Perioperative use of bispectral (BIS) monitor for a pressure ulcer patient with locked‐in syndrome (LIS)

Abstract

The bispectral (BIS) monitor uses brain electroencephalographic data to measure the depth of sedation and pharmacological response during anaesthetic procedures. In this case, the BIS monitor was used for another purpose, to demonstrate postoperatively to the nursing staff that a patient with history of locked‐in syndrome (LIS), who underwent pressure ulcer debridement, had periods of wakefulness and apparent sensation, even with his eyes closed. Furthermore, as patients with LIS can feel pain, despite being unable to move, local block or general anaesthesia should be provided for sharp surgical debridement and other painful procedures. This use of the BIS has shown that as a general rule, the staff should treat the patient as though he might be awake and sensate even if he does not open his eyes or move his limbs. The goal of this study was to continuously monitor pain level and communicate these findings to the entire wound team, i.e. anaesthesiologists, surgeons and nurses.

Introduction

Comprehensive care of patients includes a thorough assessment. Even when a patient is unable to communicate with health care professionals, it is important to remember that a patient is capable of feeling pain especially during procedures associated with causing pain, such as surgery. In this article, we describe the case of one such patient, who due to locked‐in‐syndrome (LIS) could not express his needs for pain management during a surgical procedure. By recognising his unique needs in addition to his more ordinary concerns, the staff selected to manage his care were able to provide appropriate treatment for his pressure ulcer. Furthermore, the insights of the patient's wife, who had had the most behavioural observation of the patient, provided the clue that her husband did indeed have periods of wakefulness, even when his eyes were closed. The anaesthesiologist, with the use of the bispectral (BIS) monitor was able to show this fact to the nursing staff. The goal of this study was to continuously monitor pain level and communicate these findings to the entire wound team, i.e. anaesthesiologists, surgeons and nurses.

Locked‐in‐syndrome (LIS)

LIS results from de‐efferentation or loss of motor function, such that a patient is conscious, self‐ventilating and alert despite being unable to speak or move. The only movements that are normally preserved are vertical eye movements and blinking 1, 2, 3. Despite several extensive reports in the literature, the concept did not become mainstream among neurologists until Plum and Posner 4 introduced the term “Locked‐in syndrome” (LIS). LIS is also known as cerebromedullospinal disconnection, de‐efferented state, pseudocoma and ventral pontine syndrome 1, 2, 3, 4, 5.

The most common cause of LIS is basilar artery thrombosis causing ventral pontine infarction 1, 2, 3, 4, 5, 6. Other pathologies include pontine haemorrhage and central pontine myelinolysis. Bilateral ventral midbrain and internal capsule infarcts can present a similar diagnosis 1, 2, 3, 4, 5, 6. The condition leaves the patient with intact sensation, but no motor control, which increases the risk for all complications of immobility including pressure ulcers. As LIS is a relatively rare condition, medical, nursing and other health care staff are often not familiar with the needs of these patients who require constant care.

What is BIS?

The electroencephalogram (EEG) measures voltage (microvolts) across the brain. The pattern can display waves in various frequencies and phases, which are associated with various depths of consciousness (Figure 1). Few clinicians have the knowledge, skill and expertise to differentiate between the various waveforms. The electrode montage is attached to the patient's forehead for EEG (voltage) measurement and connects via a cable to the processing and display unit (Figure 2). The BIS EEG displays a number between 0 and 100 that can be correlated with the different levels of consciousness (Figure 3).

Figure 1.

Bispectral monitor display. © O’Neill and Ayello 2012.

Figure 2.

Electrode montage connects to a cable. © O’Neill and Ayello 2012.

Figure 3.

Bispectral numerical trends. © O’Neill and Ayello 2012.

How was BIS developed

The BIS index was initially created by subjecting patients or volunteers to carefully controlled levels of sedation. At each behaviourally defined level of sedation, from wide awake through completely unresponsive, samples of EEG were taken. A discriminant function was then optimized to produce the highest performance of correct classification of new samples of EEG.

The details of the components of the discriminant function and the process of computing the index are laid out in a review by Rampil 7. Along with a ratio of beta frequency power at light levels of sedation, and a measure of EEG suppression at deepest levels of sedation, BIS includes a component derived from the bispectrum of the EEG. The bispectrum is a measure of the relative synchrony or phase‐locking of frequencies in the EEG. The result of this calculation produces an index with performance results that are clinically relevant.

Interpreting the BIS value

BIS represents the probability that a patient will respond to a command, but not to the probability that the patient will remember being asked to follow the command. If the BIS value is above 80, it is highly likely that the patient will follow a command, but if the BIS value is below 60, it is highly unlikely that the patient will follow a command. The response curves for each class of drugs nearly overlie each other, indicating that the index is nearly drug‐independent with respect to the level of consciousness determination.

Bispectral monitoring (BIS) for drug titration

For patients who have intact sensation but no motor control, such as patients under the influence of neuromuscular blockade or LIS, health care professionals need a way to assess the patient's level of awareness. This is especially true during procedures where pharmacological intervention, such as anaesthesia, is used in their care. BIS monitoring can be used to measure depth of sedation and response to hypnotic drugs, with the goal of preventing awareness under general anaesthesia. Historically, the reflex withdrawal to a surgical stimulus (yes or no) was a binary measure of the depth of anaesthesia.

In fact, there is a very common misunderstanding of what it means to be awake. Many times, surgeons would tell the anaesthesiologist that the patient was ‘waking up’ if the patient moved, even when the surgical patient had enough hypnotic to be amnestic. This subcortical reflex behaviour represents sub‐therapeutic analgesia or antinociception, and not necessarily sub‐therapeutic hypnotic. However, neuromuscular blockers such as pancuronium can function as chemical restraints preventing skeletal muscle movement even though the brain has insufficient hypnotics for unconsciousness or insufficient analgesics for pain control. Thus, the patient can be ‘awake’, aware of surroundings, have recall and feel pain to surgical stimulus, all the while unable to move or to communicate the horror of vivisection. Clearly, movement does not mean the patient is alert and lack of response does not signify lack of consciousness; this is a fairly common misconception.

By titrating anaesthetic drugs using the BIS, an anaesthesiologist can customize the rate of drug administration to the patient's individual needs rather than relying only on pharmacokinetic models or neurological examination. BIS values over 70 are associated with a high rate of recall, whereas those below 70 are associated with a very low rate of recall. Prolonged BIS values under 40 especially with high suppression ratios are associated with undesirable outcomes and increased mortality. Monk 8 showed that cumulative deep hypnotic time had a relative risk of 1·244, or a 24·4% increased risk of death per hour of time BIS was less than 45. Although the correlation between hypnotics or inhalational anaesthetics may not be linear, increasing doses monotonically decreases BIS values. The target BIS and the resultant rate of anaesthetic administration is dependent on the phase of the anaesthetic. During the maintenance phase of the anaesthetic, the target BIS is usually between 40 and 60, depending on physiological and surgical factors. During emergence, the BIS values are expected to increase towards recovery values or baseline pre‐induction values.

Case report

To illustrate the importance of appropriate anaesthesia during a potentially painful procedure, we report a case of a 74‐year‐old male with LIS in which we used BIS monitoring. The patient had multiple comorbidities (Table 1 Pertinent Patient History and Clinical Data) and presented to the medical centre for surgical debridement of his sacral pressure ulcer (Figure 4). Adequate debridement is an important component of wound bed preparation as it improves the chance of wound closure 9. Furthermore, pressure ulcers also need to be debrided and cultured for targeted antibiotic therapy to decrease the risk of osteomyelitis and sepsis 10.

Table 1.

Pertinent patient history and clinical data. © O’Neill and Ayello 2012.

Past Medical History: Hypertension (HTN), brainstem stroke in 2008 that led to quadriplegic (post CVA) and ‘locked‐in‐syndrome (LIS)’, colon cancer, glaucoma. One year prior to this admission had acute renal failure secondary to antibiotics requiring haemodialysis for several months, peripheral vision loss and dysphagia.

Past Surgical History: In 2009 had Colostomy, PEG and Trachestomy

Medications: Current medications include the following: heparin‐injection 5000 units subq q12, Proventil (albuterol) 3 ml via SVN q12h, Beneprotein Powder daily, Reglan (metoclopramide) 10 mg IVPB q6h, multivitamins oral liquids 5 ml daily

Allergies: No Known Allergies

Figure 4.

Initial presentation of sacral pressure ulcer. © O’Neill and Ayello 2012.

Pre‐operative evaluation

The anaesthesia team was consulted pre‐operatively since his spouse had concerns about pain management. The patient's wife was particularly concerned about his treatment while he had his eyes closed, as this was when nursing would often treat him as though he were asleep. The wife claimed to know when the patient was awake or asleep based on facial movements.

After a discussion with his spouse and evaluating the patient, the anaesthesia team developed a plan to use the BIS technology to assure that the patient would have the sacral pressure ulcer surgery under a hypnotic anaesthetic state. We showed that he could be both awake or asleep, but most importantly, he could be awake with his eyes closed (Figures 5, 6, 7).

Figure 5.

Sleeping with eyes closed. © O’Neill and Ayello 2012.

Figure 6.

Awake with eyes open. © O’Neill and Ayello 2012.

Figure 7.

Awake with eyes closed. © O’Neill and Ayello 2012.

Part of the implementation of the plan was the necessity of educating the bedside nurses on the surgical unit about the use of BIS in the patient's management.

A BIS sensor was placed on the patient for a 2‐h observational time frame to show that there was electrophysiological evidence of him being awake. In addition, we attempted to associate the BIS values with behaviour such as eye opening. The BIS numbers fluctuated from 50 to 90 during this period. This observation suggested that without anaesthetic drugs, the patient had some sleep–wake cycling. There were periods of ‘high’ BIS values (over 70) and open eyes (Figure 6). There were periods of ‘low’ BIS values (under 70) and eyes closed (Figure 5). Interestingly, there were periods of high BIS with eyes closed (Figure 7). This shows that the patient could be awake with his eyes closed, as the wife suggested. Normally, eye lids are closed when one is sleeping assuming normal eyelid, orbicularis oculi muscle and facial nerve function. The case of eyes open with low BIS has not been observed in this patient.

Operative course

In the operating room, BIS with EMG trending monitoring was performed in addition to the routine monitoring as recommended by the American Society of Anesthesiologists (ASA). A balanced anaesthesia (intravenous and inhalational) via tracheostomy was given and BIS values were maintained between 40 and 50. This anaesthesia technique has been described in the literature in more detail 11, 12. Once a hypnotic state was accomplished, sharp surgical debridement was performed with patient in the lateral position. Specimens were sent for pathology and microbiology. Haemostasis was obtained and a dressing was applied prior to his transfer to the recovery room without any intraoperative complications.

Postoperative course

After surgery, the patient was transferred to the post anaesthesia care unit (PACU) before going to a postoperative step down unit (SDU). The BIS monitoring was used briefly in the PACU to improve the understanding of the staff about the concept of LIS.

The nurses were instructed to treat the patient as though he were awake especially when the BIS values were over 70 regardless of whether his eyes were open or closed. His vigilant wife appreciated the effort of the staff to understand the patient's neurological disability and to show empathy in the care of her spouse. Both the wife and the nurse made observations of his BIS values and how they were influenced by social interactions at the bedside.

Discussion

LIS prevents motor and verbal expression, but still allows sensory input. As can be expected, this chronic condition is one of the most dreaded neurological syndromes. In recent years, there has been media attention paid to LIS, with movies such as ‘The Diving Bell and the Butterfly’ receiving international acclaim. However, despite raising awareness of this condition, health care staff may not be knowledgeable about the best protocol to treat a patient with LIS. In this case report, one of the wife's greatest concerns was that health staff often did not treat her husband with the constant care he required, and would often incorrectly treat him as though he were asleep, even though sometimes he was actually awake.

General anaesthesia can pharmacologically create a condition similar to LIS. The use of neuromuscular blockade without adequate hypnotics and analgesics can result in a patient who moves in a state of paralysis, but has sensation. For the patient, this is a horrifying experience, as it is comparable to vivisection. The risk of awareness under general anaesthesia is about 1 in 1000 and BIS can be used to minimize this risk.

Originally, BIS was used in critical care units to aid with sedation 13. Although there are guidelines for BIS monitoring quantitatively, BIS values need to be interpreted in the context of the procedure, pharmacology and measurement limitations (artefacts). Perception of intraoperative painful stimuli during anaesthesia was compared using somatosensory‐evoked potential index (SSEP) and bispectral (BIS) index 14. The effect of pain on SSEP and BIS during anaesthesia can be correlated 15. Thus, BIS is commonly used to ensure amnesia, and has been studied using a process‐dissociation procedure to analyse memory formation during anaesthesia 16.

For years, anaesthesiologists have been administering general anaesthesia without the ability to measure the neuroelectrophysiology on a consistent basis. Consequently, anaesthesia providers relied on their clinical judgement, rather than monitoring to estimate the depth of anaesthesia 17. Different levels of sedation are associated with measureable changes in auditory event‐related potentials, bispectral index and entropy 18. When patients have their eyes closed, especially in the presence of neuromuscular blockade, the anaesthesia provider wants to know whether the patient is actually sleeping 19. The tibial pressure pain effect on BIS can be abolished by propofol–remifentanil in anaesthetic doses 20. The contrast of nociceptive flexion reflex and BIS as monitors can be used to compare various anaesthesia protocols 21. More research regarding the use of BIS and other monitors could help clarify some of these questions.

Key knowledge acquired from this clinical experience can be found in Table 2. This case presented the opportunity to use the BIS for a non‐anaesthetic purpose. We demonstrated to the staff that the patient with LIS varies from an asleep state to an awake state, and should be treated with appropriate care at all times. In addition, the BIS, EMG and eyelids respond to both verbal and tactile stimulus. The BIS monitor served as a staff education tool to improve the understanding of an unusual neurological disability (LIS). BIS and EMG trending patterns in the absence of neuromuscular blockade in operating room can be used to help guide the use of hypnotics for sleep and opioids for analgesia; therefore, we chose to use BIS as an adjuvant to clinical assessment for postoperative analgesia.

Table 2.

Patient‐centred concerns for locked‐in‐syndrome (LIS). © O’Neill and Ayello 2012.

1. Patient‐centred care focuses on the patient and family concerns and needs throughout the hospitalization.

2. Do not make assumptions that an unresponsive patient does not feel pain.

3. Control of pain during and after surgical procedures needs to be considered in the plan of care.

4. Bispectral (BIS) monitoring with drug titration is one of the options for providing pain relief during sharp surgical debridement.

5. Communication and education of staff regarding use of BIS monitoring and LIS issues improves patient care.

Conclusion

The experience with BIS has been promising. The perioperative use of BIS especially in patients with LIS requires staff education and clearly defined protocols. As a further benefit, BIS monitors are financially very affordable. This simple system of monitoring may prove to be cost‐efficient over the long run, and allow for a better understanding about the needs of patients with LIS. Patient‐centred needs were met with the help of BIS technology. BIS allowed the staff to address the patient‐centred concerns (as expressed by his wife), of pain during surgical debridement and postoperative analgesia even though he had LIS.

Acknowledgements

The authors acknowledge Lisa Draghi, PA, Faymarie Hall, PA, Tamar Stone, PA, Tobin Thomas, PA, Amelia McCafferty, RN, Nadia Sohan, RN, Thomas J. J. Blanck, M.D., Ph.D., and Andrew Rosenberg, M.D for their help.

This work was supported by a grant from the National Institutes of Health, R01 LM008443 04.