Anaesthesia for MRI, ECT, Cardioversion
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Transcript of Anaesthesia for MRI, ECT, Cardioversion
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ANAESTHESIA FOR
MRI, ECT AND CARDIOVERSION
DR. ELDOANISH
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Anesthesia outside the OT• Radiology – CT , MRI , Interventional
• Cardiology – Cardioversion , Catheterization
• Psychiatry – ECT
• Gastro – Colonoscopy , ERCP
• Urology - ESWL
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ASA guidelines for non OR anesthesia locations• Reliable oxygen source with back up
• Suction source
• Waste gas scavenging
• Adequate monitoring equipment to meet basic standard anesthesia monitoring
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• A self inflating hand resuscitating bag
• Adequate illumination of patient and machine
• Emergency cart with drugs and equipment
• A reliable means of communication for assistance
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Problems faced in outside locations
• Awkward layout for an anesthetist
• Unfamiliar equipment
• Older machine models
• Remoteness of the location and unavailability of assistance
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• Personnel less familiar with aspects of anesthesia than the OR staff
• Diagnostic equipment hamper access to the patient
• Pipped gases and suction might not be available
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Anesthesia for MRI
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Principle of MRI• Atoms with odd number of protons when subjected to
magnetic field will align themselves to the field
• The magnetic field for an MRI is measured in terms of Tesla
• 1 T = 10, 000 guass
• MRI machines have strengths varying from 0.15 – 2 T
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HAZARDS OF MRI• Long imaging time ( > 20 minutes)
• Any patient movement even physiological ( cardiac and vascular flow , peristalsis ) produces artifacts
• Loud noices (> 90 db ) . So mandate noise protection
• Intense magnetic field causes thermal injuries especially at sites of ECG electrodes , pulse oximeter probes
• Avoid loops in monitoring wires and contact with conductors
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• Dislodgement of ferrous substances ( vascular clips , sharpnel , shunts , pacemakers , icd, mechanical heart valves , wired ETT)
• Iron containing materials like scissors , pens , keys , gas cylinders can be attracted into it at extremely high velocities resulting in fatal injuries.
• In MRI Brain, the airway will not be assessable during the procedure. So airway should be well maintained
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MRI Suite• Zone 1 : Public zone , free access
• Zone 2 : interface b/n public area and mri suite . All movement by non mri personnel is supervised
• Zone 3 : Area within which introduction of ferro magnetism is prohibited
• Zone 4 : Scanning room
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Monitoring in MRI Suite• Central o2 / N2o / air
• Electrical power sources.
• ECG : ST and T abnormalities are seen because static magnetic field can induce voltage changes to the blood flow in the aorta.
• ECG can be ridden with multiple artifacts.
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• Thermal injuries through the elctrodes. MRI compatible ecg electrodes made of carbon graphite are available. Avoid coiling.
• NIBP : Usually no interference. connections b/n BP cuff and hoses should be plastic.
• Pulse oximetry – Thermal injuries
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• Capnography : MRI compatible capnogram machine should be used. If not available the machine should be placed as far away from the magnetic field as possible . So a long sampling line can result in delay in signal transduction.
• Quench monitoring : The magnet superconductors are kept cool within liquid N2. If this coolant evaporates the ambient o2 falls rapidly. A quench monitor measures the ambient o2 levels.
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Anesthetic Equipment• Machines to be made of stainless steel / brass /
aluminium
• Cylinders made of aluminum
• Plastic laryngoscopes
• Copper stylet
• ET Tube : Spring valve within the cuff distort the image . Avoid reinforced tubes.
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Anesthesia Technique 1 . Verbal assurance : Explain to the patient regarding
the procedure and assure the patient .
2 . Sedation : useful in children , anxious adults , those with language barrier.
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Drugs commonly used for sedation• Trichlofos sodium 50 -75 mg /kg ½ hour prior to
procedure
• Oral chloral hydrate 80 – 100 mg /kg
• Midazolam , orally ( 0.25 – 0.75 mg /kg) iv ( 0.03-0.08 mg /kg
• Ketamine , orally 5-10 mg /kg im 2-3 mg/kg.
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Chloral hydrate• Sedative and hypnotic drug with barbiturate-like
features. • Onset time if applied orally is 15–30min, and duration is
60–120min.• If given in therapeutic doses it has only a slight effect
on ventilation and blood pressure, but its therapeutic index is small.• Dosing is between 80 and 100mg/kg.• Side effects: nausea and vomiting, long recovery times
and postoperative agitation have to be considered.
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Pentobarbital• short-acting barbiturate.
• Oral or rectal dosing is 3–6mg/kg.
• Time until onset of sedation is 15–60min, and duration is 60–240min.
• Potential relevant cardiovascular and respiratory depression and the contraindications in patients with porphyria have to be considered.
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Ketamine• Commonly ignored as a sedative for MRI as it has an
analgesic component which is not necessary for MRI.
• Dosing is 1–1.5mg/kg when applied intravenously or 4–5mg/kg when injected intramuscularly.
• Onset time is 1–3min, and duration is 15–30min.
• Ketamine used alone may be useful for sedation in patients with respiratory risk factors.
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Midazolam• Used alone is not suitable for MRI sedation as its
duration is too short for a successful procedure of 20–30min.
• It has to be either re-injected or used in combination with fentanyl or pentobarbital or ketamine.
• The combination of sedatives is a risk factor for respiratory complications.
• Combined sedation drug use in children is not acceptable because the effects are hardly predictable and therefore risky.
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Propofol• Propofol seems to be a perfect drug for sedation
because it is effective, has a short recovery time and can easily be titrated to the required sedation level.• Dosing is normally 2–5mg/kg/h intravenous• Short induction and a recovery time of 8min are
convincing advantages of propofol use • When using propofol only for sedation purposes the low
therapeutic tolerance has to be stressed.• Consequently the physician must monitor the
respiratory rate and manage the paediatric
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Dexmedetomidine• Selective alpha-2 agonist which can be used by non
anaesthesiologists. • No relevant respiratory effects of this drug are known.• Haemodynamic side-effects such as low blood pressure and low
heart rate are common. • A loading dose of 1 mcg/kg over 10min followed by 0.5 mcg/kg/h
as an infusion for sedation maintenance is recommended. • Life-threatening complications have to be expected if
dexmedetomidine is used in combination with digoxin. • Because of these side-effects the drug is not suitable for patients
with cardiac compromise.
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• Several studies investigating dexmedetomidine for sedation have been published recently.
• Mason and colleagues [30] reported MRI procedures for 747 children and showed successful imaging in 97.6%. • Cardiovascular side-effects (bradycardia never
exceeding a 20% range from standard values) were seen in 16%. • Oxygen saturation was always above 95%.
• In children with obstructive sleep apnoea syndrome a comparison between dexmedetomidine and propofol for MRI sleep induction revealed effective sedation without the need for additional airway equipment in 88.5 versus 70% of scans [31].
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• Some other investigations found no difference in successful scanning between dexmedetomidine and propofol in 60 children between 1 and 7 years old but propofol showed advantages in induction, recovery and discharge time.
• No oxygen desaturation was seen in the dexmetedomidine-sedated children.
• Similar results were reported by Heard and collegues, who compared a midazolam–dexmedetomidine combination with propofol for sedation
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• Lubisch et al. published a retrospective study of children with autism and other neuro behavioural disorders. Three hundred and fifteen patients with a mean age of 3.9 years were sedated with dexmedetomidine, most commonly for MRI, while 90% of patients received concomitant midazolam. Seven patients required intervention for cardiac events and one for a respiratory event. There were two episodes of recovery-related agitation; 98.7% of sedations were successfully completed [34].• Dexmedetomidine could, if one takes account of the
contraindication of cardiovascular comorbidity, be a favourable sedative drug for MRI scanning.
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Contraindications for sedation• Potential for airway obstruction
• h/o apnoeic spells
• Resp diseases with a saturation of < 94 % on RA
• Raised ict
• Epilepsy
• Recent food intake
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General anesthesia• critically ill and uncoperative individuals
• Airway is secured either with LMA/ ETT in an induction room adjacent to scan room with all standard monitors.
• Post induction transfer patient to scan room and resume ventilation.
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• Maintain anesthesia with volatile agents / propofol
• At the end of procedure patient is returned back to induction room and awakened.
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Anaesthesia for ECT
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Procedure• Programmed electrical stimulation of cns to trigger seizure
activity
• After induction of anesthesia 2 electrodes are attached to patients scalp
• Seizure is monitored by observing the patient as well as EEG
• The minimum seizure duration needed for therapy to be effective is 25 secs.
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Physiolocal effects• CNS increased icp , cbf
• Initial exagerrated PNS activity bradycardia , asystole , premature ventricular contractions.
• This is followed by a symp surge tachycardia , hypertension . ST depressions and t inversions
• Secondary to sympathetic overactivity the sympathetic surge peaks 2 minutes following stimulation and is usually self limiting
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• Nor adrenaline and adrenaline levels increase following ect
• Glucose haemostasis is affected . NIDDM have a favorable response , but worsening of IDDM.
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Interactions• TCA : • Blocks reuptake of NA , 5 HT and DA
• increases central sympathetic tone .
• anticholinergic , antihistaminic & sedative effects .
• A combination of TCA + Atropine can increase post op delirium .
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• MAOI : Blocks metabolism of NA , 5 HT and DA
• The use of indirectly acting sympathomimetics can lead to hypertensive crisis.
• Reduce dose of direct acting sympathomimetics to treat hypotension .
• They are hepatic microsomal inhibitors , so can prolong duration of opiods .
• Meperidine to be avoided as it causes fatal excitatory response
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• Lithium : • prolongs NMB . • Prolongs action of BZD , barbiturates.
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Need for anesthesia
• To reduce psychological / physical trauma
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PAC• Co existing conditions : neurological , cardiac ,
osteoporosis
• Concomitant medications with special emphasis on anti psychotics
• Involve bystander too in history taking since patient might be a poor historian.
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Induction• IV induction is usually preferred .
• Standard pre induction monitors
• Glycopyrollate 5 mcg/kg to prevent bradycardia as well as for antisialagogue effect
• Adequate pre oxygenation
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• Methohexital : 0.75-1 mg/kg most commonly used.
• Propofol : 0.75 mg / kg can also be used , but decreases the seizure duration
• TPS and BZDS are avoided anticonvulsive action
• Etomidate can prolong seizure duration , so is also an alternative
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Neuromuscular blockade• Prevents physical trauma.
• Only partial block is needed as peripheral seizure visualization shouldn’t be hampered.
• A BP cuff can be inflated and kept in the limb intended for seizure visualization prior to administering NMB
• SCH : 0.5 mg/kg most commonly used
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• Once relaxation is adequate and mask ventilation proper a soft bite block is kept .
• If additional stimuli are needed repeat iv anesthetics / sevoflurane can be used.
• Intubation might be warranted in those with GERD , hiatal hernia , pregnancy
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• Post procedure ventilation is done until patient awakens
• Esmolol / Labetolol can be used to control episodes of tachycardia and hypertension . Labetolol preferred .
• Accurate documentation of drugs used and any outward events like arrhythmias , hypertension and post op agitation .
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Contra indications for ECT• Phaeochromocytoma
• Increased ICP
• Recent CVA
• Cardiovascular conduction defects
• High risk pregnancy
• Aortic / cerebral aneurysm
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Cardioversion
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• To convert supraventricular and ventricular arrhythmias to sinus rhythm by delivery of a DC shock
• In case of a long standing arrhythmia with no associated hemodynamic instability cardi0version is done on op basis.
• In case of a chronic AF , rule out presence of atrial thrombi prior to cardioversion.
• Standard monitoring and all emergency equipment needs to be available
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• The patient is pre oxygenated and given a small dose of iv anesthetic until he / she is un responsive.
• Immediately prior to counter shock , remove the mask and ensure no person is touching the person / the cart• • After cardioversion is completed the patient is ventilated
with 100% oxygen until consciousness is regained.
• If done on an emergency basis , adequate fasting might not be done . Intubation is a good option .
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