Multimodal General Anesthesia - Its Components and Working Principle

Introduction:

Any major surgical procedure involves the use of anesthesia mandatorily to make the procedure pain-free and uneventful. The use of anesthesia is significant in terms of the choice of the appropriate drug and its safe administration and rapid recovery without any adverse effects.

What Is General Anesthesia?

General anesthesia is defined as a temporary, reversible, and controlled loss of consciousness produced by administering drugs called anesthetics. The patient is in a sleep-like state without feeling or sensation of painful stimulus-induced during surgeries. The patient experiences analgesia, amnesia, sedation, and paralysis.

• Amnesia: The loss of remembrance of memories and facts for a specific time period. General anesthesia causes amnesia of the surgical memory and experience to prevent the patient from experiencing traumatic memories of the surgery. So, general anesthetics inhibit arousal and awareness during surgery. As a result, the patient tends to be completely unaware of the procedure.

• Analgesia: The term analgesia refers to the loss of sensation of pain. An analgesic drug belongs to a class of painkillers that do not change the state of consciousness and sensory awareness or suppress nerve impulse conduction.

• Sedation: The sedative group of drugs is used to produce sedation in patients, which puts them in a state of deep sleep with relaxation and calmness. The level of sedation can range from mild to deep, depending on the extent of surgery and the time it takes.

• Paralysis: Anesthetics produce paralysis of muscles, which means a reversible and temporary loss of the ability to control and move the body's muscles.

What Is Multimodal General Anesthesia?

Multimodal anesthesia (MMA) is the application of more than one drug category to produce anesthesia, along with minimizing the side effects associated with each drug used in the combination. Each drug acts on different receptors involved in the pain pathway of the nervous system with the aim of inducing improved general anesthesia.

What Are the Components of Multimodal General Anesthesia?

Multimodal general anesthesia uses different pharmacological classes of drugs acting synergistically to produce an effective analgesic state. Anesthesiologists solely rely on ether for maintaining general anesthesia. But multimodal general anesthesia uses each drug in less quantity, thereby reducing the chances of side effects and increasing the desirable effects from each drug. There is no standardized combination of drugs used in multimodal general anesthesia. The drugs can be administered through the intravenous route, infiltration, or regional anesthesia.The set of drugs used are:

• Opioids.

• Non-opioids.

• Non-steroidal anti-inflammatory drugs.

• Gabapentinoids.

• Local anesthetics.

• Ketamine.

What Is the Working Principle of Multimodal General Anesthesia?

Opioids were the only drug used to produce anesthesia. But these drugs have some significant undesirable side effects, which were unavoidable due to the large quantity of drugs used during the procedure. Multimodal general anesthesia prevents the overuse of opioids. It incorporates some drugs, like those that act on specific targets along the pain pathway, like dexmedetomidine, and some drugs with less specific targets, like magnesium. Doing so increases the ratio of benefits to side effects. The main goal of anesthesia is to manage nociception during the operation and manage pain after surgery. Nociception is the series of processes the body undergoes to receive a painful or harmful stimulus, convert it into chemical molecules and identify the stimulus to help the defense system to generate a response. The working mechanism of multimodal general anesthesia can be explained using an example. The drugs used will belong to each of the following classes listed below.

• Alpha-2 Agonists: These drugs include dexmedetomidine and clonidine, which act on alpha-2 agonist receptors that are situated throughout the central and peripheral nervous system. They have analgesic effects and cause sedation, vasodilation, and bradycardia (decreased heart rate), making the drug safe. They are used as an adjuvant to general anesthesia and minor surgical procedures.

• Anticonvulsants: They are anti-epileptic drugs used generally to control seizures. They work by suppressing the abnormal excitement in the brain by inhibiting the transmission of the chemical responsible for producing neuronal excitement. They are used to relieve postoperative pain and act as analgesics. Examples of anticonvulsants used in general anesthesia include Gabapentin and Pregabalin. They are also used in chronic neuropathic pain.

• N-methyl N-Aspartate Antagonists: The drug belonging to this category acts on N-methyl N-aspartate receptors and inhibits them. The inhibition produces anesthesia which is known as dissociative anesthesia. Dissociative anesthesia is a unique type of anesthesia in which patient experience catalepsy( the lack of awareness of surroundings and less communication with society with behavioral problems), catatonia (muscular rigidity with less sensitivity to pain and external stimulus), along with analgesia and amnesia. The patient feels dissociated from their own body and reality and is in a deep trance-like state. Ketamine is an excellent example of this type.

• Local Anesthetics: Lidocaine and Bupivacaine are the most commonly used local anesthetics. It is used as an adjuvant to general anesthesia, which gives postoperative analgesia and fewer side effects.

• Acetaminophen: The drug is widely used over-the-counter to alleviate pain. It produces an analgesic effect by inhibiting the COX pathway, inhibiting prostaglandin secretion, the main chemical responsible for producing pain. They can be given pre or post-operatively for pain relief and to minimize the need for opioids.

• Non-steroidal Anti-Inflammatory Drugs: NSAIDs include Diclofenac, Ketorolac, Ibuprofen, Meloxicam, and Celecoxib. They act by inhibiting the cyclooxygenase enzyme which produces prostaglandins. They are very effective painkillers for postoperative pain.

How Does Pain Pathway Work?

Pain is experienced by the body when a painful stimulus is given to the body through a process called the pain pathway. The pathway starts from the point of external stimulus to the nervous component, which perceives the stimuli and induces the appropriate response.

There are four phases in the pain pathway which are:

• Transduction: It is the stage in which the noxious stimuli either mechanical, chemical, or heat, activate the nerve endings of the area and convert them into a neuronal signal.

• Transmission: It is the transportation of electrical impulses from the nerve ending to the brain via the cranial and peripheral nerves.

• Modulation: In this stage, the pain signal is altered along its transmission resulting in varied pain perceptions by different individuals.

• Perception: It is the phase where the person realizes the harmful stimulus as a feeling of pain and produces an emotional or mechanical response to it.

Conclusion:

The use of multimodal anesthesia by anesthesiologists can improve the quality of anesthesia produced and decrease the unwanted side effects. Even though the opioids procedure has significant side effects, they are still the first choice for acute pain control. The use of adjuvant drugs can regularize the quantity of opioids used. As a result, the incidence of postoperative pain and neurological side effects can be reduced.