Neuromonitoring is an umbrella term used to describe the various invasive and noninvasive

Transcription

1 Feature Neuromonitoring Indications and Utility in the Intensive Care Unit CATHERINE HARRIS, PhD, MBA, CRNP Information on the use of neuromonitoring in intensive care units is scattered but significant. Nurses who do not care for neurologically impaired patients on a daily basis may not have a strong understanding of the utility of various neuromonitoring techniques, why they are used, or how they are interpreted. Two main types of neuromonitoring that are frequently seen but poorly understood are reviewed here: transcranial Doppler sono - graphy and electrophysiology. Information on these techniques tends to be either superficial with limited applicability to the critical care setting or very technical. This review provides information about neuromonitoring to help guide critical care nurses providing care to neurologically impaired patients. (Critical Care Nurse. 014;34[3]:30-40) Neuromonitoring is an umbrella term used to describe the various invasive and noninvasive techniques that are available for monitoring functioning of the central nervous system. Neuromonitoring techniques are essential tools used in evaluating patients with neurological injury in critical care settings. Neuromonitoring is typically used when a clinical neurological examination is either difficult or not practical to perform, such as during an operative procedure or when the patient s mental status has deteriorated. Depending on the technique used, neuromonitoring allows the health care staff to evaluate motor and sensory function, brain activity, blood flow, and intracranial pressures. Nurses must be able to use various neuromonitoring techniques and interpret their results to provide the best care for their patients. However, useful and user-friendly information on the indications and utility of neuromonitoring is scarce. In this article, I review pertinent types of noninvasive neuromonitoring techniques encountered in intensive care units, transcranial Doppler monitoring and electrophysiology, for their indications, use, and applicability to patient care. Invasive monitoring such as intracranial monitoring is not covered here. CNE Continuing Nursing Education This article has been designated for CNE credit. A closed-book, multiple-choice examination follows this article, which tests your knowledge of the following objectives: 1. Describe neuromonitoring with transcranial Doppler monitoring and electrophysiology for the neurologically impaired patients. Identify normal and abnormal findings with transcranial Doppler monitoring and electrophysiology 3. Discuss the indications, use, and applicability of transcranial Doppler monitoring and electroencephalography in the neurocritical patient 014 American Association of Critical-Care Nurses doi: 30 CriticalCareNurse Vol 34, No. 3, JUNE 014

2 Transcranial Doppler Monitoring Transcranial Doppler (TCD) monitoring is a noninvasive technique that uses ultrasonic waves to measure the velocity of blood flow in the brain. 1 A pulsed Doppler -MHz portable ultrasound machine can be used at the bedside to measure changes in blood flow. TCD monitoring is most frequently used to detect and follow the course of vasospasm in patients with aneurysmal subarachnoid hemorrhage.,3 However, TCD monitoring can be used any time that knowledge of cerebral circulation and the state of blood flow to the brain is of importance. Table 1 lists both conventional and experimental uses of TCD monitoring. 4-6 Advantages of using TCD monitoring include the following: it allows real-time detection of changes in blood flow, it is relatively inexpensive, it can be repeated frequently or used continuously if needed, and most hospital systems already have an ultrasound department. In order to perform TCD monitoring, an ultrasound probe is placed on specific locations on the skull where the bone is very thin, called cranial windows. The 3 main cranial windows are temporal, orbital, and occipital. Each window allows access to different arteries. These bony windows must be thin enough to allow insonation of the artery. Insonation refers to the exposure of the artery to ultrasound waves. Thick skull bones do not allow passage of an ultrasound signal from the transducer. In the case of no signal return, the technician reports that there are no windows on TCDs. If the windows are accessible, the TCD transducer will insonate or expose an artery to an ultrasound signal through the bone (Figure 1). The ultrasound beam bounces off erythrocytes in the insonated artery and returns the signal to the transducer. 8 The signal is interpreted by software and presented as a series of numbers, which are then used to determine flow velocity. There is also an auditory confirmation of insonation of the artery, as the flowing blood makes a Author Catherine Harris is an assistant professor at Jefferson School of Nursing and an acute care nurse practitioner in the neurocritical care unit at Jefferson Hospital for Neuroscience in Philadelphia, Pennsylvania. Corresponding author: Catherine Harris, PhD, MBA, CRNP, Thomas Jefferson University, School of Nursing, 901 Walnut Street, Suite 83, Philadelphia, PA ( catherine.harris@jefferson.edu). To purchase electronic or print reprints, contact the American Association of Critical- Care Nurses, 101 Columbia, Aliso Viejo, CA Phone, (800) or (949) (ext 53); fax, (949) ; , reprints@aacn.org. Table 1 Uses for transcranial Doppler imaging a Conventional Assessment for intracranial stenosis Detection of cerebral emboli Assessment for collateral flow patterns Assessment for cerebral blood flow Evaluation of stroke risk in children with sickle cell disease Experimental Detection of cerebral venous thrombosis Evaluation of autoregulation Evaluation of arteriovenous malformations Continuous monitoring during angiography Evaluation of blood flow during a migraine a Based on information from the American Institute of Ultrasound in Medicine, 4 Marshall et al, 5 and Tsivgoulis et al. 6 swooshing sound corresponding to each heartbeat, which the technician can hear and see on the TCD screen (Figure ). If the swooshing sound is dampened, the technician may attempt to relocate the artery. Table provides important information regarding normal values of TCDs. In the first column is the name of the cranial window. The second column lists the associated arteries that can be identified in that window, and the third column shows at Neuromonitoring allows motor and sensory what depth function, brain activity, blood flow, and the arteries intracranial pressures to be evaluated. would be expected. The last column is the anticipated mean flow velocity of the arteries. Higher values or no value may indicate abnormal flow or lack of flow. After performing TCD monitoring, the technician prints out an output sheet of various numbers (Figure 3) that indicate the different arteries that were insonated in both hemispheres. Each artery may be repeated several times on both the right and left sides because of the variation in flow rates. The important numbers are the ones that reflect the depth at which each artery was insonated and the mean flow velocities. If there is a large deviation from normal depth or from the patient s baseline, the TCD numbers should be viewed with some skepticism. Findings on clinical examination should always take priority, and other imaging techniques such as computed tomographic angiography may be warranted. The mean flow velocity reflects the average rate of blood flow through the artery. The peak flow velocity is significantly higher than the mean flow velocity and is subject to fluctuations in the patient s heart rate and blood pressure. Therefore, the peak flow velocity varies CriticalCareNurse Vol 34, No. 3, JUNE

3 Suboccipital window: Vertebral artery Basilar artery Ophthalmic artery MCA ICA ACA 3 Transorbital window: ICA Ophthalmic artery 1 window: MCA ACA, PCA PCA Basilar artery 4 Jaw angle window: ICA ECA, CCA Vertebral artery Figure 1 Transcranial Doppler imaging windows and insonated arteries. Abbreviations: ACA, anterior cerebral artery; CCA, common carotid artery; ECA, external carotid artery; ICA, internal carotid artery; MCA, middle cerebral artery; PCA, posterior cerebral artery. Reprinted from Schell et al, 7 with kind permission from Springer Science+Business Media B.V. L-EX-ICA L-EX-ICA L-OA L-Siphon L-Siphon L-MCA BA BA BA R-EX-ICA 50 R-EX-ICA 50 R-EX-ICA 5 R-OA 50 R-OA 50 R-Siphon Table Normal findings on transcranial Doppler imaging Window Orbital Orbital Occipital Occipital Artery Middle cerebral Anterior cerebral Posterior cerebral Terminal internal carotid Internal carotid artery siphon Ophthalmic Vertebral Basilar Depth, mm Flow velocity, mean (SD), cm/s 55 (1) 50 (11) 40 (10) 39 (9) 45 (15) 0 (10) 38 (10) 41 (10) Figure Transcranial Doppler imaging output. Abbreviations: BA, basilar artery; Ex, external; ICA, internal carotid artery; L, left; MCA, middle cerebral artery; OA, ophthalmic artery; R, right. more widely than the mean flow velocity. The mean flow velocity is considered more stable and thus a more reliable indicator of blood flow in the brain, so it has been established as the criterion to follow. 9 After subarachnoid hemorrhage, TCD monitoring may be ordered daily or twice daily to assess the mean flow velocity. Primary providers who order TCD monitoring will be most interested in the mean flow velocity of the middle cerebral artery (MCA), the anterior cerebral artery (ACA), and the basilar artery because they are the largest vessels and thus have the potential to cause the most devastating strokes. They are also the 3 3 CriticalCareNurse Vol 34, No. 3, JUNE 014

4 Left Right Label Depth Edv PI RI Label Depth Edv PI RI MHz L-EX-ICA R-EX-ICA L-EX-ICA R-EX-ICA L-OA R-EX-ICA L-Siphon R-OA R-OA L-Siphon R-Siphon L-MCA R-VA L-MCA R-VA L-MCA R-VA L-MCA R-VA L-MCA R-VA 66 L-MCA R-MCA L-MCA R-MCA L-MCA R-MCA L-MCA R-MCA L-MCA/ACA R-MCA R-MCA L-MCA/ACA R-MCA/ACA L-ACA R-MCA/ACA L-ACA L-ACA R-ACA L-T-ICA R-ACA L-PCA P R-MCA L-PCA P R-MCA L-PCA P R-MCA L-VA R-T-ICA L-VA R-T-ICA L-VA R-PCA P L-VA R-PCA P L-VA R-PCA P L-VA R-PCA P BA BA BA Left Lindegaard ratio =.97 Right Lindegaard ratio =.95 Figure 3 Transcranial Doppler imaging output numbers. Abbreviations: ACA, anterior cerebral artery; BA, basilar artery; Edv, end-diastolic velocity; EX, external; ICA, internal carotid artery; L, left; MCA, middle cerebral artery; OA, ophthalmic artery; P1, first section of posterior cerebral artery; PCA, posterior cerebral artery; PI, pulsatility index; RI, resistance index; T, terminus; VA, vertebral artery. CriticalCareNurse Vol 34, No. 3, JUNE

5 arteries that are large enough for endovascular intervention if warranted. Significant increases or decreases in the mean flow velocity should be reported to the primary provider, as they may reflect important changes in circulation in the brain. A significant increase in mean flow velocity may be due to increasing severity of vasospasm or hyperemia. A significant decrease in mean flow velocity may reflect an impending or completed stroke. An extremely important change to report is when a previously high mean flow velocity is no longer detectable, again possibly indicating a stroke. Patients with consistently high mean flow velocity in the MCA should be monitored very closely for potential stroke. Another very important number to follow is the Lindegaard ratio. This ratio is the mean flow velocity in the MCA divided by the mean flow velocity in the ipsilateral internal carotid artery (ICA). 10 This ratio helps to distinguish between true vasospasm and hyperemia. Hyperemia is an increase in blood flow, which increases mean flow velocity, possibly as a result of hypervolemia, but does not indicate Changes in the mean flow velocity of the vasospasm. In middle or anterior cerebral artery and the hyperemia, basilar artery are signs of trouble. the mean flow velocity in the MCA increases to more than 00 cm/s, but the Lindegaard ratio does not increase because an associated increase in blood flow to the ICA also occurs. Table 3 shows the criteria for various degrees of vasospasm. The output numbers on TCDs should not be used by themselves as the sole criteria for making clinical decisions and should always be correlated with findings on the patient s neurological examination. Technical errors are common, especially if the technician does not perform TCD often. Results may be dependent on the skill of the technician. Often, results can change dramatically when the only difference is that a different technician is performing the TCD monitoring. Alternatively, errors may occur if the bone windows are thickened or the vessels are difficult to access and/or the patient is uncooperative, confused, or combative. TCD: Nursing Implications Nurses at the bedside are responsible for ensuring that TCD monitoring is done in a timely fashion and for making sure that the patient is in optimal condition for the technician to perform the procedure. Patients who Table 3 flow velocities and Lindegaard ratios by severity of vasospasm Vasospasm severity None Mild Moderate Severe Flow velocity, mean (SD), cm/s < > >00 Lindegaard ratio a < -3 >3-6 >6 a Ratio of flow velocity in middle cerebral artery to flow velocity in internal carotid artery. are combative and confused may need behavioral or pharmacological intervention before the start of the procedure. Nurses who are aware of the timing of the study can make sure that patients are in bed and prepared. Nurses might also consider having a patient care assistant stay with the patient to help assuage fears or redirect the patient s attention. Because the procedure can be limited by movement or agitation, nurses can greatly facilitate the situation by using their organizational skills and some forethought about how the patient might respond. After the procedure is completed, the nurse should review the mean velocities of the MCA and compare those values with values from the previous day. If there are any significant categorical differences, such as an increase from mild to moderate spasm or moderate to severe spasm, the nurse should alert the provider. Also if there is an increase in the Lindegaard ratio above or loss of the ability to find the artery, the nurse should alert the provider. Electrophysiology Neurological electrophysiology includes monitoring of various electrical impulses in the body. In the intensive care unit, the most frequently encountered neuroelectrophysiology techniques are electroencephalography (EEG) and one of its derivatives, bispectral (BIS) monitoring. Other derivatives of EEG include somatosensory evoked potentials (SSEPs) and brainstem auditory evoked potentials (BAEPs). These last studies are more frequently used in the operating room; however, they may be used as adjunctive studies in assessing for brain damage and brain death. SSEPs and BAEPs can be used to evaluate the extent of brain damage and assist providers in discussing prognoses with patients families. Some experimental studies 11,1 have also been done to evaluate the utility of 34 CriticalCareNurse Vol 34, No. 3, JUNE 014

6 SSEPs and BAEPs in the intensive care unit, but at this time those techniques are not the standard of care. An EEG is the evaluation of spontaneous electrical activity in the brain used to guide seizure management, assess level of consciousness, detect cerebral ischemia, and monitor effects of medications such as barbiturates in coma induction. The brain consists of billions of neurons, all of which release an electrical charge. Neurons are charged by the constant flux of ions such as sodium and potassium across their membranes. The ions are transferred in and out of the cell body by membrane transport proteins. Neurons send electrical impulses (action potentials) from the cell body via myelinated axons, which provide the signal to release neurotransmitters from synaptic vesicles. This process is how the neurons communicate with the body to perform various functions. Although the electrical charge of 1 neuron is too small for EEG to pick up alone, the synchronous activity of millions of neurons generates a measurable charge. Scalp electrodes can be used to monitor the fluctuations of the electrical charges of neurons. Evidence of seizure activity can be seen on an EEG in the form of abnormal fluctuations of voltage displayed as spikes and fluctuating waveforms. EEG features do not correspond to specific anatomy; rather, they correspond to territories of brain activity that cluster together. Therefore, EEG is often used as an adjunctive technique to validate results of other diagnostic tests. EEG features are measured in terms of amplitude, latencies, frequency, symmetry, and patterns (Table 4). The amplitude of a variable is a measure of its change over time. The amplitude of an EEG feature is compared with either known norms or a person s baseline. The highest value of an amplitude is called the peak. Latencies are a Attribute Amplitude Latency Frequency Table 4 Electroencephalography attributes Measures Microvolts (mv) Milliseconds (ms) Hertz (Hz) Evaluation Low or high Fast or slow Fast or slow measure of a time delay between a stimulus and its response. The latency comes just before the amplitude on the EEG. Frequencies are oscillations that are synchronized activity corresponding to a series of neuronal networks. 13 Some commonly known frequency bands are delta, theta, alpha, beta, gamma, and mu waves (Table 5). 14 Symmetry is assessed visually on EEGs to ascertain if both hemispheres are Patients with consistently high mean flow roughly velocity in the middle cerebral artery should equivalent. be monitored very closely for potential stroke. Finally, patterns can be identified, such as burst suppression, status epilepticus, or brain death (Figure 4). Nurses can and should be taught to identify these 3 patterns, all of which are extremely important in treatment of patients. Status epilepticus can be either convulsive or nonconvulsive, so interpretation of EEG waves can be difficult and beyond the purview of bedside nurses. However, any change in mental status of a patient may prompt the nurse to look at the EEG if it is being continuously monitored. Typical markings of status epilepticus are spikes in amplitude, although such spikes vary widely depending on the type of seizure. Movement of the EEG leads may also cause artifact that may mimic the look of seizure activity, so the nurse may receive a Table 5 Frequency bands a Type Delta Location Frontal Hertz (Hz) <4 Amplitude High Normal occurrence Slow-wave sleep Pathological occurrence Metabolic encephalopathy, diffuse injury Metabolic encephalopathy Coma Benzodiazepines Cognitive decline Autism, social and cognitive deficits Theta Alpha Beta Gamma Mu Random Posterior head Symmetrical Somatosensory cortex Sensorimotor cortex High Low Drowsiness Eye closing, relaxed Alert, active, concentration Cross-modal sensory Rest-state motor neurons a Based on information from Blanco et al CriticalCareNurse Vol 34, No. 3, JUNE

7 Normal EEG Status epilepticus Burst suppression Brain death Figure 4 Electroencephalography (EEG) patterns. call from the epileptologist who is monitoring the patient for clarification. Burst suppression is evidenced by voltage attenuation with bursts of generalized activity. Burst suppression is seen in clinical states such as anoxic brain injury or prolonged resuscitation or it can be induced with medications such as pentobarbital or propofol. When burst suppression is pharmacologically induced, providers will typically ask the nurses to titrate the medications to a certain number of bursts per minute. For example, in an induced coma, the order may read to titrate either a pentobarbital or propofol infusion to 4 to 6 bursts per minute. If a standard EEG screen displays 15 seconds of information, the nurse should see a minimum of 1 burst of electrical activity on the screen at any given time, but no more than. An accurate assessment of 36 CriticalCareNurse Vol 34, No. 3, JUNE 014

8 burst suppression clearly depends on the time sequence of the computer screen, which should be verified and documented. Brain death is the cessation of any activity on EEG. In this scenario, the nurses can alert providers that no activity has been seen on EEG for an extended period. This information may prompt providers to initiate other evaluation methods to confirm brain death. Despite an effort to identify the meaning of patterns, their interpretation remains largely elusive and it is difficult to correlate EEG patterns with clinical condition. One derived measure of EEG has been interpreted to correlate with level of consciousness. The BIS monitor detects a slowed pattern of electrical activity and correlates to depth of anesthesia. 15 BIS monitoring uses statistically based and complex equations to derive a sum of EEG parameters that include time and frequency. These composite measures are then assessed in relation to various signal components. This process allows the BIS monitor to detect certain patterns, which can then be correlated with depth of anesthesia. In an awake patient, the BIS monitor would detect a small amplitude with a fast frequency, whereas in moderate sedation, the BIS monitor would detect an increase in amplitude at a slower frequency. In a patient under general anesthesia, the BIS monitor would detect a large amplitude at a very slow frequency. In a patient under deep anesthesia, the BIS monitor would detect an isoelectric charge that looks similar to an EEG consistent with brain death (Figure 4). BIS monitoring is commonly used in intensive care units to ascertain the level of consciousness of the patient. Sedative and anesthesia can be titrated on the basis of the BIS monitoring, depending on the needs of the patient. The lower the number on the BIS monitor, the deeper the level of anesthesia 16 (Table 6). BAEPs and SSEPs are also derivatives of EEG that correlate with specific electrical impulses. SSEPs are used to monitor spinal cord ascending pathways and their functional integrity. Tiny needle electrodes are placed in the skin along the medial nerve and the posterior tibial nerve. Scalp electrodes capture the response of an electrical stimulation that is generated through the needles. Once the stimulus is given peripherally, there is a certain amount of time that is expected to elapse before the scalp electrodes record the response. If there is a delay or no response is recorded, a break in the integrity of the ascending pathways of the spinal cord is indicated. A break in Table 6 Index for bispectral monitoring device a Index range > >60-90 > <0 a Based on information from Kelly. 16 the function of the system could be due to a malfunction in the neuromonitoring system, the presence of central nervous system depressants/paralytic agents, or spinal cord injury or brain injury. SSEPs might be used in the intensive care unit in a patient who does not wake up after surgery or as an adjunctive diagnostic tool in determining brain death. In brain death, no response would be captured through the scalp electrodes despite an intact spine. BAEPs are used to evaluate the function and integrity of the brainstem. BAEPs also entail the placement of electrodes on the scalp. BAEPs are elicited by the application of brief transient stimuli such as audible clicks in the ears. The response is then received and recorded via electrodes. Five common types of waves that are recorded Clinical state Awake Light to moderate sedation General anesthesia Burst suppression Isoelectric electroencephalogram Table 7 Waves seen in brainstem auditory evoked potentials Wave P1 (wave I) P (wave II) P3 (wave III) P4 (wave IV) P5 (wave V) Probable anatomic correlate Distal acoustic wave Proximal acoustic nerve/cochlear nucleus Lower pons Mid/upper pons Lower midbrain The lower the number on the BIS monitor, the deeper the level of anesthesia. from BAEPs correspond to anatomic locations (Table 7). BAEPs are more robust than SSEPs because BAEPs are more resistant to effects of medications or anesthesia. Disorders of the ear such as labyrinthitis do not affect BAEPs. Even hearing loss does not preclude the use of BAEPs. Wave V is used to assess hearing loss in the clinical setting; however, waves I through IV can still be assessed for a baseline. BAEPs are largely affected only CriticalCareNurse Vol 34, No. 3, JUNE

9 by a structural abnormality such as a stroke, tumor, or cerebral edema in the brainstem. Signal changes may start to occur when intracranial pressures exceed 30 mm Hg. 17 The presence of BAEPs will disappear in more than 80% of patients who are clinically brain dead. Because BAEPs are not 100% sensitive and specific for brain death, they can be used as an adjunctive diagnostic tool, but they cannot be used alone to declare brain death. Electrophysiology: Nursing Implications Nurses are typically not responsible for reading or interpreting EEG, SSEPs, or BAEPS; however, they do monitor continuous EEG for burst suppression and follow BIS recordings to determine a patient s level of consciousness. Therefore, it is important for nurses to understand how these techniques work. Furthermore, knowledge of these techniques assists nurses in explaining to patients families what is going on and educating them on what it all means. Nurses are instrumental in this process, but educating patients families requires a solid understanding of the technology. Summary This article reviewed important noninvasive neuromonitoring techniques that are commonly used in neurocritical care settings. For nurses who work in a general critical care setting and do not encounter neurocritical care patients on an everyday basis, understanding key techniques in neurocritical care is essential. EEG and TCD play a major role in understanding a patient s overall neurological status and prognosis. Nurses must understand the importance of these techniques, how they work, and how to interpret their meaning in the context of the individual patient. Understanding neuromonitoring is an essential aspect of working with critically ill neurological patients. CCN Financial Disclosures None reported. Now that you ve read the article, create or contribute to an online discussion about this topic using eletters. Just visit and select the article you want to comment on. In the full-text or PDF view of the article, click Responses in the middle column and then Submit a response. To learn more about neuromonitoring, read Intracranial Pressure Waveform Morphology and Intracranial Adaptive Capacity by Fan et al in the American Journal of Critical Care, November 008;17: Available at References 1. Aaslid R, Markwalder TM, Normes H. Noninvasive transcranial Doppler ultrasound recording of flow velocity in basal cerebral arteries. J Neurosurg. 198;57: Treggiari-Venzi MM, Suter PM, Romand JA. Review of medical prevention of vasospasm after aneurysmal subarachnoid hemorrhage: a problem of neurointensive care. Neurosurgery. 001;48: Oyama K, Criddle L. Vasospasm after aneurysmal subarachnoid hemorrhage. Crit Care Nurse. 004;4:58-60,6, American Institute of Ultrasound in Medicine. AIUM practice guideline for the performance of a transcranial Doppler ultrasound examination for adults and children. J Ultrasound Med. 01;31: Marshall SA, Nyquist P, Ziai WC. The role of transcranial Doppler ultrasonography in the diagnosis and management of vasospasm after aneurysmal subarachnoid hemorrhage. Neurosurg Clin North Am. 010;1: Tsivgoulis G, Alexandrov AV, Sloan MA. Advances in transcranial Doppler ultrasonongraphy. Curr Neurol Neurosci Rep. 009;9: Schell R, Cole D, Lichtor JL, Miller RD. Neurophysiologic monitors. In: Miller RD, Lichtor JL, eds. Atlas of Anesthesia. Vol. 3. New York, NY: Springer Publishing; 00:chap Padayachee TS, Kirkham FJ, Lewis RR, et al. Transcranial measurement of blood velocities in the basal cerebral arteries using pulsed Doppler ultrasound: a method of assessing the circle of Willis. Ultrasound Med Biol. 1986;1: Sloan MA, Alexandrov AV, Tegeler CH, et al. Transcranial Doppler ultrasonography in 004: a comprehensive evidence-based update. Neurology. 004;6(9): Lindegaard KF, Nornes H, Bakee SJ, Sorteberg W, Nakstad P. Cerebral vasospasm after subarachnoid haemorrhage investigated by means of transcranial Doppler ultrasound. Acta Neurochir Suppl (Wien). 1988;4: Amantini A, Amadori A, Fossi S. Evoked potentials in the ICU. Eur J Anaesthesiol Suppl. 008;4: Emerson RG, Pedley TA. Clinical neurophysiology: electroencephalography and evoked potentials. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Butterworth- Heinemann: 01:chap 3A. 13. Andrade-Valenca LP, Dubeau F, Mari F, Zelmann R, Gotman J. High-frequency oscillations recorded on scalp EEG. Neurology. 011;77: Blanco JA, Stead M, Krieger A, et al. Data mining neocortical high-frequency oscillations in epilepsy and controls. Brain. 011;134(10): Olson D, Chioffi SM, Macy GE, Meek LG, Cook HA. Potential benefits of bispectral index monitoring in critical care: a case study. Crit Care Nurse. 003;3(4): Kelly SD. Monitoring Consciousness: Using the Bispectral Index during Anesthesia. nd ed. Boulder, CO: Covidien; Im JJ, Park BR. Does oxygen deficit to the cerebral blood flow caused by subdural hematoma and/or increased intracranial pressure affect the variations in auditory evoked potentials in white New Zealand rabbits? Neurosci Lett. 00;317: CriticalCareNurse Vol 34, No. 3, JUNE 014

10 CCN Fast Facts CriticalCareNurse The journal for high acuity, progressive, and critical care nursing Neuromonitoring Indications and Utility in the Intensive Care Unit Facts Neuromonitoring techniques are essential tools used in evaluating patients with neurological injury in critical care settings. Nurses must be able to use various neuromonitoring techniques and interpret their results in order to provide the best care for their patients. Transcranial Doppler Monitoring Transcranial Doppler (TCD) monitoring is a noninvasive technique that uses ultrasonic waves to measure the velocity of blood flow in the brain. A pulsed Doppler -MHz portable ultrasound machine can be used at the bedside to measure changes in blood flow. To perform TCD monitoring, an ultrasound probe is placed on specific locations on the skull where the bone is very thin, called cranial windows. The 3 main cranial windows are temporal, orbital, and occipital. Each window allows access to different arteries. The Table provides important information regarding normal values of TCDs. In the first column is the name of the cranial window. The second column lists the associated arteries that can be identified in that window, and the third column shows at what Table Normal findings on transcranial Doppler imaging Window Orbital Orbital Occipital Occipital Artery Middle cerebral Anterior cerebral Posterior cerebral Terminal internal carotid Internal carotid artery siphon Ophthalmic Vertebral Basilar Depth, mm Flow velocity, mean (SD), cm/s 55 (1) 50 (11) 40 (10) 39 (9) 45 (15) 0 (10) 38 (10) 41 (10) depth the arteries would be expected. The last column is the anticipated mean flow velocity of the arteries. Higher values or no value may indicate abnormal flow or lack of flow. Nurses should ensure that TCD monitoring is done in a timely fashion and make sure that the patient is in optimal condition for the technician to perform the procedure. After the procedure is completed, the nurse should review the mean velocities of the middle cerebral artery and compare those values with values from the previous day. If there are any significant categorical differences, the nurse should alert the provider. Also if there is an increase in the Lindegaard ratio above or loss of the ability to find the artery, the nurse should alert the provider. Electrophysiology In the intensive care unit, the most frequently encountered neuroelectrophysiology techniques are electroencephalography (EEG) and one of its derivatives, bispectral (BIS) monitoring. An EEG is the evaluation of spontaneous electrical activity in the brain used to guide seizure management, assess level of consciousness, detect cerebral ischemia, and monitor effects of medications such as barbiturates in coma induction. EEG features are measured in terms of amplitude, latencies, frequency, symmetry, and patterns. It is difficult to correlate EEG patterns with clinical conditions. One derived measure of EEG has been interpreted to correlate with level of consciousness. The BIS monitor detects a slowed pattern of electrical activity and correlates to depth of anesthesia. Nurses are typically not responsible for reading or interpreting EEGs; however, they do monitor continuous EEG for burst suppression and follow BIS recordings to determine a patient s level of consciousness. Knowledge of these techniques assists nurses in explaining to patients families what is going on and educating them on what it all means. Nurses are instrumental in this process, but educating patients families requires a solid understanding of the technology. CCN Harris C. Neuromonitoring Indications and Utility in the Intensive Care Unit. Critical Care Nurse. 014;34(3): CriticalCareNurse Vol 34, No. 3, JUNE