SPINAL ANAESTHESIA by C Quantock

Overview Anatomy Physiology Bony structure Spinal cord Blood supply Somatic blockade Visceral blockade

Overview Anaesthetic Factors influencing spinal Complications

Anatomy Bony Structure Spinous process C2 felt below occiput Vertebra prominens (C7) at cervicothorasic junction Line drawn between iliac crests usually pass between L4/5 spinous processes Sacrum palpable, and sacral hiatus irregular depression above between gluteal clefts (weight dependant)

Anatomy Bony Structure 33 vertebrae, 5 regions; Cervical, thorasic, lumbar, sacral, coccygeal. Double C curve. Structurally similar parts: vertebral body, intervertebral discs, anterior and posterior longitudinal ligaments (ventral stability). Pedicles and laminae create vertebral foramen – confluence of which creates spinal canal.

Anatomy Bony Structure Spinous process posteriorly provides ligamentous insertion (dorsal stability) Supraspinous ligament, interspinous ligament, ligamentum flavum (joins laminae and covers dura – epidural space between these two)

Anatomy Spinal Cord Lies within spinal canal covered by meningies. Epidural space (veins and fatty tissue). Dura mata – confluent with intracranial dura, extends as far as S2. Subdural space – confluent with cranial subdural space. Arachnoid membrane. Subarachnoid space – CSF. Pia attached to spinal cord.

Anatomy Spinal Cord Spinal cord shorter than spinal coloumn, increasing distance nerves travel to corresponding intervertebral foramen. Below L1 forms cauda equina.

Anatomy Blood Supply Two sources: anterior spinal artery, posterior spinal arteries. Posterior spinal arteries: Rich collateral supply, supplies posterior third of cord. Origin: cerebral arterial system. Contributions: subclavian, intercostal, lumbar, sacral arteries.

Anatomy Blood Supply Anterior spinal artery. Supplies ventral two thirds of cord. Contributions: branches of vertebral artery, radicular branches from cervical, thorasic and lumbar sacral regions. Posteriolateral arteries to upper thorasic region. Artery of Adamkiewicz (single segmental branch of aorta) supplies nearly all flow to lower thorasic and lumbar regions.

Physiology Physiological response determined by interrupting afferent and efferent nerve supply to somatic and visceral structures. Somatic structures related to sensory and motor innervation. Visceral structures related to autonomic innervation.

Physiology Somatic Blockade Prevention of pain and muscle relaxation objectives. After injection, spread of LA in CSF, becomes less concentrated as it speads cephalad. Cm is minimum concentration of LA reqiired to block a nerve. Cm varies depending on the nerve type needed to be blocked.

Physiology Somatic Blockade Nerve roots have a mixture of fiber types. This varing of LA concentration that results in zone of differential blockade. Symapthetic (cold). Sensory (pain and light touch). Motor. C fibers (deep pressure, rough movement) may be difficult to block.

Physiology Visceral Blockade CVS Sympathetic denervation. Fibers arise from T1-L1. T5-L1 control vascular smooth muscle. Blockade increases venous capacitance, decreasing venous return. T1-T4 cardiac accelerator fibers. Blockade results in unopposed vagal activity, resulting bradycardia.

Physiology Visceral Blockade Pulmonary Primary influence is via truncal motor blockade. Intercostal muscles impaired to level of blockade. Abdominal muscles impaired by most blocks. Phrenic nerve rarely blocked. Diaphragm maintains TV, MV, IRV. COPD patients with dependancy on abdominals for active expiration may be affected.

Physiology Visceral Blockade GIT Vagal mediated increased peristalsis. Gastric emptying unaffected. Gut distension less. Liver blood flow decreases proportionately to MAP.

Anaesthetic Indications: Lower extremity, hip peritoneum, lower abdomen, lumbar spine. Urological endoscopic surgery. Obstetrics

Anaesthetic Contraindications: Absolute: refusal, severe hypovolaemia, coagulopathy, R ICP, sepsis, fixed output states. Relative: Psycotic/demented state, antiplatlet drugs, duration of surgery prolonged.

Anaesthetic Administer in fully equipped environment. Needles used. Quinke. Whitacre. Sprotte. Blunt needles, and higher gauge result in less incidence of spinal headache.

Anaesthetic Sterile technique. Position – need to flex spine. Sitting. Lateral decubitus. prone. Approach. Midline. paramedian.

Factors Influencing Spinal Agent (few remain in use today) Procaine: rapid OOA, short DOA Tetracaine: intermediate OOA, long DOA Lignocaine: rapid OOA, short DOA Bupivacaine: slow OOA, long DOA Dose Vasoconstrictors: exogenously administered can increase DOA

Factors Influencing Spinal Specific gravity. CSF: 1.003-1.008 at 37°C. 0.5% Bupivacaine: 1.0058. 0.5% Bupivacaine in 8.25% dextrose: 1.027. Relationship between the two affects solution migration and eventual extent of block (hyperbaric, isobaric and hypobaric technique).

Factors Influencing Spinal Hyperbaric technique (agent SG>CSF SG). Spread dependant on posture from time of injecion to when agent no longer expected to be moving. Isobaric technique (agent SG=CSF SG). Sensory level 3-4 segments above site of injection. Hypobaric technique (agent SG<CSF SG). Prone headdown position.

Factors Influencing Spinal Posture. During injection of LA. Before binding of LA. Intra-abdominal pressure. Changes in contures of subdural space. Total volume of CSF decreased. Spinal curvature. Kyphoscoliosis and kyphosis associated with decrease CSF volume.

Factors Influencing Spinal Age. Spinal and epidural spaces become smaller and less complient, more cephalad spread. Obesity. Associated with increased intra-abdominal pressure and thus cephalad spread. Pregnancy. Increased intra-abdominal pressure and increased venous plexus volume.

Factors Influencing Spinal Spread of agent. Dose injected. Lipid solubility. Vascularity of tissue. Surface area exposed. Redistrubution. Involved in termination of spinal anaesthetic. Occurs via vascular reabsorption in epidural space.

Complications Pain on injection. Backache. Headache. No evidences that they exacerbate chronic back pain. Headache. Downward traction of CNS onto meningies. Start 6-12 hrs after LP, throbbing frontal. Needle size most important factor assoc with incidence. Treatment : conservative, epidural blood patch (99% effective).

Complications Urinary retention. Meningitis. Vascular injury. Chemical:transverse myelitis, anterior spinal cord syndrome. Infectious meningitis. Vascular injury. Epidural haematoma, suspect if spinal not resolving in reasonable period of time, sudden progression after resolution of symptoms.

Complications Nerve injury. Due to placement of needle. Incidence 1:10 000. Prevention :depends on detection of paraesthesia during needle insertion.

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