MONITORING THE LEVEL OF PARALYSIS DURING SURGERY: DO YOU NEED A PERIPHERAL NERVE STIMULATOR?

Clinical Case for Discussion:  One week before you graduate from anesthesia residency, you lose the peripheral nerve stimulator you use to monitor neuromuscular blockade.  Should you bother to purchase another one?

Discussion: Fast forward to your first day in post-residency private practice.  Your first case is a colectomy on an obese, 5 foot 2 inch, 100-kilogram male with adenocarcinoma of the sigmoid colon.  You bring the patient into the operating room, anesthetize him with propofol, and inject 10 mg of vecuronium into his IV.  You wait 90 seconds before intubating the trachea.  The surgeon enters the room.  After the Timeout, the patient is placed in lithotomy position.  The surgeon performs a rectal exam and sigmoidoscopy under anesthesia.

“We’ve got a problem,” the surgeon announces.  “The tumor has grown since my last exam, and it’s too close to the anus to treat with simple colectomy.  He needs a total proctocolectomy, and I didn’t give him informed consent for that.  We need to wake him up and come back another day.”  He shrugs his shoulders, and walks out of the room.  (Seem like an far-fetched scenario?  It’s not–this exact incident happened to me at Stanford about 8 years ago.)

You are stunned.  “Come back another day?”   The circulating nurse shakes her head.  She and the scrub tech are looking at you–waiting for you to wake up the patient.  It’s only been twelve minutes since you injected the muscle relaxant, and you have no nerve stimulator.  Being a resourceful Stanford graduate, you call another anesthesia attending and ask to borrow her nerve stimulator.  When the nerve stimulator is delivered to you, you discover no twitches at either the patient’s facial nerve or ulnar nerve.

The nurse asks, “Is there a problem?”

You answer, “Not really, but I can’t wake up the patient until the muscle relaxant wears off further.” You decide to wait until one twitch returns before you administer neostigmine/glycopyrrolate reversal.  You sit down, the nurse sits down, and the scrub tech scrubs out.  The operating room seems absurdly quiet for thirty minutes while you wait to reverse the muscle relaxant.  Forty minutes later, you extubate the trachea and take the patient to the Post Anesthesia Care Unit.

After you finish your Stanford residency, you need to be prepared for faster surgeons and shorter operative times.  Overdosing patients with muscle relaxants is a common mistake when newly-trained anesthesiologists leave residency.  The operative time for a laparoscopic appendectomy may be as little as fifteen minutes.  A pediatric tonsillectomy may last only twelve minutes.  An anterior cruciate ligament repair may last only 45 minutes.

In private practice, you will probably use modest doses of vecuronium or rocuronium when paralysis is necessary.  If the surgeon finishes earlier than expected, you always want to be able to reverse muscle relaxation and awaken the patient without delay. Whenever appropriate, you will prefer to use an LMA instead of an endotracheal tube, partly because the LMA insertion does not require a muscle relaxant, and partly because it’s easier for the patient to breath spontaneously with an LMA.

How about the need for a nerve stimulator to monitor neuromuscular blockade?  I polled the thirty-three private anesthesiology attendings at Stanford via email, regarding their practices using nerve stimulators and muscle relaxants.  I learned the following:  Most practitioners do not administer additional muscle relaxant following intubation unless surgical conditions demand it. Most practitioners do not reverse muscle relaxants if no dose was given in the last hour of a case.

Almost every private attending still owns a nerve stimulator.  Half of the attendings use a nerve stimulator routinely whenever they administer muscle relaxants, but half the attendings use the device occasionally or rarely, relying on clinical criteria and judgment alone in regards to the level of neuromuscular blockade. Is this practice wise, or not?

The American Society of Anesthesiologists Standards for Basic Anesthesia Monitoring, posted on www.asahq.org, does not list the use of a peripheral nerve stimulator as a standard.

However, in Miller’s Anesthesia, 2008 Edition, Chapter 47 on Neuromuscular Monitoring, author Jørgen Viby-Mogensen makes the following statements:

  • “Many anesthesiologists do not agree with extensive use of nerve stimulators and argue that they manage quite well without these devices. However, the question is not how little an experienced anesthetist can manage with but rather how to ensure that all patients receive optimal treatment.”
  • “It is difficult and often impossible to exclude with certainty clinically significant residual curarization by clinical evaluation of recovery of neuromuscular function.”

The author further states that the following clinical tests of postoperative neuromuscular recovery are NOT reliable:

  • Sustained eye opening
  • Protrusion of the tongue
  • Arm lift to the opposite shoulder
  • Normal tidal volume
  • Normal or nearly normal vital capacity
  • Maximum inspiratory pressure less than 40 to 50 cm H2O

The author states that the following clinical tests of postoperative neuromuscular recovery ARE reliable:

  • Sustained head lift for 5 seconds
  • Sustained leg lift for 5 seconds
  • Sustained handgrip for 5 seconds
  • Maximum inspiratory pressure 40 to 50 cm H2O or greater

The author concludes that  “Adequate recovery of postoperative neuromuscular function cannot be guaranteed without objective neuromuscular monitoring.”

In private practice in Palo Alto, most of us use a MiniStim unit Model MS-1B Miniature Nerve Stimulator (Life-Tech, Houston, Texas), a simple device with one red button for Tetanus, and one green button for Twitch.  The MiniStim assessment of tetanus or twitch response is done by visual and tactile evaluation of muscle movement, with no quantitation of blockade.

Is there any good reason to avoid using a nerve stimulator?  The benefit/risk ratio of using the device approaches infinity.  If you ever lose it, you can purchase another one on the Internet for a mere $155.  I’ve had my current unit for ten years, during which I’ve administered 7000 anesthetics.  The cost of the MiniStim so far works out to be about 2 cents per case.

During residency or during the years afterward, a MiniStim and a stethoscope are arguably the only tools of your own you need to carry into an operating room to conduct a 21st-century general anesthetic.

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