Anaesthesia in scoliosis

Dr. S. Parthasarathy MD., DA., DNB, MD (Acu),

Dip. Diab.DCA, Dip. Software statistics PhD (physio)

Mahatma gandhi medical college and research institute, puducherry, India

What is it ??

• Scoliosis is a lateral curvature and rotation of the thoraco-lumbar vertebrae(commonly) with

a resulting rib cage deformity.

When it is problematic – cobb angle

• > 10 * abnormal • > 65* respiratory • > 100 * Rt HF

• > 40 * - surgery

• 1 to 2 degrees/year

The initial classification was given by Schulthess W

• Cervico thoracic• Thoracic• Thoracolumbar• Lumbar• Combined double primary

The list is very big

• Idiopathic common – 70 % cases

• Neuropathic Poliomyelitis Syringomyelia Friedreich’s ataxia

• Myopathic Myopathies

• Osteopathic vertebral anomalies – infection, TB, tumors

Incidence

• 10 -- 30 degrees – 3 % • more than 30 degrees -- 0.3 %

• Adolescents

• Female : male -- 3:1

Why to correct ??

• to correct the curve • fuse the spine, • improving posture• halting the progression of pulmonary dysfunction.

• The approach may be• posterior, anterior or combined • depending on the cause and severity of the

curvature

Correction – example

Preanaesthetic check up

What is special ?? Location ?? Etiology??

Airway assessment

• upper thoracic or cervical spine• Traction devices • Duchenne – tongue hypertrophy• discuss preoperatively the stability of the spine

with the surgeon• previous radiotherapy of the head and neck can

cause diffculty in direct laryngoscopy

Airway assessment

• Xrays and CT scan neck SOS

• A decision must be made, whether to intubate the patient awake or asleep.

Respiratory system

• Restrictive lung defect • VC decrease TLC decrease• RV may increase • RV /TLC increase ? Allow full exhalation• Secretions retained infections • Resp. Rate may increase

Scoliosis and loss of lung volume

The problems are

• abnormal thoracic cage geometry producing a marked decrease in chest wall compliance

• There is a mechanical defect

• Exceptions include congenital and infantile scoliosis where there is lung hypoplasia

Factors

• More than 70 degrees and • More than 7 vertebrae • Hypoxemia, progressing to PHT and Rt heart

failure – not necessarily hypercarbia Responses abnormal ventilatory patterns in response to hypoxemia and hypercarbia

Factors associated with post operative mechanical ventilation requirements

• pre-existing neuromuscular disease,• severe restrictive pulmonary dysfunction with

a vital capacity(VC) of <35% predicted• congenital heart defects,• Right ventricular failure,• obesity, • anterior thoracic spine surgery • blood loss of >30ml/kg

Preop correction

• Infection

• Bronchodilators

• Incentive spirometry

Cardiovascular system

• Less common

• But more dangerous

Cardiovascular system• ↑ PVR • PHT and RVF.• mitral valve prolapse• restrictive pericarditis with a possible secondary

pericardial effusion.• Limited cardiac filling decreases any potential

increases in cardiac output – surgery and anaes ?? • Duschenne – cardiomyopathy • Marfan s – AR and MR

ECG

• Tachycardia, • prolonged PR and QRS intervals,• ST abnormalities, • bundle branch block,• Q waves in the left precordial leads and tall R

waves in the right precordial leads. • Ejection fraction may be decreased on

echocardiogram.

Special in preop

• When does it start • The number of alveoli increases from

approximately 20 million at birth to 250 million at 4 years of age

• Where is it ?? • Cervical or thoracic • Number of vertebrae ??

Preop summary

• Airway • CVS • RS • Neuro

• History examination and document

Investigations

• Routine • Xrays• ECG • Echo • PFT • Blood grouping and typing• rehearse the wake-up test during the

preoperative visit .

Premedication • Antisialogogue – FOL , position

• Antibiotics and bronchodilators

• Preop prophylaxis with high dose corticosteroids should

be considered for patients with a preexisting neurologic

deficit.

• Sedatives and heavy narcotics ?

• DVT --- The use of compression stockings and/or

pneumatic boots is recommended

Anaesthetic techniques

General anaesthesia

Induction

• Intravenous is ideal

• no to Scoline• hyperkalemic response in presence of

myopathies or denervation.• It may also cause malignant hyperthermia in

certain syndromes

Intubation

• FOL awake

• NDPs

• Double lumen tube in anterior approach to

thoracic spines

Positions • Anterior approach to thoracic spine

• Posterior approach to lumbar spine

• Anterior approach to lumbar spine

• Position changes intraop • Peripheral nerves, eyes, genitals and bony points

should be padded and protected

Monitoring

• ECG ,SPO2,Temperature,ETCO2, urine output , blood loss , NMJ monitoring

• CVP monitoring according to necessity • Open chest and prone position – role of CVP ??• TEE better than CVP in prone position ?? • Catheter and output – monitor both !!

Arterial line

• The prolonged anaesthesia in unusual positions,

combined with significant blood loss, haemodynamic

effects of thoracic surgery and need for deliberate

hypotension mandate an invasive arterial line.

• Also serial blood gas measurements may be done

where required

spinal cord monitoring – stagnara • The ‘wake-up’ test provides a snapshot of

spinal cord motor function. • Surgery is halted, the volatile agent switched

off and emergence allowed. • The patient is asked to move their feet, ok -

then anesthesia can be recommenced• Beware of tubes, catheters • Any paraperesis – remove hardware, stabilize

hemodynamics

Defects in wake up test ?? • Sensory deficits - ?? • Preoperative paraperesis ??• Intra operative recall -- !! • Temporary test – problem can come later ?• Squeeze hand and then proceed !!• If he does , immediate give propofol / agent/

narcotics

SSEP monitoring

• SSEP monitoring involves stimulating a peripheral

nerve often the posterior tibial nerve, and then

detecting a response with epidural or scalp

electrodes.

• The evoked potentials are averaged more than 2–

3 min to eliminate background noise then

displayed as voltage against time.

SSEP

• A square wave stimulus • 50-250 micro sec duration,• strength 20-50 mA, • stimulation rate 1 6 Hz is commonly used.

• Hypothermia, hypotension may influence SSEP

SSEP • 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

SSEP

<50%

> 10 %

SSEP

0.5–1.0 MAC isoflurane, desflurane or sevoflurane. -- SSEP – OK – monitoring

Nitrous oxide potentiates the depressant effect of volatile anesthetics

IV anesthetics generally affect SSEPs less than inhaled Etomidate ,ketamine increases cortical SSEP amplitude Opioids – not much change • Neuromuscular blocking agents may reduce

background noise

SSEP

• Bolus IV anaesthetics ?? • Wait for 5- minutes to stabilize after vaporizer

dial change• Sevoflurane better if rapid changes are needed

• If in doubt , perform wake up test

Clonus test

• Clonus can normally be elicited in patients with intact spinal reflexes and lack of central inhibition

• Coming out of GA • It does not require patient cooperation• clonus can be elicited – may be an injury to cord • absence of clonus does not reliably predict injury

Motor evoked potentials (MEPs) • MEP monitoring involves stimulating the motor cortex by

electrical impulses transcranially and detecting the

resulting signal at spinal level with epidural electrodes or

from muscles as a compound muscle action potential

(CMAP)

• MEPs are markedly depressed by almost all anaesthetic

agents

• Minimum dose ketamine and record

• May not absolutely reliable

Motor cortex Stimulation – biceps brachii CMAP

Something becomes abnormal in cord monitoring ??

• Maintain BP • 100 % oxygen • Iv fluids • Blood to correct anemia

• Perform wake up test , adjust or remove instrumentation

Temperature

• Body temperature can decrease considerably

during the operation.

• Temperature monitoring, i.v. fluid warmers

and warm air blankets should be commenced

at induction and continued throughout

surgery.

Blood conservation:

• Major scoliosis surgery – 10 – 30 ml /kg go upto 50 ml

• Decrease surgical time

• Position proper, relax abdominal muscles

• Antifibrinolytic agents e.g. aprotinin inhibits plasmin

and kallikrein and preserves platelet function – use as

an infusion

• Autologous blood donation

• Hypotensive anaesthesia

Postop pain relief is painful

• Children • Large incisions • Cognitive impairment• Preop painful conditions

Post op pain relief

• Good postoperative analgesia is essential to allow

frequent physiotherapy and early mobilization, and

so reduce the risk of respiratory complications

• Systemic opioids , NSAIDs (after 24 hours) , PCA,

• paravertebral block, Epicath – can be kept by the

surgeon end operatively

Post op paralysis

• The incidence of motor deficit or paraplegia

after surgical correction of scoliosis in the

absence of spinal cord monitoring, has been

quoted as between 3.7 and 6.9%.

• This can be reduced by intra operative

monitoring to 0.5%

Some more perioperative complications

• Fat embolism • Air embolism • Coagulopathy • Visual loss • Necessity for postoperative ventilation • Hyponatremia

Summary

• Definition and incidence• Cobbs angle and severity• Etiology • Pre op : : airway, RS, CVS, Neuro , premed• Induction , airway, scoline ?? Monitors • Blood loss • Emergence and post op problems

•Thank you all