What are the recent developments in neuroanaesthesia?

Recent Developments in Neuroanaesthesia

The most significant recent advances in neuroanaesthesia center on mandatory quantitative neuromuscular monitoring, refined protocols for safe transfer of brain-injured patients, and the integration of processed EEG monitoring for sedation management during neurological procedures.

Neuromuscular Blockade Management

The most critical advancement is the strong recommendation for routine quantitative neuromuscular monitoring throughout all anaesthesia cases, particularly in neuroanaesthesia where rapid, high-quality neurological assessment is essential 1.

• Quantitative adductor pollicis monitoring is now the standard for diagnosing residual neuromuscular blockade, with a train-of-four ratio (T4/T1) of at least 0.9 required to eliminate residual blockade 2.
• No clinical test is sensitive enough to detect residual neuromuscular blockade; only quantitative instrumental monitoring can reliably assess recovery 2.
• Residual neuromuscular blockade is associated with higher morbidity and mortality within the first 24 hours postoperatively, increased risk of critical respiratory events, postoperative pneumonia, and delayed discharge 2, 3.
• Pharmacological reversal following muscle relaxant use is strongly recommended to prevent these complications 2.

Reversal Agent Protocols

• After administering non-depolarizing muscle relaxants, wait for spontaneous reversal with four detectable muscle responses at the adductor pollicis following train-of-four stimulation before administering neostigmine 2.
• Administering neostigmine before adequate spontaneous recovery (four train-of-four responses) results in longer time to achieve full reversal and is ineffective 2.
• Sugammadex has emerged as a selective reversal agent for steroidal muscle relaxants, offering advantages in timing and efficacy 1.

Brain-Injured Patient Transfer Protocols

Comprehensive 2019 guidelines from the Association of Anaesthetists and the Neuro Anaesthesia and Critical Care Society have standardized transfer practices 1.

Physiological Targets During Transfer

Specific blood pressure targets vary by injury type 1:

• Traumatic brain injury: Systolic BP >110 mmHg (and MAP >90 mmHg); <150 mmHg if within 6 hours of onset and immediate surgery not planned 1.
• Intracerebral haematoma/haemorrhagic stroke: Systolic BP >140 mmHg 1.
• Acute ischaemic stroke: Systolic BP >110 mmHg; <185 mmHg if candidate for/received IV thrombolysis, or <220 mmHg if thrombolysis contraindicated and being transferred for thrombectomy 1.
• Spontaneous subarachnoid haemorrhage: Systolic BP <160 mmHg 1.

Ventilation Parameters

• Target PaCO2 of 4.5-5.0 kPa across all brain injury types 1.
• If impending uncal herniation with raised ICP, brief hyperventilation to PaCO2 4.0-4.5 kPa is justified, combined with mannitol (0.5 g/kg) or hypertonic saline (2 ml/kg of 3% saline) 1.
• Target PaO2 ≥13 kPa for traumatic brain injury, intracerebral haematoma, and subarachnoid haemorrhage; for acute ischaemic stroke, aim for peripheral oxygen saturation ≥95% only, avoiding hyperoxia 1.
• Minimum 5 cmH2O PEEP to prevent atelectasis; PEEP up to 10 cmH2O does not adversely affect cerebral perfusion 1.

Intubation Indications

Specific criteria now mandate tracheal intubation before transfer 1:

• GCS ≤8 1
• Significantly deteriorating conscious level (fall in GCS of two points or more, or fall in motor score of one point or more) 1
• Loss of protective laryngeal reflexes 1
• Failure to achieve PaO2 ≥13 kPa (though lower target acceptable in acute ischaemic stroke with saturation ≥95%) 1
• Hypercarbia (PaCO2 >6 kPa) or spontaneous hyperventilation (PaCO2 <4.0 kPa) 1
• Bilateral fractured mandible, copious bleeding into mouth, or seizures 1

Induction Protocol for Brain-Injured Patients

A standardized rapid sequence induction technique is recommended 1:

• High-dose fentanyl (3-5 µg/kg), alfentanil (10-20 µg/kg), or target-controlled infusion of remifentanil (Cpt ≥3 ng/ml); use lower doses in unstable patients 1.
• Induction agent dose chosen to maintain adequate MAP; ketamine 1-2 mg/kg may be useful in haemodynamically unstable patients 1.
• Neuromuscular blockade with suxamethonium 1.5 mg/kg or rocuronium 1 mg/kg 1.
• Neuromuscular monitoring should be attached before induction to confirm blockade before intubation 1.

Advanced Monitoring Technologies

Processed EEG Monitoring

• Portable, battery-powered processed EEG (pEEG) devices are now recommended for safe transfer of sedated patients who have received neuromuscular blocking agents 1.
• Processed EEG monitors are useful for titration of sedation to effect during maintenance of anaesthesia 1.
• This technology allows objective assessment of sedation depth when clinical examination is impossible due to neuromuscular blockade 1.

Continuous Monitoring Requirements

During transfer, continuous monitoring must include 1:

• GCS, pupillary size and reaction to light
• ECG and pulse oximetry
• Invasive arterial blood pressure (preferable, though urgent transfer should not be delayed for arterial line insertion; NIBP acceptable alternative in acute ischaemic stroke)
• Capnography and urine output via urinary catheter

Sedation and Anaesthetic Management

Target-Controlled Infusion (TCI)

• TCI regimes are now preferred for maintenance of sedation during transfer when available, as they facilitate stable sedation 1.
• If an agent other than propofol was used for induction, care must be taken when subsequently instituting TCI to avoid precipitating hypotension 1.

Positioning

• Patients should be positioned with 20-30° head-up tilt during transfer 1.
• Ambulance trolleys that allow this degree of tilt while maintaining spinal immobilisation are encouraged 1.

Stroke-Specific Advances

Mechanical Thrombectomy Era

• Mechanical thrombectomy is now recommended in addition to IV thrombolysis for patients with demonstrable proximal artery occlusions in the anterior circulation who can be treated within 24 hours of symptom onset 1.
• If IV thrombolysis is contraindicated, mechanical thrombectomy is recommended as first-line treatment 1.
• This has created urgent need for rapid transfer protocols to specialist neuroscience centres 1.

Time-Critical Treatment Windows

• Standard treatment for acute ischaemic stroke in patients presenting within 4.5 hours is IV thrombolysis using tissue plasminogen activator 1.
• The 4-hour target from injury to surgery for expanding haematomas remains the commonly accepted standard, though not evidence-based; networks should work towards auto-acceptance criteria for brain-injured patients 1.

Enhanced Recovery Protocols

Multimodal approaches now emphasize rapid neurological assessment 3:

• Extensive phase-specific perioperative interventions to prevent early postoperative complications and minimize opioid exposure 3
• Protocolized short-acting anaesthetics to reduce time to extubation 3
• Nonopioid medications and regional techniques as part of multimodal analgesia to reduce perioperative opioid use 3

Neuroanesthesia-Specific Drug Considerations

Propofol in Neurosurgery

• Propofol administered by infusion or slow bolus with hypocarbia decreases intracranial pressure independent of arterial pressure changes 4.
• In controlled trials, propofol reduced cerebrospinal fluid pressure by 46% ± 14% while mean arterial pressure changed only -4% ± 17% 4.
• In head trauma patients, propofol infusion with hyperventilation controlled intracranial pressure while maintaining cerebral perfusion pressure 4.

Ketamine Rehabilitation

• Ketamine is now recommended for perioperative pain management in surgery with high risk of acute or chronic postoperative pain, with maximum dose of 0.5 mg/kg/h after induction 3.
• Continuous infusion at 0.125-0.25 mg/kg/h should be stopped 30 minutes before end of surgery to avoid postoperative hallucinations 3.
• Ketamine 1-2 mg/kg is useful in haemodynamically unstable brain-injured patients during induction 1.

Common Pitfalls to Avoid

• Failure to monitor neuromuscular function quantitatively leads to undetected residual blockade 2.
• Administering neostigmine too early (before four train-of-four responses visible) results in ineffective reversal 2.
• Relying on clinical tests alone to assess recovery from neuromuscular blockade is inadequate 2.
• Transferring actively bleeding, hypotensive patients without stabilization compromises outcomes 5.
• Not reducing propofol infusion rates after extended periods results in excessively high blood concentrations 4.
• Delaying fluid resuscitation while waiting for blood products in trauma patients worsens outcomes 5.