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Objectives To give an overview of regional anesthesia To review the anatomy and physiology of spinal and epidural anesthesia

Regional Anesthesia Coined by Harvey Cushing A localized area of the body can be rendered pain free and operated upon without losing consciousness Involves a block of a spinal nerve with local anesthetics The introduction of local anesthesia followed that of general anesthesia by about 40 years, starting in 1860 with the numbing effect of cocaine on the tongue. Corning described the use of cocaine in spinal anesthesia in 1885.

Pros and Cons of Regional Anesthesia Simplicity, because the costs are reasonable, agents are easily injected, post-op care is lessened Decreases the autonomic and endocrine response to stress through interference with afferent nerve conduction Suitable in cases where patient’s cooperation is required, in patients who are risks for aspiration Surgery itself produces a stress response. General anesthesia adds to the stress response.

Pros and Cons of Regional Anesthesia Lack of patient acceptance Impracticality of anesthesizing some body areas Effects and complications of local anesthetics resulting in morbidities and mortalities Fear of injections, of being awake during the procedure

Neuraxial Blocks Spinal, Epidural, Caudal Anesthesia Results in sympathetic block, sensory analgesia, and motor block after insertion of a needle and delivery of drug in the plane of the centroneuraxis

ANATOMY Spinal column extends from foramen magnum to sacral hiatus Vertebral column: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal vertebrae Spinal cord extends cephalad from the brainstem via the foramen magnum and extends distally in the conus medullaris, L3 in infants,L1 in adults.

Bony Landmarks

Anatomy of the Vertebra Spinal canal contains spinal cord and coverings, pia, arachnoid and dura Spinal cord extends from foramen magnum to L1 – L2 Subarachnoid space between arachnoid and pia mater, contains CSF 3 membranes that protect the spinal cord are 1. dura mater or tough mater, outermost and extends up to S2. 2. Arachnoid mater is the middle layeror cobweb mother, also ends at S2, 3. pia mater or soft mother, clings to the surface of the spinal cord and ends in the filum terminale, which helps to hold the spinal cord to the spinal column.

Absolute Contraindications to Spinal Anesthesia Patient refusal Sepsis at the site of injection Hypovolemia Coagulopathy Indeterminate neurologic disease Increased intracranial pressure

Spinal Anesthesia Placement of LA solutions into the subarachnoid space, often lumbar Landmarks: vertebral spinous processess iliac crests Selected interspaces: L3, L4, L4-L5

Techniques Midline approach Lateral or paramedian approach Taylor approach Taylor Approach: the Taylor or lumbosacral approach is a paramedian approach directed at the L5-S1 interspace

Spinal Anesthesia Spinal tap: Midline Skin Subcutaneous tissue Supraspinous ligament Interspinous ligament Ligamentum flavum Dura mater Subdural Space Arachnoid Mater Subarachnoid Space Landmark: Tuffier’s line – line between iliac crests passing through L4 – L5 interspace or L4 spinous process itself Paramedian Approach: Skin Subcutaneous tissue, Ligamentum Flavum, Duramater, Subdural space, Arachnoid Mater, subarachnoid space

Level / Distribution Position during first few minutes Baricity of LA solution: density of LA density of CSF (1.001-1.005) Dose of the Anesthetic injected Baricity: density of local anesthetic divided by the density of the local anesthetic at 37oC

LA solutions HYPERBARIC – add glucose (dextrose) to increase density; settle to dependent region HYPOBARIC – add sterile water; floats up to the nerves innervating surgical site ISOBARIC – dilute with CSF; NaCL

Duration Drugs used: Tetracaine/ bupivacaine> lidocaine> procaine Vasoconstrictor – Epinephrine, Phenylephrine Tissue vasoconstriction decreases SC blood flow and vascular absorption, prolonging the duration of the anesthetic 0.1 ml of Epinephrine in 10 ml LA =1:100,000 sol: .1 ml in 20ml = 1:200,000 solution, etc

Physiology Spinal anesthesia interrupts sensory, motor and sympathetic nervous system Classic concept: conduction blockade through small diameter, unmyelinated (sympathetic fibers) before interrupting conduction via larger myelinated (sensory and motor) fibers

Level and Distribution Desired level is dependent on type of surgery The SNS nerves are the first to be blocked, early evaluation is by temperature discrimination Level of sensory anesthesia is evaluated by pinprick

Skeletal muscle power is tested by asking patient to dorsiflex foot (S1-S2), raise legs (L2-L3), or tense abdominal rectus muscles (T6-T12)

Physiologic Effects of Spinal Anesthesia Cardiovascular Effects: L1 and B adrenergic blockers = decrease HR and BP Pulmonary Effects: TV unchanged Gastro-intestinal Effect: increased vagal activity results in inc peristalsis of GIT= nausea High levels of motor anesthesia produces paralysis of abdominal and intercostal muscles, decreased ability to cough and expel secretions Treatment of nausea: Atropine Respiratory arrest 2o to hypoperfusion of respiratory centers in the brainstem

Physiologic Effects of Spinal Anesthesia Renal Effects:Ureters are contracted, and ureterovesical orifice is relaxed: urinary retention Block of afferent impulses from the surgical site leads to absence of adrenocortical response to pain Decreased bleeding may reflect decreased BP Increased blood flow to LE decreased thromboembolism

complications Neurologic Injury – includes Cauda Equina syndrome, hematomas, abscess formation, arachnoiditis, meningitis

POSTSPINAL HEADACHE Frontal/ occipital, worsened by sitting, improved by supine Tinnitus, decreased hearing, diplopia Due to decreased CSF pressures and resulting tension on meningeal vessels and nerves as a result of leakage of CSF thru dural hole Diplopia is due to traction on abducens nn. Prevalent in young females, large gauge spinal needle Dr. august Bier first described this in 1898 after experimenting on himself. PDPH is due to loss of CSF

Treatment: Bed rest, analgesics Hydration (> 3L/d) to inc CSF production Epidural blood patch (10-20ml) to seal dura Caffeine-sodium benzoate

HIGH SPINAL excessive level of sensory and motor anesthesia associated with difficulty breathing or apnea, arterial hypoxemia or hypercarbia Apnea reflects ischemic paralysis of medullary ventilatory centers due to profound hypotension and associated with decreased CBF

Treatment: support breathing and circulation Positive pressure ventilation with face mask IVF and sympathomimetics Head-down to inc. venous return; head-up will jeopardize CBF medullary ischemia Intubation of trachea in those at risk for aspiration (parturients)

Cardiovascular Collapse Bradycardia precedes cardiac arrest ACLS should be initiated early Tx: atropine, Epinephrine, volume loading

Epidural Anesthesia Similar to spinal anesthesia except local anesthetics reach blood level concentrations sufficient to cause systemic effects on their own

Unlike spinal, (-) zone of differential SNS block and zone of differential motor block may average 4 rather than 2 segments below sensory Effects on breathing and GIT resemble those produced by spinal anesthesia

Complications 1. ACCIDENTAL DURAL PUNCTURE Appearance of CSF (warm) at hub; at this point may opt to spinal, or attempt epidural at a different interspace Post-spinal headache is likely due to large hole in dura

HIGH SPINAL Accidental subarachnoid injection of large volumes of LA used produces rapid evidence of high spinal

3.. LA TOXICITY Due to high dose of local anesthetic used, rich venous plexuses, accidental intravascular injection may occur

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