Central Nerve Blocks Mostafa Kamel February 2010

Regional Anesthesia Objectives –History –Anatomy –Identify Anatomic Landmarks –Define Steps for spinal, epidural, or caudal needle –Distinguish level of anesthesia after administration of regional –Factors affecting level and duration of block –Explain potential complications and treatments

Regional anesthesia - Definition Rendering a specific area of the body, e.g. foot, arm, lower extremities, insensate to stimulus of surgery or other instrumentation

History cocaine isolated from erythroxylum coca Koller uses cocaine for topical anesthesia Halsted performs peripheral nerve block with local Bier first spinal anesthetic

Spinal Anatomy 33 Vertebrae –7 Cervical –12 Thoracic –5 Lumbar –5 Sacral –4 Coccygeal

Anatomy

Anatomy

Anatomy

Anatomy Spinal cord ends inSpinal cord ends in –Neonate L3-4 –Adult L1 Dural ends inDural ends in –Neonate S4 –Adult S2

Epidural Space Space that surrounds the spinal meninges –Potential space Ligamentum Flavum –Binds epidural space posteriorly Widest at Level L2 (5-6mm) Narrowest at Level C5 (1-1.5mm)

Physiology Principle site of action : nerve rootPrinciple site of action : nerve root Anterior nerve root: efferent motor and autonomic outflowAnterior nerve root: efferent motor and autonomic outflow Posterior nerve root: somatic & visceral sensationPosterior nerve root: somatic & visceral sensation

Regional

Spinal Anesthesia Indications & Advantages –Full stomach –Anatomic distortions of upper airway –TURP surgery –Obstetrical surgery (T4 Level) –Decreased post-operative pain –Continuous infusion

The Good Cheap High Patient Satisfaction Well Tolerated in Pulmonary Disease Maintain Patent Airway Selective Muscle Relaxation Decreased Blood Loss Decreased Incidence of DVT and PE

The Bad Difficult Placement in Elderly Hypotension Patient Can Talk Patient Anxiety Not Reliable for Surgery > 2 hours

The Ugly Bleeding Post-Dural Puncture Headache Transient Neurological Syndrome Total Spinal

Hypotension Bradycardia Arm involvement Shortness of Breath Patient Anxiety Loss of Consciousness

Epidural Anesthesia Indications Acute Pain Syndromes Chronic Pain Syndromes Intra & post operativelyLow Back Pain AHZPHN Ischemic painCRPS Renal painSpinal Cord Stimulators Visceral Abdominal PainChronic Malignancy Obstetric analgesiaEpiduroscopy

Contra-Indications Inadequate equipment for GA Bleeding Dyscrasia’s Hypovolemia Patient Refusal Sepsis/Bactermia Anatomic Deformities of the Spine Neurological Disease Increased ICP Fixed Cardiac Output States

The Good Cheap High Patient Satisfaction Well Tolerated in Pulmonary Disease Maintain Patent Airway Selective Muscle Relaxation Decreased Blood Loss Decreased Incidence of DVT and PE

The Bad Difficult Placement in Elderly Hypotension Patient Can Talk Patient Anxiety

The Ugly High Epidural Local Anesthetic Toxicity Total Spinal Accidental Dural Puncture

Contra-Indications for Regional Anesthesia Patient Refusal Coagulopathy Localized Skin Infection Elevated ICP Hypovolemia Uncooperative Patient Pre-Existing Neurological Disease Spinal Column Abnormalities Fixed Cardiac Output States

Spinal Technique Preparation & Monitoring –EKG –NBP –Pulse Oximeter Patient Positioning –Lateral decubitous –Sitting –Prone (hypobaric technique)

Landmark landmark: iliac crest spinous process  L4-5landmark: iliac crest spinous process  L4-5

Spinal Technique Midline Approach –Skin –Subcutaneous tissue –Supraspinous ligament –Interspinous ligament –Ligamentum flavum –Epidural space –Dura mater –Arachnoid mater Paramedian or Lateral Approach –Same as midline excluding supraspinous & interspinous ligaments

Spinal Anesthesia Levels

Somatic Blockade

Spinal Anesthesia Contraindications –Absolute: Refusal Infection Coagulopathy Severe hypovolemia Increased intracranial pressure Severe aortic or mitral stenosis –Relative: Use your best judgment

Spinal Anesthesia Complications –Failed block –Back pain (most common) –Spinal head ache More common in women ages Larger needle size increase severity Onset typically occurs first or second day post-op Treatment: –Bed rest –Fluids –Caffeine –Blood patch

Spinal Anesthesia Fluid Test for CSF Return –Clear –Free flow –Aspiration into syringe –Litmus Paper –Urine dip stick –Temperature –Taste… If you’re man enough…

Spinal Anesthesia Spread of Local Anesthetics –First to cauda equina –Laterally to nerve rootlets and nerve roots –May defuse to spinal cord –Primary Targets: Rootlets Roots Spinal cord

Epidural Anatomy Safest point of entry is midline lumbar Spread of epidural anesthesia parallels spinal anesthesia –Nerve rootlets –Nerve roots –Spinal cord

Epidural Anesthesia Order of Blockade –B fibers –C & A delta fibers Pain Temperature Proprioception –A gamma fibers –A beta fibers –A alpha fibers

Epidural Anesthesia Test Dose: 1.5% Lido with Epi 1:200,000 –Tachycardia (increase >30bpm over resting HR) –High blood pressure –Light headedness –Metallic taste in mouth –Ring in ears –Facial numbness –Note: if beta blocked will only see increase in BP not HR Bolus Dose: Preferred Local of Choice –10 milliliters for labor pain –20-30 milliliters for C-section

Epidural Anesthesia Distances from Skin to Epidural Space –Average adult: 4-6cm –Obese adult: up to 8cm –Thin adult: 3cm Assessment of Sensory Blockade –Alcohol swab Most sensitive initial indicator to assess loss of temperature –Pin prick Most accurate assessment of overall sensory block

Epidural Anesthesia Complications –Penetration of a blood vessel –Hypotension (nausea & vomiting) –Head ache –Back pain –Intravascular catheterization –Wet tap –Infection

Blood Patch Increase pressure of CSF by placing blood in epidural space If more than one puncture site use lowest site due to rosteral spread May do no more than two 95% success with first patch Second patch may be done 24 hours after first

Caudal Anesthesia Anatomy –Sacrum Triangular bone 5 fused sacral vertebrae Needle Insertion –Sacrococcygeal membrane –No subcutaneous bulge or crepitous at site of injection after 2-3ml

Caudal Anesthesia Post Operative Problems –Pain at injection site is most common –Slight risk of neurological complications –Risk of infection Dosages –S5-L2: 15-20ml –S5-T10: 25ml

Central neuraxial blockade - “Spinal” Injection of local anesthetic into CSF Uses: –profound anesthesia of lower abdomen and extremities Advantages: –technically easy (LP technique), high success rate, rapid onset Disadvantages: –“high spinal”, hypotension due to sympathetic block, post dural puncture headache.

Central Neuraxial Blockade - “epidural” Injection of local anesthetic in to the epidural space at any level of the spinal column Uses: –Anesthesia/analgesia of the thorax, abdomen, lower extremities Advantages: –Controlled onset of blockade, long duration when catheter is placed, post-operative analgesia. Disadvantages: –Technically complex, toxicity, “spinal headache”

Cardiovascular Effects Blockade of Sympathetic Preganglionic Neurons –Send signals to both arteries and veins –Predominant action is venodilation Reduces: –Venous return –Stroke volume –Cardiac output –Blood pressure –T1-T4 Blockade Causes unopposed vagal stimulation –Bradycardia »Associated with decrease venous return & cardioaccelerator fibers blockade »Decreased venous return to right atrium causes decreased stretch receptor response

Hypotension Treatment –Best way to treat is physiologic not pharmacologic –Primary Treatment Increase the cardiac preload –Large IV fluid bolus within 30 minutes prior to spinal placement, minimum 1 liter of crystalloids –Secondary Treatment Pharmacologic –Ephedrine is more effective than Phenylephrine

Respiratory System Healthy Patients –Appropriate spinal blockade has little effect on ventilation High Spinal –Decrease functional residual capacity (FRC) Paralysis of abdominal muscles Intercostal muscle paralysis interferes with coughing and clearing secretions Apnea is due to hypoperfusion of respiratory center

Regional Anesthesia

Differential Blockade Spinal nerve roots : mixtures of fiber typesSpinal nerve roots : mixtures of fiber types Concentration gradientsConcentration gradients Typically results in sympathetic blockade 2 segments higher than sensory blockTypically results in sympathetic blockade 2 segments higher than sensory block

Autonomic Blockade Cardiovascular effectCardiovascular effect –Typically, ↓BP –May be ↓HR and cardiac contractility  degree (level) of sympathectomy –Venodilation : sympathetic block –Venous return & SVR  –HR  : sympathetic cardiac accelerator fiber T1-4

Autonomic Blockade Cardiovascular effectCardiovascular effect –Minimize degree of hypotension Volume loading mL/kgVolume loading mL/kg Head-down positionHead-down position Vasopressor drugVasopressor drug Left uterine displacementLeft uterine displacement

Autonomic Blockade Respiratory effectsRespiratory effects High spinal block : intercostal, abdominal m. paralysis –Caution in patients severe lung disease block T7

Autonomic Blockade Gastrointestinal functionGastrointestinal function –Vagal tone dominant → contracted gut with active peristalsis Urinary tractUrinary tract –renal function –Loss of autonomic bladder control →urinary retention Metabolic & endocrineMetabolic & endocrine

Indication Lower abdominal, urogenital, lower extrimity surgeryLower abdominal, urogenital, lower extrimity surgery Conjunction with general anesthesiaConjunction with general anesthesia

Contraindication AbsoluteAbsolute –Patient refusal –Skin infection at injection site –Coagulopathy –Severe hypovolemia

Contraindication RelativeRelative –Sepsis –Bacteremia –Increase intracranial pressure –Psychosis or dementia –Peripheral neuropathy

Spinal/Epidural Anesthesia

Position

Anatomy

Epidural Anesthesia

Resuscitation

VasopressorVasopressor resuscitation resuscitation

Needles

Approach

Spinal Anesthetic Agents Only preservation free solutionOnly preservation free solution Hyperbaric solution : heavier than CSFHyperbaric solution : heavier than CSF Hypoboric solution : lighter than CSFHypoboric solution : lighter than CSF CSF : specific gravity at 37 C

Drug Doses & Block Levels LEVELTime L4T10T4 0.5% Heavy bupivacaine 4-8 mg8-12 mg14-20 mg mins 0.5% Isobaric bupivacaine mg15-20 mg- 180 mins

Factors affecting level of SB Baricity of anesthetic solutionBaricity of anesthetic solution Position of patientPosition of patient Drug dosageDrug dosage Site of injectionSite of injection

Assessing level of blockade Sensory level : pinprickSensory level : pinprick Sympathectomy : skin temperatureSympathectomy : skin temperature Motor : Bromage scaleMotor : Bromage scale

Complication AcuteLate Cardiac arrest Backache High/Total spinalUrinary retention AnaphylaxiaTransient Neurologic Symptoms (TNS) Systemic toxicityPostdural puncture headache (PDPH) HypotensionCauda Equina Syndrome Meningitis & Arachnoiditis Epidural abscess

Complication Late onset BackacheBackache Urinary retentionUrinary retention –Male > female –Use shortest acting & least amount of drug –Limit amount of iv fluid

Complication Late onset Transient Neurologic Symptoms (TNS)Transient Neurologic Symptoms (TNS) –Back pain radiating to legs without sensory/motor deficits –Occurring after resolution of SB, spontaneously within several days

Complication Late onset Postdural puncture headache (PDPH)Postdural puncture headache (PDPH) –CSF leaks from dural puncture site –Typically; bilateral, fronto- occipital/retroorbit –Hallmark : asso. with position –Onset hrs after procedure

Complication Late onset Postdural puncture headache (PDPH)Postdural puncture headache (PDPH) –Related to Needle size, type and pt. populationNeedle size, type and pt. population –Treatment : ConservativeConservative Epidural blood patchEpidural blood patch

Complication Late onset Cauda Equina Syndrome & other neurologic deficitsCauda Equina Syndrome & other neurologic deficits Meningitis & ArachnoiditisMeningitis & Arachnoiditis Epidural abscessEpidural abscess Spinal& epidural hematomaSpinal& epidural hematoma

Thank you for your attention