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Neurologic Monitoring Mani K.C Vindhya M.D Asst Prof of Anesthesiology Nova Southeastern University.

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Presentation on theme: "Neurologic Monitoring Mani K.C Vindhya M.D Asst Prof of Anesthesiology Nova Southeastern University."— Presentation transcript:

1 Neurologic Monitoring Mani K.C Vindhya M.D Asst Prof of Anesthesiology Nova Southeastern University

2 Introduction to EEG Interpretation Basic EEG Interpretation. You basically study an EEG for three things -- frequency, amplitude, and symmetry. Basic EEG Interpretation. You basically study an EEG for three things -- frequency, amplitude, and symmetry. 1. Frequency. The electrical waveform of the EEG is divided into sine waves of specific frequencies (cycles/sec or Hertz = Hz). The mnemonic I use to remember the frequencies is: 1. Frequency. The electrical waveform of the EEG is divided into sine waves of specific frequencies (cycles/sec or Hertz = Hz). The mnemonic I use to remember the frequencies is: DON'T TOUCH A BRAIN, or DON'T TOUCH A BAGEL – DON'T TOUCH A BRAIN, or DON'T TOUCH A BAGEL – D. T. A. B. D. T. A. B. Delta waves = 0 to 3 Hz -- Deep Anesthesia or Deep "Stage 4" Sleep Delta waves = 0 to 3 Hz -- Deep Anesthesia or Deep "Stage 4" Sleep Theta waves = 4 to 7 Hz -- general anesthesia and hyperventilation Theta waves = 4 to 7 Hz -- general anesthesia and hyperventilation Alpha waves = 8 to 13 Hz -- Awake but relaxed, eyes closed Alpha waves = 8 to 13 Hz -- Awake but relaxed, eyes closed Beta waves = 14 to 30 Hz -- awake and alert (eyes open) or excitement phase of anesthesia Beta waves = 14 to 30 Hz -- awake and alert (eyes open) or excitement phase of anesthesia

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4 Amplitude -- measured in microvolts (uV). Sometimes amplitude is expressed as power, which is the amplitude squared, (uV)2. Amplitude -- measured in microvolts (uV). Sometimes amplitude is expressed as power, which is the amplitude squared, (uV)2. Low amplitude = < 20 microvolts (uV) Low amplitude = < 20 microvolts (uV) Medium amplitude = 20 to 50 uV Medium amplitude = 20 to 50 uV High amplitude = > 50 uV High amplitude = > 50 uV Symmetry. Do the EEG waveforms look the same on each side? Symmetry. Do the EEG waveforms look the same on each side?

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6 Summary of Factors Affecting the EEG Summary of Factors Affecting the EEG Increased frequency Increased frequency Barbiturates, benzodiazepines, etomidate, propofol (low dose) Barbiturates, benzodiazepines, etomidate, propofol (low dose) Inhalational agents (< 1 MAC) Inhalational agents (< 1 MAC) Nitrous oxide 30-70% (acts on NMDA receptors) Nitrous oxide 30-70% (acts on NMDA receptors) Ketamine (acts on NMDA receptors) Ketamine (acts on NMDA receptors) Hypoxia (initially) Hypoxia (initially) Hypercarbia (mild) Hypercarbia (mild) Seizures Seizures Decreased frequency/increased amplitude Decreased frequency/increased amplitude Barbiturates, etomidate, propofol (moderate dose) Barbiturates, etomidate, propofol (moderate dose) Opioids Opioids Inhalation agents (> 1 MAC) Inhalation agents (> 1 MAC) Hypoxia (mild) Hypoxia (mild) Hypocarbia (moderate to extreme) Hypocarbia (moderate to extreme) Hypothermia Hypothermia

7 Decreased frequency, decreased amplitude Decreased frequency, decreased amplitude Barbiturates (high dose) Barbiturates (high dose) Hypoxia (mild) Hypoxia (mild) Hypercarbia (severe) Hypercarbia (severe) Hypothermia (< 35 oC) Hypothermia (< 35 oC) Electrical silence Electrical silence Barbiturates (coma dose) Barbiturates (coma dose) Etomidate, propofol (high dose) Etomidate, propofol (high dose) Isoflurane, desflurane, sevoflurane (2 MAC) Isoflurane, desflurane, sevoflurane (2 MAC) Hypoxia (severe) Hypoxia (severe) Hypothermia (< oC) Hypothermia (< oC) Brain death Brain death

8 Effects of anesthetics on the EEG: Effects of anesthetics on the EEG: 1. Can be expressed as graphs showing frequency on the x-axis and amplitude on the y-axis 1. Can be expressed as graphs showing frequency on the x-axis and amplitude on the y-axis 2. Awake individual -- alpha and beta activity, about 20 uV amplitude 2. Awake individual -- alpha and beta activity, about 20 uV amplitude

9 Fentanyl and other narcotics -- classically produce high amplitude, low frequency delta wave activity Fentanyl and other narcotics -- classically produce high amplitude, low frequency delta wave activity

10 Inhalational anesthetics: Low concentrations -- increase frequency & amplitude, Low concentrations -- increase frequency & amplitude, or "EEG activation" or "EEG activation" Higher concentrations -- high amplitude theta acticity Higher concentrations -- high amplitude theta acticity Isoflurane -- starts with "iso" because it produces an isoelectric Isoflurane -- starts with "iso" because it produces an isoelectric "flat" EEG at > 2 MAC (This is true for sevoflurane and desflurane, too) Enflurane -- starts with an "E" because it is Epileptogenic, especially with along with hyperventilation and hypocapnia. Seizures markedly increase frequency. Enflurane -- starts with an "E" because it is Epileptogenic, especially with along with hyperventilation and hypocapnia. Seizures markedly increase frequency. Sevoflurane – can also cause “seizure” activity (> 1.5 MAC) Sevoflurane – can also cause “seizure” activity (> 1.5 MAC)

11 Sodium pentothal and other barbiturates produce a whole spectrum of different effects, depending on the dose: Sodium pentothal and other barbiturates produce a whole spectrum of different effects, depending on the dose: EEG activation -- in low doses EEG activation -- in low doses Barbiturate spindles Barbiturate spindles Slow delta wave activity Slow delta wave activity Burst suppression -- defined as an isoelectric EEG with < 6 Burst suppression -- defined as an isoelectric EEG with < 6 bursts of EEG activity per minute = the desired endpoint for barbiturate coma (cerebral protection) bursts of EEG activity per minute = the desired endpoint for barbiturate coma (cerebral protection) Isoelectric or "flat" EEG Isoelectric or "flat" EEG

12 Other intravenous anesthetics: a. Many of the other IV anesthetics suppress the EEG, as does sodium pentothal: – –Propofol – –Etomidate – –Ketamine b. These IV anesthetics may show seizure-like (spike and wave) activity on the EEG.

13 To avoid peri-operative drug-induced seizures in epileptic patients: To avoid peri-operative drug-induced seizures in epileptic patients: Continue anti-convulsant therapy. Continue anti-convulsant therapy. Consult with patient’s neurologist to discuss management. Consult with patient’s neurologist to discuss management. Avoid etomidate. Avoid etomidate. Do not use sevoflurane routinely. Do not use sevoflurane routinely. Limit maximum concentration to < 1.5 MAC. Limit maximum concentration to < 1.5 MAC.

14 Effects of hypoxia on the EEG: Effects of hypoxia on the EEG:

15 Effects of hypocarbia on the EEG (similar to mild hypoxia): Effects of hypocarbia on the EEG (similar to mild hypoxia):

16 Effects of Anesthetics and Hypoxia on the EEG Effects of Anesthetics and Hypoxia on the EEG Hypoxia and many anesthetics: Hypoxia and many anesthetics: IV anesthetics (pentothal, propofol, etomidate) IV anesthetics (pentothal, propofol, etomidate) Inhaled anesthetics (isoflurane, sevoflurane, desflurane) Inhaled anesthetics (isoflurane, sevoflurane, desflurane) Share similar effects on EEG: Share similar effects on EEG: High frequency, high amplitude High frequency, high amplitude Low frequency, high amplitude Low frequency, high amplitude EEG burst suppression EEG burst suppression Isoelectric EEG Isoelectric EEG

17 Types of processed EEGs Types of processed EEGs Processed EEGs use power spectrum analysis to break the EEG down into its component frequencies. Processed EEGs use power spectrum analysis to break the EEG down into its component frequencies.

18 Bispectral index (BIS) is generated in part by power spectrum analysis. Bispectral index (BIS) is generated in part by power spectrum analysis. Compressed Spectral Array (CSA) expresses EEG as “hills and valleys.” Compressed Spectral Array (CSA) expresses EEG as “hills and valleys.” Frequency – on the x-axis Frequency – on the x-axis Amplitude – shown as height of the hill, or y-axis Amplitude – shown as height of the hill, or y-axis Time. The “hills and valleys” are stacked over time on a 3-D z- axis. Time. The “hills and valleys” are stacked over time on a 3-D z- axis.

19 Example of effect of carotid occlusion on CSA: Example of effect of carotid occlusion on CSA: Arrow marks time of left carotid artery occlusion

20 Density Spectral Array (DSA) Density Spectral Array (DSA) Similar to CSA Similar to CSA Expresses “hills and valleys” as “dark and light.” Expresses “hills and valleys” as “dark and light.”

21 Lifescan (Periodic Analysis) – expressed EEG activity as “telephone poles” Lifescan (Periodic Analysis) – expressed EEG activity as “telephone poles”

22 Introduction to Evoked Potentials – –Sensory evoked potentials (or responses) Brainstem auditory evoked responses Somatosensory evoked potentials Visual evoked responses

23 Brainstem auditory evoked potentials or responses (BAEP's or BAER’s) Brainstem auditory evoked potentials or responses (BAEP's or BAER’s) Specialized form of EEG monitoring Specialized form of EEG monitoring Background EEG activity is electronically subtracted out. Background EEG activity is electronically subtracted out. The EEG waveform evoked by auditory stimulus (clicking The EEG waveform evoked by auditory stimulus (clicking in ear) remains. in ear) remains.

24 Shape of a typical BAEP = seven peaks Shape of a typical BAEP = seven peaks Latency = time to first peak (usually 2 msec) Latency = time to first peak (usually 2 msec) Amplitude = height of the peaks Amplitude = height of the peaks

25 The seven peaks of the BAEP are believed to correspond to passage of a stimulus through "generators" in the auditory nerve, brainstem and cortex. The seven peaks of the BAEP are believed to correspond to passage of a stimulus through "generators" in the auditory nerve, brainstem and cortex.

26 What do we look for during surgery? What do we look for during surgery? Mainly two things: Mainly two things: Increase in latency (> 10%) Increase in latency (> 10%) Decrease in amplitude (<50%) Decrease in amplitude (<50%) These two changes could be indicative of impending injury or ischemia in the BAEP pathway

27 BAER's are barely affected by anesthetics: BAER's are barely affected by anesthetics: 1. No anesthetic drug produces a change in BAER’s that could be mistaken for a surgically induced change. 1. No anesthetic drug produces a change in BAER’s that could be mistaken for a surgically induced change. 2. Etomidate decreases amplitude and increases latency (but this is not clinically significant). 2. Etomidate decreases amplitude and increases latency (but this is not clinically significant).

28 Somatosensory evoked potentials Somatosensory evoked potentials Upper extremity: Median nerve SSEP has “M” shape Upper extremity: Median nerve SSEP has “M” shape

29 Lower extremity: Posterior tibial nerve SSEP has “W” shape Lower extremity: Posterior tibial nerve SSEP has “W” shape

30 What do we look for during surgery? What do we look for during surgery? Decrease in SSEP amplitude Decrease in SSEP amplitude Increase in latency (time to first peak or dip) Increase in latency (time to first peak or dip) Six I’s that inhibit SSEP’s: Six I’s that inhibit SSEP’s: Inhaled anesthetics, including isoflurane Inhaled anesthetics, including isoflurane N2O doesn’t decrease amplitude alone, but has a synergistic effect with volatile agents. N2O doesn’t decrease amplitude alone, but has a synergistic effect with volatile agents. IV agents, but to a lesser extent than inhaled anesthetics IV agents, but to a lesser extent than inhaled anesthetics Etomidate = the exception; it increases SSEP amplitude Etomidate = the exception; it increases SSEP amplitude Ischemia/hypoxia Ischemia/hypoxia Injury, to the spinal cord or anywhere in SSEP pathway Injury, to the spinal cord or anywhere in SSEP pathway “Ice cold” temperatures (< 34.5 oC) “Ice cold” temperatures (< 34.5 oC) Incompetence (observer foul-ups) Incompetence (observer foul-ups)

31 Summary of effects of anesthetics on SSEP’s: Summary of effects of anesthetics on SSEP’s: Inhaled anesthetics – dose-related decrease in amplitude Inhaled anesthetics – dose-related decrease in amplitude and increase in latency and increase in latency Use less than 1 MAC volatile agent Use less than 1 MAC volatile agent Nitrous oxide – profound depressant effect on SSEPs, especially when used in combination with volatile agent Nitrous oxide – profound depressant effect on SSEPs, especially when used in combination with volatile agent

32 Intravenous agents Intravenous agents a. Propofol and thiopental a. Propofol and thiopental Small decrease in amplitude and increase in latency Small decrease in amplitude and increase in latency Propofol is commonly used for TIVA Propofol is commonly used for TIVA (total IV anesthetic technique) (total IV anesthetic technique) Opioids – negligible effects on SSEPs Opioids – negligible effects on SSEPs Ketamine and etomidate – increase SSEP amplitude Ketamine and etomidate – increase SSEP amplitude (Etomidate is exceptional. It increases SSEP amplitude but decreases BAEP amplitude.) (Etomidate is exceptional. It increases SSEP amplitude but decreases BAEP amplitude.) Anesthesia for SSEP’s (progression from routine to desperate) Anesthesia for SSEP’s (progression from routine to desperate) Volatile agent / N2O / narcotic Volatile agent / N2O / narcotic Volatile agent / narcotic Volatile agent / narcotic Volatile agent / propofol / narcotic Volatile agent / propofol / narcotic TIVA: total IV anesthetic with propofol and narcotic TIVA: total IV anesthetic with propofol and narcotic Etomidate / narcotic (really desperate) Etomidate / narcotic (really desperate) Increases amplitude Increases amplitude Adrenocortical suppression with etomidate Adrenocortical suppression with etomidate

33 Other Evoked Potentials Other Evoked Potentials Visual evoked potentials Visual evoked potentials M shape M shape Long latency Long latency Sensitive to all anesthetics except opiates Sensitive to all anesthetics except opiates

34 Motor evoked potentials Evoked by transcranial electrical or magnetic stimulation Evoked by transcranial electrical or magnetic stimulation Effects of anesthetics are profound. Effects of anesthetics are profound. Same anesthetic progression as with SSEP’s Same anesthetic progression as with SSEP’s

35 Why bother to test motor function? Why bother to test motor function? SSEP’s mainly test for dorsal (posterior) spinal cord function. SSEP’s mainly test for dorsal (posterior) spinal cord function. Motor EP’s mainly test for ventral (anterior) spinal cord function. Motor EP’s mainly test for ventral (anterior) spinal cord function.

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37 Anterior Spinal Artery Syndrome Anterior Spinal Artery Syndrome

38 Transcranial Doppler (TCD) Transcranial Doppler (TCD) A. Carotid endarterectomy -- might be used during CEA cross-clamping to detect emboli or decreased cerebral blood flow velocity A. Carotid endarterectomy -- might be used during CEA cross-clamping to detect emboli or decreased cerebral blood flow velocity

39 Vasospasm Vasospasm TCD can be used to detect vasospasm after aneurysmal SAH. TCD can be used to detect vasospasm after aneurysmal SAH. Vasospasm causes an increase in cerebral blood flow velocity. Vasospasm causes an increase in cerebral blood flow velocity.

40 Thank you


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