3patients requiring sedation or general anesthesia for neuroradiology, why? Anxiety and panic disorders.Claustrophobia.Developmental delay and learning difficulties.Cerebral palsy.Seizure disorders.Movement disorders.Severe pain.Acute trauma with unstable cardiovascular, respiratory, or neurologic function.Significant comorbidity.Pediatric age group.
4Special considerations for anesthesia in remote areas Senior anesthesiologist is prefered, not a trainee.Anesthesia equipment and the imaging equipment compete for the already narrow space of the radiology unit.The anesthesia workstation and the monitors are usually the oldest in the facility.Lack of communication between the anesthesiologist and the radiology staff.
5Inadequate preoperative patient preparation. Considerations for day case anesthesia (patient selection, anesthetic techniques, recovery and discharge).
6asa guidelines for anesthesia outside operating room Reliable Oxygen source (pipelines – cylinders).Adequate Suction.Scavenging system (if inhalational agents are used).Anesthesia machine with equivalent standards to that in OR and maintained to same standards.Adequate monitoring equipments to allow adherence to ASA standards for basic monitoring.
7Electrical outlets :Sufficient for anesthesia machine and monitors.Adequate illumination :Battery operated backups.Sufficient space :- For personnel and equipments.- Easy access to patient, anesthesia machine, and the monitor.Resuscitation equipment immediately available :- CPR equipments.- Emergency drugs.- Defibrillator.
8monitoring Universal standards : Standard I : requires a qualified anesthesia personnel to be present in the room throughout the conduct of anesthesia.Standard II : continous evaluation of the patient's oxygenation, ventilation, circulation, and temperature( ECG - pulse oximetry - capnography - NIBP ).
9anesthetic techniques Techniques vary from no anesthesia / minimal or deep sedation (i.e. MAC) / up to general anesthesia.It depends on :patient’s medical condition.desired level of anesthesia.procedure to be performed.duration of procedure.
10definition of ga and levels of sedation Minimal sedation( anxiolysis )Moderate sedation( previously called conscious sedation )Deep sedationGeneral anesthesiaResponsivenessNormal response to verbal stimulationPurposeful response to verbal or tactile stimulationsPurposeful response following repeated or painful stimulationUnarousable even with painful stimulationAirwayUnaffectedNo intervention requiredIntervention may be requiredIntervention requiredSpontaneous ventilationAdequateMay be inadequateFrequently inadequateCardiovascular functionUsually maintainedMay be impaired
11monitored anesthesia care (MAC) Administration of drugs with anxiolytic, hypnotic, analgesic, and amnestic properties either alone or in combination with local or regional anesthesia.Preoperative assessment :Detailed history & examination of the patient (similar to that done before GA).+Evaluation of ability of the patient to remain motionless & if necessary actively cooperate throughout the procedure.Fasting status.
12The following drugs are used in MAC ( SAFE drugs ): PropofolSedative / hypnotic.Short half life.Extra-hepatic clearance.Rapid & clear headed recovery.less incidence of post procedural sedation, drowsiness.Has anti emetic properties (Subhynotic dose of 10 mg is said to be effective ).
13Anxiolytic, amnestic, and hypnotic properties. BenzodiazepinesAnxiolytic, amnestic, and hypnotic properties.Midazolam :Commonly used for moderate to deep sedation.Short elimination half life (1 to 4hrs).Dose : up to 0.1 mg/kg IV.Diazepam :Longer elimination half life ( > 20 hrs).active metabolites (desmethyl diazepam, oxazepam).
14OpioidsProvide analgesia component in balanced anesthesia technique.Disadvantage: do not provide amnesia.Adverse effectsRespiratory depression.muscle rigidity .nausea / vomiting.Urinary retention (esp. old age).Sedation / anesthetic drug interaction :Opioids + benzodiazepines : synergism in hypnotic / analgesic / amnestic properties.
15Typical adult intravenous ranges DrugTypical adult IV dose rangeBenzodiazepinesMidazolam1-2 mg (0.02 to 0.1 mg/kg)DiazepammgOpioid analgesicsAlfentanil5-20 µg/kg bolus 2 min. prior to stimulusFentanylµg/kg bolus 2-4 min. prior to stimulusRemifentanilInfusion 0.1 µg/kg/min. 5 min prior to stimulusWean to 0.05 µg/kg/min as toleratedAdjust up or down in increments of µg/kg/min Dose accordingly when co-administered with midazolam or propofolAvoid bolusesHyponoticsPropofolµg/kg boluses25-75 µg/kg/min infusionDexmedetomidineLoading dose: µg/kg over min.Maintenance infusion: up to 1 µg/kg/h
16Recommended doses of drugs for sedation in pediatric patients : Chloral hydrate :50 to 100 mg/kg PO.used in healthy infants & children.Can produce mild to moderate hypoxia.Diazepam : 0.1 mg/kg.Midazolam :0.05mg/kg IV.0.5 mg/kg PO.Morphine :mg/kg IV.Ketamine :mg/kg IV , 2-3 mg/kg IM , 5 mg/kg PO.
17General anesthesia technique Endotracheal intubation & IPPV, or LMA with spontaneous breathing / IPPV.Induction of general anesthesia : Propofol / Thiopentone.Maintenance of anesthesia : volatile anesthetics / TIVA.At the end of procedure patient is transported to recovery area where further care is provided by trained anesthesia personnel.
18Radiology suite showing necessity for anesthesia equipment and anesthesiologist to be remote from the patient's head
20Computed TomographyCT is a medical imaging method in which an image of the inside of an object is generated from a large series of 2D images taken around a single axis of rotation.Used for diagnostic or therapeutic purposes.Hypodense (dark) areas denote infarction.Hyperdense (bright) areas denote calcification or hemorrhage.
21Problems faced by anesthesiologist : Inaccessibility to patients.Interference with monitoring.In an intubated patient, care should be taken that sides of scanning tunnel do not dislodge the circuit.Adverse effects of contrast media.Exposure to ionizing radiation.
22Anesthetic considerations Patient monitoring :Basic monitoring standards.Monitors should be easily viewed.Anesthetic considerationsElectiveEmergencyPreanesthetic visit on day of the procedure.Head injury patients with ongoing blood loss or raised ICP.Considered full stomach patients.Either scanned awake or intubated following rapid sequence induction.
23Contrast media are often used in CT scan. Types : Iodinated : hyperosmolar & toxic.Non iodinated : low osmolarity & fewer side effects.Adverse effects :Nephrotoxicity.idiosyncratic reactions.anaphylactic/ anaphylactoid reactions.
24Low-osmolarity contrast media (%) Contrast related adverse reactionsAdverse reactionsHigh-osmolaritycontrast media (%)Low-osmolarity contrast media (%)Nausea and vomiting6.01.0Urticaria0.5Hoarseness, sneezing, cough, dyspnea, facial edema2.6Hypotension0.10.01
25Treatment: usually supportive ttt BronchodilatorsCorticosteroidsEpinephrinePatients with past history of reaction to contrast mediaPrednisolone 50 mg IV, 12 h. & 2 h. prior to the procedure.Antihistaminics immediately before the procedure.
26Contrast induced nephropathy : Acquired ARF.Incidence is higher with hyperosmolar agents, especially in dehydrated patients.For prevention, maintain proper hydration before, during, and after the procedure.Usually self limiting & resolves within 2 weeks.Acetyl Cysteine / Ascorbic acid can be used.
27More with CT scan than any other radiological procedure. Acetyl cysteine 600 – 1200 mg orally twice daily for 2 days before procedure & 2 days after procedure.Ascorbic acid 3 gm PO, 2 h before procedure / and 2 gm twice daily, the day after procedure.Radiation exposure :More with CT scan than any other radiological procedure.Radiation toxicity :Somatic effects.Genetic injury.Dosimeters: to monitor exposure.
28Radiation exposure is limited by : Ionizing Radiation follows Inverse square law. Radiation exposure decreases proportional to square of distance from the source.Radiation exposure is limited by :lead aprons.thyroid shields.using movable leaded glass screens. Anesthesiologist can stand across the screen & monitor the patient.
29Magnetic resonance imaging Can differentiate areas of dissimilar anatomy.Noninvasive.No ionizing radiation used.Provides excellent soft tissue contrast.Can obtain image in any plane.Differentiates between white & grey matter, permits resolution of CSF flow.Disadvantages: Time consuming, patient movement can produce artifact, Noise > 90db.
30Categories of patient requiring anesthesia or sedation in MRI Patient CategoryRequirementPediatricSedation / anesthesiaDevelopmental delay or psychiatric illnessEducation, sedation or anesthesiaIntensive careIntubation & IPPVRaised intracranial pressureBeware of CO2 retention with sedation
31Concerns in anesthetic management for mri Patient accessibility & visibility.Absolute need to exclude ferromagnetic objects.Interference / malfunction of equipments caused by changing magnetic fields.Potential degradation of images caused by radiofrequency currents from monitoring equipments.Possibility of heat generation within monitoring wires as a result of electromagnetic conduction.
32Recommendations to prevent thermal injury Inspection of monitor wires before every use.Avoid loop formation of monitoring wires, keeping them straight.Avoid conductors touching the patient at more than one location.To avoid above listed problems , anesthesiologist must be involved in planning & construction of MRI suites.
33Mri compatible monitoring equipment ECG: liquid crystal screens, high impedance graphite electrodes & leads.Blood pressure: oscillometer with nonferrous guage.Respiratory gas: side stream sampling with long sampling line.Temperature: skin temperature sensing strips (burns reported with probes).Pulse oximeter: non-ferromagnetic model
34MRI compatible anesthetic equipment Laryngoscope: plastic scopes with paper or aluminium covered lithium cells.Stylet: copper model available.Endotracheal tube: spring within cuff valve may distort images; nonmagnetic version is available, avoid metal reinforced tubes & metal connectors.Laryngeal mask airway: spring within cuff valve may distort images; nonmagnetic version is available.Ventilators: compatible versions are available.
35Anesthetic machine: nonmagnetic machine, aluminium cylinders required ( e.g. Aestiva-5 MRI workstation from Datex Ohmeda).Infusion pumps: extensions are needed.Self inflating bags: valveless with no magnetic parts.Suction: wall mounted with a 10 m tubing.Defibrillators: resuscitation usually carried out outside magnetic field (We don’t perform CPR on MRI table).
36Implanted devices or objects representing a contraindication to MRI : Cardiac pacemaker.Some artificial cardiac valves.Metal eye splinter.Vascular clips.Interventional radiology device.Orthopedic device (prosthetic joint , wires , plates , screws).
37Anesthesia for interventional neuroradiological procedures Most commonly :Occlusive procedures:Embolization of cerebral & dural AVM.Coiling of cerebral aneurysms.Opening procedures:Thrombolysis of thromboembolic stroke.Ballon dilatation of vessels.Vascular access:Femoral / carotid / brachial artery.
38Anesthetic Goals Maintenance of patient’s immobility. Physiologic stability.Manipulation of regional & systemic blood flow.Evaluation of coagulation profile.Treating complications that can occur during the procedure.Rapid transition between sedation & awake responsive state.Providing brain protecting measures.
39Anesthetic management Pre-procedural anesthetic evaluation, careful neurologic examination (preexisting deficits & Glasgow Coma Score).Airway examination (better to secure airway early in patients with risk of airway compromise).Adequate intravenous access established.Standard anesthesia monitoring established.Invasive arterial blood pressure monitoringDeliberate hypotensionDuring embolization of AVM - coiling of aneurysm.Drugs used as esmolol - SNP - labetolol.
40Deliberate hypertension To increase collateral flow to ischemic areas.Drugs used are phenylephrine - vasopressin.Urinary catheter: use of large amounts of radiologic contrast media & osmotic diuretic agents.Sedation: combination of BZD & opioids.GA: accomplished by volatile agents or TIVA (considering desirability of fast emergence for neurologic evaluation).Padding of pressure points.Antiemetic can be given.
41Heparin is used in some procedures: 70 units/Kg, to achieve ACT 2-3 times the normal range. Protamine can be used to reverse heparin effect at the end of the procedure.Complications of Liquid embolic agents:e.g. Cyanoacrylate glue (rapidly polymerizing)The polymerization process results in heat liberation into the surrounding tissues during embolization.Systemic absorption leading to acute hemorrhage and pulmonary embolism.
42Complications of interventional neuroradiological procedures CNS :Hemorrhagicaneurysm perforation.intracranial vessel injury.Occlusivethromboembolic phenomenon.displacement of coil.vasospasm.OTHERS :Contrast reaction.Contrast nephropathy.Hemorrhage at puncture site - groin hematoma.
43management of complications Initial resuscitation.Communicate with radiologist.Call for help.Secure the airway & ventilate with 100% O2.Determine whether problem is hemorrhagic or occlusive :If hemorrhagic: immediate heparin reversal, deliberate hypotension.If occlusive: delibrate hypertension.Consider Mannitol , dexamethasone , anticonvulsants.
44Gamma knife radiosurgery Definition :Gamma knife radiosurgery is a type of radiation therapy used to treat tumors and other abnormalities in the brain (e.g. AVM , Trigeminal neualgia).In Gamma knife radiosurgery, specialized equipment focuses as many as 200 tiny beams of radiation on a tumor or other target. Although each beam has very little effect on the brain tissue it passes through, a strong dose of radiation is delivered to the site where all the beams meet.
45The accuracy of Gamma knife radiosurgery results in minimal damage to healthy tissues surrounding the target and, in some cases, a lower risk of side effects compared with other types of radiation therapy. Also, gamma-knife radiosurgery is often a safer option than traditional brain surgery.Gamma knife radiosurgery is usually a one session therapy completed in a single day.