anesthetic considerations for spinal surgery

Anesthesia For Spinal Surgery

Dr.Alaka Purohit Associate professor

DEPARTMENT OF ANAESTHESIOLOGY

S.M.S. MEDICAL COLLEGE JAIPUR

• Spinal conditions requiring spinal surgery

• Surgical procedures

• Anesthetic considerations

• Unique challenges for spinal surgery

Anesthesia For Spinal Surgery

General Indications for Spine Surgery

Neurologic dysfunction (compression)Structural instabilityPathologic lesionsDeformityPain

Intervertebral disc lesions

Spondylolisthesis

Spinal conditions requiring spinal surgery

Spinal stenosis

Scoliosis Kyphosis

Spinal tumor

Spinal conditions requiring spinal surgery

Surgical procedures

Laminotomy Laminectomy Discectomy

Surgical procedures

Fusion and FixationInstrumentation

Pre-Operative Assessment

Airway Assessment: . TMD, . Mouth opening . 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.

Anesthetic considerations

Anesthetic considerations (cont)

RESPIRATORY SYSTEM:

• Any existing ventilatory impairment• Any signs of pulmonary infection, asthma etc • spine deformities eg. Scoliosis kyphosis ankylosis etc.

Anesthetic considerations (cont)

Cardiovascular System

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

Anaesthetic considerations (cont)

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.In < 3 weeks of the injury, spinal shock may still be present. After this time, autonomic dysreflexia may occur.

Anaesthetic considerations (contd)

Renal and Liver function assessment

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)

Anaesthesia technique

Premedication:Consideration of immense pain in patients

with degenerative diseases – opiodspremedication sparingly used in patients

with difficult airways or ventilatory impairment.

Anaesthesia technique(cont) Induction: Choice of induction technique: i.v. 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 Intra-operative monitoring

Anaesthesia technique (contd)

Intubation: (cervical spine surgery)

Awake or asleep Awake intubation: Risk of aspiration Neuro assessment : an unstable c-spine Presence of a neck stabilization device: halo traction

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

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

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

Emergence Fully awake,telling name Responding to commands Able to manage his/her own airway

Anaesthesia technique(Contd)

Unique challenges for spinal surgery

Positioning

Intra-operative monitoring

Spinal cord injury

Post-operative visual loss (POVL)

Positioning

Prone position : most spinal proceduresSupine position with head traction in

anterior approach to cervical spineSitting or lateral decubitus position :

occasionlly

Positioning

Prone position for thoracic and dorsal-spine procedure

Positioning

Prone position for C-spine procedure

Prone position Induction and intubation in supine position Turn prone as a single unit requiring at least four people Neck should be in neutral position Head may be turned to the side not exceeding the patients

normal range of motion or face down on a cushioned holder.

Arms should be at the sides in a comfortable position with the elbow flexed ( avoiding excessive abduction at the shoulder

Chest should rest on parallel rolls (foams )or special supports (frame) to facilitate ventilation

Check oral endotracheal tube, ckt, other attachments Check breath sounds bilaterally

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, abdominal pressure: epidural venous pressure bleeding (frames elevates)

Pressure necrosis of the nose, ear, forehead, breasts (female), and genitalias (males)

Monitor disconnects are hard to avoid;carefully manage.

Anesthetic problems of the prone position(contd)

Nerves:

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

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

Spine Surgery- Monitoring

Routine Arterial line CVP/ PA catheter Neurophysiologic:

. Wake up test

. SSEP

. MEP

. EMG

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.

Anesthesia requirements: As easy and as rapid to institute as possible Reliable but quickly antagonized Wakening should be smooth No pain during the test No recall

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

Wake-up test

SSEP (somato sensory evoked potentials)1. The most common neurophysiological method for monitoring the intra-operative spinal functional integrity

2. The stimulus applied to the peripheral N (tibial or ulnar)

3. The recording electrodes placed: cervical region, scalp, or epidural space during surgery

4. Baseline data obtained after skin incision

5. Responses are recorded intermittently during surgery

6. A reduction in the amplitude by 50% and an increase in the latency by 10% are considered significant.

7. SSEP tests only dorsal column function not motor

8. Rarely - post operative neurologic deficit reported despite preservation of SSEP intraoperatively

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

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

Anesthetics and SSEPs

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

MEPs ( Muscle evoke potentials)

Motor cortex stimulated by electrical or magnetic means

Myogenic responses

Neurogenic responses: peripheral N or spinal cord

Anaesthetics and MEPS( Muscle evoke potentials)

Inhalational anesthetics suppress myogenic MEPs in a dose-dependent manner

Paired pulses or a train of pulses cannot overcome the suppressive effects

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.

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

Anesthetics and MEPs

Spinal cord injury1. Neurological damage during surgery and anesthesia is not limited to the site of surgery.

2. Paraplegia and quadriplegia have been reported as a result of poor pt positioning.

3. There are reports of pts with spinal disease who have suffered neurological damage either at levels remote from the site of surgery or during surgery unconnected with their spinal disease.

4. Neurological damage is more likely at or near the site of surgery on the spine.

Risk factors:• Length and type of surgical procedure

• Spinal cord perfusion pressure

• Underlying spinal pathology

• Pressure on neural tissue during surgery

Spinal cord injury

Spine surgery: Conditions of Increased Risk

Spinal distractionSub laminar wiringInduced hypotensionInadvertent cord compressionCertain instrumentation (Luque rods)Ligation of segmental arteries

Risk Factors for Postoperative Airway Compromise

Duration of surgeryAmount of blood transfusionObesity, airway pressureOperations of greater than 4 cervical

levels or involving C2

Epstein NE. J Neurosurg 94:185 2001

Methods of Reducing Blood Loss and Limiting Homologous

Transfusions

Proper positioning to reduce intraabdominal pressure

Surgical hemostasisDeliberate hemodilution (?)Preoperative donation of autologous blood

Controlled Hypotensive Anaesthesia

• Definition: It is the elective lowering of arterial B.P.• Advantage : Minimization of surgical blood loss

Better wound visualization• Methods : Proper positioning

Positive pressure ventilation

Administration of hypotensive drugs

sodium nitropruside B - Blockers

Nitroglycerine Propofol

Trimethaphan Inhalational

Adenosine (Halothane/ isofluran)

Controlled Hypotensive Anaesthesia (contd)

Safe level of hypotension : - In healthy young individuals mean arterial

pressure as low as 50 to 60 mm of Hg is tolerated with out complication.

- Chronically hypertensive patients have altered autoregulation of CBF and reduction of MAP more than 25% of base line not tolerated.

- Patient with H/o transient ischemic attacks may not tolerate any decline in cerebral perfusion.

Controlled Hypotensive Anaesthesia (contd)

Relative contra indication :Pt having predisposing illnesses that lesson the margin of safety for adequate organ perfusion

Severe anaemia

Hypovolemia,

Atherosclerotic vascular disease

Renal and Hepatic insufficiency

Cerebrovascular disease

Uncontrolled glaucoma

Controlled Hypotensive Anaesthesia (contd)

Complications: ( more likely in pt with anaemia) Cerebral thrombosis

Hemiplegia

Acute tubular necrosis

Massive hepatic necrosis

Myocardial infarction

Cardiac arrest

Blindness from retinal artery thrombosis

or ischemic optic neuropathy

Controlled Hypotensive Anaesthesia (contd)

Monitoring:• Intra arterial blood pressure monitoring• E.C.G. with S.T. segment analysis• Central venous monitoring• Measurement of urinary output• Monitoring of neurologic function (rarely)

Injuries: Eye

Corneal abrasionsOrbital edemaPostoperative visual loss ( POVL)

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%).

Conclusions

Understand and appreciate the anatomy and physiology of the spinal cord

Communicate with your surgeonsExplore new techniques but remember to

perfuse and monitor the patient

Thank You