Ilembula Hospital Tapani Tuppurainen

Anesthesia is a creek word and means loss of sensation This loss of sensation can be total, regional or local Medications which produce anesthesia are called anesthetics. The total loss of sensation caused with anesthetics is called general anesthesia. It means unconsciousness, a kind of sleep, but it is more dangerous, because the patient is no more able to take care of himself. A patient under general anesthesia is never allowed to be left alone.

How do anesthetics work? All anesthetics block totally the transmission of information flowing through the nervous system in our body. General anesthetics shut the brain down in a more or less complicated way. Local anesthetics produce block when they have penetrated inside the nerves. The nerves can be blocked around a wound or just in the fracture when the local anesthetic is injected. This is real local anesthesia.

Regional anesthesia We can block a large bundle of nerves, like the nerves going to the arm. There are anatomically several places where this can be done. We speak about plexus anesthesia. If local anesthetic is injected around the spinal cord outside the dura mater, we speak about epidural anesthesia. If the anesthetic is injected inside the dura mater and mixed with cerebrospinal fluid, we speak about spinal anesthesia.

Facts about the nervous system The brain and spinal cord are metabolically very active. From cardiac output 20 to 25% goes to the brain. Cerebral autoregulation looks for, that the blood flow to the brain is stable. Blood brings oxygen and sugar. If the brain can not get them, the cells start to be damaged in a few minutes. The huge information highway between brain and body is called spinal cord. All nerves are coming from or going to spinal cord, except the 12 cerebral or brain nerves.

cont Brain and spinal cord are swimming in so called cerebrospinal fluid CSF. This fluid is a little bit heavier than water because of proteins, electrolytes, sugar and cells. It protects the brain. The knowledge of this fluid is very important for us anesthetists doing spinal anesthesia.

Segmental innervation of human body

Nerves All fibers are not of the same kind in a nerve Motoric Sensoric Temperature sensing Pain sensing Pressure sensing Fast and slow Nerves bringing information are called afferent Nerves transporting information from spinal cord to periphery are called efferent

Autonomous nervous system Nerves which are outside our conscious control are called autonomous. They regulate our metabolism and circulation. Autonomous nervous system has two parts. The activating part is called sympathicus and the restorating part is called parasympathicus. Autonomous nervous systems take also part in hormonal regulation in the body.

Neural physiology The single nerve fiber follows the law of everything or nothing, it lets the information go on or not. The nerve is like a two lane road where cars driving on afferent and efferent lanes transport information. In the periphery the nerves are thin, but near spinal cord more and more roads are joining to the nerve and the nerve gets thicker. Then comes heavy rain and cuts off the road. The cars can not any more pass this place, but they are able to drive on both sides of the defect in both direction. The rain or anesthetic has an effect only there where it sits.

If the patient has already spinal, epidural or plexus anesthesia it is possible localize single nerves with help of neurostimulator for postoperative pain relief. Especially patients with circulatory problems, like transplantation of fingers or arms, profit from this technology, because the catheter can be left in place for several days. This can be done after operation and the procedure is pain free for the patient, because he is anesthetized!

How much anesthetic depends on Distance between place of injection and the nerve When doing infiltration anesthesia it is normal to infiltrate near wound to keep the amount anesthetic inside safe limits. Injection inside the dura mater means a short way for the agent to penetrate to place of action. A dose of 10mg to 15mg bupivacain is normally sufficient for adults. In epidural anesthesia the dose needed is about 7,5 to ten times more to get the same spread of anesthesia. The reason is longer way to the nerve and more tissue layers to pass.

Physical quality of bupivacain and lidocain in spinal anesthesia The physical properties of both agents have very big importance when injected and mixed with CSF. Baricity or specific gravity. These terms are used to describe how much the substance weights compared with water Hypobar means lighter than water Isobar means as heavy as water Hyperbar means heavier than water

Bupivacain and Lidocain The baricity influences the mixing of fluids. The temperature influences baricity. We all know how fat eyes swim in the soup or how warm water rises up and cold water sinks down. The CSF is a little heavier, about 6 grams per liter, than water Bupivacain plain is isobar but a pit lighter than CSF. It tends to rise up in CSF before penetrating and getting fixated in nerves, which takes about ten minutes.

cont It is possible to influence the baricity of anesthetics. With added sugar the agents can be made hyperbar. They sink in CSF instead of rising and anesthetize segments in the lower body, especially when injected in sitting position. It is more safe to inject bupivacain plain in lateral decubitus position. The likelihood of high spread of anesthesia is less. It is also good to remember in this hot climate, that warm weather makes the agents lighter!!

How soon can we start to operate? Spinal anesthesia with all agents is faster than epidural anesthesia. Bupivacain onset time in spinal anesthesia is up to 10 minutes, in epidural up to 30 minutes and in plexus anesthesia 20 to 30 minutes. Lidocain has shorter onset times in all regional anesthesias. The onset time depends on many factors and qualities of the agents. Remember to test, that anesthesia sits!!

Clinical effects Bupivacain has clearly longer effect than lidocain, but the onset time is shorter with lidocain. In normal daily work the duration of anesthesia should influence the choice of anesthetic. The spread of spinal anesthesia with bupivacain depends more on dose in mg than volume injected. In epidural anesthesia the volume injected designates the spread of anesthesia. Bupivacain is more toxic for the heart than lidocain if accidentally injected intravenously during epidural anesthesia.

Consequences The brain gets no information from the anesthetized body parts The anesthetic stops all orders from brain. If intercostal muscles are anesthetized the patients complain heaviness. Respiration stops if cervical segment 4 is anesthetized. Autoregulation of circulation is out of duty and all blood vessels are open. This means pooling of circulating blood volume in area anesthetized and blood pressure falls. The decrease is worse or catastrophic if the patient is hypovolaemic.

Consecq. continued Give always volume when doing spinal anesthesia, from 1000 ml saline only 300 ml remain in the blood vessels, the rest is distributed in extra cellular space! Follow blood pressure at the beginning often, to get information about the way, how the patient reacts. Follow the saturation and start immediately oxygen if saturation falls below 90. Put the Cesarean section patients in left lateral tilt, because the abdominal muscles of mother will be relaxed. The uterus prevents the blood flow in vena cava and aorta when patient is laying supine. Almost all gravid women tend to chose spontaneously lateral decubitus position before delivery. The baby deserves all our activity to come to this world with all his brain cells intact!

Complications Neural damage. Because the spinal cord can reach down until L2, make injection more down, between L3/4. For other regional procedures very good knowledge of anatomy is essential. Vasovagal reaction, often young men. Total spinal anesthesia with circulatory arrest and respiratory failure Most common, up till 40%, is head ache. It can be prevented when using thin needles gauge 25 or 27. Thicker needles should be used only for diagnostic purposes Infection

Thank you for your attention! Asante sana!