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  Table of Contents 
Year : 2016  |  Volume : 17  |  Issue : 2  |  Page : 58-61

Entropy-guided use of a unique cocktail in awake craniotomy

Department of Anesthesia, Rajiv Gandhi Cancer Institute, Rohini, New Delhi, India

Date of Submission23-Mar-2016
Date of Acceptance28-Jul-2016
Date of Web Publication16-Dec-2016

Correspondence Address:
Dr. Soumi Pathak
Flat No. 6, Kamdhenu Apartment, Rohini, New Delhi - 110 085
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-0311.193100

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The major benefit of awake craniotomy is to enable a tailored resection that can theoretically maximize the extent of the tumor resection and can minimize the neurological damages. There is still no consensus as to the best anesthetic technique. We describe here a case report where a combination of propofol infusion and dexmedetomidine along with intermittent doses of fentanyl, and fentanyl patch was used with entropy monitoring to assess the depth of sedation in a patient for awake craniotomy.

Keywords: Awake craniotomy, dexmedetomidine, entropy, propofol

How to cite this article:
Chowdhury I, Pathak S, Bhargava A K, Bhatia S. Entropy-guided use of a unique cocktail in awake craniotomy. Indian Anaesth Forum 2016;17:58-61

How to cite this URL:
Chowdhury I, Pathak S, Bhargava A K, Bhatia S. Entropy-guided use of a unique cocktail in awake craniotomy. Indian Anaesth Forum [serial online] 2016 [cited 2023 Jun 1];17:58-61. Available from: http://www.theiaforum.org/text.asp?2016/17/2/58/193100

  Introduction Top

Awake craniotomy is commonly indicated for procedures that require awake functional cortical mapping, where the lesion is located in proximity to the eloquent cortical tissues that are indispensable for defined cortical functions. The motor, sensory, visual, and language cortex have been successfully mapped during awake craniotomy. Anesthetic goals are to maintain an awake, cooperative, and comfortable patient who is pain-free and hemodynamically stable. Various institutions and anesthesiologists have their own preferred techniques for awake craniotomies, including scalp block, conscious sedation, asleep-awake-asleep (AAA) techniques, and asleep-awake techniques. There is still no consensus as to the best anesthetic technique.[1],[2] Commonly used anesthetic agents are propofol, fentanyl, and remifentanil, and more recently, the alpha-2 agonist dexmedetomidine has gained popularity for use in awake craniotomy owing to its unique analgesic property, less disinhibition, and minimal respiratory depressant effects. However, additional studies are necessary to optimize the procedure, reduce complications, and improve patient tolerance.

We describe here a case report in which a combination of propofol infusion and dexmedetomidine along with intermittent doses of fentanyl, and fentanyl patch was used with entropy monitoring to assess the depth of sedation in a patient for awake craniotomy.

  Case Report Top

A 34-year-old 68 kg female patient presented with complaints of continuous headache over the vertex region of 6 months duration. The headache was of throbbing and non-radiating in nature which worsened on bending forward and progressively increased in severity and was associated with vomiting and vertigo. The patient reported some relief with analgesics. She did not complain of any visual disturbance. There was no history of alcohol or drug abuse, chronic pain disorders, low tolerance to pain, and anxiety or psychiatric disorders. Her physical examination was normal with no focal neurological deficit or features suggestive of increased intracranial tension. The ophthalmological evaluation did not reveal any visual field defect and fundus was normal. On examination, the airway was categorized as modified Mallampati Class I with adequate mouth opening and neck extension. Computed tomogram (CT) scan [Figure 1] of the brain revealed an infiltrating tumor of the fronto parietal lobe and corpus callosum with midline shift of 6 mm. [Figure 2] showing midline shift due to tumor. She was posted for awake craniotomy as the tumor was very near to the motor area. All her blood investigations were normal. A day before the surgery, she was given realistic description of the entire procedure, expected discomforts, level of cooperation desired, tasks that must be performed, and possibility of adverse event that was explained. The sounds (monitor alarms, cranial drilling, elektroknife, ultrasonic surgical aspirator) that may be heard or discomforts of unchangeable position were also explained to her. On the day of surgery, a fentanyl patch (DURAGESIC-50® Transdermal patch) was applied on her upper chest at 6 am. She was given alprazolam 0.25 mg along with ondansetron 2 mg, 1 h before shifting to the operation theater. Airway devices, local anesthetics, sedative drugs, and other medications were made easily available for adverse events. The operating room temperature was optimized; the surgical table was covered with soft, thick dressing, and the surgical team was instructed to speak and move only if necessary.
Figure 1: Transverse section

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Figure 2: Coronal section

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In the operation theater, the patient was calm and all monitors were applied. Her pulse was 82/min and her blood pressure was 140/90. After taking an intravenous access, 1 mg midazolam, 8 mg dexamethasone, 1 g paracetamol, and 100 ml mannitol intravenous were given. Entropy (Datex-Ohmeda S/5, Helsinki, Finland) [Figure 3] electrodes were applied on her forehead after cleaning with ether and the initial value was response/state entropy (RE/SE): 90/70. Dexmedetomidine infusion was started at 1 μg/kg for 20 min and then was decreased to 0.2 μg/kg/h. Propofol infusion was started at the rate of 20 mg/h. She was given a bolus 30 mcg of fentanyl and six nerves were blocked bilaterally to completely anesthetize the scalp (supratrochlear, supraorbital, zygomaticotemporal, auriculotemporal, and lesser and greater occipital nerves) using 30 ml of 0.25% bupivacaine in an anterior band block from the supraorbital ridge to the anterior of tragus of the ear. The incision line was infiltrated with 1% lignocaine with adrenaline 30 ml. She had mild discomfort during the scalp block, for which we increased the propofol infusion. Central line was inserted, radial artery cannulation was done Her head was placed on a soft ring, oxygen was given by nasal prong, and a carbon dioxide sampling catheter was applied below the nostril which gave the respiratory rate along with EtCO2 . The patient with tape was catheterized for urinary output monitoring. The temperature was maintained using warm blanket. Cleaning and draping were done in such a way that her face and jaw were accessible all the time. During the raising of the bone flap, her RE/SE rose to 90/80 which was settled with 30 mcg bolus of fentanyl and 20 mg bolus of propofol and the dexmedetomidine infusion was increased to 7 ml/h (0.467 mcg/kg/h) and propofol was increased to 12 ml/h (48 mg/h). To allay the slight discomfort of the patient, a bolus of propofol was given just before dural incision. The details of propofol and dexmedetomidine infusion and the patient's hemodynamic response are given in [Table 1] and [Figure 4]. Arterial blood gas done at 1st and 2nd h was normal. As the resection proceeded in a relaxed brain and the surgeon asked her to move her right leg and right arm at the interval of 15-20 min, at these times she promptly followed the commands without us having to discontinue or decrease any of the infusions. At the fourth time, however, she was not able to fully lift her hand and further surgical resection was discontinued. The total duration of the surgery was 2 h. Dexmedetomidine was discontinued at skin closure, and propofol infusion was tapered and discontinued after dressing. Her postoperative period was pain-free and uneventful. Her follow-up CT scan showed a small clot at the tumor bed. She was discharged after 3 days after she had regained full power in her right hand and she did not recall any intraoperative event.
Figure 3: Entropy electrodes

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Figure 4: Haemodynamic, entropy and propofol infusionrate

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Table 1: Haemodynamic, entropy, propofol and dexmeditomidine infusions rate at different interval time

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  Discussion Top

The awake craniotomy technique was introduced for surgical treatment of epilepsy and has subsequently been used in patients undergoing surgical management of supratentorial tumors, arteriovenous malformation, deep brain stimulation, and mycotic aneurysms near critical regions of the brain.[1],[2],[3] This approach aims to maximize lesion resection while sparing important foci such as the motor, somatosensory, and language areas, and preventing functional disabilities with less postoperative morbidity, lesser Intensive Care Unit stay, and thus facilitating early discharge from the hospital, with a better prognosis and improved quality of life. It is also associated with lesser utilization of resources and greater patient satisfaction. One of the recent large populations of cohort study involving 575 patients showed that awake craniotomy was associated with higher total gross resection rate and fewer permanent neurological deficits as compared to tumor resection under general anesthesia. The primary goal of an anesthetist is to make the operation safe and effective while reducing the psychophysical distress of the patient. Many authors have described different protocols for anesthetic care during awake craniotomy based on Monitored Anesthesia Care (MAC) or general anesthesia (the so-called AAA technique), but none of these techniques have any demonstrated advantage over other. Careful patient selection is one of the major components of successful awake craniotomy. The selection should be individualized and based on the airway assessment, risks of sedation failure, patient's cooperation, and the risks of intraoperative surgical complications such as bleeding. A history of alcohol or drug abuse, chronic pain disorders, low tolerance to pain, and anxiety or psychiatric disorders are known risk factors for sedation failure. The selection of patients presenting with seizures or mixed dysphasia, having a history of using multiple anticonvulsants or undergoing perioperative loading of phenytoin is associated with the loss of intraoperative cooperation and results in failed awake craniotomies.

The requirement regarding the depth of anesthesia varies markedly at the different stages of surgery. Oversedation may lead to apnea, hypoxemia, hypercapnia, and cerebral swelling, whereas undersedation may result in agitation, arterial hypertension, and tachycardia. Avoidance of hypercapnia and hypoxemia, adequate cerebral perfusion pressure and brain relaxation, may not be easily achieved in awake craniotomy patients with uncontrolled airways. Adequate local anesthesia can usually be achieved either using a scalp block or using a regional field block.

In our case, entropy-guided MAC was administered using dexmedetomidine and propofol infusions with intermittent bolus of fentanyl and propofol.[4] The patient had entropy values of RE/SE of 65/55 throughout the resection period and rising to RE/SE of 85/70 when she was given command to move her arm. Dexmedetomidine is a highly selective alpha-2 agonist with a short half-life. It has sedative, analgesic and, anesthetic sparing effect without respiratory depression. This combination provided analgesia and hypnosis level which was guided by entropy. During periosteum elevation and dura incision, the entropy rose to RE/SE of 98/89 and which was managed with bolus fentanyl and propofol.

Spectral entropy[5] is able to discriminate between the level of wakefulness and surgical anesthesia. Entropy monitoring is based on acquisition and processing of raw electroencephalogram and facial electromyography. Rath and Prabhakar had used entropy, but their patient entropy values had fallen below RE/SE of 48/46 resulting in respiratory depression, and they also had to discontinue propofol infusion before awaking their patient during surgery. In our patient, the entropy values correlate well with the hypnotic component of anesthesia and guided us in balancing our sedation level. The analgesic property of dexmedetomidine[6] along with the hypnotic component of propofol provided us a perfect level of sedation with the entropy values never falling below RE/SE of 60/50. There was no seizure, hypertension, or loss of patient cooperation. The total dose of intravenous fentanyl was 100 mcg. We had also placed a fentanyl patch 50 μg on the patient's right shoulder which reduced the total analgesic requirement. There was no postoperative headache, nausea or vomiting. There was transient neurological weakness in the right arm, which also recovered after 24 h. Although 30% of patients recall considerable pain, our patient had no recall. GE sensor entropy strips are now available, in which all the electrodes are separate and thus have the flexibility in their placement.

  Conclusion Top

Awake craniotomy can be a very well-tolerated procedure provided a proper patient selection, proper planning, strict monitoring; utmost vigilance and meticulous combination of hypnotic and analgesic agents are done. Thus, we conclude that dexmedetomidine and propofol infusion along with fentanyl gave a perfect entropy value and depth of anesthesia for awake craniotomy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Piccioni F, Fanzio M. Management of anesthesia in awake craniotomy. Minerva Anestesiol 2008;74:393-408.  Back to cited text no. 1
Chui J. Anaesthesia for awake craniotomy: An update. Rev Colomb Anestesiol 2015;43 Suppl 1:22-8.  Back to cited text no. 2
Kallapur BG, Bhosale R. Use of dexmedetomidine infusion in anaesthesia for awake craniotomy. Indian J Anaesth 2012;56:413-5.  Back to cited text no. 3
[PUBMED]  Medknow Journal  
Hans P, Bonhomme V, Born JD, Maertens de Noordhoudt A, Brichant JF, Dewandre PY. Target-controlled infusion of propofol and remifentanil combined with bispectral index monitoring for awake craniotomy. Anaesthesia 2000;55:255-9.  Back to cited text no. 4
Rath GP, Prabhakar H. Spectral entropy monitoring in a patient undergoing awake craniotomy. J Neurosurg Anesthesiol 2007;19:144.  Back to cited text no. 5
Bekker AY, Kaufman B, Samir H, Doyle W. The use of dexmedetomidine infusion for awake craniotomy. Anesth Analg 2001;92:1251-3.  Back to cited text no. 6


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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