J. Marcus. University of Louisville.

Unlike the potent volatile anesthetics in clinical use cheap 100mg sildigra amex, N O does2 not produce significant skeletal muscle relaxation purchase sildigra 100 mg with amex, but it does have modest analgesic effects buy sildigra cheap online. Despite a long track record of use purchase sildigra uk, controversy has surrounded N O in four areas: its role in postoperative nausea and vomiting;7 2 its potential toxic effects on cell function via inactivation of vitamin B ; its12 adverse effects related to absorption and expansion into air-filled structures and bubbles; and lastly, its effect on embryonic development. The most valid and most clinically relevant concern is the ability of N O to expand air-filled2 spaces because of its greater solubility in blood compared to nitrogen. Other closed spaces may occur as a result of disease or surgery, such as a pneumothorax. Since nitrogen in air-filled spaces cannot be removed readily via the bloodstream, N O delivered to a patient diffuses from the2 blood into these closed gas spaces quite easily until the partial pressure equals that of the blood and alveoli. Compliant spaces will continue to expand until sufficient pressure is generated to oppose further N O flow into the space. Seventy-five percent N O can expand a pneumothorax to double or triple2 its size in 10 and 30 minutes, respectively. Air-filled cuffs of pulmonary artery catheters and endotracheal tubes also expand with the use of N O,2 possibly causing tissue damage via increased pressure in the pulmonary artery or trachea, respectively. Accumulation of N O in the middle ear can diminish2 hearing postoperatively and is contraindicated for tympanoplasty because the8 increased pressure can dislodge a tympanic graft. Neuropharmacology of Inhaled Anesthetics Minimum Alveolar Concentration Pharmacodynamic effects of anesthetics are based on their dosing. Loss of consciousness typically precedes the absence of stimulus-induced movement by a wide margin. Concentrations of inhaled anesthetics that provide loss of self-awareness and recall are about 0. Interestingly, transition from awake to unconscious and back typically shows some hysteresis in that it quite consistently takes 0. The pattern depicted here is characteristic of all of the anesthetics examined (enflurane, halothane, and isoflurane). The nonlinear responses of cerebral metabolism to low concentrations of halothane, enflurane, isoflurane and thiopental. Unfortunately, no single mechanism explains these alterations, supporting the view that anesthesia is the net result of numerous and widely varying physiologic alterations. Nitrous oxide departs from the potent agents in several important respects, and is therefore discussed separately. Although neuroprotection from volatile anesthetics is a well-defined concept, the volatile anesthetics can cause injury in certain conditions via cerebral vasodilation and increases in intracranial pressure. A full understanding of the anesthetic effects on cerebral physiology helps prevent adverse cerebral events in clinical practice. This phenomenon has been called2 uncoupling, but from a mechanistic standpoint, true uncoupling of flow from metabolism may not occur. The net effect on the cerebral vessels depends on the sum of indirect vasoconstricting and direct vasodilating influences. Figure 18-11 Cerebral blood flow (and velocity) measured in the presence of normocapnia and in the absence of surgical stimulation in volunteers receiving halothane or isoflurane. Cerebral blood flow velocity measured before and during sevoflurane and desflurane anesthesia up to 1. This may relate to the airway irritant effects of desflurane30 rather than a specific alteration in neurophysiology. The bottom line is that all three potent agents may be used at appropriate doses, especially with adjunctive and compensatory therapies, in nearly any neurosurgical procedure. Both sevoflurane and desflurane34 2 have been shown to improve neurologic outcome after incomplete cerebral ischemia in a rat model. These alterations are associated with increased morbidity and mortality in the first year after surgery from causes such as decubiti, pneumonia, and deep vein thrombosis. In the elderly in particular, subtle39 cognitive dysfunction can persist long after expected drug clearance. It is clear from the wide variations in the results available in the literature that more research is required into this important topic. Interestingly, the development43 of postoperative delirium after exposure to N O in a mixed anesthetic has a2 similar incidence to that when not exposed, suggesting that the mechanisms, while possibly different, are not additive. In subcortical modalities, such as brainstem auditory evoked potentials, these agents are associated with negligible effects. In general, visual evoked potentials are somewhat more sensitive to the effects of the volatile anesthetics than somatosensory evoked potentials. The evoked response is most commonly recorded as a muscle potential or a peripheral nerve signal. The trigger is typically transosseous activation via electrical or magnetic stimulation. Nitrous oxide may be neuroprotective in rat models of cerebral ischemia, but other work suggests it is neurotoxic. The Circulatory System Hemodynamics The cardiac, vascular, and autonomic effects of the volatile anesthetics have been defined through a number of studies carried out in human volunteers not undergoing surgery. Myocardial Contractility Myocardial contractility indices have been directly evaluated in animals and indirectly evaluated in human volunteers during the administration of each of the volatile anesthetics. Isoflurane, desflurane, and sevoflurane produced similar dose-dependent reductions in indices of myocardial function in an autonomically denervated dog model (Fig. Echocardiographic- determined indices of myocardial function in healthy humans, including the more noteworthy measurement of the velocity of circumferential fiber shortening have not been diminished by isoflurane, desflurane, or sevoflurane. Despite the small reduction in baseline contractility, the anesthetics did not affect the ability of the myocardium to respond to an acute increase in cardiac preload. Thus, functional reserve of the heart was not impaired by the volatile anesthetics. In patients without pre-58 existing diastolic dysfunction, volatile anesthetics do not have any clinically relevant negative effect on early diastolic relaxation, although resultant decrease in global atrial function may impact late diastolic left ventricular filling. The conscious control data were assigned 100%, and subsequent reductions in the inotropic state are depicted for both 1 and 1. M , slope of the regional preloadw recruitable stroke work relationship; dP/dt50, change in pressure per unit of time. Spontaneous ventilation in theory would improve the safety of volatile anesthetic administration because the anesthetic concentration that produces cardiovascular collapse exceeds the concentration that results in apnea. Nitrous oxide is commonly combined with potent volatile anesthetics to maintain general anesthesia. It increases sympathetic nervous system activity and vascular resistance when given in a 40% concentration. Blood flow to liver, kidneys, and gut is decreased, particularly at deep levels of anesthesia. In contrast, blood flow to the brain, muscle, and skin is increased or not changed during general anesthesia. In humans,63 increases in muscle blood flow are noted with isoflurane, desflurane, and sevoflurane with minimal differences between anesthetics at equipotent concentrations. Volatile anesthetics have direct effects on cardiac pacemaker cells and conduction pathways. The ether-based anesthetics—isoflurane, desflurane, and sevoflurane—required three- to sixfold greater doses of epinephrine to cause arrhythmias. Desflurane has not been evaluated in terms of ischemia and outcome77 in a patient population with coronary disease undergoing noncardiac surgery. Most studies would suggest that determinants of myocardial oxygen supply and demand, rather than the anesthetic, are of far greater importance to patient outcomes. Cardioprotection from Volatile Anesthetics A preconditioning stimulus such as brief coronary occlusion and ischemia initiates a signaling cascade of intracellular events that helps protect the cardiac myocyte and reduce reperfusion myocardial injury following subsequent ischemic episodes. This delayed effect relates to induction of nitric oxide synthase, superoxide dismutase, and heat-shock proteins. The volatile anesthetics given before (preconditioning) or immediately after (postconditioning) mimic ischemic preconditioning and trigger a similar cascade of intracellular events resulting in reduced myocardial injury and myocardial protection that lasts beyond the elimination of the anesthetic. Pharmacologic blockade of these factors reduces or eliminates the cardioprotective effect of ischemic or volatile anesthetic preconditioning. Lipophilic volatile anesthetics diffuse through myocardial cell membranes and alter mitochondrial electron transport, leading to reactive oxygen species formation. Preconditioned hearts may tolerate ischemia78 for 10 minutes longer than nonconditioned hearts. They should be discontinued 24 to 48 hours prior to elective surgery in high-risk patients.

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Moreover buy discount sildigra line, as patients receiving device therapy are living longer purchase 100mg sildigra mastercard, they are more likely to undergo device exchanges or develop infections buy cheap sildigra 50mg on line. Infections are more common during revision procedures than primary device implantation [10] buy 25mg sildigra with mastercard. Overall, 6319 patients were enrolled at 44 medical centers and followed for a year. Forty-two patients developed device- related infectious complications during the 12-month follow-up period. Early re- intervention, for instance to evacuate a pocket hematoma or lead revision, was found to be a leading risk factor for infection. The presence of fever 24 h prior to 14 Cardiac Device Related Endocarditis 189 implantation was also associated with an increased risk for subsequent device infec- tion. No significant difference was seen in the infection rate between single versus dual chamber devices. Interestingly, patients who had a temporary pacing wire prior to insertion of a permanent device were twice as likely to develop device infection when compared to those who did not have a temporary pacing system. A review of Danish registry of 46,299 patients who underwent pacemaker implan- tation reported 596 cases of infection. In this analysis, patients who underwent device replacement procedures were at a higher risk for infection as compared to patients with their initial pacemaker implantation. Additional risk factors, which were found to be significant in multivariable analysis, were male sex, younger age of patient at time of implantation (longer time living with a device), and absence of perioperative antimicrobial prophylaxis. Dual chamber pacing mode, though significant in the uni- variate analysis, was not statistically significant in the multivariate model [13]. In a retrospective, single center case–control study, patients with device infections were more likely to be diabetic, had conges- tive heart failure, were on oral anticoagulation therapy and had prior device manipu- lation. Renal insufficiency was associated with much higher rate of infection (42 % among infected patients compared to 13% in control patients) [16]. Device generator pocket infection with microorganism tracking along the trans- venous leads to involve intra-cardiac portion of the electrode. Hematogenous seeding of the transvenous leads or device generator pocket from bloodstream infection from a remote focus. Infection of the generator pocket could occur at the time of device implantation or during device manipulation (generator exchange/upgrade or lead revision/manip- ulation). Device pocket can also get contaminated and infected if the generator or leads erode through the skin. Occasionally it may not be possible to distinguish whether indolent device infection is the cause of skin erosion or the result of genera- tor or lead erosion. Possibility of bacterial contamination of the device generator at the time of implantation was studied in an investigation by Da Costa et al. In 2 of the cases Staphylococcus schleiferi was isolated, which was molecularly identical to the strain initially found in the pacemaker pocket, suggesting that pocket contamination occurred at the time of implantation [20 ]. Unlike staphylococci, gram-negative bloodstream infections typically do not result in hematogenous seeding of the device leads. Both the confirmed cases had a generator site infection, suggesting that device was the source of bloodstream infection. There were no cases of hematogenous seeding of leads by gram-negative bacteremia from a distant focus. Various bacteria have different virulence factors that enable them to attach to a foreign device. Once bound to prosthesis surfaces, staphylococci establish a biofilm (slime layer) which is a surface-associated community of one or more microbial species that are firmly attached to each other and the solid surface. They are encased in an extracellular polymeric matrix that holds the biofilm together [25]. Organisms in a biofilm are more resistant to antimicrobial therapy possibly due to the physical pro- tection from the layer of matrix which encases them [27]. Moreover, low metabolic activity and slower rate of replication of bacteria encased in the biofilm makes them more resistant to killing by cell-wall active agents (beta-lactams and glyclopep- tides) that primarily target rapidly replicating bacteria. Device Related Factors Physical and biochemical properties of the polymer used to make the device genera- tor shell, lead insulation material and electrode tips can play a vital role in allowing or inhibiting bacterial adhesion. One of the main parameters that predict bacterial adhesion is the degree of hydrophobicity of the device surface. The higher the hydrophobicity of surface material, the greater the bacterial adhesion [25 , 28 ]. The impact of choice of device materials on the risk of infection is not well characterized and should be explored. Up to 7% of the cultures were negative, primarily due to prior exposure to antibiotics. In the first few weeks after implantation, device infections are predominantly due to S. The prevalence of methicillin resistance among the staphylococci species causing device infections varies based on the geographical location and various studies have shown different rates [30 , 33]. Patients with pocket site infections typically present with pain, erythema, drainage, swelling, tenderness or dehiscence at the site of the generator. As device leads are in close proximity to tricuspid valve, right-sided endocarditis can develop with septic emboli to lungs. Majority (81%) of the patients presented with fever and 149 (84%) had positive blood cul- tures. The tricuspid valve was most frequently involved (43 cases) and the pulmonic valve being the least affected (one case only). A positive culture (either blood or lead culture) was obtained in 53 out of 60 cases (88%). In a retrospective study from Sweden that included 44 episodes of pacemaker endocarditis, 38 patients presented with fever without any other focal signs of device infection. Fourteen percent of the cases had systemic embolic phenomenon, with lungs being the most common site [22]. All the patients undergoing routine hemodialysis presented with bloodstream infections in this series and 77 % of the patients had fever and leukocytosis on presentation. Differentiating a lead thrombus from “true” vegetation on the basis of echocar- diography can be very difficult. The scan also helped in outlining the extent of infection by show- ing if the infected area involved only the generator pocket or affected the leads as well. It was found to have a sensitivity of 94% and a negative predictive value of 94 % [43]. No activity was seen in patients in Group C and mini- mum activity was seen in Group B patients. Six patients were found to have superficial infection and were treated with antibiotics only. Only one false positive was seen, in a patient who had a Dacron pouch in place around the generator [47]. Hence the reli- ability of this approach in patients with an antibiotic mesh or envelope is not known. It is also unclear how prolonged use of antibiotics would affect the results of this particular imaging modality. Identification of the causative microorganisms is critical for choosing optimal antimicrobial therapy. Therefore, once the decision has been made to remove the device, cultures of the pocket tissue, deep pocket swab, and device surface swab should be obtained at the time of extraction. In the case of pocket site infections, culture of tissue from the pocket has a higher yield than swabs from the pocket site [48]. Also, lead tip cultures are not always reliable in the presence of a pocket infection as lead tips can potentially get contaminated during extraction through an infected pocket environment [49]. Sonication of the extracted device to disrupt biofilm on the device surfaces can improve the microbiological diagnosis of infection. In the infected group, significant bacterial growth was observed in 54 % of sonicate fluids, significantly greater than the sensitivities of pocket swab (20 %), device swab (9 %), or tissue (9 %) culture. Of note, majority of patients had received antibiotics prior to device removal in this study.

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Microneurosurgery order sildigra in india, Volume 4b: Microneurosurgery of bined surgical and radiotherapeutic treatment of 260 patients purchase sildigra 120mg with visa. Extrasellar extensions of pituitary adenomas: (section of 1905;8:953–1024 neurology) purchase 25 mg sildigra with amex. Transsphenoidal microsurgery for prolactin- Neurosurg 1953;10:301–316 secreting pituitary adenomas buy generic sildigra 100 mg line. Anatomical observa­ Pituitary Adenomas and Related Lesions with Emphasis on Trans­ tions of the subarachnoid cisterns of the brain during surgery. J Neu­ sphenoidal Microsurgery: New York: Appleton-Century-Crofts; 1982: rosurg 1976;44:298–302 277–306 38. Acta Neurochir Suppl (Wien) 1996;65:16–17 microsurgery of pituitary macroadenomas with long­term follow­ 39. J Neurosurg 1983;59:395–401 The one-piece orbitozygomatic approach: the MacCarty burr hole 60. Incidence and management of com­ and the inferior orbital fssure as keys to technique and application. Neurosurgery magnetic resonance imaging to determine the extent of resection 2008;62(6, Suppl 3):1233–1239 of pituitary macroadenomas during transsphenoidal microsurgery. Transcranial epidural approach to pituitary tumors ex­ Neurosurgery 2001;49:1133–1143, discussion 1143–1144 tending beyond the sella. Cerebrospinal fuid rhinorrhea sion 551–552 following trans-sphenoidal pituitary macroadenoma surgery: 42. Clin Neurol Neurosurg 2008;110: treatment of craniopharyngiomas: experience with 168 patients. The orbitozygomatic infratemporal Comparison between the microscope and endoscope in the direct approach: a new surgical technique. Surg Neurol 1986;26:271– endonasal extended transsphenoidal approach: anatomical study. Neurosurgery 1980;7:111–117 region, with emphasis on the extended approaches and parasellar 24 Extended Endonasal, Endoscopic Transsphenoidal Approach versus Craniotomy for Giant Pituitary Macroadenomas 261 approaches: surgical experience in 105 cases. En­ 55:539–547, discussion 547–550 doscopic cranial base surgery: classifcation of operative approaches. Microscopic and endoscopic trans- Neurosurgery 2008;62:991–1002, discussion 1002–1005 sphenoidal surgery. Transnasal en­ 1529–1530 doscopic resection of a cavernous sinus hemangioma: technical note 66. Skull Base 2008;18:309–315 transsphenoidal approach for nonadenomatous suprasellar tumors. Endoscopic J Neurosurg 2005;102:832–841 endonasal transclival resection of chordomas: operative technique, 67. The endoscopic transnasal transsphenoidal approach for the closure in minimal­access endoscopic cranial base surgery. Laryngoscope 2006;116:1882–1886 transsphenoidal, transplanum transtuberculum approach for resec­ 77. J Neurosurg 2007;106:400–406 approach for surgical management of pituitary adenomas invading 70. Endoscopic pituitary surgery: an endonasal approach for anterior cranial base and suprasellar lesions: early experience. Neurosurgery 2009;64:677–687, discus­ 223 sion 687–689 Stereotactic Radiosurgery and 25 Fractionated Radiation for Pituitary Tumors Bruce E. Brown The use of radiation for scientifc and medical purposes dates High-energy electromagnetic radiation interacts with back over 100 years with the discovery of the x-ray by Conrad matter, removing electrons from their orbits, resulting in Roentgen in 18951 and the isolation of radium by Madame ionization and the release of energy. In the 1920s, Coutard and Regaud are not dependent on the atomic number of the substance showed that by dividing the total dose into many smaller with which the x-ray is interacting, but only on the density treatments, delivered over several weeks, tumors could be of the absorbing material. The start of the modern era of external- the energies typically used for diagnostic radiology but is beam radiation therapy began with the appearance of the inefective with the higher energies typically used in radio- cobalt-60 machines in the mid-1950s. In addition the lack of penetration of electrons, they are rarely used in to photons, linear accelerators are able to produce electrons, the treatment of intracranial diseases. In contrast, other which have a fnite range in tissue that allows tailoring the forms of particulate radiation, such as protons and neu- depth of penetration to the exact clinical situation. The technology of radiation delivery much heavier particles, such as protons, α-particles (nu- continues to undergo rapid development and change. The density of ionizations along the pathway of these par- ticles is much greater than that of x-rays. In contrast to neutrons, the advantage of protons is in their dose distri- I Physical Properties of Radiation 4 bution. Protons deposit most of their energy at the end of Ionizing radiation is composed of particulate radiation and their track range in tissue, called the Bragg peak. Although some radiation treat- ergy delivered to tissue proximal to the peak is minimal. Electromagnetic ra- deposited in large amounts in a region while sparing the diation is part of a continuum of waveform energy known as adjacent tissues. Near the high-energy (short ticle beam treatment planning, the need for a cyclotron wavelength) end of this spectrum lie the electromagnetic to generate the protons, and the expense of these units, waves used therapeutically (x-rays, gamma rays) to treat pa- there are only a limited number of facilities around the tients. X-rays are obtained from an extranuclear process when an accelerated electron strikes a target with a high atomic number, causing decel- I Biologic Properties of Radiation eration of the electron with the production of polyenergetic x-rays through the process of “bremsstrahlung” (braking When photon radiation hits a cell it will most likely inter- radiation). In contrast, gamma rays are emitted from the act with water because cells are primarily composed of nucleus during nuclear decay. Therefore, a device is needed to accurately direct efect is the predominant process in heavy particle reposition the patient on a day-to-day basis. To Cell Death from Radiation provide consistent references points, fducial markers are placed on the mask. Because the treatment may last several weeks, a gle-strand breaks seem to play a relatively minor role in the repeatable head fxation device is an absolute requirement lethality of ionizing radiation compared with double-strand 5 for any facility performing stereotactic radiation therapy breaks. These devices often include a relocatable head frame capable of repairing single-strand breaks with great ef- stabilized by a mouth-guard–type bite block. Therefore, the critical lesions caused by radiation are less” stereotactic systems can achieve an accuracy of better double-strand breaks. If a Once an immobilization device has been constructed, cell accumulates sufcient radiation damage, its later prog- the patient undergoes a treatment simulation and planning eny may be unable to go through mitosis successfully and session in the treatment position. Several cell divisions may occur before the lethal formed using conventional fuoroscopic units to visualize efects of radiation are expressed. Some cells do not have to go through mitosis to planning scans are conducted under the same conditions succumb to radiation but instead die from programmed cell 6 (on a fat table with custom immobilization devices) used death or apoptosis. An apoptotic event is irreversible, and for treatment of the patient on the linear accelerator. By achieving a homoge- gery the repair mechanisms of even normal tissues can be neous dose distribution, areas of excessive dose are avoided, overwhelmed, and radiation damage can occur along with thereby decreasing the risk of radiation damage. Methods to accomplish this dosimetric goal doses per fraction (3 to 7 Gy) to achieve a lower total dose include the use of multiple, nonoverlapping, conformal radia- (20 to 30 Gy), has also been employed by some centers. Computer-controlled tungsten fractionation or high-dose, single-fraction techniques, there leaves, or multileaf collimators, are individual leaves that shift are no long-term studies on tumor control or toxicities. In addition to blocks, wedges are often added to alter the radiation beam dose distribution to allow more uni- I Stereotactic Radiosurgery form dose distribution within the treatment volume. Instead of clinicians defning beam di- cise delivery of radiation to an imaging-defned target. Lars rections, beam weights, wedges, blocks, and margins, and Leksell,9 neurosurgeon at the Karolinska Institute in Stock- then computing and displaying dose distributions to assess holm, Sweden, conceived the concept of stereotactic radio- whether the treatment plan will lead to an acceptable out- surgery in 1951. His goal was to develop a method for the come, they do the opposite or “inverse” treatment planning. Sophisti- sell10 coupled stereotactic localization with the delivery of a cated algorithms of the inverse treatment planning system large, single-fraction dose of ionizing radiation. Hundreds to thou- tance and has become an integral part of both neurosurgery sands of small, modulated radiation beams strike a tumor and radiation oncology. Advances in neuroimaging and im- site with varying intensities, and from many angles, to at- proved computer software have made radiosurgery safer tack the target in a complete 3D manner. A comparison of and more efective in the management of a wide range of linear accelerator–based radiosurgery, fxed noncoplanar disorders afecting the nervous system. In contrast to conven- Typically, the patient receives fve treatments a week, one tional fractionated radiation therapy, radiosurgery does not a day, Monday through Friday. Along with these daily treat- rely on the increased radiation sensitivity of the target com- ments, most centers utilizing stereotactic radiotherapy also pared with the normal brain.

Suction applied to the airway can help facilitate a more rapid deflation of the lung buy sildigra canada. In some cases buy sildigra online from canada, carbon dioxide is insufflated into the pleural cavity to facilitate visualization cheap 50mg sildigra with mastercard. Hemodynamic2 compromise presents a picture similar to that because of tension pneumothorax cheap sildigra 50 mg mastercard. Many of these patients are appropriately managed using high-frequency ventilatory techniques; therefore, these techniques are described first (see Chapter 28). High-Frequency Ventilation With conventional positive-pressure ventilation, V and rates usually exceedT or approach those in the normal, spontaneously breathing patient. Gas transport to the alveoli occurs by convection in the larger airways, and then by convection and molecular diffusion in the more distal airways and alveoli. High-frequency ventilation differs from conventional positive-pressure ventilation in that smaller V and more rapid rates are used. Gas transportT may depend more on molecular diffusion, high-velocity flow, and coaxial gas flow in the airways, with gas in the center moving distally and that in the periphery moving proximally. The ventilatorT used has a negligible internal compliance so the V generated, which usuallyT approximates the dead space volume, equals the volume set on the ventilator and represents all fresh gas. The high instantaneous gas flows generated facilitate gas exchange and movement in the conducting airways. An example of the former is the percutaneous placement of a transtracheal catheter or placement of a catheter through the nose or mouth with its distal end above the carina. This technique has been used during bronchoscopy, tracheal resection, and reconstructive surgery. When open systems are used, the gas outflow pathway is not established mechanically and depends on natural airway patency. The closed system is superior because it integrates both airway patency and outflow protection. The jet and entrained gas flows cause forward motion of the mass of gas in the airways. Also, with use of high fresh gas flows from an anesthesia circuit, inhaled anesthetics may be delivered as an entrained gas mixture. High-frequency oscillation ventilation uses a mechanism that oscillates gas at rates of 400 to 2,400 breaths/min. In this system, V is small (50 to 80 mL),T and gas exchange occurs through enhanced molecular diffusion and coaxial airway flow. PaO2 increased compared with that obtained during simple collapse of the nondependent lung. Another advantage of high- frequency ventilation is that the rapid-rate small V can be delivered throughT 2632 small tubes or catheters so if an airway has to be divided, the passage of a small tube across the surgical field permits ventilation of the distal airway and lung tissue. This use has been applied during sleeve resection of the lung, tracheal reconstruction, and surgery for tracheal stenosis. In all three situations, the surgeon is able to work easily around the small catheter used to provide the high-frequency ventilation. Drainage is performed with the patient sitting up and leaning toward the affected side. Supplemental oxygen should be administered, and the patient should be constantly reassured. Neuroleptanalgesia is satisfactory in providing a suitably cooperative patient, and the airway is then pretreated with topical anesthesia. Selection of the largest possible tube provides a close fit in the trachea, which helps stabilize the tube. Once the tube is adequately positioned in the trachea, there may be a considerable outpouring of pus from the tracheal lumen if an empyema is present; therefore, this lumen should be immediately suctioned using a large-bore suction catheter. The healthy and possibly the affected lung may then be ventilated; adequacy of oxygenation and ventilation is assessed by pulse oximetry and arterial blood gas analysis. With either technique, the chest drainage tube must be left unclamped to avoid any bouts of coughing and to prevent the buildup of a tension pneumothorax in the event that a predisposing valvular mechanism exists. A rapid-sequence induction with ketamine or propofol followed by a relaxant has also been described, but is associated with considerable risk of contamination and tension pneumothorax. The use of small V results in minimal gas loss through the fistula, which may healT more quickly. In addition, hemodynamic effects are usually minimal and spontaneous efforts at ventilation are usually abolished, thereby decreasing the work of breathing and eliminating the need for relaxants or excessive sedation. Lung Cysts and Bullae Air-filled cysts of the lung are usually bronchogenic, postinfective, infantile, or emphysematous. A bulla is a thin-walled space filled with air that results from the destruction of alveolar tissue. The walls are, therefore, composed of visceral pleura, connective tissue septa, or compressed lung tissue. In general, bullae represent an area of end-stage emphysematous destruction of the lung. Patients may be considered for surgical bullectomy when dyspnea is incapacitating, when the bullae are expanding, when there are repeated pneumothoraces owing to rupture of bullae, or if the bullae compress a large area of normal lung. If the bulla or cyst communicates 2634 with the bronchial tree, positive-pressure ventilation may cause it to expand or even to rupture, if it is compliant, producing a situation analogous to tension pneumothorax. Nitrous oxide should be avoided because it causes expansion of any air spaces in the body, including bullae. Once the chest is open, even more of the V may enter the compliant bulla,T which is no longer limited by chest wall integrity, and an increase in ventilation is needed until the bulla is controlled. The anesthetic management of these patients is challenging, particularly if the disease is bilateral. The avoidance of positive-pressure ventilation (when possible) helps decrease the likelihood of the potential problems described previously, although oxygenation may be precarious with spontaneous ventilation. Once the endotracheal tube is in place, each lung may be controlled separately, and adequate ventilation can be applied to the healthy lung if bilateral disease is not present. Gentle positive-pressure ventilation with rapid, small V and pressures not to exceedT 10 cm H O may be used during the induction and maintenance of anesthesia,2 especially if the bullae have been shown to have no or only poor bronchial communication by preoperative ventilation scanning. While the surgery is being performed, as each bulla is resected, the operated lung can be separately ventilated to check for air leaks and the presence of additional bullae. If positive-pressure ventilation is to be applied before the chest is opened, the possibility of a tension pneumothorax must be kept in mind, and treatment should be readily available. The diagnosis of pneumothorax may be made by a unilateral decrease in breath sounds (this may be difficult to distinguish in a patient with bullous disease), increase in ventilatory pressure, progressive tracheal deviation, wheezing, or cardiovascular changes. Alternatively, general anesthesia is induced only after the surgeon has prepared the operative field and draped the patient. In the event of sudden deterioration in the patient’s condition during induction, the surgeon may perform an immediate median sternotomy. In any event, the time from induction of anesthesia to sternotomy must be kept to a minimum. The side with the largest bulla and least lung function, as assessed before surgery by ventilation and perfusion scans, should be operated on first. Unlike most cases of pulmonary resection, patients after bullectomy are left with a greater amount of functional lung tissue than was previously available to them, and the mechanics of respiration are improved. During this time, the positive airway pressure used should be minimized to avoid causing a pneumothorax owing to rupture of suture or staple lines or of residual bullae. Anesthesia for Resection of the Trachea Tracheal resection and reconstruction are technically difficult for the surgeon and challenging for the anesthesiologist. Indications for this type of procedure include congenital lesions (agenesis, stenosis), neoplasia (primary or secondary), injuries (direct or indirect), infections, and postintubation injuries (caused by an endotracheal tube or tracheotomy). For the surgical team, the major problems are maintenance of ventilation to the lungs while the airway is being operated on and postoperative integrity of the anastomoses. In this respect, the presence of lung disease sufficiently severe to require postoperative ventilatory support is a relative contraindication to tracheal resection or reconstruction. Monitoring of these patients should include placement of an arterial cannula in the left radial artery to permit continuous measurement of blood pressure during periods of innominate artery compression.