Anaesthesia awareness - why use a paralytic?

Question

According to a 2004 US study, approximately 1-2 in a thousand patients who undergo general anaesthesia in the US (this amounts to 20,000-40,000 people, out of a total of 20 million who undergo GA each year) will experience "anaesthesia awareness"; becoming conscious during surgery, and in 42% of cases feeling the pain of the procedure.

Because a paralytic is administered routinely as a part of GA, patients who experience anaesthesia awareness are unable to notify the surgeons of their pain, and are essentially tortured (albeit accidentally) during the operation.

My question is this - why is a paralytic so necessary that this risk would be taken for it's sake? The only thing I can think of is to suppress reflex movements that could interfere with the procedure, but it seems that there should be some way to solve this problem without complete paralysis of the peripheral nervous system. Perhaps a spinal nerve block near the cervical vertibrae in addition to the paralytic? You wouldn't be able to move, but you couldn't feel pain below the neck either.

Insight anyone?

Answer 1

Well, that study is considered somewhat flawed due to a bias introduced into the survey. A better study makes it look more like 1 in 200,000 or so. Still, not a nice thing.

Paralytics are commonly used for a lot of things. Depends on the surgery for one. Simple procedures don't tend to do it. Delicate ones, or ones that involve opening the body cavity use it more frequently. One is, as you mention is to suppress reflex movements of the muscles. The last thing you want when reattaching nerves or blood vessels is any kind of twitching on the part of the patient. Another reason is for control - analgesic agents tend to suppress breathing, many anesthetics do as well. Since many of these drugs are administered as gasses, this can be problematic. If you're paralyzed, you can be mechanically ventilated, and then you aren't going to stop breathing due to the pain killers or anesthetics used in the surgery. It also can keep up a more consistent administration of inhaled drugs.

This last bit is quite important. Anesthesia is perhaps the most brutal and unforgiving of any medical specialty. There's a reason these folks pay half a million dollars or more a year in malpractice insurance. They're basically managing your entire body while a surgeon works at you, and that's a very hard thing to do.

As for a spinal block, for one, the more drugs you use the more difficult it is to manage things - and then there's the respiration problem again. Second, higher spinal blocks which are necessary to stop signals from the shoulders on down are -extremely- dangerous - far more so than the surgery itself in some cases. Essentially if we did this more people would die, be paralyzed, or damaged in some way.

Answer 2

At least a short acting paralyzing agent such as succinylcholine is almost always used at the time that anesthesia is first being delivered.  This period of time is termed "induction," while the process of placing the breathing tube into the airway is called "intubation."  This is a time period and a procedure that anesthesiologists take very seriously, and for good reason.  

If complications occur in this phase of the patient's care, they can lead to a loss of control of the airway, and of the effective ability to deliver oxygen to the patient.  Accidents during induction are extremely rare and the delivery of anesthesia is made very safe, and it is in part due to the delivery of the short acting paralytic that makes the patient hold still.

Once the patient is induced, however, there are numerous possibilities.  In many surgical procedures, for example, a neuromuscular blocking agent (paralytic) is not needed at all.  It is sufficient that the patient be appropriately anesthetized.  Any procedure that deals primarily with the skin and soft tissue, would be a good example.  There is no inherent reason to paralyze someone in order to remove a skin cancer.  However, if they do continue to demonstrate muscular activity even after being delivered appropriate amounts of anesthetic agent, a "muscle relaxant" (another PC term for a neuromuscular blockade) might be utilized.

In some situations, these agents are actually to be avoided at all costs.  The reason is that they work by interfering with the conduction of nerve impulses into muscle tissue, and in some operations, one of the first clues that an important nerve is close at hand is the twitching of the associated muscle.  To use a paralytic is therefore to lose that clue and put the nerve at unnecessary risk.  Examples of such operations include the axillary (armpit) dissection associated with cancer surgery for the breast, and thyroidectomy which exposes the recurrent laryngeal nerve leading into the larynx.  

Abdominal surgeries often require the administration of neuromuscular blockade because the patient will make efforts to breathe and/or they will recruit the abdominal muscles in nonspecific contractions that we often refer to as "bucking".  This can make safe exposure of the surgical anatomy difficult or impossible.  In many cases, the use of  neuromuscular blockade is an option that may or may not be utilized during all or some of the operation.  To a degree, it depends on the surgeon's situation and the anesthetist/anesthesiologist's decision making.  

Even if the patient doesn't "buck", the presence of a background level of muscular tone can become irritating when it reduces the working space available.  For example, I do a lot of laparoscopic surgery which involves inflating the abdominal cavity with carbon dioxide gas and then working inside that space using a video scope and long thin instruments.  If the patient "grips", I may not see the characteristic contractions of "bucking" but I'll find my working space suddenly diminished.  For laparoscopic surgery, a neuromuscular blockade is very helpful.

Are their other ways to achieve this same goal without using a systemic chemical?  Sure.  It's very possible to do lower abdominal surgery on an awake patient using spinal anesthesia.  My wife has had two C-sections and I kept her company for both!  Spinal anesthetic is actually quite effective for fixing groin hernias, too.  However, if I were to work in the upper reaches of the abdominal cavity, the utility of this method drops off dramatically.  The reason for this is that it's difficult to get a high spinal level of anesthesia without risking the possibility that the level will creep up TOO high and stop the muscles of breathing.

Invading into the spine isn't to be taken lightly, though.  This is an additional invasive procedure with the potential for complications, and complications *DO* happen.  The capabilities of spinal anesthesia supplement and augment the capabilities of anesthesiologists, but it cannot replace the need for neuromuscular blockade.

Were I to undergo abdominal surgery, I'd want to utilize general anesthesia  and I'd be happy to receive paralytic if needed.

This was a good question.