Recently a patient asked me if being under general anesthesia was like being asleep. Well, the answer I gave him was not wholly true and for good reason. Let’s explore that.
There are three states of decreased arousal – a coma, sleep and general anesthesia.
A coma is a period of prolonged unconsciousness due to injury to the brain. A comatose patients typically lies still with eyes closed, unresponsive to physical stimuli. At the start of the comatose state, patients may withdraw from painful stimuli or even grimace but as the coma deepens, even these reactions may vanish. EEG (electroencephalogram) shows low frequency, high amplitude waves.
Sleep is a state of very decreased arousal that is controlled by centers in the hypothalamus, brain stem, and forebrain. It is necessary for a human’s well-being. Humans cycle between two phases of sleep – REM (rapid eye movement) sleep and NREM (non-rapid eye movement sleep).
REM sleep last about 90 -120 min and is characterized by dreaming, erections, inability to move and high frequency, low amplitude waveforms on EEG.
NREM sleep has three phases and has low frequency and high amplitude waves on EEG. Restfulness is achieved in this phase of sleep. There are parts there is muscle activity and parts where muscle activity is rather low.
Lastly is general anesthesia. This is a reversible drug-induced state of unconsciousness, amnesia, analgesia, and being motionless. EEG shows low-frequency high amplitude waves. There are four phases of general anesthesia – light, intermediate, deep and profound phases. Surgery is usually performed between the intermediate and deep phases. A profound phase is achieved for procedures where the brain needs to be protected or to stop intractable seizures. As anesthesia deepens, the waves on EEG go from a decrease in number and amplitude to a flatline in the profound state.
So which state is general anesthesia closer to?
You guessed right – a coma.
General anesthesia is a reversible drug-induced coma. The sites in the brain that seem to be affected in a coma are the sites most anesthetics work to effect unconsciousness. For example, propofol induces unconsciousness by it’s effects in the cortex, mid-brain, thalamus and brain-stem. These same areas have been noticed to be affected in comatose patients.
A patient in a coma does not react to pain, just like a patient under general anesthesia, at least when the depth is adequate. Under general anesthesia a limb can be amputated, the appendix removed or even a hip replaced. Now try that in a patient sleeping at night.
Sleep refreshes. General anesthesia does not. Now, pure propofol anesthesia seems to have that refreshing effect. It has been found that propofol can help recover from sleep deprivation.
Sleep also has cycles, something that general anesthesia and the comatose state do not have.
The changes seen on the EEG during sleep differ from those seen the comatose state and under general anesthesia.
So I guess it was understandable that I did not tell the patient the whole truth. Imagine being told before your anesthetic as a lay person that you were going to be placed in a coma! With the kind of patients we see, I bet more than half of them might flee. I’d rather they believe they are going to have a nice, long nap. Ignorance is at times truly bliss.