I don't think it's common to do general anesthesia for colonoscopy (or gastroscopy). Doctors do a minor anesthesia (intoxication) so you sleep while the operation in performedbut that's not a general anesthesia.
In a general anesthesia you can't breath on your own so they stick a tube in your mouth. And it needs a special doctor (anesthesiologist) to perform the general anesthesia.
In a general anesthesia you can't breath on your own so they stick a tube in your mouth. And it needs a special doctor (anesthesiologist) to perform the general anesthesia.