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General anesthesia produces a state of induced, controlled and reversible loss of consciousness, which is the end result of sedation, analgesia, amnesia and muscle paralysis.
It is a vital component of surgery, without which the patient would experience excruciating pain and the body’s stress response could lead to great morbidity and mortality. While the precise mechanism of action is unclear, it is known that general anesthesia blocks the passage of nervous signals and the resultant processing of these signals in the central nervous system.
.jpg "Doctor is preparing anesthesia for surgery. Image Credit: Cherries / Shutterstock")
Unlike general anesthesia, which exerts its effects on the entire body, especially the central nervous and cardiopulmonary systems, local anesthesia has more confined, site-specific effects. Like general anesthesia, however, local anesthesia blocks the passage of signals along nerves before they can send messages of pain stimuli to the central nervous system. Patients generally do not feel any pain during surgical procedures, but they may experience pain during the injection of local anesthetics and this is related to the injecting technique employed.
Sedation is the depression of awareness, which ensures that the patient response to external stimuli becomes somewhat limited. This depression may be minimal, which corresponds to anxiety relief; or it may be moderate or deep. With minimal sedation, the patient is responsive to tactile or verbal stimuli, but only responsive to painful or repeated stimuli with the latter.
Anesthesia in general is very safe. Its safety profile is always increasing, due to advancements in medicine, surgery and technology. Furthermore, the training that anesthesiologists receive world over ensures that patient safety is their number one priority. During general anesthesia the patient’s airway is secured and several digital monitors are used to safeguard physiological parameters and keep them above the level that is compatible with life. In the operating room, anesthesiologists keep track of the depth of anesthesia as well as patient oxygenation, ventilation, temperature and hemodynamics. At hand are intravenous fluids and resuscitation kits for immediate use should anything go awry.
Local anesthesia is typically even safer than general anesthesia, because it bypasses the systemic effects seen with the latter. The side effect profile is also better with local anesthesia, which could, however, result in some swelling and redness at the injection site or an allergic reaction. However, systemic toxicity can occur if there is inadvertent administration of local anesthetic into a blood vessel or if too much of the local anesthetic agent is used. This can cause systemic consequences of the same type that are seen with general anesthesia.
When there is systemic toxicity due to local anesthesia or general anesthesia, it may result in only minor complications, such as nausea, vomiting, confusion and agitation. The more serious complications of general anesthesia, such as malignant hyperthermia (due to an inherited condition that presents with hyperkalemia, hypercarbia, metabolic acidosis and a lethal increase in body temperature when the patient receives general anesthesia), are fortunately very rare. Sedation, like anesthesia, is usually safe. However, caution is taken to prevent administering sedation in excess, which can cause respiratory depression. As is the case with general anesthesia, emergency drugs and equipment are always at hand should they become necessary.
In general, anesthesia during pregnancy is safe. General anesthetics do not appear to have a teratogenic effect on humans. Notwithstanding this fact, evidence shows that general anesthetics together with surgery increase the risk that a woman may experience a miscarriage or give birth prematurely. Moreover, there is an associated increased risk of low birth weight and infant death. Risks of miscarriage are increased if anesthesia and surgery take place during the first trimester of gestation, while the risk of premature birth is increased if they occur during the 2nd and 3rd trimesters. It is thus prudent to delay surgery wherever possible.