2. Objectives of presentation
• Understanding of spinal anesthesia.
• Physiological effects of spinal anesthesia.
• Pharmacology of spinal anesthesia.
• Treatment of different manifestations that
arise during spinal anesthesia.
• Complications of spinal anesthesia.
• Evaluation of spinal anesthesia.
7. Physiological effects of spinal anesthesia
Relatively small dose and volume to achieve
dense sensory blockade.
Spinal nerve root contain varying mixture of the
fibers including somatic and autonomic fibers
and they vary in their sensitivity to local
anesthetic blockade.
8.
9. Physiological effects of spinal anesthesia
Differential block
Order of sensitivity to local anesthetics
Sympathetic > temperature > pain > touch > motor
Sympathetic block is highest than the sensory block
(pain, light touch) which in turn is higher than the
motor blockade.
10. Physiological effects of spinal anesthesia
Most of physiological side effects of spinal
anesthesia are a consequence of sympathetic
blockade produce by local anesthetic.
Degree of sympathetic block is related to height
of sensory anesthesia.
The effects of sympathetic blockade also involve
the actions of parasympathetic nervous system.
11. Physiological effects of spinal anesthesia
• Clinically, most important effect of
sympathetic block during spinal anesthesia are
on the cardiovascular system.
• Vasodilation
• More marked on venous side of circulation
• Hypotension
• Compensatory vasoconstriction may occur.
12.
13. Physiological effects of spinal anesthesia
• At high level of spinal anesthesia, the cardiac
accelerator fibers which exit spinal cord at T1-
T4 will be blocked
• Blood pooling
• Reduce organ perfusion and cardiac output.
• Unopposed vagal tone
• Cardiac arrest
14. Treatment of CVS manifestation
• To maintain brain and cardiac perfusion,
administration of oxygen, fluid infusion,
manipulation of patient position and
administration of vasoactive drugs are all
options.
• Patients are typically administered a bolus
(500-1000mL) of fluid prior to the
administration of spinal anesthesia in an
attempt to prevent some of the deleterious
effect of spinal blockade.
15. Treatment of CVS manifestation
• Drugs with chronotropic and venoconstrictive
properties are also given. e.g. ephedrine, 5-
10mg intravenously, often is the drug of
choice.
• Besides ephedrine, direct acting α1 adrenergic
receptor agonist such as phenylephrine can be
administered either by bolus or continuous
infusion.
16. Physiological effects of spinal anesthesia
• Sympathetic fibers originating from T5-L1
inhibit peristalsis. This together with a flaccid
abdominal musculature produce excellent
operating conditions for bowel surgery
• Pulmonary problems will be due to intercostal
muscles paralysis and will reduce patient
ability to cough and clear secretions and may
produce dyspnea. It mostly occur due to
medullary ischemia secondary to hypotension.
17. Pharmacology of Spinal Anesthesia
• Currently used drugs for spinal anesthesia in
U.S. are
• Lidocaine: for short procedures.
• Tetracaine: for intermediate to long
procedures.
• Bupivacaine: for long procedures.
• Procaine: for diagnostic blocks
18. Pharmacology of Spinal Anesthesia
• Factors contributing to distribution of local
anesthetics in CSF are:
• Amount of drug injected.
• Speed of injection.
• Temperature of injectate.
• Baricity of the drug injected.
• Position of patient.
• Addition of vasoconstrictor.
19. Complications of spinal anesthesia
• Certain neurological problems may occur
• Possible causes include introduction of foreign
substance in subarachnoid space, infection,
hematoma, mechanical trauma.
• Treatment usually is in effective.
• High concentrations of local anesthetic can
cause irreversible block.
• Lumbar puncture may cause postural
headache.
20. • Treatment involve bed rest and analgesics.
• If this approach fails, an epidural blood patch
with the injection of autologous blood can be
performed.
• Intravenous caffeine (500mg as benzoate salt
administered over 4 hours) is also advocated.
