Local Anesthetics 5

Local Anesthetics

General principles • Chemistry. Esters

Amides

-Procaine -Chloroprocaine -Tetratcaine -Cocaine

-Lidocaine -Mepivacaine -Bupivacaine -Etidocaine -Prilocaine -Ropivacaine

Metabolism

Metabolism

-Hydrolysis by pseudo-

-Liver

cholinesterase enzyme 2

General principles B.Mechanism of action 1.Local anesthetics block nerve conduction 2. Local anesthetics interact directly with specific receptors on Na+ channel 3. Physiochemical properties High lipid solubility protein binding pKa Lower pH of the drug solution

4.Differential blockade of nerve fibers 5. Sequence of clinical anesthesia. 6. Pathophysiologic factors . 3

Clinical uses of local anesthetics

The drugs in common use are lignocaine, bupivacaine and prilocaine, their characteristics are shown in Table. The choice of drug depends on the speed of onset and duration of action required. Epinephrine (adrenaline) prolongs the latter.

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Characteristics of local anaesthetic drugs Maximum dose Agent

Duration (h)

Plain (mg/kg)

Lignocaine 1–3 Bupivacaine 1–4 Prilocaine 1–3

3 2 4

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With epinephrine (mg/kg) 7 2 8

Local anaesthetic drugs have serious side effects if given in excess, or inadvertently released into the circulation. Toxicity is manifested in a variety of ways ranging from mild excitation to serious neurological and fatal cardiac sequelae.

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Symptoms and signs of local anaesthetic toxicity • Anxiety • Restlessness • Nausea • Tinnitus • Circumoral tingling • Tremor • Tachypnoea • Clonic convulsions • Arrhythmias – ventricular fibrillation – asystole 7

Recommendations for the safe use of epinephrine in local anaesthetic solutions • No hypoxia • No hypercapnia • Caution with arrhythmogenic volatile agents, for example, halothane • Concentration of ≤1:200,000 • Dose <20 ml of 1:200,000 in 10 minutes • Total dose <30 ml/hour

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Requirements before starting regional anaesthesia • Informed consent • Vascular access • Resuscitation drugs and equipment • Sterility of anaesthetist • Sterility of operative site • No contraindications to procedure • Correct dosage of local anaesthetic drug

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Epidural 、 Spinal and Caudal

anaesthesia

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General considerations A.Preoperative assessment B. The area where the block is to be administered should be examined C. A history of abnormal bleeding and a review of the patient's medications D. Patients should be given a detailed explanation E. patients should receive appropriate monitoring and have an intravenous (IV) line in place

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Segmental level required for surgery A knowledge of the sensory, motor, and autonomic distribution of spinal nerves will help the anesthetist determine the correct segmental level required for a particular operation and help anticipate the potential physiologic effects of producing a block to that level. illustrates the dermatomal distribution of the spinal nerves.

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Segmental level required for surgery Key Dermatomes & Levels -C1-C2: Oops… -C3,4,5: Keep the diaphragm alive… -T1-T4: Cardioaccelerator -T4: Nipple line -T6: Xyphoid process -T10: Umbilicus -S2,3,4: Keep the penis off the floor… 13

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Contraindications to peridural anesthesia

A. Absolute 1.Patient refusal. 2.Localized infection at skin puncture site. 3.Generalized sepsis (e.g., septicemia, bacteremia). 4.Coagulopathy. 5.Increased intracranial pressure. B. Relative 1.Localized infection peripheral to regional technique site. 2.Hypovolemia. 3.Central nervous system disease. 4.Chronic back pain. 15

Section 1

Epidural anesthesia

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Epidural anesthesia is achieved by introduction of anesthetics into the epidural space.

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Anatomy The epidural space runs from the base of the skull to the bottom of the sacrum at the sacrococcygeal membrane. The spinal cord, cerebrospinal fluid and meninges are enclosed within it .

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Anatomy The spinal cord becomes the cauda equina at the level of L2 in an adult and the cerebrospinal fluid stops at the level of S2. The epidural space is 3–6mm wide and is defined posteriorly by the ligamentum flavum, the ante-rior surfaces of the vertebral laminae, and the articular processes. Anteriorly it is related to the posterior longitudinal ligament and laterally is bounded by the intervertebral 33 foramenae and4the pedicles. Vertebra (inc coccygeal) Curvature( 弯曲） L1 and S2 (end of cord/dura) Angle of spinal processes 19

Anatomy

The contents of the epidural space are: • nerve roots • venous plexus • fat • lymphatics

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Anatomy This is an accurate, and even colorful representation of the Epidural space in relation to other structures present in the vertebral area

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Anatomy

The view from above looking down, gives an interesting perspective on the planes traversed with the epidural needle

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Epidural anesthesia technique --Preparation Obtain an epidural anesthesia kit Check the contents of the kit for the following items -Skin local -Test dose -16-18g Husted or Touhy needle -Glass syringe -Epidural catheter with adapter for injection -Various needles for local, “seeker”, etc. 23

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Epidural anesthesia technique Positioning Sitting vs. lateral decubitis -Most beginners do better sitting -ALL patients should be on the monitor before starting  Encourage the patient to extrude their lower back -Use yourself as an example - “Push your back out toward me, arched like a mad cat” - “pretend you are the world’s largest boiled shrimp” This will open up the interspace, help ID your landmarks, and improve your chances 

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Paramedian Approach: Larger Aperture Better feel

Epidural anesthesia technique Approach 1.Midline easier

2.Paramedian when there is narrowing of the interspace or difficulty in flexion of the spine

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Epidural anesthesia  Epidural anesthesia technique  Preparation of the skin is done in a circular motion from the center out to the periphery  Use all 3 scrub brushes  Place eye drape centered over your target  You can use either the end of your pen or your fingernail to make an indentation in the back to find your target more readily

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Epidural Anesthesia  Epidural anesthesia technique  Skin wheal is accomplished with plain lidocaine • Be fairly generous

 Seeker needle is placed and more local injected on removal  Some people like to use an 18g needle to break the skin, followed by the epidural needle into the same hole • This is because the epidural needle is not sharp and significant pressure may be required to break the skin with it

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Epidural Anesthesia  Epidural anesthesia technique  The needle is inserted using landmarks and position identical to that used in spinal anesthesia  Advance the needle and go through the supraspinous ligament (feels gritty) and seat it in the intraspinous ligament  Now the needle should not droop when you let go  Remove the stylet at that time and place your glass syringe tightly onto the hub of the needle

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Epidural anesthesia

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Epidural Anesthesia  Epidural anesthesia technique  Loss of resistance technique • • • •

Some people use saline Some use air Some wet the barrel with saline and use air Some use a combination of air and saline

 Advance the needle 1mm at a time, then ballot the syringe

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Epidural Anesthesia  Epidural anesthesia technique  Loss of resistance technique • Maintain contact with the skin with your nondominant hand • You will notice the resistance increase when you enter the ligamentum flavum – This is not always the case in OB

• Continue to advance until air/saline injects with ease • Injecting saline may help “tent” the dura and make catheter placement easier • If fluid rushes back at you when you disconnect the syringe, it is probably CSF

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Epidural Technique (Loss of Resistance Technique)

Hand-position Note depth Air or Saline debate Catheter 3-5 cm in space (should go easily) 34

Air vs Saline LOR Technique

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Hanging drop technique  Consider for Cervical Epidurals (thin epidural space)  Prone or sitting

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Epidural anesthesia

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Epidural Anesthesia  Epidural anesthesia technique • If you think you may have wet tapped the patient, but are not sure, or if you aspirate fluid from your catheter, you can test it using glucose test strips

 The catheter has a large mark on it to signify the end of the needle  You advance the catheter 2.5 to 4cm  Hold the catheter as you remove the needle  When the catheter is visible at the skin, grasp it there and pull the needle the rest of the way off

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Epidural Anesthesia  Epidural anesthesia technique  Place the catheter injection adapter onto the catheter • Push the end of the catheter into the adapter and screw it closed • Give it a gentle tug to ensure it is seated and clamped

 Tape the catheter in the manner. The techniques vary greatly

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Epidural Anesthesia  Epidural anesthesia technique  Using sterile technique, draw up your test dose • Aspirate the catheter to ensure you do not see fluid or blood • Inject 3ml of test dose (pt.should be on the monitor) – If catheter is intravenous, you should notice a 20% increase in B/P and Heart rate, due to the 15ug epinephrine – If the catheter is subarachnoid, you should notice a sympathectomy and partial sensory/motor block ensure

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Epidural Anesthesia  Epidural anesthesia technique  The rule of thumb is 0.5-1.5ml of local per segment of block desired  3-5ml of local every 3 minutes until level desired is reached  Slow dosing decreases the untoward sympathectomy complications  Baricity is not a factor in the epidural space, because there is no other fluid normally present

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Epidural anesthesia

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Epidural anesthesia

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Epidural Anesthesia  Epidural anesthesia technique  Place the patient in the position of comfort if laboring  For non labor patients, do not position them for surgery until you are sure you have an adequate block  Gravity matters! It will influence the direction and spread of the block, so consider it’s implications during your dosing regimen

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Epidural anesthesia

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Epidural Anesthesia  Combined spinal/epidural technique       

Spinal anesthetic followed by epidural infusion Combines rapid onset with sustained analgesia May be used for surgery/post op pain management May be used for labor/delivery Access epidural space Spinal needle fits through the lumen of the epidural Epidural needle is special – must have “back eye”

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Epidural anesthesia

Undocumented concern exists that some of the epidural injection can migrate subarachnoid, causing an increased level of block

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Epidural Anesthesia  Immediate complications of epidurals  Sympathetic nervous system disruption (sympathectomy) • Severe hypotension (pre-ganglionic sympathetic block) – Peripheral vasodilation – Venous pooling – Reduction in venous return

• High block may result in anesthetizing cardiac accelerators (T1-T4), with resulting slowed heartrate called the “Bainbridge Reflex”

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Epidural Anesthesia  Immediate complications of epidurals  Perioperative hypotension • • • • • • •

Rapid position changes Skeletal muscle tone loss Decreased venous return Reflex surgical stimulation Low volume status Preoperative medications Concurrent medical problems

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Epidural Anesthesia  Immediate complications of epidurals  Perioperative management of hypotension • Non glucose containing crystalloid solutions – 5mL/kg bolus

• Elevated heart rate – phenylephrine (if no contraindications) • Decreased heart rate – ephedrine (if no contraindications) • Risk of mortality increases the longer hypotension persists • Be careful using trendelenburg position, especially when you are using a hyperbaric spinal or high volume epidural 51

Epidural Anesthesia  Immediate complications of epidurals  Hypertension • • • • • •

Rare, but does happen Anxiety Pain Vasopressors Consider vasodilators, narcotics, anxioulytics Always consider discomfort in the places that are NOT anesthetized.

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Epidural Anesthesia  Immediate complications of epidurals  Hypoxia and/or hypercarbia • High level of block can be insidious • Remember C3,4,5 keeps the diaphragm alive • Once your level of blockead has exceeded C3, phrenic nerve paralysis will ensue • Perception of intercostal nerves and abdominal excursion is lost at the level of T2-4 • Intercostal nerves account for 20% of tidal breathing – some of our patients don’t tolerate that well!

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Epidural Anesthesia  Immediate complications of epidurals  Hypoxia and/or hypercarbia • Anxiety due to inability to sense tidal breathing may occur • Increased doses of sedatives and/or narcotics can compound your problem • Hypoventilation increases with decreasing level of consciousness • With intercostal nerve paralysis, cough becomes ineffective • May lead to inability to protect the airway

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Epidural Anesthesia  Total spinal/epidural Can lead to acute pulmonary collapse Treated symptomatically Intubation required Will loose consciousness Will be severely hypotensive, requiring vasopressor infusion  Unopposed parasympathetic system leads to bradycardia and vomiting     

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Epidural Anesthesia  Immediate complications of epidurals  Nausea and/or vomiting • Parasympathetically mediated • Always rule out neurological hypoxia as the first cause • Factors that increase neurological hypoxia: – – – – –

ETOH (ethyl alcohol ) Obesity Prone position Apprehension High level of blockade

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Epidural Anesthesia  Immediate complications of epidurals  Intravascular injection • You can never over test dose a catheter • You should re-test dose if it has been 4 hours since placement or last bolus • IV lidocaine leads to neurologic symptoms, such as ringing in the ears, metallic taste in mouth, numbness and/or tingling around the mouth • Epinephrine 15ug should be enough to cause hypertension, palpitations, anxiety, tachycardia

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Epidural Anesthesia  Immediate complications of epidurals  Intravascular injection • ALWAYS aspirate your catheter before you inject… EVERY time • Positive blood aspiration requires immediate removal and/or replacement of catheter • Positive CSF aspiration is problematic- use blood glucose strip to test if unsure, or CSF will precipitate when mixed with thiopental (not as accurate)

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Epidural Anesthesia  Immediate complications of epidurals  Subarachnoid injection • • • •

Immediate change in sensorium Anxiety Dyspnea Immediate intubation and vasopressor support are crucial to survival • Discontinue the catheter • Call for help!

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Epidural Anesthesia  Delayed complications of epidurals  Post dural puncture headache (PDPH) • Can occur after either obvious or occult dural puncture • CSF leaks chronically out of the hole in the dura • Decreased amount of available CSF in Subarachnoid space • Medulla and brainstem sag into foramen magnum • Resulting stretching of the meninges and pulling on the tentorium cause the headache

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Epidural Anesthesia  Delayed complications of epidurals  Post dural puncture headache (PDPH) • Headaches most common in parturients, as they already have a decreased CSF production and engorged epidural veins • The proposed causes are related to – – – –

Needle type and size Direction of the bevel Number of punctures Patient position

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Epidural Anesthesia  Delayed complications of epidurals  Post dural puncture headache (PDPH) • Incidence decreases with age • More common in women than men • Patient expectations have been correlated with incidence • Symptoms include: – – – – – –

Increased pain with upright position Frontal/occipital headache Stiff neck and shoulders Nausea and/or vomiting Vertigo( 头晕、眼花 ) Blurred vision 62

Epidural anesthesia

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Epidural Anesthesia  Delayed complications of epidurals  Post dural puncture headache (PDPH) • Conservative treatment is always attempted first – – – – –

Bed rest Vigorous hydration (if tolerated) Use of sedatives and opioids Abdominal binder for ambulation Caffeine and niacin

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Epidural Anesthesia  Delayed complications of epidurals  Post dural puncture headache (PDPH) • Definitive treatment is epidural blood patch – Epidural space is accessed using sterile technique – 30cc of blood drawn from dependent antecubital of patient – Blood is slowly injected into epidural needle until the patient complains of pressure in the back – Pt. Placed supine flat in bed for 2 hours – Severe backache (you artificially induced one heck of a bruise!) almost always follows (tx with ice, analgesics)

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Epidural Anesthesia  Delayed complications of epidurals  Low back pain • Many patients will complain of backache after epidural removed • Traumatic procedure with large needle • Consider if patient positioning during surgery could have exacerbated symptoms • Were there multiple attempts/punctures? • Prolonged labor?

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Epidural Anesthesia  Delayed complications of epidurals  Urinary retention • Common in labor • Most places place foley after epidural in place • Sympathetic blockade allows for parasympathetic override • Bladder distention may occur with fluid bolus • Full bladder can impede fetal decent • Narcotics can exacerbate urinary retention • Allow attempt to void, if possible

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Epidural Anesthesia  Delayed complications of epidurals  Infection • Septic meningitis • Aseptic meningitis • Adhesive arachnoiditis

 Intraneural injection  Injection of wrong medications  Undiagnosed neurological disease

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Epidural Anesthesia  Technical difficulties in epidurals  Broken needles • Most common cause is “burying the needle”  Broken or sheared catheters • NEVER pull a catheter back through the insertion needle • ALWAYS chart that the tip of the catheter was intact when you removed it • Visually inspect all catheters before inserting them  Glass from broken vials in the epidural space • Break away from the tray and use a 4X4 • Use filter needles • Do not core the bottom of the vial when drawing from it

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Section 2

Spinal anesthesia

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Spinal anesthesia involves the administration of local anesthetic into the subarachnoid space.

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Anatomy 1.The spinal canal extends from the foramen magnum to the sacral hiatus. 2.Three interlaminar ligaments bind the vertebral processes together: supraspinous ligament interspinous ligament ligamentum flavum 3. The spinal cord extends the length of the vertebral canal during fetal life, ends at about L-3 at birth, and moves progressively cephalad to reach the adult position near L-1 by 2 years of age. 88

Anatomy 4. The spinal cord is invested in three meninges: The pia mater. The dura mater. The arachnoid . 5. The subarachnoid space lies between the pia mater and the arachnoid and extends from the attachment of the dura at S-2 to the cerebral ventricles above. The space contains the spinal cord, nerves, cerebrospinal fluid (CSF), and blood vessels that supply the cord. 89

Physiology 1.Neural blockade. Smaller C fibers conveying autonomic impulses are more easily blocked than the larger sensory and motor fibers. 2. Cardiovascular. Hypotension is directly proportional to the degree of sympathetic blockade produced. 3. Respiratory. Low spinal anesthesia has no effect on ventilation. With ascending height of the block into the thoracic area, there is a progressive ascending intercostal muscle paralysis.

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Physiology 4.Visceral effects Bladder. Intestine. 5. Renal blood flow is maintained, except with severe hypotension. 6. Neuroendocrine. 7. Thermoregulation.

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Technique 1.Spinal needle.

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Technique 2.Patient position. a.lateral position . b.sitting position c.prone position

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Technique 3.Procedure a.The L2-3, L3-4, or L4-5 interspaces are commonly used for spinal anesthesia. b. Disinfect a large area of skin with an appropriate antiseptic solution. c. Check the stylet for correct fit within the needle. d. Raise a skin wheal with 1% lidocaine and a 25-gauge needle at the spinal puncture site.

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Technique e. Approaches 1.Midline. 2.Paramedian. 3.Needle placement. 4.Remove the stylet 5.Administration of anesthetic.

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Technique

f. Closely monitor (every 60 to 90 seconds) blood pressure, pulse, and respiratory function for 10 to 15 minutes. Determine the ascending anesthetic level by noting the response to gentle pinprick or a cold alcohol swab. Stabilization of the local anesthetic level takes about 20 minutes.

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Determinants of level of spinal blockade

1.Drug dose. 2. Drug volume. 3. Turbulence of CSF. 4. Baricity of local anesthetic solution. 5. Increased intraabdominal pressure. 6. Spinal curvatures.

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Complications 1.Hypotension 2. Bradycardia 3. Paresthesias. 4. Bloody tap. 5. Dyspnea 6. Apnea 7. Nausea and vomiting 8. Postdural puncture headache 9. Backache. 10. Urinary retention. 11. Neurologic impairment 12. Infection 98

Summary Epidural techniques are more difficult to master, so knowledge of “where your needle is” is vital

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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 100

Section 3 Caudal anesthesia (Learn by yourself)

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References(video) http://v.blog.sohu.com/u/vw/318279 http://v.blog.sohu.com/u/vw/289724 http://v.blog.sohu.com/u/vw/877237 http://v.blog.sohu.com/u/vw/1627820

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Peripheral nerves are classified according to size and function

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Neural blockade of peripheral nerves usually progresses in the following order: a. Sympathetic block with peripheral vasodilation and skin temperature elevation. b. Loss of pain and temperature sensation. c. Loss of proprioception. d. Loss of touch and pressure sensation. e. Motor paralysis.

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Pathophysiologic factors a. A decrease in cardiac output reduces the volume of distribution and plasma clearance of local anesthetics, increasing plasma concentration and the potential for toxicity. b. Severe hepatic disease may prolong the duration of action of amino amides. c.Renal disease has minimal effect. d. Patients with reduced cholinesterase activity (newborns and pregnant patients) and patients with atypical cholinesterase may have an increased potential for toxicity. e.Fetal acidosis may result in greater transplacental transfer and trapping of local anesthetics from mother to her fetus and thus may have an increased potential for fetal toxicity. 106

Spine Landmarks/Positions (Fetal, Sitting, Prone)

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Sitting Position

Advantages: Ease of placement

Disadvantages: Vasovagal Onset w/ hypo or hyperbaric Sedation

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Landmarks L1 End of cord S2 End of dura

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Reverse Trendelenburg Position

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steep Trendelenburg position 112

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