What could be more frightening that being awake but paralysed and unable to breathe? No, I’m not talking about “Awake”, the scientifically inaccurate recent movie that dramatizes the rare but distressing experience of being awake in the middle of surgery. Rather, I am referring to the equally upsetting events that sometimes occur during recovery from general anesthesia.
Here is a vivid description, sent to a forum on the excellent consumer health site NetWellness, where I field questions about anesthesia:
“I have just had my ovaries and tubes removed because of my family history. When I woke in the recovery room, I had the most terrible experience of my life. My eyes were open, but I could not move or breath. No air would go in or out, I could not raise my arms in distress or do anything to raise the alarm that I could not breath, only stare into the eyes of the nurse. I thought, any minute now I am going to die, It was so distressing, I have been having flash backs ever since.”
Muscle relaxants were one of the great advances in anesthesia. Introduced in the 1940s and based initially on curare, the Amazonian hunting poison, these drugs have become essential tools in modern anesthesia and critical care. Like all useful medicines however they are not without their drawbacks. You would not have wanted to be among the first patients who got curare, as the appropriate doses were being worked out! But now that doses are well established, and “antagonist” drugs like neostigmine can be given to hasten the return of muscle function, why do some patients have the experiences described above?
Anesthesiologists may fail to appreciate that many patients who appear to have full return of muscle function are in fact really weak for quite some time during recovery from general anesthesia.
In standard clinical practice, the effects of muscle relaxants may be monitored “clinically” (by observation) or through the use of neuromuscular blockade monitors. Clinical signs that a patient has recovered muscle function include the return of grip strength, ability to lift the head off the pillow, and to take a strong, deep breath.
The monitors provide additional evidence. Though relatively inexpensive, easy to use, and advocated by professional opinion leaders, they are not always applied. And even when they are used, they turn out to be far from perfect measures of muscle strength.
Even when the monitoring devices are used, it may not be possible to appreciate small degrees of weakness. The standard measure of weakness or strength is called the “Train of Four,” which is four muscle twitches in succession triggered by electrically stimulating, through the skin, a nerve in the forearm or the face. Recovery is present when all four twitches are present and are equally strong. Unfortunately the human eye cannot detect subtle degrees of weakness, such as when the fourth twitch is less than 70%, or 90%, of the strength (amplitude) of the first twitch. This decrease in strength is called “fade”. We cannot adequately detect fade visually. Fade can only be properly assessed using more sophisticated monitors that measure, or represent, the actual force of contraction. These monitors are more expensive and most institutions don’t use them outside the research setting.
A train of four (TOF) ratio of 90% or more is now considered the standard for recovery, following a number of studies that showed considerable weakness in many patients during recovery when the minimum was 70% Plus the usual clinical signs of recovery should be present.
Symptoms of inadequate recovery include a profound feeling of weakness. In volunteers (yes, study volunteers were, amazingly, persuaded to accept being given low doses of muscle relaxants to simulate the process of recovery) there are also objective findings of throat (pharynx) weakness, which increases the risk of aspiration (stomach contents going to the lungs), blocked air passages (airway obstruction) and impaired hypoxic ventilatory drive (the automatic increase in breathing when blood oxygen levels are low). Also common are visual disturbances, facial weakness, inability to drink through a straw or bite firmly, difficulty in sitting or speaking and a general feeling of fatigue.
It is interesting that the clinical “gestalt” of this problem does not really square with these rather dramatic research findings. Few patients in recovery appear distressed as a result of muscle weakness. It may be that many cases of anxiety in the recovery period are due to unappreciated weakness.
As a patient, the prospect of being awake and paralysed is enough to put one off having surgery altogether. The saving grace may be that even when patients are weak, they are almost always sufficiently drowsy to not be bothered by it, or to remember the experience. I am not sure how reassuring that is.
How does this affect YOU?
The good news is that with careful attention to muscle relaxant dosing and selection, the use of antagonists given with appropriate timing, and of monitoring, the unhappy experience described above should be rare. Muscle relaxants are not always needed in general anesthesia and good clinical judgment allows the anesthesiologist to restrict their use only to cases when they are really necessary.
Another important factor is that, despite weakness, trained recovery room staff will not let your breathing be compromised to the point of danger. Oxygen levels are routinely and continuously monitored. If breathing is inadequate, oxygen is given, and measures are taken to assist breathing or to gently open the air passages.
Finally, a new drug might relegate this problem to the past. The drug is called sugammadex. Sugammadex effectively neutralizes muscle relaxants of the steroid class (this includes the common relaxants vecuronium and rocuronium) within 1 to 3 minutes, even when large doses of relaxant have been given. Sugammadex is expected to become available within the next couple of years.
GS Murphy. Residual neuromuscular blockade: incidence, assessment, and relevance
in the postoperative period. MINERVA ANESTESIOL 2006;72:97-109
Image of chondodendron tomentosum (curare) leaf is from http://www.blueplanetbiomes.org