| Anesthesia | |
|---|---|
A child being prepared to go under anesthesia
| |
| Pronunciation | /ˌænɪsˈθiːziə, |
| MeSH | E03.155 |
| MedlinePlus | anesthesia |
| eMedicine | 1271543 |
Anesthesia or anaesthesia (from Greek "without sensation") is a state of controlled, temporary loss of sensation or awareness that is induced for medical purposes. It may include analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), or unconsciousness. A patient under the effects of anesthetic drugs is referred to as being anesthetized.
Anesthesia enables the painless performance of medical procedures that would otherwise cause severe or intolerable pain to an unanesthetized patient, or would otherwise be technically unfeasible. Three broad categories of anesthesia exist:
- General anesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation.
- Sedation suppresses the central nervous system to a lesser degree, inhibiting both anxiety and creation of long-term memories without resulting in unconsciousness.
- Regional and local anesthesia, which block transmission of nerve impulses from a specific part of the body. Depending on the situation, this may be used either on its own (in which case the patient remains conscious), or in combination with general anesthesia or sedation. Drugs can be targeted at peripheral nerves to anesthetize an isolated part of the body only, such as numbing a tooth for dental work or using a nerve block to inhibit sensation in an entire limb. Alternatively, epidural or spinal anesthesia can be performed in the region of the central nervous system itself, suppressing all incoming sensation from nerves outside the area of the block.
Risks during and following anesthesia are difficult to quantify, since many may be related to a variety of factors related to anesthesia itself, the nature of the procedure being performed and the patient's medical health. Examples of major risks include death, heart attack and pulmonary embolism whereas minor risks can include postoperative nausea and vomiting and hospital readmission. Of these factors, the person's health prior to the procedure(stratified by the ASA physical status classification system) has the greatest bearing on the probability of a complication occurring. Patients typically wake within minutes of anesthesia being terminated and regain their senses within hours.
Medical uses
The purpose of anesthesia can be distilled down to three basic goals or endpoints:
- hypnosis (a temporary loss of consciousness and with it a loss of memory. In a pharmacological context, the word hypnosis usually has this technical meaning, in contrast to its more familiar lay or psychological meaning of an altered state of consciousness not necessarily caused by drugs).
- analgesia (lack of sensation which also blunts autonomic reflexes)
- muscle relaxation
Different types of anesthesia affect the endpoints differently. Regional anesthesia, for instance, affects analgesia; benzodiazepine-type sedatives (used for sedation, or "twilight anesthesia") favor amnesia; and general anesthetics
can affect all of the endpoints. The goal of anesthesia is to achieve
the endpoints required for the given surgical procedure with the least
risk to the patient.
The anesthetic area of an operating room
To achieve the goals of anesthesia, drugs act on different but
interconnected parts of the nervous system. Hypnosis, for instance, is
generated through actions on the nuclei in the brain and is similar to the activation of sleep. The effect is to make people less aware and less reactive to noxious stimuli.
Loss of memory (amnesia) is created by action of drugs on multiple (but specific) regions of the brain. Memories are created as either declarative or non-declarative memories in several stages (short-term, long-term, long-lasting) the strength of which is determined by the strength of connections between neurons termed synaptic plasticity. Each anesthetic produces amnesia through unique effects on memory formation at variable doses. Inhalational anesthetics
will reliably produce amnesia through general suppression of the nuclei
at doses below those required for loss of consciousness. Drugs like midazolam produce amnesia through different pathways by blocking the formation of long-term memories.
Tied closely to the concepts of amnesia and hypnosis is the concept of consciousness.
Consciousness is the higher order process that synthesizes
information. For instance, the "sun" conjures up feelings, memories
and a sensation of warmth rather than a description of a round, orange
warm ball seen in the sky for part of a 24‑hour cycle. Likewise, a
person can have dreams (a state of subjective consciousness) during
anesthetic or have consciousness of the procedure despite having no
indication of it under anesthetic. It is estimated that 22% of people dream during general anesthesia and 1 or 2 cases per 1000 have some consciousness termed "awareness during general anesthesia".
Techniques
Safe anesthesia care depends greatly on well-functioning teams of highly trained healthcare workers. The medical specialty centred around anesthesia is called anesthesiology, and medical doctors
who practise it are termed anesthesiologists. Non-medical healthcare
workers involved in anesthesia provision have varying titles and roles
depending on the jurisdiction, and include nurse anesthetists, anesthetic nurses, anesthesiologist assistants, anaesthetic technicians, physicians' assistants (anaesthesia), operating department practitioners and anesthesia technologists. International standards for the safe practice of anesthesia, jointly endorsed by the World Health Organization and the World Federation of Societies of Anaesthesiologists,
highly recommend that anesthesia should be provided, overseen or led by
anesthesiologists, with the exception of minimal sedation or
superficial procedures performed under local anesthesia.
A trained, vigilant anesthesia provider should continually care for the
patient; where the provider is not an anesthesiologist, they should be
locally directed and supervised by an anesthesiologist, and in countries
or settings where this is not feasible, care should be led by the most
qualified local individual within a regional or national
anesthesiologist-led framework. The same minimum standards for patient safety
apply regardless of the provider, including continuous clinical and
biometric monitoring of tissue oxygenation, perfusion and blood
pressure; confirmation of correct placement of airway management devices by auscultation and carbon dioxide detection; use of the WHO Surgical Safety Checklist; and safe onward transfer of the patient's care following the procedure.
Anesthesia is unique in that it is not a direct means of
treatment; rather, it allows others to do things that may treat,
diagnose, or cure an ailment which would otherwise be painful or
complicated. The best anesthetic, therefore, is the one with the lowest
risk to the patient that still achieves the endpoints required to
complete the procedure. The first stage in anesthesia is the
pre-operative risk assessment consisting of the medical history, physical examination and lab tests.
Diagnosing a person's pre-operative physical status allows the
clinician to minimize anesthetic risks. A well completed medical
history will arrive at the correct diagnosis 56% of the time which
increases to 73% with a physical examination. Lab tests
help in diagnosis but only in 3% of cases, underscoring the need for a
full history and physical examination prior to anesthetics. Incorrect
pre-operative assessments or preparations are the root cause of 11% of
all adverse anesthetic events.
| ASA class | Physical status |
|---|---|
| ASA 1 | Healthy person |
| ASA 2 | Mild systemic disease |
| ASA 3 | Severe systemic disease |
| ASA 4 | Severe systemic disease that is a constant threat to life |
| ASA 5 | A moribund person who is not expected to survive without the operation |
| ASA 6 | A declared brain-dead person whose organs are being removed for donor purposes |
| E | Suffix added for patients undergoing emergency procedure |
One part of the risk assessment
is based on the patients' health. The American Society of
Anesthesiologists has developed a six-tier scale that stratifies the
patient's pre-operative physical state. It is called the ASA physical status. The scale assesses risk as the patient's general health relates to an anesthetic.
The more detailed pre-operative medical history aims to discover genetic disorders (such as malignant hyperthermia or pseudocholinesterase deficiency), habits (tobacco, drug and alcohol use), physical attributes (such as obesity or a difficult airway) and any coexisting diseases (especially cardiac and respiratory diseases) that might impact the anesthetic. The physical examination helps quantify the impact of anything found in the medical history in addition to lab tests.
Aside from the generalities of the patients health assessment, an
evaluation of specific factors as they relate to the surgery also need
to be considered for anesthesia. For instance, anesthesia during childbirth must consider not only the mother but the baby. Cancers and tumors that occupy the lungs or throat create special challenges to general anesthesia.
After determining the health of the person undergoing anesthetic and
the endpoints that are required to complete the procedure, the type of
anesthetic can be selected. Choice of surgical method and anesthetic
technique aims to reduce risk of complications, shorten time needed for
recovery and minimise the surgical stress response.
General anesthesia
A vaporizer holds a liquid anesthetic and converts it to gas for inhalation (in this case sevoflurane)
Anesthesia is a combination of the endpoints (discussed above) that
are reached by drugs acting on different but overlapping sites in the central nervous system. General anesthesia (as opposed to sedation or regional anesthesia) has three main goals: lack of movement (paralysis), unconsciousness, and blunting of the stress response.
In the early days of anesthesia, anesthetics could reliably achieve
the first two, allowing surgeons to perform necessary procedures, but
many patients died because the extremes of blood pressure and pulse
caused by the surgical insult were ultimately harmful. Eventually, the
need for blunting of the surgical stress response was identified by Harvey Cushing, who injected local anesthetic prior to hernia repairs. This led to the development of other drugs that could blunt the response leading to lower surgical mortality rates.
The most common approach to reach the endpoints of general anesthesia
is through the use of inhaled general anesthetics. Each anesthetic has
its own potency which is correlated to its solubility in oil. This
relationship exists because the drugs bind directly to cavities in
proteins of the central nervous system, although several theories of general anesthetic action
have been described. Inhalational anesthetics are thought to exact
their effects on different parts of the central nervous system. For
instance, the immobilizing effect of inhaled anesthetics results from an effect on the spinal cord whereas sedation, hypnosis and amnesia involve sites in the brain. The potency of an inhalational anesthetic is quantified by its minimum alveolar concentration
or MAC. The MAC is the percentage dose of anesthetic that will prevent
a response to painful stimulus in 50% of subjects. The higher the MAC,
generally, the less potent the anesthetic.
Syringes prepared with medications that are expected to be used during an operation under general anesthesia maintained by sevoflurane gas:
- Propofol, an hypnotic
- Ephedrine, in case of hypotension
- Fentanyl, for analgesia
- Atracurium, for neuromuscular blockade
- Glycopyrronium bromide (here under trade name "Robinul"), reducing secretions
The ideal anesthetic drug would provide hypnosis, amnesia, analgesia,
and muscle relaxation without undesirable changes in blood pressure,
pulse or breathing. In the 1930s, physicians started to augment inhaled
general anesthetics with intravenous
general anesthetics. The drugs used in combination offered a better
risk profile to the person under anesthesia and a quicker recovery. A
combination of drugs was later shown to result in lower odds of dying in
the first 7 days after anesthetic. For instance, propofol (injection) might be used to start the anesthetic, fentanyl (injection) used to blunt the stress response, midazolam (injection) given to ensure amnesia and sevoflurane
(inhaled) during the procedure to maintain the effects. More recently,
several intravenous drugs have been developed which, if desired, allow
inhaled general anesthetics to be avoided completely.
Equipment
The core instrument in an inhalational anesthetic delivery system is an anesthetic machine. It has vaporizers, ventilators,
an anesthetic breathing circuit, waste gas scavenging system and
pressure gauges. The purpose of the anesthetic machine is to provide
anesthetic gas at a constant pressure, oxygen for breathing and to
remove carbon dioxide or other waste anesthetic gases. Since
inhalational anesthetics are flammable, various checklists have been
developed to confirm that the machine is ready for use, that the safety
features are active and the electrical hazards are removed. Intravenous anesthetic is delivered either by bolus doses or an infusion pump. There are also many smaller instruments used in airway management and monitoring the patient. The common thread to modern machinery in this field is the use of fail-safe systems that decrease the odds of catastrophic misuse of the machine.
Monitoring
An anesthetic machine with integrated systems for monitoring of several vital parameters.
Patients under general anesthesia must undergo continuous physiological monitoring to ensure safety. In the US, the American Society of Anesthesiologists
(ASA) has established minimum monitoring guidelines for patients
receiving general anesthesia, regional anesthesia, or sedation. These
include electrocardiography (ECG), heart rate, blood pressure, inspired
and expired gases, oxygen saturation of the blood (pulse oximetry), and
temperature.
In the UK the Association of Anaesthetists (AAGBI) have set minimum
monitoring guidelines for general and regional anesthesia. For minor
surgery, this generally includes monitoring of heart rate, oxygen saturation, blood pressure, and inspired and expired concentrations for oxygen, carbon dioxide,
and inhalational anesthetic agents. For more invasive surgery,
monitoring may also include temperature, urine output, blood pressure, central venous pressure, pulmonary artery pressure and pulmonary artery occlusion pressure, cardiac output, cerebral activity,
and neuromuscular function. In addition, the operating room environment
must be monitored for ambient temperature and humidity, as well as for
accumulation of exhaled inhalational anesthetic agents, which might be
deleterious to the health of operating room personnel.
Sedation
Sedation (also referred to as dissociative anesthesia or twilight anesthesia) creates hypnotic, sedative, anxiolytic, amnesic, anticonvulsant,
and centrally produced muscle-relaxing properties. From the
perspective of the person giving the sedation, the patient appears
sleepy, relaxed and forgetful, allowing unpleasant procedures to be more
easily completed. Sedatives such as benzodiazepines are usually given with pain relievers (such as narcotics, or local anesthetics or both) because they do not, by themselves, provide significant pain relief.
From the perspective of the person receiving a sedative, the
effect is a feeling of general relaxation, amnesia (loss of memory) and
time passing quickly. Many drugs can produce a sedative effect
including benzodiazepines, propofol, thiopental, ketamine
and inhaled general anesthetics. The advantage of sedation over a
general anesthetic is that it generally does not require support of the
airway or breathing (no tracheal intubation or mechanical ventilation) and can have less of an effect on the cardiovascular system which may add to a greater margin of safety in some patients.
Regional anesthesia
Sonography guided femoral nerve block
Backflow of cerebrospinal fluid through a spinal needle after puncture of the arachnoid mater during spinal anesthesia
When pain is blocked from a part of the body using local anesthetics,
it is generally referred to as regional anesthesia. There are many
types of regional anesthesia either by injecting into the tissue itself,
a vein that feeds the area or around a nerve trunk that supplies
sensation to the area. The latter are called nerve blocks and are
divided into peripheral or central nerve blocks.
The following are the types of regional anesthesia:
- Infiltrative anesthesia: a small amount of local anesthetic is injected in a small area to stop any sensation (such as during the closure of a laceration, as a continuous infusion or "freezing" a tooth). The effect is almost immediate.
- Peripheral nerve block: local anesthetic is injected near a nerve that provides sensation to particular portion of the body. There is significant variation in the speed of onset and duration of anesthesia depending on the potency of the drug (e.g. Mandibular block).
- Intravenous regional anesthesia (also called a Bier block): dilute local anesthetic is infused to a limb through a vein with a tourniquet placed to prevent the drug from diffusing out of the limb.
- Central nerve blockade: Local anesthetic is injected or infused in or around a portion of the central nervous system (discussed in more detail below in Spinal, epidural and caudal anesthesia).
- Topical anesthesia: local anesthetics that are specially formulated to diffuse through the mucous membranes or skin to give a thin layer of analgesia to an area (e.g. EMLA patches).
- Tumescent anesthesia: a large amount of very dilute local anesthetics are injected into the subcutaneous tissues during liposuction.
- Systemic local anesthetics: local anesthetics are given systemically (orally or intravenous) to relieve neuropathic pain
Nerve blocks
When local anesthetic is injected around a larger diameter nerve that transmits sensation from an entire region it is referred to as a nerve block or regional nerve blockade. Nerve blocks are commonly used in dentistry, when the mandibular nerve is blocked for procedures on the lower teeth. With larger diameter nerves (such as the interscalene block for upper limbs or psoas compartment block for lower limbs) the nerve and position of the needle is localized with ultrasound
or electrical stimulation. The use of ultrasound may reduce
complication rates and improve quality, performance time, and time to
onset of blocks. Because of the large amount of local anesthetic
required to affect the nerve, the maximum dose of local anesethetic has
to be considered. Nerve blocks are also used as a continuous infusion,
following major surgery such as knee, hip and shoulder replacement
surgery, and may be associated with lower complications.
Nerve blocks are also associated with a lower risk of neurologic
complications compared to the more central epidural or spinal neuraxial
blocks.
Spinal, epidural and caudal anesthesia
Central neuraxial anesthesia is the injection of local anesthetic around the spinal cord to provide analgesia in the abdomen, pelvis or lower extremities. It is divided into either spinal (injection into the subarachnoid space), epidural (injection outside of the subarachnoid space into the epidural space) and caudal (injection into the cauda equina or tail end of the spinal cord). Spinal and epidural are the most commonly used forms of central neuraxial blockade.
Spinal anesthesia
is a "one-shot" injection that provides rapid onset and profound
sensory anesthesia with lower doses of anesethetic, and is usually
associated with neuromuscular blockade (loss of muscle control). Epidural anesthesia
uses larger doses of anesthetic infused through an indwelling catheter
which allows the anesthetic to be augmented should the effects begin to
dissipate. Epidural anesthesia does not typically affect muscle control.
Because central neuraxial blockade causes arterial and vasodilation, a drop in blood pressure is common. This drop is largely dictated by the venous side of the circulatory system which holds 75% of the circulating blood volume. The physiologic effects are much greater when the block is placed above the 5th thoracic vertebra. An ineffective block is most often due to inadequate anxiolysis or sedation rather than a failure of the block itself.
Acute pain management
Pain that is well managed during and immediately after surgery
improves the health of patients (by decreasing physiologic stress) and
the potential for chronic pain. Nociception
(pain sensation) is not hard-wired into the body. Instead, it is a
dynamic process wherein persistent painful stimuli can sensitize the
system and either make pain management difficult or promote the
development of chronic pain. For this reason, preemptive acute pain
management may reduce both acute and chronic pain and is tailored to the
surgery, the environment in which it is given (in-patient/out-patient)
and the individual patient.
Pain management is classified into either pre-emptive or on-demand. On-demand pain medications typically include either opioid or non-steroidal anti-inflammatory drugs but can also make use of novel approaches such as inhaled nitrous oxide or ketamine. On demand drugs can be administered by a clinician ("as needed drug orders") or by the patient using patient-controlled analgesia
(PCA). PCA has been shown to provide slightly better pain control and
increased patient satisfaction when compared with conventional methods. Common preemptive approaches include epidural neuraxial blockade or nerve blocks. One review which looked at pain control after abdominal aortic surgery
found that epidural blockade provides better pain relief (especially
during movement) in the period up to three postoperative days. It
reduces the duration of postoperative tracheal intubation by roughly half. The occurrence of prolonged postoperative mechanical ventilation and myocardial infarction is also reduced by epidural analgesia.
Risks and complications
Risks and complications as they relate to anesthesia are classified
as either morbidity (a disease or disorder that results from anesthesia)
or mortality
(death that results from anesthesia). Quantifying how anesthesia
contributes to morbidity and mortality can be difficult because a
person's health prior to surgery and the complexity of the surgical
procedure can also contribute to the risks.
Anesthesia-related deaths by ASA status
Prior to the introduction of anesthesia in the early 19th century, the physiologic stress from surgery caused significant complications and many deaths from shock.
The faster the surgery was, the lower the rate of complications
(leading to reports of very quick amputations). The advent of
anesthesia allowed more complicated and life-saving surgery to be
completed, decreased the physiologic stress of the surgery, but added an
element of risk. It was two years after the introduction of ether
anesthetics that the first death directly related to the use of
anesthesia was reported.
Morbidity can be major (myocardial infarction, pneumonia, pulmonary embolism, renal failure/insufficiency, postoperative cognitive dysfunction and allergy) or minor (minor nausea,
vomiting, readmission). There is usually overlap in the contributing
factors that lead to morbidity and mortality between the health of the
patient, the type of surgery being performed and the anesthetic. To
understand the relative risk
of each contributing factor, consider that the rate of deaths totally
attributed to the patient's health is 1:870. Compare that to the rate
of deaths totally attributed to surgical factors (1:2860) or anesthesia
alone (1:185,056) illustrating that the single greatest factor in
anesthetic mortality is the health of the patient. These statistics can
also be compared to the first such study on mortality in anesthesia
from 1954, which reported a rate of death from all causes at 1:75 and a
rate attributed to anesthesia alone at 1:2680.
Direct comparisons between mortality statistics cannot reliably be
made over time and across countries because of differences in the
stratification of risk factors, however, there is evidence that
anesthetics have made a significant improvement in safety but to what degree is uncertain.
Rather than stating a flat rate of morbidity or mortality, many factors are reported as contributing to the relative risk
of the procedure and anesthetic combined. For instance, an operation
on a person who is between the ages of 60–79 years old places the
patient at 2.3 times greater risk than someone less than 60 years old.
Having an ASA score of 3, 4 or 5 places the person at 10.7 times greater
risk than someone with an ASA score of 1 or 2. Other variables include
age greater than 80 (3.3 times risk compared to those under 60), gender
(females have a lower risk of 0.8), urgency of the procedure
(emergencies have a 4.4 times greater risk), experience of the person
completing the procedure (less than 8 years experience and/or less than
600 cases have a 1.1 times greater risk) and the type of anesthetic
(regional anesthetics are lower risk than general anesthetics). Obstetrical, the very young and the very old are all at greater risk of complication so extra precautions may need to be taken.
On 14 December 2016 the Food and Drug Administration issued a
Public Safety Communication warning that "repeated or lengthy use of
general anesthetic and sedation drugs during surgeries or procedures in
children younger than 3 years or in pregnant women during their third
trimester may affect the development of children’s brains."
The warning was criticized by the American College of Obstetricians and
Gynecologists, which pointed out the absence of direct evidence
regarding use in pregnant women and the possibility that "this warning
could inappropriately dissuade providers from providing medically
indicated care during pregnancy."
Patient advocates noted that a randomized clinical trial would be
unethical, that the mechanism of injury is well-established in animals,
and that studies had shown exposure to multiple uses of anesthetic
significantly increased the risk of developing learning disabilities in
young children, with a hazard ratio of 2.12 (95% confidence interval, 1.26–3.54).
Recovery
The immediate time after anesthesia is called emergence. Emergence from general anesthesia or sedation requires careful monitoring because there is still a risk of complication. Nausea and vomiting are reported at 9.8% but will vary with the type of anesthetic and procedure. There is a need for airway support in 6.8%, there can be urinary retention (more common in those over 50 years of age) and hypotension in 2.7%. Hypothermia,
shivering and confusion are also common in the immediate post-operative
period because of the lack of muscle movement (and subsequent lack of
heat production) during the procedure.
Postoperative cognitive dysfunction (also known as POCD and post-anesthetic confusion) is a disturbance in cognition after surgery. It may also be variably used to describe emergence delirium
(immediate post-operative confusion) and early cognitive dysfunction
(diminished cognitive function in the first post-operative week).
Although the three entities (delirium, early POCD and long-term POCD)
are separate, the presence of delirium post-operatively predicts the
presence of early POCD. There does not appear to be an association
between delirium or early POCD and long-term POCD.
According to a recent study conducted at the David Geffen School of
Medicine at UCLA, the brain navigates its way through a series of
activity clusters, or "hubs" on its way back to consciousness. Dr.
Andrew Hudson, an assistant professor in anesthesiology states,
"Recovery from anesthesia is not simply the result of the anesthetic
'wearing off,' but also of the brain finding its way back through a maze
of possible activity states to those that allow conscious experience.
Put simply, the brain reboots itself."
Long-term POCD is a subtle deterioration in cognitive function,
that can last for weeks, months, or longer. Most commonly, relatives of
the person report a lack of attention, memory and loss of interest in
activities previously dear to the person (such as crosswords). In a
similar way, people in the workforce may report an inability to complete
tasks at the same speed they could previously. There is good evidence that POCD occurs after cardiac surgery and the major reason for its occurrence is the formation of microemboli.
POCD also appears to occur in non-cardiac surgery. Its causes in
non-cardiac surgery are less clear but older age is a risk factor for
its occurrence.
History
The first attempts at general anesthesia were probably herbal remedies administered in prehistory. Alcohol is one of the oldest known sedatives and it was used in ancient Mesopotamia thousands of years ago. The Sumerians are said to have cultivated and harvested the opium poppy (Papaver somniferum) in lower Mesopotamia as early as 3400 BC.
The ancient Egyptians had some surgical instruments, as well as crude analgesics and sedatives, including possibly an extract prepared from the mandrake fruit. Bian Que (Chinese: 扁鹊, Wade–Giles: Pien Ch'iao, c. 300 BC) was a legendary Chinese internist and surgeon who reportedly used general anesthesia for surgical procedures.
Throughout Europe, Asia, and the Americas a variety of Solanum species containing potent tropane alkaloids were used for anesthesia. In 13th-century Italy, Theodoric Borgognoni
used similar mixtures along with opiates to induce unconsciousness, and
treatment with the combined alkaloids proved a mainstay of anesthesia
until the nineteenth century. Local anesthetics were used in Inca civilization where shamans chewed coca leaves and performed operations on the skull while spitting into the wounds they had inflicted to anesthetize. Cocaine was later isolated and became the first effective local anesthetic. It was first used in 1859 by Karl Koller, at the suggestion of Sigmund Freud, in eye surgery in 1884. German surgeon August Bier (1861–1949) was the first to use cocaine for intrathecal anesthesia in 1898. Romanian surgeon Nicolae Racoviceanu-Piteşti (1860–1942) was the first to use opioids for intrathecal analgesia; he presented his experience in Paris in 1901.
Early Arab writings mention anesthesia by inhalation. This idea
was the basis of the "soporific sponge" ("sleep sponge"), introduced by
the Salerno school of medicine in the late twelfth century and by Ugo Borgognoni (1180–1258) in the thirteenth century. The sponge was promoted and described by Ugo's son and fellow surgeon, Theodoric Borgognoni (1205–1298). In this anesthetic method, a sponge was soaked in a dissolved solution of opium, mandragora,
hemlock juice, and other substances. The sponge was then dried and
stored; just before surgery the sponge was moistened and then held under
the patient's nose. When all went well, the fumes rendered the patient
unconscious.
Sir Humphry Davy’s Researches chemical and philosophical: chiefly concerning nitrous oxide (1800), pages 556 and 557 (right), outlining potential anesthetic properties of nitrous oxide in relieving pain during surgery
The most famous anesthetic, ether, may have been synthesized as early as the 8th century,
but it took many centuries for its anesthetic importance to be
appreciated, even though the 16th century physician and polymath Paracelsus
noted that chickens made to breathe it not only fell asleep but also
felt no pain. By the early 19th century, ether was being used by humans,
but only as a recreational drug.
Meanwhile, in 1772, English scientist Joseph Priestley discovered the gas nitrous oxide. Initially, people thought this gas to be lethal, even in small doses, like some other nitrogen oxides. However, in 1799, British chemist and inventor Humphry Davy
decided to find out by experimenting on himself. To his astonishment he
found that nitrous oxide made him laugh, so he nicknamed it "laughing
gas".
In 1800 Davy wrote about the potential anesthetic properties of nitrous
oxide in relieving pain during surgery, but nobody at that time pursued
the matter any further.
American physician Crawford W. Long
noticed that his friends felt no pain when they injured themselves
while staggering around under the influence of diethyl ether. He
immediately thought of its potential in surgery. Conveniently, a
participant in one of those "ether frolics", a student named James
Venable, had two small tumors he wanted excised. But fearing the pain of
surgery, Venable kept putting the operation off. Hence, Long suggested
that he have his operation while under the influence of ether. Venable
agreed, and on 30 March 1842 he underwent a painless operation. However,
Long did not announce his discovery until 1849.
.jpg)
Contemporary re-enactment of Morton's 16 October 1846, ether operation; daguerrotype by Southworth & Hawes
Morton's ether inhaler
Horace Wells conducted the first public demonstration of the inhalational anesthetic at the Massachusetts General Hospital in Boston in 1845. However, the nitrous oxide was improperly administered and the patient cried out in pain. On 16 October 1846, Boston dentist William Thomas Green Morton gave a successful demonstration using diethyl ether to medical students at the same venue. Morton, who was unaware of Long's previous work, was invited to the Massachusetts General Hospital to demonstrate his new technique for painless surgery. After Morton had induced anesthesia, surgeon John Collins Warren removed a tumor from the neck of Edward Gilbert Abbott. This occurred in the surgical amphitheater now called the Ether Dome.
The previously skeptical Warren was impressed and stated, "Gentlemen,
this is no humbug." In a letter to Morton shortly thereafter, physician
and writer Oliver Wendell Holmes, Sr. proposed naming the state produced "anesthesia", and the procedure an "anesthetic".
Morton at first attempted to hide the actual nature of his anesthetic substance, referring to it as Letheon. He received a US patent for his substance, but news of the successful anesthetic spread quickly by late 1846. Respected surgeons in Europe including Liston, Dieffenbach, Pirogov, and Syme
quickly undertook numerous operations with ether. An American-born
physician, Boott, encouraged London dentist James Robinson to perform a
dental procedure on a Miss Lonsdale. This was the first case of an
operator-anesthetist. On the same day, 19 December 1846, in Dumfries
Royal Infirmary, Scotland, a Dr. Scott used ether for a surgical
procedure. The first use of anesthesia in the Southern Hemisphere took place in Launceston, Tasmania, that same year. Drawbacks with ether such as excessive vomiting and its explosive flammability led to its replacement in England with chloroform.
Discovered in 1831 by an American physician Samuel Guthrie
(1782–1848), and independently a few months later by Frenchman Eugène
Soubeiran (1797–1859) and Justus von Liebig (1803–73) in Germany,
chloroform was named and chemically characterised in 1834 by
Jean-Baptiste Dumas (1800–84). In 1842, Dr Robert Mortimer Glover in London discovered the anaesthetic qualities of chloroform on laboratory animals. In 1847, Scottish obstetrician James Young Simpson
was the first to demonstrate the anesthetic properties of chloroform on
humans and helped to popularise the drug for use in medicine. Its use spread quickly and gained royal approval in 1853 when John Snow gave it to Queen Victoria during the birth of Prince Leopold. During the birth itself, chloroform met all the Queen’s expectations; she stated it was “delightful beyond measure”.
Unfortunately, though free of ether's flammability and consequent
explosion hazard, chloroform is not as safe pharmacologically,
especially when administered by an untrained practitioner (medical students,
nurses, and occasionally members of the public were often pressed into
giving anesthetics at this time). This led to many deaths from the use
of chloroform that (with hindsight) might have been preventable. The
first fatality directly attributed to chloroform anesthesia was recorded
on 28 January 1848 after the death of Hannah Greener.
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 the administration of inhalational anesthetics, the forerunner of today's anesthesia machines.
The first comprehensive medical textbook on the subject, Anesthesia, was authored in 1914 by anesthesiologist Dr. James Tayloe Gwathmey and the chemist Dr. Charles Baskerville.
This book served as the standard reference for the specialty for
decades and included details on the history of anesthesia as well as the
physiology and techniques of inhalation, rectal, intravenous, and
spinal anesthesia.
Of these first famous anesthetics, only nitrous oxide is still
widely used today, with chloroform and ether having been replaced by
safer but sometimes more expensive general anesthetics, and cocaine by more effective local anesthetics with less abuse potential.
Society and culture
Almost all healthcare providers use anesthetic drugs to some degree,
but most health professions have their own field of specialists in the
field including medicine, nursing and dentistry.
Doctors specializing in anaesthesiology, including perioperative care, development of an anesthetic plan, and the administration of anesthetics are known in the US as anesthesiologists and in the UK, Canada, Australia, and NZ as anaesthetists or anaesthesiologists. All anesthetics in the UK, Australia, New Zealand, Hong Kong and Japan are administered by doctors. Nurse anesthetists also administer anesthesia in 109 nations. In the US, 35% of anesthetics are provided by physicians in solo practice, about 55% are provided by anesthesia care teams (ACTs) with anesthesiologists medically directing anesthesiologist assistants or certified registered nurse anesthetists (CRNAs), and about 10% are provided by CRNAs in solo practice. There can also be anesthesiologist assistants (US) or physicians' assistants (anaesthesia) (UK) who assist with anesthesia.
Special populations
There are many circumstances when anesthesia needs to be altered for special circumstances due to the procedure (such as in cardiac surgery, cardiothoracic anesthesiology or neurosurgery), the patient (such as in pediatric anesthesia, geriatric, bariatric or obstetrical anesthesia) or special circumstances (such as in trauma, prehospital care, robotic surgery or extreme environments).
