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Anaesthesia for minimally invasive neurosurgery
Best Practice & Research Clinical Anaesthesiology Vol. 16, No. 1, pp. 81±93, 2002
doi:10.1053/bean.2002.0209, available online at http://www.idealibrary.com on
6 Anaesthesia for minimally invasive neurosurgery Neus FaÁbregas
MD, PhD
Anesthesiology Consultor, Anesthesiology, Associate Professor Anesthesiology Department, Hospital clinic, Universitat de Barcelona, Villarroel 170, 08036 Barcelona Spain
Rosemary Ann Craen*
MBBS, FANZCA, FRCPC
Associate Professor Department of Anesthesia, University of Western Ontario, London Health Sciences Center, 339 Windermere Road, London, Ontario, Canada N6A 5A5
Technological advances in imaging, computing and surgical instrumentation have encouraged the application of minimally invasive surgical techniques to various neurosurgical disorders. This chapter discusses the wide application of neurosurgery and the implications for anaesthesia, focusing on the speci®c anaesthetic considerations for neuroendoscopy, stereotactic procedures and radiosurgery. Key words: neuroendoscopy; stereotactic surgery; anaesthetic considerations; complications.
Over the last decade there has been a trend towards shorter, less invasive surgical procedures within every surgical discipline. In the neurosurgical arena, technological advances in imaging, computing, optics and miniaturization have encouraged the increasing trend to applying minimally invasive surgical techniques to a variety of neurosurgical procedures. The potential advantages include accurate localization of intracranial lesions, especially those in the eloquent areas of the brain or those usually inaccessible to conventional surgery, and the potential for less trauma to healthy brain, blood vessels and nerves. Neuroendoscopic procedures also have great advantages in dealing with tissue sampling and gross morphological analysis of ventricular and cisternal structures, tumour or infective lesions. In addition, the use of an endoscope avoids larger openings of intracranial or intraspinal spaces and this leads to other bene®ts such as shorter operating time, reduced blood loss, early recovery and discharge from hospital ± and with it greater patient acceptance and presumably improved neurological outcome. However, as with all minimally invasive procedures, there remains a potential for complications accompanied by intra or post-operative morbidity and mortality. The rapid developments of minimally invasive surgery have impacted on the neurosurgical and neuroanaesthesia care of neurosurgical patients. The anaesthesiologist must now provide a continuum of care from the radiology suite to the operating suite. From an anaesthesia viewpoint, the main goals in the management of *Author for correspondence 1521±6896/02/01008113 $35.00/00
c 2002 Elsevier Science Ltd. *
82 N. FaÁbregas and R. A. Craen Table 1. Neuroendoscopic procedures. Diagnosis
Surgical intervention
Non-communicating hydrocephalus Multiloculated hydrocephalus
Ventriculostomy (third ventricle) Ventriculo-peritoneal shunt manipulation ± ventricular tip placement Biopsy or tumour retrieval Removal or fenestration of cysts Ventriculostomy Cystocisternostomies (arachnoid cysts) Drainage Endoscopic trans-sphenoidal Endoscopic strip craniectomy Endocavitary syringostomy Third ventriculostomy Intra-operative visual monitoring Arthroscopic microdiscectomy Endoscopic foraminoplasty
Intraventricular brain tumour Cysts (arachnoid, colloid, intraparenchymal) Subdural haematomas, brain abscesses Pituitary pathology Sagittal craniosynostosis Syringomyelia Intramedullary pathology Spinal diseases
the neurosurgical patient remain the same: careful pre-operative assessment and planning, meticulous cerebral haemodynamic control to ensure adequate cerebral perfusion pressure, provide immobility and select an anaesthetic technique which allows for swift emergence from anaesthesia and neurological assessment. This chapter discusses the wide application of neuroendoscopy (Table 1) and the implications for anaesthesia, focusing on the speci®c anaesthetic considerations for neuroendoscopy, stereotactic procedures and radiosurgery.
BRAIN NEUROENDOSCOPY Uncomplicated non-communicating hydrocephalus, due to aqueductal stenosis or to space-occupying lesions of the midbrain or posterior fossa, is the main indication for endoscopic treatment in patients older than 1 year.1±3 The surgeon performs an endoscopic third ventriculostomy (ETV) by making a hole in the ¯oor of the third ventricle, thus allowing movement of the cerebrospinal ¯uid (CSF) out of the blocked ventricle and into the interpeduncular cistern to relieve the hydrocephalus. This procedure usually takes approximately 45 minutes. Success in terms of the procedure is generally considered to be the avoidance of a shunt in a patient who otherwise would have been shunted.4 Hydrocephalic paediatric patients, in particular, bene®t from ETV because they undergo repeat procedures as they grow with multiple shunt revisions.1 A common complication of the traditionally placed ventriculo-peritoneal shunt system is the obstruction of the ventricular catheter tip from adjacent tissue. A recent study found that ventricular catheter placement with the aid of a rigid ®bre-optic endoscope, oering visual con®rmation of the position of the tip, is a safe and ecient technique with improved accuracy over conventional methods.5 Selected intraventricular tumours may be removed completely via an endoscopic approach, thus avoiding craniotomies and brain retraction. The duration of the endoscopic procedures is usually shorter than expected with open microsurgery.6 The technique also allows biopsies of pineal region tumours as well as making an ETV in the same procedure.7,8 The endoscopic management of an arachnoid cyst is a safe and
Anaesthesia for minimally invasive neurosurgery 83
eective treatment option ± as is the resection of colloid cysts of the third and lateral ventricles.9±12 Strip craniectomy is the removal of a strip of bone containing a fused cranial suture for the treatment of cranial synostosis in the newborn and infants. The procedure itself can range from a simple strip craniectomy to cranial vault remodelling involving extensive scalp mobilization. As a result, these operations are associated with huge blood losses and venous air embolism. The introduction of the endoscope to assist strip craniectomies has led to a signi®cant reduction in blood loss and operative time and has reduced the incidence of venous air embolism.13,14 During transphenoidal pituitary surgery the use of the endoscope provides additional operative manoeuvrability.15 Endoscopic endonasal hemisphenoidotomy has been described for the resection of a pituitary lesion con®ned to the sella.16 Endoscope-assisted microsurgery for cerebral aneurysms has also been described.17 SPINAL NEUROENDOSCOPY Spinal endoscopy is not new, having been reported as early as in the l930s. Miniature endoscopes (1.2 mm) allow visualization of cysts and disc fragments. In syringomyelia, the ¯exible endoscope allows perforation of the septa under direct vision, allowing the communication of all chambers in a safe and non-traumatic way.18,19 Spinal endoscopy may be the diagnostic method of choice for epidural ®brosis.20 Arthroscopic microdiscectomy describes an endoscopic surgical technique that can be performed as an intradiscal discectomy or as an extradiscal (transforaminal) procedure. As in open discectomy, the goal is to resect the herniated disc fragments and decompress nerve roots. However, open laminotomy or laminectomy is recommended when intracanalicular compression is present.21 A microendoscopic posterior laminoforaminotomy is an eective alternative for the treatment of unilateral cervical radiculopathy secondary to lateral or foraminal disc herniation or spondylosis.22 Complications such as medulla-radicular irritation, bradycardia and respiratory depression in the awake patient have been reported, the latter events probably resulting from the large volumes of epidural ¯uid used (upwards of 1200 cc). Anaesthetic concerns include prone positioning, providing an immobile patient and rapid awakening to assess neurological function. However, some maintain that the safest way to do these procedures is to have the patient awake intra-operatively under light sedation.20,21,23 THE SURGICAL APPROACH IN BRAIN NEUROENDOSCOPY The ventricular system and the subarachnoid space of the brain and spinal cord provide suitable conditions for the use of an endoscope. A basic understanding of the surgical technique and instrumentation is essential for the anaesthesiologist in order to anticipate potential complications that may arise. Patient position for endoscopic entry into the third ventricle is usually supine with slight ¯exion of the neck, or with the head tilted from 458 to 908, depending on the planned procedure (Figure 1). The cranium may be ®xed in a head frame. Through a coronal burr hole, the endoscope is introduced into the ventricle system via the frontal horn and advanced to the third ventricle where the mammillary bodies, an important landmark, can been visualized. The tuber cinereum is located immediately beyond these structures. Beneath this membrane is the basilar artery and the basal
84 N. FaÁbregas and R. A. Craen
Figure 1. Operating room set-up during neuroendoscopy using a frame-less neuronavigation device.
cisterns. In patients with aqueduct stenosis, fenestration of this membrane creates an opening through which CSF can be drained, bypassing the aqueduct of Sylvius. Several methods have been described to create this fenestration, including the rigid endoscope, a blunt probe or the use of lasers. The opening is then futher dilated with a balloon catheter to ensure patency and to secure haemostasis. The endoscope, which has a channel for aspiration and a working channel through which a variety of instruments can be passed, is ®xed by an adapted articulated arm to avoid unexpected and hazardous movements. Operating in ¯uid-®lled cavities requires intermittent or continuous warmed (378C) irrigant ¯uid (either Ringer's lactate or normal saline) to maintain adequate ventricular pressure and good visibility. The ¯uid is usually infused under pressure (or may be gravity fed) and allowed to egress passively through an open port of the endoscope. Inadequate venting of the irrigant ¯uid will lead to marked increases in intracranial pressures. While increased intracranial pressure may be detected clinically by bradycardia and hypertension, we have found that these cardiovascular changes occur late.24 Early detection of inadequate drainage of intracranial ¯uid is crucial and is easily achieved by measuring the pressure within the endoscope. Toxic reaction such as high fever and headaches have been described due to meningeal irritation which can occur with large volumes of saline irrigation. Arti®cial cerebrospinal ¯uid (CSF without protein) has been used and reported to reduce the incidence of these toxic reactions.25 Surgical complications, such as acute increases in intracranial pressure, injury to brain structures, including the basilar artery and haemorrhage, have been described. Intracranial bleeding secondary to instrumentation can be catastrophic, especially if
Anaesthesia for minimally invasive neurosurgery 85
there is a delay in detection and treatment. Intracranial hypotension may follow sudden ventricular decompression and removal of cerebrospinal ¯uid causing pressure changes at the mid-brain and hypothalamus level. This in turn can lead to sudden alterations in heart rate and blood pressure. Hypothermia can occur, especially in small children, with the use of large volumes of irrigation and the wetting of drapes. Of the complications listed in Table 2, cardiac arrhythmias are the most frequently described. It is important to note that many of these arrhythmias are transient in nature and range from bradycardia, tachycardia, premature ventricular contractions, supraventricular tachycardias to asystole; they are due mainly to mechanical factors ± for example, stimulation of the ¯oor of the third ventricle with the endoscopic tip or inadequate venting of the irrigant, and will respond to nonpharmacological methods such as withdrawal of the endoscope or venting of the intracranial irrigant ¯uid. Signi®cant bradycardia, however, is more common in the paediatric population ± up to 41% in one series ± and may require the use of atropine or glycopyrrolate.26
ANAESTHETIC CONSIDERATIONS IN BRAIN NEUROENDOSCOPY The major goals are to provide an immobile patient during the procedure and rapid awakening immediately after the procedure to allow early assessment of neurological function and rapid detection of potentially reversible surgical complications. While some cases may be performed under local anaesthesia and sedation1,9 general anaesthesia with endotracheal intubation and controlled ventilation is preferred in order to ensure immobility and because sudden intracranial pressure changes may lead to vomiting. Nitrous oxide is avoided to prevent its eusion into air trapped in the ventricles and the subdural space following decompression of the ventricles. Although there are dierences between anaesthetic agents in terms of their eects on the central nervous system and intermediate outcomes, such as the quality of recovery, there is no evidence that the choice of anaesthetic agent or opioid supplement aects the neurological outcome.27 To date, no prospective randomized or retrospective study in neurosurgical patients has shown a superior patient outcome with one anaesthetic compared with another. Therefore, the decision to use a particular anaesthetic should be based on patient characteristics, intracranial pathology and the anaesthesiologist's familiarity with the agent to assure careful and appropriate use. However, in the presence of increased intracranial pressure, when propofol is used
Table 2. Intra-operative complications. Cardiac arrhythmia Haemodynamic variability Raised intracranial pressure Episodic intracranial circulatory insuciency Intracranial hypotension Haemorrhage (0.5±2%)4,28,41 Air embolism Hypothermia
86 N. FaÁbregas and R. A. Craen
there is a greater margin of safety over that of the volatile agents because propofol is a potent vasoconstrictor which reduces raised intracranial pressure. The type of monitoring depends on the procedure, the age of the patient and accompanying medical problems. In addition to standard monitors (electrocardiography, oximetry, capnography, neuromuscular blockade and body temperature monitoring) intra-arterial monitoring is recommended in view of the haemodynamic variability frequently seen and the need for arterial blood gas sampling. An exception would be in repeat and short ETV procedures in healthy paediatric patients. Intracranial pressure monitoring is invaluable because of the potential for sudden rapid increases in intracranial pressure. An easy way to do this is to measure the pressure inside the endoscope by connecting a ¯uid-®lled catheter from a stopcock located on the irrigation lumen of the neuroendoscope to a pressure-transducer which is zeroed at the skull base (Figure 2). Middle cerebral artery blood ¯ow velocity can be measured with a 2 MHz transcranial Doppler probe attached to the temporal window. This allows `real time' cerebral blood ¯ow to be monitored and allows for early detection of intracranial circulatory insuciency during the transient periods of high intracranial pressures which occur as a result of lack of adequate venting of the irrigating solution.24
POST-OPERATIVE COMPLICATIONS Endoscopic neurosurgical procedures are expected to be associated with a low rate of post-operative complications. However, as this is still a growing speciality, there are few publications on the incidence and type of complications. Table 3 lists the range of post-operative complications which can occur and which anaesthesiologists need to be irrigation solution camera and working channel
aspiration channel roller pump
pressure transducer
Figure 2. Schematic diagram demonstrating how to monitor pressure within the endoscope. A ¯uid-®lled catheter is connected by a stopcock located on the irrigation lumen of the neuroendoscope to a pressuretransducer which is zeroed at the skull base. Reproduced from FaÁbregas et al (2000, Journal of Neurosurgical Anesthesiology 12: 21±28) with permission.
Anaesthesia for minimally invasive neurosurgery 87
cognizant of as they can occur early in the post-anaesthestic care period. In a recently published review, Buxton et al28 quotes a directly attributable mortality rate in adults of 3% (endoscopic third ventriculostomies) and an overall mortality of 0.6% (all age groups and aetiology). The complication of delayed awakening is of particular concern to anaesthesiologists. Early detection and diagnosis (usually by CT) is imperative to exclude treatable causes such as intracranial haemorrhage. Our personal experience, however, indicates that a more common cause of delayed awakening may be due to the neuroendoscopic procedure itself. We found that intra- operative high peak pressures inside the endoscope, and not the length of navigation period, was associated with a delay in awakening.29 Close monitoring of serum electrolytes is recommended in neonates, especially in the acute post-operative period following EVT. The syndrome of inappropiate secretion of antidiuretic hormone (SIADH) has been described following EVT and is most probably related to supra-opticohypophyseal tract functional disruption.30
STEREOTACTIC PROCEDURES Stereotactic systems relate pre-operatively obtained computed tomography (CT) or magnetic resonance systems (MRI) to an extracranial reference system. The latter is achieved using either framed systems that require the application of a head frame, or frame-less systems. Using online image guidance systems, the surgical targeting of a lesion becomes more precise and can be accomplished through a small craniotomy opening. In particular, the technique allows for access to deep-seated lesions often inaccessible by conventional techniques. The presence of the head frame represents an obstacle to ready access to the airway (Figures 3 and 4). The frame, however, provides a directional and depth guide to surgical instrumentation. The newer systems involve `frame-less stereotaxy' with the use of scalp markers which act as ®ducial points to relate surgical instruments to the computer-generated image. A pair of cameras mounted above the operating ®eld provides a stereoscopic view of the surgical instrument to the computer, and the
Table 3. Post-operative complications. Delay in awakening (15%)41 Pneumoencephalus, pneumoventricle (2%)41 Convulsions Transient anisocoria (16%)41 Transient hemiparesis (6%)41 Haemorrhage (6%),41 cerebral infarction (1.5%)28 Transient fever, meningism Infection (1±9%)1,28,41 Short-term memory loss (4%)41 Diabetes insipidus (0.5±1%)4,41 SIADH Transient cerebrospinal leaks (1%)4 Chronic subdural haematomas (1.5%)4 Traumatic basilar aneurysm Hydrocephalus (6%)41 SIADH, secretion of antidiuretic hormone.
88 N. FaÁbregas and R. A. Craen
Figure 3. Patient in stereotactic frame undergoing a brain biopsy in the semi-recumbent position. This head frame prevents ready access to the airway.
surgeon is given a horizontal, sagittal and coronal view of the position of the tip of the instrument in the operating ®eld. CT- and MRI-guided intracranial procedures (stereotactic surgery) include needle and open biopsies of various lesions, including tumours, abscesses, implantation of depth electrodes and tumour resection. Functional stereotactic surgery refers to the use of stereotaxy in altering the function of the brain by either stimulating or ablating anatomical brain structures. In movement disorders such as Parkinson's disease, essential tremor, hemiballismus and dystonias, functional stereotactic ablation (pallidotomy, thalamotomy), or stimulation (subthalamic stimulation, globus pallidus stimulation) have been used eectively to control symptoms and signs.31 In the treatment of seizure disorders, there is renewed interest in using stereotaxy to either destroy the seizure focus, reduce the epileptogenic focus, or interrupt the pathways of
Anaesthesia for minimally invasive neurosurgery 89
Figure 4. Patient in stereotactic frame undergoing a brain biopsy in the semi-recumbent position. This head frame prevents ready access to the airway.
seizure propagation as a means of treating temporal lobe epilepsy.32 A variety of ablation techniques are available to the neurosurgeon.32 They have in common the potential to deliver a physical destructive force to ablate neural tissues and include mechanical and energy sources. In the past, heat, cold, wax and alcohol have been used. More recently radio-frequency lesioning has become popular. Lesioning is produced with a probe that utilizes a radio-frequency current causing ionic oscillations and temperature increases to 858C for 1±2 minutes in the target brain tissue. There is also a trend to the use of external ionizing radiation (stereotactic radiosurgery) such as is available with the gamma knife, linear accelerator and proton beam, and the insertion of radioactive seeds such as yttrium-90 as a source of brachytherapy. The gamma knife has been used successfully to treat acoustic neuromas,33 arteriovenous malformations,34 trigeminal neuralgia and other neuropathic pain syndromes.35
90 N. FaÁbregas and R. A. Craen
ANAESTHETIC CONSIDERATIONS FOR STEREOTACTIC PROCEDURES The anaesthetic management for stereotactic procedures begins outside the operating room. Therefore, the anaesthesiologist must be prepared to provide a continuum of care from the radiology suite to the operating room and, at the same time, provide optimal conditions for imaging, localization of the lesion and repeated neurological assessments. The patient's disease, the surgical procedure, the presence of a head frame and the surgeon's needs and expectations all dictate the choice of anaesthetic technique and agents. The presence of a space-occupying lesion with increased intracranial pressure precludes the use of drugs which depress respiration and increase the arterial carbon dioxide tension. Careful use of sedatives such as midazolam, in small aliquots, may be all that is necessary to provide adequate operating conditions. Non-pharmacological measures, such as ensuring good communication, providing constant reassurance and distraction, can signi®cantly reduce the need for sedation. Lesioning for patients with movement disorders, such as Parkinson's disease, preclude the use of drugs which may alter the degree of tremor and prevent patient participation necessary in target localization and the immediate observation of the eect of lesioning. These drugs include beta-blockers, droperidol, metoclopramide, benzodiazepines and clonidine.36 Propofol is also contraindicated as there have been reports that its use may illicit abnormal movements or may improve the tremor.37 The majority of stereotactic procedures is performed in an awake patient with little to no sedation. As the major complication of stereotactic surgery is intracranial bleeding, performing the procedure under local anaesthesia aords an additional degree of safety in that it allows for early detection and prompt treatment. The stereotactic frame is applied with the use of local anaesthesia either by regional nerve blocks (supra-orbital and greater occipital nerve blocks) or by subcutaneous in®ltration using 3±5 ml of 0.5% plain bupivacaine with a long 25-gauge needle.38 In some cases sedation may be needed initially for placement of the frame. General anaesthesia with endotracheal intubation may be necessary in the following circumstances: if the patient is very young, if the patient is confused and unable to cooperate or if the lesion is such that positioning would be dicult with the patient awake, for example in prone position. Standard monitors (electrocardiography, oximetry, capnography, body temperature) are usually applied and intra-arterial monitoring is not generally required. Intra-operative complications include injury of vital brain structures, intracranial haemorrhage (1±3%),39 seizure, venous air embolism and cardiac arrhythmias. Signs of intracranial haemorrhage may exhibit as a sudden change in conscious level, confusion or hemiparesis. Seizures are often self-limiting and focal but can also be grand mal ± necessitating rapid removal of the head frame. Venous air embolism can occur because these patients are commonly in a sitting or semi-recumbent position and may exhibit as a cough, complaints of chest pain or feeling of anxiety. The treatment includes prevention of further entrainment of air by packing with gelfoam and the use of the Trendelenburg position. Cardiac arrhythmias, especially bradycardia, can occur especially during stimulation of the amygdala and hippocampus regions of the brain.40 All of these complications underscore the fact that, although these procedures require little to no anaesthesia, there is a need for the presence of a vigilant anaesthesiologist to deal with the medical emergencies of the neurosurgically compromised patient.
Anaesthesia for minimally invasive neurosurgery 91
SUMMARY Improvements in imaging, computing, optics and miniaturization have encouraged the increasing trend of applying minimally invasive techniques to a variety of neurosurgical disorders. The potential advantages include accurate localization of lesions, shorter operating time, early discharge from hospital and, with it, greater patient acceptance and presumably improved neurological outcome. However, as with other endoscopic surgical techniques, there is a steep learning curve for neuroendoscopic procedures. The decision as to which approach is best for which lesion (operator- and patientdependent) can come only from long-term follow-up and large series, yet to come. Endoscopic third ventriculostomy in the treatment of hydrocephalus is the most commonly performed neuroendoscopic procedure. Patients presenting may range in age from newborn to geriatric. The most common intra-operative complication is transient arrhythmia caused mainly by mechanical factors. Inadequate venting of the irrigant ¯uid may result in sharp increases in intracranial pressures and this has been associated with a delay in awakening from anaesthesia. Monitoring intra-arterial pressure and intracranial pressure within the endoscope can provide valuable information and guide interventional therapy. Many stereotactic procedures are done on an awake patient with little to no sedation. However, careful pre-operative assessment is necessary to ascertain the extent of the disease process being treated and patient suitability. The anaesthesiologist must be prepared to provide a continuum of care from radiology suite to the Practice points . endoscopic third ventriculostomy in non-communicating hydrocephalus, at any age, is the main indication for endoscopic treatment in neurosurgery. A great number of other intraventricular procedures can be performed . general anaesthesia with endotracheal intubation is preferred for neuroendoscopies to ensure immobility and because sudden intracranial pressure changes may led to vomiting . nitrous oxide is avoided to prevent its eusion into air trapped ventricles and the subdural space following decompression of the ventricles . monitoring is the same as for a craniotomy. An arterial line is mandatory except in endoscopic third venticulostomy in paediatrics . the irrigation ¯uid needs to be warm and with electrolytes and osmolarity similar to CSF . early detection of inadequate drainage of intracranial irrigation ¯uid is crucial and easily achieved by measuring the presure within the endoscope . TCD continuous monitoring (temporal window : MCA) may distinguish situations with CBF impairment due to high intracranial pressure because of the inadequate venting or the irrigation ¯uid . cardiac arrhythmias is the intraoperative complication most frequently described. When a sudden bradycardia appears in a paediatric patient, alert the surgeon to perforate the ¯oor of the third ventricle or to withdraw the scope away . reversible focal neurological signs may appear postoperatively, but a CT scan is needed to be sure there is not a intracranial bleeding. Delay in awakening is frequent if high intracranial pressures (> 30 mmHg) have been reached
92 N. FaÁbregas and R. A. Craen
Research agenda . endoscopic neurosurgical procedures is still a growing specialty and there are few publications on the anaesthetic management or the incidence and type of intraoperative and postoperative complications . which intracranial pressure and how long can be maintained during the neuroendoscopic procedure without harming is not known . an irrigation ¯uid CSF-like is nowadays too expensive to be generally available, more research is needed
operating room and, at the same time, provide optimal conditions for imaging, localization of the lesion and repeated neurological assessments. Acknowledgements Enric Ferrer MD, PhD and Luis Caral MD, neurosurgeons, with whom the ®rst author has been working in this ®eld for more than 8 years ± many thanks for their support in the preparation of the manuscript and ®gure.
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doi:10.1053/bean.2002.0209, available online at http://www.idealibrary.com on
6 Anaesthesia for minimally invasive neurosurgery Neus FaÁbregas
MD, PhD
Anesthesiology Consultor, Anesthesiology, Associate Professor Anesthesiology Department, Hospital clinic, Universitat de Barcelona, Villarroel 170, 08036 Barcelona Spain
Rosemary Ann Craen*
MBBS, FANZCA, FRCPC
Associate Professor Department of Anesthesia, University of Western Ontario, London Health Sciences Center, 339 Windermere Road, London, Ontario, Canada N6A 5A5
Technological advances in imaging, computing and surgical instrumentation have encouraged the application of minimally invasive surgical techniques to various neurosurgical disorders. This chapter discusses the wide application of neurosurgery and the implications for anaesthesia, focusing on the speci®c anaesthetic considerations for neuroendoscopy, stereotactic procedures and radiosurgery. Key words: neuroendoscopy; stereotactic surgery; anaesthetic considerations; complications.
Over the last decade there has been a trend towards shorter, less invasive surgical procedures within every surgical discipline. In the neurosurgical arena, technological advances in imaging, computing, optics and miniaturization have encouraged the increasing trend to applying minimally invasive surgical techniques to a variety of neurosurgical procedures. The potential advantages include accurate localization of intracranial lesions, especially those in the eloquent areas of the brain or those usually inaccessible to conventional surgery, and the potential for less trauma to healthy brain, blood vessels and nerves. Neuroendoscopic procedures also have great advantages in dealing with tissue sampling and gross morphological analysis of ventricular and cisternal structures, tumour or infective lesions. In addition, the use of an endoscope avoids larger openings of intracranial or intraspinal spaces and this leads to other bene®ts such as shorter operating time, reduced blood loss, early recovery and discharge from hospital ± and with it greater patient acceptance and presumably improved neurological outcome. However, as with all minimally invasive procedures, there remains a potential for complications accompanied by intra or post-operative morbidity and mortality. The rapid developments of minimally invasive surgery have impacted on the neurosurgical and neuroanaesthesia care of neurosurgical patients. The anaesthesiologist must now provide a continuum of care from the radiology suite to the operating suite. From an anaesthesia viewpoint, the main goals in the management of *Author for correspondence 1521±6896/02/01008113 $35.00/00
c 2002 Elsevier Science Ltd. *
82 N. FaÁbregas and R. A. Craen Table 1. Neuroendoscopic procedures. Diagnosis
Surgical intervention
Non-communicating hydrocephalus Multiloculated hydrocephalus
Ventriculostomy (third ventricle) Ventriculo-peritoneal shunt manipulation ± ventricular tip placement Biopsy or tumour retrieval Removal or fenestration of cysts Ventriculostomy Cystocisternostomies (arachnoid cysts) Drainage Endoscopic trans-sphenoidal Endoscopic strip craniectomy Endocavitary syringostomy Third ventriculostomy Intra-operative visual monitoring Arthroscopic microdiscectomy Endoscopic foraminoplasty
Intraventricular brain tumour Cysts (arachnoid, colloid, intraparenchymal) Subdural haematomas, brain abscesses Pituitary pathology Sagittal craniosynostosis Syringomyelia Intramedullary pathology Spinal diseases
the neurosurgical patient remain the same: careful pre-operative assessment and planning, meticulous cerebral haemodynamic control to ensure adequate cerebral perfusion pressure, provide immobility and select an anaesthetic technique which allows for swift emergence from anaesthesia and neurological assessment. This chapter discusses the wide application of neuroendoscopy (Table 1) and the implications for anaesthesia, focusing on the speci®c anaesthetic considerations for neuroendoscopy, stereotactic procedures and radiosurgery.
BRAIN NEUROENDOSCOPY Uncomplicated non-communicating hydrocephalus, due to aqueductal stenosis or to space-occupying lesions of the midbrain or posterior fossa, is the main indication for endoscopic treatment in patients older than 1 year.1±3 The surgeon performs an endoscopic third ventriculostomy (ETV) by making a hole in the ¯oor of the third ventricle, thus allowing movement of the cerebrospinal ¯uid (CSF) out of the blocked ventricle and into the interpeduncular cistern to relieve the hydrocephalus. This procedure usually takes approximately 45 minutes. Success in terms of the procedure is generally considered to be the avoidance of a shunt in a patient who otherwise would have been shunted.4 Hydrocephalic paediatric patients, in particular, bene®t from ETV because they undergo repeat procedures as they grow with multiple shunt revisions.1 A common complication of the traditionally placed ventriculo-peritoneal shunt system is the obstruction of the ventricular catheter tip from adjacent tissue. A recent study found that ventricular catheter placement with the aid of a rigid ®bre-optic endoscope, oering visual con®rmation of the position of the tip, is a safe and ecient technique with improved accuracy over conventional methods.5 Selected intraventricular tumours may be removed completely via an endoscopic approach, thus avoiding craniotomies and brain retraction. The duration of the endoscopic procedures is usually shorter than expected with open microsurgery.6 The technique also allows biopsies of pineal region tumours as well as making an ETV in the same procedure.7,8 The endoscopic management of an arachnoid cyst is a safe and
Anaesthesia for minimally invasive neurosurgery 83
eective treatment option ± as is the resection of colloid cysts of the third and lateral ventricles.9±12 Strip craniectomy is the removal of a strip of bone containing a fused cranial suture for the treatment of cranial synostosis in the newborn and infants. The procedure itself can range from a simple strip craniectomy to cranial vault remodelling involving extensive scalp mobilization. As a result, these operations are associated with huge blood losses and venous air embolism. The introduction of the endoscope to assist strip craniectomies has led to a signi®cant reduction in blood loss and operative time and has reduced the incidence of venous air embolism.13,14 During transphenoidal pituitary surgery the use of the endoscope provides additional operative manoeuvrability.15 Endoscopic endonasal hemisphenoidotomy has been described for the resection of a pituitary lesion con®ned to the sella.16 Endoscope-assisted microsurgery for cerebral aneurysms has also been described.17 SPINAL NEUROENDOSCOPY Spinal endoscopy is not new, having been reported as early as in the l930s. Miniature endoscopes (1.2 mm) allow visualization of cysts and disc fragments. In syringomyelia, the ¯exible endoscope allows perforation of the septa under direct vision, allowing the communication of all chambers in a safe and non-traumatic way.18,19 Spinal endoscopy may be the diagnostic method of choice for epidural ®brosis.20 Arthroscopic microdiscectomy describes an endoscopic surgical technique that can be performed as an intradiscal discectomy or as an extradiscal (transforaminal) procedure. As in open discectomy, the goal is to resect the herniated disc fragments and decompress nerve roots. However, open laminotomy or laminectomy is recommended when intracanalicular compression is present.21 A microendoscopic posterior laminoforaminotomy is an eective alternative for the treatment of unilateral cervical radiculopathy secondary to lateral or foraminal disc herniation or spondylosis.22 Complications such as medulla-radicular irritation, bradycardia and respiratory depression in the awake patient have been reported, the latter events probably resulting from the large volumes of epidural ¯uid used (upwards of 1200 cc). Anaesthetic concerns include prone positioning, providing an immobile patient and rapid awakening to assess neurological function. However, some maintain that the safest way to do these procedures is to have the patient awake intra-operatively under light sedation.20,21,23 THE SURGICAL APPROACH IN BRAIN NEUROENDOSCOPY The ventricular system and the subarachnoid space of the brain and spinal cord provide suitable conditions for the use of an endoscope. A basic understanding of the surgical technique and instrumentation is essential for the anaesthesiologist in order to anticipate potential complications that may arise. Patient position for endoscopic entry into the third ventricle is usually supine with slight ¯exion of the neck, or with the head tilted from 458 to 908, depending on the planned procedure (Figure 1). The cranium may be ®xed in a head frame. Through a coronal burr hole, the endoscope is introduced into the ventricle system via the frontal horn and advanced to the third ventricle where the mammillary bodies, an important landmark, can been visualized. The tuber cinereum is located immediately beyond these structures. Beneath this membrane is the basilar artery and the basal
84 N. FaÁbregas and R. A. Craen
Figure 1. Operating room set-up during neuroendoscopy using a frame-less neuronavigation device.
cisterns. In patients with aqueduct stenosis, fenestration of this membrane creates an opening through which CSF can be drained, bypassing the aqueduct of Sylvius. Several methods have been described to create this fenestration, including the rigid endoscope, a blunt probe or the use of lasers. The opening is then futher dilated with a balloon catheter to ensure patency and to secure haemostasis. The endoscope, which has a channel for aspiration and a working channel through which a variety of instruments can be passed, is ®xed by an adapted articulated arm to avoid unexpected and hazardous movements. Operating in ¯uid-®lled cavities requires intermittent or continuous warmed (378C) irrigant ¯uid (either Ringer's lactate or normal saline) to maintain adequate ventricular pressure and good visibility. The ¯uid is usually infused under pressure (or may be gravity fed) and allowed to egress passively through an open port of the endoscope. Inadequate venting of the irrigant ¯uid will lead to marked increases in intracranial pressures. While increased intracranial pressure may be detected clinically by bradycardia and hypertension, we have found that these cardiovascular changes occur late.24 Early detection of inadequate drainage of intracranial ¯uid is crucial and is easily achieved by measuring the pressure within the endoscope. Toxic reaction such as high fever and headaches have been described due to meningeal irritation which can occur with large volumes of saline irrigation. Arti®cial cerebrospinal ¯uid (CSF without protein) has been used and reported to reduce the incidence of these toxic reactions.25 Surgical complications, such as acute increases in intracranial pressure, injury to brain structures, including the basilar artery and haemorrhage, have been described. Intracranial bleeding secondary to instrumentation can be catastrophic, especially if
Anaesthesia for minimally invasive neurosurgery 85
there is a delay in detection and treatment. Intracranial hypotension may follow sudden ventricular decompression and removal of cerebrospinal ¯uid causing pressure changes at the mid-brain and hypothalamus level. This in turn can lead to sudden alterations in heart rate and blood pressure. Hypothermia can occur, especially in small children, with the use of large volumes of irrigation and the wetting of drapes. Of the complications listed in Table 2, cardiac arrhythmias are the most frequently described. It is important to note that many of these arrhythmias are transient in nature and range from bradycardia, tachycardia, premature ventricular contractions, supraventricular tachycardias to asystole; they are due mainly to mechanical factors ± for example, stimulation of the ¯oor of the third ventricle with the endoscopic tip or inadequate venting of the irrigant, and will respond to nonpharmacological methods such as withdrawal of the endoscope or venting of the intracranial irrigant ¯uid. Signi®cant bradycardia, however, is more common in the paediatric population ± up to 41% in one series ± and may require the use of atropine or glycopyrrolate.26
ANAESTHETIC CONSIDERATIONS IN BRAIN NEUROENDOSCOPY The major goals are to provide an immobile patient during the procedure and rapid awakening immediately after the procedure to allow early assessment of neurological function and rapid detection of potentially reversible surgical complications. While some cases may be performed under local anaesthesia and sedation1,9 general anaesthesia with endotracheal intubation and controlled ventilation is preferred in order to ensure immobility and because sudden intracranial pressure changes may lead to vomiting. Nitrous oxide is avoided to prevent its eusion into air trapped in the ventricles and the subdural space following decompression of the ventricles. Although there are dierences between anaesthetic agents in terms of their eects on the central nervous system and intermediate outcomes, such as the quality of recovery, there is no evidence that the choice of anaesthetic agent or opioid supplement aects the neurological outcome.27 To date, no prospective randomized or retrospective study in neurosurgical patients has shown a superior patient outcome with one anaesthetic compared with another. Therefore, the decision to use a particular anaesthetic should be based on patient characteristics, intracranial pathology and the anaesthesiologist's familiarity with the agent to assure careful and appropriate use. However, in the presence of increased intracranial pressure, when propofol is used
Table 2. Intra-operative complications. Cardiac arrhythmia Haemodynamic variability Raised intracranial pressure Episodic intracranial circulatory insuciency Intracranial hypotension Haemorrhage (0.5±2%)4,28,41 Air embolism Hypothermia
86 N. FaÁbregas and R. A. Craen
there is a greater margin of safety over that of the volatile agents because propofol is a potent vasoconstrictor which reduces raised intracranial pressure. The type of monitoring depends on the procedure, the age of the patient and accompanying medical problems. In addition to standard monitors (electrocardiography, oximetry, capnography, neuromuscular blockade and body temperature monitoring) intra-arterial monitoring is recommended in view of the haemodynamic variability frequently seen and the need for arterial blood gas sampling. An exception would be in repeat and short ETV procedures in healthy paediatric patients. Intracranial pressure monitoring is invaluable because of the potential for sudden rapid increases in intracranial pressure. An easy way to do this is to measure the pressure inside the endoscope by connecting a ¯uid-®lled catheter from a stopcock located on the irrigation lumen of the neuroendoscope to a pressure-transducer which is zeroed at the skull base (Figure 2). Middle cerebral artery blood ¯ow velocity can be measured with a 2 MHz transcranial Doppler probe attached to the temporal window. This allows `real time' cerebral blood ¯ow to be monitored and allows for early detection of intracranial circulatory insuciency during the transient periods of high intracranial pressures which occur as a result of lack of adequate venting of the irrigating solution.24
POST-OPERATIVE COMPLICATIONS Endoscopic neurosurgical procedures are expected to be associated with a low rate of post-operative complications. However, as this is still a growing speciality, there are few publications on the incidence and type of complications. Table 3 lists the range of post-operative complications which can occur and which anaesthesiologists need to be irrigation solution camera and working channel
aspiration channel roller pump
pressure transducer
Figure 2. Schematic diagram demonstrating how to monitor pressure within the endoscope. A ¯uid-®lled catheter is connected by a stopcock located on the irrigation lumen of the neuroendoscope to a pressuretransducer which is zeroed at the skull base. Reproduced from FaÁbregas et al (2000, Journal of Neurosurgical Anesthesiology 12: 21±28) with permission.
Anaesthesia for minimally invasive neurosurgery 87
cognizant of as they can occur early in the post-anaesthestic care period. In a recently published review, Buxton et al28 quotes a directly attributable mortality rate in adults of 3% (endoscopic third ventriculostomies) and an overall mortality of 0.6% (all age groups and aetiology). The complication of delayed awakening is of particular concern to anaesthesiologists. Early detection and diagnosis (usually by CT) is imperative to exclude treatable causes such as intracranial haemorrhage. Our personal experience, however, indicates that a more common cause of delayed awakening may be due to the neuroendoscopic procedure itself. We found that intra- operative high peak pressures inside the endoscope, and not the length of navigation period, was associated with a delay in awakening.29 Close monitoring of serum electrolytes is recommended in neonates, especially in the acute post-operative period following EVT. The syndrome of inappropiate secretion of antidiuretic hormone (SIADH) has been described following EVT and is most probably related to supra-opticohypophyseal tract functional disruption.30
STEREOTACTIC PROCEDURES Stereotactic systems relate pre-operatively obtained computed tomography (CT) or magnetic resonance systems (MRI) to an extracranial reference system. The latter is achieved using either framed systems that require the application of a head frame, or frame-less systems. Using online image guidance systems, the surgical targeting of a lesion becomes more precise and can be accomplished through a small craniotomy opening. In particular, the technique allows for access to deep-seated lesions often inaccessible by conventional techniques. The presence of the head frame represents an obstacle to ready access to the airway (Figures 3 and 4). The frame, however, provides a directional and depth guide to surgical instrumentation. The newer systems involve `frame-less stereotaxy' with the use of scalp markers which act as ®ducial points to relate surgical instruments to the computer-generated image. A pair of cameras mounted above the operating ®eld provides a stereoscopic view of the surgical instrument to the computer, and the
Table 3. Post-operative complications. Delay in awakening (15%)41 Pneumoencephalus, pneumoventricle (2%)41 Convulsions Transient anisocoria (16%)41 Transient hemiparesis (6%)41 Haemorrhage (6%),41 cerebral infarction (1.5%)28 Transient fever, meningism Infection (1±9%)1,28,41 Short-term memory loss (4%)41 Diabetes insipidus (0.5±1%)4,41 SIADH Transient cerebrospinal leaks (1%)4 Chronic subdural haematomas (1.5%)4 Traumatic basilar aneurysm Hydrocephalus (6%)41 SIADH, secretion of antidiuretic hormone.
88 N. FaÁbregas and R. A. Craen
Figure 3. Patient in stereotactic frame undergoing a brain biopsy in the semi-recumbent position. This head frame prevents ready access to the airway.
surgeon is given a horizontal, sagittal and coronal view of the position of the tip of the instrument in the operating ®eld. CT- and MRI-guided intracranial procedures (stereotactic surgery) include needle and open biopsies of various lesions, including tumours, abscesses, implantation of depth electrodes and tumour resection. Functional stereotactic surgery refers to the use of stereotaxy in altering the function of the brain by either stimulating or ablating anatomical brain structures. In movement disorders such as Parkinson's disease, essential tremor, hemiballismus and dystonias, functional stereotactic ablation (pallidotomy, thalamotomy), or stimulation (subthalamic stimulation, globus pallidus stimulation) have been used eectively to control symptoms and signs.31 In the treatment of seizure disorders, there is renewed interest in using stereotaxy to either destroy the seizure focus, reduce the epileptogenic focus, or interrupt the pathways of
Anaesthesia for minimally invasive neurosurgery 89
Figure 4. Patient in stereotactic frame undergoing a brain biopsy in the semi-recumbent position. This head frame prevents ready access to the airway.
seizure propagation as a means of treating temporal lobe epilepsy.32 A variety of ablation techniques are available to the neurosurgeon.32 They have in common the potential to deliver a physical destructive force to ablate neural tissues and include mechanical and energy sources. In the past, heat, cold, wax and alcohol have been used. More recently radio-frequency lesioning has become popular. Lesioning is produced with a probe that utilizes a radio-frequency current causing ionic oscillations and temperature increases to 858C for 1±2 minutes in the target brain tissue. There is also a trend to the use of external ionizing radiation (stereotactic radiosurgery) such as is available with the gamma knife, linear accelerator and proton beam, and the insertion of radioactive seeds such as yttrium-90 as a source of brachytherapy. The gamma knife has been used successfully to treat acoustic neuromas,33 arteriovenous malformations,34 trigeminal neuralgia and other neuropathic pain syndromes.35
90 N. FaÁbregas and R. A. Craen
ANAESTHETIC CONSIDERATIONS FOR STEREOTACTIC PROCEDURES The anaesthetic management for stereotactic procedures begins outside the operating room. Therefore, the anaesthesiologist must be prepared to provide a continuum of care from the radiology suite to the operating room and, at the same time, provide optimal conditions for imaging, localization of the lesion and repeated neurological assessments. The patient's disease, the surgical procedure, the presence of a head frame and the surgeon's needs and expectations all dictate the choice of anaesthetic technique and agents. The presence of a space-occupying lesion with increased intracranial pressure precludes the use of drugs which depress respiration and increase the arterial carbon dioxide tension. Careful use of sedatives such as midazolam, in small aliquots, may be all that is necessary to provide adequate operating conditions. Non-pharmacological measures, such as ensuring good communication, providing constant reassurance and distraction, can signi®cantly reduce the need for sedation. Lesioning for patients with movement disorders, such as Parkinson's disease, preclude the use of drugs which may alter the degree of tremor and prevent patient participation necessary in target localization and the immediate observation of the eect of lesioning. These drugs include beta-blockers, droperidol, metoclopramide, benzodiazepines and clonidine.36 Propofol is also contraindicated as there have been reports that its use may illicit abnormal movements or may improve the tremor.37 The majority of stereotactic procedures is performed in an awake patient with little to no sedation. As the major complication of stereotactic surgery is intracranial bleeding, performing the procedure under local anaesthesia aords an additional degree of safety in that it allows for early detection and prompt treatment. The stereotactic frame is applied with the use of local anaesthesia either by regional nerve blocks (supra-orbital and greater occipital nerve blocks) or by subcutaneous in®ltration using 3±5 ml of 0.5% plain bupivacaine with a long 25-gauge needle.38 In some cases sedation may be needed initially for placement of the frame. General anaesthesia with endotracheal intubation may be necessary in the following circumstances: if the patient is very young, if the patient is confused and unable to cooperate or if the lesion is such that positioning would be dicult with the patient awake, for example in prone position. Standard monitors (electrocardiography, oximetry, capnography, body temperature) are usually applied and intra-arterial monitoring is not generally required. Intra-operative complications include injury of vital brain structures, intracranial haemorrhage (1±3%),39 seizure, venous air embolism and cardiac arrhythmias. Signs of intracranial haemorrhage may exhibit as a sudden change in conscious level, confusion or hemiparesis. Seizures are often self-limiting and focal but can also be grand mal ± necessitating rapid removal of the head frame. Venous air embolism can occur because these patients are commonly in a sitting or semi-recumbent position and may exhibit as a cough, complaints of chest pain or feeling of anxiety. The treatment includes prevention of further entrainment of air by packing with gelfoam and the use of the Trendelenburg position. Cardiac arrhythmias, especially bradycardia, can occur especially during stimulation of the amygdala and hippocampus regions of the brain.40 All of these complications underscore the fact that, although these procedures require little to no anaesthesia, there is a need for the presence of a vigilant anaesthesiologist to deal with the medical emergencies of the neurosurgically compromised patient.
Anaesthesia for minimally invasive neurosurgery 91
SUMMARY Improvements in imaging, computing, optics and miniaturization have encouraged the increasing trend of applying minimally invasive techniques to a variety of neurosurgical disorders. The potential advantages include accurate localization of lesions, shorter operating time, early discharge from hospital and, with it, greater patient acceptance and presumably improved neurological outcome. However, as with other endoscopic surgical techniques, there is a steep learning curve for neuroendoscopic procedures. The decision as to which approach is best for which lesion (operator- and patientdependent) can come only from long-term follow-up and large series, yet to come. Endoscopic third ventriculostomy in the treatment of hydrocephalus is the most commonly performed neuroendoscopic procedure. Patients presenting may range in age from newborn to geriatric. The most common intra-operative complication is transient arrhythmia caused mainly by mechanical factors. Inadequate venting of the irrigant ¯uid may result in sharp increases in intracranial pressures and this has been associated with a delay in awakening from anaesthesia. Monitoring intra-arterial pressure and intracranial pressure within the endoscope can provide valuable information and guide interventional therapy. Many stereotactic procedures are done on an awake patient with little to no sedation. However, careful pre-operative assessment is necessary to ascertain the extent of the disease process being treated and patient suitability. The anaesthesiologist must be prepared to provide a continuum of care from radiology suite to the Practice points . endoscopic third ventriculostomy in non-communicating hydrocephalus, at any age, is the main indication for endoscopic treatment in neurosurgery. A great number of other intraventricular procedures can be performed . general anaesthesia with endotracheal intubation is preferred for neuroendoscopies to ensure immobility and because sudden intracranial pressure changes may led to vomiting . nitrous oxide is avoided to prevent its eusion into air trapped ventricles and the subdural space following decompression of the ventricles . monitoring is the same as for a craniotomy. An arterial line is mandatory except in endoscopic third venticulostomy in paediatrics . the irrigation ¯uid needs to be warm and with electrolytes and osmolarity similar to CSF . early detection of inadequate drainage of intracranial irrigation ¯uid is crucial and easily achieved by measuring the presure within the endoscope . TCD continuous monitoring (temporal window : MCA) may distinguish situations with CBF impairment due to high intracranial pressure because of the inadequate venting or the irrigation ¯uid . cardiac arrhythmias is the intraoperative complication most frequently described. When a sudden bradycardia appears in a paediatric patient, alert the surgeon to perforate the ¯oor of the third ventricle or to withdraw the scope away . reversible focal neurological signs may appear postoperatively, but a CT scan is needed to be sure there is not a intracranial bleeding. Delay in awakening is frequent if high intracranial pressures (> 30 mmHg) have been reached
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Research agenda . endoscopic neurosurgical procedures is still a growing specialty and there are few publications on the anaesthetic management or the incidence and type of intraoperative and postoperative complications . which intracranial pressure and how long can be maintained during the neuroendoscopic procedure without harming is not known . an irrigation ¯uid CSF-like is nowadays too expensive to be generally available, more research is needed
operating room and, at the same time, provide optimal conditions for imaging, localization of the lesion and repeated neurological assessments. Acknowledgements Enric Ferrer MD, PhD and Luis Caral MD, neurosurgeons, with whom the ®rst author has been working in this ®eld for more than 8 years ± many thanks for their support in the preparation of the manuscript and ®gure.
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