Spinal ,Epidural & Caudal Anesthesia

Spinal ,Epidural & CaudalAnesthesia دكترحميدرضاشتابي دستياربيهوشي

The differences: Spinal anesthesia Requires a small mass (volume) of drug, virtually devoid of systemic pharmacologic effect . Epidural anesthesia Necessitates use of a large mass of local anesthetic that produces pharmacologically active systemic blood levels, which may be associated with side effects and complications unknown with spinal anesthesia. Combined spinal & epidural Blurs some of these differences but adds flexibility to critical care.

The use of neuraxial blocks: • Provide postoperative analgesia • Decreaseperioperative morbidity • Decrease length of hospital stay • More efficient use of our increasingly health care

Strong contraindication: • Patient refusal • A patient's inability to maintain stillness during the needle puncture • Raised intracranial pressure, which theoretically may predispose to brainstem herniation. • Exposing the neural structures to unacceptable risk of injury

Relative contraindications: • 1-Must be weighed against the potential benefits include intrinsic and idiopathic coagulopathy, such as that occurring with administration of Coumadin or heparin • 2-Skin or soft tissue infection at the proposed site of needle insertion

3-Severe hypovolemia • 4-Lack of anesthesiologist experience • Preexisting neurologic disease (e.g., lower extremity peripheral neuropathy) (legal)

ANATOMY: Subarachnoid L.A. affect their sensory block at the spinal cord, which is continuous cephalad with the brainstem through the foramen magnum and terminates distally in the conusmedullaris. This distal termination, because of differential growth rates between the bony vertebral canal and central nervous system (CNS), varies from L3 in the infant to the lower border of L1 in the adult.

Dorsal (sensory) roots are generally larger than anterior (motor) roots, the dorsal roots are often blocked more easily. LumbosacralCSF volume varies from patient to patient, in part because of differences in body habitus and weight. Except for body weight, the volume of CSF does not correlate with other anthropomorphic measurements available clinically.

Surrounding the spinal cord in the bony vertebral column are three membranes (from within to the periphery): • Pia mater • Arachnoid mater • Dura mater

Dura Arachnoid Pia mater

The pia mater: • Highly vascular membrane • Closely invests the spinal cord and brain The arachnoids mater: • Delicate, nonvascular membrane • Closely attached to the dura • The principal barrier to drugs crossing in and out of the CSF

Dura mater (Theca): • The third and outermost membrane • Fibroelasticmembrane • Direct extension of the cranial dura mater • Extends as spinal dura mater from the foramen magnum to S2, where the filumterminale (an extension of the pia mater beginning at the conusmedullaris) blends with the periosteum on the coccyx.

Subarachnoid space contains: • CSF • Spinal nerves • A trabecular network • Blood vessels • Continuesto S2

The subdural space: • A potential space • Between the dura mater and the arachnoid • Contains a small amounts of serous fluid • Not used by anesthesiologists • Due to inject into this space ,failed spinal anesthesia happened or rare Total Spinalafter epidural anesthesia.

The epidural space: • Surrounding the dura mater • Used by anesthesiologists • Extends from the foramen magnum to the sacral hiatus • Surrounds the dura mater anteriorly, laterally, and more usefully, posteriorly.

The epidural space is bounded: • Anteriorly by the posterior longitudinal ligaments • Laterally by the pedicles the intervertebralforamina • Posteriorlyby the ligamentumflavum.

The epidural space in segmented and it’snot uniform. Anatomic dissection and computed tomographicepidurography have also suggested epidural space septa.

Posterior to the epidural space is: • The ligamentumflavum = The yellow ligament • As a single ligament • Composed of two ligamentaflava, the right and the left • Is not uniform from skull to sacrum, nor even within an intervertebral space.

Extending from the external occipital protuberance to the coccyx posterior to these structures is the supraspinous ligament, which joins the vertebral spines .

Contents of the epidural space: • The nerve roots • Fat • Areolar tissue • Lymphatics • Blood vessels which include the well-organized Batson venous plexus.

There is evidence that adipose tissue in the epidural space diminishes with age. Another anatomic change in epidural space anatomy that has long been promoted is that intervertebralforamina decrease in size with increasing age. The decrease in epidural space adipose tissue withage may dominate the age-related changes in epidural dose requirements.

For caudal anesthesia • Epidural anatomy • Variations in sacral anatomy • The sacrum the fusion of the 5 sacral vertebrae. • The sacral hiatus failure of the laminae of S5and usually part of S4 to fuse in the midline.

Variably shaped. • Sized inverted V shaped bony defect, covered by the posterior sacrococcygeal ligament, a functional counterpart to the ligamentumflava. • May be identified by locating the sacral cornua, the remnants of the S5 articular processes.

The sacral canal contains: • The terminal portion of the dural sac, which typically ends to a line joining the PSIS, or S2. • The termination of the dural sac being lower in children, although the ease of palpating the sacral hiatus in children may make pediatric caudal technique easier overall. • A venous plexus which is part of the valveless internal vertebral venous plexus.

It is estimated from magnetic resonance imaging (MRI) studies that the volume of the caudal canalin adults, excluding the foramina and dural sac, is about 10 to 27 mL. Perhaps this wide variability in volumeaccounts for some of the variation in block height with caudal anesthesia.

Spinal, epidural, and caudal neuraxial blocks result in: • Sympathetic block • Sensory analgesia • Motor block • dose • Depending on concentration Of L.A • volume

PHYSIOLOGIC EFFECTS (N.A.B): • Cardiovascular Effects • Respiratory Effects • Gastrointestinal Function • Renal Function

Cardiovascular Effects: • Similar to the combined use of IV alpha 1 and beta adrenergic blockers: Decreased HR & BP • The sympathectomydepends on the height of the block as extending for abovetwo to six dermatomes the sensory level with spinal anesthesia and at the same levelwith epidural anesthesia.

The sympathectomycauses venous and arterial vasodilation. • If normal cardiac output: • Total peripheral resistance 15% to 18% in normovolemic healthy patients.

In elderly patients with cardiac disease: • SVR 25% after spinal anesthesia • Cardiac output 10%. • Heart rate during highneuraxial block typically decreases blockade of the cardioaccelerator fibers arising from T1 to T4.

Heart rate in right atrial filling. Kety and colleagues: Spinal.A. to midthoracic levels with procaine…….. In patients with essential hypertension: - 26% mean arterial pressure (MAP) - 12% cerebral blood flow (CBF) .

The extraction of oxygen wasunchanged because myocardial work, as expressed by myocardial use of oxygen, paralleled the decrease in mean arterial pressure and coronary blood flow.

During T10 block, there was no significant change in organ blood flow. • During T1 block 22% decrease in mean arterial pressure(MAP), cerebral and myocardial blood flows(CBF) were insignificantly altered.

After arterial BP decreases to a level for which treatment is necessary( mean arterial pressure more than 30%),ephedrine, a mixed adrenergic agonist, provides more appropriate therapy for the noncardiac circulatory sequelae of neuraxial block than a pure a-adrenergic agonist. Decrease in BP will be minimized by administration of crystalloidsintravenously before the block .

250 to 2000 ml preblock hydrationregimens appear to temporarily increase preload and cardiac output without consistently increasing arterial pressure or preventing hypotension.

Respiratory Effects: Tidalvolumeunchangedduring high spinal anesthesia Vitalcapacitydecreases a small amount from 4.05 to 3.73L. vital capacity in expiratory reserve volume related to paralysis of abdominal muscles necessary for forced exhalation, rather than a decrease in phrenic or diaphragmatic function.

The rare respiratory arrest associated with spinal anesthesia is also unrelated to phrenic or inspiratory dysfunction, but rather to hypoperfusion of the respiratory centersin the brainstem.

Neuraxial block should be used cautiously in respiratory cripples because of paralysis of respiratory muscles. Except for the severely compromised patient with respiratory failure, inspiratory muscle function during neuraxial blocks should be adequate to maintain ventilatory function.

Gastrointestinal Function: • Nausea and vomiting in up to 20% of patients related to GI hyperperistalsisdue to unopposed parasympathetic (vagal) activity. • Atropine is effective in treating nausea associated with high (T5) Spinal. • This gastrointestinal hyperperistalsis has the advantage of providingexcellent surgical conditions because of a contracted gut.

The decrease in hepatic blood flow during spinal anesthesiaparallels the decrease in MAP. • When epidural analgesia is continued into the postoperative period, there may be a protective effect on the gastric mucosa because intra mucosal PH is higher during postoperative epidural analgesia than with systemic analgesia.

Renal Function: • Despite predictable decreases in renal blood flow accompanying neuraxial block, the decrease is of little physiologic importance. • Neuraxial blocks are a frequent cause of urinary retention, which delays discharge of outpatients and necessitates etebladdercathrizationin inpatients.

Lower concentrations of local anesthetic are necessary for paralysis of bladder function than for motor nerves to lower extremities. • It is prudent to avoid administration of excessive volumes of crystalloid solutions intravenously to patients undergoing spinal anesthesia.

Spinal ,Epidural & Caudal Anesthesia