Anesthesiology is the field of medicine focusing on interventions that bring about a state of anesthesia, which is characterized by a reversible loss of consciousness, as well as analgesia, amnesia, and muscle relaxation.
State of anesthesia
- Induced via the administration of gaseous or injectable agents before surgical procedures or other medical interventions
- Analgesia: relief from pain or the prevention of pain
- Amnesia: loss of awareness and/or memory of pain/experience
- Hypnosis: temporary unconsciousness or the absence of anxiety
- Paralysis: adequate muscle relaxation
Certified personnel who perform and manage anesthesia
- Certified registered nurse anesthetists
- Anesthesia assistants
Settings where anesthesia is performed
- Endoscopy suites
- Interventional radiology suites
- Interventional cardiology laboratories
- Ambulatory surgical centers (centers for “day surgery”)
- Post-anesthesia care units (PACUs)
- The practice of medicine was transformed in the middle of the 19th century with the discovery of general anesthesia.
- In previous centuries, surgery was performed as a last resort and desperate measure due to the unbearable pain it caused.
- The use of chemical compounds to induce a state of anesthesia in modern medicine dates back to the 18th century with the introduction of inhaled anesthetics.
|4000 BCE–0 CE||The use of opium poppy; herbal remedies using Hyoscyamus niger, Mandragora, and aconitum; and acupuncture performed with bones, cannabis vapors, and carotid compression is documented in records from ancient China, Greece, and Egypt.|
|2000 CE–present||The American Society of Anesthesiologists establishes a Simulation Education Network (SEN) to continue educating and certifying anesthesiologists.|
Focused evaluation and planning for anesthesia should be completed in advance for all surgeries, interventions, and procedures.
- Risk stratification is an important part of preoperative planning.
- Low-risk individuals can be evaluated immediately before anesthesia on the day of the procedure.
- Low-risk individuals are those who are:
- < 65 years of age
- Having stable and adequately controlled medical conditions
- Undergoing low-risk procedures
- Risk increase with:
- Complexity of comorbid medical conditions
- Complexity of planned anesthesia and/or medical/surgical procedures
- Duration of planned anesthesia and/or medical/surgical procedures
- Low-risk individuals are those who are:
- Intermediate-to-high risk may need stabilization and/or optimization of comorbid medical conditions prior to anesthesia and/or planned procedures.
- Emergency anesthesia and/or planned procedure necessitate the initiation of measures with minimal preparation time and are, by their very nature, high risk.
- Assessing medical status and readiness for the planned procedure
- Reducing the risks of anesthesia and surgery
- Creating an anesthetic plan and preparing the individual
Components of preoperative evaluation
- Clinical evaluation:
- Medical history
- Current medications
- History of prior anesthesia and surgeries
- Physical examination
- Risk assessment:
- Evaluation of factors that increase the likelihood of perioperative morbidity and mortality
- An objective observation commonly used by the anesthesiology team to create ventilation and intubation plans
- Assessment of the anatomy of the head and neck to determine the difficulty of intubation:
- Mallampati classification is used to assess ease of airway access for intubation.
- Graded I–IV based on the difficulty associated with oropharyngeal characteristics
- Inclusion of the individual’s underlying health problems
- Identification of medication allergies
- Response to prior anesthesia methods
- Other aids in risk assessment include:
- Prognostic biomarkers (e.g., B-type natriuretic peptide)
- CBC (to rule out anemia, infection, thrombocytopenia)
- Electrolyte panel (to evaluate electrolyte imbalance and metabolic disturbance)
- Coagulation studies (to evaluate for coagulopathy)
- Creatinine, GFR
- Functional status/ability to engage in daily activities as reported subjectively by the individual
- Optimization of diseases and comorbidities:
- Optimally managing and treating comorbidities before surgery and anesthesia to decrease morbidity and mortality
- Common examples include:
- Ischemic heart disease
- Heart failure
- Obstructive sleep apnea
- Diabetes mellitus
- Thyroid disease
- Smoking cessation at least 2 weeks before surgery
- Preoperative testing:
- Diagnostic testing for preexisting conditions and comorbidities should be obtained preoperatively to monitor conditions postoperatively.
- Patient-specific testing, for example:
- If blood transfusion is anticipated, blood typing and crossmatching are imperative before surgery and anesthesia.
- If a woman of childbearing age is to undergo surgery and anesthesia, a pregnancy test is indicated to avoid fetal loss.
|Preexisting disease/condition||Diagnostic testing|
|Age > 65 years||Albumin, creatinine, hemoglobin|
|Alcohol abuse||ECG, electrolytes, hemoglobin, liver function test, platelet count, PT/INR|
|Anemia||CBC, creatinine, ferritin, iron, transferrin saturation, TSH, T3, T4, vitamin B12, blood typing, screening|
|Cardiac disease||BNP, ECG, +/- stress testing|
|Diabetes||Creatinine, HbA1c, glucose|
|Liver disease||Albumin, BUN, creatinine, electrolytes, hemoglobin, liver function test, platelet count, PT/INR|
|Pulmonary disease||Chest X-ray|
|Thyroid disease||T3, T4, TSH|
TSH: thyroid-stimulating hormone
|American Society of Anesthesiologists physical status classification||Definition||Examples|
|I||A normal, healthy individual without known diseases||Healthy, nonsmoker, minimal alcohol use|
|II||An individual with mild systemic disease||Current smoker, mild hypertension, mild lung disease|
|III||An individual with severe systemic disease||Poorly controlled hypertension or diabetes mellitus, chronic obstructive pulmonary disease|
|IV||An individual with severe systemic disease that is a constant threat to life||Recent MI, severely reduced ejection fraction, sepsis, ARDS|
|V||An individual who is not expected to survive without the intended operation||Brain bleed, ruptured aneurysm, massive trauma|
|VI||An individual declared brain dead or whose organs are being harvested|
- Essential for the affected individual’s satisfaction and safety
- Provides information on how to reduce the risks of surgery and anesthesia:
- Stop smoking before and after surgery.
- Medications that are to be taken or avoided before surgery
- Cessation of eating and drinking by midnight prior to the procedure to prevent aspiration of gastric contents
- Sanitary measures prior to the procedure (e.g., antibacterial soap prep)
- Involve the individual in the decision-making and planning steps.
- Answer all questions.
- Address all concerns.
- Based on the premise that individuals have the right to receive information and ask questions about recommended treatments so that they can make well-informed decisions about their care
- Treating physicians should discuss all risks and complications associated with the procedure and associated anesthesia before asking for informed consent.
- Results in the individual’s agreement or refusal to undergo a specific medical intervention
- Usually obtained in a written format
The creation of a plan for anesthesia involves the consideration of:
- Surgery requirements
- Duration of surgery
- Postoperative considerations
- The individual’s preference
- Preferences of the surgeon and the anesthesiologist
- Pain management
- Pulmonary hygiene
- Early interventions
- Requirement of ICU vs appropriate hospital wing vs outpatient care for recovery
Types of Anesthesia
Several types of anesthesia are used for surgery or other medical procedures. Choosing the appropriate type depends on:
- Procedure to be performed
- Procedure requirements
- Area that needs to be anesthetized
- Duration of surgery
- Patient-specific comorbidities
- Postoperative anesthesia plans and considerations
- Individual’s preference
- Preferences of the provider and the anesthesiologist
Types of anesthesia:
- Peripheral nerve block
- IV regional anesthesia
- Monitored anesthesia care (MAC)
- Drug-induced loss of consciousness
- Affects the whole body
- Appropriate for most major surgical procedures
- The goal of general anesthesia is to attain:
- Muscle relaxation with immobility
- Blockage of noxious stimuli during surgery
The 3 stages of general anesthesia are:
- Accomplished via inhalation or IV
- Airway management is integral and is initially via a face mask followed by the transition to endotracheal intubation.
- Typically achieved via a primary inhalation technique using IV drugs
- Goal is to reduce the total dosage of any 1 agent; thus, anesthetic combinations are commonly used.
- Involves removing anesthetic agents and reversing their residual effects for the return of consciousness and movement
- Extubation can be performed when the individual can protect their airway, follow simple commands, and ventilate without assistance.
|Class||Commonly used drugs|
|IV sedative-hypnotics||Propofol, etomidate, ketamine|
|IV adjuvants||Opioids, lidocaine, midazolam|
|Inhalation agents||Nitrous oxide, halothane, isoflurane|
|Neuromuscular blockers||Vecuronium, rocuronium, succinylcholine|
- A type of anesthesia that involves anesthetizing the nerves of the CNS
- Neuraxial anesthesia is commonly used for lower abdominal and lower extremity surgeries or for pain relief.
- 2 main types:
- Spinal anesthesia: A needle is inserted between the vertebrae and the anesthetic is injected directly into the subarachnoid space.
- Epidural anesthesia: A catheter is inserted between the vertebrae and the anesthetic is injected directly into the epidural space.
Peripheral nerve blocks
- A type of regional anesthesia
- The anesthetic is injected near a specific nerve or a bundle of nerves to block sensations of pain from a specific area of the body.
- Commonly used for procedures involving the upper and lower extremities
- Fluoroscopy or ultrasound guidance is often used for needle or catheter insertion and placement.
- Long-acting local anesthetics provide prolonged postoperative analgesia.
Intravenous regional anesthesia (IVRA)
- Also known as a “Bier block”
- Less invasive alternative to peripheral nerve blocks
- Suitable for shorter procedures of the hand, forearm, and foot
- Estimated blockage time: approximately 1.5 hours
- Appropriate for surgeries lasting 1 hour or less
- Compression and exsanguination of the extremity using an Esmarch bandage
- A tourniquet is used to keep the blood out of the extremity and retain anesthesia.
- An infusion of 0.5% lidocaine via a peripheral vein establishes anesthesia.
- The surgeon can work in a completely anesthetized and bloodless surgical field for a limited time.
Monitored anesthesia care
- Involves monitoring an individual’s vitals and administering sedatives, anxiolytics, or analgesics accordingly
- Commonly used during outpatient procedures
- If needed, anesthesiologists are ready to convert to general anesthesia at any time.
- A common example is administering propofol whenever an anesthesiologist deems it necessary during an endoscopy based on the individual’s vitals and mobility.
- Used by the anesthesiology team during a procedure
- Pulse oximetry
- Noninvasive blood pressure monitoring device
- Integrated monitors with alarms
Monitoring of ventilation
- Serialized visual inspection, auscultation, palpation, and O2 saturation
- Ventilation monitoring is essential during anesthesia due to the risk of respiratory depression and hypoxia.
- Ventilation is monitored in several ways:
- Clinical monitoring:
- Visualization of chest excursion
- Auscultation of breath sounds
- Movement of the reservoir bag
- O2 saturation monitor
- Capnography: a graph showing the respiratory rate and CO2 concentration over time
- Other measures:
- End-tidal CO2 concentration
- Inspired O2 concentration
- Quantitative volume of expired gas
- Clinical monitoring:
Monitoring of hemodynamics
- Serialized recording of automated blood pressure, ECG, and HR
- More accurate hemodynamic monitoring can be achieved via invasive approaches such as:
- Intra-arterial pressure monitor
- Central venous pressure monitor
- Pulmonary artery catheter
- Transesophageal echocardiography (TEE) probes
- Hemodynamics are monitored based on:
- Vitals signs
- Fluids (IV input and urine output)
- Vasoactive drugs can be administered to maintain optimal intravascular volume status throughout anesthesia.
Monitoring of neurologic status
- Neurologic status may be difficult to assess in individuals who are sedated and/or paralyzed.
- EEG may be used for the neuromonitoring of cortical function.
- IM paraspinal and/or limb electrodes may be used to monitor nerve stimulation during neurosurgical, orthopedic, or interventional spinal procedures.
- Intracranial pressure may be monitored during neurosurgical procedures.
Depth of anesthesia
- Monitored based on end-tidal concentrations of inhalation anesthetics
- The goal of anesthesia is stage II or III, depending on the type of anesthesia chosen.
- Stage III requires endotracheal intubation for airway protection.
- If the desired stage III enters stage IV, prompt reversal is necessary.
|Stage I||Conscious and rational with decreased pain perception|
|Stage II||Unconscious and reflexive with an irregular breathing pattern|
|Stage III||Inability to protect the airway due to increased muscle relaxation|
|Stage IV||Cardiovascular and respiratory depression (medullary)|
All individuals are monitored postoperatively in a PACU, where standard procedures are followed:
- Antiemetics for postoperative nausea and/or vomiting
- Fluid administration and monitoring for the inability to void via strict inputs and outputs
- Respiratory, cardiovascular, and neurological monitoring
- Monitoring and control of hypothermia and hyperthermia
- Pain control
- Reassurance, reorientation, and potential drug reversal for delayed emergence (failure to return to a conscious state within 60 minutes of anesthesia cessation)
- Recovery assessment
- Reduction of postoperative adverse events
- Streamline discharge
- Transferring to an ICU vs appropriate hospital wing vs outpatient care for recovery
- Falk, S. (2020) Overview of anesthesia. Retrieved October 15, 2021, from https://www.uptodate.com/contents/overview-of-anesthesia
- Robinson, D., Toledo, A.H. (2012). Historical development of modern anesthesia. Journal of Investigative Surgery: The Official Journal of the Academy of Surgical Research, 25, 141–149. https://doi.org/10.3109/08941939.2012.69032
- Harrah, S. (2015). Medical Milestones: Discovery of Anesthesia & Timeline. University of Medicine and Health Sciences. https://www.umhs-sk.org/blog/medical-milestones-discovery-anesthesia-timeline
- Nizamuddin, J. (2019). Anesthesia for surgical patients. Schwartz’s Principles of Surgery, 11e. McGraw-Hill. https://accessmedicine-mhmedical-com.ezproxy.unbosque.edu.co/content.aspx?bookid=2576§ionid=216218112
- Romero-Ávila, P. (2021). Historical development of the anesthetic machine: From Morton to the integration of the mechanical ventilator. Brazilian Journal of Anesthesiology (English Edition), 71, 148–161. https://www.sciencedirect.com/science/article/pii/S0104001421000361?via%3Dihub
- Wood Library-Museum of Anesthesiology. History of Anesthesia. Retrieved June 21, 2021, from https://www.woodlibrarymuseum.org/history-of-anesthesia/