Conscious sedation for awake craniotomy in intraoperative magnetic resonance imaging operating theater

Abstract

This case report describes the first case in intraoperative magnetic resonance imaging operating theater (iMRI OT) (BrainSuite®) of awake craniotomy for frontal lobe glioma excision in a 24-year-old man undergoing eloquent cortex language mapping intraoperatively. As he was very motivated to take pictures of him while being operated upon, the authors adapted conscious sedation technique with variable depth according to Ramsey's scale, in order to revert to awake state to perform the intended neurosurgical procedure. The patient tolerated the situation satisfactorily and was cooperative till the finish, without any event. We elicit in this report the special environment of iMRI OT for lengthy operation in pinned fixed patient having craniotomy.

INTRODUCTION

Intraoperative mapping of intended areas of brain resection constitutes an essential part of modern neurosurgery. It was found that intraoperative stimulation of near speech and motor regions may prevent unnecessary nervous tissue damage.[1–3] Furthermore, using neuronavigation and intraoperative magnetic resonance imaging (iMRI) allows maximum resection of the tumor and compensates for brain shift as the surgery progresses.[4,5] This procedure requires an awake, cooperative patient to assess motor and verbal responses. Sometimes, the patient may be not cooperative during this procedure due to psychological profile or extreme fear from the notion of being awake during surgical intervention while the skull is fixed and then opened. This report describes the author's experience with an awake craniotomy on a man who was motivated to be subjected to awake technique before and during testing language mapping under conscious sedation from start to the end of the surgery.

CASE REPORT

A 24-year-old male (weight: 69 kg; height: 168 cm) presented to the Neurosciences Center at King Fahad Medical City (KFMC). He complained of one sudden episode of seizure, for which a brain computerized tomography (CT) scan was done, which revealed a left frontal lobe tumor. An awake craniotomy was planned including intraoperative brain mapping, for resection of epileptogenic foci close to eloquent cortex, i.e. motor and speech areas of the brain, for language and motor function.

Preoperative assessment showed that the patient was a smoker of 20 cigarettes a day. Medically, he was known to have mild intermittent bronchial asthma for which he was on treatment with β2 agonist (salbutamol nebulizer).

On examination, the patient was conscious, oriented to place, time and dates, alert, with no signs of limbs weakness or speech abnormalities. He was informed by the speech specialist and surgeon all about the expected operation and his role to reduce and prevent any side effects. Emphasis was given on the point that he was going to be awake during testing and he would have two to three sessions of iMRI. Anesthesiologists answered all the questions regarding pain and sedation and were present beside him throughout the operation. He was very excited about being operated upon in BrainSuite® theater. He requested to have his pictures taken during the procedures and he gave his consent to use it for medical publications.

No preoperative medication was prescribed. His vitals were: HR 80 beats/minute, RR 20 beats/minute, SPO₂ 97% room air, BP 130/80 mmHg, temperature 36.9°C. Laboratory investigations were all within normal ranges.

In intraoperative magnetic resonance imaging operating theater (iMRI OT), intravenous line was established. Standard monitoring was initiated (ECG, NIBP, skin temperature and pulse oximetry). The patient was placed in supine position. Oxygenation, while breathing air, was enriched through a nasal oxygen catheter that was delivering at a rate of 2 l/minute. Conscious sedation was maintained with continuous infusions of Propofol (20–40 μg/kg/minute) and Fentanyl at the rate of 2 μg/kg/hour infusion rates.

Depth of sedation was adjusted by the attending anesthesiologists according to the patient's comfort, hemodynamic and respiratory parameters, and was kept at 2-4 Ramsay's sedation scale.

Scalp block was established with the use of 80 ml of 0.125% bupivacaine and 5 μg/ml of adrenaline, by the surgeon.

MRI environment would dictate strict obedience to instruction and adherence for MRI compatibility.[5,6] All protective measures were taken in order to make the patient comfortable and to prevent damage during MRI procedures. Ear plugs as well as head shield coil were used.

Three MRIs were planned. Critical care was taken when the operating table top was moved to and from the MRI tube.

Within the same week of the surgery, baseline full language and cognitive-linguistic assessments were done. The patient showed normal receptive and expressive language skills along with normal cognitive-linguistic skills. Additionally, a trial of intraoperative assessment using picture naming task (50 pictures or more) was done on the day of operation.

Speech-language pathologist (SLP) coordinated with the neurophysiologists and neurosurgeons regarding the timing and type of stimulation. During surgery, the patient was asked to perform counting (regularly from 1 to 10 over and over) and provide naming (proceeded by the carrier phrase “this is a”). The two tasks were used to identify the essential language sites known to be inhibited by stimulation. SLPs were observing for any disturbance in language functions during the stimulations and alerting the surgeon. During the tumor resection, the patient continued to count and/or name pictures when the resection became closer to the subcortical language structures.

The patient was assessed 2 days post surgery by the SLP using the same language and cognitive-linguistic assessment tools that were used preoperatively. Assessment showed intact receptive and expressive language skills.

DISCUSSION

The iMRI OT is newly established at KFMC. Two years have passed and various difficult neurosurgical operations have been done with great success. Awake craniotomy was done to benefit from iMRI and navigation facilities[4,5]

Figures demonstrate surgical preparation of the patient under conscious sedation and skull block positioned on the table [Figure 1] and the surgical incision from surgical side [Figure 2]. The other part is protecting the patient hearing [Figure 3] and head [Figure 4] before entering MRI tube. This to protect patient from the high noise and from possible effect of magnetic power which may attract flying metal objects in high speed toward the patients. [see Table 1]. The patient after been prepared and connected to rourine monitors is ready to enter MRI tube monitored by anesthesiologist radiologist and anesthesia technologist using specialy designed magnetic compatable surgical table top railed into the tube. [Figure 5]

Figure 1.

The patient after scalp block and under conscious sedation pinned to the table and draped ready for craniotomy

Figure 2.

Scalp incision under scalp block and conscious sedation

Figure 3.

Patient's ears are plugged with earphones with recitation of quran, as he requested to help him cope with iMRI noise

Figure 4.

Patient's head covered with head shield (coil) after ears are plugged with earphones with recitation of quean as he requested to help him cope with iMRI noise. The airway is protected by keeping the patient in conscious sedation (natural airway)

Table 1.

The key components of the BrainSuite iMRI

Figure 5.

Patient's movement carried on surgical table top, to and from MRI tube, with extreme care for connected monitored and intravenous lines. One of the authors [FS] is pictured in the far right caring for the patient

iMRI will be done before and as many time needed to check the precision of tumor surgical excision. [Figure 6a and b]

Figure 6.

(a) Pre operative (preop.): Left frontal lobe mass lesion, low signal in T1 WI, and High signal intensities in T2 WI , with homogeneous enhancement and necrotic area in Post Gad T1 WI. (b) preop. Left frontal lobe mass lesion showed high signal intensities in T2 W Image. (c) preop. Left frontal lobe mass showed Inhomogeneous enhancement and necrotic area in Post Gad T1 W image. (d) Post Operative (post op.) Left frontal surgical cavity (Enchephalomalaxia) at previously . (e) post op. Left frontal surgical cavity (Enchephalomalaxia) at previously removed frontal lobe mass showed high signal intensity (CSF intensity) in T2 W image. emoved frontal lobe mass showed low signal intensity (CSF intensity) in T1 W image. (f) post op. Left frontal surgical cavity (Enchephalomalaxia) at previously removed frontal lobe mass with minimal linear enhancement in post GAD T1 WI represent reactive enhancement without residual mass.

The surgeon would operate with the advantage of dynamic imaging navigation, allowing maximum tumor tissue resection with avoidance of brain tissue shift effect, which is experienced in brain surgery. The updated pictures are projected on wall-mounted huge satellite screens placed in front of the surgeon and his assistants.[1]

Surgical team operates outside the effect of MRI influence but they should observe MRI compatibility code.[6] Operating inside this environment necessitates adaptation of MRI compatibility and other anesthesia technique adjustments [Table 2].

Table 2.

Issues of concern to anesthesia staff in iMRI OT

Awake craniotomy for seizure foci resection is currently popular since it allows a complete resolution of seizure foci without increasing neurological deficit.[3–5] This requires “asleep, awake, asleep” anesthesia technique to keep an awake, comfortable patient who cooperates with intraoperative testing.

Anesthetic drugs are selected according to their short half-lives and ease of titration. The selection of Propofol and Fentanyl was based on earlier reports on its success. Using such drugs concurrently can cause powerful respiratory depression.[3,6] Neuroanesthesia team should be vigilant for events such as hypoventilation, apnea, and chest wall rigidity.

Several options are available for airway management during awake craniotomy including endotracheal intubation with endotracheal tube (ETT), laryngeal mask airway (LMA), nasal airway and non intubation technique preserving natural airway. In SLP, verbal response is important so ETT and LMA are avoided

Adverse events during an awake craniotomy can include nausea, intraoperative anxiety, seizures, and brain engorgement.[7,8] Nausea and/or vomiting may result in significant morbidity. The latter risk was reduced by ranitidine, ondansetron, metoclopramide, dexamethasone, and glycopyrrolate administration. Appropriate patient selection is critical to success. In this case, the patient was ideal for the technique. Nevertheless, a detailed preoperative explanation of the anesthesia plan was important for the operators to go ahead. Efforts were focused on reassuring the patient, followed by supplementation of sedo-analgesics regimen. Most importantly, it was explained to the patient that there would be no pain when he would be subjected to testing.

The anesthesia team should always keep in mind that intraoperative urgent intubation is technically difficult and slow to secure in the case of seizures. Although it did not happen in this case, the team should be ready with the plan for controlling it swiftly, i.e. surgeon's application of ice water irrigation if operative field and discontinuation of stimulation, administration of anticonvulsants intravenously, and if respiratory instability occurs, intubation and controlled ventilation.[7,8]

In conclusion, with a careful approach by supporting the psychological aspects and motivating the patient in order to tolerate the procedure, the current analgesia and anesthesia techniques during awake craniotomy can be adjusted quickly to a controlled operative time. This case may open the avenues to operate on a cooperative patient in Brainsuite environment.