BIS monitoring:From the OR to the ICUFind out how bispectral index monitoring can give you an objectivemeasure of your patient's level of sedation.

By Ellie Z. Franges, RN, APRN,BC, CNRN, MSN

Caring for critically ill patients in the ICU can presentmultiple challenges. Because of the physiologic dynamicsof critical illness, predicting the patient's need for anal-gesia and sedation is difficult. Until recently, the onlyphysiologic measures we had to ensure appropriatemedication use were indirectly tied to patient comfort.This method often resulted in oversedation for patients,increasing ICU stays, and overall morbidity.

Bispectral index (BIS) monitoring, an objective mea-sure of the patient's response to sedation, has been usedin anesthesia for over a decade. This technology is find-ing its way into the ICU to provide a means of assessingthe adequacy of sedation and preventing oversedation ofcritically ill patients.

In addition, because the BIS monitor reflects elec-troencephalographic data, it adds to the objective infor-mation regarding brain activity.

BIS is also used to monitor sedation in patients withneurologic disorders, and clinical trials use BIS monitor-ing to improve sedation protocols in endoscopy and in-terventional endoscopy.

What BIS revealsBIS monitoring measures cerebral electrical activity de-rived from an electroencephalogram (EEC). The BIS de-vice reads the electrical activity from a sensor placed onthe patient's forehead and converts several parametersinto a single numeric value that correlates to sedationlevel. The digital BIS value ranges from 0 (isoelectricEEC) to 100 (fully conscious).1

The BIS monitoring system consists of a sensor and adisplay monitor. The sensor is an electrode strip. Threeof the electrodes, when properly placed, pick up EEC ac-tivity. A fourth electrode is used to measure artifact andelectromyographic (EMG) resistance, which sends sig-nals that contaminate EEC readings. The sensor is con-

nected to the monitor that displays a single-channel EECtracing and the BIS score.

The monitor also provides information that can con-firm the reliability of the data. A high signal quality in-dex (SQI) indicates a reliable BIS value. The suppressionratio (SR), noted as a numeric value, indicates the per-centage of isoelectric EEC.2 The suppression ratio valuesare inverse to the BIS values. A tracing without any iso-

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electric periods would have an SR of 0, whereas a fullyisoelectric tracing would have an SR of 100.3 The valueof the EMG indicator, which reflects muscle stimulation,will rise with any occurrence that increases muscle toneor movement. As the EMG value rises, the BIS value be-comes less reliable.3

Monitoring how-toBeginners to BIS monitoring can use the following tech-nique.

Placing the sensor: You can place the electrode stripon either side of the patient's forehead. First, gentlyclean and dry the patient's forehead to remove oils. Thesensor strip, which doesn't require any additional skinpreparation, has three circles to ensure placement torecord EEC activity. Circle one is centered 2 inchesabove the nose. Circle four is placed above the eyebrowin a parallel fashion. Circle three is centered on the tem-ple between the corner of the eye and the hairline. (Cir-cle two doesn't have a specific placement.)

Once the strip is placed, secure it by pressing aroundthe edges of each circle, then press and hold each circlefor at least 5 seconds to secure contact to the skin.4

Monitoring: Use the interface cable to connect thesensor to the monitor. The BIS monitor will display theraw EEC tracing, and within several minutes the BIS nu-meric value will stabilize. Check the SQI for reliability ofsignal. Document the baseline value; use the BIS value totitrate sedative medication. (See BIS sedation scale.)

Care and troubleshootingThe BIS monitor requires little in the way of trou-bleshooting. The sensor should be changed every 24hours. The monitor will alert you when the 24-hourperiod is over.

If the SQI decreases, check that the sensor is still ingood contact with the patient's forehead. Remember, ifthe EMG activity increases, the accuracy of your BISvalue decreases. Because EMG resistance reflects muscleactivity, search for and treat the cause of the EMG activ-ity. If it's pain, your interventions will include adminis-tering analgesics. If it's seizure, administer antiepileptics.If the patient needs to be immobile for medical treat-ment (such as an imaging study), you may need to ob-tain an order to add muscle relaxants or paralytics to thepatient's medication.

BIS in actionLet's look at some scenarios in which BIS monitoringcan be used.

Marisol Jiminez, 44, arrives at the ED after the sud-

BIS sedation scale

Bispectral index values for monitoring the sedationlevel in critically ill patients.

Clinical StateAnxiolysisModerate sedationDeep sedation

BIS100—patient awake, responds to normal voice9080—patient responsive to loud commands or tactile

stimuli7060—patient unresponsive to verbal stimuli5040—hypnotic state3020100—flat-line electroencephalogram

Source: Aspect Medical Systems, http://www.aspectmedical.com.

den onset of what she describes as the worst headacheof her life. She had no focal neurologic deficits. Mildnuchal rigidity and headache were present on admis-sion. A computed tomography (CT) scan of the headdemonstrated a subarachnoid hemorrhage suspiciousfor a middle cerebral artery aneurysm. A CT angiogramconfirmed the presence of a left middle cerebral arteryaneurysm. Ms. Jiminez was taken to the OR for clipobliteration of the aneurysm. She was given propofolfor sedation because of its short half-life; a neurologicexam can be performed quickly after the infusion isstopped.

She remained intubated and sedated postoperatively,and the BIS monitor provided objective informationabout her level of sedation. A postoperative CT scancompleted the morning after surgery showed no new he-morrhage, good clip position, and no indication of cere-bral edema. During the morning exam, with thepropofol infusion off for 20 minutes, Ms. Jiminez wassleepy and commands with both upper extremities;however, her response was quicker on the left side thanthe right.

Early on the second postoperative day, her BIS val-ues were trending lower than the desired range. The CTscan was repeated and showed no change from her im-

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mediate postoperative scan. She had a transcranialDoppler study, which demonstrated high velocitiessuggestive of vasospasm. At the same time, propofolwas titrated down with no change in BIS values. Afterthe transcranial Doppler sonography, she was takenimmediately to the interventional radiology suite for acerebral arteriogram, which confirmed the vasospasm.She was treated with intra-arterial papaverine. After 20minutes, a repeat arteriogram demonstrated no furthervasospasm, so she was maintained on triple-H therapy(hypertension, hypervolemia, and hemodilution, de-signed to increase cerebral perfusion and reduce therisk of vasospasm). Her BIS values at this time were 40to 50.

Twenty-four hours after the intra-arterial papaverinewas administered and while Ms. Jiminez was still ontriple-H therapy, her BIS values dropped again. A CTscan of the head showed no change, but her intracranialpressure (ICP) values were trending upward from 15 to18 mm Hg and transcranial Doppler values showed in-creased velocities. Triple-H therapy was maximized.Throughout this period, she remained sleepy with someweakness of her right arm and would follow commandsonly intermittently. Her BIS values continued to trenddownward as her ICP values trended up, despite treat-ment with cerebrospinal fluid drainage and mannitol. Arepeat CT scan 12 hours later (3.5 days postoperatively)demonstrated the development of a left middle cerebralartery infarction. Sedation was titrated off as BIS valuescontinued to trend low. Her ICP numbers remained inthe 20 to 25 mm Hg range, refractory to treatment. Herneurologic status during this time period worsened. Sheno longer responded to verbal stimulation, she was de-cerebrate to deep pain, her pupils were 5 mm, and shewas sluggish to reaction.

By the end of the third postoperative day, her neuro-logic exam had worsened despite treatment for va-sospasm and increased ICP. Her BIS values had droppedto 0. Her neurologic exam was consistent with cerebraldeath, and a cerebral blood flow scan was consistentwith no flow. Her family, following her wishes, re-quested an evaluation for organ donation. Twelve hourslater, her neurologic exam remained consistent withbrain death and she was pronounced dead and taken tothe OR for organ harvest.

Now let's consider another case. Tom Cameron,. 25,is admitted to the trauma center following a motorcyclecrash. His Glasgow Coma Score on admission was 6(normal is 15). A CT scan of the head showed a largesubdural hematoma with underlying contusions. He wasurgently taken to the OR for evacuation of the

hematoma and placement of a ventriculostomy for ICPmonitoring. Upon arrival in the ICU, he was restless andagitated, refusing to follow commands and fighting theventilator. His ICP values were 18 to 20 mm Hg. He wassedated with fentanyl and lorazepam.

Mr. Cameron was placed on BIS monitoring with thegoal of maintaining a BIS value of 50 to 60. On the sec-ond postoperative day, however, his BIS value increasedto 80, and he was restless, agitated, not following com-mands, and attempting to pull out his endotrachealtube. The lorazepam and fentanyl infusions were in-creased, and within 45 minutes the BIS values returnedto the desired range. Over the course of the next 48hours, the sedation was gradually titrated down and theBIS values increased. Mr. Cameron's ICP values re-mained normal, and he was extubated on the fifth post-operative day.

A measure ©f successIn both of these cases, the BIS monitor was helpful inproviding an objective measure of the patient's responseto sedation and to limiting the amount of sedation used.In Ms. Jiminez's case, because the neurologic decline wassuggested by the falling BIS numbers despite the reduc-tion in sedation, successful organ recovery was facili-tated.

In Mr. Cameron's case, as he recovered from surgery,BIS values increased, indicating that his sedation couldbe increased without oversedating him. This system al-lowed for easier, more prompt extubation and a de-creased stay in the ICU.

Overall, BIS monitoring is an easy-to-use adjunct tomonitoring sedation in the critically ill patient that mayreduce costs, morbidity, and mortality related to seda-tion in the ICU. •

REFERENCES

1. Riker RR, Fraser GL, Wilkins ML. Comparing bispectral index and suppres-sion ratio with burst suppression of the electroencephalogram during pento-barbital infusions in the adult intensive care patients. Pharmacotherapy.2003;23(9):1087-1093.

2. Olson DM, Chioffi SM, Macy GE, et al. Potential benefits of bispectral indexmonitoring in critical care: A case study. Crit Care Nurse. 2003;23(4):45-52.

3. Fatovich DM, Gope M, Paech MJ. A pilot trial of BIS monitoring for proce-dural sedation in the emergency department. Emergency Medicine Australasia.2004;16(2}:103-107.

4. Aspect Medical Systems. Sedation Assessment in the ICU—Bispectral IndexMonitoring, 2003. http://www.aspectmedical.com/resources/elearning.

5. Aspect Medical Systems. BIS Monitoring in Critical Care—Advances in Seda-tion Assessment, 2004. http://www.aspectmedical.com/resources/elearning.

Ellie Franges is a nurse practitioner of neurosurgery at St. Luke's Hospital andHealth Network in Bethlehem, Pa.

Adapted from BIS monitoring migrates from OR to ICU. Nursing Critical Care.2006:1(51:58-61.

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