Preload-Dependent States Traditionally, neuraxial blockade has been considered contraindicated in patients with severe aortic stenosis AS and other preload-dependent conditions, such as hypertrophic obstructive cardiomyopathy asymmetric septal hypertrophy, ASH , due to the risk of acute decompensation in response to decreased systemic vascular resistance SVR.
The later stages of AS are associated with decreased diastolic compliance, impaired relaxation, increased myocardial oxygen demand, and decreased perfusion of the endocardium. Decreased SVR in the setting of either GA or neuraxial blockade leads to decreased coronary perfusion and contractility, with a further reduction in cardiac output CO and worsening hypotension. Bradycardia, tachycardia, and other dysrhythmias are also poorly tolerated.
The current evidence regarding regional anesthesia in patients with AS is based on case reports and lacks the scientific validity provided by randomized controlled trials. However, it appears that carefully titrated CSE and continuous epidural and spinal techniques, most commonly with invasive monitoring, may be acceptable options for patients with AS.
Single-shot spinal anesthetics are generally contraindicated, as gradual onset of sympathetic blockade is essential. Anesthetic goals for patients with ASH are similar, with emphasis on maintaining preload, afterload, euvolemia, and vascular resistance, while avoiding tachycardia and enhanced contractility. Invasive monitoring and, if necessary, intermittent transthoracic echocardiography may help guide fluid and vasopressor requirements, as well as guide management in the event of acute decompensation.
Epidural Placement in Anesthetized Patients Initiation of epidural blockade in adults under GA is controversial due to concerns that these patients cannot respond to pain and may therefore be at increased risk for neurologic complications.
Indeed, paresthesias during nerve block performance and pain on LA injection have been identified as risk factors for serious neurologic deficits after regional techniques. Consequently, some experts consider close communication with the patient an essential component of safe epidural performance. Current data support the practice of epidural insertion in awake or minimally sedated patients, but needle and catheter placement in anesthetized adults may be an acceptable alternative in selected cases.
Studies of lumbar epidural insertion while patients are undergoing GA have demonstrated that the risk of neurologic complications is small. Overall, the relative risk of administration of epidural blockade in anesthetized patients, compared with epidural placement in awake patients, is unknown due to the low overall incidence of serious neurologic complications associated with regional anesthesia.
Needle Insertion Through a Tattoo Concerns that puncturing a tattoo during epidural placement may have adverse sequelae appear unsubstantiated in the literature. Theoretical risks are related primarily to the introduction of a potentially toxic or carcinogenic pigment into the epidural, subdural, or subarachnoid space.
However, to date no significant complications related to inserting a needle through a tattoo have been reported in the literature, although potential long-term consequences cannot be dismissed. An understanding of the anatomy of the vertebral column, spinal canal, epidural space and its contents, and commonly encountered anatomic variations among individuals is essential for the safe and effective initiation of epidural blockade.
A three-dimensional mental image of vertebral column anatomy also aids in troubleshooting when identification of the epidural space is equivocal or when complications of epidural catheterization, such as unilateral blockade, intravascular cannulation, or catheter migration, occur.
This section presents the basic anatomic considerations for successful epidural anesthesia and analgesia and reviews several controversies in the field of applied anatomy, including the accuracy of anatomic landmarks to estimate the spinous process level, the existence or lack thereof of a subdural compartment, and the contents of the epidural space.
General Appearance Seven cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 3 to 5 most commonly 4 fused coccygeal vertebrae comprise the vertebral column. The vertebral column is straight when viewed dorsally or ventrally. When viewed from the side, the cervical and lumbar regions are concave posteriorly lordosis , and the thoracic and sacral regions are concave anteriorly kyphosis Figure 3.
The four physiologic spinal curves are fully developed by 10 years of age and become more pronounced during pregnancy and with aging. In the supine position, C5 and L3 are positioned at the highest points of the lordosis; the peaks of kyphosis occur at T5 to T7 and at S2. Structure of Vertebrae With the exceptions of C1 and C2 and the fused sacral and coccygeal regions, the general structure of each vertebra consists of an anterior vertebral body corpus, centrum and a posterior bony arch.
The arch is formed by the laminae; the pedicles, which extend from the posterolateral margins of the vertebral body; and the posterior surface of the vertebral body itself. In addition to the spinous processes, which are formed by the fusion of the laminae at midline, the vertebral arch supports three pairs of processes that emerge from the point where the laminae and pedicles join: two transverse processes, two superior articular processes, and two inferior articular processes.
Adjacent vertebral arches enclose the vertebral canal and surround portions of the longitudinal spinal cord. The spinal canal communicates with the paravertebral space by way of gaps between the pedicles of successive vertebrae.
These intervertebral foramina serve as passageways for the segmental nerves, arteries, and veins. There is substantial variation in the size and shape of the vertebral bodies, the spinous processes, and the spinal canal at different levels of the vertebral column Figure 4. C3 through C7 have the smallest vertebral bodies, while the spinal canal at this level is wide, measuring 25 mm.
These cervical vertebrae, with the exception of C7, have short, bifurcated spinous processes. C7, the vertebra prominens, has a long, slender, and easily palpable horizontal spinous process protruding at the base of the neck that often serves as a surface landmark during epidural procedures.
However, the first thoracic spinous process may be equally or more prominent than C7 in up to one-third of male individuals, as well as in thin patients and in patients with scoliosis and degenerative diseases. The vertebra prominens may also be difficult to distinguish from C6 in up to half of individuals, most commonly females. The thoracic vertebral bodies are larger than the cervical vertebral bodies and are wider in the posterior than anterior dimension, contributing to the characteristic thoracic curvature.
The long and slender thoracic spinous processes, with tips that point caudally, are most sharply angled between T4 and T9, making insertion of the epidural needle in the midline more difficult in the midthoracic region. Beyond T10, they increasingly resemble those in the lumbar region. Each thoracic vertebra articulates with ribs along the dorsolateral border of its body, a feature that may help distinguish the lower thoracic and upper lumbar regions.
The inferior angle of the scapula and the 12th rib are widely used in clinical practice to estimate the level of the cross the L1 spinous process Table Surface Anatomic Landmarks to Identify the Spinal Level Surface landmarks are often used to identify the intended spinal level during initiation of epidural anesthesia Figure 5.
Common pitfalls to using skeletal landmarks to identify the level of puncture include the following: The vertebra prominens is commonly confused with C6 and T1; the scapula may be difficult to identify during TEA placement in obese patients; tracing the vertebra attached to the 12th rib can be misleading, particularly in obese patients; and the line connecting the posterior superior iliac spines, often used to identify S2, commonly crosses the midline at variable levels between L5 and S1.
Anesthesiologists have a poor record of estimating the correct interspace based on external landmarks. Lirk et al confirmed the tendency of trained anesthetists to place the epidural needle more cranially than intended, most often within one interspace of the predicted level, also in the cervical and thoracic spinal column.
Overall, given the importance of selecting the correct site of puncture, caution is advised when using surface anatomic landmarks to identify intervertebral spaces. The increasing reliance on ultrasound determination of the spinal level may decrease the incidence of complications related to misidentification of the intended interspace.
General Adjacent vertebrae of the cervical, thoracic, and lumbar regions, excluding C1 and C2, are separated and cushioned by fibrocartilaginous intervertebral disks.
The soft, elastic core of each disk, the nucleus pulposus, is composed primarily of water, as well as scattered elastic and reticular fibers. The fibrocartilaginous annulus fibrosis surrounds the nucleus pulposus and attaches the disks to the bodies of adjacent vertebrae.
The disks, which account for up to one-quarter of the length of an adult vertebral column, lose their water content as we age, contributing to the shortening of the vertebral column, reducing their effectiveness as cushions, and rendering them more prone to injury, particularly in the lumbar region.
The articular processes arise at the junction between the pedicles and laminae. Superior and inferior articular processes project cranially and caudally, respectively, on both sides of each vertebra. The vertebral arches are connected by facet joints, which link the inferior articular processes of one vertebra with the superior articular processes of the more caudal vertebra. The facet joints are heavily innervated by the medial branch of the dorsal ramus of the spinal nerves.
This innervation serves to direct contraction of muscle that moves the vertebral column. The Longitudinal Ligaments The anterior and posterior longitudinal ligaments support the vertebral column, binding the vertebral bodies and intervertebral disks together Figure 6.
The posterior longitudinal ligament, which forms the anterior wall of the vertebral canal, is less broad than its anterior counterpart and weakens with age and other degenerative processes. Clinically, disk herniation occurs primarily in the paramedian portion of the posterior disk, at weak points in the posterior longitudinal ligament. This area comprises the anterior epidural space, as opposed to the more clinically relevant posterior epidural space, and should not interfere with epidural needle placement.
The Supraspinous and Interspinous Ligaments Several other ligaments that support the vertebral column serve as key anatomic landmarks during epidural needle placement. The supraspinous ligament connects the tips of the spinous processes from C7 to L5; above C7 and extending to the base of the skull, it is called the ligamentum nuchae.
This relatively superficial, inextensible ligament is most prominent in the upper thoracic region and becomes thinner and less conspicuous toward the lower lumbar region. The interspinous ligament, directly anterior to the supraspinous ligament, traverses the space between adjacent spinous processes in a posterocranial direction. It is less developed in the cervical region, which may contribute to a false LOR during cervical epidural procedures.
On histological examination, the interspinous ligament appears to have intermittent midline cavities filled with fat. During initiation of epidural placement via the midline approach, these ligaments serve as appropriate sites to engage the needle, although some practitioners may engage the needle closer to the epidural space, in the ligamentum flavum.
The Ligamentum Flavum The ligamentum flavum connects the lamina of adjacent vertebrae from the inferior border of C2 to the superior border of S1. Laterally, it extends into the intervertebral foramina, where it joins the capsule of the articular process. Anteriorly, it limits the vertebral canal and forms the posterior border of the epidural space.
At each spinal level, the right and left ligamentum flava join discontinuously in an acute angle with the opening oriented in the ventral direction, occasionally forming midline gaps filled with epidural fat. In contrast to the collagenous inter- and supraspinous ligaments, the ligamentum flavum comprises primarily thick, elastic fibers arranged longitudinally in a tight network. Areas of ossification of the ligamentum flavum occur at different levels of the vertebral canal and appear to be a normal variant.
These bony spurs, which may contribute to preexisting neurological symptoms and could potentially impede epidural needle advancement, are most commonly encountered in the lower thoracic region, between T9 and T11, and diminish in both frequency and size in the caudal and cranial directions. The ligamentum flavum has variable characteristics, many of which are disputed in the literature, at different vertebral levels. First, its thickness varies at different levels and, possibly, in different physiologic states, with a range of 1.
In isolated pregnant patients, the ligamentum flavum has been reported to be as thick as 10 mm, presumably due to edema. Thickness of the ligamentum flavum at different vertebral levels. Vertebral Level Thickness mm Cervical 1. Its thickness also varies within each interspace.
Veins connecting the posterior external and internal vertebral venous plexuses not uncommonly traverse the caudal portion of the gaps.
In another cadaveric study, Lirk et al determined that thoracic midline gaps were less frequent than cervical gaps but more frequent than those in the lumbar region, with an incidence as high as In cadaveric studies of the lumbar ligamentum flavum, gaps were found most commonly at L1 and L2 Clinically, these gaps may contribute to failure to identify the epidural space using the LOR technique at midline. The depth to the epidural space at midline may also be affected. They are common in the cervical spine and decrease in frequency in the thoracic and lumbar regions.
The variable thickness of the ligamentum flavum and the presence of midline gaps may contribute to failure to identify the epidural space. The vertebrae serve primarily to support the weight of the head, neck, and trunk; transfer that weight to the lower limbs; and protect the contents of the spinal canal, including the spinal cord.
An extension of the medulla oblongata, the spinal cord serves as the conduit between the CNS and the peripheral nerves via 31 pairs of spinal nerves 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal Figure 8. The adult cord measures approximately 45 cm or 18 inches and has two regions of enlarged diameter at C2—T2 and at T9—L2, areas that correspond with the origin of the nerve supplies to the upper and lower extremities.
However, its level of termination varies with age, as well as among individuals of similar age groups. As a result of a discrepancy in the pace of growth of the spinal cord and vertebral column during development, the spinal cord at birth ends at approximately L3.
By 6—12 months of age, the level of termination parallels that of adults, most commonly at L1. A collection of strands of neuron-free fibrous tissue enveloped in pia mater comprises the filum terminale and extends from the inferior tip of the conus medullaris to the second or third sacral vertebra.
Spinal Nerves Spinal nerves are classified as mixed nerves because they contain both a sensory and a motor component and, in many cases, autonomic fibers. Each nerve forms from the fusion of dorsal sensory and ventral somatic and visceral motor nerve roots as they exit the vertebral canal distal to the dorsal root ganglia, which contain the cell bodies of sensory neurons on either side of the spinal cord and lie between the pedicles of adjacent vertebrae.
In general, dorsal roots are larger and more easily blocked than ventral roots, a phenomenon that may be explained in part by the larger surface area for exposure to LAs provided by the bundled dorsal roots. At the cervical level, the first pair of spinal nerves exits between the skull and C1.
Subsequent cervical nerves continue to exit above the corresponding vertebra, assuming the name of the vertebra immediately following them. However, a transition occurs between the seventh cervical and first thoracic vertebrae, where an eighth pair of cervical nerves exits; thereafter, the spinal nerves exit below the corresponding vertebra and take the name of the vertebra immediately above. The spinal nerves divide into the anterior and posterior primary rami soon after they exit the intervertebral foramina.
The anterior ventral rami supply the ventrolateral side of the trunk, structures of the body wall, and the limbs. The posterior dorsal primary rami innervate specific regions of the skin that resemble horizontal bands extending from the origin of each pair of spinal nerves, called dermatomes, and the muscles of the back.
Clinically, knowledge of dermatomes is essential when planning anesthetics to specific cutaneous regions Figure 9 , although anesthesia may not be conferred reliably to the underlying viscera due to a separate innervation, and there is significant overlap in spinal nerve innervation of adjacent dermatomes Table An intricate relationship exists between the spinal nerves and the autonomic nervous system Figure Preganglionic sympathetic nerve fibers originate in the spinal cord from T1 to L2 and are blocked to varying degrees during epidural anesthesia.
They exit the spinal cord with spinal nerves and form the sympathetic chain, which extends the entire length of the spinal column on the anterolateral aspects of the vertebral bodies. The chain gives rise to the stellate ganglion, splanchnic nerves, and the celiac plexus, among other things.
There are potential benefits and marked drawbacks to epidural blockade of the sympathetic nervous system. TEA appears to increase GI mobility by blocking the sympathetic supply to the inferior mesenteric ganglia, thereby reducing the incidence of postoperative ileus.
Epidural anesthesia may also nerve block the systemic stress response to surgery, in part by blockade of the sympathetic nervous system. However, mid- to low-thoracic sympathetic blockade may be associated with dilation of the splanchnic vascular beds, a marked increase in venous capacitance, a decrease in preload to the right heart, and many of the other undesirable effects see Physiologic Effects of Epidural Blockade. Cranial and sacral components comprise the parasympathetic nervous system.
The vagus nerve, in particular, provides parasympathetic innervation to a broad area, including the head, neck, the thoracic organs and parts of the digestive tract. Parasympathetic innervation of the bladder, the descending large intestine, and the rectum originate at spinal cord levels S2 to S4. Spinal Meninges Spinal meninges cover the cord and nerve roots and are continuous with the cranial meninges that surround and protect the brain Figure The tough, predominantly collagenous outermost layer, the dura mater, encloses the CNS and provides localized points of attachment to the skull, sacrum, and vertebrae to anchor the spinal cord within the vertebral canal.
Cranially, the spinal dura mater fuses with periosteum at the level of the foramen magnum; caudally, it fuses with elements of the filum terminale and contributes to formation of the coccygeal ligament; laterally, the dura mater surrounds nerve roots as they exit the intervertebral foramina. The dura mater touches the spinal canal in areas, but does not adhere to it except in pathologic conditions.
It also confers both permeability and mechanical resistance to the dural sac, which terminates at S1 to S2 in adults and S3 to S4 in babies. The spinal nerve root cuffs, which have been postulated to play a role in the uptake of epidurally administered LAs, are lateral projections of both the dura mater and the underlying arachnoid lamina. The flexible arachnoid mater, the middle meningeal layer, is loosely attached to the inner aspect of the dura and encloses the spinal cord and surrounding CSF within the subarachnoid space.
It is composed of layers of epithelial-like cells connected by tight and occluding junctions, which impart its low permeability. The cell layers of the arachnoid mater are oriented parallel to the long axis of the spinal cord cephalocaudad , a finding that has led some investigators to claim that the architecture of the arachnoid mater, rather than the dura mater, accounts for the difference in headache rates between perpendicular and parallel insertions of beveled spinal needles.
A discontinuous subarachnoid septum septum posticum that stretches from the posterior spinal cord to the arachnoid may contribute to irregular spread of LAs in the subarachnoid space. The innermost meningeal layer, the pia mater, closely invests the underlying spinal cord and its blood vessels, as well as nerve roots and blood vessels in the subarachnoid space, and appears to have fenestrated areas that may influence the transfer of LAs during subarachnoid nerve blocks.
Caudally, the pia mater continues from the inferior tip of the conus medullaris as the filum terminale and fuses into the sacrococcygeal ligament. It is possible that a cavity can be created at the arachnoid-dura interface that may explain patchy or failed epidural nerve blocks with higher-than-expected cephalad spread so-called subdural nerve blocks. Early research suggested that the subdural extra-arachnoid space comprised a true potential space, with serous fluid that permitted movement of the dura and arachnoid layers alongside each other.
However, recent evidence suggests that, unlike a potential space, this arachnoid-dura interface is an area prone to mechanical stress that shears open only after direct trauma, such as air or fluid injection. It is also possible that these clefts may actually occur between layers of arachnoid instead of between dural border cells at the arachnoid-dura interface.
Injection of a large volume of LA intended for the epidural space in this area may result in a subdural nerve block. Blood Supply Vertebral and segmental arteries supply the spinal cord. A single anterior spinal artery and two posterior spinal arteries, and their offshoots, arise from the vertebral arteries and supply the anterior two-thirds of the spinal cord and the remainder of the cord, respectively Figure The anterior artery is thin at the midthoracic level of the spinal cord, an area that also has limited collateral blood supply.
Segmental arteries, which emerge from branches of the cervical and iliac arteries, among others, spread along the entire length of the spinal cord and anastomose with the anterior and posterior arteries. The artery of Adamkiewicz is among the largest segmental arteries and is most commonly unilateral, arising from the left side of the aorta between T8 and L1.
With regard to the venous system, anterior and posterior spinal veins, which anastomose with the internal vertebral plexus in the epidural space, drain into the azygos, the hemiazygos, and internal iliac veins, among other segmental veins, via intervertebral veins. The internal vertebral venous plexus consists of two anterior and two posterior longitudinal vessels with a variable distribution and is postulated to be involved in bloody or traumatic epidural needle and catheter placements.
Epidural Space The epidural space surrounds the dura mater circumferentially and extends from the foramen magnum to the sacrococcygeal ligament. If you can not feel your contractions, then pushing may be difficult to control. For this reason, your baby might need additional help coming down the birth canal. This is usually done by the use of forceps. For the most part, epidurals are effective in relieving pain during labor. Some women complain of being able to feel pain, or they feel that the drug worked better on one side of the body.
Cunningham, F. Gary, et al, Ch. What is an Epidural? What is an epidural? How is an epidural given? An antiseptic solution will be used to wipe the waistline area of your mid-back to minimize the chance of infection.
A small area on your back will be injected with a local anesthetic to numb it. A needle is then inserted into the numbed area surrounding the spinal cord in the lower back. After that, a small tube or catheter is threaded through the needle into the epidural space. The needle is then carefully removed, leaving the catheter in place to provide medication either through periodic injections or by continuous infusion.
The catheter is taped to the back to prevent it from slipping out. What are the different types? Regular Epidural After the catheter is in place, a combination of narcotic and anesthesia is administered either by a pump or by periodic injections into the epidural space.
What are the benefits of epidural anesthesia? An epidural provides a route for very effective pain relief that can be used throughout your labor. The anesthesiologist can control the effects by adjusting the type, amount, and strength of the medication. Unlike with systemic narcotics, only a tiny amount of medication reaches your baby.
What are the risks of epidural anesthesia? You have to stay still for 10 to 15 minutes while the epidural is put in, and then wait up to 20 minutes before the medication takes full effect.
Epidurals may cause your blood pressure to suddenly drop. For this reason, your blood pressure will be routinely checked to help ensure adequate blood flow to your baby.
If there is a sudden drop in blood pressure, you may need to be treated with IV fluids, medications, and oxygen. You may experience a severe headache caused by leakage of spinal fluid. After your epidural is placed, you will need to alternate sides while lying in bed and have continuous monitoring for changes in fetal heart rate. There is no credible evidence that it does either. When a woman needs a C-section, other factors usually are at play, including the size or position of the baby or slow progression of labor due to other issues.
There is some evidence that epidurals can speed the first stage of labor by allowing the mother to relax. The amount of medication that reaches the baby from the epidural is very small, and there is no evidence that it causes any harm. Epidurals are very safe; serious complications are extremely rare. However, as with all medications and medical procedures, there are potential side effects:. A spinal block is sometimes used in combination with an epidural during labor to provide immediate pain relief.
A spinal block, like an epidural, involves an injection in the lower back. While you sit or lie on your side in bed, a small amount of medication is injected into the spinal fluid to numb the lower half of the body. It brings good relief from pain and starts working quickly, but it lasts only an hour or two and is usually given only once during labor. Ask your doctor about these possible complications:.
The nurse may ask you to try to urinate. This is to make sure your bladder muscles are working. Anesthesia relaxes the bladder muscles, making it hard to urinate. This can lead to a bladder infection. Hernandez A, Sherwood ER. Anesthesiology principles, pain management, and conscious sedation. Philadelphia, PA: Elsevier; chap Spinal, epidural, and caudal anesthesia.
Basics of Anesthesia. Review provided by VeriMed Healthcare Network. Editorial team. Spinal and epidural anesthesia. The doctor who gives you epidural or spinal anesthesia is called an anesthesiologist. For an epidural: The doctor injects medicine just outside of the sac of fluid around your spinal cord.
This is called the epidural space. The medicine numbs, or blocks feeling in a certain part of your body so that you either feel less pain or no pain at all depending on the procedure.
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