Aneurysm surgery ranks among the most technically demanding operations in neurovascular and vascular surgery. In these procedures, there is one factor that is just as — and sometimes even more — decisive than the surgeon’s skill: anaesthetic management. Regardless of the type of aneurysm involved, in an environment where the vessel wall is so delicate and carries the potential to rupture at any moment, the anaesthetist’s role extends far beyond simply putting the patient to sleep. Controlling blood pressure minute by minute, ensuring cerebral protection, maintaining the blood in a state that is neither prone to clotting nor to excessive bleeding, and bringing the patient safely off the operating table — all of this rests on the shoulders of the anaesthesia team.

Why Is Anaesthesia So Critical in Aneurysm Surgery?

In a routine surgical procedure, the primary goals of anaesthesia are to eliminate pain, suppress consciousness, and keep the patient motionless. In aneurysm surgery, however, in addition to these three objectives, an extraordinarily delicate set of physiological balances must be maintained throughout.

Consider a cerebral aneurysm. This already structurally weakened balloon can rupture at any sudden rise in blood pressure — during intubation, in response to surgical stimulation, or during emergence from anaesthesia. On the other hand, excessively lowering the blood pressure can cause the brain tissue itself to undergo ischaemia. For this reason, the anaesthetist is constantly attempting to walk along an ever-shifting balance throughout the entire operation.

Preoperative Assessment: Preparation Before Surgery

In every aneurysm surgery case, the anaesthetic plan begins with a comprehensive patient-specific assessment.

Neurological Status: Particularly in cases of ruptured aneurysm, the patient’s neurological condition is scored using standardised systems such as the Hunt-Hess classification or the World Federation of Neurosurgical Societies (WFNS) scale. This score directly influences the anaesthetic risk and the requirement for intensive care.

Cardiac and Pulmonary Assessment: In patients who have suffered a subarachnoid haemorrhage (SAH), neurogenically mediated cardiac arrhythmias, myocardial injury, and pulmonary oedema may be present. ECG, echocardiography, and chest radiograph are therefore routinely evaluated.

Electrolyte and Volume Status: Hyponatraemia (low sodium), hypovolaemia, and cerebral salt wasting syndrome are commonly encountered following SAH. Correcting these imbalances before anaesthesia is of critical importance.

Medication History: In patients taking anticoagulants or antiplatelet agents, coagulation tests are assessed and reversal agents planned where necessary.

Anaesthetic Induction: The Most Critical Phase

In aneurysm surgery, induction — the process of bringing the patient under anaesthesia — is one of the most hazardous stages of the entire procedure. The laryngoscopic stimulus during intubation activates the sympathetic nervous system and provokes a sudden rise in blood pressure. For an aneurysm with an already weakened vessel wall, this surge can be catastrophic.

For this reason, the induction protocol is carefully prepared:

Controlled Induction: A combination of rapidly acting opioids (fentanyl, remifentanil), intravenous anaesthetics such as propofol or thiopental, and lidocaine is used to blunt the haemodynamic response to intubation.

Beta-blocker or Vasodilator Premedication: Agents such as labetalol, esmolol, or nicardipine are administered before intubation in an attempt to prevent blood pressure elevation.

Rapid and Precise Intubation: Laryngoscopy is completed in the shortest possible time by experienced anaesthetists. Video laryngoscopy assists by improving visualisation and reducing intubation time.

Maintenance of Anaesthesia: The Balance Sustained Throughout the Operation

Once the operation has begun, the anaesthetist’s task is to maintain continuously changing physiological parameters within a narrow window of safety.

Total Intravenous Anaesthesia (TIVA): This approach, increasingly favoured in aneurysm surgery today, employs infusions of propofol and remifentanil. Compared to inhalational agents, it suppresses cerebral metabolism more effectively, provides better control of intracranial pressure, and facilitates compatibility with neurophysiological monitoring.

Inhalational Anaesthesia: Agents such as isoflurane, sevoflurane, and desflurane may also be used; however, it must be borne in mind that at high concentrations they can cause cerebral vasodilation and elevate intracranial pressure, necessitating careful titration.

Neuromuscular Blocking Agents: Patient immobility is maintained throughout the operation; however, where neurophysiological monitoring (such as motor evoked potentials) is being performed, the depth of neuromuscular blockade must be meticulously adjusted.

Blood Pressure Management: A Fine Balance

Blood pressure management in aneurysm surgery constitutes perhaps the most critical dimension of anaesthetic care.

In Unruptured Aneurysms: The general principle is to avoid hypertension. Until the moment the clip is applied, mean arterial pressure (MAP) is maintained at normotensive or mildly hypotensive levels — though never at a level that would compromise cerebral perfusion.

During Temporary Occlusion: When a temporary clip is placed on a vessel near the aneurysm neck during surgery, MAP is gently elevated to support collateral perfusion and enhance cerebral protection.

In Ruptured Aneurysms (Post-SAH): The situation is considerably more complex. On one side lies the risk of rebleeding from the ruptured aneurysm (avoid hypertension); on the other, the risk of cerebral vasospasm and ischaemia developing after SAH (avoid hypotension). The delicate balance between these two risks must be meticulously managed.

Cerebral Protection: Neuroprotection Strategies

In aneurysm surgery, the brain is the direct target of both the anaesthetic and the surgical manoeuvres. Neuroprotection strategies are therefore of paramount importance.

Hyperventilation: Controlled mild hypocarbia (low CO₂) induces cerebral vasoconstriction, reducing brain volume and improving surgical access. However, if taken too far it can cause ischaemia; careful titration is mandatory.

Mannitol: This osmotic diuretic is used to reduce cerebral oedema, protect the blood-brain barrier, and improve the operative field of view.

Barbiturate Coma or Burst Suppression with Propofol: During high-ischaemia-risk periods such as temporary occlusion, burst suppression on EEG is induced to reduce the cerebral metabolic rate and decrease the brain’s oxygen consumption.

Hypothermia: Mild to moderate hypothermia (33-35°C) may be employed for cerebral protection in complex cases requiring prolonged temporary occlusion. Deep hypothermic circulatory arrest is applied in specific indications such as giant aortic aneurysms; in this technique, body temperature is lowered to 18°C and the entire circulation is temporarily halted with cardiopulmonary bypass support.

Corticosteroids: Used in some centres to reduce cerebral oedema, though the level of evidence in routine practice remains a matter of debate.

Neurophysiological Monitoring

In modern aneurysm surgery, anaesthesia monitors not only physiological parameters but also brain function in real time.

EEG (Electroencephalography): Continuously monitors cerebral activity; reflects the depth of burst suppression and detects potential ischaemic changes.

Somatosensory Evoked Potentials (SSEP): Assess the integrity of sensory pathways; used as an early warning signal of ischaemia particularly during temporary occlusion.

Motor Evoked Potentials (MEP): Monitor the function of motor pathways; require neuromuscular blockade to be kept to a minimum.

Transcranial Doppler (TCD): Measures cerebral blood flow velocity; valuable for early detection of vasospasm development.

Anaesthesia in Endovascular Aneurysm Treatment

Endovascular procedures such as coiling and flow diverter stent placement may require a different anaesthetic approach compared to classical open surgery.

General Anaesthesia: Ensures complete patient immobility and allows rapid intervention in the event of complications. It is preferred for prolonged procedures and in patients from whom cooperation cannot be obtained.

Sedation with Local Anaesthesia (MAC): Applicable in selected patients at experienced centres, this approach avoids the potential complications of general anaesthesia and permits neurological assessment. Because the patient is awake, neurological evaluation can be performed during the procedure.

Anticoagulation Management: Heparin is administered during endovascular procedures to prevent clot formation within the catheter; dosing is guided by ACT (activated clotting time) monitoring.

Contrast Agent and Renal Protection: Because the contrast medium used for intraoperative angiography can be nephrotoxic, renal function is closely monitored and adequate hydration is maintained.

The Postoperative Period: The Battle Continues in the Intensive Care Unit

The success of aneurysm surgery is not confined to the operating theatre; the postoperative period is every bit as critical as the operation itself.

Timing of Extubation: The patient should be extubated neither too early nor too late. In premature extubation, coughing and straining can raise blood pressure to dangerous levels; in delayed extubation, the risks of prolonged mechanical ventilation come into play. The ideal is to extubate the patient at the moment when neurological status can be fully assessed, the patient is cooperative, and respiratory parameters are adequate.

Vasospasm Management: Cerebral vasospasm — one of the most feared complications following SAH — typically peaks between days 4 and 14. Nimodipine (a calcium channel blocker) is administered prophylactically to all SAH patients. Triple-H therapy — comprising hypervolaemia, hypertension, and haemodilution — is applied during the vasospasm period to support cerebral perfusion.

Pain Management: Postoperative pain control is achieved through a balanced combination of opioid and non-opioid analgesics; doses are meticulously adjusted with careful attention to the risks of respiratory depression and sedation.

Hyperglycaemia Control: Elevated blood glucose worsens cerebral ischaemia; glucose levels are therefore kept under close surveillance throughout the perioperative period.

The Challenges of Anaesthesia in Emergency Aneurysm Surgery

In cases of ruptured aneurysm, anaesthesia presents a far more demanding picture than in elective operations:

• The patient most often presents with impaired consciousness, haemodynamic instability, and a risk of aspiration of gastric contents, requiring rapid sequence intubation.
• Intracranial pressure (ICP) may already be elevated; no manoeuvre should be allowed to elevate it further.
• Hyponatraemia, hypovolaemia, and cardiac complications must be managed simultaneously.
• Time for preoperative assessment is extremely limited; decisions must be made swiftly and correctly.

Conclusion: The Invisible Hero

The success of aneurysm surgery is shaped by the surgeon’s hands, the anaesthetist’s mind, and the continuity provided by the intensive care team. The anaesthetist serves as an invisible yet indispensable figure beneath the lights of the operating theatre. By monitoring every breath, every fluctuation in blood pressure, and every brain wave, the anaesthetist preserves the physiological safety framework within which the operation takes place.

For every patient and family confronting aneurysm surgery, knowing how comprehensive a teamwork this process demands is both reassuring and a powerful reminder of just how precious the advances made in this field truly are.

Prof. Dr. Mehmet Şenoğlu Neurosurgeon, İzmir

Note: This article is intended for informational purposes only. Please consult a qualified physician for diagnosis and treatment.