Cerebral Aneurysm clipping: anes management

Anesthetic goals in this patient population revolve around 1) preventing large changes in blood pressure 2) facilitating surgical exposure [via hyperventilation and osmotic diuresis] 3) ensuring adequate collateral circulation if temporary clips are placed during surgery 4) minimizing deleterious increases in ICP and 5) allowing for rapid wakeup and neurologic examination. As with other patients with CNS injury, remember to avoid hypoventilation (ie use opiates with caution). With regards to the above:

Keep nitroglycerin, esmolol, and short acting vasopressors readily available. Consider short-acting opioids (remifentanil) and/or a skull block. Many of these patients will be on nimodipine, which may make blood pressure control more difficult.

Consider short-lived hyperventilation prior to induction, as well as when requested by surgeons (to assist in relaxation). Keep in mind, however, that excessive hyperventilation can be harmful – hyperventilation is known to lower ICP however CBF drops 3-4% for every 1 mm Hg decrease in PCO₂ (Ref. 1) – this is dangerous as CBF may drop by as much as 50% following TBI (Ref. 2, 3). Hyperventilation is highly controversial (Ref. 4), with the 2007 Cochrane Database Review concluding that there is inadequate data to assess whether benefit or harm exists. (Ref. 5) The Brain Trauma Foundation recommends against chronic hyperventilation. (Ref. 6) – Andrews recommends 35 mm Hg

Large bore IV access should be obtained because of the possibility of intraoperative rupture. If an intraoperative rupture does occur, the anesthesiologist may be required to do any of the following: induce hypotension, induce arrest (with adenosine), or place manual pressure on the ipsilateral carotid. If significant difficulty is anticipated, hypothermic arrest may be planned (arterial and venous access, FAST patches).

Randomized, multicenter (30) trial of 1001 patients with a WFNS score of 1-3 preoperatively following SAH, scheduled for clipping within 14 days of rupture, randomly assigned to target temperature 33C vs 36.5C. There were no significant differences in the duration of ICU stay, total length of hospitalization, rates of death at follow-up, or the destination at discharge. Postoperative bacteremia was more common in the hypothermia group (5 percent vs. 3 percent, P=0.05) (Ref. 7)

23% of these patients will have neurogenic pulmonary edema, and respiratory complications are the second most common cause of death (after neurologic complications)

Anesthesia for Aneurysm Clipping

• Avoid rapid changes in MAP or ICP with induction and surgical stimulation (pinning, burr holes, incision of dura)
• Large bore IV access in case of rupture
• Adequate brain relaxation (brief hyperventilation, mannitol)
• Maintenance of cerebral perfusion pressure / collateral blood flow
• Rapid wake up
• Beware respiratory complications