Spinal anesthesia Rahmeh Alsukkar

Anatomy

The vertebral column consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal segments. The vertebral column usually contains three curves. The cervical and lumbar curves are convex anteriorly, and the thoracic curve is convex posteriorly

Five ligaments hold the spinal column together Five ligaments hold the spinal column together. The supraspinous ligaments connect the apices of the spinous processes from the seventh cervical vertebra (C7) to the sacrum. The supraspinous ligament is known as the ligamentum nuchae in the area above C7. The interspinous ligaments connect the spinous processes together. The ligamentum flavum, or yellow ligament, connects the laminae above and below together. Finally, the posterior and anterior longitudinal ligaments bind the vertebral bodies together.

The three membranes that protect the spinal cord are the dura mater, arachnoid mater, and pia mater. The dura mater, or tough mother, is the outermost layer. The dural sac extends to the second sacral vertebra (S2). The arachnoid mater is the middle layer, and the subdural space lies between the dural mater and arachnoid mater. The arachnoid mater, or cobweb mother, also ends at S2, like the dural sac. The pia mater, or soft mother, clings to the surface of the spinal cord and ends in the filum terminale, which helps to hold the spinal cord to the sacrum. The space between the arachnoid and pia mater is known as the subarachnoid space, and spinal nerves run in this space, as does CSF

Spinal Cord Extends from foramen magnum to Adult : lower border of L1 in /upper border of L2 Infants/children : L3 It is about 45 cm long Duramater, Subarachnoid space & subdural space: S2 in adults( S3 in children) S. C gives 31 pairs of spinal nerve An extension of piamater , the FILUM TERMINALE penetrate the dura and attach the terminal end of spinal cord [conus medullaris]to the periosteum of the coccyx

When preparing for spinal anesthetic blockade, it is important to accurately identify landmarks on the patient

Dermatomes Dermatomal Level Surface Landmark C8 Little finger T1,T2 Inner aspect of the arm T4 Nipple line, root of scapula T7 Inferior border of scapula ,Tip of xiphoid T10 Umbilicus L2 to L3 Anterior thigh S1 Heel of foot Dermatomes

SURFACE ANATOMY Anatomic Landmarks to Identify Vertebral Levels Features C7 Vertebral prominence, the most prominent process in the neck T7 Inferior angle of the scapula L4 Line connecting iliac crests S2 Line connecting the posterior superior iliac spines Sacral hiatus Groove or depression just above or between the gluteal clefts above the coccyx

Positions

Lateral Decubitus Position A commonly used position for placing a spinal anesthetic is the lateral decubitus position. Ideal positioning consists of having the back of the patient parallel to the edge of the bed closest to the anesthesiologist, with the patient’s knees flexed to the abdomen and neck flexed It is beneficial to have an assistant to help hold and encourage the patient to stay in this position. 

Sitting Position   The sitting position is utilized for low lumbar or sacral anesthesia and in instances when the patient is obese and there is difficulty in finding the midline in the lateral position. When performing a saddle block, the patient should remain in the sitting position for at least 5 min after a hyperbaric spinal anesthetic is placed to allow the spinal to settle into that region.

Prone Position 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.

Technique of Lumbar Puncture 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 in order to find the body of L4 or the L4-5 interspace. Other interspaces can be identified, depending on where the needle is to be inserted. The skin should be cleaned with sterile cleaning solution, and the area should be draped in a sterile fashion. A small wheal of local anesthetic is injected into the skin at the site of insertion. More local anesthetic is then administered along the intended path of the spinal needle insertion to a depth of 1 to 2 in.

Spinal : approaches Structure Pierced Midline Approach 2. PARAMEDIAN APPROACH Midline Approach Paramedian approach Skin Subcutaneous fat Supraspinous ligament Interspinous ligament Ligamentum flavum Ligmentum flavum Dura mater Subdural space Arachnoid mater Subarachnoid space

Midline Approach The back should be draped in a sterile fashion. With advancement of needle Two “pops” are felt. The first is penetration of the L. flavum & second is the penetration of dura-arachnoid membrane. The stylet is then removed, and CSF should appear at the needle hub. For spinal needles of small gauge (26-29 gauge), this usually takes 5-10 sec

Paramedian Approach Calcified interspinous ligament or difficulty in flexing the spine The needle should be inserted 1 cm lateral and 1 cm inferior of the superior spinous process of desired level. Angle should be 10-25 toward midline The ligamentum flavum is usually the first resistance identified.

SPINAL NEEDLE Spinal needles fall into two main categories: (i) those that cut the dura : Quincke- Babcock needle, the traditional disposable spinal needle (iI) those with a conical tip(Pencil tip) : Whitacre and Sprotte needles If a continuous spinal technique is chosen, use of a Tuohy or Hustead needle can facilitate passage of the catheter QUINCKE WHITACRE SPROTEE

Blunt tip (pencil-point) needle decreased the incidence of PDPH Sprotte is a side-injection needle with a long opening. It has the advantage of more vigorous CSF flow compared with similar gauge needles.

epidural anesthesia

Anatomy

Epidural Space The epidural space is the area between the dura mater (a membrane) and the vertebral wall, containing fat and small blood vessels. The space is located just outside the dural sac which surrounds the nerve roots and is filled with cerebrospinal fluid.

Patient Positioning There are three positions used for the administration of epidural anesthesia: sitting , lateral decubitus , and prone.

Sitting Position Advantages of sitting position 1. Easier to identify midline, particularly in obese and scoliotic patients 2. Practitioners more experienced in sitting position 3. Shorter procedure time 4. Shorter distance from skin to epidural space 5. Greater cephalad spread of hypobaric solution

Lateral Decubitus Position

1. Sedation can be used more liberally Reduced patient movement 2 1. Sedation can be used more liberally Reduced patient movement 2. Increased patient comfort 3. Improved patient cooperation 4. Improved patient satisfaction 5. Reduced catheter displacementDecreased incidence of epidural vein cannulation 6. Attenuation of vagal reflexes 7. Hemodynamic changes better tolerated Bedside assistance may not be 8. required Intentional unilateral block for surgical procedures feasible

Technique of Epidural Anaesthesia Using local anaesthetic raise a subcutaneous wheal at the midpoint between two adjacent vertebrae. Inflitrate deeper in the midline and paraspinously to anaesthetise the posterior structures. Insert epidural needle to the skin at this point, and advance through the supraspinous ligament, with the needle pointing in a slightly cephalad direction. Then advance the needle into the interspinous ligament, which is encountered at a depth of 2-3 cm.until distinct sensation of increased resistance is felt as the needle passes .

* With 5-10ml of air in the syringe, attach it to the hub of the needle once it has entered the interspinous ligament. The plunger is gently pressed, and if there is resistance ("bounce"), the needle is very carefully advanced, with the dorsum of both hands resting against the back to provide stability. * After 2-3mm, the plunger is again gently pressed, and this procedure is repeated as the needle is carefully advanced through the tissues. * The distinctive decrease in resistance when the needle enters the ligamentum flavum is felt, and the process is continued in 2mm increments. * There is usually a distinctive "click" when the needle enters the epidural space, and provided great care is taken, and the needle only advanced in 2mm increments, the needle should stop before it reaches the dura. * At this point air can be injected into the epidural space very easily. The syringe is removed and the catheter threaded as below.

* Remove the syringe and thread the catheter gently via the needle into the epidural space. * The catheter has markings showing the distance from its tip, and should be advanced to 15-18cm at the hub of the needle, to ensure that a sufficient length of catheter has entered the epidural space. * Remove the needle carefully, ensuring that the catheter is not drawn back with it. * The markings on the needle will show the depth of the needle from the skin to the epidural space, and this distance will help determine the depth to which the catheter should be inserted at the skin. * For example, if the needle entered the epidural space at a depth of 5cm, the catheter should be withdrawn so that the 10cm mark is at the skin, thus leaving approximately 5cm of the catheter inside the epidural space, which is an appropriate length.

approaches There are four common approaches to the epidural space: midline, paramedian, Taylor (modified paramedian), and caudal

Midline and paramedian approaches With the midline technique, a Tuohy needle is introduced, directed slightly cephalad, through the skin in the midline between the two spinous processes at the level of the desired block. The needle passes through the supraspinous ligament, the interspinous ligament and the fused pair of ligamentum flavae before it enters the epidural space. A sudden ‘give’ may be felt as the needle tip exits the ligamentum flavum and enters the epidural space Lateral deviation or a “wobbly” needle indicates that the needle is not properly engaged in ligament, necessitating withdrawal and re-direction toward midline.

If a paramedian approach is chosen, the Tuohy needle is inserted through the skin at a point about 1.5 cm lateral to the mid point of the spinous process immediately below the level of the desired block. The needle is advanced perpendicular to the skin, through the underlying fat and muscle, until it strikes the vertebral lamina. It is then withdrawn slightly, redirected cephalad and medially, and walked off the lamina until it pierces the ligamentum flavum and enters the epidural space. The dura mater is held against the posterior wall of the vertebral canal by the pressure of the CSF inside the dura. Regardless of approach, on cannulation of the epidural space the dura mater is indented by the tip of the Tuohy needle.

Paramedian epidural technique  Epidural needle engaged in midline ligament

Caudal technique For regional blockade of the caudal epidural space the patient is usually positioned in a lateral or prone position. The caudal space is approached through the tough sacrococcygeal ligament that covers the sacral hiatus. It is identified as a midline indentation in the sacrum at a point forming the apex of an equilateral triangle made with the posterior superior iliac spines. For the caudal epidural technique a 23 or 21 G needle is placed over the sacrococcygeal membrane at an angle of about 60o to the coronal plane and perpendicular to the other planes, with the bevel facing anteriorly to allow it to pass along the anterior sacral wall without piercing it. There is usually a loss of resistance as the membrane is pierced. The needle should then be lowered to an angle of about 20o and advanced a short distance. The dura is not approximated to the point of needle entry into the epidural space (as it is at other spinal levels), but is always at least 34 mm away in adults. Therefore a needle up to 25 mm long can be used safely without risk of dural puncture. In children, the dural sac is closer and the needle should be advanced only a short distance

Taylor Approach The Taylor approach is a modified paramedian approach utilizing the large L5–S1 interspace. It is an excellent approach for hip surgery or for any lower extremity surgery in trauma patients who cannot tolerate the sitting position. This approach may provide the only available access to the epidural space patients with ossified ligaments.in 1. With the patient in the sitting or lateral position, a skin wheal is placed 1 cm medial and 1 cm caudad to the posterior superior iliac spine. 2. The epidural needle is inserted into this site in a medial and cephalad direction at a 45° to 55° angle. 3. As in the classic paramedian approach, the first resistance felt before entry to the epidural space is on entry into the ligamentum flavum. 4. If the needle contacts bone (usually the sacrum), the needle should be walked off the bone into the ligament and then into the epidural space in progressively more medial and cephalad directions.patients with ossified ligaments.