Subject: Re: REMIFENTANIL
I tend to do a lot of TIVA (total intravenous anesthesia). Especially with the prone patient in whom we are monitoring Visual Evoked Potentials (as a study of "postoperative blindness", in progress) because the inhalation agents obliterate the visual evokes.
And then in neuroanesthesia, for open craniotomy (vascular and tumor), as well as in neurointerventional, where patients may be awake/asleep/awake/asleep for functional testing during AVM (arteriovenous malformations) embolizations, and during anterior cervical spine cases, where we monitor the recurrent laryngeal nerve motor evoked responses via an endotracheal tube stimulator....(are you glad you're not in some academic center with all this fuss?)...or in any case, where I need a very quick alteration of depth of analgesia without delayed emergence:
REMIFENTANIL is my "drug of choice".
TIVA induction is 2-5 (usually 5) mg midazolam, 250 ug fentanyl, vecuronium 8 mg, and 100 mg lidocaine prior to propofol titrated to a BIS (Bispectral index)/Aspect EEG (electroencephalogram-graph) monitor of 60 or less (when you can use the BIS)...with remifentanil at 0.2 ug/kg/min started immediately on an IV pump and propofol at 50-200 ug/kg/min to maintain a BIS of 65 or less (burst suppression at higher propofol doses titrated to a BIS of 20 or so and an SR (suppression ratio) of 66 or more on the BIS when burst suppression is indicated).
Where perfusion becomes of concern (at when isn't (is it not) of concern ?), altering the infusion of remifentanil rather than the propofol helps to maintain MAP (mean arterial pressure) and the EEG can help assess functional cerebral perfusion (at least in the frontal lobe site of the BIS monitor placement) as well as ETC02 (endtidal carbon dioxide) can assess decreased CO (cardiac output) effects in the pulmonary vasculature or decrease urine output, decrease GFR (glomerular filtration rate).
Depending upon the duration of the case and the propofol infusion "load", I usually stop the propofol 20 minutes prior to emergence and run the finish on remifentanil as needed (up to 0.4 ug/kg/min without delays in emergence). Extubation and emergence can be facilitated with flumazenil (0.5 mg IV) and the endotracheal tube "pulled" upon eye opening and following command ("open your mouth"), regardless of spontanteous ventilation (in the "normal patient") as remifentanil does not seem to have a clinically significant effect on the CO2 response curve following emergence (as does sufentanil or other longer acting opioids/opiates). The now awake patient will breath on command if for some reason the ETCO2 is below respiratory drive threshold or may be assisted for a few minutes, until spontaneous, regular respiration is demonstrated..
Emergence is rapid and allows for a functional assessment in the OR (operating room) prior to PACU (post anesthesia care unit or recovery room). The 20 minute emergence time after DC (discontinuing) propofol allows for assessment of hemodynamic responses and the control of BP (blood pressure), usually with bolus nicardipine (0.5 to 1 mg and/or infusion at 5 mg/hr) prn (per registered nurse), or labetalol or esmolol qs (quantity sufficient) to achieve target post operative BP levels.
Of course, whenever I don't need TIVA, I use remifentanil infusion with low dose sevoflurane (0.5 - 1 %) which works very well (in my hands <G>) at 3 l/min flows.
For longer spine instrumentation cases, sufentanil ( 1 mg/kg/hr) replaces remifentanil.
In the past, I have used dexmedetomidine, in combination with all of the above, as an intraoperative infusion. It works especially well in craniotomies, as emergence is not only rapid, but the postoperative analgesia "window" is approximately 20 minutes.
Once functional assessment is performed in the OR, the rapidly diminishing analgesia can be restored with your anlgesic of choice.