Cerebral aneurysm surgery can be performed through a craniotomy or endovascularly (intra-arterial approach). Open aneurysm surgery through a craniotomy involves careful dissection to expose the aneurysm followed by placement of surgical clips to obliterate the aneurysm. Endovascular repair involves coil embolization of the aneurysm with subsequent thrombosis of the aneurysm dome/sac. The anatomy of the aneurysm and cerebral vessels, location (anterior or posterior circulation), durability of the repair/reoccurrence rate, and surgeon’s experience all play into the decision to pursue open vs. endovascular repair.
Hemodynamic Control: Avoidance of hypertension is paramount in these procedures. Pre-induction placement of an arterial line facilitates tight hemodynamic control. Use of laryngotracheal anesthesia with topical lidocaine (i.e. LTA) or remifentanil bolus can blunt the hemodynamic response to endotrachea intubation. Patients having elective surgery for aneurysm repair are, as expected, lower risk for intraoperative rupture than those having emergent surgery in the setting of aneurysmal subarachnoid hemorrhage.
Avoidance of movement: While this seems intuitive, this is the major reason for the use of general anesthesia in endovascular aneurysm surgery. Neuromuscular blockade provides an important safety margin in both endovascular and open repair (especially during microscopic dissection).
Temporary Clipping and Adenosine Arrest: -Temporary clip application may be used by the surgeon to occlude proximal blood flow and decompress/soften the aneurysm to facilitate dissection around the dome of the aneurysm and permanent clip application (for example, clip occlusion of the proximal MCA to allow for permanent clip application to an aneurysm more distal at the MCA bifurcation). -Alternately, temporary circulatory arrest with intravenous adenosine may be used to achieve this same endpoint (decompress/soften the aneurysm to facilitate dissection around the dome of the aneurysm and permanent clip application). Adenosine is dosed to provide approximately 30-45 seconds of severe hypotension. See references for details (Guinn et al.; Bebawy et al.).
Pharmacologic Neuroprotection and Therapeutic Hypothermia: Temporary clip application cuts off blood supply to a region of the brain and induces temporary ischemia. Longer duration of temporary clipping is known to cause permanent neurologic injury in some patients (Hindman et al.). Short clip applications are usually well tolerated. Available evidence (from the IHAST study) suggest no benefit to pharmacologic neuroprotection or hypothermia in patients having temporary clipping of short duration (< 10min; Hindman et al.). There is insufficient data to determine whether either therapy is beneficial in patients having longer temporary clip duration (>10min), or undergoing adenosine arrest. The IHAST trial demonstrated that therapeutic hypothermia was safe in patients undergoing aneurysm surgery (craniotomy) but resulted in no improvement in neurologic outcome (Todd et al.).
Practical Concerns: It can be difficult to predict the duration of temporary clipping. Therefore, many neuroanesthesiologists and vascular neurosurgeons prefer the use of pharmacologic neuroprotection (i.e. propofol burst suppression) prior to temporary clipping or adenosine arrest. Therapeutic hypothermia (32-34 deg C) is typically reserved for cases where long temporary clip ligation will be necessary or for complex cerebrovascular bypass cases. Hyperthermia should be universally avoided during brain surgery.
- Hindman BJ, Bayman EO, Pfisterer WK, Torner JC, Todd MM; IHAST Investigators.No association between intraoperative hypothermia or supplemental protective drug and neurologic outcomes in patients undergoing temporary clipping during cerebral aneurysm surgery: findings from the Intraoperative Hypothermia for Aneurysm Surgery Trial. Anesthesiology. 2010 Jan;112(1):86-101. PMID: 19952722
- Guinn NR, McDonagh DL, Borel CO, Wright DR, Zomorodi AR, Powers CJ, Warner DS, Lam AM, Britz GW. Adenosine-induced transient asystole for intracranial aneurysm surgery: a retrospective review. J Neurosurg Anesthesiol. 2011 Jan;23(1):35-40. PMID: 20706138
- Bebawy JF, Gupta DK, Bendok BR, Hemmer LB, Zeeni C, Avram MJ, Batjer HH, Koht A. Adenosine-induced flow arrest to facilitate intracranial aneurysm clip ligation: dose-response data and safety profile. Anesth Analg. 2010 May 1;110(5):1406-11. PMID: 20418302
- Todd MM, Hindman BJ, Clarke WR, Torner JC; Intraoperative Hypothermia for Aneurysm Surgery Trial (IHAST) Investigators. Mild intraoperative hypothermia during surgery for intracranial aneurysm. N Engl J Med. 2005 Jan 13;352(2):135-45. PMID: 15647576