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EPIDURAL ANAESTHESIA- Anatomy, physiology, technique and drugs used
- 1. EPIDURAL ANAESTHESIA MODERATOR: DR SWATHIHEGDE PRESENTER: DR REMI SEBASTIAN
- 2. Epidural analgesia isused to supplement general anaesthesia for surgical procedures in patients of all ages with moderate to severe comorbid disease; provide analgesia in in the intraoperative, postoperative, peripartum and end of life settings; and can be used as primary anaesthetic for the surgeries from the mediastinum to lower extremities. It is also used increasingly for diagnostic procedures, acute pain therapy, chronic pain management.
- 3. 1. Epidural anaesthesiais slower in onset, helpful for hemodynamically fragile patients 2. Postop analgesia 3. Thoracic epidural is a part of enhanced recovery after surgery (ERAS) protocol for patients undergoing major intraabdominal and intrathoracic surgeries 4. CSE : intrathecal component can produce rapid anaesthesia and epidural catheter can be used later to enhance and prolong the anaesthesia
- 4. TIMELINE • 1880s -J Leonard Coring : proposed injecting an anaesthetic solution into epidural space. • 1901 – Jean Sicard & Fernand Cathelin : first intentional administration of epidural anaesthesia (single shot caudal nerve blocks with cocaine) • 1921 – Pages : lumbar epidural anaesthesia • 1930 – Dogliotti : LOR technique (Dogliotti’s principle) Gutierrez : hanging drop technique • 1931 – Aburel : continuous epidural catheter for pain relief • 1941 – Hingson & Edwards : continuous caudal anaesthesia with indwelling needle • 1947 – Curbelo : lumbar epidural catheterisation • 1979 – Behar : epidural morphine analgesia
- 5. EPIDURAL SPACE ANATOMY •Epidural space surround the dura mater and extend from foramen magnum to sacral hiatus. • Anterior : posterior longitudinal ligament Lateral : pedicles & intervertebral foramina ( transmission of intra abdominal pressure) Posterior : Ligamentum flavum • Contents : nerve roots fat areolar tissue lymphatics & blood vessels
- 7. THEORIES ON NEGATIVEPRESSURE IN EPIDURAL SPACE 1. The Cone Theory: ligamentum flavum initially bulges in front of the advancing needle and rapidly returns to the resting position once the ligament is perforated. 2. The negative pressure is increased by flexion of the spine 3. The Transmission Theory: transmitted pressure from the pleural cavity through intervertebral foramina.
- 8. SKIN TO EPIDURALDISTANCE • Varies at different levels of vertebral column. • At lumbar level studies on parturients show a range of depth from 2 to 9 cm with 89% in the range of 3.5 to 7.5 cm. • Other factors: patient positioning, edema of skin, degree of flexion, angle of needle insertion. • Distance between ligamentum flavum and dura is estimated as 7mm.
- 9. PHYSIOLOGICAL EFFECTS • Similarto those of spinal anaesthesia with the exception that LA blood levels reach concentrations sufficient enough to produce systemic effects on their own. • Differential blockade Sensory, motor and sympathetic nerve functions are blocked at different rates and to different degrees Depends on - Diameter and myelination - Differences in nerve lipid membrane and ion channel composition - LA type and concentration • Segmental blockade
- 10. FACTORS AFFECTING EPIDURALLA DISTRIBUTION AND BLOCK HEIGHT DRUG FACTORS: Volume: 1 TO 2ML OF SOLUTION TO BE INJECTED PER SEGMENT TO BE BLOCKED Dose: 1-2 ml / segment in lumbar epidural 0.7ml/segment for thoracic epidural 3ml/segment for caudal epidural
- 11. • PATIENT FACTORS: 1.AGE : 40% LESS VOLUME- decreased leak from intervertebral foramine, increased sensitivity to drugs. 2. PREGNANCY: less amount of drug ( engorgement of epidural veins) 3. HEIGHT: < 5 ft – 1ml per segment or 0.1ml per segment for every 2 in. above 5 ft Continuous positive airway pressure increases the height of thoracic epidural block. • PROCEDURE FACTORS: 1. LEVEL OF INJECTION : upper cervical injection- spread is mostly caudal mid thoracic equally cephalad and caudal lumbar- more cephalad than caudal 2. PATIENT POSITION : preferential spread and faster onset to the dependent side in lateral decubitus position
- 12. • Studies byQuinn Hogan on frozen cryomictrotome cadaver sections concluded that, “ distribution of solution in epidural space is non uniform. Rather than a uniform advancing front, spread is directed among paths between structures according to pressures by which they are compressed.” • Age related differences: adipose tissue in epidural space decrease with age. Hence higher level and faster onset. • Clinical unpredictability
- 13. FATE OF DRUGINJECTED IN EPIDURAL SPACE DRUG UPTAKE • The epidural injected LA can get distributed to the CSF through meninges to exert its neural blocking effect (bioavailability in CSF <20% ) • Lost through vascular absoption into capillary vessels and systemic circulation. • Uptake into epidural fat DRUG DISTRIBUTION 1. Crossing the dura mater into subarachnoid space. 2. Longitudinal and circumferential spread within epidural space(enhanced by volume injected) 3. Exit through intervertebral foramina ( elderly and spinal stenosis) 4. Binding to epidural fat ( slows vascular absorption) 5. Vascular absorption to epidural vessels.
- 14. DRUG ELIMINATION • Absorbedby vessels in pia mater, epidural vessels through back diffusion before entering systemic circulation. • The systemic absorption of lignocaine, bupivacaine following lumbar epidural administration has been shown to be biphasic, with a rapid initial absorption phase followed by a much slower absorption phase. • With epidural anaesthesia, the systemic toxicity is very likely after inadvertent intravascular injection of an epidural dose • Relatively small safety margin.
- 15.
- 17. INDICATIONS • Surgeries oflower extremities, perinium, pelvic girdle, lower and upper abdomen, cardiothoracic surgeries. • LUMBAR EPIDURAL BLOCK: major orthopedic surgeries of lower limb, lower limb vascular surgeries, genitourinary procedures,obstetric and gynecological procedures • THORACIC EPIDURAL BLOCK: thoracic and upper abdominal surgeries, along with GA for cardiac surgeries, mastectomy • CERVICAL EPIDURAL: cervical – brachial neuraxial pain, thyroid surgeries, upper limb surgeries
- 20. CONTRAINDICATIONS • RELATIVE: 1. coagulopathy 2.sepsis 3. preexisting neurological disease 4. spine deformity • ABSOLUTE: 1. patient refusal 2. localised sepsis 3. allergy to drugs 4. raised ICP 5. severe coagulation abnormalities
- 21. PROCEDURE AND PREPARATION •Review of PAE and informed consent • Large bore IV access • ASA standard monitors attached • Keep ready airway equipments and emergency drugs • Check the contents in epidural kit for their functioning
- 23. NEEDLES • The epiduralneedles are larger than spinal needles to improve the tactile feel as the needle advances through ligamentum flavum. • Usually 18G with surface markings at 1cm to identify depth of insertion. • Tuohy’s needles are most commonly used; 16 to 18 g with 15 to 30 degree curved blunt Huber tip to reduce the risk of accidental dural puncture and guide the catheter cephalad. • Allows the passage of 20g spinal needle • Wings for better control of needle advancement
- 27. Epidural catheter • Flexible,calibrated, durable radioopaque plastic • Single end hole and multiorifice • Nylon or polyamide • Wire reenforced epidural catheter appear to reduce the incidence and complications associated like, epidural vein cannulation, parasthesia, and inadequate analgesia.
- 28. Use of multiorifice cathetersin pregnant women resulted in more frequent incidence of epidural vein cannulation
- 29. Patient positioning • SITTING:1.easier to identify midline especially in obese and scoliotic patients, good flexion 2. shorter procedure time 3.shorter distance from skin to space 4. greater cephalad spread for hypobaric solutions. 5. avoid rotation of spine
- 30. • LATERAL DECUBITUS 1.Sedation can be used more liberally 2. Reduced patient movement and more comfortable 3. Reduced catheter displacement 4. Attenuation of vagal reflexes 5. Hemodynamic changes better tolerated
- 31. SKIN PREPARATION • Removejewelry on fingers and wrists • Careful handwashing before gloving • Chlorhexidine with alcohol and povidone iodine with alcohol provide effective skin decontamination • Drape the patient under sterile conditions
- 32. TECHNIQUE • Midline approach,paramedian approach, modified paramedian(Taylor approach) and caudal. • Local anaesthetic 1-2 cc is injected at the planned insertion site and a skin wheal is raised. • The epidural needle is placed bevel up and introduced • The blunted tip is designed to avoid puncture of dura, inwardly push the dura without puncturing it • It is passed slowly through the supraspinous ligament and seated in interspinous ligament and stylet is removed. • The needle should be still supported even after letting go of the needle.
- 33. If the needleis merely inserted into supraspinous ligament and then LOR or hanging drop insertion is begun there is an increased chance of false loss of resistance, possibly because of defects in interspinous ligament. False positive rates can be 30%
- 34. EPIDURAL SPACE IDENTIFICATION •LOSS OF RESISTANCE TECHNIQUE • HANGING DROP • USG
- 35. LOR • Relies onthe different tissue densities as needle passes through ligaments to epidural space • As the needle enters the epidural space the resistance disappears. • LOR TO AIR Simple, easy to recognise accidental dural puncture complications: pneumocephalus, pdph, large amount of air interfere with distribution of LA, venous air embolism, patchy block
- 36. • LOR TOSALINE WITH OR WITHOUT AIR BUBBLE advantages : fewer dural puncture, fewer pdph, easier insertion of catheter, fewer parasthesias, fewer incomplete block • 2-3 ml of saline or saline with clearly visible air bubble is taken in the syringe • The bubble provides a guage of the appropriate pressure to be applied. • The saline can be injected for fluid predistention • Disadvantage: difficult to readily detect accidental dural puncture
- 37. Intermittent v/s continuous •INTERMITTENT Grasp the epidural needle firmly with both hands and advance it mm by mm. The ligamentum flavum will feel gritty and firm In between each advancement firmly tap the plunger of LOR syringe Once the tip of needle enter epidural space the plunger will collapse
- 38. CONTINUOUS 1. BROMAGE TECHNIQUE. Makea fist with the non dominant hand and place carpel- metacarpel joints in patients back. Firmly grasp the the shaft of epidural needle between thumb and forefinger Slowly advance the needle by rolling your fist into patients back Use dominant hand to apply continuous pressure to the plunger and stop advancing when plunger collapses.
- 39. 2. DOUGHTY TECHNIQUE Bracethe needle with nondominant hand to control its advance Grasp the barrel of LOR syringe with dominant hand so metacarpel head of index finger is positioned on end of plunger Slowly advance the the needle by by balancing the driving pressure from your dominant hand with resistance from bracing hand till the plunger collapses 3. Son - of – Doughty Here the driving pressure is applied directly to the plunger of saline filled lor syringe
- 41. Hanging drop technique •Relies on the subatmospheric pressue of the epidural space • More pronounced in cervical and lumbar region, only useful in sitting position • Epidural needle with wing is required • A drop of saline is placed at the hub of the needle once needle is engaged in ligament • The needle is advanced continuously with the thumb and index fingers firmly grasping the wings and the third through fifth fingersof both hands positioned against patients back. • Entry to epidural space is signaled by entry of the drop into hub of needle
- 44. NEWER METHODS 1. EPIDRUM™ 2.EPISURE ™ AUTODETECT™ SYRINGE 3. DRIP INFUSION METHOD
- 45. USG GUIDED NEURAXIALTECHNIQUE ADVANTAGES 1. To identify the correct interspace 2. Reduces the number of attempts 3. Minimizes the risk of complications 4. No undue prolongation of the procedure
- 47. • Local anaestheticcan be injected either through needle or catheter • Catheter allows the provision of epidural anaesthesia and analgesia as long as needed. • Threading assist device is is fixed at the hub of the needle • Insert about 5cm in the epidural space: if less – chance of dislodgement, if more – chance of entering a blood vessel. • Once inserted hold the catheter about 1cm from hub of the needle, gently withdraw the needle sliding it along the catheter until the hub meets the finger tips. • Repeat the process till the tip of needle is out of skin, grasp the catheter between the needle and the skin and slide the needle off the catheter. • The connector and bacterial filter attached. • A clear occlusive dressing should be applied
- 49. TSUI TEST • Confirmsepidural catheter position. • Stimulation of spinal nerve roots with a low electrical current conducted through normal saline in the epidural space and an electrically conducting catheter. • At 1 to 10mA current corresponding muscle twitches can be used to locate catheter position. • Subarachnoid and subdurally placed positioned catheter elicit motor response at much lower threshold current (<1mA) as the catheter is very close or directly in contact with highly conductive CSF.
- 50. PARAMEDIAN APPROACH • Midto high thoracic region where the angulation of spine and narrow spaces render midline approach difficult. • Needle inserted 1 to 2 cm lateral to inferior tip of of the spinous process corresponding to the vertebra above the desired interspace • Needle advanced horizontally until lamina is reached and redirected medially and cephaledto enter epidural space TAYLOR APPROACH • L5 – S1 interspace, useful in trauma patients who cannot tolerate sitting position • Needle is inserted 1cm medial and 1cm inferior to PSIS and is angled medially and cephalad at 45 to 55 degree angle.
- 51. CSE • Needle throughneedle technique is the most common. • After identifying the epidural space insert a long small guage spinal needle – subtle pop as dura is pierced • Stabilize the needle and the stylet is withdrawn • Clear and free flow also ensures that the epidural needle is indeed in the epidural space. • After injecting the subarachnoid medication epidural catheter is threaded. • Advantage : faster block, lesser intrathecal local anaesthetic, small dural hole enhance the spread of subsequent epidural medication, epidural injection of LA or saline can raise the the level of sensory block even after SAB has been stabilized( epidural volume extension – EVE)
- 52. TEST DOSE • ALLEPIDURAL CATHETERS SHOULD BE TESTED THROUGHOUT THEIR USE. 1. To prove that catheter is not in an unintentded space 2. To prove that catheter is in epidural space. • First withdraw and inject a small dose of local anaesthetic i.e 30 to 45 mg lidocaine or 5 to 10mg bupivacaine and look for signs of subarachnoid anaesthesia • Limitations : 1. in parturients some report warmth and motor weakness after epidural injection of 30 to 45 mg lidocaine 2. Small dose of lidocaine can also cause extensive sensory and sympathetic block • Intravascular local anaesthetic injection can produce seizure and cardiac arrest
- 53. • The mostwidely used intravenous test dose is small volume of 1.5% lidocaine with epinephrine • Iv epinephrine 15mcg will increase hr by 10 beats/min, and SBP by 15mmhg • This response is blunted by sedation, GA, beta blockade, advanced age, preexisting neuraxial block • Pain: false positive tachycardia • Subdural catheter: maybe the cause of excessive epidural block(subdural space extends floor of third ventricle)
- 54. • Because notest dose is foolproof and even working epidural catheter can migrate inject all drugs in increments small enough that they will not cause harm if misplaced. • If an epidural catheter does not behave as expected, do not inject more drug, remove and replace it.
- 55. DOSING REGIMEN • LAconcentration determines the density of the nerve block, while the volume and total dose of LA determine the spread. • Initial loading dose: 1-2 ml / segment in lumbar epidural 0.7ml/segment for thoracic epidural 3ml/segment for caudal epidural The loading dose to be administered through catheter in 3 to 5ml aliquots at 3 to 5min intervals. • Maintenance of desired level of anaesthesia can be accomplished through intermittent or continuous dosing after initial loading dose. • With manual boluses 1/4th to 1/3rd of initial amount can be administered at timed intervals according to duration of action of initial LA.
- 56. • Patient controlledepidural analgesia(pcea) with infusions of low concentration Las and opioid adjuncts are increasingly used for postoperative analgesia and laboring patients. • Pumps that deliver automated mandatory boluses at timed intervals with or without a basal infusion have been developed. TOP UP DOSING • Should be administered before the level of nerve block has receded more than 2 dermatomes. • 1/4th to 1/3rd of original loading dose can be given • Inadequate sensory level: high volume low concentration LA top up • Denser nerve block/ second stage of labor: low volume high concentration topup
- 57. CAUDAL ANAESTHESIA • Popularin pediatric anaesthesia, also in adults when 1.sacral anaesthetic spread is desired.(perineal, anal, rectal procedures) 2. spinal surgery scar preventing lumbar anaesthetic procedure 3. chronic and cancer pain management. To reduce the chances of failure, usg and fluoroscopic guidance. • In adults twice the lumbar epidural dose is required to achieve a similar block • The spread is also variable hence unreliable for procedures above umbilicus.
- 59. • The sacrococcygealligament which is the extension of ligamentum flavum overlies the sacral hiatus between the two sacral cornua. • To identify the hiatus the line between PSIS is taken as one side of an equilateral triangle
- 60. • USG andfluoroscopy can also be used to identify the space. PATIENT POSITION 1. Prone: adults 2. Lateral decubitus : children ( to maintain airway) 3. Knee chest : infrequent Additionally spread the lower extremity about 20 degree with heels rotated laterally to minimize gluteal muscle congtraction and ease needle insertion
- 61. • The indexand middle fingers of the palpating hand are placed on the sacral cornua and after local infiltration the caudal needle is placed at an angle of 45 degree to sacrum • As caudal canal is enter a decrease in resistance is felt • The needle is advanced till bone is hit and slightly withdrawn and redirected such that the angle of insertion to skin is is decreased • LOR is sought to confirm entry to epidural space
- 62. COMPLICATIONS OF NEURAXIAL ANAESTHESIA IMMEDIATE •Hypotension • Bradycardia • High/ total spinal • Cardiac arrest • Affective dyspnoea DELAYED • Paraplegia • Cauda equina syndrome • Epidural hematoma • Post dural puncture headache • Meningitis • Arachinoiditis
- 63. Specific complications ofepidural anaesthesia • Inadvertant dural puncture • Total subarachnoid block • Misplacement • Migration of indwelling epidural catheter • Kinking / occlusion of catheter • Breaks on removal
- 64. SUBDURAL INJECTION • Smalldose of LA in subdural space can have profound hemodynamic and sympatholytic effects • Incidence 0.1% - 0.82% • Higher than anticipated motor and nerve block with poor caudal spread and sacral sparing • Horners syndrome, facial and corneal anaesthesia, dyspnoea. • Mild to moderate hypotension • MANAGEMENT: Cardiovascular and respiratory support.
- 65. LOCAL ANAESTHETIC SYSTEMICTOXICITY • Excessive plasma concentration of LA due to unintensional epidural vein cannulationor subsequent catheter migration. • Dosing the catheter in 3 to 5ml increments with frequent negative aspiration for blood and csf is recommended
- 66. • Refrain fromadministering additional LA • Immediate airway support, seizure control, preparadeness for cardiopulmonary resuscitation • Lipid emulsion (20%) therapy to be commenced with an initial loading dose of 1.5ml/kg followed by continuous infusion of 0.25ml/kg/min for a minimum of 10min after circulatory stability has been achieved.
- 67. SUMMARY • Epidural techniqueprovide optimal pain relief following major surgeries and is associated with fewer cardiovascular, respiratory and hematological complications when compared with GA. • The time to return of GI functions, and the length of intensive care stay appear to be reduced with epidural block. • It is also associated with prolonged survival in cancer patients.
- 68. REFERENCES • MILLER’S ANAESTHESIA9TH EDITION • BARASH CLINICAL ANAESTHESIA 5TH EDITION