Download Back to basics of anesthesia

Ilembula Hospital 17.2.2015
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!