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What's New in Neuroanesthesia
What's New in Neuroanesthesia
What's New in Neuroanesthesia
What's New in Neuroanesthesia
What's New in Neuroanesthesia
What's New in Neuroanesthesia
What's New in Neuroanesthesia
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What's New in Neuroanesthesia

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  • 1. “What’s New in Neuroanesthesia” Irene P. Osborn, M.D. Director, Division of Neuroanesthsia Mount Sinai Medical Center New York, N.Y. The specialty of neuroanesthesia continues to evolve with changes in neurosurgical procedures, developments in operative technology, and advances in neuro-imaging. This discussion will focus on new anesthetic agents, new monitoring devices, new surgical procedures and new thinking about the management of central nervous system (CNS) disease. What hasn't changed? -Intracranial components -Intracranial elastance (compliance) curve -Regulation of cerebral blood flow (CBF) by metabolic and chemical factors -Autoregulation and "coupling" of CBF to metabolic activity -Effects of anesthetic agents Methods to acutely decrease intracranial pressure (ICP) include: -head up position -deliberate hyperventilation -barbiturates/sedatives -osmotic and/or renal tubular diuretics/ hypertonic saline* -CSF drainage Anesthetic Agents Propofol Propofol was originally recommended with caution because of its potential to decrease mean arterial pressure (MAP) and thus, cerebral perfusion pressure (CPP). It is now recognized as a useful agent in neuroanesthesia, particularly for induction, sedation or as a component of total intravenous anesthesia (TIVA). It produces a decrease in CBF, cerebral metabolic rate (CMRO2), and ICP. Propofol's ability to provide "brain protection" is currently being studied and debated. ADVANTAGES: DISADVANTAGES: rapid onset of effect potential hypotension rapid recovery ? prolonged action decrease CBF,ICP,CMRO2 reliance on I.V. access neurophysiologic monitoring cost Desflurane This volatile anesthetic agent has effects similar to isoflurane on CBF and ICP.
  • 2. Concentrations of 1.5 MAC or higher may increase CBF and thus, cerebral blood volume. Emergence from anesthesia with desflurane is more rapid than with isoflurane and with minimal biodegradability, it may be preferred in patients undergoing prolonged procedures. ADVANTAGES: DISADVANTAGES: rapid onset & emergence ? coughing decreased CMRO2 potential inc. CBF, ICP min. biodegradability cost Sevoflurane This agent also has similar effects on CBF and ICP yet onset and emergence from anesthesia is more rapid. Sevoflurane has a "less noxious" smell and can be used more efficiently for mask inductions in children and adults. It is considered costly for long procedures but may be useful when no IV access is present. Potential for causing renal injury is still being studied. Remifentanil The profound hemodynamic control and ultra-short half-life of remifentanil have made it an attractive agent for neuroanesthesia. In patients with supratentorial brain tumors, remifentanil and alfentanil were compared. Neither opioid caused a significant increase in ICP. Its lack of residual analgesia results in significant discomfort, which must be relieved before excessive hypertension occurs postoperatively. Monitoring Monitoring in neuroanesthesia now includes cerebral oximetry as well as neurophysiologic techniques such as EEG and evoked potentials. Monitoring of motor- evoked potentials allows for accurate mapping of the motor cortex and brain-stem if needed. (figure). A new EEG parameter, the bispectral index (BIS) is now gaining acceptance as a guide to monitoring anesthetic depth and the hypnotic effect of anesthetic agents. Intraoperative titration using BIS may allow for more rapid recovery from anesthetics and may be used for monitoring of burst supression. New Procedures Stereotactic Biopsy/ Craniotomy Stereotaxis is the accurate location of a definite circumscribed area within the brain, with minimal damage to the remainder of the organ, by moving a probe or electrode along coordinates for measured distances from certain external points or landmarks of the skull. This produces a smaller incision, potential for decreased blood loss and more rapid recovery for the patient. Anesthetic techniques have varied according to the patient, location of the lesion, and surgical preference. Potential problems: seizures, bleeding, airway loss, air embolism Local Anesthesia with Sedation-
  • 3. ADVANTAGES: DISADVANTAGES: less expensive patient discomfort less equipment needed potential for respiratory depression patient may assist in movement loss of airway during seizure ability to assess neuro status limited patient positioning General Anesthesia with Endotracheal Intubation- ADVANTAGES: DISADVANTAGES: airway secured additional monitoring & equipment control of ventilation Inability to monitor neuro status amnesia/anesthetic depth personnel for transport blood pressure control ? expense Solutions: Careful selection of patients Communication with surgeons Alternative techniques- laryngeal mask with/without intubation* Awake craniotomy Craniotomy in the awake state has been performed since ancient times. Present day indications may include resection of a lesion in the eloquent or speech center of the brain. Surgical procedures for the treatment of seizures, tumors, or arteriovenous malformation have been performed in the awake patient. With refinement of neurophysiological monitoring techniques, awake craniotomies are necessary in only a small percentage of patients. However, surgery for movement disorders has again increased the use of this technique. Advantages: - Ability to identify the seizure focus and minimize brain injury - Minimal anesthetic effects to suppress seizure activity and rapid recovery Disadvantages: - prolonged surgical procedure with awkward body positioning - need for patient cooperation to evaluate language, memory, and motor skills - potential for significant patient discomfort- pain, nausea, recall - potential for emergent airway management should the patient become uncooperative or persistent seizure activity occur Awake craniotomy requires a responsive patient who can safely and comfortably cooperate for a long neurosurgical procedure. Anesthetic techniques The goals are to: 1) provide adequate sedation and analgesia for bone flap removal 2) achieve an appropriate level of consciousness for cortical speech or seizure focus mapping 3) maintain patient comfort, hemodynamic stability, and prevent complications Complications include nausea, excessive sedation, seizures, and patient intolerance. Numerous techniques for conscious sedation and monitored anesthesia care have been described. It is also extremely important to provide adequate local anesthesia. Local anesthesia:
  • 4. This component is crucial and may be administered by the surgeon and/or the anesthetist. The best technique is that which specifically blocks the nerves, which innervate the scalp. In addition, infiltration may be administered for the area of incision. Girvin has described the technique using bupivacaine 0.5% with epinephrine, 1:200,000 that has duration of 8-9 hours. This solution is injected at described landmarks and requires 20 minutes for full onset. This may be performed in the operating room after the patient has been given sedation or prior to arrival. It is important to be aware of the total amount of local anesthetic administered. (Figure 1) Intravenous agents: Traditionally, techniques using intravenous narcotics and neuroleptic drugs have been successful for conscious sedation during the awake procedure. Fentanyl and droperidol have been commonly used and may be administered by bolus or infusion techniques. Fentanyl and droperidol are effective in minimizing the discomfort associated with scalp infiltration and the surgical procedure. It is important to titrate the dose carefully and to be aware of the more painful parts of the surgery. While fentanyl is useful, the shorter-acting agent, alfentanil, has more advantages as it can be easily given by infusion (0.5-0.25 ug/kg/min) and maintained throughout the preparation and start of surgery. The dose, which allows spontaneous ventilation and comfort, is maintained until approximately 20 minutes before testing is required. Remifentanil has recently been reported for this use as it has a shorter duration of action requiring less than 5 minutes for offset when administered with a propofol infusion. Propofol is extremely useful as the sedative/hypnotic component of awake craniotomy. The infusion may begin as soon as the patient is positioned and continue throughout preparation and surgery until cooperation is required. While not a substitute for analgesia, propofol supplements the effect and provides a controlled level of sedation. Sedation with propofol may have an additional protective effect against local anesthetic toxicity and potential to decrease the incidence of nausea. A background infusion of 50-150 ug/kg/min with intermittent boluses is sufficient for sedation. Droperidol is still an important component for providing sedation and preventing nausea and vomiting. Intraoperative testing All infusions should be discontinued approximately 20 minutes before testing and the patient is allowed to awaken. With the patient awake and the brain exposed, direct cortical readings are performed. The goal of electrocorticography is to delineate the full extent of interictal epileptiform activity. The exposed cortex is then stimulated to map out important neurologic areas. The patient may be asked to perform certain tasks during stimulation. After the epileptogenic focus is identified and functional areas have been mapped, resection is initiated. The brain itself has no sensation, so pain is experienced only with traction or coagulation of blood vessels. The patient may be gradually sedated again during this portion of the case. Coughing and hypertension should be minimized during this period to potentially reduce the risk of intracranial
  • 5. bleeding. “Awake/asleep” Techniques: Some patients may not tolerate being awake for these prolonged procedures. In our experience using LMA for young adults, patients could be induced and asleep for the resection after the intraoperative testing was finished. This allows the surgeon a “quiet field” as many patients become hypercarbic while awake and sedated. Other procedures: Neuroendoscopy Gamma knife/ radiosurgery Conclusion The 90's were declared the "Decade of the Brain". The application of new anesthetics and techniques to new, minimally invasive procedures can help to achieve the promised goals of rapid recovery and better outcome. Expanding technology and thoughtful consideration of the neurosurgical patient as a whole will help to save more brains for the future. References 1). Todd MM, Warner DS, et al. A prospective, comparative trial of three anesthetics for craniotomy. Anesthesiology 78:1005, 1993. 2). Ornstein E, Young, WL. et al. Desflurane and isoflurane have similar effects on cerebral blood flow in patients with intracranial mass lesions. Anesthesiology 79:498, 1993. 3). Berkowitz RA, Hoffman WE, Cunningham F. Changes in cerebral blood flow velocity in children during sevoflurane and halothane anesthesia. J Neurosurg Anesthesiol 8:194- 198, 1996. 4). Warner DS, Hindman BJ, Todd MM, et al. Intracranial pressure and hemodynamic effects of remifentanil vs. alfentanil in patients undergoing supratentorial craniotomy. Anesth Analg 83:348, 1996. 5). Girvin JP. Neurosurgical considerations and general methods for craniotomy under local anesthesia. In Anesthetic Considerations for Craniotomy in Awake Patients. Int. Anesthesiology Clinics. 24:89- 107, 1986. 6). Gignac E, Manninen PH, Gelb AW. Comparison of fentanyl, sufentanil and alfentanil for awake craniotomy for epilepsy. Can J. Anaesth 40:421-4, 1993. 7). Johnson KB, Egan TD. Remifentanil and propofol for awake craniotomy: case report with pharmacokinetic simulations. J Neurosurgical Anesthesiology 10: 25-29, 1998. 8) Hagberg C, Berry J, Hacque S. The laryngeal mask for awake craniotomy in pediatric patients. Anesthesiology 83:A184, 1995.
  • 6. 9) Osborn IP, Ferson DZ, Zahos PA. The laryngeal mask for airway control in awake craniotomy. American Association of Neurological Surgeons. Orlando, 1995. 10) Young WL, Pile-Spellman J. Anesthetic considerations for interventional neuroradiology. Anesthesiology 80:427, 1994. 11) Pinowsky ML, Fishman RL, Reeves ST, et al. The effect of bupivacaine skull block on the hemodynamic response to craniotomy. Anesth Analg 83:1256, 1966.
  • 7. 9) Osborn IP, Ferson DZ, Zahos PA. The laryngeal mask for airway control in awake craniotomy. American Association of Neurological Surgeons. Orlando, 1995. 10) Young WL, Pile-Spellman J. Anesthetic considerations for interventional neuroradiology. Anesthesiology 80:427, 1994. 11) Pinowsky ML, Fishman RL, Reeves ST, et al. The effect of bupivacaine skull block on the hemodynamic response to craniotomy. Anesth Analg 83:1256, 1966.

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