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Anesthesia

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Anesthesia or anaesthesia (see spelling differences) has traditionally meant the condition of having the perception of pain and other sensations blocked. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. It comes from the Greek roots an-, "not, without" and aesthētos, "perceptible, able to feel". The word was coined by Oliver Wendell Holmes, Sr. in 1846.

Today, the term general anesthesia in its most general form can include:

Types

There are several forms of anesthesia:

  • General: anesthesia resulting in amnesia, with a loss of protective airway reflexes. While usually administered with inhalational agents, general anesthesia can be achieved with intravenous agents, such as propofol. Amnesia is the main characteristic, while analgesia and muscle relaxation may be present, to varying degress.
  • Regional: Loss of pain sensation, with varying degrees of muscle relaxation, in certain regions of the body. Administered with local anesthesia to peripheral nerve bundles, such as the brachial plexus in the neck. Examples include the interscalene block for shoulder surgery, axillary block for wrist surgery, and femoral nerve block for leg surgery. While traditionally administered as a single injection, newer techniques involve placement of indwelling catheters for continuous or intermittent administration of local anesthetics.
    • Spinal: aka "Sub Arachnoid Block" Refers to a regional block resulting from a small volume of local anesthetics being injected into the cerebrospinal fluid.
    • Epidural: Regional block resulting from an injection of local anesthetic into the epidural space. The epidural space is a potential space that lies underneath the ligamenta flava, and outside the dura mater (outside layer of the spinal canal).
  • Local anesthesia is similar to regional anesthesia, but exerts its effect on a smaller area of the body.

Not all surgical procedures require anesthetic. Sometimes conscious sedation is used.

History

Anesthesia was used as early back as the Incas. Shamans chewed cocoa leaves and drilled holes in the heads of their patients (to let the bad spirits escape) while spitting into the wounds they'd inflicted. The mixture of cocaine, resin and saliva numbed the site allowing hours of drilling. [citation needed]

Also, Dioscorides, for example, reports potions being prepared from opium and mandragora as surgical anesthetics.

In the East, in the 10th century work Shahnameh, the author describes a caesarean section performed on Rudaba when giving birth, in which a special wine agent was prepared by a Zoroastrian priest, and used to produce unconsciousness for the operation. Although largely mythical in content, the passage does at least illustrate knowledge of anesthesia in ancient Persia.

Non-pharmacological methods

Hypnotism and acupuncture have a long history of use as anesthetic techniques. In China, Taoist medical practitioners developed anesthesia by means of acupuncture. Chilling tissue (e.g. with ice) can temporarily cause nerve fibers (axons) to stop conducting sensation, while hyperventilation can cause brief alteration in conscious perception of stimuli including pain (see Lamaze).

In modern anesthetic practice, these techniques are seldom employed.

Herbal derivatives

The first herbal anesthesia was administered in prehistory. Opium and Cannabis were two of the most important herbs used. They were ingested or smoked. Alcohol was also used, its vasodilatory properties being unknown. In early America preparations, datura, with the active ingredient scopolamine, was used, as was coca. In Medieval Europe various preparations of mandrake were tried as was henbane (hyoscyamine).

In 1804, the Japanese surgeon Hanaoka Seishū performed general anaesthesia for the operation of a breast cancer (mastectomy), by combining Chinese herbal medicine know-how and Western surgery techniques learned through "Rangaku", or "Dutch studies". His patient was a 60-year-old woman called Kan Aiya.[1] He used a compound he called Tsusensan, based on the plants Datura metel, Aconitum and others.

Early gases and vapours

Contemporary re-enactment of Morton's October 16, 1846, ether operation; daguerrotype by Southworth & Hawes.

In the West, the development of effective anesthetics in the 19th century was, with Listerian techniques, one of the keys to successful surgery. Henry Hill Hickman experimented with carbon dioxide in the 1820s. The anaesthetic qualities of nitrous oxide (isolated in 1773 by Joseph Priestley) were discovered by the British chemist Humphry Davy about 1799 when he was an assistant to Thomas Beddoes, and reported in a paper in 1800. But initially the medical uses of this so-called "laughing gas" were limited - its main role was in entertainment. It was used on 30 September 1846 for painless tooth extraction upon patient Eben Frost by American dentist William Thomas Green Morton. Horace Wells Connecticut, a travelling dentist, had demonstrated it the previous year 1845, at Massachusetts General Hospital. Wells made a mistake, in choosing a particularly sturdy male volunteer, and the patient suffered considerable pain. This lost the colourful Wells any support. Later the patient told Wells he screamed in shock and not in pain. A subsequently drunk Wells died in gaol, by cutting his femoral artery, after allegedly assaulting a prostitute with sulphuric acid.

Another dentist, William E. Clarke, performed an extraction in January 1842 using a different chemical, diethyl ether (discovered by Valerius Cordus in 1540). In March 1842 in Danielsville, Georgia, Dr. Crawford Long was the first to use anaesthesia during an operation, giving it to a boy (John Venables) before excising a cyst from his neck; however, he did not publicize this information until later.

On October 16, 1846, another dentist, William Thomas Green Morton, invited to the Massachusetts General Hospital, performed the first public demonstration of diethyl ether (then called sulfuric ether) as an anesthetic agent, for a patient (Edward Gilbert Abbott) undergoing an excision of a vascular tumour from his neck. In a letter to Morton shortly thereafter, Oliver Wendell Holmes, Sr. proposed naming the procedure anæsthesia.

Anesthesia pioneer Crawford W. Long

Despite Morton's efforts to keep "his" compound a secret, which he named "Letheon" and for which he received a US patent, the news of the discovery and the nature of the compound spread very quickly to Europe in late 1846. Here, respected surgeons, including Liston, Dieffenbach, Pirogoff, and Syme undertook numerous operations with ether. An American born physician, Boott who had travelled to London, encouraged a leading dentist, Mr James Robinson, to perform a dental procedure on a Miss Lonsdale. This was the first case of an operator-anaesthetist. On the same day, Saturday 19 December 1846 in Dumfries Royal Infirmary, Scotland, A Dr Scott used ether for a surgical procedure. The first use of anaesthesia in the southern hemisphere took place in Launceston, Tasmania, that same year. Ether has a number of drawbacks, such as its tendency to induce vomiting and its flammability. In England it was quickly replaced with chloroform.

Discovered in 1831, the use of chloroform in anaesthesia is usually linked to James Young Simpson, who, in a wide-ranging study of organic compounds, found chloroform's efficacy on 4 November 1847. Its use spread quickly and gained royal approval in 1853 when John Snow gave it to Queen Victoria during the birth of Prince Leopold. Unfortunately, chloroform is not as safe an agent as ether, especially when administered by an untrained practitioner (medical students, nurses and occasionally members of the public were often pressed into giving anaesthetics at this time). This led to many deaths from the use of chloroform which (with hindsight) might have been preventable. The first fatality directly attributed to chloroform anaesthesia (Hannah Greener) was recorded on 28 January 1848.

John Snow of London published articles from May 1848 onwards 'On Narcotism by the Inhalation of vapours' in the London Medical Gazette. Snow also involved himself in the production of equipment needed for inhalational anaesthesia.

The surgical amphitheatre at Massachusetts General Hospital, or "ether dome" still exists today, although it is used for lectures and not surgery. The public can visit the amphitheater on weekdays when it is not in use.

Anesthetists (Anesthesiologists in the USA) and the profession

Physicians specialising in peri-operative care, development of an anesthetic plan, and the administration of anesthetics are known as anaesthetists in the UK or, in the U.S., anesthesiologists. In the U.S., the training of a physician anesthesiologist typically consists of 4 years of college, 4 years of medical school, 1 year of internship, and 3 years of residency. In the UK training lasts a minimum of seven years after the awarding of a medical degree and two years of basic residency, and takes place under the supervision of the Royal College of Anaesthetists. Other countries have similar systems.

In the UK, completion of the examinations set by the Royal College of Anaesthetists leads to award of the Diploma of Fellowship of the Royal College of Anaesthetists (FRCA). In the US, completion of the written and oral Board examinations by a physician anesthesiolgist allows one to be called "Board Certified" or a "Diplomate" of the American Board of Anesthesiology.

The role of the anaesthetist is changing. It is no longer limited to the operation itself. Many anaesthetists consider themselves to be peri-operative physicians, and will involve themselves in optimizing the patient's health before surgery (colloquially called "work-up"), performing the anaesthetic, following up the patient in the post anesthesia care unit and post-operative wards, and ensuring optimal analgesia throughout.

In the U.S., nurse practitioners specializing in anesthesia are known as Nurse Anesthetists or CRNAs. CRNAs have a bachelors degree, at least 1 year of critical care nursing experience, and a masters degree in nurse anesthesia. The average CRNA student has 5-7 years of experience before entering school. In the United Kingdom, personnel known as ODPs (operating department practitioner) or Anaesthetic nurses provide support to the anesthetist.

All anaesthetics in the UK, Australia, New Zealand and Japan are administered by physicians. In America, the IOM has demonstrated that anesthesia safety has increased fifty fold in the past twenty years. No scientific evidence exists that there is a difference in safety between the various anesthesia providers.

Anesthetic equipment and physics

In modern anesthesia, a wide variety of medical equipment is desirable depending on the necessity for portable field use, surgical operations or intensive care support. Anesthesia practitioners must possess a comprehensive and intricate knowledge of the production and use of various medical gases, anaesthetic agents and vapours, medical breathing circuits and the variety of anaesthetic machines (including vaporizers, ventilators and pressure gauges) and their corresponding safety features, hazards and limitations of each piece of equipment, for the safe, clinical competence and practical application for day to day practice.

Anesthetic agents

Local anaesthetics

The first effective local anaesthetic was cocaine. Isolated in 1859, it was first used by Karl Koller, at the suggestion of Sigmund Freud, in ophthalmic surgery in 1884. Before that doctors had used a salt and ice mix for the numbing effects of cold, which could only have limited application. Similar numbing was also induced by a spray of ether or ethyl chloride. A number of cocaine derivatives and safer replacements were soon produced, including procaine (1905), Eucaine (1900), Stovaine (1904), and lidocaine (1943).

Local anesthetics are agents which prevent transmission of nerve impulses without causing unconsciousness. They act by binding to fast sodium channels from within (in an open state).

Classification: Local anesthetics can be either ester or amide based.

Ester local anesthetics (eg. procaine, amethocaine, cocaine) are generally unstable in solution and fast acting, and allergic reactions are common.

Amide local anesthetics (eg. lidocaine, prilocaine, bupivicaine, levobupivacaine, ropivacaine and dibucaine) are generally heat stable, with a long shelf life (around 2 years). They have a slower onset and longer half life than ester anaesthetics, and are usually racemic mixtures, with the exception of levobupivacaine (which is S(-)-bupivacaine) and ropivacaine (S(-)-ropivacaine). These agents are generally used within regional and epidural or spinal techniques, due to their longer duration of action which provides adequate analgesia for surgery, labor and symptomatic relief.

Only preservative free local anesthetic agents may be injected intrathecally.

Adverse effects of local anaesthesia

Local anesthetic drugs are toxic to the heart (where they cause arrhythmia) and brain (where they cause unconsciousness and seizures). Arrhythmias may be resistant to defibrillation and other standard treatments, and may lead to loss of heart function and death.

The first evidence of local anesthetic toxicity involves the nervous system, including agitation, confusion, dizziness, blurred vision, tinnitus, a metallic taste in the mouth, and nausea that can quickly progress to seizure and cardiovascular collapse.

Direct infiltration of local anesthetic into skeletal muscle will cause temporary paralysis of the muscle.

Toxicity can occur with any local anesthetic as an individual reaction of the patient, and possible toxicity may be tested with pre-operative procedures to avoid toxic reactions during surgery.

Early opioids and hypnotics

Opioids were first used by Racoviceanu-Piteşti, who reported his work in 1901.

Current inhaled general anesthetic agents

Current IV general or sedative agents

Muscle relaxants

Adverse effects of muscle relaxants

Succinylcholine may cause hyperkalemia if given to burn patients, or paralysed (quadraplegic, paraplegic) patients. The mechanism is reported to be through upregulation of acetylcholine receptors in those patient populations. Succinylcholine may also trigger malignant hyperthermia in susceptible patients.

Another potentially disturbing adverse effect is anesthesia awareness. In this situation, patients paralyzed with muscle relaxants may awaken from their anesthesia. If this fact is missed by the anaesthesiologist, the patient may be aware of their surroundings, but be incapable of moving or communicating that fact. Neurological monitors are becoming increasingly available which may help decrease the incidence of awareness.

Opioid analgesics

  • Naloxone, although chemically similar to some analgesics, is not a painkiller and reverses the effects of morphine-like agents.

Volatile agents

These are specially formulated organic liquids, which evaporate readily into vapors, which are given by inhalation for induction and/or maintenance of general anaesthesia. The ideal anesthetic vapor or gas should be non-flammable; non-explosive; lipid soluble; possess low blood gas solubility; have no end organ (heart, liver, kidney) side effects; not be metabolized and be non-irritant when breathed by patients.

No anesthetic vapor currently in use meets all of these requirements. The vapors in current use are halothane, isoflurane, desflurane and sevoflurane. Nitrous oxide is still in widespread use, making it one of the most long lived and successful drugs in use.

In theory, any anesthetic vapor can be used for induction of general anesthesia. However, most of the vapors are irritating to the airway, resulting in coughing, laryngospasm and overall difficult inductions. Commonly used agents for inhalational induction include sevoflurane and halothane. All of the modern vapors can be used alone or in combination with other medications to maintain anesthesia (nitrous oxide is not potent enough to be used as a sole agent).

Currently research into the use of xenon as an anesthetic gas is being pursued but it is very expensive to produce, and requires special equipment for delivery, monitoring and scavenging of unused gas.

Volatile agents are frequently compared in terms of potency, which is inversely proportional to the minimum alveolar concentration. Potency is directly related to lipid solubility. This is known as the Meyer-Overton hypothesis. However, certain pharmacokinetic properties of volatile agents have become another point of comparison. Most important of those properties is known as the blood:gas partition coefficient. This concept refers to the relative solubilty of a given agent in blood. Those agents with a lower blood solubility (i.e. a lower blood:gas partition coefficient, e.g. desflurane) give the anesthesia provider greater rapidity in titrating the depth of anesthesia, and permit a more rapid emergence from the anesthetic state upon discontinuing their administration. In fact, newer volatile agents (e.g. sevoflurane, desflurane) have been popular not due to their potency [minimum alveolar concentration], but their versatility for a faster emergence from anesthesia, thanks to their lower blood:gas partition coefficient.

Anesthetic monitoring

Patients being treated under general anesthetics must be monitored to ensure the patient's continued safety. This will generally include monitoring of heart rate (via ECG), oxygen saturation (via pulse oximetry), blood pressure, inspired and expired gases (for oxygen, nitrous oxide, carbon dioxide, and volatile agents), and may also include monitoring of temperature, arterial blood pressure and waveforms, central venous pressure, cerebral activity (via EEG), neuromuscular activity (via peripheral nervous monitoring), cardiac output, and urine output. In addition, the operating room's environment must be monitored for temperature and humidity and for buildup of exhaled inhalational anesthetics which might impair the function of operating room personnel. Also, preventative measures to avoid the buildup of static electricity must be observed as many anesthetics are flammable and can be ignited by static discharges.


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References

  1. ^ Utopian surgery: Early arguments against anaesthesiain surgery, dentistry and childbirth


See also

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