aneurysm to facilitate clip ligation in complex aneurysms where temporary clips are difficult to apply.[11] The negative chronotropic and dromotropic effects of adenosine help induce profound systemic hypotension, the duration of which should be carefully coordinated with the surgeon to facilitate optimal circumferential exposure and aneurysm clipping. Preoperative planning with availability of transcutaneous ventricular pacing, exclusion of contraindications to adenosine, and adequate preparedness to manage complications have led to safe implementation of adenosine use.[11] Adenosine has also been tried during difficult resections, sudden major vascular injury, and during endovascular embolisation of complex arteriovenous malformations to facilitate a brief bloodless field.[12] Rapid ventricular pacing is another technique employed in some centres where the pacing wire inserted through the central venous access facilitates clipping of complex aneurysms and has been proven safe and efficient.[13] A gradual step-up of the heart rate to 150–200 beats per minute (bpm) is titrated to reduce the mean arterial blood pressure (MAP) to around 50 mmHg to facilitate clipping.

Management of awake craniotomies

Awake craniotomy is increasingly being employed as a standard of care for the surgical management of lesions close to the eloquent areas of the brain due to improved preoperative radiological delineation, intraoperative lesion mapping, and use of intraoperative magnetic resonance imaging (iMRI). The current awake-asleep-awake technique and monitored anaesthesia care (MAC) techniques are further refined to enhance patient comfort during surgery. An awake yet pain-free sedated yet arousable and cooperative patient who is haemodynamically stable is the goal of every anaesthesiologist involved in these cases.[14] For optimum sedation during different phases of the surgical procedure, short-acting anaesthetic drugs with titration using bispectral index monitoring is used. Either continuous or target-controlled infusion (TCI) of propofol at the rate of either 2–3 mg/kg/h or TCI target effect-site concentration (Ce) of 1-2 μg/mL has a better titratable profile during the more noxious phases of surgery before reaching the tumour. Intravenous dexmedetomidine (at a bolus of 0.5–1 μg/kg over 10 minutes followed by 0.2–0.7 μg/kg/h) has been shown to have an opioid-sparing effect, preventing intraoperative haemodynamic surges, nausea, vomiting, and hypercarbia common to these surgeries. It provides arousable sedation by preserving the patient’s spontaneous breathing at the prescribed doses. Short-acting opioids, namely, fentanyl (0.5–1 μg/kg boluses) and remifentanil (0.05–0.1 μg/kg/min, C_e = 1–3 ng/mL if TCI protocol), are supplemented for analgesia and anxiolysis.[15] The evolving use of high-flow nasal oxygenation during awake craniotomies serves as a bridge to tide over the need for definitive airway access, especially in patients with obstructive sleep apnoea. The non-invasive continuous monitoring of the oxygen reserve index further guides the early detection of hypoxia in these patients.[16]

Management of awake spine surgeries

Awake spinal surgeries including endoscopic procedures have become the “go-to” option for patients and neurosurgeons due to enhanced recovery.[17] This is currently employed for laminectomies with or without microdiscectomies, foraminotomies, anterior cervical discectomy and fusions, lumbar fusions, and dorsal column stimulator placements.[18]

Role of regional anaesthesia in neurosurgery

The scope of regional anaesthesia extends beyond scalp block for awake craniotomies. This includes infraorbital nerve block for transsphenoidal resection of a suprasellar tumour, cervical plexus block for carotid endarterectomy, trigeminal nerve block for the management of trigeminal neuralgia, and transversus abdominis plane block for ventriculoperitoneal shunt surgeries. Use of regional anaesthesia using neuraxial blockade in the subarachnoid, epidural, and combined subarachnoid epidural planes is increasingly preferred over general anaesthesia (GA) for lumbar microsurgical procedures.[19] Likewise, ultrasound-guided cervical plexus blocks (superficial, intermediate, and deep) for anterior cervical discectomy and fusions, brachial plexus blocks for carotid endarterectomy, erector spinae, and paravertebral blocks for cervical/thoracic/lumbar surgeries and iliac crest bone graft harvest are increasingly being used to circumvent the morbidity associated with GA. Additionally, non-GA scenarios permit live neurofeedback that aids the surgeons in gauging their proximity to critical neural structures, reducing the risk of neuronal injury.

Anaesthesia for functional neurosurgery

Functional neurosurgeries through deep brain stimulation (DBS) were initially used for the management of Parkinsonism. Their application has now expanded to include movement disorders (essential tremor, dystonia, myoclonus, chorea, torticollis, spasticity), chronic pain (trigeminal neuralgia, cluster headaches, cancer pain, chronic pain syndromes), psychiatric disorders (chronic depression and obsessive-compulsive disorders), multiple sclerosis, and refractory seizures.[20]

Microelectrode recording (MER), used to locate various brain nuclei, are affected by anaesthetic agents. Agents such as benzodiazepines, barbiturates, volatile agents, propofol, thiopentone, and etomidate interfere with MER through potentiation of the inhibitory actions of gamma-aminobutyric acid within the basal ganglia. Dexmedetomidine is demonstrated as a reliable anaesthetic adjunct to maintain anaesthesia during MER.[21] Though these procedures are usually done under MAC, studies comparing GA with MAC have shown that both are effective, with good surgical outcomes.

Anaesthetic management of procedures requiring neuronavigation

Neuronavigation allows precise tumour localisation and employs stereotaxis as a means of non-invasive precise localisation of the target tissue relative to known surface reference points. This can be either frame-based or frameless. The ability to perform real-time intraoperative guidance during brain and spinal surgeries increases the accuracy and safety of neurosurgery.[22] Immediate preoperative mapping of the tumour coordinates should remain unaffected by significant anaesthetic interventions, namely, administration of hyperosmotic agents and diuretics, alteration of head position, hyperventilation, and alteration of physiological parameters that affect brain shift, especially until the surgeon gains tumour access.[23]

Anaesthesia for intraoperative magnetic resonance imaging

Similar to neuronavigation, iMRI accurately identifies the lesion, helps in planning, and facilitates resection with accuracy. However, iMRI poses significant anaesthetic challenges. The anaesthesiologist must understand the unique needs of the procedures, which include recognition of the different MRI safety zones, meticulous screening, and exclusion of metallic components that can threaten personnel and patient safety. An MRI setup can either be a regular operating theatre (OT) equipped with a portable magnetic resonance imaging (MRI) scanner/dedicated MRI theatre/MRI scanner located remote to the OT/MRI scanner installed adjacent to the standard OT.[24] A recent advancement includes hybrid OT or interventional MRI for combined neurosurgical and radiological interventions.[25] An updated practice advisory on anaesthetic care for MRI by the American Society of Anesthesiologists has emphasised screening for and eliminating removable metallic devices such as pacemakers, neurostimulators, cochlear implants, aneurysm clips, or vascular stents, etc., that could cause serious injury within a magnetic field. In-depth knowledge about magnetic resonance (MR)–safe, MR-conditional, and MR-unsafe equipment guides the safe use of necessary medical devices at appropriate points of patient care. MRI-compatible anaesthesia machines should be used. All other appliances should be placed outside the 5 Gauss line to avoid radiofrequency interference or artefacts.[26] Direct access to airway and intravenous line sites is limited. Ventilatory and vascular connections should be secured appropriately. Direct patient observation may be compromised by acoustic noise, darkened environment, and obstructed line of sight. Protective hearing equipment should be used during MRI scanning to protect against high-level acoustic noise. It is imperative to avoid flexometallic endotracheal tubes (ETTs) for intubation. The pilot balloon of the ETT should be taped away from the head to mitigate the risk of artefacts. Monitoring cables, wires, and intravenous catheter tubing should not be coiled or placed in direct contact with the patient’s skin to avoid the risk of burn injuries. The use of fibreoptic and wireless technology is preferred to avoid the interaction of electronic monitors with MRI images.

Enhanced recovery after neurosurgery

The recent concept of enhanced recovery after surgery (ERAS) has its applicability demonstrated in neurosurgery in both cranial and spine surgeries.[27] A paradigm shift towards “day care surgery” is upcoming in the neurosurgical speciality. Preoperative patient counselling, minimisation of preoperative fasting duration, pre-emptive analgesia, opioid-free, opioid-sparing, and multi-modal analgesia, minimally invasive access, targeted intraoperative fluid management, early removal of catheters and drains, early postoperative enteral feed resumption, and early ambulation are critical aspects of this concept.[28]

Expanding the scope of non–operating room anaesthesia in the neurosciences

Non–operating room anaesthesia for neurodiagnostic and neuro-interventional procedures is now being extended to procedures like stereotactic biopsies, Gamma Knife, focused ultrasound, stereotactic laser hippocampectomy for medically refractory epilepsy, etc.

Focused ultrasound (FUS) is a newly developed, focused, non-invasive, targeted lesion-based treatment of intracranial abnormalities. This entails target localisation through a series of low-power sonications focussed on the target lesion to increase the target temperature to 40°C-45°C, which is detected by real-time MR thermal imagery. Following target confirmation, final sonications raise the target temperature to 55°C–63°C, creating the desired tumour tissue ablation.[29]

Medically refractory Parkinson’s disease and essential tremors are the two United States Food and Drug Administration (US FDA)-approved indications for FUS. Anaesthetic management for FUS varies across maintaining an awake state for cortical mapping or conscious sedation and general anaesthesia for indicated cases. Airway access is a specific concern in these patients due to the head frame applied to conduct this intervention.[30]

B) NEWER ADVANCEMENTS IN NEUROCRITICAL CARE

Management of stroke patients presenting for mechanical thrombectomy

The current accepted safe therapeutic window of intervention within six hours for mechanical thrombectomy in patients with acute ischaemic stroke due to large vessel occlusion may be extendable even up to 24 hours, based on the findings related to the patient outcome in the DAWN (Diffusion-Weighted Imaging or Computerized Tomography Perfusion Assessment with Clinical Mismatch in the Triage of Wake Up and Late Presenting Strokes Undergoing Neurointervention with Trevo) trial[31] The trial showed similar patient outcomes in the extended therapeutic window of upto 24 hours which has led to prospects of further research in this area.[31]

The SIESTA (Sedation Vs Intubation for Endovascular Stroke TreAtment),[32] GOLIATH (General or Local Anesthesia in Intra Arterial Therapy),[33] and ANSTROKE (Anesthesia During Stroke)[34] trials demonstrated no difference between conscious sedation and GA in patients undergoing thrombectomy for large anterior circulation occlusions. The findings of these trials have redirected focus on modifiable factors such as periprocedural blood pressure management during the management of these patients. These studies have highlighted that periprocedural hypotension with a reduction in MAP by >40% from baseline was an independent predictor for poor neurological outcome.[35]

Management of traumatic brain injury

The clinical practice guidelines for managing patients with traumatic brain injury (TBI) are under periodic/constant upgradation based on the evolving evidence of the effectiveness of each therapeutic intervention. Accordingly, the Brain Trauma Foundation guidelines have proposed vital modifications in the thresholds for intervention and management of said injury. The ICP threshold for instituting corrective manoeuvres has been revised from 20 mmHg to 22 mmHg.[36] A recent Cochrane review provides evidence for the non-inferiority of hypertonic saline (HTS) for reducing elevated ICP. The paediatric TBI guidelines have reiterated the role of HTS for osmotherapy. They recommend administration of 3% HTS as a bolus of 2–5 mL/kg over 10–20 minutes for acute use and a continuous infusion of 3% HTS at doses of 0.1–1.0 mL/kg/h. For refractory ICP, a bolus of 23.4% HTS at 0.5 mL/kg with a maximum of 30 mL has been recommended.[37]

Advanced neuromonitoring

Multimodal monitoring (MMM) encompasses goal-directed management of cerebral and haemo dynamic thresholds individualised for each patient and continuously tailored to suit the physiological perturbations during different phases of brain injury. Concurrent monitoring of the cerebral electrophysiology, haemodynamic status, oxygenation, and metabolism using multiple modalities provides more valuable insight into the true interpretation of the patient’s underlying condition and guides restorative therapies. The inclusion of brain tissue oxygen monitoring, pressure reactivity index and cerebral microdialysis are crucial components of MMM.[38]

The newer technique of telemetric ICP monitoring beyond the approved implantation phase of 90 days allows for patient monitoring during normal daily activities for the evaluation and treatment of complicated ICP disorders.[39] The utility of surface acoustic wave ICP sensors capable of wireless and passive information transmission are being explored in patients with hydrocephalus, hypertension, and TBI.[40]

SUMMARY

Neuroanaesthesia techniques have evolved to meet the challenges of neurosurgery successfully. Methods such as the use of ketamine in neurosurgical patients, which were earlier considered to be harmful, are now being incorporated into perioperative management strategies. More emphasis is now laid on intraoperative neuromonitoring for both brain structures in the form of intraoperative computed tomography and iMRI. Anaesthesia for functional neurosurgery, procedures requiring neuronavigation, and regional anaesthesia for neurosurgery are other areas that are evolving. The role of the neuroanaesthesiologist has expanded outside the operating room in situations like acute stroke management and other neurocritical areas and is expected to grow further in the coming years.

Financial support and sponsorship

There is no financial support or sponsorship involved.

Conflicts of interest

There are no conflicts of interest.