Approach - TIVA. Usually 4 pumps will be used: propofol, remifentanyl or sufentanil, nicardipine, and norepinephrine or phenylephrine. A common combination is propofol started at 0.1-0.2 mg/kg/min and remifentanil 0.5-1.0 mcg/kg/min. Paralytic - Paralytic will be contraindicated in cases of SSEP monitoring. Positioning - ACA, MCA aneurysms: supine with head turned (make sure head is not rotated to the point of occluding jugulars, instead prop up the shoulder to turn the torso). PICA aneurysms: lateral decubitus, sometimes with arm in a sling. BP Parameters - Cerebral autoregulation can be altered, depending on the pathology. If this is the case, cerebral perfusion pressure (CPP) will be directly proportional to mean arterial pressure (MAP). For this reason and considerations of the possibilities of a rupture, these patients have very specific blood pressure parameters. The parameters are set by the surgeon, but very commonly it's to keep mean arterial pressure within 10% of baseline and a MAP between 70 - 90 mmHg. Have a pressor and anti-hypertensive ready. ABG - After an arterial line is placed, draw an ABG and calculate the ETCO2-PaCO2 gradient. Aim for a PaCO2 of 32-35 mmHg. BIS monitor - If the neuromonitoring team is not available, consider using a BIS monitor to assess burst suppression. Aneurysm Rupture & BP Spikes - There are specific times where aneurysm rupture/BP Spikes are especially high risk. These are prior to aneurysm clipping, direct laryngoscopy, surgical pinning, foley placement, and initial incision. Tactfully timed propofol and/or opioid boluses, 2% lidocaine at the pin sites, etc can help to avoid BP surges during the most stimulating parts of the case. Adenosine - If the aneurysm ruptures, adenosine (0.2 - 0.4 mg/kg rapid bolus, followed by a rapid flush to clear the line) will produce a bloodless field for 45 seconds during which a clip can be applied. The patient will briefly go into asystole, so be sure to notify the OR team before pushing. Reduce ICP - Surgeon preference. Methods to reduce of ICP can include mannitol, dexamethasone, head elevation, and/or mild hyperventilation. Avoid patient temperature greater than 37 C. Facilitation of SSEPs - Keep volatile agent at less than 0.5 MAC and use opioid and propofol infusion as part of your maintenance. Maintain blood pressure within 10% of baseline as hypotension may prolong latency and decrease amplitude of evoked potentials. For burst suppression, start with a propofol bolus around 1 mg/kg. Also increase the propofol infusion by 50% then titrate to EEG. Talk to the neuromonitoring personnel in the room to assess the extent of the burst suppression (50% should be enough). You must maintain the MAP during burst suppression. Indocyanine Green (IC) - Surgeons preference. This may be used intraop at the surgeon's request to assess vasculature. If requested, mix the IC green with the 10cc diluent (it foams) and push 2.5-5 mL (bubble free). Immediately flush with fluid until the line is visibly clear.
