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Anesthesia for Neurosurgery
Anesthesia for Neurosurgery HOWARD R. TERRY, JR., M.D. EDWARD F. DAW, M.D. JOHN D. MICHENFELDER, M.D. GERALD F. TUOHY, M.D. ROSS H. MILLER, M.D.
The basis of good anesthesia for neurosurgery consists of a perfect airway with minimal resistance, light general anesthesia without coughing or straining, adequate ventilation, nonflammable and nonexplosive anesthetic agents, and a speedy return to consciousness at the end of the surgical procedure. Space does not permit a historical review of neurosurgery from the time when anesthesia was unknown through the development of general anesthesia when flammable and explosive agents were a necessity, even with cautery. Neither does it permit a discussion of neurosurgery and general anesthesia before the use of endotracheal tubes. A review of their development to the present use of nonflammable agents, muscle relaxants, respirators, gas machines with circle systems and nonkinkable cuffed endotracheal tubes shows remarkable changes. These changes are reflected in greatly decreased morbidity and mortality as well as in bolder and more radical neurosurgical procedures than were possible a few decades earlier. The development of anesthesia along with advances in the use of blood, blood derivatives, and fluid therapy, the advent of antibiotics, the use of cortisone, and the development and improvement in diagnostic neuroradiologic techniques has led to great advancement in neurosurgery.l, 2,7,8 Anesthetic techniques for neurosurgery in well-staffed and wellsupplied operating units probably vary less in principle now than during any other period. These techniques will continue to improve as anesthesiologists gain further knowledge in the fields of neurophysiology, neuropharmacology, neuroanatomy, and neuropathology. After a review of present methods of anesthesia in neurosurgery, an anesthesiologist cannot
899
900
TERRY, DAW, MICHENFELDER, TuOHY, MILLER
help wondering what minimal equipment he would attempt to take into an undeveloped part of the world or into a combat area where gas cylinders, massive anesthesia equipment, and large stores of drugs might not be available. As advancements are made and experience is gained, anesthesiologists should not forget earlier experiences with good, proved techniques of local and regional anesthesia, 6 including the open-drop use of chloroform, ether, and possibly halothane with a portable hand ventilator and, it is hoped, an endotracheal tube. 8- 5 If these older techniques are forgotten, time may prove that we are actually unprepared and less experienced than we thought.
GENERAL ANESTHESIA VERSUS LOCAL ANESTHESIA
The value of general anesthesia versus local anesthesia is an age-old problem in the management of the neurosurgical patient. When craniotomy is necessary, the skin, fascia, temporal muscle, periosteum, and certain parts of the dura are sensitive to pain. Other regions are relatively insensitive to pain. Thus, local infiltration with anesthetic solutions, such as 1 per cent lidocaine (Xylocaine), can produce satisfactory anesthesia for major and minor operations. What are some of the reasons that anesthesiologists now use general anesthesia almost entirely for neurosurgical procedures? Patients want to be comfortable and sedated, and local anesthesia leaves much to be desired. One cannot predict with accuracy which patients will cooperate, and nothing is quite so frustrating to both the surgeon and the anesthesiologist as an uncooperative patient. Many patients with intracranial disease are confused and therefore uncooperative. They are poor candidates for local anesthesia. Even a rational patient who must lie on the operating table in one position for several hours under emotional stress will probably be unable to cooperate fully. Furthermore, stimulation of motor or sensory portions of the brain may produce localized or generalized motor or sensory activity of the patient, with movement in the surgical field and loss of an airway. Finally, the duration of all known anesthetic agents, even with epinephrine (Adrenalin), is insufficient to cover the time required for some surgical procedures. For these reasons a qualified anesthesiologist feels that he has better control if the patient is under general anesthesia with an endotracheal tube than if he is under local anesthesia. General anesthesia today answers most of the disadvantages of local anesthesia with little added disadvantage to the patient. It is true that many physicians still 'lse local anesthesia, and their methods should not be criticized, particularly when only inexperienced persons are available to administer general anesthesia. The tendency, therefore, has been toward the use of general anesthesia for most neurosurgical procedures if adequately trained anesthesiologists are available.
ANESTHESIA FOR NEUROSURGERY
901
Premedication for general anesthesia and neurosurgery varies from institution to institution. In principle, it is a good rule to bring most patients to the operating room without premedication, since respiratory depression resulting from premedication may increase intracranial pressure. Opiates and their analogues, therefore, are prescribed with caution, and in some hospitals premedication is not advised. At times anesthesiologists will administer whatever medication is needed prior to or after induction of anesthesia through the intravenous route. Some uncooperative patientsfor example, small children-require a mild degree of preoperative sedation.
INDUCTION AND MAINTENANCE
The choice of anesthetic agents has been reduced in recent years to nonflammable agents. Intravenous induction of anesthesia is highly beneficial to patients, particularly those who may not be sedated. It results in smoother induction than does inhalation induction. A common procedure is relatively rapid induction with a barbiturate-thiopental (Pentothal) sodium or methohexital (Brevital)-followed by the administration of oxygen and succinylcholine in doses sufficient to prevent coughing or straining. An adequate airway is established by means of a flexible but nonkinkable cuffed endotracheal tube of the largest size that can be passed through the glottis. For maintenance we use halothane, nitrous oxide and oxygen, or halothane and oxygen. Other centers sometimes add combinations of nitrous oxide and oxygen with trichloroethylene or methoxyflurane (Penthrane). During hypotension, anesthesia can be reduced and maintained with doses of short-acting succinylcholine. The choice of anesthesia has revolved around three factors: (1) nonflammable and nonexplosive qualities, (2) rapid emergence at the end of the procedure, and (3) utmost safety to patient and personnel. At present the described techniques are being accepted universally. Nitrous oxide and oxygen alone are insufficient to maintain anesthesia for most neurosurgical· procedures, although prior to the advent of halothane, trichloroethylene, and Penthrane, nitrous oxide and oxygen were supplemented with drip or intermittent doses of opiates. This procedure fulfilled the need for a nonflammable agent; however, unless the anesthesiologist was experienced in neurosurgical anesthesia and familiar with the surgical team, it was difficult to have the patient awake at the end of the procedure, particularly without coughing or straining. Perhaps it is needless to say that cyclopropane, ethylene, and various forms of ether-although they have been used in neurosurgery-were dangerous in that an explosion or fire could be extremely damaging to the patient and to the operating room personnel. In these days of medicolegal problems, there would be no defense for such a technique if other methods were readily available.
902
TERRY,
DAW,
MICHENFELDER, TUOHY, MILLER
Modern anesthetic systems are designed for rebreathing and present no undue resistance to expiration. A low-resistance circle system is in widespread use in the United States. At times the anesthetic machine may be some distance from the patient and therefore two methods are widely used. Both the T piece and the Y piece have their advocates. Simply by fitting a bag to the end of a Y connection on the expiratory limb of the machine, control of respirations can be speedily instigated. However, with the improvement of circle systems and reduction of resistance, they are increasing in favor, particularly in those areas where respirators are being used.
VENTILATION
Ventilation in anesthesia for neurosurgery is in a state of flux. The importance of adequate ventilation without respiratory resistance is well known. Retention of carbon dioxide, particularly at levels that at one time might have been encountered during spontaneous respirations in patients managed with Pentothal, nitrous oxide, oxygen, and curare, is known to play havoc with the neurosurgical operating field and to be dangerous to the patient. During the period of drop doses of ether with its hypoxia, depressed respiration and constantly varying levels of anesthesia, ventilation was not possible to the degree that it now is with a respirator and light general anesthesia. Generally patients can be ventilated adequately by manual assistance or control of their respirations, but for long neurosurgical procedures a properly applied respirator provides better and more consistent ventilation. This is particularly true in patients who, because of anatomic build, surgical position, or pulmonary pathologic states, would be difficult to ventilate. However, much work remains to be done in regard to the possible deleterious effect of hyperventilation in extreme ranges (very low pC0 2) in various types of neurologic conditions. If hyperventilation proves to be a danger, perhaps it can be avoided by modification of respirator techniques. In addition to the foregoing considerations regarding ventilation, the management of these patients should include the placement of a stethoscope in the esophagus or on the chest, use of a bland petroleum-base ophthalmic ointment to protect the eyes against drying, and avoidance of orbital pressure and abrasions during movement. One or more carefully selected intravenous routes should be secured for the administration of necessary drugs and for replacement of blood. A large-bore flexible plastic needle is usually used. In the presence of a possible vascular lesion, two or more good intravenous routes are a necessity. Intravenous routes must be adequate for administration of dehydrating agents, for example 30 per cent urea or mannitol, and the extremities must be watched for possible infiltration of these sclerosing agents.
ANESTHESIA FOR NEUROSURGERY
903
POSITIONING OF PATIENT
Four classic positions are used in neurosurgery: (1) supine, (2) prone, (3) sitting, and (4) lateral. After induction of anesthesia and when the vital signs are stable, the patient is slowly placed in position. The supine position is used for operations on the anterior fossa and lesions in the frontal and temporal regions. The patient's head is raised slightly and stabilized; the feet may be lowered to a degree that will encourage venous drainage from the head. The sterile drapes used by the neurosurgical team are placed above and over the patient. An adequate airway must be established and maintained throughout the procedure, because repositioning or reinsertion of the endotracheal tube is difficult if not impossible once the operation has been initiated. The prone position is used for laminectomies and, at times, in an approach to the posterior fossa. It may lead to venous congestion in the operative area. In lumbar laminectomies, undue abdominal compression in an attempt to spread the lamina of the vertebra for surgical exposure may cause obstruction of the inferior vena cava and result in venous congestion, excessive bleeding, and hypotension. The prone position is useful also for operations on the upper thoracic and cervical regions. Abrasion of the cornea or pressure on the eyes resulting in retinal arterial thrombosis must be avoided. For surgical measures on the lower part of the spinal column one of the patient's arms usually can be raised up by the side of the head so that the anesthesiologist may have a route for blood and fluids. This position does not interfere with the surgical team. However, if the patient is in the face-down position with a horseshoetype headrest for operation on the high thoracic or cervical region, the anesthesiologist may stand at the patient's head or down toward the feet; in the latter place he must be certain that the patient's airway and intravenous routes are adequate. The blood pressure cuff must be protected and, if possible, the electrocardiogram should be monitored. The patient in the prone position must have sufficient support at the iliac crest and sternum; furthermore, care should be taken not to put large rolls under the abdomen where they might obstruct the vena cava, particularly if the patient is obese. Most intervertebral disks, fusions, and explorations of the spinal cord are done with the patient in the prone position. A few surgeons consider the lateral position better then the prone position because of less venous obstruction and less bleeding. The lateral position enables the patient to be placed with the back flexed for exposure. Little venous engorgement of the epidural veins occurs with the patient in this position unless excessive flexion is needed to open the intervertebral space. Many neurosurgeons operate on the spinal cord or remove a disk with the patient in this position, and some orthopedists perform fusions thus. The lateral position is used occasionally for lumbar sympathectomies, if an anterior approach has been used previously, or for
904
TERRY,
DAW,
MICHENFELDER, TUOHY, MILLER
complete sympathectomy for hypertension. Time may prove that this position is more useful in neurosurgery than is now realized. The sitting or upright position undoubtedly provides the least congestion in the operative field for cervical laminectomy or exploration of a posterior fossa. Many neurosurgeons prefer it, because blood will flow out of the wound resulting in better exposure of the surgical field. The patient usually is placed on the operating room table in a sitting position after induction of anesthesia and intubation in the supine position. An attempt is made to place the feet in the same horizontal plane as the heart in order to avoid hypotension. In many instances the anesthesiologist prefers the sitting position to the prone position since he can observe the patient better and can reach the airway and intravenous routes more easily. Two dangers are associated with the sitting position: severe hypotension and air embolism. Hypotension can be recognized during the careful positioning of a patient and can be corrected by administration of vasopressors and blood. The incidence of air embolism is difficult to assess and accurate figures are not available. The esophageal stethoscope and electrocardiogram will help in early recognition of air emboli. Careful surgical technique and hemostasis in opening and closing wounds will minimize the danger of air being sucked into a vein. An anesthesiologist must be ready to apply positive airway pressure and pressure to the veins of the neck should a sinus be entered or should a large vessel be sucking in air.
SPECIAL TECHNIQUES FOR NEUROSURGERY
Special techniques are commonly required during anesthesia for neurosurgery, more so, in fact, than in any other area of anesthesia. Induced and controlled hypotension may be necessary in surgical treatment for certain vascular lesions. Various techniques are presented in the paper on ·'Controlled Hypotension" by Daw, Didier and Theye (pages 1003-1012). Induced and controlled hypothermia by surface methods and extracorporeal techniques have their place in neurosurgical anesthesia. With the use of air-conditioned operating rooms, unintentional or inadvertent hypothermia is not uncommon in adults, and constant alertness and immediate application of counteracting measures are required to avoid this complication in children. These techniques are discussed in detail in the papers on "Induced Hypothermia: Physiologic Effects, Indications, and Techniques" by Michenfelder, Terry, Daw and Uihlein, and "The Pediatric Patient in the Operating Room" by Dawson and Lynn (pages 889-898,949-959). Another special technique used in anesthesia for neurosurgery is subarachnoid drainage. Usually after the patient is asleep, a malleable metal needle is inserted into the lower lumbar region and is attached to a 100-ml. syringe so that the subarachnoid space may be drained after a bone
ANESTHESIA FOR NEUROSURGERY
905
flap is removed. This drainage, if it functions properly, will give remarkable exposure for lesions in the region of the circle of Willis and the optic chiasm, and is commonly used to expose aneurysms of the circle of Willis, pituitary or optic nerve tumors, and certain meningiomas along the base of the skull. Under sterile technique, infection is a minor problem, and with good sterile technique, subarachnoid drainage can far outweigh the theoretical disadvantages of infection. Care must be taken not to remove an excessive amount of fluid prior to removal of the bone flap since an acute subdural hematoma may occur from a tear in small cortical vessels attached to the dura. If severe intracranial pressure exists, subarachnoid drainage should be used with caution or avoided. Dehydrat.ing agents are used occasionally, if intracranial pressure is greatly increased. Dehydrating agents are not a substitute for diagnosis of a lesion causing increased intracranial pressure and resection adequate to relieve the pressure. Numerous dehydrating agents are available and useful, as is subarachnoid drainage, for improved surgical exposure which lessens morbidity and mortality.
THE POSTOPERATIVE PERIOD
The immediate postoperative period for the neurosurgical patient is equally important as the preoperative and operative periods, and anesthesiologists can aid by having the patient awake at the end of the neurosurgical procedure in order that a base-line neurologic examination can be made. The results of such examination aid the neurosurgeon in determining whether any change that has developed in the patient's condition is due to cerebral edema or to postoperative hemorrhage. Postoperative hemorrhage requires early recognition and evacuation. The neurosurgical patient is observed for a period in the postanesthesia room and in a special neurosurgical constant-care unit where physicians and nurses especially trained in neurologic and anesthetic methods are available.
CONCLUSIONS
The anesthesiologist is an important member of the neurosurgical team in his careful support of the patient during neurosurgery. He can be of as great help in reducing the morbidity and mortality as the neurosurgeon is in accurately diagnosing the pathologic lesion and eradicating it. As anesthesiologists and neurosurgeons have improved their techniques, the mortality from neurosurgical procedures has been reduced and the need for reoperation because of reactionary hemorrhage and cerebral edema is decreasing.
906
TERRY, DAW, MICHENFELDER, TUOHY, MILLER
REFERENCES 1. Ballantine, R. I.: A Practice of General Anesthesia for Neurosurgery. Boston, Little, Brown & Company, 1960, 152 pp.
2. Carnegie, D. M.: Anesthesia and analgesia for neurosurgery. In Evans, F. T., and Gray, Cecil: General Anaesthesia. London, Butterworth & Co., Ltd., 1959, vol. 2, pp. 141-155. 3. Macintosh, R. R.: Oxford inflating bellows. Brit. M. J. 2:202 (July 25) 1953. 4. Macintosh, Robert: A plea for simplicity. Brit. M. J. 2:1054-1057 (Oct. 29) 1955. 5. Parkhouse, James, and Simpson, B. R.: A restatement of anaesthetic principles. Brit. J. Anaesth. 31:464-469 (Oct.) 1959. 6. Pitkin, G. P.: Conduction Anesthesia. 2nd Ed. Philadelphia, J. B. Lippincott Company, 1953, 1005 pp. 7. Wyke, B. D.: Physiology of the nervous system: Some principles of general neurophysiology relating to anaesthesia. In Evans, F. T., and Gray, Cecil: General Anaesthesia. London, Butterworth & Co., Ltd., 1959, vol. 1, pp. 125-237. 8. Wylie, W. D., and Churchill-Davidson, H. C.: Neurosurgical Anaesthesia. In A Practice of Anaesthesia. Chicago, Year Book Publishers, Inc., 1961, pp. 765-798.
The basis of good anesthesia for neurosurgery consists of a perfect airway with minimal resistance, light general anesthesia without coughing or straining, adequate ventilation, nonflammable and nonexplosive anesthetic agents, and a speedy return to consciousness at the end of the surgical procedure. Space does not permit a historical review of neurosurgery from the time when anesthesia was unknown through the development of general anesthesia when flammable and explosive agents were a necessity, even with cautery. Neither does it permit a discussion of neurosurgery and general anesthesia before the use of endotracheal tubes. A review of their development to the present use of nonflammable agents, muscle relaxants, respirators, gas machines with circle systems and nonkinkable cuffed endotracheal tubes shows remarkable changes. These changes are reflected in greatly decreased morbidity and mortality as well as in bolder and more radical neurosurgical procedures than were possible a few decades earlier. The development of anesthesia along with advances in the use of blood, blood derivatives, and fluid therapy, the advent of antibiotics, the use of cortisone, and the development and improvement in diagnostic neuroradiologic techniques has led to great advancement in neurosurgery.l, 2,7,8 Anesthetic techniques for neurosurgery in well-staffed and wellsupplied operating units probably vary less in principle now than during any other period. These techniques will continue to improve as anesthesiologists gain further knowledge in the fields of neurophysiology, neuropharmacology, neuroanatomy, and neuropathology. After a review of present methods of anesthesia in neurosurgery, an anesthesiologist cannot
899
900
TERRY, DAW, MICHENFELDER, TuOHY, MILLER
help wondering what minimal equipment he would attempt to take into an undeveloped part of the world or into a combat area where gas cylinders, massive anesthesia equipment, and large stores of drugs might not be available. As advancements are made and experience is gained, anesthesiologists should not forget earlier experiences with good, proved techniques of local and regional anesthesia, 6 including the open-drop use of chloroform, ether, and possibly halothane with a portable hand ventilator and, it is hoped, an endotracheal tube. 8- 5 If these older techniques are forgotten, time may prove that we are actually unprepared and less experienced than we thought.
GENERAL ANESTHESIA VERSUS LOCAL ANESTHESIA
The value of general anesthesia versus local anesthesia is an age-old problem in the management of the neurosurgical patient. When craniotomy is necessary, the skin, fascia, temporal muscle, periosteum, and certain parts of the dura are sensitive to pain. Other regions are relatively insensitive to pain. Thus, local infiltration with anesthetic solutions, such as 1 per cent lidocaine (Xylocaine), can produce satisfactory anesthesia for major and minor operations. What are some of the reasons that anesthesiologists now use general anesthesia almost entirely for neurosurgical procedures? Patients want to be comfortable and sedated, and local anesthesia leaves much to be desired. One cannot predict with accuracy which patients will cooperate, and nothing is quite so frustrating to both the surgeon and the anesthesiologist as an uncooperative patient. Many patients with intracranial disease are confused and therefore uncooperative. They are poor candidates for local anesthesia. Even a rational patient who must lie on the operating table in one position for several hours under emotional stress will probably be unable to cooperate fully. Furthermore, stimulation of motor or sensory portions of the brain may produce localized or generalized motor or sensory activity of the patient, with movement in the surgical field and loss of an airway. Finally, the duration of all known anesthetic agents, even with epinephrine (Adrenalin), is insufficient to cover the time required for some surgical procedures. For these reasons a qualified anesthesiologist feels that he has better control if the patient is under general anesthesia with an endotracheal tube than if he is under local anesthesia. General anesthesia today answers most of the disadvantages of local anesthesia with little added disadvantage to the patient. It is true that many physicians still 'lse local anesthesia, and their methods should not be criticized, particularly when only inexperienced persons are available to administer general anesthesia. The tendency, therefore, has been toward the use of general anesthesia for most neurosurgical procedures if adequately trained anesthesiologists are available.
ANESTHESIA FOR NEUROSURGERY
901
Premedication for general anesthesia and neurosurgery varies from institution to institution. In principle, it is a good rule to bring most patients to the operating room without premedication, since respiratory depression resulting from premedication may increase intracranial pressure. Opiates and their analogues, therefore, are prescribed with caution, and in some hospitals premedication is not advised. At times anesthesiologists will administer whatever medication is needed prior to or after induction of anesthesia through the intravenous route. Some uncooperative patientsfor example, small children-require a mild degree of preoperative sedation.
INDUCTION AND MAINTENANCE
The choice of anesthetic agents has been reduced in recent years to nonflammable agents. Intravenous induction of anesthesia is highly beneficial to patients, particularly those who may not be sedated. It results in smoother induction than does inhalation induction. A common procedure is relatively rapid induction with a barbiturate-thiopental (Pentothal) sodium or methohexital (Brevital)-followed by the administration of oxygen and succinylcholine in doses sufficient to prevent coughing or straining. An adequate airway is established by means of a flexible but nonkinkable cuffed endotracheal tube of the largest size that can be passed through the glottis. For maintenance we use halothane, nitrous oxide and oxygen, or halothane and oxygen. Other centers sometimes add combinations of nitrous oxide and oxygen with trichloroethylene or methoxyflurane (Penthrane). During hypotension, anesthesia can be reduced and maintained with doses of short-acting succinylcholine. The choice of anesthesia has revolved around three factors: (1) nonflammable and nonexplosive qualities, (2) rapid emergence at the end of the procedure, and (3) utmost safety to patient and personnel. At present the described techniques are being accepted universally. Nitrous oxide and oxygen alone are insufficient to maintain anesthesia for most neurosurgical· procedures, although prior to the advent of halothane, trichloroethylene, and Penthrane, nitrous oxide and oxygen were supplemented with drip or intermittent doses of opiates. This procedure fulfilled the need for a nonflammable agent; however, unless the anesthesiologist was experienced in neurosurgical anesthesia and familiar with the surgical team, it was difficult to have the patient awake at the end of the procedure, particularly without coughing or straining. Perhaps it is needless to say that cyclopropane, ethylene, and various forms of ether-although they have been used in neurosurgery-were dangerous in that an explosion or fire could be extremely damaging to the patient and to the operating room personnel. In these days of medicolegal problems, there would be no defense for such a technique if other methods were readily available.
902
TERRY,
DAW,
MICHENFELDER, TUOHY, MILLER
Modern anesthetic systems are designed for rebreathing and present no undue resistance to expiration. A low-resistance circle system is in widespread use in the United States. At times the anesthetic machine may be some distance from the patient and therefore two methods are widely used. Both the T piece and the Y piece have their advocates. Simply by fitting a bag to the end of a Y connection on the expiratory limb of the machine, control of respirations can be speedily instigated. However, with the improvement of circle systems and reduction of resistance, they are increasing in favor, particularly in those areas where respirators are being used.
VENTILATION
Ventilation in anesthesia for neurosurgery is in a state of flux. The importance of adequate ventilation without respiratory resistance is well known. Retention of carbon dioxide, particularly at levels that at one time might have been encountered during spontaneous respirations in patients managed with Pentothal, nitrous oxide, oxygen, and curare, is known to play havoc with the neurosurgical operating field and to be dangerous to the patient. During the period of drop doses of ether with its hypoxia, depressed respiration and constantly varying levels of anesthesia, ventilation was not possible to the degree that it now is with a respirator and light general anesthesia. Generally patients can be ventilated adequately by manual assistance or control of their respirations, but for long neurosurgical procedures a properly applied respirator provides better and more consistent ventilation. This is particularly true in patients who, because of anatomic build, surgical position, or pulmonary pathologic states, would be difficult to ventilate. However, much work remains to be done in regard to the possible deleterious effect of hyperventilation in extreme ranges (very low pC0 2) in various types of neurologic conditions. If hyperventilation proves to be a danger, perhaps it can be avoided by modification of respirator techniques. In addition to the foregoing considerations regarding ventilation, the management of these patients should include the placement of a stethoscope in the esophagus or on the chest, use of a bland petroleum-base ophthalmic ointment to protect the eyes against drying, and avoidance of orbital pressure and abrasions during movement. One or more carefully selected intravenous routes should be secured for the administration of necessary drugs and for replacement of blood. A large-bore flexible plastic needle is usually used. In the presence of a possible vascular lesion, two or more good intravenous routes are a necessity. Intravenous routes must be adequate for administration of dehydrating agents, for example 30 per cent urea or mannitol, and the extremities must be watched for possible infiltration of these sclerosing agents.
ANESTHESIA FOR NEUROSURGERY
903
POSITIONING OF PATIENT
Four classic positions are used in neurosurgery: (1) supine, (2) prone, (3) sitting, and (4) lateral. After induction of anesthesia and when the vital signs are stable, the patient is slowly placed in position. The supine position is used for operations on the anterior fossa and lesions in the frontal and temporal regions. The patient's head is raised slightly and stabilized; the feet may be lowered to a degree that will encourage venous drainage from the head. The sterile drapes used by the neurosurgical team are placed above and over the patient. An adequate airway must be established and maintained throughout the procedure, because repositioning or reinsertion of the endotracheal tube is difficult if not impossible once the operation has been initiated. The prone position is used for laminectomies and, at times, in an approach to the posterior fossa. It may lead to venous congestion in the operative area. In lumbar laminectomies, undue abdominal compression in an attempt to spread the lamina of the vertebra for surgical exposure may cause obstruction of the inferior vena cava and result in venous congestion, excessive bleeding, and hypotension. The prone position is useful also for operations on the upper thoracic and cervical regions. Abrasion of the cornea or pressure on the eyes resulting in retinal arterial thrombosis must be avoided. For surgical measures on the lower part of the spinal column one of the patient's arms usually can be raised up by the side of the head so that the anesthesiologist may have a route for blood and fluids. This position does not interfere with the surgical team. However, if the patient is in the face-down position with a horseshoetype headrest for operation on the high thoracic or cervical region, the anesthesiologist may stand at the patient's head or down toward the feet; in the latter place he must be certain that the patient's airway and intravenous routes are adequate. The blood pressure cuff must be protected and, if possible, the electrocardiogram should be monitored. The patient in the prone position must have sufficient support at the iliac crest and sternum; furthermore, care should be taken not to put large rolls under the abdomen where they might obstruct the vena cava, particularly if the patient is obese. Most intervertebral disks, fusions, and explorations of the spinal cord are done with the patient in the prone position. A few surgeons consider the lateral position better then the prone position because of less venous obstruction and less bleeding. The lateral position enables the patient to be placed with the back flexed for exposure. Little venous engorgement of the epidural veins occurs with the patient in this position unless excessive flexion is needed to open the intervertebral space. Many neurosurgeons operate on the spinal cord or remove a disk with the patient in this position, and some orthopedists perform fusions thus. The lateral position is used occasionally for lumbar sympathectomies, if an anterior approach has been used previously, or for
904
TERRY,
DAW,
MICHENFELDER, TUOHY, MILLER
complete sympathectomy for hypertension. Time may prove that this position is more useful in neurosurgery than is now realized. The sitting or upright position undoubtedly provides the least congestion in the operative field for cervical laminectomy or exploration of a posterior fossa. Many neurosurgeons prefer it, because blood will flow out of the wound resulting in better exposure of the surgical field. The patient usually is placed on the operating room table in a sitting position after induction of anesthesia and intubation in the supine position. An attempt is made to place the feet in the same horizontal plane as the heart in order to avoid hypotension. In many instances the anesthesiologist prefers the sitting position to the prone position since he can observe the patient better and can reach the airway and intravenous routes more easily. Two dangers are associated with the sitting position: severe hypotension and air embolism. Hypotension can be recognized during the careful positioning of a patient and can be corrected by administration of vasopressors and blood. The incidence of air embolism is difficult to assess and accurate figures are not available. The esophageal stethoscope and electrocardiogram will help in early recognition of air emboli. Careful surgical technique and hemostasis in opening and closing wounds will minimize the danger of air being sucked into a vein. An anesthesiologist must be ready to apply positive airway pressure and pressure to the veins of the neck should a sinus be entered or should a large vessel be sucking in air.
SPECIAL TECHNIQUES FOR NEUROSURGERY
Special techniques are commonly required during anesthesia for neurosurgery, more so, in fact, than in any other area of anesthesia. Induced and controlled hypotension may be necessary in surgical treatment for certain vascular lesions. Various techniques are presented in the paper on ·'Controlled Hypotension" by Daw, Didier and Theye (pages 1003-1012). Induced and controlled hypothermia by surface methods and extracorporeal techniques have their place in neurosurgical anesthesia. With the use of air-conditioned operating rooms, unintentional or inadvertent hypothermia is not uncommon in adults, and constant alertness and immediate application of counteracting measures are required to avoid this complication in children. These techniques are discussed in detail in the papers on "Induced Hypothermia: Physiologic Effects, Indications, and Techniques" by Michenfelder, Terry, Daw and Uihlein, and "The Pediatric Patient in the Operating Room" by Dawson and Lynn (pages 889-898,949-959). Another special technique used in anesthesia for neurosurgery is subarachnoid drainage. Usually after the patient is asleep, a malleable metal needle is inserted into the lower lumbar region and is attached to a 100-ml. syringe so that the subarachnoid space may be drained after a bone
ANESTHESIA FOR NEUROSURGERY
905
flap is removed. This drainage, if it functions properly, will give remarkable exposure for lesions in the region of the circle of Willis and the optic chiasm, and is commonly used to expose aneurysms of the circle of Willis, pituitary or optic nerve tumors, and certain meningiomas along the base of the skull. Under sterile technique, infection is a minor problem, and with good sterile technique, subarachnoid drainage can far outweigh the theoretical disadvantages of infection. Care must be taken not to remove an excessive amount of fluid prior to removal of the bone flap since an acute subdural hematoma may occur from a tear in small cortical vessels attached to the dura. If severe intracranial pressure exists, subarachnoid drainage should be used with caution or avoided. Dehydrat.ing agents are used occasionally, if intracranial pressure is greatly increased. Dehydrating agents are not a substitute for diagnosis of a lesion causing increased intracranial pressure and resection adequate to relieve the pressure. Numerous dehydrating agents are available and useful, as is subarachnoid drainage, for improved surgical exposure which lessens morbidity and mortality.
THE POSTOPERATIVE PERIOD
The immediate postoperative period for the neurosurgical patient is equally important as the preoperative and operative periods, and anesthesiologists can aid by having the patient awake at the end of the neurosurgical procedure in order that a base-line neurologic examination can be made. The results of such examination aid the neurosurgeon in determining whether any change that has developed in the patient's condition is due to cerebral edema or to postoperative hemorrhage. Postoperative hemorrhage requires early recognition and evacuation. The neurosurgical patient is observed for a period in the postanesthesia room and in a special neurosurgical constant-care unit where physicians and nurses especially trained in neurologic and anesthetic methods are available.
CONCLUSIONS
The anesthesiologist is an important member of the neurosurgical team in his careful support of the patient during neurosurgery. He can be of as great help in reducing the morbidity and mortality as the neurosurgeon is in accurately diagnosing the pathologic lesion and eradicating it. As anesthesiologists and neurosurgeons have improved their techniques, the mortality from neurosurgical procedures has been reduced and the need for reoperation because of reactionary hemorrhage and cerebral edema is decreasing.
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TERRY, DAW, MICHENFELDER, TUOHY, MILLER
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2. Carnegie, D. M.: Anesthesia and analgesia for neurosurgery. In Evans, F. T., and Gray, Cecil: General Anaesthesia. London, Butterworth & Co., Ltd., 1959, vol. 2, pp. 141-155. 3. Macintosh, R. R.: Oxford inflating bellows. Brit. M. J. 2:202 (July 25) 1953. 4. Macintosh, Robert: A plea for simplicity. Brit. M. J. 2:1054-1057 (Oct. 29) 1955. 5. Parkhouse, James, and Simpson, B. R.: A restatement of anaesthetic principles. Brit. J. Anaesth. 31:464-469 (Oct.) 1959. 6. Pitkin, G. P.: Conduction Anesthesia. 2nd Ed. Philadelphia, J. B. Lippincott Company, 1953, 1005 pp. 7. Wyke, B. D.: Physiology of the nervous system: Some principles of general neurophysiology relating to anaesthesia. In Evans, F. T., and Gray, Cecil: General Anaesthesia. London, Butterworth & Co., Ltd., 1959, vol. 1, pp. 125-237. 8. Wylie, W. D., and Churchill-Davidson, H. C.: Neurosurgical Anaesthesia. In A Practice of Anaesthesia. Chicago, Year Book Publishers, Inc., 1961, pp. 765-798.