Anesthesia definition and types of anesthesia

Anesthesia definition and types of anesthesia

Anesthesia - The intentional establishment of loss of PAIN sensation or of consciousness to make a surgical OPERATION possible. Anesthesia may be local, regional, or general, depending on the operation and on the individual’s health circumstances and preferences. Doctors sometimes use local and regional forms of anesthesia to treat severe or CHRONIC PAIN not related to surgery.

Anesthesia today is very effective as well as safe. There are several types of anesthesia and numerous anesthetic agents. The anesthesiologist or anesthetist selects the types and agents according to the operation and the person’s health conditions and health status, and may combine types and agents to achieve the desired anesthetic effect. The risks of anesthesia vary with the type and agent though are generally minimal.

Individual response to anesthetic agents varies, so the anesthesiologist or anesthetist very closely monitors the person’s vital signs and level of anesthesia throughout the operation. After the operation monitoring continues in the postanesthesia care unit (PACU), also called the recovery room, until the person has emerged from anesthesia enough to go to a hospital room or for discharge home (AMBULATORY SURGERY).

Local Anesthesia

Local anesthesia numbs a small area of the body for minor operations such as removal of a LIPOMA (benign tumor of fatty tissue) or NEVUS (SKIN lesion such as a mole). The surgeon generally administers local anesthesia by injection into and surrounding the site of the operation. Local anesthetic agents block the ability of neurons (NERVE cells) to send nerve signals, preventing the perception of pain. Some local anesthetic agents contain EPINEPHRINE, a vasoconstrictor that reduces bleeding.

The effect of a local anesthetic may last from 20 minutes to 12 hours or longer, depending on the agent and the extent of infiltration of the area. Surgeons sometimes use local anesthetic to infiltrate the area of an operative site at the end of the operation to provide extended pain relief. Surgeons may combine local anesthesia and conscious sedation to reduce anxiety and improve the person’s level of comfort during and after the operation. Some amount of a local anesthetic enters the BLOOD circulation and can cause sensations such as lightheadedness or a feeling that the lips are buzzing.

COMMON LOCAL AND REGIONAL ANESTHETIC AGENTS
benzocaine bupivacaine chloroprocaine
etidocaine lidocain emepivacaine
prilocaine procaine ropivacaine
tetracaine    

Regional Anesthesia

Regional anesthesia is an injection that infiltrates nerves to blocks pain signals from a large area of the body. An anesthesiologist or anesthetist administers regional anesthesia. The most common forms of regional anesthesia include

  • regional nerve block, in which the anesthesiologist or anesthetist administers a single injection of the anesthetic agent into or around a major nerve to block sensation from the fingers, hand, arm, toes, foot, or leg
  • caudal, in which the anesthesiologist or anesthetist administers a single injection of the anesthetic agent into the caudal canal in the sacrococcygeal (tailbone) region of the spine to block sensation in the pelvis and perineum
  • epidural, in which the anesthesiologist or anesthetist places a thin catheter into the space surrounding the SPINAL CORD and injects the anesthetic agent, potentially as a steady flow or repeated times, to block sensation from the point of injection downward for operations on the lower abdomen and lower extremities
  • spinal, in which the anesthesiologist or anesthetist administers a single injection of the anesthetic agent directly into the CEREBROSPINAL FLUID around the spinal cord to block sensation from the point of injection downward for operations on the abdomen and lower extremities

Many of the anesthetic agents are the same for regional anesthesia as for local anesthesia. As occurs with local anesthetics, a small amount of the anesthetic agent enters the blood circulation and can cause mild effects such as HEADACHE or TINNITUS (ringing in the ears). These effects generally go away within an hour. Because caudal, epidural, and spinal anesthesia affect the pelvic region and the muscles of the BLADDER, the surgeon may instruct placement of a urinary catheter until the anesthetic wears off. The surgeon may sometimes leave the epidural catheter in place for 24 to 48 hours for postoperative administration of light anesthesia or ANALGESIC MEDICATIONS for pain relief.

Regional nerve blocks, caudal anesthesia, and epidural anesthesia may take up to 20 minutes to become effective. Spinal anesthesia takes effect immediately. Though regional anesthesia blocks only the sensory nerves, movement of the anesthetized region is difficult because the lack of sensation makes the affected body parts feel heavy and uncontrollable. A person has adequately recovered from regional anesthesia when he or she can safely walk or regains preanesthesia sensation or movement of the affected area.

Complications are rare with regional anesthesia though may include prolonged labor during CHILDBIRTH, irritation or bleeding at the injection site, drop in BLOOD PRESSURE, and post-anesthesia headache (with epidural or spinal anesthesia). Infection and injury to the nerves are possible though extremely rare. Recovery from regional anesthesia is generally uneventful and fairly rapid.

Conscious Sedation

Conscious sedation alters a person’s awareness of pain and activities taking place to and around him or her. With conscious sedation a person generally can answer questions, respond to instructions, and tell the doctor whether he or she is experiencing pain or discomfort though has little or no memory of the operation and events surrounding it when full consciousness returns. Surgeons often use conscious sedation to improve a person’s comfort and reduce anxiety during minor operations, usually in combination with local or regional anesthesia. Usually an anesthesiologist or anesthetist administers the sedative medication intravenously with ongoing monitoring of the person’s response to the medication, level of awareness, and vital signs such as BREATHING rate, HEART RATE, and blood pressure.

Rarely, a person may experience NAUSEA or headache after conscious sedation. More rarely, a person may have distressing memories of the operation. Though a person appears to return to normal consciousness quickly, the medication may remain at a level in the blood circulation that affects perception and function for 24 hours after its administration. Doctors caution people to avoid driving or performing activities that require alertness and coordination for at least 24 hours after conscious sedation.

Potential Drug Interactions with Anesthesia

Many prescription medications, OVER-THECOUNTER (OTC) DRUGS, NUTRITIONAL SUPPLEMENTS, and MEDICINAL HERBS AND BOTANICALS can interfere with anesthesia or BLOOD clotting. It is important to tell the surgeon of all such medications and products. The surgeon or the anesthesiologist may request the person to stop taking certain drugs or herbs for a period of time before and sometimes also after surgery.

General Anesthesia

General anesthesia establishes a state of deep UNCONSCIOUSNESS in which the anesthetic agents circulate in the body to block pain signals, prevent movement, and block memory of the operation. The anesthetic agents may be gases the person inhales or medications (such as sedatives, hypnotics, and MUSCLE relaxants) the anesthetist or anesthesiologist injects intravenously. An endotracheal tube inserted through the MOUTH, into the THROAT, and to the top of the trachea allows the anesthesiologist to seal the airway to prevent foreign matter from entering the LUNGS, as the anesthetic suppresses the COUGH REFLEX that would normally keep mucus and debris from entering the trachea. The endotracheal tube also ensures that oxygen and anesthetic gases directly enter the lungs. General anesthesia is the standard for operations on the upper abdomen and chest as well as for many major orthopedic operations. In some circumstances the anesthesiologist may combine epidural or spinal anesthesia with general anesthesia. Many general anesthesia agents are fast acting and short lived, allowing rapid anesthetic induction as well as quick recovery.

COMMON GENERAL ANESTHETIC AGENTS
Inhaled
enflurane halothane isoflurane
methoxyflurane nitrous oxide  
Injected
etomidate KETAMINE methohexital
propofol thiopental  

Sophisticated equipment allows precise and safe administration of inhaled anesthetics, including ongoing adjustments of carbon dioxide and oxygen concentrations. The anesthesiologist or anesthetist continuously monitors the person’s vital signs, including breathing rate, oxygen saturation, heart rate, blood pressure, and body temperature. The most common side effects of general anesthesia are nausea, VOMITING, a slow return to normal bowel activity, and a prolonged sense of grogginess. The anesthesiologist or anesthetist can administer medications to ease or relieve these symptoms. Sore throat is a common complaint after general anesthesia, a consequence of the endotracheal tube.

Though most general anesthetic agents do not persist in the body at functional levels beyond 24 to 36 hours, many people feel they are not quite themselves for several days after general anesthesia. Postoperative analgesic medications can exacerbate this perception. Walking, to the extent possible, and stool softeners help BOWEL MOVEMENT return to normal. Allergic reaction to anesthetic agents is uncommon but occurs, so it is important to tell both the surgeon and the anesthesiologist or anesthetist of any allergies, including to foods. Smoking, certain prescription medications, ILLICIT DRUG USE, and ALCOHOL consumption affect the ways in which various anesthetic agents function in the body.

It is important to avoid driving or engaging in activities that require focused attention (including making important decisions and signing legal documents) until it is clear that the effects of general anesthesia have completely worn off.

A rare but potentially life-threatening complication of general anesthesia is malignant hyperthermia, in which the person’s body temperature rises rapidly and high, muscles become rigid or SPASM, and heart rate and blood pressure vacillate wildly and widely. Doctors believe malignant hyperthermia has a genetic foundation because it occurs in families, though the precise genetic involvement remains unknown. Death as a complication of general anesthesia, though possible, is very rare. Continued advances in anesthetic agents and administration techniques are improving the experience and safety of general anesthesia.

See also NEURON; POSTOPERATIVE PROCEDURES; PREOPERATIVE PROCEDURES; SURGERY BENEFIT AND RISK ASSESSMENT; WOUND CARE.

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