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CNS MONITORING

CNS MONITORING. www.anaesthesia.co.in anaesthesia.co.in@gmail.com. MAINLY CONSISTS OF:. Evoked potentials Electroencephalography and monitoring of anesthetic depth Monitoring intracranial pressure Monitoring the neuromuscular junction Specialized neurophysiological monitoring.

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CNS MONITORING

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  1. CNS MONITORING www.anaesthesia.co.inanaesthesia.co.in@gmail.com

  2. MAINLY CONSISTS OF: • Evoked potentials • Electroencephalography and monitoring of anesthetic depth • Monitoring intracranial pressure • Monitoring the neuromuscular junction • Specialized neurophysiological monitoring

  3. EVOKED POTENTIALS Useful in • Evaluation of certain neurological disorders • Monitoring functional integrity of sensory and motor pathways during many surgical procedures • Preventing potential injury to the vital neural structures

  4. Extremely small amplitude (microvolts) electrical potentials generated by nervous tissue in response to stimulation

  5. Source of evoked potentials • Application of a stimulus to the nervous system is followed by the development of a neural signal which is transmitted along a specific pathway • Represented as waveforms, voltage over time and are described in terms of amplitude, latency and morphology

  6. NEAR FIELD POTENTIALS • Neuronal potentials created by depolarization are immediately below the recording electrode • Large amplitude and exhibit marked changes in size and waveform with even small alterations in position of the recording electrode • Initial positive wave

  7. FAR FIELD EVOKED POTENTIALS • A depolarizing volley within the central nervous system white matter tracts travels toward the cortical mantle • Produced by the deeper nuclei and tracts and are widely distributed • Amplitude and morphology remain relatively constant despite changes in electrode position

  8. METHOD OF STIMULATION AND RECORDING • STIMULATION • RECORDING METHODS • 10-20 electrode placement system • Electrode, impedance,artifacts,deal with electrostatic and magnetic interference

  9. SOMATOSENSORY EVOKED POTENTIAL • Electrical responses of brain or spinal cord to electrical stimulation of peripheral nerves • Stimulus is a brief electric pulse delivered to the distal portion of the nerve • Adjust the intensity of the stimulus so there is a small muscle twitch • Activates low threshold myelinated nerve fibers-dorsal root- spinal column-gracile and cuneate nuclei-brainstem-thalamus-cortex • Diagnosis of spinal cord diseases • Intraoperative monitoring of some surgical procedures

  10. MEDIAN NERVE SSEP • Useful in assessing the conduction in upper cervical cord and brain • When used in conjunction with lower extremity SSEPs helps to recognize lesions between cauda equina and cervical spinal cord • Stimulating electrode is at wrist • Channel 1-contralateral central cortex • Channel 2-c2/c7 • Channel 3-erbs point 1-EP2

  11. TIBIAL NERVE SSEP • Obtained by stimulation of either the tibial or peroneal nerve • Stimulating electrode-behind medial malleolus • Channel 1-frontal midline region • Channel 2-L1-T12 • Channel 3- popliteal fossa

  12. CONDITIONS PRODUCING CHANGES IN SSEP • variable and complex effects on SSEPs and central conduction time • Surgical anesthesia-prolonged latency and diminshed amplitude • Premedication with atropine,morphine and diazepam can attenuate SSEP • Thiopentone coma-dec ampl,inc lat • Halogenated anesthetic-dose related method • Nitrous oxide 50%or more with fenanyl-dec ampl,inc latency • Hypotension and hypothermia increase laency and dec amplitude • Adjunct drugs,antibiotics and other cvs drugs • Spinal surgery-narcotic/narcotic inhalational

  13. SSEP AND SPINAL CORD FUNCTION • Spinal surgery • Thoracic aortic surgery • Spinal arteriography and therapeutic transvascualar embolization • Extracranial carotid reconstruction, carotid endarterectomy( difficulty in detecting only motor tract ischemia ), cerebrovascualr surgery with induced hypotension and clippping and intraoperative localization for sensorimotor cortex • Intracranial vascular surgery(median nerve for MCA • Tibial nerve for ACA • Basilar artery surgery

  14. False negative SSEP-2-22% • False postive SSEP-2% • Changes in SSEPs indicate CNS ischemia • Small areas of injury,motor area injury or lenticulostriate area injury may not be associated with changes

  15. AUDITORY EVOKED POTENTIALS • Assessment of peripheral auditory function and the integrity of central auditor pathways • Clicks generated by applying a brief square wave by tone pips (brief tone bursts)to activate restricted portion of the membrane of the cochlea • Electrodes are placed athe vertex and on the ear lobes • Age, sex, body temperature and hearing can alter

  16. Anesthetic agents have dose related effects • Thio and propofol may have an effect • Hypotension and hypothermia may produce changes • Monitoring in surgery of CPA tumours, posterior fossa, cavernous sinus and brainstem

  17. VISUAL EVOKED POTENTIALS • Useful outside the OT in diagnosis of disease optic nerve and pathways • Difficult in OT • Used in surgery involving optic chiasma, pituitary gland • anesthetic agents change them greatly

  18. MOTOR EVOKED POTENTIALS • Detect damage to motor cortex or • Motor pathway from motor cortex to muscle • We use NMBA, recording from epidural space has been recommended • Not popular because of complexity and time involved in setting up monitors, interpretation of evoked responses.

  19. SPECIALIZED NEUROPHYSIOLOGIC MONITORING • TRANSCRANIAL DOPPLER USG • JUGULAR BULB OXIMETRY • NEAR INFRARED SPECTROSCOPY • BRAIN PARENCHYMAL OXYGEN TENSION

  20. IDEAL MONITOR FOR CEREBRAL ISCHEMA WOULD BE NONINVASIVE, SIMPLE , AT BEDSIDE OR OT, PROVIDE CONTINUOUS DETECTION OF GLOBAL , REGIONAL AND GLOBAL ISCHEMIA

  21. JUGULAR BULB OXIMETRY • GLOBAL MEASURE , FAILS TO DETECT REGIONAL ISCHEMIA • NIRS AND POP ARE LOVALIED • TCD USG IS CAPABLE OF MONITORING A LARGE PROPORTION OF CBP BUT IS NOT IN ALL SITUATIONS

  22. TRANSCRANIAL DOPPLER USG • CAROTID ENDARTERECTOMY -DECISION TO SHUNT DETECTION OF EMBOLI POSTOPERATIVE HYPOPERFUSION -POSTOPERATIVE OCCLUSION • CARDIAC SURGERY • SUBARACHNOID HEMORRHAGE • HEAD INJURY AUTOREGULATION VASOSPASM BRAIN DEATH

  23. JUGULAR BULB OXIMETRY • CHOICE OF SIDE • EQUIPMENT AND TECHNIQUE • COMPLICATIONS AND CONTRINDICATIONS

  24. CLINICAL APPLICATIONS • TRAUMATIC BRAIN INJURYINTERPRETATION OF jbo SATURATION • NEUROSURGICAL ANESTHESIA • CPB • LIMITATIONS

  25. NEAR INFRARED SPECTROSCOPY • EQUIPMENT AND TECHNIQUE • CLINICAL APPLICATIONS • LIMITATIONS

  26. BRAIN PARENCHYMAL OXYGEN TENSION • EQUIPMENT AND TECHNIQUE • CLINICAL APPLICATIONS • LIMITATIONS

  27. EEG • MONITORING ADEQUATE BLOOD PRESSURE AND OXYGEN SATURATION WILL NOT PREVENT CEREBRAL ISCHEMIA • OCCURRENCE OF SEIZURES • DEGREE OF BARBITURATE BURST SUPPRESSION’ • LEVEL OF SEDATION PRODUCED BY DRUGS

  28. EEG is not the product of propagated action potentials • Myelinization of axons tends to limit spread of ionic current to a few hundred micrometers, making it impossible to record axon potentials on the scalp • EEG is derived from summation of nearly synchronous depolarization of cell bodies and dendrites, • scalp tends to act as an averager of positive and negative voltages

  29. methods • Place 21 electrodes on the scalp at locations standardized by the international 10-20 system • Place in pairs for bipolar recording or individually using a common reference • Electrode-lowest impedance and highest quality signal • Metallic cups • Needle electrode

  30. PROBLEMS • Extremely susceptible to noise • High electrode impedance-improper site preparation, poor adhesion, mechanical disruption desiccation, oxidation or broken contacts, proper electrode application • Accurate placement

  31. EEG WAVEFORMS

  32. COMPRESSED SPECTRAL ARRAYS • SIMPLIFIED DISPLAY OF AMPLITUDES AND FREQUENCIES • Conversion of EEG signal from amplitude as a function of time to amplitude as a function of frequency’ time domain to frequency domain • Makes it easier to see effects • better assesses • individual spectra are computed every few seconds and then stacked or compressed into an array CSA for easy comparison

  33. DENSITY MODULATED SPECTRAL ARRAYS

  34. INDICATIONS FOR EEG • Assures cerebral well being • Shunt placement during carotid endarterectomy • Cardiac surgery • For regional sensitivity-16-32 channels • Acute monitoring of periopertive changes-7-8 channels • Hemispheric differnce-2 channels • Ischemia and cerebral protection by barbiturate therapy • Detection of seizure • Progress and prognosis in coma

  35. Sensitivity is high • Specificity can be affected by anesthetic technique and analysis methods • not to be used as isolated guide

  36. BIS • INDICATIONS DIFFERENTIATES THE NEED FOR DEEPER HYPNOSIS, MORE ANALGESIA OR DIRECT AUTONOMIC CONTROL DIRECT MEASUREMENT OF THE FUNCTIONAL EFFECTS OF THE DRUGS ON THE BRAIN ALLOWS INDIVIDUALIZED PHARMACOLOGICAL TT. MONITORING OF SEDATION IN ICU DOSE OF BARBITURATES FOR CEREBRAL PROTECTION THERAPY

  37. INDIVIDUALIZED DOSING` • CLINICALLY STANDARD EFFECTIVE DOSE • TARGET CONTROLLED INFUSION SYSTEMS • DEFINITIONS OF MAC • DIFFERENT GOALS FOR DIFFERENT PTS • DIFF ANESTHETIC APPROACHES BY DIFFERENT CLINICIANS • DIFF GOALS AT DIFFERENT TIMES IN THE INDIVIDUAL CSE

  38. Components of anesthetic depth • Many monometric parameters from EEG have been investigated • Median frequency • Spectral edge frequency • Various power bands • Magic no. to describe anesthetic effects on the EEG has eluded definition

  39. STATISTICALLY DERIVED MULTIPARAMETRIC INDICES ARE • BIS • MIDLATENCY AUDITORY EVOKED RESPONSE INDEX • AUTOREGRESSIVE MODELS OF Mac-narcograph

  40. initially used prediction of movement • Now improved artifact detection and rejection • Recognizes and eliminated ECG contamination • EMG contamination is problematic(temporalis and frontalis muscles picks up signals in the range of beta rhythm

  41. BIS was statistically derived to correlate with response to command and not specifically to recall, the variance between drugs is wider for recall but nonetheless falls to very low below 80

  42. WHAT IT IS AND WHT IT ISNOT • NOT A MAC=METER • DOES NOT PREDICT LIKELIHOOD OF MOVEMENT IN RESPONSE TO AND INCISON • NOT A PREDICTOR OF ANY FUTURE BEHAVIOR BUT AN INDICATOR OF THE LEVEL OF SEDATION OVER THE LAST MINUTE

  43. CEREBRAL ISCHEMIA CAN OCCUR WITHOUT A NOTABLE DECREASE IN BIS

  44. ANESTHETIC MGT WITH BIS • USE DRUG TILL AVERAGE BIS IS 50 • USE ANALGESIC TILL MINIMUM VARIATION OVER A FEW MTS IS LESS THAN 10 • IF UNEXPLAINED TACHYCARDIA OR HYPERTENSION , TRIAL OF ANALGESIC BEFORE TITRATING AUTONOMIC RESPONSE

  45. IF HPOTENSION OCCURS • DECREASE DOSE OF ANALGESIC • ASSESS THE VOLUME STATUS AND TT WITH SYMPATHETIC AGONISTS • DURING CLOSURE, DECREASE SEDATIVE DOSE TO INCREASE TO 65 • IF ABOVE 70, TOO SOON , ADD SHORT ACTING SEDATIVE( INHALATION, IDOCAINE, PROPOFOL

  46. MAKE PACO2 RISE TO 40, PATIENT STARTS BREATHING • IF RR IS ABOVE NORMAL SUPPLEMENT ANALGESIA DURING EMERGENCE • CONTINUED RISE IN BIS WILL ASSURE A RAPID EMERGENCE WITHOUT THE NEED TO WITHHOLD NARCOTICS • SEDATION AND ANALGESIA CONTROLLED, REMAINING HEMODYNAMIC RESPONSES CAN BE CONTROLLED USING DRUGS

  47. LIMITATIONS • SPURIOUS READINGS WITH CONTAMINATION (HIGH IMPEDENCE OR POOR CONTACT • EMG ACTIVITY FROM FRONTALIS MUSCLE DIRECTLY BENEATH BIS ELECTRODES( WHICH OCCCURS IN ALL FREQUENCIES TILL BETA RHYTHM • GIVE SMALL DOSE OF NMBA TO SEE IF VALUES RETURN • IF DOESN’T DECREASE, SMALL DOSE OF SEDATIVE SHOULD BE TRIED(PT NEEDED MORE SEDATION)

  48. PARADOXICAL AROUSAL RESPONSE • Sudden drop to low values seen at light anesthetic level with minimal analgesia provoked by strong noxious stimulus with very sudden onset and resolution • Treat it with narcotics • Large swings in BIS (>10) over 1 to 2 mts suggest the need for increased analgesia

  49. ENTROPY • Shannon in 1948 • Johnson and Shore in the year 1984. • The wave forms of entropy value of zero or near zero are predictable and • those with very high entropy value (for eg.100) are totally unpredictable.

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