84 page ANESTHESIA For NEUROSURGERY Presentation on CD

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Anesthesia and Neurosurgery, 2003, 84 pages (slides)

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Anesthesia and Neurosurgery Cerebral Physiology Cerebral Pathology Effects of Anesthetic Agents on Cerebral Physiology Electrophysiology: Intraoperative Monitoring Intraoperative Fluid Management for Neurosurgical Patients Anesthesia for Supratentorial Masses Anesthesia for Infratentorial Masses Anesthesia for Pituitary Lesions Cerebral Aneurisms: Anesthetic Consideration Cerebral Vascular Malformations: Anesthetic Considerations Occlusive Cerebral vascular Disease: Anesthetic Considerations Anesthesia for Epilepsy and Epilepsy Surgery Anesthesia for Pediatric Neurosurgery Anesthesia for Surgery of the Spine and Spinal Cord Pre-existing Neurological Disease and Anesthesia Diseases of Muscle and Anesthesia Management of Severe Head Injury Management of Brain Death Head Injury--Contusion Intracranial Pressure Compliance Curve Cerebral Perfusion Pressure MAP-CVP/ICP Normal is 100 mm Hg Slowing of EEG at 50 mm Hg Isoelectric EEG at 40-25 mm Hg Irreversible brain damage at <10 mm HG Cerebral Blood Flow: PaCO2 CO2: CBF is directly proportional to PaCo2 between PaCo2 of 20-80 mm Hg The CO2 diffuses through the BBB and forms H+ and HCO3- The H+ ion affects CBF CBF drops 1cc/100 gms /min/1mm hg drop in PaCO2 CBF-Extrinsic Mechanisms Temperature-Isoelectric EEG at 20 degrees C Viscosity-DO2 best at HCT of 30 Autonomic Influences PaO2 Vasospasm Neurophysiology- CBF Miller Cerebral Blood Flow and Metabolic Rate with Catecholamine Agonists-Miller Physiology- CMRO2 Cerebral Physiology-Normal Numbers Autoregulation Myogenic and Metabolic Mechanisms CBF--CPP Blood Brain Barrier Lipid barrier allows passage of lipid soluble substances but excludes ionized molecules The blood brain barrier is disrupted by: Severe HTN Tumors Trauma Strokes Infection Hypercapnea Hypoxia And Sustained Seizure activity Cerebral Spinal Fluid Found in the Cerebral Ventricles and Cisterns in the Subarachnoid space 20 cc’s per hour production Volume of CSF--150 mls Active secretion of sodium in the choroid plexuses with isotonic fluid produced Steroids, Lasix, Isoflurane, Spironolactone Decrease production Intracranial Hypertension Increased intracranial pressure (Above 15 mm Hg) When ICP is greater than 30 mmHg then cerebral blood flow progressively decreases Cushing Response--Reflex slowing of heart rate and increased blood pressure Plateau A waves--Due to autoregulatory mechanisms Cerebral Edema Vasogenic Edema Cytotoxic Edema Interstitial Edema Treatment Hyperventilaiton Elevate head of bed Hyperosmolar agents-Mannitol, Lasix Drain CSF Cerebral Edema and Fluids Fluids: Crystaloids: Isoosmotic non-dextrose containing solutions—Normal Saline Euvolemia Hetastarch, and Albumin Hypertonic Saline No Dextrose Mannitol and Lasix Steroids for Vasogenic edema Effect of Inhalational Agents All Agents increase ICP Decrease in Cerebral Metabolic Rate Autoregulation is impaired “Uncoupling of Cerebral Blood flow” Luxury Perfusion Circulatory Steal Isoflurane Increases CSF Resorption 1.5 Mac of Enflurane associated with Seizures N20 CBF-Volatile Anesthetic Effects-Miller CBF/Isoflurane Regional Differences in CBF CBF/CMRO2-Volatile Agents-Miller CBF/CMRO2—IV anesthetic agents N20--CBF Effect of Intravenous Agents Except Ketamine all intravenous agents either have no effect of reduce cerebral metabolic rate and cerebral blood flow Cerebral Autoregulation and CO2 responsiveness are preserved with all agents Barbiturates Hypnosis Depression of cerebral metabolic rate Reduction of cerebral blood flow due to increased resistance Anticonvulsant activity -Unlike isoflurane barbiturates reduce cerebral metabolic rate uniformly Blockaid of sodium channels Decrease intracellular calcium influx Scavenging or suppression of free radical formation Retardation of cerebral edema Opioids All Opioids have minimal effects on Cerebral Blood Flow, CMRO2, and intracranial Pressure Morphine and Meperidine not usually used in Neuroanesthesia Etomidate Decreases the cerebral metabolic rate, cerebral blood flow in a non-uniform way affecting cortex more than brainstem More stable hemodynamics Decreases CSF production Myoclonic movements common Some seizure activity has been noted in patients with seizures Propofol Decreases cerebral blood flow and CMRO2 consumption Has anticonvulsant activity Very useful agent for Neuroanesthesia Benzodiazepines Decrease cerebral blood flow and cerebral metabolic rate Prolonged emergence can be seen in some elderly patients Ketamine Dilates the cerebral vasculature and increases cerebral blood flow Selective activation of certain areas(Limbic and Reticular) is partially offset by other areas (Somatosensory and Auditory) Ketamine can increase CSF production Anesthetic Adjuncts Lidocaine: Decreases cerebral metobolic rate, cerebral blood flow and intracranial pressure but to lesser degree than other agents. Causes increasing cerebral vascular resistance Droperidol: Little effect on CMRO2 and Blood flow Vasodilators Most vasodilaters induce cerebral vasodilatation and increase cerebral blood flow in a dose related fashion Therefore increase in intracranial pressure can be seen Vasopressors With normal autoregulation, vasopressors increase cerebral blood flow only when MAP is greater than 150-160 B1 Agonists-Increase in cerebral metabolic rate B-blockers-Little effect on cerebral blood flow A2-Adrenergic agonists produce vasoconstriction Muscle Relaxants Succinylcholine can increase ICP Histamine releasers can lower blood pressure Usually little effect on ICP Astrocytoma Physiology of Brain Protection The Brain is very vulnerable to ischemia due to high oxygen consumption and total dependence on aerobic glucose metabolism After 3-8 minutes without blood irreversable brain injury occurs Intracellular K decreases Extracellular Na increases Intracellular Ca++ increases Glutamate is released Sustained increases in intracellular Ca++ activates lipases and proteases which initiate and propagate structural damage to neurons Brain Protection Focal Ischemia: The brain tissue surrounding a severely damaged area may suffer marked functional impairment by still remain viable Global Ischemia: Includes circulatory arrest as well as global hypoxia Hypothermia-Circulatory Arrest Hypothermia--Autoregulation Cerebral Blood flow-pH management Miller Neuronal Calcium Cerebral Ischemia Cerebrovascular Disease CEA Cardiac Disease To Shunt or not to shunt Awake vs Asleep Monitoring Awake patient EEG SSEP Xenon Washout TCD Stump Pressures Note Autoregulation is lost therefore CBF is pressure dependent Brain Protection Hypothermia Anesthetic agents- Calcium channel blockers--Nimodipine Methylprednisolone-Within 8 hours Trilazad-Steroid Acadesine Magnesium dexmedetomidine-NMDA receptor dextromethorphan-NMDA Receptor Vit E Neuroanesthesia Part 2 Cerebrovascular Disease CEA Cardiac Disease To Shunt or not to shunt Awake vs Asleep Monitoring Awake patient EEG SSEP Xenon Washout TCD Stump Pressures Note Autoregulation is lost therefore CBF is pressure dependent Head Injury--Contusion Subdural Hematoma Head Trauma Patterns of injury- Primary is form direct parenchimal disruption at the the time of injury and Secondary occurs later due to hyoxia, hypercapnea, hypotension, intracranial hypertension, and herniation Glascow Coma Scale World Federation of Neurosurgeons Scale Head Trauma Examination Presence of skull fracture increases chance of significant intracranial lesion Monitors: Intracranial monitoring is usually indicated for patients with significant contusions, intracerebral hemorrhage, or tissue shifts Airway Obstruction, Hypoventilation, Pulmonary Contusion, Fat Emboli, Neurogenic Pulmonary Edema, Cervical Spine Injury, Full Stomach Rapid sequence required for intubation Hypotension, Cardiac Dysrythmias can be seen Cerebral Perfusion Pressure should be maintained between 70-110 mm Hg DIC and DI can be seen. Seizures Decreased GABA activity Increased Glutamate Abnormal Calcium Currents Partial Complex Generalized Status Epilepticus Take your own Pulse Thiopental 50-100 Dilantin 500-1000mg slowly Intubate Pentobarbital Coma Seizures Drugs to avoid Ketamine Methohexital Atracurium Meperidine Enflurane Venous Air Embolism 300 ml of air or greater is estimated to be fatal 50% of children less than age 5 and 20-30% of adults have a patent foramen ovale TEE, Precordial doppler, Changes in PA pressure, decreased ETCO2, and ETN2, can be monitored NO N20 Electroconvulsive Therapy Need about 400-700 seizure seconds Parasympathetic discharge Sympathetic discharge Contraindications: Recent Stroke, Increased ICP, Pregnancy, Glaucoma, and Retinal Detachment... Methohexital and Succinylcholine is most often used Astrocytoma Anesthesia For Craniotomy-Not Posterior Fossa Premedication-Best avoided Monitoring-Arterial line-Central venous access Induction-Slow controlled intubation Positioning-Watch internal jugular veins Maintenance-Most stimulating times No Hyperglycemia Most stimulation Laryngoscopy Skin incision Bone Dura Emergence-Need to awaken quickly Posterior Fossa Surgery Obstructive hydrocephalus Injury to brainstem structures Unusual positioning Pneumocephalus Postural Hypertension Venus air embolism-No Nitrous Anesthesia of Surgery of the Spine Most often performed for symptomatic nerve root or cord compression Care must be taken to maintain the neck in a neutral position. When prone, the eyes need to be checked with care The arms need to be padded and checked with care Abdominal compression may impede venous return cause increase blood loss Massive blood loss from aortic or vena cava injury can result with occult blood loss Autonomic Hyperreflexia Lesions above T6 Surgery after stroke Asymptomatic cervical bruits are noted in up to 4% of patients over 40 .4-3.3% risk of stroke following nonneurologic surgery in patients with known cerebrovascular disease Asymptomatic Carotid Bruit does not increase risk of stroke but does increase chance of coronary artery disease Open heart surgery has a 4% risk of stroke Wait 6 weeks after stroke to perform elective surgery Patients with TIA’s have a 30-40% chance of developing a thrombotic stroke in 5 years No Sux! Monitoring--EEG Intravenous Agents Inhalational Anesthetics Biphasic Pattern--Fast Low Amplitude-Slow Large Amplitude Isoflorane--Isoelectric EEG-1-2Mac Enflurane--Burst suppression N2O causes increased frequency and amplitude (High Amplitude Activation) EEG -Montage EEG—Cardiac Surgery Processed--EEG Evoked Potentials Somatosensory Evoked Potentials VEP EMG B.E.A.R.S. Inhalational anesthetics have the greatest effect on evoked potentials Decreased amplitude and decreased Latency SSEPS—Agent effects Anesthesia and Craniotomy for Aneurysms Aneurysms: 10-30% of patients have more than one aneurysm 35% Mortality Symptoms: Cranial nerve palsies, visual field deficits, headache, and eye or neck pain Diagnosis: CT Scan and Lumbar Puncture Need very careful blood pressure control Expect lots of blood loss Controlled hypotension may need to be used Watch for cerebral artery spasm Pre-existing Neurological Diseases Diseases of Muscle Alzheimer’s Disease Multiple Sclerosis Parkinsons Disease Gullaine-Barre Diseases of Muscle Muscular Dystrophies Myopathies Myotonias Myositis Inborn errors of metabolism Parkinson’s Disease Continue Parkinson’s Medications No Anti-dopamine drugs: Phenothiazines, butyrophenones, and metoclopramide can worsen symptoms Watch for abrupt changes in blood pressure Diphenhydamine is especially valuable for tremor and a good sedative for these patients Direct acting vasopressors are recommended Alzheimer’s Disease 20% of patients over 80 characterized by a slow decline in intellectual function A deficiency of choline acetyltranferase is seen Get informed consent Avoid anticholinergics Expect emergence delerium Multiple Sclerosis Demyelination at random and multiple sites in the brain and spinal cord Increased in body temperature cause exacerbation of symptoms, presumably by decreased nerve conduction Elective surgery should be ignored during relapse regardless off anesthetic technique Spinal anesthesia should be avoided Epidurals are safe Avoid heating the patient Gullain-Barre Syndrome A.I.D.P. Watch for autonomic dysfunction No SUX Anesthesia and Neurosurgery Cerebral Physiology Cerebral Pathology Effects of Anesthetic Agents on Cerebral Physiology Electrophysiology: Intraoperative Monitoring Intraoperative Fluid Management for Neurosurgical Patients Anesthesia for Supratentorial Masses Anesthesia for Infratentorial Masses Anesthesia for Pituitary Lesions Cerebral Aneurisms: Anesthetic Consideration Cerebral Vascular Malformations: Anesthetic Considerations Occlusive Cerebral vascular Disease: Anesthetic Considerations Anesthesia for Epilepsy and Epilepsy Surgery Anesthesia for Pediatric Neurosurgery Anesthesia for Surgery of the Spine and Spinal Cord Pre-existing Neurological Disease and Anesthesia Diseases of Muscle and Anesthesia Management of Severe Head Injury Management of Brain Death