anesthesia (an?es-the'zha) [ ¹an- + esthesi- + -ia]
Partial or complete loss of sensation, with or without loss of consciousness, as a result of disease, injury, or administration of an anesthetic agent, usually by injection or inhalation.
Preoperative:Before induction of anesthesia, contact lenses, hearing aids, dentures (partial plates as well as full sets), wristwatches, and jewelry are removed. The anesthesiologist or nurse-anesthetist interviews and examines the patient briefly, assessing general respiratory and cardiovascular health. The patient is questioned regarding compliance with prescribed preoperative fasting. The American Society of Anesthesiologists Guidelines recommend minimum fasting as follows: 2 hours for clear liquids, 4 hours for breast milk, 6 hours for formula, nonhuman milk, or a light meal (tea and toast), and 8 hours for a regular meal (easily remembered as “2-4-6-8”). These guidelines may be modified by individual surgeons for particular patients and their conditions. Baseline vital signs are assessed and recorded. An ECG, CBC, serum chemistries, and urinalysis are ordered for many general surgeries unless results of recent tests are available. Allergies, previous surgeries, and any untoward responses to anesthetic agents are reviewed, along with any special patient restrictions. If a menstruating female is using a tampon, it is removed and replaced with a perineal pad. Depending on the patient’s health status and the planned procedure, nasal oxygen, monitoring electrodes, and graduated compression stockings are applied. An intravenous route is established, and, after determining that the proper informed consent form has been signed, induction relaxation medication is administered.
Postoperative: During emergence from general anesthesia, the patient's airway is protected and vital signs monitored. Level of consciousness, status of protective reflexes, motor activity, and emotional state are evaluated. The patient is reoriented to person, place, and time; this information is repeated as often as necessary. For patients who have received ketamine, a quiet area with minimal stimulation is provided. Children may be disoriented, hallucinatory, or physically agitated as they emerge from general anesthesia. A security toy and the presence of parents may help them maintain orientation and composure. The temperatures of elderly patients should be monitored, heat loss prevented, and, as necessary, active rewarming provided. The mental status and level of consciousness of each patient should be carefully observed for changes. Patients' eyeglasses and hearing aids are returned to them as soon as possible. Before nerve block anesthesia, an intravenous infusion is established to ensure hydration. The patient is protected with side rails and other safety measures, and the anesthetized body part is protected from prolonged pressure. For regional anesthesia, sympathetic blockade is assessed by monitoring sensory levels along with vital signs (the block will wear off from head to toe, except for the sacrum and perineum, which wear off last). In obstetrics, maternal hypotension results in diminished placental perfusion and potential fetal compromise; therefore, hydration and vital signs must be closely monitored. Outcomes indicating returned sympathetic innervation include stable vital signs and temperature, ability to vasoconstrict, perianal pinprick sensations (“anal wink”), plantar flexion of the foot against resistance, and ability to sense whether the great toe is flexed or extended. The patient must tolerate oral fluids (unless restricted) and urinate before discharge. If the patient is at risk for postanesthesia headache, oral or intravenous hydration is administered, and the patient is encouraged to remain flat in bed. Prescribed analgesics are administered, and comfort measures, breathing exercises, abdominal support, and position changes are provided.
2. The science and practice of anesthesiology.
A level of unconsciousness just above the level of complete surgical anesthesia. The patient does not respond to verbal stimuli but does react to noxious stimuli (e.g., a pinprick). Basal anesthesia may be combined with local or regional anesthesia in some forms of surgery.
A regional anesthetic injected into a nerve (intraneurally) or immediately around it (paraneurally). Synonym: conduction anesthesia; neural anesthesia
Anesthesia produced by a lesion of the pons.
Anesthesia produced by insertion of a needle into the sacrococcygeal notch and injection of a local anesthetic into the epidural space. Synonym: caudal catheter
Pathological anesthesia due to a lesion of the central nervous system.
A method of inhalation anesthesia in which exhaled gases are rebreathed. This requires appropriate treatment of the exhaled gas to absorb the expired carbon dioxide and to replenish the oxygen and the anesthetic.
conduction anesthesiaBlock anesthesia
Anesthesia of the side opposite to the site of a central nervous system lesion.
A type of anesthesia marked by catalepsy, amnesia, and marked analgesia. The patient experiences a strong feeling of dissociation from the environment.
1. Pain or reduced sensation limited to either the occipital nerve or a branch of the trigeminal nerve.
2. Pain in an anesthetized zone, as in thalamic lesions.
Anesthesia induced with electric current.
electronic dental anesthesia Abbreviation: EDA
In dentistry, the use of low levels of electric current to block pain signals en route to the brain. The patient controls the current through a handheld control. The current creates no discomfort and, unlike local anesthesia, leaves no numbness to wear off once the dental work is completed. See: audioanalgesia; patient-controlled analgesia
Anesthesia in which gases are administered via a tube inserted into the trachea.
Anesthesia produced by injection of a local anesthetic into the peridural space of the spinal cord. Synonym: peridural anesthesia See: illustration
Ethylene given as a combination of oxygen 20%, cyclopropane 10%, and ethylene 70%. Because it is a rather weak anesthetic, volatile and inflammable, it is rarely, if ever, used.
Anesthesia that produces complete loss of consciousness. General anesthesia is a medically controlled coma. Patients under general anesthesia do not respond to words or touch and cannot breathe spontaneously or protect their airway.
Gwathmey's anesthesia See: Gwathmey, James
Anesthesia during which the blood pressure is lowered.
General anesthesia during which the body temperature is lowered.
Bodily anesthesia occurring in conversion disorders.
Anesthesia in which the patient is not comfortably sedated or relieved of pain. Common findings are spontaneous eye opening, grimacing, swallowing, or sweating. Vital signs may reveal unexpected hypertension or tachycardia.
infiltration anesthesia, infiltrative anesthesia
Local anesthesia produced by an injection of an anesthetic directly into the tissues.
General anesthesia produced by the inhalation of vapor or gaseous anesthetics, e.g., ether, nitrous oxide, and methoxyflurane.
Instillation of gaseous anesthetics into the inhaled air.
intrapleural anesthesia See: interpleural analgesia
intrathecal anesthesiaIntrathecal analgesia.
Anesthesia administered through a catheter advanced through the upper airway and vocal cords into the trachea.
The pharmacological inhibition of nerve impulses in a body part. It is typically used to facilitate treatment of a small lesion or laceration or to perform minor surgery. Commonly used agents include lidocaine, bupivacaine, or novocaine. All local anesthetic agents work by decreasing the flow of sodium ions into nerve cells, blocking the action potential of the cells. See: block anesthesia; infiltration anesthesia
General anesthesia produced by more than one drug, such as propofol for induction, followed by an inhaled drug for maintenance of anesthesia.
neural anesthesiaBlock anesthesia.
Caudal, epidural, or spinal anesthesia.
Application, usually by dropping, of a volatile anesthetic agent onto gauze held over the nose and mouth.
Injection of a local anesthetic at the roots of spinal nerves.
peridural anesthesiaEpidural anesthesia.
perineural anesthesiaPerineural analgesia.
Local anesthesia produced when a nerve is blocked with an appropriate agent.
The first stage of general anesthesia, before unconsciousness.
Local anesthesia used primarily in obstetrics (e.g., to facilitate pelvic surgery or childbirth). The pudendal nerve on each side, near the spinous process of the ischium, is blocked.
General anesthesia produced by introduction of an anesthetic agent into the rectum, used esp. in managing pediatric patients.
An obsolete synonym for cryoanesthesia.
Nerve or field blocking, causing loss of sensation in a dermatome innervated by a specific nerve. See: block anesthesia; infiltration anesthesia
saddle block anesthesia
Anesthesia produced by introducing the anesthetic agent into the fourth lumbar interspace to anesthetize the perineum and the buttocks.
Anesthesia due to a pathological or surgically induced lesion of a nerve root.
Loss of genital sensation, with accompanying secondary sexual dysfunction.
INJECTION OF SPINAL ANESTHESIA
1. Anesthesia resulting from disease or injury to conduction pathways of the spinal cord.
2. Synonym: subarachnoid block See: illustration
Anesthesia produced by injection of anesthetic into the subarachnoid space of the spinal cord.
Common adverse reactions to spinal anesthesia include backache, bradycardia, headache, lowered blood pressure, and urinary retention.
Anesthesia produced by injection of an anesthetic into the splanchnic ganglion.
stages of anesthesia
The distinct series of steps through which anesthesia progresses. The first stage of pharmacologically induced general anesthesia includes preliminary excitement until voluntary control is lost. Because hearing is the last sense to be lost, the conversation of operating room staff should be guarded during this stage. The second stage consists of loss of voluntary control. In the third stage there is entire relaxation, no muscular rigidity, and deep regular breathing.
Depth of anesthesia at which relaxation of muscles and loss of sensation and consciousness are adequate for the performance of surgery.
Loss of sense of touch.
Local anesthesia induced by application of an anesthetic directly onto the surface of the area to be anesthetized.
total intravenous anesthesia Abbreviation: TIVA
The sole use of intravenous drugs without any inhalational agents for operative or procedural anesthesia.
Loss of sensation resulting from nerve injury.
The injection of large volumes of diluted lidocaine, bicarbonate, and epinephrine subcutaneously for use in local anesthesia. This procedure is most often used before liposuction to limit blood loss and pain.
State of light anesthesia. See: twilight sleep