Anesthesia, or anaesthesia, has traditionally meant the condition of having sensation (including the feeling of pain) blocked or temporarily taken away.
Anesthesia, or anaesthesia, has traditionally meant the condition of having sensation (including the feeling of pain) blocked or temporarily taken away. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. The word was coined by Oliver Wendell Holmes, Sr. in 1846. Another definition is a “reversible lack of awareness”, whether this is a total lack of awareness (e.g. a general anaesthetic) or a lack of awareness of a part of the body such as a spinal anaesthetic or another nerve block would cause.
Today, the term general anaesthesia in its most general form can include:
- Analgesia: blocking the conscious sensation of pain
- Hypnosis: producing unconsciousness
- Amnesia: preventing memory formation;
- Paralysis: preventing unwanted movement or muscle tone
- Obtundation of reflexes, preventing exaggerated autonomic reflexes.
Patients undergoing anesthesia usually undergo preoperative evaluation. It includes gathering history of previous anesthetics, and any other medical problems, physical examination, ordering required blood work and consultations prior to surgery.
There are several forms of anesthesia. The following forms refer to states achieved by anesthetics working on the brain:
- General anesthesia: “Drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation.” Patients undergoing general anesthesia can often neither maintain their own airway nor breathe on their own. While usually administered with inhalational agents, general anesthesia can be achieved with intravenous agents, such as propofol.
- Deep sedation/analgesia: “Drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation.” Patients may sometimes be unable to maintain their airway and breathe on their own.
- Moderate sedation/analgesia or conscious sedation: “Drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation.” In this state, patients can breathe on their own and need no help maintaining an airway.
- Minimal sedation or anxiolysis: “Drug-induced state during which patients respond normally to verbal commands.” Though concentration, memory, and coordination may be impaired, patients need no help breathing or maintaining an airway.
General anaesthesia is a complex procedure involving:
Prior to surgery, the anesthetist interviews the patient to determine the best combination of drugs and dosages and the degree to which monitoring is required to ensure a safe and effective procedure. Key factors of this determination are the patient’s age, weight, medical history, current medications, previous anesthetics, and fasting time. Patients are typically required to fill out this information on a separate form during the pre-operative evaluation. Depending on the existing medical conditions reported, the anaesthetist will review this information with the patient either during the pre-operative evaluation or on the day of the surgery.
Truthful and accurate answering of the questions is important so that the anaesthetist can select the proper anaesthetic drugs and procedures. For example, a heavy drinker or drug user who does not disclose their chemical uses could be under medicated, which could then lead to anaesthesia awareness or dangerously high blood pressure. Commonly used medications such as Viagra can interact with anaesthesia drugs; failure to disclose such usage can endanger the patient.
An important aspect of this assessment is that of the patient’s airway, involving inspection of the mouth opening and visualization of the soft tissues of the pharynx. The condition of teeth and location of dental crowns and caps are checked, neck flexibility and head extension observed. If an endotracheal tube is indicated and airway management is deemed difficult, then alternative placement methods such as fiberoptic intubation may be used.
Administration of General Anesthesia
The anesthesiologist may give a pre-medication by injection or by mouth anywhere from a couple of hours to a couple of minutes before the onset of surgery to induce drowsiness and relaxation.
The most common drugs used for pre-medication are narcotics (opioids such as fentanyl) and sedatives (most common benzodiazepines such as midazolam).
The general anaesthetic is administered in either the operating theatre itself or a special ante-room. General anesthesia can be induced by intravenous (IV) injection, or breathing a volatile anaesthetic through a facemask (inhalational induction). Onset of anaesthesia is faster with IV injection than with inhalation, taking about 10-20 seconds to induce total unconsciousness.] This has the advantage of avoiding the excitatory phase of anaesthesia (see below), and thus reduces complications related to induction of anaesthesia. An inhalational induction may be chosen by the anesthesiologist where IV access is difficult to obtain, where difficulty maintaining the airway is anticipated, or due to patient preference (e.g. children). Commonly used IV induction agents include propofol, sodium thiopental, Etomidate, and ketamine. The most commonly-used agent for inhalational induction is sevoflurane because it causes less irritation than other inhaled gases.
The duration of action of IV induction agents is generally 5 to 10 minutes, after which time spontaneous recovery of consciousness will occur. In order to prolong anaesthesia for the required duration (usually the duration of surgery), anaesthesia must be maintained. Usually this is achieved by allowing the patient to breathe a carefully controlled mixture of oxygen, nitrous oxide, and a volatile anaesthetic agent or by having a carefully controlled infusion of medication, usually propofol, through an IV. The inhalation agents are transferred to the patient’s brain via the lungs and the bloodstream, and the patient remains unconscious. Inhaled agents are frequently supplemented by intravenous anesthetics, such as opioids (usually fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam). Though for a propofol based-anaesthetic, supplementation by inhalation agents is not required. At the end of surgery the volatile or intravenous anaesthetic is discontinued. Recovery of consciousness occurs when the concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes depending upon the duration of surgery).
Other medications will occasionally be given to anaesthetized patients to treat side effects or prevent complications. These medications include antihypertensives to treat high blood pressure, drugs like ephedrine and phenylephrine to treat low blood pressure, drugs like albuterol to treat asthma or laryngospasm/bronchospasm, and drugs like epinephrine or diphenhydramine to treat allergic reactions. Sometimes glucocorticoids or antibiotics are given to prevent inflammation and infection, respectively.
Stages of Anesthesia
Stage I: Also known as the “induction”, is the period between the initial administration of the induction medications and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at the time.
Stage II: Also known as the “excitement stage”, is the period following the loss of consciousness and marked by excited and delirious activity. During this stage, respiration and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, breath-holding, and pupillary dilation. Since the combination of spastic movements, vomiting, and irregular respirations may lead to airway compromise, rapidly acting drugs are used to minimize the time in this stage and reach stage 3 as fast as possible.
Stage III: “surgical anaesthesia”. During this stage, the skeletal muscles relax, and the patient’s breathing becomes regular. Eye movements slow, and then stop, and surgery can begin.
It has been divided into 3 planes:
Plane 1: roving eyeballs…..ends with fixed eyeballs
Plane 2: loss of corneal and laryngeal reflexes.
Plane 3: pupil dilate and light reflex is lost
Plane 4: intercostal paralysis, shallow abdominal respiration, dilated the pupil.
Stage IV: Also known as “overdose”, is the stage where too much medication has been given and the patient has severe brain stem or medullary depression. This results in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.
For all the Latest Information on Anesthesia & the up to date Research information on General Anesthesia & Local Anesthesia you can visit the following sites:
www.annals.in: Annals of Cardiac Anaesthesia (ACA) a quarterly peer-reviewed international journal is the official journal of the Indian Association of Cardiovascular Thoracic Anesthesiologists.
www.iars.org : An international Society committed to improving clinical care, education & research in Anesthesia, Pain Management & postoperative medicine
www.asahq.org: Founded in 1905, the American Society of Anesthesiologists is an educational, research and scientific associations with 43,000 members organized to raise and maintain the standards of the medical practice of anesthesiology and improve the care of the patient.
www.boas.org: The British Ophthalmic Anaesthesia Society is an organization of Anesthetists, Ophthalmologists and other clinicians who are committed to sharing education and information which will enable them to provide the highest level of anaesthetic management during ophthalmic surgery.
http://medind.nic.in/iad/iadm.shtml: The British Ophthalmic Anaesthesia Society is an organization of Anesthetists, Ophthalmologists and other clinicians who are committed to sharing education and information which will enable them to provide the highest level of anaesthetic management during ophthalmic surgery.
www.esraeurope.org: The European Society of Regional Anaesthesia (ESRA) is a specialized association that brings together anesthesiologists and other physicians and scientists who are engaged in the techniques of regional anaesthesia for surgery, obstetrics and pain control.
www.anaesthesiologists.org: The World Federation of Societies of Anesthesiologists (WFSA) is a unique organization in that it is a society of societies. By virtue of membership in a national society, an anesthesiologist is automatically a member of WFSA.
www.theiaforum.org: This is India’s First Free Online Journal of Anaesthesiology, Critical Care and Pain Management.
www.worldanaesthesia.org: Support anaesthesia in the developing world through appropriate training, material and equipment.
www.oaa-anaes.ac.uk: The Obstetric Anesthetists’ Association (OAA) was formed in 1969 to promote the highest standards of anaesthetic practice in the care of mother and baby and has an international membership of over 2000.
anesthesiology.org: The Journal of American Society of Anesthesiologist.
oxfordjournals.org: BJA publishes original articles in all branches of Anaesthesia
freemedicaljournals.com: Promoting free access to medical journals like JAMA.
isaweb.in: The Indian Society of Anesthesiologists is recognized by the Medical Council of India, & is affiliated to the World Federation of Societies of Anesthesiologists.
cja-jca.org: Each issue of the CJA gives readers access to the latest advances in anesthesia. The CJA publishes peer-reviewed, high-profile clinical research, basic research with an impact apparent to clinicians, and expert reviews and opinions to assist the anesthesiologist in the field.
eyeanesthesia.org: High Quality Anesthesia care through Training & Education.
AnestCadiz: European website of Anaesthesiology, Critical Care & Pain Treatment
saarcjoa.org: SAARC journal of Anesthesia.
iactaonline.org: Associates & Affiliates into one organization all anesthesiologists who are currently practicing Cardiac Anesthesia or are actively involved in Cardiac Anesthesia.