CNIM - Practice Questions with correct Answers

What time constant would be the most effective for cutting out low frequency noise from your SSEP cortical responses? - Answer- Answer: 10 mS SSEP cortical responses are in the typical frequency range of 100-200 Hz. That being said, let's see what time constant would give us a good Low Frequency Filter. Remember LFF filters out everything below the cut off frequency and passes higher frequencies. Formula to know: Cut off Frequency = 1 / Time Constant (tc) 1/.01 s = 100 Hz 10 ms = .01 s This answer would filter out everything below 100 Hz so it would eliminate all the frequencies lower than 100 Hz and pass desired response and all higher frequencies. In order to achieve asynchronous stimulation you need to: - Answer- delay the second stimulator, so the stim goes "left, right, left, right" What is the active electrode for recording popliteal fossa sciatic nerve response after PTN stimulation at the ankle? - Answer- PF distal: appropriate montage for recording pop fossa response is Pf (distal) - Pf (proximal). The distal electrode is placed directly behind the knee in the leg crease, and the proximal electrode is placed 2-4 cm proximal. The response recorded is the N9 propagated afferent volley A negative electrical field is recorded by the negative input of the amplifier channel, while a reference electrode in the positive input records no activity of interest. What is true about the output? - Answer- An upward deflection represents a negative polarity waveform. By convention, activity of interest is applied to the negative input of the amplifier. At a distinct moment in time, the differential amplifier subtracts the negative input from the positive input, yielding the "difference" between the two inputs. If the output is a positive number, the waveform will point upward, and this upward deflection represents the fact that the information input was MORE NEGATIVE than the information in the positive input. Requirements for classifying SSEP data as "replicating" and therefore monitorable prior to surgical manipulation - Answer- Replicating amplitude within 15% Minimum of 2 trials (300-500 averages each) per limb Replicating morphology of the waveform Replicating latency within 1% Appropriate SSEP replication criteria - Answer- 1% latency, 15% amplitude Which contact lies on the precentral gyrus? - Answer- 4 precentral gyrus = motor cortex How can the polarity of waveform B be described? - Answer- Negative in the referential channel, cancelled in the bipolar channel First look at the montage to determine the obligate waveform of interest. B is the N34 waveform. We know this because it is recorded by a scalp electrode that is referenced to a non-cephalic electrode. Since the generator of the N34 is the brainstem, we know that a scalp-scalp (bipolar) channel will cancel the waveform. Most common complication of TcMEPs - Answer- tongue lacerations If you run a TcMEP with the anode at C4 and the cathode at C3 - Answer- the left AH response should be larger remember: unlike other modalities, the action potentials fire under the anode (+) for TcMEPs. The TcMEP pathway decussates in the medulla (around 85-90% of fibers cross over before descending down the corticospinal tract). Ipsilateral muscles (same side as anode) will likely record small CMAPs (or absent but not necessarily). Contralateral responses should be larger. During resection of an intracranial tumor that is located in midline and near the central sulcus, which of the following will be the most beneficial modality? - Answer- PTN SSEPs Phase reversal is of course beneficial when working near the central sulcus. However, most sources indicate that phase reversal SSEPs are only most effectively performed following upper limb stimulation, not PTN stimulation. Therefore, PTN SSEPs will be the more critical modality. Following TcMEP stimulation at C1-C2, you successfully elicit responses from the upper extremities but not from the lower extremities. What corrective action might be helpful in troubleshooting? - Answer- Move stimulating electrodes more anterior. Keep in mind that C1 and C2 are situated directly over the central sulcus. MacDonald recommends placing electrodes 1-2 cm anterior to central sulcus. Benefit of using corkscrew electrodes for TcMEP stimulation at the scalp - Answer- they have lower impedances and they are less likely to become dislodged 2016 ACNS guidelines describe corkscrews as optimal choice of stimulation electrode for MEPs. Apraxia definition - Answer- A motor disorder caused by damage to the brain in which the individual has difficulty performing tasks or movements when asked. The nature of the brain damage determines the severity, and the absence of sensory loss or paralysis helps to explain the level of difficulty. Muscles of the face and extremities may be affected. Axonotmesis - Answer- when the nerve sheath remains intact but the axons may be divided following traction or crush injury. The condition can result in complete loss of muscle (motor) function, sensations and autonomic functions transmitted by the affected nerve. The recovery usually takes several months to years. Friedrich's Ataxia - Answer- autosomal recessive genetic disease that causes degeneration of sensory neurons of the spinal cord, resulting in difficulty walking, loss of sensation in the extremities, and impaired speech. often concomitant with hypertrophic cardiomyopathy, scoliosis, and diabetes mellitus. Results in gradual inability to walk and eventual loss of sight and hearing. -loss of proprioception -symptoms usually begin between ages 5-15 but can appear as early as 18 months or as late as 30 years -first symptom usually difficulty in walking vestibular schwannoma is typically located - Answer- on the 8th cranial nerve between the internal auditory meatus and the brainstem - also called acoustic neuroma A patient presents with left side cranial nerve palsies and right side extremity palsies. Where is the lesion? - Answer- Brainstem Green dot on power cord - Answer- hospital grade/safe for large pieces of equipment Appropriate bandpass for SSEP filter settings - Answer- 30-800 Hz ACNS guidelines suggest using 30-1000 Hz as a bandpass in the OR. In practicality, 1000 HFF is too high. Typically we use 30-300 Hz for cortical channels and slightly higher for subcortical channels. Appropriate rep rate for BAEP monitoring - Answer- 12.41 Hz ACNS recommends 5-12 Hz Rep rate should not be cleanly divisible into 60 Hz Faster stim rates sometimes needed, but exceeding 30 Hz is not advised and may attenuate waveforms Intravenous drug used to maintain hypotension - Answer- Propofol Ketamine and etomidate will: - Answer- increase amplitude of evoked potentials Ketamine - Answer- mainly used for starting and maintaining anesthesia induces trance like state while providing pain relief, sedation, and memory loss. Soidium amytal and and phenobarbital - Answer- examples of barbiturates barbiturates are drugs that act as CNS depressant, andd therefore produce wide sprectrum of effects, from mild sedation to total anesthesia. They are also effects, from mild sedation to total anesthesia. Also effective as anxiolytics, hypnotics, and antionvulsants. Barbiturates display mild analgesic effects and may react with a patient's other medications or sedatives, but they are not used in the OR setting for analgesic properties. Etomidate - Answer- short-acting IV anesthetic agent used for induction of general anesthesia and sedation Malignant Hyperthermia - Answer- genetic disease that causes fast rise in body temperature and severe muscle contractions when they get general anesthesia. What might be monitored during a jugular bulb tumor surgery? - Answer- CN VII-XII After induction of general anesthesia, the patient is place in the dorsal position with the head held in a Mayfield clamp and turned 45 degrees to the opposite side. The opposite jugular vein must be free from compression. A nasogastric tube is inserted and intraoperative monitoring of facial and lower cranial nerves is performed. Cranial nerve IV can be monitored using electrodes inserted into the - Answer- superior oblique What type of electrode is recommended for monitoring facial nerve? - Answer- Hook wire - per guidelines, optimal for facial nerve SEMGs and tEMGs. Helps with specificity since the leads are much smaller and go into the muscle better. Pick up less far field activity. During a C5 decompression involving the axillary nerve, from which muscle should you record? - Answer- Deltoid SSEPs above C6 - Answer- Median Nerve SSEPs below C6 and above C8 - Answer- Ulnar Nerve ISOLA instrumentation - Answer- spinal hooks with rods Spinal cord detethering procedure may be used to treat - Answer- shortened filum terminale filum terminale is an extension of the pia mater that extends from the bottom of the spinal cord and attaches to the bottom of the coccyx. A shortened filum terminale is characteristic of a tethered spinal cord, in which the filum terminale is short and pulls the spinal cord downward in the spinal column. When would DSSEPs be most useful? - Answer- When individual nerve roots are at risk During CEAs, the spectral edge should be set to - Answer- 90-97% This will show where 90-97% of the power is located. What is an EPSP? - Answer- A temporary depolarization of a cell caused by the flow of positive ions into the cell What is an IPSP? - Answer- A temporary hyperpolarization of a cell caused by the flow of negative ions into the cell. This hyperpolarization returns the cell to its resting potential. What EEG presentation would be anticipated following induced hypothermia? - Answer- Burst suppression - inducing hypothermia will slow EEG activity, eventually leading to burst suppression followed by iso-electric EEG (electrocerebral silcence) If there are 100 total cycles displayed within a 10 second timebase of EEG, what is the most likely classification of the activity? - Answer- Alpha To calculate frequency of the activity: count number of cycles displayed in a given timebase and divide by the timebase. Hertz = cycles per second. 100/10 = 10 Hz, Alpha activity is 8-13 Hz If there are 65 total cycles displayed within a 10 second timebase of EEG, what is the most likely classification of the activity? - Answer- Theta (4-8Hz) Out of the following: Middle Cerebral Artery, Posterior Communicating Artery, and Anterior Cerebral Artery, which does not contribute to the circle of willis? - Answer- Middle Cerebral Artery - the MCA emerges from the internal carotid artery and immediately courses out laterally to supply the lateral cortex. The posterior communicator, anterior cerebral artery and anterior communicator are the major vessels that create the "circle" at the base of the brain. The Medial Geniculate Nucleus of the thalamus is a relay station for which type of sensory information? - Answer- auditory Where is the first synapse in the dorsal column medial lemniscus pathyway? - Answer- cervico-medullary junction Which of the following are pyramidal tracts? corticospinal rubrospinal reticulospinal corticobulbar - Answer- corticospinal - cortex to spinal cord corticobulbar - cortex to brainstem The artery of adamkiewicz is a radicular artery that - Answer- contributes to the anterior spinal artery and supplies most of the thoracic spinal cord To elicit responses from the left side of the body using transcortical stimulation, the cathode for TcMEP stimulation is best placed at: - Answer- C3 The anode is the primary depolarizing pole for TcMEP stimulation, so if the cathode is placed at C3, the assumption is that the anode is at C4. Appropriate time window for spontaneous EMG recording - Answer- 5 seconds (between 2-5 seconds) In our FDA approved TcMEP stimulation equipment, what is the common range of intensity for delivering stimulus? - Answer- 0-1000 V Common EP systems allow for intensities up to 1000V for TcMEP stimulation with a stim duration of 50 microseconds. When the stim duration is changed to 75 microseconds, the maximum intensity automatically adjusts to 800V. Most appropriate filter settings for MEP and EMG recordings - Answer- 30-3000 Hz Muscle responses have a much wider and less predictable frequency range than responses recorded from the brain. Therefore, filter settings should be wide, allowing very low and very high frequencies to enter the amplifier. True or false: Utiliztion of T-EMG with TOF = 3/4 should be adequate for screw testing. - Answer- False - for pedicle screw testing, 4/4 is necessary as threshold values could be skewed. How many pairs of spinal nerves are in the lumbar, sacral, and coccygeal spine respectively? - Answer- 5, 5, 1