Rebecca Johnson, CA 3

Neuraxial Anesthesia:Spinal epidural Caudal November 29, 2012 Rebecca Johnson, CA3

Outline • Anatomy • Mechanism of Action • Systemic Manifestations • Indications/Contrandications • Anticoagulants/Antiplatelets • Anatomic Approaches • Spinal Anesthesia • Epidural Anesthesia • Caudal Anesthesia • Complications

All of the following are true EXCEPT: • A. The interspinous ligament attaches to the ligamentumflavum. • B. The ligamentumnuchae continues inferiorly as the supraspinous ligament. • C. The ligamentumflavum is thickest in the midline and elastin is the primary component. • D. The epidural space terminates cranially at C1. • E. The epidural space is bounded inferiorly by the sacrococcygeal ligament.

Answer: • Boundaries of Epidural Space: • Posterior: • ligamentumflavum/vertebral laminae • Anterior: • posterior longitudinal ligament • Lateral: • vertebral pedicles/intervertebral foramina • Inferior: • sacrococcygeal ligament covering sacral hiatus • Superior: • foramen magnum • D.

Vertebral Column • 7 cervical vertebrae • 12 thoracic vertebrae • 5 lumbar vertebrae • 5 fused sacral vertebrae • Rudimentary coccygeal vertebrae • Paired spinal nerves exit at each level, C1 to S5 • At cervical level • nerves arise above respective vertebrae • Starting at T1 • nerves exit below their vertebrae • As a result… • 8 cervical nerve roots but only 7 cervical vertebrae

Spinal Canal • Contains: • Spinal cord • Meninges (3 layers) • Pia Mater • Arachnoid Mater • Dura Mater • Fatty tissue • Venous plexus • CSF • Subdural space • Poorly demarcated, potential space that exists between the dura and arachnoid membranes

Anatomic features pertinent to the performance of neuraxial blockade include all EXCEPT: • A. In adults, the spinal cord ends at L1-L2. • B. The angulation of the spinous process of the thoracic vertebrae makes a paramedian approach preferable. • C. In adults the dural sac ends at S2. • D. The largest interspace in the vertebral column is L4-L5. • E. Midline insertion of an epidural needle is least likely to result in unintended meningeal puncture.

Answer • D. • The largest interspace is L5-S1. • The ligamentumflavum is farthest from the spinal meninges in the midline, measuring 4-6mm at L2-L3 interspace.

Anatomy • The spinal cord extends from the foramen magnum to the level of L1 in adults • In infants, the spinal cord ends at L3 and moves up as they grow older • Lower nerve roots course some distance before exiting the intervertebral foramina • Forms the cauda equina • Pushing vs piercing the cord • The dural sac, subarachnoid and subdural spaces usually extend to S2 in adults • Often to S3 in children

Blood Supply • Anterior 2/3 of cord • Anterior spinal artery • vertebral artery • Posterior 1/3 of cord • Two posterior spinal arteries • posterior inferior cerebellar arteries • Radicular arteries • intercostal arteries in the thorax • lumbar arteries in the abdomen • The artery of Adamkiewicz • Aorta • Typicallyunilateral and on the ___ side? • Left • Major blood supply to the anterior, lower 2/3 of the spinal cord • Injury to this artery can result in …? • Anterior spinal artery syndrome

Mechanism of Action • Principal site of action - nerve root • Local anesthetic bathes the nerve root in the subarachnoid space or epidural space • Spinal anesthesia: • Direct injection of LA into CSF • Relatively small dose and volume to achieve dense sensory and motor blockade • Epidural/Caudal anesthesia: • Same LA concentration is achieved at nerve roots only with much higher volumes and quantities • Level for epidural anesthesia • Must be close to the nerve roots that are to be anesthetized

Somatic Blockade • Sensory blockade interrupts both somatic and visceral painful stimuli • Motor blockade produces skeletal muscle relaxation • Provides excellent OR conditions • LA effect on nerve fibers varies according to many factors: • Size of the nerve fiber • Myelination • Concentration achieved • Duration of contact • Smaller and myelinated fibers aremore easily blocked

Somatic Blockade • Spinal nerve roots contain varying mixtures of these fiber types and they vary in their sensitivity to the LA blockade • This results in a differential block • Which nerve fibers are blocked by the lowest sensitivity to LA? • A. pain • B. motor • C. sympathetic • D. touch • Order of sensitivity: • Sympathetic > pain > touch > motor

Somatic Blockade • Sympathetic block is highest, generally 2(up to 6) segments higher than the sensory block (pain, light touch) • Which in turn is usually 2-3 segments higher than the motor blockade

Autonomic Blockade • Block of efferent autonomic transmission • sympathetic and some parasympathetic blockade • Sympathetic outflow from the spinal cord • Thoracolumbar • Sympathetic preganglionic nerve fibers • exit the spinal cord with the spinal nerves from T1 to the L2 level and • may course many levels along sympathetic chain before synapsing with a postganglionic cell in a sympathetic ganglia • Parasympathetic outflow • Craniosacral • Parasympathetic preganglionic fibers exit the spinal cord with the cranial and sacral nerves • Neuraxial anesthesia does not block the vagus nerve • decreased sympathetic tone and/or unopposed parasympathetic tone

A pt receives a spinal anesthetic with a sensory level of T5. Which of the following is likely to occur? • A. The small bowel will be dilated and relaxed. • B. Glomerular filtration will be decreased by one third. • C. Tidal volume will be reduced by one third. • D. The cardioaccelerator nerves will be unaffected. • E. Blood pressure will lower predominantly by decreasing venous return.

Answer • E • Level of sympathetic block can be 2-6 levels higher than sensory block.

Cardiovascular Manifestations • Variable decreases in blood pressure • +/- decrease in heart rate and cardiac contractility • Generally proportional to degree of the sympathectomy • Arterial and venous smooth muscle vasomotor tone: • Innervated by sympathetic fibersfrom T5 to L1 • Blocking these nerves causes: • vasodilation of the venous capacitance vessels • pooling of blood • decreased venous return to the heart • Arterial vasodilation may also decrease SVR • May be minimized by compensatory vasoconstriction above the level of the block

Cardiovascular Manifestations • A high sympathetic block • prevents compensatory vasoconstriction • blocks the sympathetic cardiac accelerator fibers that arise at …? • T1–T4 • Profound hypotension may occur • Vasodilation combined with bradycardia and decreased contractility • Exaggerated if venous return is further compromised • head-up position or gravid uterus • Sudden cardiac arrest sometimes seen with spinal anesthesia • Unopposed vagal tone

Cardiovascular Manifestations • Steps to minimize the degree of hypotension: • Volume loading with 10–20 mL/kg of IVF • partially compensates for the venous pooling • LUD in the third trimester of pregnancy • minimizes obstructionto venous return • Hypotension may still occur • Increase IVFs • Autotransfusion - head-down position • Vasopressors (phenylephrine/ephedrine) • Excessive or symptomatic bradycardia • Atropine • If profound hypotension and/or bradycardia persist • Epinephrine (5–10 mcg)

Pulmonary Manifestations • Usually are minimal • diaphragm innervated by the phrenic nerve with fibers originating from C3–C5 • Even with high thoracic levels… • tidal volume is unchanged • only a small decrease in vital capacity • from loss of abdominal muscles' contribution to forced expiration • Phrenic nerve block may not occur even with total spinal anesthesia • apnea often resolves with hemodynamic resuscitation • suggests that brain stem hypoperfusion is responsible

Pulmonary Manifestations • Severe chronic lung disease patients • Rely upon accessory muscles of respiration • Coughing and clearing of secretions require these muscles • High levels of neural blockade impair these muscles • Use caution in patients with limited respiratory reserve • Must weigh against the advantages of avoiding airway instrumentation and PPV • Surgery above the umbilicus • Pure regional technique may not be thebest choice

Pulmonary Manifestations • Thoracic or upper abdominal surgery • Decreased diaphragmatic function postop • Decreased FRC • Atelectasis and hypoxia via V/P mismatch • Postop thoracic epidural analgesia may improve pulmonary outcome • decrease the incidence of pneumonia and respiratory failure • improve oxygenation • decrease duration of vent support

GI Manifestations • Sympathetic outflow originates at T5–L1 • Sympathectomy - vagal tone dominance • small, contracted gut with active peristalsis • Excellent operative conditions for lapprocedures when used as an adjunct to GENA • Postoperative epidural analgesia has been shown to hasten return of GI function • Hepatic blood flow will decrease with reductions in MAP from any anesthetic technique • Intraabdominal surgery - decrease in hepatic perfusion related more to surgical manipulation than to anesthetic technique.

Urinary Tract Manifestations • Renal blood flow – maintainedthrough autoregulation • little clinical effect upon renal function • Neuraxial anesthesia at the lumbar and sacral levels blocks both sympathetic and parasympathetic control of bladder function • Loss of autonomic bladder control results in urinary retention until the block wears off • If no urinary catheter is anticipated perioperatively: • use the shortest acting and smallest amount of LA necessary for the procedure • limit the amount of IVF as much as possible • Monitored pt for urinary retention to avoid bladder distention following neuraxial anesthesia

Metabolic & Endocrine Manifestations • Surgical trauma produces a neuroendocrine response • localized inflammatory response • activation of somatic and visceral afferent nerve fibers • increases in ACTH, cortisol, epinephrine, NE, and vasopressin • activation of the renin–angiotensin–aldosterone system • Clinical manifestations: • HTN, tachycardia, hyperglycemia, protein catabolism, suppressed immune responses, and altered renal function • Neuraxial blockade can partially suppress (during major invasive surgery) or totally block (during lower extremity surgery) this stress response • Reduction in catecholamine release • may decrease perioperative arrhythmias and reduce the incidence of ischemia • Neuraxial block should precede incision and extend postop

Indications for Neuraxial • Used alone or in conjunction with GENA for most procedures below the neck • Most useful for: • lower abdominal • inguinal • urogenital • rectal • lower extremity surgery • Lumbar spinal surgery may also be performed under spinal anesthesia • Upper abdominal procedures • difficult to achieve a sensory level adequate for patient comfort yet avoid the complications of a high block • Spinal anesthesia for neonatal surgery

Contrandications Coagulopathy or other bleeding diathesis Inability to communicate with pt Infection at the site of injection Preexisting neurological deficits Patient refusal Sepsis Absolute Relative Controversial • Inability to communicate with pt • Prior back surgery at site of injection • Complicated surgery • Prolonged operation • Major blood loss • Maneuvers that compromise respiration • Patient refusal • Infection at the site of injection • Coagulopathy or other bleeding diathesis • Severe hypovolemia • Increased intracranial pressure • Severe aortic stenosis • Severe mitral stenosis • Preexisting neurological deficits • Sepsis • Uncooperative patient • Demyelinating lesions • Stenotic valvular heart lesions • Severe spinal deformity

Oral Anticoagulants • Long-term warfarin therapy • Must be stopped • Need PT/INR to be normalized • Perioperative thromboembolic prophylaxis • If initial dose given > 24 h prior to the block or if more than one dose was given • PT and INR need to be checked • If only one dose given within 24 h • Safe • Removing an epidural catheter from patients receiving low-dose warfarin (5 mg/d) • Safe

Antiplatelets • Aspirin and NSAIDs • Alone don’t appear to increase risk of spinal hematoma • More potent agents • Ticlopidine (Ticlid) • 14 days • Clopidogrel (Plavix) • 7 days • Abciximab (Rheopro) • 48 h • Eptifibatide (Integrilin) • 8 h

Unfractionated Heparin • Minidose subQ prophylaxis • OK to proceed • Patients to receive heparin intraoperatively • 1 h or more before heparin administration • A bloody epidural or spinal does not necessarily require cancellation of surgery • discussion of the risks with the surgeon • careful postoperative monitoring needed • Removal of an epidural catheter • 1 h prior to dosing • or 4 h followingdosing • Patients on therapeutic doses of heparin (elevated PTT) • Avoid neuraxial • The risk of spinal hematoma is undetermined in the setting of full anticoagulation for cardiac surgery

LMWH (Enoxaparin, Dalteparin, -parin) • Intro of Lovenox in the US in 1993 • Reports of spinal hematomas associated with neuraxial anesthesia • Many involved intraop or early postop use, and several also taking antiplatelets • If bloody needle or catheter placement occurs • Delay until 24 hrs postop • Postop LMWH thromboprophylaxis if epidural catheter in place • Remove 2 hrs prior to the first dose • Or 10 hrs after last dose and subsequent dosing should not occur for another 2 hrs

Fibrinolytic or Thrombolytic Tx • Best to avoid neuraxial.

Please note… • Drugs/regimens not considered to put pts at increased risk of neuraxial bleeding when used alone (minidosesubQ heparin, NSAIDS) may in fact increase the risk when combined.

Which of the following statements regarding spinal needle insertion is TRUE? • A. The first significant resistance encountered when advancing a needle using the paramedian approach is the interspinous ligament. • B. If bone is repeatedly encountered at the same depth when the needle is advanced, the needle is likely walking down the inferior spinous process. • C. The midline approach is preferred in patients with heavily calicifiedinterspinous ligaments. • D. Free flow of CSF after resolution of a paresthesia usually indicates that the needle is in a good position. • E. Penetration of the dura mater is more easily detected with a beveled needle.

Answer • D. • If a paresthesia occurs you should immediately stop advancing the needle and check for CSF. • Obtaining CSF after resolution of a paresthesia indicates the needle encountered a caudaequina nerve root in the subarachnoid space and the needle tip is in a good position. • DO NOT inject LA in presence of a persistent paresthesia!

Anatomic Approaches • Spinous processes • Cervical and lumbar spine – horizontal • Needle directed with only a slight cephalad angle • Thoracic spine – slant in a caudal direction and can overlap • Needleangled significantly more cephalad • First palpable cervical spinous process is C2 • Most prominent is…? • C7 • Inferior tip of the scapula at level of …? • Spinous process of T7 • Highest points of both iliac crests (Tuffier's line) ? • Bodyof L4 or the L4–L5 interspace • Posterior superior iliac spine • S2 posterior foramina • Sacral hiatus • Depression just above or between the gluteal clefts and above the coccyx

Midline Approach • Body positioned with the plane of the back perpendicular to the floor • Palpate for depression between the spinous processes of the vertebra above and below the level to be used • Subcutaneous tissues offer little feeling of resistance • Supraspinous and interspinous ligaments felt as an increase in tissue density • If bone contacted superficially • needle is likely hitting..? • the lower spinous process • If bone contacted at a deeper depth • and needle is in the midline it is likely hitting…? • the upper spinous process • or if it is lateral to the midline it is likely hitting…? • a lamina • Ligamentum flavum - obvious increase in resistance • At this point, spinal and epidural anesthesia differ

Paramedian Approach • May be useful in certain patients • severe arthritis • kyphoscoliosis • prior lumbar spine surgery • 2 cm lateral to the inferior aspect of superior spinous process • Penetrates the paraspinous muscles • lateral to the interspinous ligaments • needle may encounter little resistance initially and may not seem to be in firm tissue • Needle advanced at a 10–25° angle toward the midline • LOR is often more subtle than with the midline approach

Bone encountered deep • lateral part of the lower lamina • redirected only slightly upward, more toward the midline • Bone at a shallow depth • medial part of the lower lamina • redirect mostly upward and slightly more lateral

Spinal Needles • Available in an array of sizes (16–30 gauge), lengths, and bevel and tip designs • Tightly fitting removable stylet • avoids tracking epithelial cells into the subarachnoid space • 2 broad groups 1. Sharp (cutting)-tipped • Quincke needle is a cutting needle with end injection 2. Blunt tip (pencil-point) needles • Whitacre – roundedpoint with side injection • Sprotte –rounded point with long side opening • markedly decreased the incidence of PDPH

Spinal Catheters • Very small subarachnoid catheters are currently no longer approved in the US • Association with cauda equina syndrome. • Larger catheters designed for epidural use are associated with relatively high complication rates when placed subarachnoid.

Rebecca Johnson, CA 3