Anaesthesia and perioperative care
Anaesthesia controls sensation and consciousness for procedures, while perioperative care manages the patient's condition before, during and after surgery.
Scope of anaesthesiology
Anaesthesiologists are physicians who manage comfort and vital life functions before, during and after surgery. Their work also includes emergency departments, intensive care units, pain management clinics and procedures such as cardiac ablation for atrial fibrillation. Advances in anaesthesia have expanded what surgery can treat, while the specialty's diagnostic and treatment work extends beyond the operating room.
Perioperative care
Before surgery
The preoperative visit includes a review of medical and surgical history, planning and anticipation of problems in the operating room. Patients whose physical condition needs improvement may be referred to their primary care or specialist physician for optimisation. The anaesthesiologist classifies health using the American Society of Anesthesiologists (ASA) physical status classification.
| Class | Physical status |
|---|---|
| ASA 1 | Normal healthy patient |
| ASA 2 | Patient with mild systemic disease |
| ASA 3 | Patient with severe systemic disease |
| ASA 4 | Patient with severe systemic disease that is a constant threat to life |
| ASA 5 | Moribund patient not expected to survive without the operation |
| ASA 6 | Declared brain-dead patient whose organs are being removed for donation |
The letter E after the number identifies an emergency case.
On the day of surgery, the anaesthesiologist reviews records for changes since the clinic visit, explains what to expect and provides an opportunity for questions. An intravenous line is placed, and a benzodiazepine such as midazolam may be given to relieve anxiety. Opioids such as fentanyl or morphine may be given incrementally for pain. Measures to neutralise gastric acid and reduce gastric volume are used for patients at increased aspiration risk, including those with a recent meal, trauma, pregnancy or acid reflux. Peripheral nerve blocks or epidural catheters may provide intraoperative pain control, with indwelling catheters also providing postoperative analgesia. Patients are monitored frequently in the holding area and checked by the nurse and surgeon before transfer to the operating room.
During surgery and recovery
The procedure and the patient's medical history inform the choice among general anaesthesia, regional anaesthesia and monitored anaesthesia care. During surgery, the anaesthesiologist manages consciousness, pain, breathing, heart rhythm and blood pressure, and diagnoses and treats medical problems arising during surgery or recovery. Comorbidities and conditions such as obesity make management of critical life functions more complex.
After surgery, specially trained nurses monitor the patient in the postanaesthesia care unit under the anaesthesiologist's guidance. Vital signs are monitored until the patient is fully awake and clinically stable, while nausea, vomiting, hypertension and pain are treated until the patient is comfortable and ready for discharge home or transfer to another hospital bed.
General anaesthesia
General anaesthesia produces unconsciousness through drugs with different effects. The aims of general anaesthesia are listed below.
- Hypnosis: producing unconsciousness.
- Amnesia: preventing memory formation.
- Analgesia: blocking the conscious sensation of pain.
- Paralysis: preventing unwanted movement or muscle tone.
- Obtundation of reflexes: preventing exaggerated autonomic reflexes.
Anaesthesia proceeds through induction, maintenance and emergence. Induction runs from the start of anaesthetisation to adequate anaesthesia for the intended procedure and can use intravenous or inhalational agents. Emergence is the recovery of normal function after general anaesthesia.
An endotracheal tube is a flexible plastic tube that can pass through the mouth and larynx into the trachea, with a laryngoscope used to view the larynx during intubation. It connects the patient to an anaesthesia machine whose ventilator delivers oxygen and inhalational agents; a laryngeal mask airway or face mask may be used instead. Rapid-sequence induction is used for patients at increased risk of aspirating gastric contents. Specialised pumps deliver intravenous agents for maintenance when that approach is chosen. Muscle relaxants keep the patient immobile, while the anaesthesiologist maintains physiological stability and safety in the unconscious patient with depressed reflexes.
Regional anaesthesia
Regional anaesthesia acts on the part of the body being operated on, delivering pain-relieving drugs or local anaesthetics such as lidocaine near the nerves carrying pain messages from the incision. It can use a single dose before surgery or continuous or repeated dosing through a small catheter, and can provide prolonged postoperative analgesia. Epidural analgesia delivers drugs through a catheter around the spinal canal, while intrathecal administration introduces them into the subarachnoid space to mix with cerebrospinal fluid.
Epidural analgesia gained acceptance in Europe and South America before North America, with labour and delivery analgesia prompting its adoption by several hospitals. Epidural and spinal anaesthesia can provide anaesthesia for surgery below the umbilicus.
Monitored anaesthesia care
Monitored anaesthesia care accompanies diagnostic or therapeutic procedures and includes a presurgical visit, intraoperative care and postanaesthesia management. It may involve sedation, analgesia and relief of anxiety, or anxiolysis, according to the patient's needs. The anaesthesiologist supports vital functions, treats clinical problems and provides medications, psychological support and physical comfort needed for safe completion of the procedure. The provider must be prepared to administer general anaesthesia when necessary, including when the airway needs to be secured.
Monitoring and emergence
Monitoring includes pulse oximetry, blood pressure measurement, electrocardiography and end-tidal carbon dioxide monitoring. Complex surgery may require transoesophageal echocardiography, which provides real-time information about heart size, shape, pumping capacity, wall motion and tissue damage, and helps assess valves and abnormal blood flow. Its ultrasound transducer is positioned in the oesophagus to view valves and chambers without interference from the ribs or lungs.
At the end of surgery, medications are reduced as the patient wakes, sometimes with reversal agents, particularly for muscle relaxants. Naloxone reverses opioid effects, and flumazenil reverses benzodiazepine effects; either may be used when necessary.
Development of anaesthesia
Surgical pain relief and inhaled agents
Early surgical pain relief included alcoholic mixtures, pressure on nerves and blood vessels, inhalants, substances applied locally and mesmerism, with variable results. Medieval manuscripts described a soporific sponge containing ingredients thought to include scopolamine and opium: inhalation was intended to induce unconsciousness, followed by a vinegar-soaked sponge to wake the patient, although recovery did not always occur.
Valerius Cordus described ether synthesis in 1540, and Joseph Priestley discovered nitrous oxide in 1772. Humphry Davy described nitrous oxide's analgesic potential in 1800, and Henry Hill Hickman demonstrated carbon dioxide's effects in small animals in 1824 and proposed inhalation in humans, without gaining acceptance. In 1839, the French surgeon Louis Velpeau still considered removing surgical pain an unreal possibility.
Several people claimed priority for anaesthesia: Crawford Long removed a neck tumour under ether in 1842 but published in 1849; Charles Jackson claimed to have recognised ether's anaesthetic properties in 1842 without using it as an anaesthetic; and Horace Wells recognised nitrous oxide's effects in 1844 after witnessing an injury without immediate pain and then undergoing a painless molar extraction with the gas. William Morton's public demonstration of painless tumour removal under ether followed in 1846. Oliver Wendell Holmes Sr coined the word anaesthesia in 1846. John Snow investigated the basic science of anaesthetic agents from 1847 to 1851. Before reliable anaesthesia, surgery could involve extreme pain: the novelist Fanny Burney described prolonged screaming during her mastectomy roughly 30 years before Morton's demonstration.
Inhaled agents entered practice as nitrous oxide for dental anaesthesia in 1844, ether in 1846 and chloroform in 1847. Historical delivery devices included nineteenth-century Schimmelbusch ether masks, paediatric ether masks from about the 1880s–1920s and Trimar masks from about the 1950s–1960s. The search for less flammable and less hepatotoxic agents continued in the early 1930s. Halothane was synthesised in 1951, but reports of liver injury prompted alternatives; methoxyflurane also caused renal and liver injury, followed by enflurane and its isomer isoflurane. The Analgizer, introduced in 1968, was a lightweight disposable plastic inhaler for self-administering methoxyflurane during labour. Later agents included sevoflurane and desflurane, with faster onset and emergence, while more reliable vaporizers improved control of delivered amounts.
Cocaine was isolated in 1859 and used by Karl Koller for ophthalmic surgery in 1884; earlier local approaches included salt with ice and ether or ethyl chloride sprays. Subsequent developments included cocaine derivatives and safer replacements such as lidocaine.
Intravenous agents and specialty recognition
Sodium evipal in 1933, sodium thiopental in 1934, curare in 1942 and propofol in 1977 changed anaesthetic practice, while fentanyl was synthesised in 1960. Intravenous agents enabled wholly intravenous anaesthesia as an alternative to inhalational anaesthesia.
Specialty recognition involved technological, socioeconomic and professional forces as well as formal training and basic science, with recognition developing in the late 1930s. Waters and Lundy in the United States, Magill and Macintosh in the United Kingdom, and Bourne and Griffith in Canada contributed to specialty development. American medical schools began appointing anaesthesiologists in the early 1900s, and Waters developed a programme in Madison, Wisconsin, and advocated for an examining board. In the 1940s, the American Medical Association approved anaesthesiology as a section distinct from surgery, supporting consultant qualifications, an approved curriculum and candidate assessment.
Patient safety and professional organisation
An estimated one to two deaths per 10,000 procedures were attributed to anaesthesia care in the 1950s–1970s. Concern about these deaths and media attention to accidents in the 1980s led the ASA to establish a safety and risk management committee, while the independent Anesthesia Patient Safety Foundation was formed for safety research and education. Equipment and technology advances helped anaesthesiologists keep patients safer during operations. Safety advances included continuous real-time monitoring, drugs with fewer side effects, and simulators for training residents and fellows. In 2005, a front-page Wall Street Journal story praised anaesthesiologists' patient safety work.
The ASA grew from a professional anaesthesia society formed by nine New York medical colleagues and served 43,000 members in 2010 as an educational, research and scientific association of physicians. Its standards set rules or minimum clinical practice requirements, guidelines recommend approaches to healthcare decisions, and statements express the opinions, beliefs and best medical judgments of its House of Delegates.
In 2010, the US training route comprised four years of undergraduate study with a premedical curriculum, four years of medical school and a four-year anaesthesiology residency, followed by eligibility for the American Board of Anesthesiology examination; subspecialty training added one or two years. Subspecialty societies address their members' educational and clinical needs, and an ASA committee maintains alignment and communication with them.
Subspecialties
Critical care anaesthesiologists provide intensive or invasive monitoring after major surgery and support patients with haemodynamic instability, respiratory or airway compromise, multiorgan dysfunction, potentially lethal cardiac dysrhythmias and sepsis. Anaesthesiology was the first medical specialty to develop a subspecialty board examination in critical care.
Paediatric anaesthesiologists manage general anaesthesia, sedation and pain for newborns through teenagers, evaluating complex problems, planning care before and after surgery and providing a nonthreatening operating-room environment. They also provide anaesthesia or sedation for magnetic resonance imaging, computed tomography and radiotherapy.
Cardiovascular anaesthesiologists care for patients undergoing cardiac, thoracic or vascular surgery, using specialised monitoring and drugs where required. Monitoring may involve arterial, central venous or pulmonary artery catheters, or transoesophageal echocardiography. Cardiopulmonary bypass often takes over heart and lung functions during cardiac surgery while the heart is kept immobile.
Other fields include ambulatory, bariatric, geriatric, neurological and obstetric anaesthesia, with some programmes offering fellowships. Ambulatory or outpatient anaesthesia is provided to patients going home the same day, while bariatric anaesthesia serves patients with morbid obesity. Anaesthesiology also developed a subspecialty covering acute and chronic pain, including cancer-related pain.