Dr. Neville Fernandes, M.D.

Topical anesthesia is usually given in the form of a cream that is applied to the skin. It can take anywhere from 60 min to 2 hours achieve full results

Most places that administer "dental anesthesia" administer either IV or oral sedatives. Depending on the dentist, he may prescribe a pill for you to take prior to the procedure or they may insert an IV and administer IV medications. Some practices may administer nitrous oxide (laughing gas) in combination with the above. For more extensive dental work, you may require to be intubated and given a general anesthetic.

That's similar to asking is it safe to drive a car. Yes, regional anesthesia is "safe". But just like driving a vehicle, bad things can happen. Even if you are following the laws meticulously, you can still be hit, slide off the road, or lose control of the vehicle in bad weather. Regional anesthesia is generally considered safe, but that doesn't preclude adverse events from occurring.

It is not uncommon for elderly people to become disoriented/confused after a general anesthetic. If he has preexisting consitions such as dementia/Alzhrimers/etc, he may be more prone to the disorienteering effects. Also other medical problems can prolong the time he requires to return to his presurgical mental status

Sedation may be required for a number of different reasons: anxiety, to ease discomfort for an uncomfortable procedure, to prevent or minimize patient movement, etc. You have to remember there is varying depths of sedation. An extremely mild sedative may be the equivalent of having a few drinks of alcohol. Or, if the situation warrants, the sedation, can be so deep that a patient will only respond to a painful stimulus. The type and depth of anesthesia is determined by a number of factors: patient's physical and mental health status, procedure being performed, duration of procedure, pain produced by the procedure, etc.

There are a number of reasons. First, the medicines (gases) we use don't allow the heart muscles to contract as strongly as they normally would. Second, all surgeries are a stressor on the body -- which means your heart is having to work harder and faster in an environment (anesthesia gases) which doesn't allow it to work at its best capacity. Then each individual is different and their comorbidities such as smoking, high blood pressure, diabetes, etc., also complicate the picture.
Hope this answers your question.