Anesthetic technique for awake artery malformation clipping with motor evoked potential and somatosensory evoked potential: A case report

Abstract

BACKGROUND

Awake craniotomy has been widely used for tumor resection, epilepsy surgery, deep brain stimulation, and carotid endarterectomy. The report on awake artery malformation clipping is rare, especially for anesthesia management.

CASE SUMMARY

A 62-year-old female diagnosed with malformation of anterior cerebral artery at the right side. We clipped the artery malformation with intraoperative neuromonitoring (IONM) in awake craniotomy. Spontaneous respiration was maintained throughout the procedure by nasopharyngeal airway during the surgery successfully.

CONCLUSION

The technique of monitoring anesthesia care can be performed successfully for the patient with IONM.

Key Words: Artery malformation; Awake craniotomy; Intraoperative neuromonitoring; Nasopharyngeal airway; Case report

Core Tip: In this case, due to the patient’s strong request for the integrity of motor function, the neurosurgeon explained the advantages and disadvantages of different surgery plans to her. This patient chose the awake craniotomy finally. Awake craniotomy was performed successfully in fully cooperative patient with stable neurological status.

INTRODUCTION

Awake craniotomy aims to minimize the risk of postoperative neurologic deficits. Over the last decades, awake craniotomy has been widely used for epilepsy lesions, glioma near the functional procedure. Awake brain mapping may facilitate resection with the preservation of functions such as speech and memory, that cannot be monitored in asleep patients. Few cases of awake craniotomy for intracranial artery malformation were reported. Awake craniotomy along with intraoperative neuromonitoring improve the treatment for artery malformation clipping. We present a case of awake artery malformation clipping with motor evoked potential (MEP) and somatosensory evoked potential (SSEP).

CASE PRESENTATION

Chief complaints

A 62-year-old female was treated in our hospital with malformation of an anterior cerebral artery at the right side.

History of present illness

The malformation of the right anterior cerebral artery was found by medical examination due to the patient complaining of numbness in the left upper limb and headache occasionally after being hit by a heavy object accidentally 8-mo ago.

History of past illness

The patient had no past history.

Personal and family history

The patient had no personal or family history.

Physical examination

The physical examination of the patient was normal.

Laboratory examinations

Preoperative blood biochemistry, electrocardiogram, chest X-ray were normal.

Imaging examinations

The brain computed tomography (CT) shows multiple nodular and stripy high-density shadows in the right frontal lobe and anterior cerebral falx. The magnetic resonance imaging (MRI) revealed A3 and A4 segment malformation of the right anterior cerebral artery before admission (Figure 1A and B). After the patient was admitted to the hospital, the patient was diagnosed with right anterior cerebral artery malformation by digital subtraction angiography (DSA) (Figure 1C and D).

Figure 1 The preoperative magnetic resonance imaging of head showing high density shade in right front lobe and next to cerebral falx. A: The axial magnetic resonance imaging (MRI); B: The sagittal MRI. The preoperative right internal carotid artery injection angiograms showing A3 segment malformation of the right anterior cerebral artery; C: Anteroposterior projection; D: Lateral projection.

FINAL DIAGNOSIS

The definitive diagnosis of this patient was the malformation of the right anterior cerebral artery.

TREATMENT

In this case, due to the patient’s strong request for the integrity of motor function, the neurosurgeon explained the advantages and disadvantages of different surgery plans to her. This patient chose the awake craniotomy finally. The written informed consent was obtained from the patient preoperatively. The electrocardiogram, noninvasive blood pressure, pulse oximetry, bispectral index (BIS) were monitored continuously. A Mayfield frame was used with ropivacaine prior to pin insertion. The patient was placed in a supine position comfortably.

Motor function was evaluated by the electrophysiologist preoperatively. Anesthesia was induced with propofol target controlled infusion of 2 ug/mL, remifentanil 0.02-0.04 ug/kg/min and dexmedetomidine 0.5 ug/kg/h. After the patient’s consciousness disappeared, a nasopharyngeal airway was placed to supply oxygen and monitor end-tidal carbon dioxide (Figure 2). The transcranial stimulating electrodes were placed for MEP and SSEP. Latency and amplitude of MEP and SSEP were recorded. Warning criteria for MEP and SSEP was a 10% increase in latency or a 50% decrease in amplitude as compared to baseline values.

Figure 2 Intraoperative photograph showing the patient positioned in supine position with head rotated to the left. She placed a nasopharyngeal airway.

Scalp nerve block including supraorbital nerve, auriculotemporal nerve, greater occipital nerve and lesser occipital nerve bilaterally, was performed with 0.2% ropivacaine 2 mL at each site for both perioperative anesthesia and postoperative pain. The neurosurgeon infiltrated the incision line with 0.2% ropivacaine 20 mL preoperatively.

According to various monitoring parameters, the dose was titrated to maintain BIS at 60 to 80, end-tidal carbon dioxide (E_TCO₂) at 35 to 50mmol/L, respiratory rate (RR) at 10-15 beats/min, heart rate at 50-100 beats/min, and mean artery pressure at 60 to 80 mmHg. Continuous intravenous infusion with propofol 1.4-1.6 ug/kg, remifentanil 0.02-0.04 ug/kg/min and dexmedetomidine 0.5 ug/kg/h maintained sedation during the pre-awake period. The dura mater was infiltrated with 1% lidocaine before incision.

Once the artery malformation was identified (Figure 3), all anesthetics were intermitted. After 10 min, the patient was brought into the awake stage with Observer’s Assessment of Alertness/Sedation 2. The motor and language examination were normal. Then temporary occlusion clips were used to isolate the distal end of lesion vessel one by one for clamping the supplying side of the artery. After the clipping of the artery, the patient communicated well. Intraoperative neurological assessment was done for contralateral motor functions in both upper and lower limb. The muscle strength and muscle tension of the proximal and distal lower extremities are symmetrical and normal. This patient was co-operative throughout the procedure. No neurological dysfunction was discovered for 30 min. All anesthetics were restarted. Neurophysiological monitoring showed that SSEP was normal and a slight decrease in MEP over 30 min. The indocyanine green angiography showed retrograde flow-induced fluorescein development in each corpus callosum artery branch after multiple isolated lesions. Then the temporary clamp was replaced by the final clipping, and the dilated and tortuous segments were removed. No complication occurred. The surgery lasts for 3 h.

Figure 3 The intraoperative finding: The dilated and tortuous segment of the right anterior cerebral artery.

Postoperative CT angiograph image confirmed the complete clipping of the artery malformation (Figure 4). There were no tortuous segments on DSA (Figure 5A and B), and no ischemic lesions on MRI (Figure 5C and D). The patient was treated with neurotrophic drugs postoperatively.

Figure 4 Postoperative computed tomography angiograph image: 3 clips used for aneurysm occlusion.

Figure 5 The postoperative right internal carotid artery injection angiograms showing no dilated and tortuous segment. A: Anteroposterior projection; B: Lateral projection. The preoperative magnetic resonance imaging (MRI) of head showing no ischemic lesions; C: The axial MRI; D: The sagittal MRI.

OUTCOME AND FOLLOW-UP

The patient was discharged without neurological deficits or other complications ten days after the surgery. The Modified Rankin Scale was 0. There was no psychological disorder for 1-year follow-up.

DISCUSSION

The incidence of pure arterial malformations is low. Pure arterial malformations have a benign natural history, and it was usually managed conservatively. Due to the rare incidence, the optimal treatment for pure arterial malformation is controversial[1]. In this case, the arterial malformation with many branches runs into the central cortex, which may affect the motor and linguistic function. Furthermore, based on the imaging data, arterial dissection can’t be completely ruled out. Considering to these factors, the surgeon finally decided that awake craniotomy may be the optimal choice for this patient.

Awake craniotomy is a reliable method of ensuring neural integrity during the excision of lesions located within or near eloquent areas. Furthermore, continuous clinical neurological monitoring can detect early deficits in the motor, sensory or language domains. Our team had rich experiences with awake craniotomy for brain tumors, but this was the first awake surgery for artery malformation clipping in our institute.

Cerebral artery malformation surgery may cause motor deficits due to brain blood flow insufficiency after clipping the artery malformation. Continuous infusion of remifentanil, dexmedetomidine and propofol has little impact on evoked potentials[2,3]. Irie et al[4] reported that the limitation of this monitoring technique is the false-negative MEP; four patients had postoperative hemiparesis without intraoperative MEP changes. Once ischemia occurs, MEP maybe not sensitive to the evaluation of movement[5]. It is reported that there is a potential advantage of awake artery malformation surgery in decreasing the risk of ischemic injury[6].

Anesthetic methods in awake craniotomy include monitoring anesthesia care (MAC) and asleep-awake-asleep (SAS)[7]. Both techniques can be performed successfully in awake craniotomy. The MAC technique uses low doses of sedative agents for conscious sedation, while maintaining the adequate depth of sedation and spontaneous ventilation. In contrast, the SAS technique uses higher doses of sedative agents to provide deep sedation. As reported, in most cases of SAS technique, laryngeal mask, even endotracheal tube is used to facilitate for mechanical ventilation[8]. Several studies reported that the MAC and SAS techniques produce similar comfort and perioperative outcomes for the patients[9].

The fixed head by headrest may be a potential risk of difficult airway, whether in the supine position or lateral position. It’s a severe challenge for the anesthesiologist to reinsert LAM or endotracheal tube intraoperatively. Maintaining airway patency is the key to improving the feasibility of artificial ventilation, especially in an emergency. Our case was accomplished with spontaneous breath by adjusting to the target concentration precisely.

The MAC technique may cause the risk of dose-dependent respiratory depression. BIS is recorded to monitor the depth of sedation. As we learned, propofol has dose-dependent depression in cardiovascular and respiratory system, while dexmedetomidine is beneficial for airway stability. Therefore, the combination of dexmedetomidine and propofol may reduce the dosage and side effects of drugs. As reported, propofol causes a reduction in tidal volume and an increase in RR[10]. In contrast, remifentanil can lead to a reduction in RR and a slight increase in tidal volume[11]. The combination of propofol and remifentanil contributes to a complex interaction in the respiratory system. Spontaneous respiration can be achieved successfully considering the interaction between the drugs[11,12]. Regional blocks are used for analgesia in awake craniotomy. Scalp nerve block and incision infiltration with ropivacaine perioperatively can make the patient obtain adequate analgesia, block the noxious stimulation, and reduce the adverse stimulation during the awaken period[13], to ensure higher awakening quality.

As Abdulrauf et al[6] responded, intraoperative aneurysm rupture can be observed under both awake craniotomy and general anesthesia[14]. Intraoperative hemodynamic variables are smoother in the asleep-awake-asleep group than in the general anesthesia group[15]. In addition, comparing to general anesthesia, awake craniotomy can release stress response, reduce median length of stay, and increase overall survival significantly in high-grade gliomas[16]. Therefore, the incidence of intraoperative arterial malformation rupture may be lower in awake craniotomy.

Intraoperative seizure is the most common cause for awake craniotomy failure, which is trigged by electrical cortical stimulation. The risk factors for seizure include stimulus length, current intensity, and the number of stimulations over the same cortical area. Intraoperative seizure can be easily control by ice saline and propofol, without permanent severe consequence[17]. This patient didn’t develop intraoperative seizure. Hence, awake craniotomy is safe for patient with arterial malformation.

CONCLUSION

The literature on awake artery malformation clipping is rare, especially for anesthesia management. In our case, anesthetic management with nasopharyngeal airway is safe and effective for awake artery malformation clipping with intraoperative monitoring. On the basis of mastering the basic skills, anesthesiologists use simple equipment and anesthetic drugs to perform the awake artery malformation clipping successfully. Although this scheme has some disadvantages, it can provide a reference for anesthesiologists in these patients, and its safety needs to be verified by large sample prospective clinical trials in the future.