spinal anestheisa and epidural anesthesia.pptx

spinal anesthesia

1. SITE OF ACTION- Target binding sites are the superficial and deep portions of spinal cord spinal nerve roots in subarachnoid and epidural space and dorsal root ganglia. Speed of neural blockade depends on size, surface area, degree of myelination of nerve fibres .(S1 and L5 posterior roots are largest and most resistant to blockade) Differential blockade „ Autonomic>sensory>motor (For eg the level of anesthesia to cold sensation most cephalad and is one to two segments higher than the level of pinprick anesthesia which in turn is one to two segments higher than the level of touch anesthesia) „ Sympathetic blockade may be two dermatomes higher than sensory block (pain, light touch) Drug penetration and uptake is directly propotional to drug mass,CSF drug concentration, contact surface area, lipid content and local tissue vascular supply and inversely related to nerve root size Concentration of drug is highest at site of injection. Time for block regression is inversely propotional to to the CSF volume Mechanism of Action 4/23/2024 2

2. PHYSIOLOGICAL EFFECTS OF SPINAL ANAESTHESIA 1.CARDIOVASCULAR SYSTEM Combined α + β blocking effect on heart Venodilatation and fall in venous return lead to low cardiac output and hypotension during onset (Bain-bridge reflex) Decreased stroke volume and heart rate Cardiac output shows a biphasic response *i.e. early transient increase followed by eventual decrease. In old age with cardiac disease SVR tend to fall by 25% whereas CO falls by only 10-15% 4/23/2024 3

3. Block of cardio acclerator sympathetic fibers from T1-T4 leads to subsequent bradycardia Extensive peripheral sympathectomy (T5-L2) also leads to bradycardia and pooling in lower extremities Hypotension triggers compensatory baroreceptor response leading to vasoconstriction and tachycardia above block level, reduction in venous return/RA filling which decreases signal output of intrinsic chronotropic receptors of RA leading to increase in parasympathetic tone. BEZOLD JARISCH REFLEX- Bradycardia and subsequent cardiac arrest due to profound hypotension via activation of 5HT3 mediated receptors of vagus and the ventricular myocardium. 4/23/2024 4

4. 2.GASTROINTESTINAL FUNCTIONS Nausea and vomiting due to GI hyper peristalsis due to unopposed vagal activity. Contracted bowel and relaxed sphincters due to sympathetic blockade. Spleen enlarges 2-3 times in high blocks when its sympathetic efferent fibers (splanchnic nerves) are blocked. Bladder and urogenital dysfunction Colonic blood supply and oxygen availability is increased. 4/23/2024 5

5. 3.RESPIRATORY SYSTEM High spinal may cause paralysis of intercostal muscles, diaphragm and accessory respiratory muscles. Cautiously given in patients with limited respiratory reserve Tidal volume remain unchanged. Vital capacity decreases minimally d/t loss of abdominal muscle contribution in forced expiration Apnea due to hypotension which causes medullary ischemia in high/total spinal cases 4. THERMOREGULATION Vasodilatation causes heat loss which is compensated by vasoconstriction and shivering above the level of block. 4/23/2024 6

6. 5.ENDOCRINE - Stress response is inhibited -response to insulin is augmented -usual increase in ADH during surgery is inhibited Spinal anesthesia in pregnacy Decreased dose requirement due to Mechanical factor : compression of IVC causes shunting of blood to the venous plexus in the vertebral canal leading to decreased vertebral canal space and CSF volume Hormonal factor – higher progesterone levels 4/23/2024 7

7. SPINAL NEEDLES Standard spinal needle consist of three parts:- -Hub -Cannula -Removable stylet Sizes available- 16 to 30 gauge. Length of spinal needle – 90mm Needles are either -Sharp or blunt at tip. -Pencil point needle. -Sharp or round bevel edge. Dura cutting needle: QUINCKE-BABCOCK and GREENE Dura seprating : WHITCRE,SPORTE AND PITKIN 4/23/2024 8

8. Spinal needle Gauge(mm) 16(1.6mm) 18(1.2mm) 19(1.1mm) 20(0.9mm) 21(0.8mm) 22(0.7mm) 23(0.6mm) 25(0.5mm) 26(0.5mm) 27(0.40mm) Colour code White Pink Cream Yellow Deep green Black Deep blue Orange Brown Grey 4/23/2024 9

9. DRUG Lidocaine is 5% and hyperbaric by addition of 7.5%dextrose Rapid onset of action and low toxicity Bupivacaine is 0.5%and made hyperbaric by addition of 8%dextrose Dose <5kg—0.5mg/kg body wt 5-15kg—0.4mg/kg body wt >15kg—0.3mg/kg body wt Ropivacaine (0.5% in dextrose) Levobupivacaine 4/23/2024 10

10. PHARMACOLOGY p K a , lipid solubility, and protein binding of the local anesthetic solution S hort-acting : P rocaine, C hloroprocaine , A rticaine I ntermediate-acting : L idocaine, P rilocaine, M epivacaine L ong-acting : T etracaine, B upivacaine, L evobupivacaine, R opivacaine

11. Procaine. O ne of the oldest spinal anesthetics, drug of choice for spinal anesthesia in the early 20th century. High failure rate, more nausea, slower time to recovery. H yperbaric drug 50 to 200 mg in a 10% concentration. Chloroprocaine . Ultra–short-acting ester LA . Rapid metabolism by pseudocholinesterase, minimal systemic or fetal effects in the setting of epidural labor analgesia. Spinal anesthesia for ambulatory surgery. P reservative-free preparations of chloroprocaine available S hort-duration & faster recovery time than procaine, lidocaine, and bupivacaine. TNS can occur with modern preparations but very few (0.6%) Doses 30-60 mg

12. Lidocaine . Rapid onset & Intermediate duration for shorter procedures that can be completed in 1.5 hours or less. Doses of 50 to 100 mg traditionally prepared as a 5% solution in 7.5% dextrose; associated with both permanent nerve injury and TNS Doses 30-60 mg Prilocaine. Prilocaine is an amide local anesthetic based on the structure of lidocaine. Prilocaine was introduced in 1965 and has an intermediate duration of action that may lend itself to use in the ambulatory surgery setting. 152 A dose of 40 to 60 mg of 2% hyperbaric prilocaine can provide a block to T10 for 100 to 130 minutes, whereas as little as 20 mg combined with fentanyl has been successfully used for ambulatory arthroscopic knee surgery. 153 Prilocaine is rarely associated with TNS. 152,154,155 In large doses (>600 mg), prilocaine can result in methemoglobinemia. This should not be an issue with doses used for spinal anesthesia, but it has been reported after epidural infusions.