Balanced anesthesia, also known as multimodal anesthesia (also spelt:

anaesthesia Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prev ...

), is a technique used to induce and maintain anesthesia in patients undergoing

surgery Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...

or certain medical procedures. This method employs a combination of

anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...

agents and other drugsand techniquesto selectively target various aspects of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

, allowing for a tailored anesthetic experience based on the individual patient's needs and the specific requirements of the procedure. The specialist physician (in

Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...

and ; in

Commonwealth A commonwealth is a traditional English term for a political community founded for the common good. The noun "commonwealth", meaning "public welfare, general good or advantage", dates from the 15th century. Originally a phrase (the common-wealth ...

and ) or veterinarian evaluates various patient factors prior to selecting an anesthetic approach. These factors include major

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

function, general condition, and compensatory capacity (ability to function despite stressors). In balanced anesthesia, appropriate agents are used in combination, at carefully-calibrated levels. The concept of balanced anesthesia was first introduced by John Silas Lundy in 1926 and has since become the predominant method of anesthesia in modern medical practice.

Rationale

The primary objectives of

general anesthesia General anaesthesia (UK) or general anesthesia (US) is medically induced loss of consciousness that renders a patient unarousable even by painful stimuli. It is achieved through medications, which can be injected or inhaled, often with an analgesi ...

include inducing unconsciousness, providing

analgesia Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute and simple to chronic and challenging. Most physicians and other health professionals ...

, facilitating muscle relaxation, and the temporary suppression of motor

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

es. Achieving muscle paralysis is often necessary for certain surgical procedures. Depending on the procedure to be undertaken, blocking transmission of

nociception In physiology, nociception , also nocioception; ) is the Somatosensory system, sensory nervous system's process of encoding Noxious stimulus, noxious stimuli. It deals with a series of events and processes required for an organism to receive a pai ...

(

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

responses to noxious stimuli and its cardiac and

hemodynamic Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously ...

effectseven in the absence of conscious pain perception), may be the aim of analgesia. Amnesiainduced through an altered state of consciousnessmay be adequate or preferred over total unconsciousness. The physiological stability of the patient has to be maintained while all this is achieved. Balanced anesthesia is employed in a range of surgical procedures to optimize patient safety and comfort. It is commonly used in major abdominal surgeries, such as bowel resections, liver surgery, and gastric bypass, where deep anesthesia and muscle relaxation are required. In cardiac surgery, balanced anesthesia facilitates precise control of heart rate and blood pressure, which is critical during these complex procedures. Additionally, orthopedic surgeries, including hip and knee replacements, utilize this approach to enhance muscle relaxation and pain management. Gynecological surgeries, such as hysterectomies and laparoscopic procedures, also benefit from balanced anesthesia to maintain patient stability and comfort throughout the operation.

Pharmacokinetic factors

The scope of

pharmacodynamics Pharmacodynamics (PD) is the study of the biochemistry, biochemical and physiology, physiologic effects of drugs (especially pharmaceutical drugs). The effects can include those manifested within animals (including humans), microorganisms, or comb ...

is the effects caused on the body by a medicine. The distribution of any pharmacologic agent, its

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...

in tissues, blood or plasma, and its clearance from the body, are the

pharmacokinetic Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to describing how the body affects a specific subs ...

features of a medicine. Unlike single-agent anesthesia, which can lead to increased adverse effects when higher doses of a single drug are administered, balanced anesthesia allows for the use of lower doses of multiple agents. This strategy minimizes the risk of

side effect In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects. A drug or procedure usually use ...

s by enabling the anesthesiologist to target specific effects through the adjustment of individual agents. The pharmacodynamics of each agent—their effects on the body—can be finely controlled, while pharmacokinetics—how these agents are distributed and cleared from the body—plays a critical role in the effectiveness of the anesthesia. Injectable anesthetic agents may be administered by constant rate infusion (CRI) which is a portion of balanced anesthetic techniques, can be made like a single intermittent dose or as a single injection. It should keep a during the time. Both the foreseeable pharmacodynamic effects and foreseeable concentration of plasma can be offered by the CRI of specific medicine. It has similarity on keeping the invariable concentration of end-tidal by using the vaporous precise device, which can provide the volatile anesthetic. When the administration rate exceeds the

clearance rate In criminal justice, clearance rate is calculated by dividing the number of crimes that are "cleared", a criminal charge being laid, or convicted by the total number of crimes recorded. Various groups use clearance rates as a measure of crimes s ...

, a stable-state concentration has been achieved by delivering the medicine as a CRI. In addition, if the medicine has distributed fully at equilibrium in the body, which is called the volume of distribution at a stable state. In case the loading dose was administered after the CRI, the time period of which will keep the concentration at a stable state equals 3 time constants or 5 terminal

half-lives Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * '' Half Life: A Parable for t ...

of the specific medicine. The bolus dose can full with the volume of the medicine in an efficient and effective way so that the medicine can be cleared and delivered. This also can promote to achieve the stable state in a prompter approach. Administering a CRI has two important methods: targeting a specific infusion rate, and making the infusion rate constant. * Make the infusion rate constant * Target a specific infusion rate

Veterinary use

Based on a 2010 review of injectable-agent use for short-duration anesthesia, the American Association of Equine Practitioners recommends the use of

xylazine Xylazine is a structural analog of clonidine and an α2-adrenergic receptor, α2-adrenergic receptor agonist, sold under many trade names worldwide, most notably the Bayer brand name Rompun, as well as Anased, Sedazine and Chanazine. Xylazine ...

as a sedative for induction of anesthesia for durations of around 20 minutes or less. In addition,

diazepam Diazepam, sold under the brand name Valium among others, is a medicine of the benzodiazepine family that acts as an anxiolytic. It is used to treat a range of conditions, including anxiety disorder, anxiety, seizures, alcohol withdrawal syndr ...

and

ketamine Ketamine is a cyclohexanone-derived general anesthetic and NMDA receptor antagonist with analgesic and hallucinogenic properties, used medically for anesthesia, depression, and pain management. Ketamine exists as its S- (esketamine) a ...

are recommended after the xylazine. For longer duration anesthesia, those over 30 minutes, the most common anesthetics is the combination of

guaifenesin Guaifenesin, also known as glyceryl guaiacolate, sold under the brand name Mucinex, among others, is an expectorant medication taken by mouth and marketed as an aid to eliminate sputum from the respiratory tract. Chemically, it is an ether of ...

, ketamine, and xylazine or

isoflurane Isoflurane, sold under the brand name Forane among others, is a halogenated ether used as a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritat ...

The technique of balanced anesthetic has been applied widely with

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s and

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

s. When general anesthesia is used for cats and dogs, the most common method is inhalant agents because they are both easy to manage and the depth of anesthesia is predictable. The depth of anesthesia can be changed and recovered if some unexpected situation occurs during surgery. Although inhaled anesthetics will cause an unconscious state in which cats and dogs will not recall or perceive pain, the depth of anesthesia may not prevent the variety of reflex reactions to harmful stimuli during the operation. In order to prevent these reflex reactions, it may be required to increase the concentration of inhalant anesthetic agents; higher rates of inhalant administration are associated with higher

cardiovascular In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

and

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...

complications. Respiratory depression may result, especially in young patients and those with preexisting systemic disease. This is associated with increased morbidity and mortality. With the balanced anesthetic technique, the low concentration of inhalant anesthetic agents and other medicines used during the operation can alter the perception of painful stimuli. In other words, using balanced anesthetic techniques for cats and dogs can decrease the morbidity and mortality effectively. Therefore, in this situation, using balanced anesthetic techniques in cats and dogs is less risky for operation than using the general anesthesia. According to a report from a teaching hospital, the rate of complications resulting in death in cats and dogs using the balanced anesthesia are relatively low, at 1/9 and 1/233 respectively.

Advantages in animals

Balanced anesthesia has various advantages in veterinary cases: In certain circumstances it is considerably cheaper than the usual anesthesia. Secondly, it can reduce the death rate. Furthermore, it offers more stable operating conditions for

veterinarian A veterinarian (vet) or veterinary surgeon is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, veterinarians also play a role in animal r ...

s. It also increase animal safety and comfort. Balanced anesthesia can make patients calm by using drugs such as:

medetomidine Medetomidine is a veterinary anesthetic drug with potent sedative effects and emerging illicit drug adulterant. It is a racemic mixture of two stereoisomers, levomedetomidine and dexmedetomidine, the latter being the isomer with the pharmac ...

midazolam Midazolam, sold under the brand name Versed among others, is a benzodiazepine medication used for anesthesia, premedication before surgical anesthesia, and procedural sedation, and to treat psychomotor agitation, severe agitation. It induces ...

, and

acepromazine Acepromazine, acetopromazine, or acetylpromazine (commonly known as ACP, Ace, or by the trade names Atravet or Acezine 2, number depending on mg/ml dose) is a phenothiazine derivative antipsychotic drug. It was used in humans during the 1950s as ...

. Keeping patients calm prior to surgery can avoid the unpredictable consequences of stress, such as

tachypnea Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing. In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea b ...

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

and

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ...

which may be harmful to the anesthetized patients. In addition,

anxiety Anxiety is an emotion characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...

and stress may cause the

nociceptive pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated wit ...

. The balanced anesthesia therefore may therefore decrease those possible complications. Another advantage of using balanced anesthesia is that it can decrease the chance of

adverse effect An adverse effect is an undesired harmful effect resulting from a medication or other intervention, such as surgery. An adverse effect may be termed a "side effect", when judged to be secondary to a main or therapeutic effect. The term compli ...

s. All medicines may have adverse effect on patients; some serious adverse effects of anesthesia may be caused by

inhalational anesthetic An inhalational anesthetic is a chemical compound possessing general anesthetic properties that is delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vaporiser ...

, although in general these medicines are highly safe and useful. Using the correct amount of balanced anesthetic agents, the adverse effects can be reduced to some extent. Balanced anesthesia can also minimize the pain patients suffer. Pain may delay

wound healing Wound healing refers to a living organism's replacement of destroyed or damaged tissue by newly produced tissue. In undamaged skin, the epidermis (surface, epithelial layer) and dermis (deeper, connective layer) form a protective barrier again ...

, decrease appetite, and even result in death. Using the proper amount of

analgesic An analgesic drug, also called simply an analgesic, antalgic, pain reliever, or painkiller, is any member of the group of drugs used for pain management. Analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in s ...

s can reduce the amount of inhalant anesthetics required and help patients reduce the pain.

Commonly-used agents for animals

The quantity of a single anesthetic which is used for balanced techniques has similarity with that which is used for standing sedation. However, compare to the doses used for TIVA (total

intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutr ...

anesthesia), which is always lower than using the single anesthetics. The doses of anesthetics required differ, and depend on the required duration of anesthesia, the requirements for anesthesia to volatile, expected pain of injection of anesthesia, the experience the anesthetist using various medicines, and other factors. The pharmacokinetics of the two most common anesthetic agents, xylazine and ketamine, used during the surgical anasthesia are:

Xylazine pharmacokinetics

Xylazine Xylazine is a structural analog of clonidine and an α2-adrenergic receptor, α2-adrenergic receptor agonist, sold under many trade names worldwide, most notably the Bayer brand name Rompun, as well as Anased, Sedazine and Chanazine. Xylazine ...

is the most widely anesthetic agent used for short-duration operations in non-human animals. It does not have a medical use in humans.

Pharmacokinetics Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to describing how the body affects a specific su ...

of xylazine may be influenced by anesthesia since after an intravenous therapy about 1.1 mg/kg, the

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of xylazine will increase to 118 minutes and the clearance will decrease to 6 mL/kg/min. Based on a recent study, if injecting the

morphine Morphine, formerly also called morphia, is an opiate that is found naturally in opium, a dark brown resin produced by drying the latex of opium poppies (''Papaver somniferum''). It is mainly used as an analgesic (pain medication). There are ...

, which is 0.1 or 0.2 mg/kg, in the vein at the same time can extend the terminal half-life to about 150 minutes and the clearance will not be influenced.

Ketamine pharmacokinetics

Ketamine Ketamine is a cyclohexanone-derived general anesthetic and NMDA receptor antagonist with analgesic and hallucinogenic properties, used medically for anesthesia, depression, and pain management. Ketamine exists as its S- (esketamine) a ...

is the most widely anesthetic agent used for longer duration operations. After an intravenous therapy, which is about 2.2 mg/kg, mixed with the 1.1 mg/kg xylazine the half-life of xylazine is approximately 66 minutes and the clearance is around 31 mL/kg/min when patients are

halothane Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful ...

-anesthetized. If only managing the xylazine and ketamine, the terminal half-life will be 42 minutes and its clearance will be 27 mL/kg/min. When the CRI of ketamine is kept stable for an hour at 2.4 mg/kg/h, the terminal half-life will be 46 minutes and the clearance will be 32 mL/kg/min.