Lidocaine Before Induction

So before a case today my preceptor asked why we give lidocaine before induction.  I told him it was for patient comfort to blunt the burning senstation caused by propofol.  He told me, "that is absolutely the worst answer I could have picked."  He was beside himself and so was I.  I must have been told this before but have lost it somewhere in the recesses of my mind. I was a little annoyed how he responded but no matter, I was there to learn.  So the "real" answer is, lidocaine is used to blunt the stimulus caused by laryngoscopy.  I guess I always thought fentanyl and paralytics took care of that.  He said reducing the burning sensation from propofol is a "side effect" of using lidocaine, not its intended purpose. The standard dose here is 60 mg of lidocaine IV.

As a side note, apparently UMKC students are notorious (according to one person) for drawing air out of an IV line and then throwing the syringe away with saline still in it.  The preferred method is just pushing the saline back into the IV line.  I know most of us already do that but in case you don't, now you know.

Rapid Shallow Breathing Index

An anesthesiologist recently explained to me the RSBI or Rapid Shallow Breathing Index.  This index is used to predict whether a patient is ready to be extubated.  It is most commonly used in the ICU, but can be used in the operating room as well.  The rapid shallow breathing index is the ratio of respiratory frequency to tidal volumes in liters.

RSBI = (f/VT)

For example, if a patient is breathing 25 breaths/min with a tidal volume of 100mL, there RSBI = (25)/(0.1) = 250 breaths/min/L

So what does this number mean?

An RSBI >100 means they are NOT ready for extubation
An RSBI <100 means they are ready for extubation