To undergo a surgical procedure, most people need some form of anesthetic.
If the procedure is small and does not involve a very deep incision, the surgeon can numb the area locally with local anesthetic and proceed. This technique is called local anesthesia and can be used even in a doctor’s office without the presence of a trained anesthesia provider.
The next level would be regional anesthesia. Using a local anesthetic, the nerve supply to a particular region of the body is blocked. This is great because not only does it allow the anesthetic to be localized but it also can be tailored to give pain relief for hours.
In instances where a local or regional anesthetic is not feasible or contraindicated, the other option is general anesthesia. Here, using either an intravenous or inhaled agent, loss of consciousness is achieved. This allows the patient to undergo surgery.
In a paper published in 2003, Vesna Jevtovic-Todorovic, an anesthesiologist then practicing in Virginia, exposed 7-day-old infant rats to a combination of two of the following – midazolam, nitrous oxide and isoflurane – for 6 hours. The exposure led to the death of nerve tissue in the developing brains of the rodents. Even worse, the rodents suffered long-lasting cognitive impairment in learning and memory, which worsened as they aged.
A few years later, the same phenomenon was observed when the same study was done using young monkeys.
This of course raised concerns in the anesthetic community, as many wondered if this phenomenon was possible in human kids.
Studies to correlate this in humans were lacking and retrospective analyses of data have given mixed results. This led to the F.D.A. and the International Anesthesia Research Society to form a group in 2009 to promote further research into this called SmartTots – Strategies for Mitigating Anesthesia-Related Neurotoxicity in Tots.
Even though there is still no human data, in 2012, the group recommended that elective surgery under general anesthesia be avoided in children younger than 3.
Late in 2014, they also stated that if an operation requiring anesthesia and sedation can reasonably be delayed, it “should possibly be postponed because of the potential risk to the developing brain of infants, toddlers and preschool children”.
At the moment, there is an ongoing study which has enrolled 700 children to study this phenomenon – A Multi-site Randomized Controlled Trial Comparing Regional and General Anesthesia for Effects on Neurodevelopmental Outcome and Apnea in Infants (GAS).
It is however not only children who seem to suffer possible negatives effects from general anesthetics on the brain. The elderly population seem to suffer from negative cognitive effects as well. Patients older than 60 seem more prone to develop delirium and some memory loss after general anesthesia and it is irrespective of the drug used. Patients with a history of dementia also fare worse.
Anesthetics cause their effect by blocking receptors in several regions of the brain (GABA, NMDA, Dopamine etc). Older patients may just have a harder time recovering from this block. There is the thought that anesthetics may induce neuronal changes that are harder to reverse in the elderly.
The use of regional techniques, when possible, prevents this problem.
One thing patients receiving general anesthesia worry about a lot is awareness. The fear that one would wake up during surgery and feel every part of the procedure. Awareness is a really rare occurrence. As the data is showing, anesthesia providers may actually be giving too much anesthetic when we use the classic definition of minimum alveolar concentration (MAC) to dose inhaled agents. This means patients are really “knocked out” and have a very slim chance of waking up. Even though explicit memory (conscious) is totally blocked, there is a chance that implicit memory (unconscious) may still be active and could lead to patients thinking they woke up. Also, chances are that as a patient emerges form anesthesia, he or she may erroneously think that they are still having surgery. Awareness is however possible during surgery of the very sick since those patients can hardly tolerate a deep general anesthetic.
So what does the future hold? The use of functional MRI during anesthetics may be a possibility in the future. We use the BIS monitor to gauge awareness but that might not be enough. Maybe the use of the EEG should be introduced. The introduction of newer drugs also hold some promise. It seems the best care in some case may be not to put patients to sleep.