Anesthesia consideration in spine surgery

Anesthesia consideration for spine surgery

1. Anesthesia consideration in Spine Surgery Dr. Tenzin Yoezer KGUMSB

2. General Indications for Spine Surgery Neurologic dysfunction (compression) Structural instability Pathologic lesions Deformity Pain

3. Surgical procedures

4. Fusion and Fixation Instrumentation

5. Anesthesia consideration Pre-Operative Assessment Airway Assessment: TMD, Mouth opening/ Mallampati Score Previous difficulty in intubation Restriction of neck movement due to disease, traction or braces Stability of the cervical spine It is essential to discuss preoperatively the stability of the spine with the surgeon

6. RESPIRATORY SYSTEM: Any existing ventilatory impairment Any signs of pulmonary infection, asthma etc spine deformities eg . Scoliosis kyphosis Ankylosis Preop VC <30-35% - prolonged ventilation after scoliosis surgery

7. Cardiovascular System Besides routine examination: B.P, heart sounds History: Hypertension Diabetes mellitus Congestive heart failure Coronary artery disease

8. Neurological assessment: The full neurological assessment should be documented. 1. In pts undergoing c-spine surgery, the anesthesiologist has a responsibility to avoid further neurological deterioration during maneuvers such as intubation , positioning and hypotensive anaesthesia . 2. Muscular dystrophies may involve the bulbar muscles, increasing the risk of postoperative aspiration. 3. The level of injury and the time elapsed since the insult are predictors of the physiological derangements of the cardiovascular and respiratory systems which occur perioperatively .

9. Neurological assessment: In < 3 weeks of the injury, spinal shock may still be present. Injuries at or >T5 – hypotension ( physiologic sympathectomy and loss of tone from the splanchnic vascular beds) 85% following recovery – autonomic hyperreflexia(severe paroxysmal HTN with bradycardia, dysarhythmia , cutaneous vasoconstriction below and vasoconstriction above the level of the injury) Stimulus- full bladder/rectum, noxious stimulus(surgery)

10. Neurological assessment: Lesions above cardiac accelerator(T1-T4) - bradycardia Hypotension due to spinal cord – poor response to IV fluids and vasopressors( risk of Pulmonary edema) Spinal cord injuries – Poilkilothermic (inability to regulate body temperature) Loss of sympathetic pathway carrying temp sensation Loss of vasoconstriction below the level of the injury.

11. Suggested preoperative investigations before major spinal surgery Minimum investigations Optional investigations Airway X-rays Cervical spine lateral view with flexion/extension views CT scan Pulmonary CXR Pulmonary function tests ABG (bronchodilator reversibility) Spirometry (FEV1, FVC) Pulmonary diffusion capacity CVS ECG Dobutamine -stress Echo Echocardiography Dypiridamole Thalliuscintigraphy Blood tests CBC,Blood sugar, electrolytes, RFT, LFT, B.T,C.T. PT/PTT Calcium (neoplastic disease)

12. Anaesthesia technique Premedication: Consideration of immense pain in patients with degenerative diseases – opiods Premedication sparingly used in patients with difficult airways or ventilatory impairment

13. Induction: Choice of induction technique: IV. or inhalation ? Pt’s medical condition Airway C-spine stability Choice of muscle relaxants: Succinylcholine or NDNMBs ? Pt’s medical condition Airway Risk of aspiration

14. Eg : Cervical spine surgery Awake or asleep? Awake intubation: Neuro assessment : an unstable c-spine Presence of a neck stabilization device: halo traction Risk of aspiration Direct or fiber-optic laryngoscopy? Direct laryngoscopy: Intubation can be achieved without any neck movement (manual in-line stabilization or a hard collar) Fiber-optic laryngoscopy: Fixed flexion deformities: involving upper T-spine/c-spine Pts wearing stabilization devices such as halo vests Anatomical reasons: micrognathia , limited mouth opening

15. Algorithm for decision making when intubating a pt for proposed surgery involving the upper T or cervical spine

16. Maintenance: Maintain a stable anesthetic depth positioning of patient, check airways Avoid sudden changes in anesthetic depth or BP Maintain a constant depth of NMB Common practice: 0.5 MAC Isoflurane / Halothane Continuous infusion of propofol Continuous remifentanyl or bolus opioids Controlled hypotensive anaesthesia

17. Reversal Patient made supine Thorough endotracheal and oral suction Oxygenated with 100% oxygen I.V.- Neostigmine Glycopyrolate Extubation : Fully awake with full motor power.

18. Emergence Fully awake Responding to commands Able to manage his/her own airway

19. Unique challenges for spinal surgery Positioning Intra-operative monitoring Spinal cord injury Post-operative visual loss (POVL)

20. Positioning Prone position : most spinal procedures Supine position with head traction in anterior approach to cervical spine Sitting or lateral decubitus position : occasionally

21. Prone position for thoracic and dorsal-spine procedure

22. Prone position Induction and intubation in supine position Adequate anesthetic depth and muscle relaxation Monitoring leads, IV lines, catheters: secure and sufficiently long to sustain position change ETT disconnected briefly; reconnected after turn Turn prone as a single unit requiring at least four people Anesthesiologist manages head and airway Neck should be in neutral position

23. Prone position Head may be turned to the side not exceeding the patients normal range of motion or face down on a cushioned holder Chest should rest on parallel rolls (foams )or special supports (frame) to facilitate ventilation Check oral endotracheal tube, other attachments Check breath sounds bilaterally

24. Head • Check for migrated monitoring wires, IV lines underneath • Eyes Padded, taped shut Lubricants: controversial • Ears Check for compression, folding of pinna

25. Arms • Padded arm-boards • Arms abducted, flexed at elbows <90⁰ arm abduction relieves tension on shoulder muscles ↓compression of axillary neurovascular bundle by humeral head Protective padding: Ulnar nerve at cubital tunnel, radial nerve in spiral groove of humerus Check for full pulses at wrist

26. Torso • Ventral longitudinal supports to relieve chest and abdominal wall compression Breasts Positioned medially and checked for compression Genitalia Pillow placed over caudal end of longitudinal supports Knees, Toes Flexed and padded, esp in prone kneeling position Pillow to support ankles off table surface

27. Anesthetic problems of the prone position Airway: ET tube kinking or dislodgement Edema of upper airway in prolonged cases Blood Vessels: Arterial or venous occlusion of the upper extremity Kinking of femoral vein with marked flexion of the hips, Increase abdominal pressure: IVC compression, increase epidural venous pressure bleeding Pressure necrosis of the nose, ear, forehead, breasts (female), and genitalias (males)

28. Nerves : Mechanisms • ↑ stretch, compression → ischemia • Occur despite adequate protection → other factors? Brachial plexus stretch or compression Ulnar N compression: pressure to the olecranon Peroneal N compression: pressure over the head of the fibula Lateral femoral cutaneous N trauma: pressure over the iliac crest

29. Injuries: Brachial plexus

30. Head and Neck: Gross hyperflexion or hyperextension of the neck External pressure over the eyes: retinal injury Lack of lubrication or coverage of eyes: corneal abrasion Headrest may cause pressure injury of supraorbital N. Excessive rotation of the neck: brachial plexus problems kinking of the vertebral artery L-spine excessive lordosis may lead to neurologic injury

31. Spine Surgery- Monitoring Routine Arterial line CVP/ PA catheter Neurophysiologic: Wake up test SSEP MEP EMG

32. Wake-up test Lightening anesthesia at an appropriate point during the procedure and observing the patient’s ability to move to command. It evaluates the gross functional integrity of the motor pathway. It was first described in 1973. Performed mostly – distraction and instrumentation Anesthesia requirements: Performed skilled anesthesiologist Reliable but quickly antagonized eg Remifentanyl Wakening should be smooth No pain during the test No recall

33. Wake-up test Technique : from case report Informed preop - they would be awake during surgery to check motor function Premed – daiazepam (0.1mg/kg) atropine (0.01mg/kg) Induction – Remifentanil – loading dose (1mg/kg over 30 secs) followed by continuous infusion(0.5 mg/kg/min) Vecuronium (0.1mg/kg)- intubation

34. Technique : from case report TOF test 30 minutes before Withdrawing volatile gas( Sevo ) 20 minutes before N20 turned off 5 mins later followed by 100% oxygen Remifentanyl infusion at analgesic rate(0.1 mg/kg/min) Called by the name Asked to move both the feet Once adequacy of spinal function achieved Re-anesthetized with Thiopentone and Diazepam for amnesic effect

35. Wake up test Anesthetic techniques: Volatile-based anesthesia Midazolam-based anesthesia Propofol -based anesthesia Remifentanyl -based anesthesia Disadvantages: Requires pt’s co-operation Poses risks to pt : falling from the table and extubation Requires practice Prolong the duration of surgery Provides information at the time of the wake-up only Does not assess sensory pathways

36. SSEP ( somato sensory evoked potentials) The most common neurophysiological method for monitoring the intra-operative spinal functional integrity. The stimulus applied to the peripheral N ( tibial or ulnar). The recording electrodes placed: cervical region, scalp, or epidural space during surgery. Baseline data obtained after skin incision. Responses are recorded intermittently during surgery. A reduction in the amplitude by 50% and an increase in the latency by 10% are considered significant. SSEP tests only dorsal column function not motor. Rarely - post operative neurologic deficit reported despite preservation of SSEP intraoperatively.

37. Indications for SSEP’s Spinal instrumentation Scoliosis correction Spinal cord operations

38. Anesthetics and SSEPs Satisfactory monitoring of early cortical SSEPs is possible with 0.5–1.0 MAC isoflurane, desflurane or sevoflurane. Nitrous oxide potentiates the depressant effect of volatile anesthetics Intravenous anesthetics generally affect SSEPs less than inhaled anesthetics Etomidate and ketamine increases cortical SSEP amplitude Clinically unimportant changes in SSEP latency and amplitude after the administration of opioids

39. Implication for SSEPs Monitoring Eliminating N2O from the background anesthetic has been shown to improve cortical amplitude sufficiently to make monitoring more reliable SSEP latency will take 5–8 min to stabilize after the step changes in volatile anesthetic concentration Adding etomidate, propofol or opioids is preferable to beginning N2O or increasing volatile anesthetic concentrations when anesthetic depth is inadequate If a volatile anesthetic is nevertheless needed rapidly, sevoflurane permits faster SSEP recovery after the acute need for volatile anesthetic has been resolved It is critical to avoid sudden changes in volatile anesthetic depth or bolus administration of intravenous anesthetics during surgical manipulations that could jeopardize the integrity of the neural pathways being monitored

40. MEPs ( Muscle evoke potentials) Motor cortex stimulated by electrical or magnetic means Myogenic responses Neurogenic responses: peripheral N or spinal cord

41. Anaesthetics and MEPS( Muscle evoke potentials) Inhalational anesthetics suppress myogenic MEPs in a dose-dependent manner N2O appears to be less suppressive than other inhaled agents. Moderate doses of up to 50% N20 have been used successfully to supplement other agents during myogenic MEP monitoring. Fentanyl, etomidate, and ketamine have little or no effect on myogenic MEP and are compatible with intra-operative recording. Benzodiazepines, barbiturates, and propofol also produce marked depression of myogenic MEP. However, successful recordings have been obtained during propofol anesthesia by controlling serum propofol concentrations and increasing stimuli rates.

42. Anesthetics and MEPs Myogenic MEPs are affected by the level of neuromuscular blockade By adjusting a continuous infusion of muscle relaxant to maintain one or two twitches in a train of four, reliable MEP responses have been recorded Motor stimulation can elicit movement, and this can interfere with surgery in the absence of neuromuscular blockade Physiologic factors such as temperature, systemic blood pressure, PaO2, and PaCO2 can alter SSEPs/MEPs and must be controlled during intra-operative recordings

43. Injuries: Eye Corneal abrasions Orbital edema Postoperative visual loss ( POVL)

44. Post-operative visual loss (POVL) POVL is a rare but devastating complication 1/1100 after prone spinal surgery Causes: Ischemic optic neuropathy (ION) (81%) Central retinal artery occlusion (13%) Unknown diagnosis (6%).

45. Post-operative visual loss (POVL) Risk factors for ischemic optic neuropathy after spinal surgery include male sex, Obesity Wilson frame use long anesthetic duration large blood loss Use of noncolloid fluids

46. Venous air embolus (VAE) is a catastrophic event Particularly at risk during laminectomy large amount of exposed bone and location of the surgical site above the level of the he art VAE presents as: unexplained hypotension increase in the end-tidal nitrogen concentration precipitous fall in the end-tidal carbon dioxide concentration Prompt diagnosis and treatment increase patient survival with VAE.

47. Venous air embolus (VAE) Management and prevention: flooding the surgical site with saline, controlling sites of air entry, repositioning the patient with the surgical site below the right atrium, aspiration of air from a multi-orifice central venous catheter, cessation of inhaled nitrous oxide, and resuscitation with oxygen, intravenous fluids, and inotropic agents. Massive embolism may necessitate supine repositioning and cardiopulmonary resuscitation.

48. References Clinical anesthesia, Barash Slides on ANAESTHESIA FOR SPINE SURGERY BASSEY, A. E. Slides on Anesthesia For Spinal Surgery Dr.Alaka Purohit