Anesthesia is an interesting and growing field in the medical world that tampers and plays with the most complex organ our bodies contain: the human brain. How we think, feel, and perceive can all be altered by the mere interaction with a chemical compound. To provide brief context, anesthesia is defined as the state of insensitivity to pain (or general sensation) induced artificially using drugs. These drugs, also known as anesthetics, capture our intrigue due to the fact that through mere arrangements of the elements, they are able to control and manipulate our senses. Typically, they come in three types: local anesthetics, regional anesthetics, and general anesthetics. It is important to understand the attributes of each distinction as they have their own unique properties and function differently inside the human body. This blog post will ultimately provide a general overview of each type.
Out of the three types, local anesthesia can be considered the least extensive and jeopardizing method due to its small scope of operation. A local anesthetic drug numbs and prevents a small, restricted area of the body from experiencing pain, while maintaining the capability of keeping the patient conscious. This method vividly contrasts against the most intensive method of anesthesia, general anesthesia, which induces complete loss of consciousness and loss of sensation throughout the entire body. Subsequently in many cases, local anesthesia is considered to be the safest method. They are primarily used for minor procedures, such as those conducted by a dentist or dermatologist.
Local anesthetics interrupt neural conduction and induce anesthesia by inhibiting the flow of sodium ions through the sodium channels embedded in membrane of a neuron. The flow of sodium ions through these channels contribute to the generation of action potential: an event along the axon of a neuron that produces an electrical impulse, ultimately enabling the ability to experience sensation and conduct motor activity (To further understand the sodium channels and action potential, watch this following informative YouTube clip http://www.youtube.com/watch?v=oRYpt8_OJms). By inhibiting this flow of sodium ions, local anesthetics are able to generate insensitivity in regions of the body. Additionally, the molecular structure of local anesthetics is generally composed of three components: the lipophilic aromatic ring, the intermediate chain, and the terminal amine. They come in the two varieties, amino-ester and amino-amides, with the primary difference being either possessing an ester or an amide intermediate chain. These components of the local anesthetic hold individual properties that allow the compound to induce anesthesia.
For example, the aromatic ring improves the lipid solubility of the overall anesthetic compound, enhancing its ability to diffuse past the nerve sheaths (insulating layer formed around nerves, also known as the myelin sheath) and into the axoplasm (cytoplasm of axom) to disrupt the flow of sodium ions.
The function of regional anesthesia is to make a particularly larger body area, compared to local anesthesia, numb in order to relieve pain or allow surgical procedures to be performed. Local anesthetics are generally used in the procedure of regional anesthesia. This type of anesthesia is usually used for orthopedic surgeries on the extremities, male or female reproductive surgery, as well as bladder and urinary tract operations. There are three types of regional anesthetics:
1.) Spinal Anesthesia
2.) Epidural Anesthesia
3.) Peripheral Nerve Blocks
In this type of regional anesthesia, a small needle is inserted through the skin and into the spine to mix with the cerebrospinal fluid (CSF). This is located in the subarachnoid space. This procedure is done to numb the body but it is significantly safer than general anesthesia. The effect of this anesthesia is felt straight away, making it extremely useful for shorter and simpler procedures.
In this type of anesthesia, a larger needle is inserted through the skin towards the spinal cord just like in spinal anesthesia. The difference is that instead of being inserted into the cerebrospinal fluid, the needle will be injected just outside of the fluid’s sac. This location is called the epidural space. The needle is inserted along with a catheter, which allows the anesthesia to last longer. The anesthesia begins to take effect in about 10-20 minutes and so it works best for longer procedures such as child birth.
Peripheral Nerve Blocks:
Studies have shown that nerve blocks are known for improving pain relief and reducing the amount of side effects. The process involves injecting the anesthetic solution as close to the nerve as possible without actually entering the nerve itself. Once the solution is absorbed into the nerve, it blocks sodium channels. This allows it to disable its electrical-like action potential, which prevents pain and causes the body to witness a lack of sensation. Since the results are better as the solution gets closer to the nerves, ultrasound devices are used to make this procedure as accurate as possible.
All of these three types of regional anesthetics are safer and provide less side effects than general anesthesia. Another advantage that this type of anesthesia is better than general anesthesia is that you are able to stay awake during all of these procedures because of the lack of pain that one feels.
General anesthesia is the oldest procedure out of the three discussed and affects the most number of bodily functions. The entire body is shut down in a medically induced coma and after waking up, there is no memory of anything after falling unconscious and before waking up. General anesthesia is typically used for larger, more complex surgical procedures such as open heart surgery for several reasons as general anesthesia is usually coupled with several different unique characteristics. Among them include analgesia, loss of response to pain throughout the entire body, amnesia, loss of memory as aforementioned, and muscle relaxation. This anesthesia is the only type where the patient loses complete consciousness.
The anesthesiologist achieves this state by exposing the patient’s central nervous system (CNS) to chemicals that affect it at different levels. These chemicals are either inhaled or injected intravenously. Modern chemicals that induce this effect include inhaled agents such as desflurane and enflurane and intravenous agents that include ketamine and etomidate. These chemicals usually affect the same sodium ion channels involved in local anesthesia, but to a greater degree.
However, general anesthesia also affects several different pathways, including the GABA and the glutamate-activated NMDA ion channels. General anesthesia, while not pinpointed to affect a certain region, usually affects one of several parts of the body: the cerebral cortex, the thalamus, and the spinal cord. This YouTube video should prepare potential patients for the effects of general anesthesia.