Spinal Anaesthesia - Anatomy & Physiology

Anatomy and physiology of spinal anaesthesia.

1. Spinal Anaesthesia Applied anatomy and physiology CHAIRPERSON:DR.S.B GANGADHAR MODERATOR :DR. PRAKASH PRESENTOR: DR.DABER PAREED

2. INTRODUCTION Spine is one of the most important part of human body It gives structure and support Protect the spinal cord

3. There are 7 cervical vertebra 12 thoracic vertebra 5 lumbar vertebra There are five sacral and four coccyx vertebra which are fused segments

4. PARTS OF THE VERTEBRA All vertebra consists of BODY anteriorly Two pedicles that project posteriorly Two lamella that connect the pedicles Lamella gives rise to the transverse process that project laterally and spinous process that project posteriorly

5. ` The pedicles of these vertebra are notched and these notches of the each adjacent pair form an intervertebral foramen through which the spinal nerves exit the vertebral canal Superior and inferior articular processes arise at the junction of the lamella and the pedicles and form joints with the adjoining vertebrae

6. LIGAMENTS The vertebral bodies are stablized by ligaments that increase in size between the cervical and lumbar vertebra.. They are Supraspinous ligament – stong , thick, fibrous band from C7 to sacrum Supraspinous continue as ligamentum nuchae from C7 and attach to the occipital protruberence at the base of the skull In ter spinous ligament - Thin , fibrous structure Extend from the apex & upper surface of a lower spine toward the root and inferior surface of the next higher vertebrae Ligamentum flavum

7. LIGAMENTUM FLAVUM The ligamentum flavum consists of yellow elastic tissue They extend in perpendicular direction between the anterior inferior surface of the upper lamina downward to the anterior superior surface of the lower lamina Thus the ligament exists as right and left half in each intervertebral space with the halves fusing in the midline

8. Ligamentum flavum IN NORMAL ADULTS Thickness- 3-5mm Height- 15-16mm Width- 16-20 mm

9. CERVICAL VERTEBRAE The 1 st cervical vertebra (atlas) has no body It consists of an anterior and posterior arch joined by the thick lateral mass. The superior articular facets are strongly concave for articulation with the occipital condyles .

10. CERVICAL VERTEBRAE The second cervical vertebrae also has similar articulating surfaces The superior articulating facets are large oval and they face upwards and outwards The inferior facets resemble that of a typical cervical vertebrae They have a small transverse process and laminae are thick and the spine is large strong and bifid

11. The typical cervical vertebrae are C3–C6. Each of these has a small flattened body and a triangular, relatively large vertebral foramen. The pedicles project laterally as well as backwards, and their superior and inferior notches are about equal. The transverse process is short and is pierced by the foramen transversarium which transmits the vertebral vessels

12. CERVICAL VERTEBRAE The first vertebrae to be clearly palpable while running down the finger through the nuchal furrow of the spine is C7. There are 8 cervical nerves All the nerves emerge from C1 to C7 that emerge above their corresponding vertebrae C 8 lies above the first thoracic vertebrae and the remaining spinal nerves emerge below their corresponding vertebrae.

13. Thoracic vertebrae The typical thoracic body is the conventional heart shaped The upper 2 bodies show a transition from the cervical type, whereas the lower vertebrae show some similarity to the lumbar bodies. The bodies of T5-T8 are flattened on their left side; this asymmetry is produced by the pressure of the descending aorta & it is these 4 vertebra that become eroded by an aneurysm of this aortic segment.

14. The vertebral foramen is circular, diameter relatively small. The spines are long and T1 projects almost horizontally backwards and is readily felt below the vertebra prominens . It is necessary to give a markedly cephalad angulation to pass between the spines since the spines of mid thoracic vertebrae are angled caudally

15. Lumbar vertebrae Lumber vertebrae is large kidney shaped. Vertebral foramen is roughly triangular, larger than the thoracic and smaller than the cervical region. The pedicles are thick and transverse process are slender They increase in length from Ll to L3,then becomes shorter again so that the third transverse process is longest

16. SACRAL VERTEBRAE The sacrum conists of 5 fused vertebrae In childhood the sacral vertebrae are connected by cartilage. But progressively fuse into single structure after puberty. In the adult only a narrow residue of the sacral discs persists. The fusion of adjacent vertebrae eliminates the intervertebral foramina.

17. The sacral hiatus is triangular and obliquely placed at the lower end of the sacrum It is formed as a result from the failure of fusion of the laminae of the 5 th sacral segment The epidural space terminates here and hence forms a convinient portal of entry into this compartment

18. EMBRYOLOGY Embryologically each vertebra develops from 3 primary ossification centres two lateral for the arch and one central body Osific granules appear about the eight month of the embryonic life where the tranverse processes laterally project They travel in 2 directions: backward to form lamina and by meeting in the midline to form spinous process. Anteriorly to meet the body and to form pedicles

19. In the early fetal life spinal cord is as long as that of the vertebral column At 3 month of the fetal life the tip of the cord is present at the 2 nd coccygeal vertebra At 6 month of life it comes to the level of S5 At birth the spinal cord is at the lower border of L3 vertebrae After 1 year of age it comes at the level of L2 DEVELOPMENT

20. Curvature of the spine Cervical curve - Convex anterior Thoracic curve - Convex posterior Lumbar curve - Convex anterior Sacrococcygeal – Convex posterior

21. VERTEBRAL ANAMOLIES Kyphosis Scoliosis Spina bifida Spina bifida occulta Meningocoele Myelomeningocoele Myelocoele

22. Kyphosis Kyphosis is an exaggerated anterior flexion of the spine resulting in a rounded or hunchback appearance. Scoliosis and kyphosis are often seen together. More common in women,

23. scoliosis Scoliosis is a complex deformity of the spine resulting in lateral curvature and rotation of the vertebrae as well as deformity of the rib cage. There is usually secondary with involvement of respiratory, cardiovascular and neurological symptoms.

24. Spina bifida Neural arch defects result from the failure of fusion of 2 arch centers. Usually this is not associated with any neurological abnormality( spina bifida occulta ), although in such cases there may be an overlying dimple, lipoma or tuft of hair to warn the observant of a bony anomaly beneath. It may occur any where in the vertebral column but majority of defects involve L5 or upper sacral regions

25. Spina bifida occulta – failure of vertebral arch fusion only. Meninges and nervous tissue are normal. Meningocele – protrusion of meninges through a posterior vertebral defect.

26. Myelomeningocele – neural tissue protrudes into, & may be adherent to, the meningeal sac. Myelocele ( rachischisis ) – failure of fusion of neural tube results in the production of an open spinal plate. This condition is incompatible with survival.

27. MENINGES The spinal meninges consists of three protective membranes which are continuous with the cranial meninges.They are Dura mater Arachnoid mater Pia mater

28. DURA MATER The outermost and thickest meningeal layer is the dura mater It is the continuation of the inner ( meningeal ) layer of the cerebral dura which is made up of dense fibrous tissue It extends foramen magnum and ends at the level of S2 where it fuses with the filum terminale The dura is thickest in the posterior midline and thinner in the lumber area. It is largely acellular except for a layer that forms the border between the dura and the arachnoid matter

29. Arachnoid It is a delicate avascular membrane which lies next to the dura matter Thin membrane that encloses the subarachnoid space and CSF. It is continuous with the cerebral arachnoid , which loosely invests the brain, and dips into the longitudinal fissure between the cerebral hemispheres.

30. Piamater It is the innermost layer of the 3 membranes It is a vascular connective tissue sheath that closely invests the brain & spinal cord, and projects into their sulci and fissures. The pia matter extends upto the tip of the spinal cord where it becomes filum terminale which anchors the spinal cord to the sacrum

31. Subarachnoid space It is the space that lies between the arachnoid matter and pia matter It contains the CSF. This space communicates with the tissue spaces around the vessels in the pia matter that accompany them as they penetrate into the cord.These extensions of the subarachnoid space is termed as the Virchow Robin Space. Its contents are CSF, nerve roots, blood vessels that suply the spinal cord

32. Subdural space The arachnoid is in close contact with the dural sheath & is separated from it by a thin film of serous fluid. Accidental placement of a catheter during epidural anaesthesia and subsequent injection of local anesthetic results in patchy anesthesia which is often unilateral and extensive

33. Epidural space It is a space in the spinal canal that is occupied by dura and its contents It Extends from the foramen magnum to end by the fusion of its lining membranes at the sacrococcygeal membrane. It contains fat, vessels , nerve and lymphatics . Cranial epidural space is entirely empty. The distance from the skin to the lumbar epidural space in the midline is on average about 5 cm.

34. Cerebrospinal fluid  ( CSF ) The CSF is the clear watery fluid contained within the cerebral ventricles and the subarachnoid space. The total volume of CSF is about 100 to 160ml in adult humans and it is produced at a rate of 20 to 25ml/hr

35. CSF is an ultra filtrate formed by active process from the choroid plexus of the lateral ventricles The epidymal cells of pia covering the blood vessels play the secretary role At 600ml of CSF is formed per day

36. About 20-25 ml of CSF is present in the ventricles 90 ml of the CSF in reservoirs in the brain 25-30 ml of CSF occupy the sub arachnoid space It is produced at a rate of 0.4ml/min It is around 25ml/hr

37. About 4/5 th of the fluid is reabsorbed via the arachnoid villi . The remaining 1/5 th of the CSF is absorbed via similar spinal arachnoid villi or escapes along the nerve sheaths in to the lymphatics .

38. The specific gravity of CSF is 1.003-1.009 Its PH is 7.4 - 7.6 Na - 140-150 meq /L Chloride - 120-130 meq /L Bicarbonate - 25-30 meq /L Proteins – 15-45 mg/dl Glucose – 50-80 mg/dl

39. Spinal cord The adult spinal cord measures approximately 41 to 48 cm in length. Weight of spinal cord is between 24 to 36 gm. It is about 1 cm in diameter with cervical and lumbosacral expansion. The spinal cord extends caudally from the brain. Its upper end is continuous with the brain ( medulla oblongata ).

40. In the newborn the spinal cord terminates in the lower border of 3 rd lumber vertebrae. In the adult spinal cord terminates at the disc between 1 st and 2 nd lumber vertebrae. The spinal cord consists of 31 pairs of spinal nerves After L1 the nerve roots course for some distance before exiting the intervertebral formina forming cauda equina (horse tail)

41. Cauda equina syndrome It is a lower motor neuron lesion which occurs due to the damage to cauda equina It is caused due to trauma, tumours and lesions, spinal stenosis and inflammatory conditions Symptoms include weakness of the muscles of the lower extremities, urinary retention, fecal incontinence, sexual dysfunction Treatment of cauda equina syndrome is surgical decompression

42. Structure of spinal cord Spinal cord presents an anterior median fissure and a shallow posterior median sulcus from which a glial posterior median septum extends half-way into the substance of the cord.

43. Contd …. In transverse section, the cord comprises a central canal an H-shaped zone of grey matter (nerve cells) and an outer zone of white matter (nerve fibers). The H shaped grey matter is termed as the transverse commisure . Each limb consists of an short broad anterior column (anterior horn) containing large motor cells and thin pointed posterior column (posterior horn) capped by substantia gelatinosa the amount of white matter declines progressively from cervical down to the lumbar region. Grey matter is greatly increased in both cervical and lumbar enlargements, which correspond to the zones of origin of motor nerves to the upper and lower limbs.

44. The central canal continues downwards from the 4 th ventricle as a narrow tube lined with ciliated ependymal cells and contains csf It transverses the whole length of the cord, dilates somewhat within the connus medularis and continues for a short distance within the filum terminale

45. ` The tracts that originate from the white matter of the spinal cord can be classified as Descending tracts Ascending tracts Descending tracts are Lateral cerebrospinal or pyramidal tract Anterior cerebrospinal or uncrossed motor tract Ascending tracts are Posterior column Spinothalamic tracts Anterior and posterior spinocerebellar tracts

46. Blood supply of spinal cord

47. The spinal cord is supplied by the anterior and posterior spinal arteries which both descend down from the level of the foramen magnum The anterior spinal artery is formed at the level of the foramen magnum by the union of the branch from each vertebral artery. It is the largest of the two arteries and it supplies the upper two third of the spinal cord The posterior spinal arteries are paired arteries and they arise from the posterior inferior cerebellar arteries They supply the posterior one third of the cord

48. The anterior and posterior spinal arteries receive additional blood supply from the intercoastal arteries in the thorax and lumbar arteries in the abdomen One of these arteries is typically large which is the artery of Adamakiewicz or arteria radicularis magna arising from the aorta It is typically unilateral and always arises on the left side providing major blood supply to anterior and lower two third of the spinal cord

49. Anterior Spinal artery syndrome Ischemia or infarction occurs in the spinal cord in the distribution of the anterior spinal artery which supplies the anterior two third of the spinal cord It s usually associated with atherosclerosis of the aorta It causes quadriparesis and impaired pain and temperature sensation Complete motor paralysis below the level of lesion due to the interruption of the corticospinal tract and loss of pain and temperature below the level of the lesion

50. The venous drianage comprises a plexus of anterior and posterior spinal veins that drain along the nerve roots through the intervertebral foramina into the segmental veins azygos veins in the thorax and lumbar veins in the abdomen and lateral sacral veins in the pelvis

51. Spinal nerves There are 8 cervical nerves(C), 12 thoracic(T), 5 lumbar (L), 5 sacral (S), and 1 coccygeal . Each is formed by the fusion of an anterior & posterior spinal root. Each pair of spinal nerves passes through a pair of intervertebral foramina.

52. Layers of spinal nerve A series of connective tissue layer surrounds each spinal nerve. Epineurium - outermost layer, consists of a dense network of collagen fibers. Perineurium -extend inward from the epineurium , dividing the nerve into a series of compartments. Endoneurium -delicate connective tissue fibers.

53. The 31 pairs of spinal nerves each of them are composed of anterior motor root and a posterior sensory root These nerve roots are compose of multiple rootlets The portion of the spinal cord that give rise to all of the rootlets of a single spinal nerve is called as cord segment The skin area innervated by the given spinal nerve and its corresponding cord segment is called a dermatome

54. SPINAL ANAESTHESIA Spinal anaesthesia is the regional anaesthesia obtained by blocking the nerve roots in the subarachnoid space The spinal subarachnoid space extends from foramen magnum to s2 in adults and s3 in children

55. HISTORY Corning accidentally administered cocaine intrathecally in order to insert a catheter into the urethra in 1885 The first spinal anaesthesia in humans was given by Beir from Germany in 1898 using 0.5% cocaine. In 1908 Einhorm discovered procaine and synthetised the agent In 1905 Pitkin popularized the method of introducing the agents intrathecally

56. STRUCTURES PIERCED The spinal needle is passed through the following structure… Skin Subcutaneous tissue Supraspinous ligament Interspinous ligament Ligamentum flavum duramater

57. Physiological responses on CVS Hypotension Symphathetic denervation Loss of vasomotor tone Arterial and venous dilation Decreased periperal vascular resistance and peripheral pooling of blood Decreased venous return to heart and hence hypotension

58. Relaxation of the skeletal muscles of the leg causes pooling of the blood and decreased venous return to heart which results in hypotension There occurs blockage of the cardio accelerator fibres located in T1 to T4 and hence it causes bradycardia and hypotension

59. Respiratory system There is a little effect on pulmonary function in patient without pre-existing lung disease. Patient with severe chronic lung disease mainly rely upon intercostals and abdominal muscles for respiration This causes relaxation of these muscles and thus causes decrease in expiration and also associate with decreased clearance of the tracheo bronchial secretions

60. AFFECTIVE DYSPNEA With the blockade of the sensory input patient may complain of difficulty in breathing The mechanism is described as an inappropriate response to the given muscular effort The patient believes that he/she is not exerting efforts suficient to maintain breathing It is managed by asking the patient to take deep breaths , providing supplementary oxygen

61. GASTRO INTESTINAL SYSTEM The gastrointestinal effect due to sympathetic blockade. The abdominal organ derive there sympathetic innervation from T6-L2. Blockade of these fibers result in unopposed parasympathetic activity by vagus nerve. It increases the contractility of the gut with normal peristalsis and relaxed sphincters Nausea is common complication of spinal and epidural. Shivering is commonly observed during spinal anaesthesia due to decrease in core temperature which is the main cause of hypothermia during spinal