Upload
dhritiman-chakrabarti
View
6.977
Download
4
Tags:
Embed Size (px)
DESCRIPTION
Citation preview
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