SULLI



OB Regional Anesthesia ReviewBaricity: equal to the density of the local anesthetic divided by the density of the CSFmain determinant of how the local anesthetic is distributed when injected into the CSFLocal anesthetics can be…..when compared to CSF:Hypobaric: Baricity<1.0, Med in H2O, ↓ density than CSF → rise; positioning of pt after injection is important (for perineal/anal sx, in prone/jackknife)Isobaric: Baricity = O, remains in the level of the injection; positioning does not affect spread of LAHyperbaric: Baricity > 1, med in dextrose, ↑ density than CSF → “fall”, positioning is important Density, Specific Gravity, and Baricity of Different Substances and Local Anesthetics??DensitySpecific Gravity BaricityWater?0.99331.00000.9930CSF?1.00031.00691.0000HypobaricTetracaineLidocaine?0.33% in water0.5% in water?0.9980N/A?1.00461.0038?0.99770.9985IsobaricTetracaineLidocaineBupivacaine?0.5% in 50% CSF2% in water0.5% in water?0.99981.00030.9993?1.00641.00661.0059?0.99951.00030.9990HyperbaricTetracaineLidocaineBupivacaineBupivacaine?0.5% in 5% dextrose5% in 7.5% dextrose0.5% in 8% dextrose0.75% in 8% dextrose?1.01361.02651.02101.0247?1.02031.03331.02781.0300?1.01331.02651.02071.0227Levels for major procedures:Body LandmarkDermatome LevelProcedureLittle fingerC8 (All cardio accelerator fibers blocked)NipplesT4Upper abdominal surgeryXiphoidT6Intestinal, gynecologic, and urologic surgeryInferior edge of ScapulaT7UmbilicusT10Vaginal delivery of a fetus, and hip surgeryL1Thigh surgery and lower leg amputationsL2Foot and ankle surgerySpinal cord ends at L1-2, place spinals below this level.Superior iliac crestL4Inferior iliac crestS2S2 to S5 (saddle block)Perineal and anal surgerySpinalEpiduralSmaller doses of LA (mg) → mg block →Larger doses of LA (ml) → Volume block → →Lower potential for toxicity →Higher potential for toxicity Faster onsetSlower onsetLimited DurationFlexible durationLower failure rate (CSF is definitive for location)Higher failure rateBaricity has an effectBaricity has no effect (no CSF to create Baricity)Doses for Spinal Blocks: Dose, Duration, and Onset of Local Anesthetics Used in Spinal Anesthesia?Dose (mg) Duration (min)Plain With 0.2mgEpinephrineOnset (min)?to T10to T4Commonly Used Lidocaine 5% Bupivacaine 0.75%?50–758–12?75–10014–20?60–7090–110?75–100100–150?3–55–8Less Commonly UsedTetracaine 0.5%Mepivacaine 2%Ropivacaine 0.75%Levobupivacaine 0.5%Chloroprocaine 3%?6–10N/A15–1710–1530?12–1660–8018–20N/A45?70–90140–160140–200135–17080–120?120–180N/AN/AN/A130–170?3–52–43–54–82–4DrugOnsetMaximum Dose(with epinephrine);Max mg dose Duration(with Epinephrine)LidocaineRapid4.5 mg/kg (7 mg/kg)300mg (500 mg)120 min (240 min)BupivacaineSlow2.5 mg/kg (3 mg/kg)175mg (225mg)4 hours (8 h)ChloroprocaineRapid (short duration)10 mg/kg (15 mg/kg)800mg (1000mg)30 min (90 min)Doses for spinal blocks depend on:Height of pt → determines the volume of the subarachnoid spaceSegmental level of anesthesia desiredDuration of anesthesia desiredDoses for Epidural blocks (Volume blocks): the volume depends on the location the catheter tip in the epidural space as the size of the segmental epidural spaces increases down the spinal cord as the spinal cord occupied less and less space.Site of procedureDose in mlChestT12-L28-12mlUpper Abdomen (Cholecyctectomy, gastric resection)L212-16mlLower AbdomenColon resection, aortic aneurysm, retro pubic prostatectomyL212-16mlHerniorrhaphyL38-12mlhysterectomyL310-14mlLower ExtremitiesAnesthesiaL410-14mlSympathetic blockL28-12mlPerineum (TURP, vaginal hysterectomy)L48-12mlBack and flank (nephrectomy)L210-14mlVaginal delivery1st stage laborL35-7ml2nd and 3rd stage laborL310-12mlNagelhout p. 1067Opioids in Regional Anesthesia:Epidural anesthesia:Hydrophilic opioids (Morphine) spread easily within CSF and can enhance surgical anesthesia and provide postoperative pain control. Lipophilic opioids (Fentanyl) rapidly absorbed into systemic circulation → no strong effect.Epidural OpioidsBolus DoseOnsetPeakDurationMorphine2-5mg20-30min30-60min12-24hrHydromorphone1 mg10-15min20-30min8-15hrsNagelhout p.1069Spinal anesthesia: Spinal doses are approximately 10 times less than the epidural doses.Morphine: 0.1-0.5mg can provide pain control for ~24hrs, but necessitates in-hospital monitoring for respiratory depression → is the traditional opioid for prolonged pain management.Fentanyl: 25mcg for short surgical procedures, pts can be discharged home the same day.Transient neurological symptoms (TNS) syndrome of pain and dysesthesias that may occur in up to 1/3 of pts receiving intrathecal doses of lidocaine. Pathogenesis of TNS is believed to represent concentration dependent neurotoxicity of local anestheticsRarely occurs with other local anestheticsMechanism responsible is unknownIncreased incidence in pts in lithotomy position, positioning for knee arthroscopy, and outpatient proceduresSymptomstypically include back pain, weakness, and numbness radiating to one or both buttocks and down the legs, or both. Does not consistently manifest with sensory/motor deficits or reflex abnormalities. Appear within first 12-24 hours after surgeryExclusively a pain syndrome, no bowel or bladder dysfunctionAll neuro, MRI and Electrophysiologic examinations are normalMost often resolve within 3 days, rarely last a week.Pain is often more severe than the surgical procedure. TreatmentNSAIDs, possibly opioids if severe pain, and trigger point injections, time to allow symptoms to passCaudal equina syndromeresult of an injury below the level of the conus, or caudal end of the cord, typically below L2. Persistent paresthesia and limited motor weakness are the most common injuriesNerve roots within the subarachnoid space are highly vulnerable to chemical damage, particularly the sacral roots which are poorly myelinated. Typically results from compression within the lumbar spinal canal or from chemical damageRisk factorsPoor subarachnoid dispersion of LABlock failure, followed by a repeat injectionFine-gauge or pencil point needleSpinal micro catheterContinuous infusionHyperbaric anesthetic solutionLithotomy positionUnintentional intrathecal injection of a large volume intended for the epidural spaceIncorrect formulation, with unsuitable preservative or antioxidantIntrathecal LIDOCAINE, particularly 5%Can be caused by an epidural hematomaTreatmentsteroids, anti-inflammatory medications, decompression if related to hematomaEpidural hematomadamage to vessel or anticoagulation can cause a hematoma to form in epidural space. Incidence <1 in 150,000Symptoms includecan initially be hard to see in pts with an epidural or spinal blockSevere, localized back pain with delayed radicular radiation that may mimic disk herniationWeaknessNumbnessUrinary incontinenceFecal incontinenceRisk factorsDifficult or traumatic epidural needle/catheter placement or spinal placementCoagulopathy or therapeutic anticoagulationSpinal deformitySpinal tumorEarly recognition is critical as delay of more than 8 hours in decompressing the spine reduces the odds of good recovery. Treatment is surgical removal of the pressure on the spine. Important to review what meds the pt is onepidural/spinals should not be done on pts taking antiplatelet drugs unless they have been held for a specific time frame. Also pts on LMWH at high risk. Timing of catheter removal is crucial as removal can cause hematoma formation as well. Blood patchregarded by many as the gold standard treatment for PDPH. Blood is drawn using sterile technique. All air is removed from the syringe. It is then injected into the epidural space near the area of the where the dura was inadvertently punctured. Idea is that the blood will help “patch” the hole in the dural space preventing continued leak of CSFPossibly blood in epidural space helps more to tamponade the leak of CSF vs actually seal the puncture. Exact volume used is debatable, average 12-15 mL is used, but can inject up to 20 mL. With larger volume. The injection is terminated when volume is instilled or pt complains of severe back, leg, or neck pain or pressure. Headache is often relieved immediatelyAfter procedure pt should lie flat and rest for 1-2 hours. Pt may resume ambulation after 2 hours but should avoid vigorous physical activity, heavy lifting, or any activity involving a valsalva maneuver. Procedure may be repeated if first fails. Often second procedure provides relief. If second fails to relieve PDPH, get neuro consult.Two main complicationsInfectionNeurologiclow back pain with neuro impairment of the lower extremities, subdural hematoma, arachnoiditis, radicular back pain, pneumocephalus, seizures, and acute meningeal irritation. SpinalAnatomy318770013398500Midline approachSkinSubcutaneous fatSupraspinous ligament320040018097500Interspinous ligamentLigamentum flavumDura materSubdural spaceArachnoid materSubarachnoid spaceParamedian approachSkinSubcutaneous fatLigamentum flavumDura mater Subdural spaceArachnoid materSubarachnoid space2971800000DermatomeThe fourth thoracic (T4) dermatome corresponds to the nipples.The sixth thoracic (T6) dermatome corresponds to the xiphoid.The tenth thoracic (T10) dermatome corresponds to the umbilicus.Table 1. Dermatomal Levels of Spinal Anesthesia for Common Surgical ProceduresProcedureDermatomal LevelUpper abdominal surgeryT4Intestinal, gynecologic, and urologic surgeryT6Transurethral resection of the prostate?Vaginal delivery of a fetus, and hip surgeryT10Thigh surgery and lower leg amputationsL1Foot and ankle surgeryL2Perineal and anal surgeryS2 to S5 (saddle block)MedicationsTable 4. Dose, Duration, and Onset of Local Anesthetics Used in Spinal Anesthesia?Dose (mg)Duration (min)PlainWith 0.2 mgEpinephrineOnset (min)?to T10to T4Commonly UsedLidocaine 5% Bupivacaine 0.75%50–75?8–1275–100?14–2060–70?90–11075–100?100–1503–5?5–8Less Commonly UsedTetracaine 0.5%?Mepivacaine 2%?Ropivacaine 0.75%?Levobupivacaine 0.5%?Chloroprocaine 3%6–10?N/A?15–17?10–15?3012–16?60–80?18–20?N/A?4570–90?140–160?140–200?135–170?80–120120–180?N/A?N/A?N/A?130–1703–5?2–4?3–5?4–8?2–4AdditivesVasoconstrictors – epinephrine and phenylephrine – limit systemic reabsorption and prolong duration of action by keeping the local anesthetic in contact with the nerve fibersAlpha-2-adrenergic agonists enhance pain relief and prolong sensory block and motor blocki.e. clonidineAcetylcholinesterase inhibitors prevent the breakdown of acetylcholine and produce analgesia when injected intrathecallyi.e. neostigmineFactors determining spinal level blockade and spreadBaricity of the local anesthetic solutionPosition of the patient during and just after injectionDose of the anesthetic injectedTable 2. Determinants of Local Anesthetic Spread in the Subarachnoid SpaceProperties of local anesthetic solutionBaricity?Dose?Volume?Specific gravityPatient characteristicsPosition during and after injection?Height (extremely short or tall)?Spinal column anatomy?Decreased CSF volume (increased Intraabdominal pressure due to increased weight, pregnancy, etc.)TechniqueSite of injection?Needle bevel directionRisks/side effectsContraindicationsAbsolutePatient refusalSepsis at the site of injectionHypovolemiaCoagulopathyIndeterminate neurological diseaseIncreased intracranial pressureRelativeInfection distinct from the site of injectionUnknown duration of surgeryComplicationsPermanent neurologic injury - can occur after needle introduction into the spinal cord or nerves, spinal cord ischemia, bacterial contamination of the subarachnoid space, or hematoma formationAfter low-molecular-weight heparin (LMWH) administration, delay spinal anesthesia for 10 to 12 hoursIf blood is noted during needle placement, delay LMWH therapy for 24 hoursIn cases of continuous spin anesthesia and accidental LMWH therapy, remove the catheter 10-12 hours after the last dose of LMWHAvoid spinal anesthesia for 14 days after the last dose of ticlopidine (Ticlid) and 7 days after clopidogrel (Plavix)Patients should not receive glycoprotein IIb/IIIa inhibitors for 4 weeks after surgery, and do not attempt spinal anesthesia until platelet function returns to normalCaudal equina syndrome – associated with the use of continuous spinal micro catheters. Use of hyperbaric 5% lidocaine for spinal anesthesia is also associated with an increased incidence of cauda equina syndromeArachnoiditis – known to occur after intrathecal steroid injection. Causes include infection, myelograms from oil-based dyes, blood in the intrathecal space, neuroirritant, neurotoxic/neurolytic substances, surgical interventions in the spine, intrathecal corticosteroids, and traumaMeningitis – bacterial or asepticPost dural puncture headache – result of loss of CSF with incidence up to 25% after spinal anesthesia. Headache is characteristically worse when the head is elevated and becomes milder or completely relieved when the patient is supine.High spinal – can result in profound respiratory impairment, most likely due to brainstem ischemia. If the blood pressure and cardiac out become too low due to vasodilation, cerebral blood flow can be impairedCardiovascular collapse – rare event. Bradycardia usually precedes cardiac arrest, and early aggressive treatment of bradycardia is warranted. Treatment with atropine, ephedrine, and epinephrine with ACLS protocol initiatedEpidural Block Patient Selection-cooperative-can also be used in the cervical and thoracic areas as well—levels at which spinal anesthesia is not advised. -a continuous technique has been found to be helpful in providing epidural local anesthesia or opioid analgesia after major surgical procedures. Pharmacologic ChoiceChloroprocaine, an amino ester local anesthetic, is a short-acting agent that allows efficient matching of the length of the surgical procedure and the duration of epidural analgesia, even in outpatients. 2-Chloroprocaine is available in 2% and 3% concentrations; the latter is preferable for surgical anesthesia and the former for techniques not requiring muscle relaxation.Lidocaine is the prototypical amino amide local anesthetic and is used in 1.5% and 2% concentrations epidurally. Concentrations of mepivacaine necessary for epidural anesthesia are similar to those of lidocaine; however, mepivacaine lasts from 15 to 30 minutes longer at equivalent dosages. Epinephrine significantly prolongs (i.e., by approximately 50%) the duration of surgical anesthesia with 2-chloroprocaine and either lidocaine and mepivacaine. Plain lidocaine produces surgical anesthesia that lasts from 60 to 100 minutes.Bupivacaine, an amino amide, is a widely used long-acting local anesthetic for epidural anesthesia. It is used in 0.5% and 0.75% concentrations, but analgesic techniques can be performed with concentrations ranging from 0.125% to 0.25%. Its duration of action is not prolonged as consistently by the addition of epinephrine, although up to 240 minutes of surgical anesthesia can be obtained when epinephrine is added.Ropivacaine, another long-acting amino amide, is also used for regional and epidural anesthesia. For surgical anesthesia it is used in 0.5%, 0.75%, and 1% concentrations. Analgesia can be obtained with concentrations of 0.2%. Its duration of action is slightly less than that of bupivacaine in the epidural technique, and it appears to produce slightly less motor blockade than a comparable concentration of bupivacaine.In addition to the use of epinephrine as an epidural additive, some anesthesiologists recommend modifying epidural local anesthetic solutions to increase both the speed of onset and the quality of the block produced. One recommendation is to alkalinize the local anesthetic solution by adding bicarbonate to it to achieve both these purposes. Nevertheless, the clinical advisability of routinely adding bicarbonate to local anesthetic solutions should be determined by local practice protocols.PlacementAnatomyWhen a lumbar approach to the epidural space is used in adults, the depth from the skin to the ligamentum flavum is commonly near 4?cm; in 80% of patients the epidural space is cannulated at a distance of 3.5 to 6?cm from the skin. In a small number of patients the lumbar epidural space is as near as 2?cm from the skin. In the lumbar region, the ligamentum flavum is 5 to 6?mm thick in the midline, whereas in the thoracic region it is 3 to 5?mm thick. In the thoracic region, the depth from the skin to the epidural space depends on the degree of cephalad angulation used for the paramedian approach as well as the body habitus of the patient. In the cervical region the depth to the ligamentum flavum is approximately the same as that in the lumbar region, 4 to 6?cm.Needle Puncture: Lumbar Epiduralidentify the midline structures, and the bony landmarks If a single-shot epidural technique is chosen, a Crawford needle is appropriate; if a continuous catheter technique is indicated, a Tuohy or other needle with a lateral-facing opening is chosen.The midline approach is most often indicated for a lumbar epidural procedure. The needle is slowly advanced until the change in tissue resistance is noted as the needle abuts the ligamentum flavum. At this point, a 3- to 5-mL glass syringe is filled with 2?mL of saline solution, and a small (0.25?mL) air bubble is attached to the needle, and if the needle tip is in the substance of the ligamentum flavum, the air bubble will be compressible. If the ligamentum flavum has not yet been reached, pressure on the syringe plunger will not compress the air bubble. Once compression of the air bubble has been achieved, the needle is grasped with the nondominant hand and pulled toward the epidural space, while the dominant hand (thumb) applies constant steady pressure on the syringe plunger, thus compressing the air bubble. When the epidural space is entered, the pressure applied to the syringe plunger will allow the solution to flow without resistance into the epidural space. An alternative technique is the hanging-drop technique for identifying entry into the epidural space. In this technique, when the needle is placed in the ligamentum flavum a drop of solution is introduced into the hub of the needle. No syringe is attached, and when the needle is advanced into the epidural space, the solution should be “sucked into” the space.The incidence of unintentional intravenous cannulation with an epidural catheter may be decreased by injecting 5 to 10?mL of solution before threading the catheter. If a catheter is inserted, it should be inserted only 2 to 3?cm into the epidural space because threading it farther may increase the likelihood of catheter malposition. Obstetric patients require catheters to be inserted to 3 to 5?cm into the epidural space to minimize dislodgement during labor analgesia.Needle Puncture: Thoracic EpiduralIn this technique, the paramedian approach is preferred because it allows easier access to the epidural space because the spinous processes in the mid-thoracic region overlap each other from cephalad to caudad. The loss-of-resistance technique and insertion of the catheter are carried out in a manner identical to that used for lumbar epidural block. Again, the hanging-drop technique is an alternative method of identifying the thoracic epidural space, although the classic Bromage needle–syringe grip is my first choice for the thoracic epidural block (Fig. 41-10).Needle Puncture: Cervical EpiduralIn the cervical epidural technique, the patient is typically in a sitting position with the head bent forward and supported on a table. The spinous processes of the cervical vertebrae are nearly perpendicular to the long axis of the vertebral column; thus, a midline technique is applicable for the cervical epidural block. The most prominent vertebral spinous processes, those of C7 and T1, are identified with the neck flexed. The second (index) and third fingers of the palpating hand straddle the space between C7 and T1, and the epidural needle is slowly inserted in a plane approximately parallel to the floor (or parallel to the long axis of the cervical vertebral spinous processes). Abutment of the needle onto the ligamentum flavum will be appreciated at a depth similar to that seen in the lumbar epidural block (i.e., 3.5 to 5.5?cm), and needle placement is then performed using the loss-of-resistance technique as in the other epidural methods. The hanging-drop method is also an option for identification of the cervical epidural space.Potential Problemssystemic toxicity resulting from intravenous injection of the intended epidural anesthetic One way to minimize intravenous injection of the pharmacologic doses of local anesthetic needed for epidural anesthesia is to verify needle or catheter placement by administering a test dose before the definitive epidural anesthetic injection. The current recommendation for the test dose is 3?mL of local anesthetic solution containing 1:200,000 epinephrine (15??g of epinephrine). Even if the test dose is negative, the anesthesiologist should inject the epidural solution incrementally, be vigilant for unintentional intravascular injection, and have all necessary equipment and drugs available to treat local anesthetic–induced systemic toxicity.Unintentional administration of an epidural dose into the spinal fluid. Blood pressure and heart rate should be supported pharmacologically and ventilation should be assisted as indicated. Usually atropine and ephedrine will suffice to manage this situation, or at least will provide time to administer more potent catecholamines. If the entire dose (20 to 25?mL) of local anesthetic is administered into the cerebrospinal fluid, tracheal intubation and mechanical ventilation are indicated because it will be approximately 1 to 2 hours before the patient can consistently maintain adequate spontaneous ventilation. When epidural anesthesia is performed and a higher-than-expected block develops after a delay of only 15 to 30 minutes, subdural placement of the local anesthetic must be considered. Treatment is symptomatic, with the most difficult part involving recognition that a subdural injection is possible.If neurologic injury occurs after epidural anesthesia, a systematic approach to the problem is necessary. The performance of cervical or thoracic epidural techniques demands special care with hand and needle control because the spinal cord is immediately deep to the site of both these epidural blocks.Epidural hematoma created with the needles or catheters. Concern about epidural hematoma formation is greater in patients who have been taking antiplatelet drugs such as aspirin or who have been receiving preoperative anticoagulants. Perioperative anticoagulant regimens that demand special consideration are the use of low–molecular-weight heparin (LMWH) or potent antiplatelet drugs concurrently with epidural block. It is currently recommended that no procedure, including withdrawal or manipulation of an epidural catheter, should occur within 12 hours after a dose of LMWH, and the next dose of LMWH should be delayed for at least 2 hours after atraumatic epidural needle or catheter insertion or manipulation. The antiplatelet drugs (e.g., ticlopidine, clopidogrel, and platelet glycoprotein IIb/IIIa receptor antagonists) are sometimes combined with aspirin and other anticoagulants. Post–dural puncture headache can result from epidural anesthesia when unintentional subarachnoid puncture accompanies the technique. When using the larger-diameter epidural needles (18 and 19 gauge), it can be expected that at least 50% of patients experiencing unintentional dural puncture will have a postoperative headachePearlsEpidural catheters can be malpositioned in a number of ways. If a catheter is inserted too far into the epidural space, it can be routed out of foramina, resulting in patchy epidural block. The catheter can also be inserted into the subdural or subarachnoid space or into an epidural vein. Similarly, the use of epidural catheters may be complicated by a prominent dorsomedian connective tissue band (epidural septum or fat pad), which is found in some patients.Another means of facilitating the success of epidural anesthesia is to allow the block enough “soak time” before beginning the surgical procedure. There appears to be a plateau effect in the doses of epidural local anesthetics; that is, once a certain quantity of local anesthetic has been injected, more of the same agent does not significantly increase the block height but rather may make the block denser, perhaps improving quality. ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download