Hi,
Let me share my experience with hypotensive anesthesia.
Our place (and by that I mean the whole of India) does not routinely follow protocols for keeping low blood pressure during anesthesia except for certain situations like spine surgeries . And even during such times the blood pressure is almost never brought down to the level which would classify as Hypotensive Anesthesia.
I started with this technique not for reduction of blood loss during surgery (which is never significant under normal circumstances for planned surgeries) but for evaluating the difference it would make on clearity of the surgical field. This I found to have a significant effect on the reduction of surgical time. The most dramatic effect was on laparoscopic surgeries, where even small amount of blood seems to block /disturbs the visibility. Sometimes during laparoscopic cholecystectomy done under normotensive anesthesia I found that the liver bed used to have blood oozing which required cautrization and under rare conditions this took a significant amount of surgical time. Not just that , but this seemed to make the operating surgeon take extra-measures during successive surgeries to prevent such oozing leading to equally more delay during surgery. After starting hypotensive anesthesia I found this problem was almost completely resolved and even the port site bleeds became exceedingly uncommon.
Now coming to the management part of the induced hypotension during anesthesia . Currently I am regularly keeping the mean blood pressure at around 60 mmHg. I know that there is still scope for further reduction of 10 mmHg but I guess for the type of surgeries done under my settings it would not translate into much benefit.
Since I am using TIVA with Propofol , the infusion itself takes care of some part of the hypotension by peripheral vasodilatation. For further reduction of blood pressure, a 10microgram infusion of nitroglycerine titrated upwards suffices. I do make sure that there is no tachycardia as the cardiac oxygen demand needs to be kept low. ( Keeping in view the fixed oxygen supply as a result of low mean blood pressure combined with disturbed autoregulation in the coronary vessels due to nitroglycerine infusion).
It is said that there are two ways the blood pressure can be reduced- by drugs reducing Preload as a result of venous pooling in capacitance vessels or by reducing afterload as a result of vasodilatation of resistance vessels. Nitroglycerine acts by both of these
But predominantly by the former. This is not a preferred method of inducing hypotension as it causes a reduction in cardiac output. This could be theoretically detrimental to tissue perfusion especially in neurosurgery or cardiac surgeries. As you may have guessed therefore the preferred method of induced hypotension in vasodilation of resistance vessels by either any halogenated vapor except for halothane or by drugs like propofol ,labitalol or nitropruside etc. That being said, I could not find any evidence from literature that nitroglycerine infusion has caused any problem during hypotensive anesthesia . I shall soon be migrating over to using nitropruside infusion . As far as Labitalol is concerned I don't think using it is a good idea as it's effect can't be terminated quickly at the end of surgery. The only concern which I have in mind about using nitropruside is the rebound hypertension said to be caused by it. I will have to see it for my self before I can really comment about it.
In case you have any suggestions for me ,please advise.
