Towards Ultrasound-guided Spinal Fusion Surgery
Between and , Grau and colleagues, from Heidelberg, Germany, published a series of studies that formed the foundation of the clinical application of US for CNB. Subsequent improvements in US technology and image processing software have allowed for greater image clarity of the spine and neuraxial structures. Also, the increasing availability of point-of-care US systems has led to further research by other investigators, which has established our current understanding of spinal sonoanatomy. In this section, the anatomy relevant for US imaging of the spine is briefly reviewed.
A vertebra is made up of two components: the vertebral body and the vertebral arch Figure 1. The vertebral arch is formed by the supporting pedicles and laminae Figure 2. Seven processes arise from the vertebral arch: one spinous process, two transverse processes, two superior articular processes, and two inferior articular processes see Figures 1 and 2. Adjacent vertebrae articulate with each other at the facet joints between the superior and inferior articular processes and the intervertebral disc between the vertebral bodies.
It is through these spaces that the US energy enters the spinal canal and makes spinal sonography and CNBs possible. The three major ligaments of the spine are the ligamentum flavum Figures 3, 4, and 5 , the anterior longitudinal ligament, and the posterior longitudinal ligament see Figure 3. The posterior longitudinal ligament is attached along the length of the anterior wall of the vertebral canal see Figures 3 , 4 , and 5. The ligamentum flavum, also referred to as the yellow ligament, is a dense layer of connective tissue that bridges the interlaminar spaces see Figure 4 and connects the laminae of adjacent vertebrae.
It is arch-like on cross-section and is widest posteriorly in the midline and in the lumbar region see Figure 5. The ligamentum flavum is attached to the anterior surface of the inferior margin of the lamina above but splits inferiorly to attach to both the posterior surface superficial component and anterior surface deep component of the lamina below. The spinous processes are attached at their tips by the supraspinous ligament, which is thick and cord-like, and along their length by the interspinous ligament, which is thin and membranous see Figure 3.
The spinal vertebral canal is formed by the vertebral arch and the posterior surface of the vertebral body see Figures 2 and 5. The openings into the spinal canal are through the intervertebral foramen along its lateral wall and the interlaminar space on its posterolateral wall. Within the spinal canal lies the thecal sac formed by the dura mater and arachnoid mater; see Figure 5 and its contents the spinal cord, cauda equina, and cerebrospinal fluid; see Figures 3 and 5. The spinal cord extends from the foramen magnum to the conus medullaris, near the lower border of the first lumbar vertebra see Figure 3 , finally terminating as the filum terminale.
However, there is normal variation in the position of the conus medullaris, and it may extend anywhere from T12 to the upper third of L3. Similarly, the dural sac is classically described as ending at the level of the second sacral vertebra S2 see Figure 3 , but this can vary from the upper border of S1 to the lower border of S4. The epidural space is an anatomical space within the spinal canal but outside the dura mater referred to as extradural; see Figures 3 and 5. It extends from the level of the foramen magnum cranially to the tip of the sacrum at the sacrococcygeal ligament see Figure 3.
The posterior epidural space is of importance for CNBs. The only structure of importance in the anterior epidural space for neuraxial blocks is the internal vertebral venous plexus. Because of the divergent nature of their US beam, curved array transducers also produce a wide field of view, particularly in the deeper areas, which is useful when using US for CNB.
Low-frequency US provides adequate penetration, but unfortunately lacks spatial resolution at the depth 5—7 cm at which the neuraxial structures are located. The osseous framework of the spine, which envelops the neuraxial structures, reflects much of the incident US signal before it even reaches the spinal canal, presenting additional challenges in acquiring good-quality images.
However, this challenge is often offset by improved image processing and advanced image optimization modes in modern US systems, and thus high-quality images of the neuraxis can still be obtained with low-frequency transducers. Although anatomical planes have already been described elsewhere in this text, the importance of understanding them for imaging of the spine dictates a further, more detailed review.
There are three anatomical planes: median, transverse, and coronal Figure 6. The median plane is a longitudinal plane that passes through the midline, bisecting the body into two equal right and left halves. Therefore, the median plane can also be defined as the sagittal plane that is exactly in the middle of the body median sagittal plane. The transverse plane, also known as the axial or horizontal plane, is parallel to the ground. The coronal plane, also known as the frontal plane, is a vertical plane that is perpendicular to the ground and at right angles to the sagittal plane dividing the body into an anterior and a posterior part.
US imaging of the spine can be performed in the transverse axis transverse scan; Figure 7 or the longitudinal axis sagittal scan; Figure 8 with the patient in the sitting, lateral decubitus, or prone position. The anatomical information obtained from these two scan planes complements each other during a US examination of the spine. The former produces the transverse spinous process view, whereas the latter produces the transverse interspinous view of the spine. Depending on the angle of the spinous processes, the transducer may have to be tilted to produce an optimal interspinous view of the neuraxial structures.
A sagittal scan can be performed through the midline median sagittal spinous process view or through a paramedian plane Figure 8. Overall, three paramedian sagittal views of the spine can be obtained from medial to lateral : 1 a paramedian sagittal lamina view see Figure 8a ; 2 a paramedian sagittal articular process view see Figure 8b ; and 3 a paramedian sagittal transverse process view see Figure 8c. Grau et al. We have found that the US visibility of neuraxial structures can be further improved when the spine is imaged in the paramedian sagittal oblique plane Figure 9.
During a paramedian sagittal oblique scan PMSOS , the transducer is positioned 2—3 cm lateral to the midline paramedian and over the laminae in the sagittal axis, tilted slightly medially toward the midline see Figure 9. The purpose of the medial tilt is to ensure that the US signal enters the spinal canal through the widest part of the interlaminar space and not the lateral sulcus of the spinal canal. Detailed knowledge of the vertebral anatomy is essential to understand the sonoanatomy of the spine. Unfortunately, cross-sectional anatomy texts describe the anatomy of the spine in traditional orthogonal planes; that is, the transverse, sagittal, and coronal planes.
This often results in difficulty interpreting the spinal sonoanatomy because US imaging is generally performed in an arbitrary or intermediary plane by tilting, sliding, and rotating the transducer. Several anatomical models have recently been developed to teach musculoskeletal US imaging techniques in human volunteers , the sonoanatomy relevant for peripheral nerve blocks in human volunteers and cadavers , and the required interventional skills in tissue-mimicking phantoms and fresh cadavers.
However, few models or tools are available to learn and practice spinal sonoanatomy or the interventional skills required for USG CNB. Since three-dimensional 3D reconstructions of high-definition CT scan data 3D volume datasets can also be used to study the osseous anatomy Figure 13b, c, d and validate the structure visualized in multiplanar 3D images Figure Computer-generated anatomical reconstructions from the Visible Human Project dataset that correspond to the US scan planes provide another useful way of studying the sonoanatomy of the spine in vivo Figure Multiplanar 3D reconstructions from archived high-resolution 3D CT datasets of the spine can also be used to study and validate the sonographic appearance of the various osseous elements and neuraxial structures of the spine.
The water-based spine phantom simplifies the process of learning the sonoanatomy of the spine in two easy steps: 1 learning the sonoanatomy of the osseous elements of the spine; and 2 learning the sonoanatomy of the soft-tissue structures that make up the spine. The water-based spine phantom is an excellent model to define the osseous anatomy of the spine and is based on a model described previously by Greher and colleagues to study the osseous anatomy of relevance to USG lumbar facet nerve block. The model is prepared by immersing a commercially available lumbosacral spine model in a water bath see Figure 10a.
A low-frequency curved array transducer is then used to scan the model through the water in the transverse and sagittal axes as one would do in vivo. Each osseous element of the spine produces a characteristic sonographic pattern. The ability to recognize these sonographic patterns is an important step toward understanding the sonoanatomy of the spine. Representative US images of the spinous process, lamina, articular processes, and transverse process from the water-based spine phantom are presented in Figures 10b, c, d and 16a, b, c.
The advantage of this waterbased spine phantom is that water produces an anechoic black background against which the hyperechoic reflections from the bone are clearly visualized. The water-based spine phantom allows a see-through, real-time visual validation of the sonographic appearance of a given osseous element by performing the scan with a marker eg, a needle in contact with it see Figure 16a. The described model is also inexpensive, easily prepared, requires little time to set up, and can be used repeatedly without deteriorating or decomposing, as animal tissuebased phantoms do.
Once the novice learns to identify the individual osseous elements of the spine in the various US scan planes, it becomes easy to define the gaps between these elements: the interspinous see Figure 10c and interlaminar spaces see Figure 16a , through which the US energy enters the spinal canal to produce the acoustic window seen on a spinal sonogram. The patient is positioned in the sitting, lateral, or prone position, with the lumbosacral spine maximally flexed.
The transducer is placed 1—2 cm lateral to the spinous process ie, in the paramedian sagittal plane at the lower back with its orientation marker directed cranially. A slight medial tilt during the scan insonates the spine in a paramedian sagittal oblique PMSO plane. First, the sacrum is identified as a flat, hyperechoic structure with a large acoustic shadow anteriorly Figure When the transducer is slid in a cranial direction, a gap is seen between the sacrum and the lamina of the L5 vertebra, which is the L5—S1 interlaminar space, also referred to as the L5— S1 gap Figures 17 and The L3—4 and L4—5 interlaminar spaces can now be located by counting upward Figure The erector spinae muscles are hypoechoic and lie superficial to the laminae.
The lamina appears hyperechoic and is the first osseous structure visualized see Figure Because bone impedes US penetration, there is an acoustic shadow anterior to each lamina. The ligamentum flavum appears as a hyperechoic band across the adjacent laminae see Figure The posterior dura is the next hyperechoic structure anterior to the ligamentum flavum, and the epidural space is the hypoechoic area a few millimeters wide between the ligamentum flavum and the posterior dura see Figure The thecal sac with the cerebrospinal fluid is the anechoic space anterior to the posterior dura see Figure The cauda equina, which is located within the thecal sac, is often seen as multiple horizontal, hyperechoic shadows within the anechoic thecal sac.
Pulsations of the cauda equina are identified in some patients. The anterior dura is also hyperechoic, but it is not always easy to differentiate it from the posterior longitudinal ligament and the posterior surface of the vertebral body because they are of similar echogenicity isoechoic and closely apposed to each other. If the transducer slides medially, that is, to the median sagittal plane, the median sagittal spinous process view is obtained, and the tips of the spinous processes of the L3—L5 vertebrae, which appear as superficial, hyperechoic crescent-shaped structures, are seen Figures 10c, 21 , and The acoustic window between the spinous processes in the median plane is narrow and often prevents clear visualization of the neuraxial structures within the spinal canal.
The articular processes of the vertebrae appear as one continuous, hyperechoic wavy line with no intervening gaps see Figure A sagittal scan lateral to the articular processes brings the transverse processes of the L3—L5 vertebrae into view and produces the paramedian sagittal transverse process view Figures 25 and The transverse processes are recognized by their crescent-shaped, hyperechoic reflections and finger-like acoustic shadows anteriorly see Figures 16c, 25, and For a transverse scan of the lumbar spine, the US transducer is positioned over the spinous process transverse spinous process view; see Figure 7a , with the patient in the sitting or lateral position.
On a transverse sonogram, the spinous process and the lamina on either side are seen as a hyperechoic reflection anterior to which there is a dark acoustic shadow that completely obscures the underlying spinal canal and thus the neuraxial structures Figures 27 and Therefore, this view is not suitable for imaging the neuraxial structures but can be useful for identifying the midline when the spinous processes cannot be palpated eg, in obese patients. However, by sliding the transducer slightly cranially or caudally, it is possible to perform a transverse scan through the interspinous or interlaminar space transverse interspinous view; Figures 7b, 29 , and A slight tilt of the transducer cranially or caudally may be needed to align the US beam with the interspinous space and optimize the US image.
In the transverse interspinous view, the posterior dura, thecal sac, and anterior complex are visualized from a posterior to anterior direction within the spinal canal in the midline and the articular processes, and the transverse processes are visualized laterally see Figures 29 and The ligamentum flavum is rarely visualized in the transverse interspinous view, possibly due to anisotropy caused by the arch-like attachment of the ligamentum flavum to the lamina. The epidural space is also less frequently visualized in the transverse interspinous view than in the PMSOS. The transverse interspinous view can be used to examine for rotational deformities of the vertebrae, such as in scoliosis.
Normally, both the laminae and the articular processes on either side should be symmetrically located see Figures 10d , 13b , and However, if there is asymmetry, a rotational deformity of the vertebral column should be suspected and the needle trajectory altered accordingly. US imaging of the thoracic spine is more challenging than the lumbar spine. The ability to visualize the neuraxial structures with US may vary with the level at which the imaging is performed, with poorer visibility of the neuraxis in the upper thoracic levels.
Regardless of the level at which the scan is performed, the thoracic spine is probably best imaged with the patient in the sitting position. In the lower thoracic region T9—T12 , the sonographic appearance of the neuraxial structures Figure 31 is comparable to that in the lumbar region because of comparable vertebral anatomy. However, the acute caudal angulation of the spinous processes and the narrow interspinous and interlaminar spaces in the midthoracic region T4—T8 results in a narrow acoustic window with limited visibility of the underlying neuraxial anatomy Figures 32 and Grau and colleagues performed US imaging of the thoracic spine at the T5—T6 level in young volunteers and correlated findings with matching magnetic resonance imaging MRI images.
They found that the transverse axis produced the best images of the neuraxial structures. However, the epidural space was best visualized in the paramedian sagittal scans. Regardless, US was limited in its ability to delineate the epidural space or the spinal cord but was better than MRI in demonstrating the posterior dura. Because a high spinal usually does not affect the cervical area, sparing of the phrenic nerve and normal diaphragmatic function occurs, and inspiration is minimally affected.
Although Steinbrook and colleagues found that spinal anesthesia was not associated with significant changes in vital capacity, maximal inspiratory pressure, or resting end-tidal PCO2, increased ventilatory responsiveness to CO2 with bupivacaine spinal anesthesia was seen. The sympathetic innervation to the abdominal organs arises from T6 to L2. Due to sympathetic blockade and unopposed parasympathetic activity after spinal blockade, secretions increase, sphincters relax, and the bowel becomes constricted. Increased vagal activity after sympathetic block causes increased peristalsis of the gastrointestinal tract, which can lead to nausea.
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Nausea may also result from hypotension-induced gut ischemia, which produces serotonin and other emetogenic substances. Hepatic blood flow correlates to arterial blood flow. There is no autoregulation of hepatic blood flow; thus, as arterial blood flow decreases after spinal anesthesia, so does hepatic blood flow. If the mean arterial pressure MAP after placing a spinal anesthetic is maintained, hepatic blood flow will also be maintained. Patients with hepatic disease must be carefully monitored, and their blood pressure must be controlled during anesthesia to maintain hepatic perfusion.
No studies have conclusively shown the superiority of regional or general anesthesia in patients with liver disease. In patients with liver disease, either regional or general anesthesia can be given, as long as the MAP is kept close to baseline. Renal blood flow is autoregulated. The kidneys remain perfused when the MAP remains above 50 mm Hg. Transient decreases in renal blood flow may occur when MAP is less than 50 mm Hg, but even after long decreases in MAP, renal function returns to normal when blood pressure returns to normal.
Again, attention to blood pressure is important after placing a spinal anesthetic, and the MAP should be as close to baseline as possible. Spinal anesthesia does not affect autoregulation of renal blood flow. It has been shown in sheep that renal perfusion changed little after spinal anesthesia. Many factors have been suggested as possible determinants of spinal blockade level.
The four main categories of factors are 1 characteristics of the local anesthetic solution, 2 patient characteristics, 3 technique of spinal blockade, and 4 diffusion. Characteristics of local anesthetic solution include baricity, dose, concentration, and volume injected. Patient characteristics include age, weight, height, gender, intra-abdominal pressure, anatomy of the spinal column, spinal fluid characteristics, and patient position.
Techniques of spinal blockade include site of injection, speed of injection, direction of needle bevel, force of injection, and addition of vasoconstrictors. The site of injection of local anesthetics for spinal anesthesia can determine the level of blockade. In some studies, isobaric spinal 0. However, no difference in block height exists when hyperbaric bupivacaine or dibucaine is injected as a spinal anesthetic in different interspaces.
Some studies have reported changes in block height after spinal anesthesia in the elderly patient as compared with the young patient, but other studies have reported no difference in block height. These studies were performed with both isobaric and hyperbaric 0. Baricity plays a major role in determining block height after spinal anesthesia in older populations. Isobaric bupivacaine appears to increase block height, and hyperbaric bupivacaine does not appear to change block height with increasing age.
Just as with site of injection, it appears that baricity plays a major role in determining block height after spinal anesthesia in older populations, and age is not an independent factor. Positioning of the patient is important for determining level of blockade after hyperbaric and hypobaric spinal anesthesia, but not for isobaric solutions. Sitting, Trendelenburg, and prone jackknife positions can greatly change the spread of the local anesthetic due to effect of gravity. The combination of baricity of the local anesthetic solution and patient positioning determines spinal block height.
The sitting position in combination with a hyperbaric solution can produce analgesia in the perineum. Prone jackknife positioning is used for rectal, perineal, and lumbar procedures with a hypobaric local anesthetic. This prevents rostral spread of the spinal blockade after injection. Combined with Trendelenburg positioning, this may help cephalad spread. This position may inadvertently be attained when a urinary catheter is placed after spinal insertion. Speed of injection has been reported to affect spinal block height, but the data available in the literature are conflicting.
In studies using isobaric bupivacaine, there is no difference in spinal block height with different speeds of injection. Even though spinal block height does not change with speed of injection, a smooth, slow injection should be used when giving a spinal anesthetic.
If a forceful injection is given and the syringe is not connected tightly to the spinal needle, the needle might disconnect from the syringe with loss of local anesthetic. Even though spinal block height does not change with speed of injection, use a smooth, slow injection when giving a spinal anesthetic. It is difficult to maintain volume, concentration, or dose of local anesthetic constant without changing any of the other variables; thus, it is difficult to produce high-quality studies that investigate these variables singly.
Axelsson and associates showed that volume of local anesthetic can affect spinal block height and duration when equivalent doses are used. Peng and coworkers showed that concentration of local anesthetic is directly related to dose when determining effective anesthesia. However, dose of local anesthetic plays the greatest role in determining spinal block duration, as neither volume nor concentration of isobaric bupivacaine or tetracaine alter spinal block duration when the dose is held constant. Studies have repeatedly shown that spinal block duration is longer when higher doses of local anesthetic are given.
When performing a spinal anesthetic, be cognizant of not only the dose of local anesthetic but also the volume and concentration so the patient is not overdosed or underdosed. The use of hyperbaric solutions minimizes the importance of dose and volume except when doses of hyperbaric bupivacaine equal to or less than 10 mg are used.
In those cases, there is less cephalad spread and a shorter duration of action. A dose of hyperbaric bupivacaine between 10 and 20 mg results in similar block height. When using hyperbaric solutions, it is important to note that patient positioning and baricity are the most influential factors on block height, except when low doses of hyperbaric bupivacaine are used.
No single intervention guarantees asepsis. Therefore, a multiprong approach is advisable. In the past, most institutions had reusable trays for spinal anesthesia. These trays required preparation by anesthesiologists or anesthesia personnel to ensure that bacterial and chemical contamination would not occur. Currently, commercially prepared, disposable spinal trays are available and are in use by most institutions.
These trays are portable, sterile, and easy to use. The ideal skin preparation solution should be bactericidal and have a quick onset and long duration. Chlorhexidine is superior to povidone iodine in all these respects. In addition, the ideal agent should not be neurotoxic.
Unfortunately, bactericidal agents are neurotoxic. It is therefore prudent to use the lowest effective concentration and allow the preparation to dry. Although subject to debate, 0. Contamination of equipment with skin preparation can theoretically lead to the introduction of neurotoxic substances into neural tissue. Of more concern is accidental neuraxial injection of antiseptic solution, possibly from antiseptic solution and local anesthetic being placed in adjacent pots.
Therefore, after skin preparation, unused antiseptic should be discarded before commencement of the procedure and intrathecal drugs should be drawn directly from sterile ampules. Tinted antiseptic solutions may decrease the likelihood of drug error and allow easy identification of missed skin during application.
Proving a benefit of individual infection control measures is difficult due to the rarity of infectious complications. Past evidence has been contradictory. Yet, in there were calls for routine face mask use after it was unambiguously proven, using polymerase chain reaction PCR fingerprinting, that a case of Streptococcus salivarius meningitis originated in the throat of the doctor who had performed a lumbar puncture. A American Society of Regional Anesthesia and Pain Medicine ASRA practice advisory recommended mask wearing in addition to removing jewelry, thorough hand washing, and sterile surgical gloves for all regional anesthesia techniques.
Major components of an aseptic technique also included a surgical hat and sterile draping. Other international professional bodies have similar guidelines. Prophylactic antibiotics are unnecessary for spinal anesthesia. If, as it happens, antibiotic prophylaxis is required for the prevention of surgical site infection, it may be prudent to administer antibiotics before insertion of a spinal needle.
The reader is referred to Infection Control in Regional Anesthesia for more information. Resuscitation equipment must be available whenever a spinal anesthetic is performed. This includes equipment and medication required to secure an airway, provide ventilation, and support cardiac function. All patients receiving spinal anesthesia should have an intravenous line. The patient must be monitored during the placement of the spinal anesthetic with a pulse oximeter, blood pressure cuff, and ECG. Fetal monitoring should be used in the case of a pregnant patient.
Shivering and body habitus may make noninvasive blood pressure measurement difficult. Consideration should be given to invasive blood pressure monitoring if the patient has significant cardiovascular disease. Needles of different diameters and shapes have been developed for spinal anesthesia. The ones currently used have a close-fitting, removable stylet, which prevents skin and adipose tissue from plugging the needle and possibly entering the subarachnoid space. Figure 10 shows the different types of needles used along with the type of point at the end of the needle.
The pencil-point needles Sprotte and Whitacre have a rounded, noncutting bevel with a solid tip. The opening is located on the side of the needle 2—4 mm proximal to the tip of the needle. The needles with cutting bevels include the Quincke and Pitkin needles. The Quincke needle has a sharp point with a medium-length cutting needle, and the Pitkin has a sharp point and short bevel with cutting edges.
Finally, the Greene spinal needle has a rounded point and rounded noncutting bevel. If a continuous spinal catheter is to be placed, a Tuohy needle can be used to find the subarachnoid space before placement of the catheter. Pencil-point needles provide a better tactile sensation of the layers of ligament encountered but require more force to insert than bevel-tip needles. The bevel of the needle should be directed longitudinally to decrease the incidence of PDPH. Small-gauge needles and needles with rounded, noncutting bevels also decrease the incidence of PDPH but are more easily deflected than larger-gauge needles.
Introducers have been designed to assist with the placement of spinal needles into the subarachnoid space due to the difficulty in directing needles of small bore through the tissues. Introducers also serve to prevent contamination of the CSF with small pieces of epidermis, which could lead to the formation of dermoid spinal cord tumors. The introducer is placed into the interspinous ligament in the intended direction of the spinal needle, and the spinal needle is then placed through the introducer.
Proper positioning of the patient for spinal anesthesia is essential for a fast, successful block. It has been shown to be an independent predictor for successful first attempt at neuraxial block. Before beginning the procedure, both the patient and the anesthesiologist should be comfortable. This includes positioning the height of the operating room table, providing adequate blankets or covers for the patient, ensuring a comfortable room temperature, and providing sedation for the patient if required.
Personnel trained in positioning patients are invaluable, and commercial positioning devices may be useful. When providing sedation, it is important to avoid oversedation. The patient should be able to cooperate before, during, and after administration of the spinal anesthetic. There are three main positions for administering a spinal anesthetic: the lateral decubitus, sitting, and prone positions. A commonly used position for placing a spinal anesthetic is the lateral decubitus position. Figure 11 shows a patient in the lateral decubitus position. It is beneficial to have an assistant to help hold and encourage the patient to stay in this position.
Depending on the operative site and operative position, a hypo-, iso-, or hyperbaric solution of local anesthetic can be injected. Strictly speaking, the sitting position is best utilized for low lumbar or sacral anesthesia and in instances when the patient is obese and there is difficulty in finding the midline. In practice, however, many anesthesiologists prefer the sitting position in all patients who can be positioned this way.
The sitting position avoids the potential rotation of the spine that can occur with the lateral decubitus position. Using a stool for a footrest and a pillow for the patient to hold can be valuable in this position.
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The patient should flex the neck and push out the lower back to open up the lumbar intervertebral spaces. Figure 12 depicts a patient in the sitting position, and the L4—L5 interspace is marked. If a higher level of blockade is necessary, the patient should be placed supine immediately after spinal placement and the table adjusted accordingly. The prone position can be utilized for induction of spinal anesthesia if the patient needs to be in this position for the surgery, such as for rectal, perineal, or lumbar procedures. A hypobaric or isobaric solution of local anesthetic is preferred in the prone jackknife position for these procedures.
This avoids rostral spread of the local anesthetic and decreases the risk of high spinal anesthesia. The prone position is utilized for spinal anesthesia if the patient needs to be in this position for the surgery, such as for rectal, perineal, or lumbar procedures. The patient is then positioned in the prone position with vigilant monitoring, including frequent verbal communication with the patient. When performing a spinal anesthetic, appropriate monitors should be placed, and airway and resuscitation equipment should be readily available.
All equipment for the spinal blockade should be ready for use, and all necessary medications should be drawn up prior to positioning the patient for spinal anesthesia. Adequate preparation for the spinal reduces the amount of time needed to perform the block and assists with making the patient comfortable.
Proper positioning is the key to making the spinal anesthetic quick and successful. Once the patient is correctly positioned, the midline should be palpated. The iliac crests are palpated, and a line is drawn between them to find the body of L4 or the L4—L5 interspace. Other interspaces can be identified, depending on where the needle is to be inserted.
The skin should be cleaned with skin preparation solution such as 0. A small wheal of local anesthetic is injected into the skin at the planned site of insertion. More local anesthetic is then administered along the intended path of the spinal needle insertion to the estimated depth of the supraspinous ligament. This serves a dual purpose: additional anesthesia for the spinal needle insertion and identification of the correct path for spinal needle placement. Care must be taken in thin patients to avoid dural puncture, and inadvertent spinal anesthesia, at this stage.
If the midline approach is used, palpate the desired interspace and inject local anesthetic into the skin and subcutaneous tissue. Next, the spinal needle is passed through the introducer. The needle passes through the subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, and subarachnoid mater to reach the subarachnoid space.
Resistance changes as the spinal needle passes through each level on the way to the subarachnoid space.
Subcutaneous tissue offers less resistance to the spinal needle than ligaments. Once this pop is felt, the stylet should be removed from the needle to check for flow of CSF. For spinal needles of higher gauge 26—29 gauge , this usually takes 5—10 seconds, but in some patients, it can take a minute or longer. Debris can obstruct the orifice of the spinal needle. If necessary, withdraw the needle and clear the orifice before attempting the spinal anesthetic again.
A common cause of failure to obtain CSF flow is the spinal needle being off the midline. The midline should be reassessed and the needle repositioned. If the spinal needle contacts bone, the depth of the needle should be noted and the needle placed more cephalad. If bone is contacted again, the needle depth should be compared with that of the last bone contact to determine what structure is being contacted. For instance, if bone contact is deeper than the first insertion, the needle should be redirected more cephalad to avoid the inferior spinous process.
If bone contact is at roughly the same depth as the original insertion, it may be lamina being contacted, and the midline should be reassessed. If bone contact is shallower than the original insertion, the needle should be redirected caudally to avoid the superior spinous process. When the spinal needle needs to be reinserted, it is important to withdraw the needle back to the skin level before redirection. Only make small changes in the angle of direction when reinserting the spinal needle as small changes at the surface lead to large changes in direction when the needle reaches greater depths.
Bowing and curving of the spinal needle when inserting through the skin or introducer can also steer the needle off course when attempting to contact the subarachnoid space. Paresthesias may be elicited when passing a spinal needle. The stylet should be removed from the spinal needle, and if CSF is seen and the paresthesia is no longer present, it is safe to inject the local anesthetic. A cauda equina nerve root may have been encountered. If there is no CSF flow, it is possible that the spinal needle has contacted a spinal nerve root traversing the epidural space.
The needle should be removed and redirected toward the side opposite the paresthesia. After free flow of CSF is established, inject the local anesthetic slowly at a speed of less than 0. Additional aspiration of CSF at the midpoint and end of injection can be attempted to confirm continued subarachnoid administration but may not always be possible when small needles are used. Once local anesthetic injection is complete, the introducer and spinal needle are removed as one unit from the back of the patient.
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The patient should then be positioned according to the surgical procedure and baricity of local anesthetic given. The table can be tilted in either the Trendelenburg or the reverse Trendelenburg position as needed to adjust the height of the block after testing the sensory level. The anesthesiologist should carefully monitor and support vital signs. If the patient has a calcified interspinous ligament or difficulty in flexing the spine, a paramedian approach to achieve spinal anesthesia can be utilized.
The patient can be in any position for this approach: sitting, lateral, or even prone jackknife. After palpating the superior and inferior lumbar spinous processes of the desired interspace, local anesthetic is infiltrated 1 cm lateral to the superior aspect of the inferior spinous process.
The needle should be directed slightly medially. This demonstrates that small changes in angulation can have pronounced effects on needle-tip placement. Although slight cephalad angulation is also required, a common error is too steep an initial approach. Other methods have been described. All techniques involve a similar vertical axis for the puncture site 1—1. They differ in the horizontal axis eg, 1 cm lateral to the spinous process, 1 cm lateral to the interspace, 1 cm lateral and 1 cm inferior to the interspace, 1 cm lateral and 1 cm inferior to the inferior aspect of the superior spinous process and the degree of cephalad angulation required.
Figure Figure 13 shows the landmarks used for a paramedian approach to spinal anesthesia. Figure 14 depicts successful performance of a paramedian spinal anesthetic. The Taylor, or lumbosacral, approach to spinal anesthesia is a paramedian approach directed toward the L5—S1 interspace. As with the paramedian approach, the patient can be in any position for this approach: sitting, lateral, or prone. This angle should be medial enough to reach the midline at the L5—S1 interspace.
After needle insertion, the first significant resistance felt is the ligamentum flavum, and then the dura mater is punctured to allow free flow of CSF as the subarachnoid space is entered. Real-time ultrasound-guided prone spinal anesthesia via the Taylor approach has been described and may improve patient comfort and compliance during the procedure. An indwelling catheter can be placed for continuous spinal anesthesia. Local anesthetics can be dosed repeatedly through the catheter and the level and duration of anesthesia adjusted as necessary for the surgical procedure.
Placement of a continuous spinal catheter occurs in a similar fashion as a regular spinal anesthetic except that a larger-gauge needle, such as a Tuohy, is used to enable the passage of the catheter. After insertion of the Tuohy needle, the subarachnoid space is found, and the spinal catheter is passed 2—3 cm into the subarachnoid space. Never withdraw the catheter back into the needle shaft because there is a risk of shearing the catheter and leaving a piece of it in the subarachnoid space. If the catheter needs to be withdrawn, withdraw the catheter and needle together and attempt the continuous spinal at another interspace.
Communication is critical to avoid a spinal catheter being mistaken for the more common epidural catheter. This involves labeling, documentation, handover, and vigilance. A gauge catheter was placed in patients; there were no reported permanent neurological outcomes. The trial compared continuous spinal analgesia with epidural analgesia and found lower initial pain scores, higher patient satisfaction, and less motor block in the spinal group, with no difference in neonatal or obstetric outcomes.
Intrathecal catheters were more difficult to remove than epidural catheters.
Spinal Anesthesia - NYSORA
Conversion to general anesthesia was as low as 0. Failed spinal anesthesia may present as complete absence of block, partial block, or inadequate duration of block. Although expertise may reduce the chance of a failed spinal, even experienced clinicians will be confronted with failed spinal blocks. After being reassured by the appearance of CSF, a subsequent failed or patchy block can leave an anesthesiologist frustrated and bewildered. A methodical approach is required when managing failed spinal blockade. In an excellent review article, Fettes et al classified failure of spinal anesthesia into five groups: failure of lumbar puncture, failure of solution injection, solution spread in the CSF, drug action on the nerve roots and cord, and patient management.
Their review is summarized next. Whenever there are problems with placing a spinal anesthetic, the anesthesiologist should reassess the position of the patient. A member of the operating room personnel who is trained to assist with patient positioning should be used. Alternatively, positioning of the patient can be enhanced with commercially available positioning devices.
These devices can help maintain spinal flexion and create a stable support for the patient, which can be useful if no trained operating room personnel are available to assist with positioning. If the proposed interspace cannot be found, the interspace above or below the original site of spinal injection can be attempted. When the sitting position cannot be used or is unsuccessful, the lateral decubitus position can be used. Either the midline or the lateral paramedian technique can be attempted. A predictably difficult back should not be used to teach inexperienced trainees.
If anatomical landmarks are imperceptible spinal ultrasonography can be used to assist lumbar puncture see section on neuraxial ultrasound. Because of the small volumes of injectate used in spinal anesthesia, apparently trivial reductions in the volume of solution may result in a less-than-adequate block. Reductions in solution injected may be the result of loss of injectate when the spinal syringe is attached to the needle hub or loss into tissues adjacent to the subarachnoid space due to needle orifice migration or the orifice straddling a number of potential spaces eg, the subarachnoid and subdural or epidural spaces.
Intentional reductions in dose, usually to decrease side effects, may also result in decreased efficacy. Failure of solution spread within the CSF may be due to spinal deformities such as kyphosis or scoliosis, previous surgery, transverse or longitudinal spinal septae, spinal stenosis, or extradural cysts.
Although usually asymptomatic, they contain CSF and may account for positive aspiration of CSF yet failure of complete block. Lumbar CSF volume is an important determinant of spread. Failure of drug action may result from the incorrect drug being administered. The correct drug may be inactive as the result of physicochemical instability less likely with modern agents or may be impaired due to chemical incompatibilities when two or more agents are used.
The phenomenon of local anesthetic resistance has been questioned in the literature. However, pain perception is far more complex, and despite perfect spinal blockade, a patient may experience discomfort or pain. Intraoperatively, a patient may require supplemental anxiolysis and analgesia or general anesthesia.
Management of a failed spinal block will depend on whether it occurs preoperatively or intraoperatively and the nature of the failure. Two important principles must be remembered when repeating a spinal block. First, the second attempt must not be identical to the first.
Second, a repeat dose may result in excessive spread of local anesthetic. Failed subarachnoid block may be the result of inadvertent subdural injection and deserves special attention. The subdural space is a potential space that only becomes real after tearing of neurothelial cells within the space as a result of iatrogenic needle insertion and fluid injection see Figure 4. Characteristic features of a SDB are a high sensory level with motor and sympathetic sparing.
This may be the result of the limited ventral capacity of the space, which results in sparing of the anterior motor and sympathetic fibers. However, a SDB may also present in a number of different ways: failed block, unilateral block, Horner syndrome, trigeminal nerve palsy, respiratory insufficiency, or unconsciousness due to brainstem involvement. Onset of nerve blockade is slower than subarachnoid block but faster than epidural block and usually resolves after 2 hours. The incidence of SDB after attempted spinal anesthesia is unknown. Because the dura is intentionally breached during attempted spinal anesthesia, the incidence of SDB may be higher compared with epidural block variously quoted as between 0.
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The size of the acquired subdural space is probably proportional to the volume of fluid injected. Therefore, typical volumes used with spinal anesthesia may not be as significant as volumes used with epidural anesthesia. Each year, the number of surgeries increase, and more are performed on an outpatient basis. As anesthesiologists, we are always looking for new ways to provide efficient anesthetic care that is safe, controls pain, allows the patient to be discharged home in a timely fashion as per postanesthesia care unit protocol, and is easily performed and reproducible.
It has previously been suggested that spinal anaesthesia may be incorporated into the outpatient surgery model. Use of a unilateral spinal block for elderly patients and outpatient surgery has undergone a resurgence. Unilateral spinal anesthesia was described in by Ruben and Kamsler. Their report concerned patients for surgical reduction of hip fracture performed under unilateral spinal blockade.
No deaths were reported, and no increase in the hazard of operation was found. Recently, attention has returned to the use of unilateral spinal anesthesia in elderly patients and for outpatient surgery. Use of unilateral spinal anesthesia results in decreased changes in systolic, mean and diastolic pressures, or oxygen saturation in elderly trauma patients eg, hip fracture.
Keeping the operative side up and using a hypobaric spinal solution in a low dose for these cases results in excellent anesthesia and remarkable hemostability when the patient is kept in the lateral position for 5—10 minutes before repositioning supine. When using hyperbaric solutions, the operative side should be dependent.
Outpatient surgery using hyperbaric 0. Less hemodynamic changes are found in the unilateral spinal anesthesia group, with quicker regression of the block and equal time to discharge home. Compared with other outpatient surgery, less motor block is required for knee arthroscopy. Doses of hyperbaric bupivacaine as low as 4—5 mg are effective when combined with unilateral positioning. Higher doses delay recovery. Addition of intrathecal opioids improves analgesia but increases opioid-related side effects. Ropivacaine does not improve recovery time.
In performing unilateral spinal anesthesia, use of a pencil-point gauge or gauge needle with the orifice directed at the operative side is suggested. Low-dose bupivacaine should be used, with hyperbaric bupivacaine operative side down in outpatient surgery and hypobaric bupivacaine operative side up in the elderly trauma patient.
A slow injection rate should be used to produce laminar flow that will assist in producing a unilateral blockade. There is little evidence that keeping a patient in the lateral position for more than 15 minutes is helpful. In , Kreis described the first spinal anesthetic for vaginal delivery. The following year, Hopkins performed the first successful spinal anesthetic for cesarean section in a woman with placenta previa.
Spinal anesthesia for labor and delivery has progressed greatly since that time. Although many arguments are made against general anesthesia in the pregnant woman due to increased risk of aspiration and difficult intubation, the anesthesiologist must be prepared to induce general anesthesia in the face of a failed or total spinal anesthetic. Obstetric regional anesthesia is a topic in itself, and as such is covered in Obstetric Regional Anesthesia.
Examples of how spinal anesthesia differs in the obstetric population are listed in Table As the population ages, more patients are presenting for surgery with pre-, intra-, or postoperative requirements for antiplatelet, anticoagulant, or thrombolytic therapy. Novel agents continue to be developed, giving rise to concerns in patients undergoing spinal anesthesia. These concerns led to the evolution of the ASRA evidence-based guidelines on regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy, now up to its third edition The reader is referred to Neuraxial Anesthesia and Peripheral Nerve Blocks in Patients on Anticoagulants for an in-depth discussion on the use of neuraxial anesthesia in the anticoagulated patient.
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Conventional palpation of surface anatomy has been shown to be unreliable. Neuraxial ultrasound aims to overcome the inaccuracies of surface anatomy with sonoanatomy. The first description of ultrasound-assisted lumbar puncture was in More recently, neuraxial ultrasound has been used as a preprocedure scan and for real-time needle placement. Much of the evidence regarding neuraxial ultrasound pertains to preprocedural scanning prior to epidural insertion, especially in the setting of obstetric anesthesia, and has been produced by a limited number of specialized centers.
This evidence shows that scanning decreases needle attempts, accurately predicts depth to the epidural space, and may improve the success rate of junior trainees. Spinal ultrasonography in the setting of single-shot spinal anesthesia is less well studied. Ultrasonography allows increased accuracy at identifying lumbar interspaces. This is important as palpation of the lumbar spine is likely to generate a higher interspace than expected, and the conus medullaris has been shown to be at times lower than the conventionally taught L1 level. These two facts not only pose a theoretical risk but also have resulted in persistent neurological injury.
An observational study in orthopedic patients demonstrated accurate ultrasonographic prediction of the depth to the dura prior to spinal insertion. Preprocedural ultrasonography has been used to achieve spinal anesthesia in clinically difficult situations such as obesity, kyphoscoliosis, and previous spinal surgery, including Harrington rods. Ultrasound scanning of the neuraxis is best learned in tailored workshops and simulations.
https://itlauto.com/wp-includes/software/3321-localiser-iphone.php Real-time ultrasound advancement of a spinal needle into the subarachnoid space is an expert skill, and practitioners should possess considerable probe and needle skills. AnnouncementValue ', ' question ': ' generational and relevant data. CoinFaqValue ', ' success ': ' Max 10 ll per poem.
Lacan's view towards ultrasound guided with Hegel's search.