Block Evaluation 2

DON’T MUDDY THE WATER

     So, here you are in the PACU with a patient that just had a big surgery. The nurse called you here because the patient is hurting (“and I’m not sure your block is working, Doctor”). The patient is ‘mostly’ alert and says that they are hurting “over there”, pointing vaguely toward the general vicinity of the surgery. They’ve been given some IV opioid in the PACU before you arrived. So, Doctor, did your block work?

     This can be a very frustrating and taxing moment. It is not an uncommon scenario, especially when new nerve blocks have been added to a program prior to adequate inservicing and education of the anesthetists in the O.R. and of the RN’s in the PACU. I’ll skip to the chase scene: You should not be in the PACU right now. There is likely more than enough information available to the anesthetist and the PACU RN to have determined the circumstances and initiated the proper plan of action (or inaction).  I will not try to bite all of that off in today’s lesson.

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There are a variety of points along the way where a nerve block can be evaluated and different clues available to lead you in the correct direction. I will discuss one of these points today and indicate why you do not want to ‘muddy the water’ at the start of the case. There are reasons why, prior to induction, a nerve block may not appear to be fully set-up yet: the patient can still move the body part, they deny numbness for several reasons, they are a patient that precludes you from being able to adequately assess the block, or it really is a ‘slow to set-up’ kind of nerve block.

     At the point (or points) of incision, you have an opportunity to see clearly what is happening without subjective bias from the patient by watching the heart rate. Assuming this is a nerve block that should cover the entire surgical area, the heart rate should not move up more than a point or two if there is an adequately dense nerve block in place. Why would it change? The sympathetic nervous system should not have been activated at all. I pay much more attention to the heart rate than the blood pressure as the blood pressure can be affected more by other unrelated factors. The same holds true for the respiratory rate for a spontaneously breathing patient. If the heart rate is unchanged, you are good to go! Keep in mind, there may be more than one nerve block to assess or two (or more) distinct sensory nerve distributions to consider. That is why I said ‘points’ of incision, but more on that later!

     Here’s the point of today’s lesson. You know what commonly happens after induction and prior to incision. The pressure drifts down, and the heart rate may slow (which can also happen with a sedated patient, but it is not usually as dramatic). Of course, we want to bump it back up while we await the ‘typical’ surgical stimulation. Here is the ‘muddying of the water’ point. I’m not saying to allow a sagging pressure that lasts too long or is too low, but a sharp increase in heart rate at the moment of incision will likely make the evaluation of the block more cumbersome and complex afterward. “What was their response to surgery?” This is the first thing I ask about or look at on the anesthesia record when I am in the PACU. I have seen students (as my anesthetists are very well aware now) that, just before the moment of incision, give some ephedrine or glycopyrrolate or phenylephrine, and ‘muddy the water’ about the patient’s physiologic response to surgery.  There are several more clues to determine the circumstances, but I will need to look further into the matter. Looking at ‘railroad tracks’ during the incision and throughout surgery makes my evaluation much more simple.

     Other things to note involve the use of a tourniquet. Often, the tourniquet goes up right about the time of incision and can cause a false positive response if it is above the level of the nerve block. It is not as dramatic as a completely failed block, but that is usually not what we are trying to evaluate. This effect, plus a little recently given ephedrine, can make the evaluation of a ‘partially’ working nerve block difficult. Lots more anesthesia record clues exist, but that will be the topic of another Tip of the Week!

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