Spinal and Regional – Flashcards

Using the iliac crests as a landmark (a line drawn between the iliac crests crosses the body of L5 or the 4-5 interspace), the L2-3, L3-4, and L4-5 interspaces are identified and the desired interspace chosen for needle insertion.

In the adult, the caudad tip of the spinal cord typically lies at the level of the first lumbar vertebra. However, in 30% of individuals the spinal cord may end at T12, while in 10% it may extend to L3

cauda equina

All spinal and epidural needles come with a tight-fitting stylet. The stylet prevents the needle from being plugged with skin or fat and, importantly, prevents dragging skin into the epidural or subarachnoid spaces, where the skin may grow and form dermoid tumors.

The needle is then advanced, in order, through the subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, and finally arachnoid mater.

If bone is encountered during needle insertion, the anesthesiologist must develop a reasoned, systematic approach to redirecting the needle. Simply withdrawing the needle and repeatedly reinserting it in different directions is not appropriate. When contacting bone, the depth should be immediately noted and the needle redirected slightly cephalad. If bone is again encountered at a greater depth, then the needle is most likely walking down the inferior spinous process and it should be redirected more cephalad until the subarachnoid space is reached. If bone is encountered again at a shallower depth, then the needle is most likely walking up the superior spinous process and it should be redirected more caudad. If bone is repeatedly encountered at the same depth, then the needle is likely off the midline and walking along the vertebral lamina .When redirecting a needle it is important to withdraw the tip into the subcutaneous tissue. If the tip remains embedded in one of the vertebral ligaments, attempts at redirecting the needle will simply bend the shaft and will not reliably change needle direction. When using an introducer needle, it also must be withdrawn into the subcutaneous tissue before being redirected. Changes in needle direction should be made in small increments because even small changes in needle angle at the skin may result in fairly large changes in position of the needle tip when it reaches the spinal meninges at a depth of 4 to 6 cm. Care should be exercised when gripping the needle to ensure that it does not bow. Insertion of a curved needle will cause it to veer off course.If the patient experiences a paresthesia, it is important to determine whether the needle tip has encountered a nerve root in the epidural space or in the subarachnoid space. When the paresthesia occurs, immediately stop advancing the needle, remove the stylet, and look for CSF at the needle hub. The presence of CSF confirms that the needle encountered a cauda equina nerve root

poor placement

If CSF is not visible at the hub, then the paresthesia may have resulted from contact with a spinal nerve root traversing the epidural space. This is especially true if the paresthesia occurs in the dermatome corresponding to the nerve root that exits the vertebral canal at the same level that the spinal needle is inserted. In this case the needle has most likely deviated from the midline and should be redirected toward the side opposite the paresthesia. Occasionally, pain experienced when the needle contacts bone may be misinterpreted by the patient as a paresthesia and the anesthesiologist should be alert to this possibility.

If the surgical procedure is to be performed in the supine position, the patient is helped onto his or her back. To prevent excessive cephalad spread of hyperbaric local anesthetic, care should be taken to ensure that the patient's hips are not raised off the bed as they turn. Once the block is placed, strict attention must be paid to the patient's hemodynamic status with blood pressure and/or heart rate supported as necessary. Block height should also be assessed early by pin prick or temperature sensation. Temperature sensation is tested by wiping the skin with alcohol, and may be preferable to pin prick because it is not painful. If, after a few minutes, the block is not rising high enough or is rising too high, the table may be tilted as appropriate to influence further spread of hypobaric or hyperbaric local anesthetics.

The first significant resistance encountered should be the ligamentum flavum. Bone encountered prior to the ligamentum flavum is usually the vertebral lamina of the cephalad vertebra and the needle should be redirected accordingly.

The epidural test dose is designed to identify epidural needles or catheters that have entered an epidural vein or the subarachnoid space. Failure to perform the test may result in IV injection of toxic doses of local anesthetic or total spinal block. Aspirating the catheter or needle to check for blood or CSF is helpful if positive

Heart rate increases may not be as evident in some patients taking beta-blocking drugs; reflex bradycardia usually occurs in these patients. beta- blocked patients, a systolic blood pressure increase of "20 mm Hg may be a more reliable indicator of IV injection.

T4-T6 hyberbaric/horizontal

Baricity - Baricity is important in determining local anesthetic spread and thus block height because gravity causes hyperbaric solutions to flow downward in CSF to the most dependent regions of the spinal column, whereas hypobaric solutions tend to rise in CSF, local dose, concentration, volume, age, weight, height, gender, pregnancy, patient position, site of injection, speed of injection, barbotage, direction of needle bevel, vasoconstrictors

Total spinal anesthesia occurs when local anesthetic spreads high enough to block the entire spinal cord and occasionally the brainstem during either spinal or epidural anesthesia. Profound hypotension and bradycardia are common secondary to complete sympathetic blockade. Respiratory arrest may occur as a result of respiratory muscle paralysis or dysfunction of brainstem respiratory control centers. Management includes vasopressors, atropine, and fluids as necessary to support the cardiovascular system, plus oxygen and controlled ventilation. If the cardiovascular and respiratory consequences are managed appropriately, total spinal block will resolve without sequelae.

Patient refusal

1. Hypovolemia or shock increase the risk of hypotension. 2. Increased intracranial pressure increases the risk of brain herniation when CSF is lost through the needle, or if a further increase in intracranial pressure follows injection of large volumes of solution into the epidural or subarachnoid spaces. 3. Coagulopathy or thrombocytopenia increase the risk of epidural hematoma. 4. Sepsis increases the risk of meningitis. 5. Infection at the puncture site increases the risk of meningitis.

Bupivicaine, 1-5min, 2-9hrs DOA

5-15min, 1-3hr DOA

Bed rest and analgesics as necessary are the mainstay of conservative treatment. Caffeine has also been shown to produce short-term symptomatic relief. Patients who are unable or unwilling to await spontaneous resolution of PDPH should be offered epidural blood patch.

Larger gauge (i.e., smaller diameter) spinal needles are less likely to cause postdural puncture headaches (PDPH), but are more readily deflected than smaller gauge needles. When using beveled needles, the incidence is higher than average at any given age if the needle is inserted perpendicular to the spinal meninges and lower if inserted parallel to the spinal meninges.

As with spinal anesthesia, choice of local anesthetic is the most important determinant of the duration of epidural block., followed by dose, then block height

Solutions with a baricity of "1.0015 can be expected to reliably behave hyperbarically. Hyperbaric solutions are typically prepared by mixing the local anesthetic in 5 to 8% dextrose. The baricity of the resultant solution depends on the amount of dextrose added; however, dextrose concentrations between 1.25 and 8% result in equivalent block heights.

epinephrine (0.2 mg) increased chloroprocaine block duration but that its use was associated with a high incidence of myalgia, arthralgia, malaise, and anorexia that lasted up to 48 hours. The authors had no explanation for the epinephrine- associated side effects, but recommended against its use with intrathecal chloroprocaine.

Differential block refers to a clinically important phenomenon in which nerve fibers subserving different functions display varying sensitivity to local anesthetic blockade. Sympathetic nerve fibers appear to be blocked by the lowest concentration of local anesthetic followed in order by fibers responsible for pain, touch, and motor function. This observation has led to the widely held belief that differences in sensitivity to local anesthetic blockade is explained solely by differences in fiber diameter, with smaller-diameter neurons exhibiting greater sensitivity than larger-diameter neurons. Although the mechanism for differential block in spinal and epidural anesthesia is not known, it is clear that fiber diameter is not the only, or perhaps not even the most important, factor contributing todifferential block. Differential block occurs with both peripheral nerve blocks and central neuraxial blocks. In the peripheral nervous system, differential block is a temporal phenomenon with sympathetic block occurring first followed in time by sensory and motor block. In contrast, with spinal and epidural anesthesia differential block is manifest as a spatial separation in the modalities blocked.

Differential block occurs with both peripheral nerve blocks and central neuraxial blocks. In the peripheral nervous system, differential block is a temporal phenomenon with sympathetic block occurring first followed in time by sensory and motor block. In contrast, with spinal and epidural anesthesia differential block is manifest as a spatial separation in the modalities blocked. This is seen most clearly with spinal anesthesia in which sympathetic block may extend as many as two to six dermatomes higher than pin-prick sensation,159 which in turn extends two to three dermatomes higher than motor block. This spatial separation is believed to result from a gradual decrease in local anesthetic concentration within the CSF as a function of distance from the site of injection. With epidural anesthesia, similar zones of differential sensory and sympathetic block are found.160Perhaps the most troublesome consequence of differential block is the occasional patient who has intact touch and proprioception at the surgical site despite adequate blockade of pain sensation. Even the most stoic patients are likely to find this unpleasant and may lie in fear that the procedure will soon become painful. In no instance should the anesthesiologist downplay the distress this may cause patients. Reassurance and judicious sedation as necessary are usually sufficient to overcome this problem.Another important neurophysiologic aspect of central neuroaxial block is that it produces sedation. and pot the effect of sedative hypnotic drugs, and markedly decreases minimum alveolar concentration of volatile anesthetics. The mechanism(s) underlying these effects is not known but "deafferentation," that is, the loss of ascending sensory input to the brain, is commonly invoked as causative.

The catheter should be advanced only 3 to 5 cm into the epidural space. Placing a longer length of catheter in the epidural space increases the risk that it will form a knot.

The epidural test dose is designed to identify epidural needles or catheters that have entered an epidural vein or the subarachnoid space. Failure to perform the test may result in IV injection of toxic doses of local anesthetic or total spinal block. Aspirating the catheter or needle to check for blood or CSF is helpful if positive.

The onset of epidural block with all local anesthetics can usually be detected within 5 minutes in the dermatomes immediately surrounding the injection site. The time to peak effect differs somewhat among local anesthetics. Shorter-acting drugs generally reach their maximum spread in 15 to 20 minutes, whereas longer-acting drugs require 20 to 25 minutes. Increasing the dose of local anesthetic speeds the onset of both motor and sensory block.

In children? the vertebral column lengthens more than the spinal cord so that at birth the spinal cord ends at about the level of the third lumbar vertebra. In the adult, the caudad tip of the spinal cord typically lies at the level of the first lumbar vertebra.

Of those factors that do exert significant influence on local anesthetic spread, the baricity of the local anesthetic solution relative to patient position is probably the most important. Baricity is defined as the ratio of the density (mass/volume) of the local anesthetic solution divided by the density of CSF

Baricity is important in determining local anesthetic spread and thus block height because gravity causes hyperbaric solutions to flow downward in CSF to the most dependent regions of the spinal column, whereas hypobaric solutions tend to rise in CSF. In contrast, gravity has no effect on the distribution of truly isobaric solutions.

.75%

The mechanism responsible for bradycardia is not clear. Blockade of the sympathetic cardioaccelerator fibers originating from T1-4 spinal segments is often suggested as the cause. The fact that bradycardia is more common with high blocks supports this mechanism. However, significant bradycardia sometimes occurs with blocks that are seemingly too low to block cardioaccelerator fibers.

The etiology is unknown but an increased incidence of nausea during spinal anesthesia is associated with blocks higher than T5, hypotension, opioid premedication, and a history of motion sickness.

Volume, 1.5ml/seg!!!!! choice of local anesthetic is the most important determinant of the duration of epidural block. Dose follows. Epi can increase duration by 80%. Chloroprocaine is shortest, lido and merpiv is int. and etido is longest lasting

Treatment of hypotension secondary to spinal and epidural block must be aimed at the root causes: decreased cardiac output and/or decreased peripheral resistance. Bolus crystalloid administration has often been advocated as a means of restoring venous return and thus cardiac output during central neuraxial blockade. However, the effectiveness of this therapy in normovolemic patients is controversial. Prehydrating patients with 500 to 1,500 mL of crystalloid does not reliably prevent hypotension, but it has been shown to decrease the incidence ofhypotension during spinal anesthesia in some, but not all, studies.167,188 Thus, although judicious crystalloid preloading of patients before central neuraxial blocks may benefit some patients, this practice cannot be relied on to prevent clinically significant hypotension in all, or even most, patients. The reason for this is that increasing preload can only increase stroke volume, which has limited ability to restore blood pressure if heart rate or systemic vascular resistance remains low. In this regard colloid solutions offer an interesting alternative to crystalloids for preloading before central neuraxial blocks. Vasopressors are a more reliable approach to treating hypotension secondary to central neuraxial blockade. Drugs with both alpha- and %-adrenergic activity have been shown to be superior to pure $-agonists for correcting thecardiovascular derangements produced by spinal and epidural anesthesia.190,191 Ephedrine is the drug most commonly used to treat hypotension. Ephedrine boluses of 5 to 10 mg increase blood pressure by restoring cardiac output and peripheral vascular resistance. Dopamine, in low-to-moderate doses, has also been shown to correct the hemodynamic changes induced by central neuraxial block.

The time to peak effect differs somewhat among local anesthetics. Shorter-acting drugs generally reach their maximum spread in 15 to 20 minutes, whereas longer-acting drugs require 20 to 25 minutes.

Itching, N/V, urine retention, resp dep, , CNS exciteation, viral reactivation, water retention, sexual dysfunction, ocular dyspfuntion, fever, constipation, sedation

Hypotension, dec SVR, dec venous return, arterial dialation, paresthesia, apnea, N/V, PDPH, urine retention

Sympathectomy2-6 dts higher, sensory 2-3dts higher, motor