Anesthesia
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia, paralysis, amnesia, and unconsciousness. Three broad categories exist to achieve these effects. General anesthesia suppresses central nervous system activity and results in total lack of sensation using either injected or inhaled drugs. Sedation suppresses the central nervous system to a lesser degree without resulting in unconsciousness. Regional and local anesthesia block transmission of nerve impulses from a specific part of the body.
The American Society of Anesthesiologists developed a six-tier scale called the ASA physical status classification to stratify patient risk before surgery. A healthy person falls into ASA 1, while an ASA 5 describes a moribund person not expected to survive without the operation. The rate of deaths totally attributed to the patient's health stands at 1:870. Compare that to the rate of deaths totally attributed to surgical factors at 1:2860 or anesthesia alone at 1:185,056. Incorrect pre-operative assessments are the root cause of 11% of all adverse anesthetic events. A well completed medical history arrives at the correct diagnosis 56% of the time which increases to 73% with a physical examination.
On the 14th of November 1804, Hanaoka Seishu became the first person to successfully perform surgery using general anesthesia in Japan. He used a formula named tsusensan which combined Korean morning glory and other herbs. In the West, Horace Wells conducted the first public demonstration of inhalational anesthetic at Massachusetts General Hospital in Boston in 1845. On the 16th of October 1846, William Thomas Green Morton gave a successful demonstration using diethyl ether to medical students at the same venue. John Collins Warren removed a tumor from Edward Gilbert Abbott during this procedure. The previously skeptical Warren stated, Gentlemen, this is no humbug. By 1895, chloroform usage reached 750,000 doses weekly in Britain before safety concerns arose.
Inhalational anesthetics bind directly to cavities in proteins of the central nervous system. The potency of an inhalational anesthetic is quantified by its minimum alveolar concentration or MAC. The MAC is the percentage dose that will prevent a response to painful stimulus in 50% of subjects. Loss of memory occurs through action on multiple specific regions of the brain where synaptic plasticity determines connection strength. Each anesthetic produces amnesia through unique effects on memory formation at variable doses. Drugs like midazolam produce amnesia by blocking the formation of long-term memories while others suppress nuclei below consciousness levels.
The core instrument in an inhalational anesthetic delivery system is an anesthetic machine with vaporizers and ventilators. It provides anesthetic gas at constant pressure and oxygen for breathing while removing carbon dioxide. Patients under general anesthesia must undergo continuous physiological monitoring to ensure safety. In the US, guidelines include electrocardiography, heart rate, blood pressure, and oxygen saturation of the blood. For more invasive surgery, monitoring may also include temperature, urine output, and cerebral activity. Anesthesia-related deaths from all causes were reported at 1:75 in a first study from 1954 compared to 1:2680 attributed to anesthesia alone today.
Nausea and vomiting are reported at 9.8% during the immediate time after anesthesia called emergence. There is a need for airway support in 6.8% of cases following the procedure. Postoperative cognitive dysfunction describes a disturbance in cognition that can last for weeks or months. Most commonly relatives report a lack of attention and memory loss in elderly patients. A recent study conducted at the David Geffen School of Medicine at UCLA found the brain navigates its way through activity clusters on its return to consciousness. Andrew Hudson states recovery is not simply the result of the anesthetic wearing off but of the brain finding its way back through a maze of possible activity states.
Common questions
What is anesthesia and what does it include?
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia, paralysis, amnesia, and unconsciousness.
When did Hanaoka Seishu perform the first surgery using general anesthesia in Japan?
On the 14th of November 1804, Hanaoka Seishu became the first person to successfully perform surgery using general anesthesia in Japan. He used a formula named tsusensan which combined Korean morning glory and other herbs.
How many deaths are attributed to anesthesia alone today compared to 1954?
Anesthesia-related deaths from all causes were reported at 1:75 in a first study from 1954 compared to 1:2680 attributed to anesthesia alone today. The rate of deaths totally attributed to anesthesia alone stands at 1:185,056 according to current data.
What percentage of adverse anesthetic events are caused by incorrect pre-operative assessments?
Incorrect pre-operative assessments are the root cause of 11% of all adverse anesthetic events. A well completed medical history arrives at the correct diagnosis 56% of the time which increases to 73% with a physical examination.
Who conducted the first public demonstration of inhalational anesthetic at Massachusetts General Hospital in Boston?
Horace Wells conducted the first public demonstration of inhalational anesthetic at Massachusetts General Hospital in Boston in 1845. On the 16th of October 1846, William Thomas Green Morton gave a successful demonstration using diethyl ether to medical students at the same venue.