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Bridalveil Falls, Yosemite - photo by JoAnn Sturman
The following describes a technique for MAC anesthesia , which I have found to be successful:
In preop patients are informed they will not be receiving a complete general anesthetic. Instead they will be made very drowsy and not recall the injection of local anesthetic, then as the case proceeds may drift in and out of consciousness, perhaps hearing the odd snatch of music or conversation. I emphasize during the case I do not want them lying on the operating room table with their eyes closed wishing they were drowsier, while I think that they are comfortably asleep. Don’t be brave–communicate!
Once the operating room monitors are connected, patients receive midazolam 2mg and alfentanyl 500 ug. Bolus a further 2mg of midazolam given in 1mg increments during prepping draping. While the surgeon is gowning the patient is given 2L N2O/lL O2 by mask and a propofol bolus of either 30 mg (females) or 40 mg (males). These medications and a 2-3 minute exposure to N2O render the patient amnestic and non moving during the injection phase.
Obviously, this is a cookbook recipe and all ovens are different. Young, robust males may receive more or wiggle a bit, while frail, elderly females may only need the initial midazolam/alfentanyl bolus, but everyone receives nitrous oxide. The additional 2mg of midazolam and the 30-40 mg propofol bolus are titrated according to patient condition but almost always given prior to injection.
Since I don’t like to waste drugs, unless the case is very brief, I will administer the remaining 500ug from the alfentanyl vial as two 250 ug boluses as the case proceeds. During longer cases the patient may begin to arouse and request more sedation. Depending on the stage of the case, this can be achieved with a further 2mg of midazolam plus or minus intermittent 30-40 mg boluses of propofol. Once again, titrate the patient.
Because podiatrists prefer to inject before the prep and are usually hovering in the room with syringe in hand, the induction process is accelerated. While the patient is moving from the gurney, the initial midazolam/alfentanyl bolus is administered. Midazolam 2 mg usually is given in 1mg increments as the monitors are being hooked up, immediately followed by the nitrous by mask, and a 30-40 mg propofol bolus. The time from entering the room to injection is reduced to about five minutes.
This technique is usually satisfactory for both the patient and the surgeon. With the initial “mini general,” the patient is oblivious to the injection and if properly titrated, usually amnestic of the remainder of the procedure. For the surgeon, the patient is usually still for the injection, which can also be preformed very shortly after entering the room.
Bridalveil Falls, Yosemite - photo by JoAnn Sturman
