Surgical procedures InstrumentationFusion and Fixation
Anesthetic considerationsPre-Operative AssessmentAirway 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 (cont)RESPIRATORY SYSTEM:•Any existing ventilatory impairment•Any signs of pulmonary infection, asthma etc•spine deformities eg. Scoliosis kyphosis ankylosis etc.
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) Renaland Liver function assessment
Anaesthesia technique Premedication: Consideration of immense pain in patients with degenerative diseases – opiods premedication 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 forproposed surgery involving the upper T or cervical spine
Anaesthesia technique(Contd)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
Unique challenges for spinal surgery Positioning Intra-operative monitoring Spinal cord injury Post-operative visual loss (POVL)
Positioning Prone position : most spinal procedures Supine position with head traction in anterior approach to cervical spine Sitting or lateral decubitus position : occasionlly
PositioningProne position for thoracic and dorsal-spine procedure
PositioningProne 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 positionAirway: ET tube kinking or dislodgement Edema of upper airway in prolonged casesBlood 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 crestHead 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
Wake-up test Lightening anesthesia at an appropriate point during theprocedure and observing the patient’s ability to move tocommand. It evaluates the gross functional integrity of themotor 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 testAnesthetic techniques: Volatile-based anesthesia Midazolam-based anesthesia Propofol-based anesthesia Remifentanyl-based anesthesiaDisadvantages: 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
SSEP (somato sensory evoked potentials)1. The most common neurophysiological method for monitoring the intra-operative spinal functional integrity2. The stimulus applied to the peripheral N (tibial or ulnar)3. The recording electrodes placed: cervical region, scalp, or epidural space during surgery4. Baseline data obtained after skin incision5. Responses are recorded intermittently during surgery6. 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 motor8. Rarely - post operative neurologic deficit reported despite preservation of SSEP intraoperatively
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
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 byelectrical or magneticmeansNeurogenic responses:peripheral N or spinal cordMyogenic responses
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.
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
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.
Spinal cord injury Risk factors:• Length and type of surgical procedure• Spinal cord perfusion pressure• Underlying spinal pathology• Pressure on neural tissue during surgery
Spine surgery: Conditions of Increased Risk Spinal distraction Sub laminar wiring Induced hypotension Inadvertent cord compression Certain instrumentation (Luque rods) Ligation of segmental arteries
Risk Factors for Postoperative Airway Compromise Duration of surgery Amount of blood transfusion Obesity, airway pressure Operations 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 hemostasis Deliberate 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 abrasions Orbital edema Postoperative 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 surgeons Explore new techniques but remember to perfuse and monitor the patient