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Pathology Resident Manual Page 88 Graded Responsibilities The first month rotation (usually in the second year of residency) focuses on the basic cytopreparatory techniques and basic diagnostic skills discount flutamide 250mg fast delivery medications given to newborns. Residents spend one week in the laboratory to learn the techniques on specimen collection and staining buy flutamide 250mg cheap medicine queen mary. Residents then spend one week learning screening of Pap smears with a senior cytotechnologist or a cytopathology fellow generic 250mg flutamide medicine quetiapine. Residents are expected to review cases everyday with the cytopathology fellow and sign out with the attending cytopathologist on a daily basis. The first month should cover negative, atypical, dysplastic, carcinoma in-situ, and invasive carcinoma of gynecological origin. In the second and third rotations, residents learn more non-gynecologic cytology, including the Fine Needle Aspiration technique, adequacy check on radiologically guided fine needle aspirations, cytology of the thyroid, salivary gland, breast, urinary tract, lymph node, soft tissue, gastrointestinal tract, and miscellaneous fluid specimens. Residents are expected to review cases that have been pre-screened by cytotechnologists, formulate a diagnosis, obtain any necessary follow-up or clinical information on the case and sign these cases out with the fellow and/or attending cytopathologist. Residents are encouraged to use supplemental learning materials including study sets and books, participate in conferences and participate in research activities in cytopathology. General Activities The Resident will work closely with the cytotechnologists to learn technical principles and early interpretation as well as some principles of organization. Whereas, the cytopathologists will be involved in all aspects of the training, instruction at the multi-headed microscope emphasizing interpretation and follow up will be the most essential aspect of the rotation. This will be done according to the following schedule: 10:00 - 12:00 am Fellow/resident review of cytologic material 1:00 - 4:00 pm Sign out of cytologic material Turnaround time: (i. Pathology Resident Manual Page 89 • Complicated non-gynecologic specimens will be completed within 48 hours. In that case they will be done within 24 hours and a report will be discussed with the clinician and documented in the chart. Equipment • 23 to 27 gauge sterile needles in a variety of lengths, with "see through" plastic hubs, and 10-20 ml disposable (preferably "slip tip") plastic syringes. Note: • The routine practice of rinsing the needle into either Cytolyte or cell culture medium allows for maximum retrieval of cytologic material and may allow you to prepare a cell block that can later be used for ancillary studies. You should probably put most if not all of such aspirates directly into Cytolyte, fixative (if you use formalin or alcohol make sure that the laboratory knows in advance), or cell culture medium. Pathology Resident Manual Page 90 • Fellows and residents may not render final interpretations. Discard any and all slides that were taken from the box for an individual case, but were not used. If there is any doubt about whether a slide belongs to a particular patient or case, please notify the cytology faculty on call. The skin is swabbed with an alcohol pad (local anesthesia is usually not required). The mass is often best immobilized between the index and middle fingers of the gloved left hand (for right-handed aspirators) or the gloved right hand (for left-handed aspirators). If you must redirect, pull the needle towards the subcutaneous tissue, without exiting the completely, change directions and repeat back and forth movements. Continue to move the needle back and forth about 10 to 15 times or until a flash of blood appears in the hub of the needle. Reattach the need and then forcibly expel the material onto a clean glass slide, near the frosted end. The quality of your interpretation is greatly dependent upon the quality of the cytologic smears. The one step technique is the one that you should use most often and works best with "thick and creamy" specimens, i. Pathology Resident Manual Page 91 o Lower the clean slide onto the specimen and it will spread without force slightly by capillary action, continue to spread without force by guiding the top slide with middle finger of the right had along the edge of the slide which holds the specimen. This also works best with the "thick and creamy" specimens that one obtains from lymph nodes are solid tumors. This technique is desirable when you want to avoid an excessively thick slide and/or when ancillary studies might be better performed on fresh cytologic preparations. The "Dab" technique or "Touch and Divide" is described below: o Expel the cellular material onto the slide as described above. The rule of thumb is that, a physician should obtain such consent "any time the skin is broken". The procedure note can be included as a part of the cytology report for all out-patient procedures. It is also important to document in the procedure note that two patient’s identifiers are confirmed and a “time out” is called to identify the site of aspiration before procedure. Defer final diagnosis until all cytologic material has been stained and evaluated. Anytime an interpretation is called to a physician, whether preliminary or final, there should be documentation of the telephone call, i. Technical Principles Residents will be exposed to the methodology of collection, fixation, cytopreparation, staining and screening cytological samples. Interpretation and Reporting Residents will be instructed on the principles involved in examining cytological preparations, applying diagnostic criteria and reporting cytopathologic findings. Incorporation in the report of ultrastructural, immunocytochemical and ploidy information will enable the resident to integrate concepts from various disciplines. Utilization and Feedback Residents will participate in the interface between cytopathology and the clinicians utilizing the laboratory in terms of reports, recommendations and submission of adequate samples, patient instruction, and other significant items. Pathology Resident Manual Page 93 Follow Up and Quality Control Residents will participate actively in correlating cytopathology diagnosis with histopathologic data derived from biopsies or surgical extirpations, They will also evaluate specimens as to the adequacy of cytopreparatory and staining methods and learn to trouble shoot deficient areas. Quality Assurance and Standards of Care Residents are expected to familiarize themselves with the current guidelines and standards of performance and care. Residents are required to have knowledge of issues related to Quality Assurance in Cytopathology, by reviewing the Cytopathology Policies and Procedures Manual (located in 1601 Bell Hospital), attending division meetings, and through self-study (www. The program director will provide formal written evaluations (formative and summative) of the fellows on a semi-annual basis. Fellows and residents are evaluated in the following areas: technical skill, morphologic skills, clinical judgment, teaching, research efforts, and the above outlined core competencies. In addition, fellows and residents have the opportunity to discuss their training in Cytology program with the program director and/or Department head on a monthly basis. Fellows and residents are required to evaluate the Cytopathology Program and Faculty on a regular basis. Fellows are encouraged to write a formal evaluation of the program at its conclusion. The autopsy is performed in a complex institutional, administrative, legal, and professional setting. The responsibility for determining when an autopsy will be performed is that of the staff consultant assigned to the autopsy service for that day. This must, however, be cleared by the staff consultant before beginning the autopsy. It will be the responsibility of the technician to see that the death certificate is signed, since the body cannot be released until this is done. One copy will be posted in the autopsy service office and one on the departmental bulletin board.
Greenacre C buy cheap flutamide 250mg line treatment of tuberculosis, et al: Psittacine beak al: Krankheiten des Wirtschaftsge- Press 250mg flutamide free shipping medications you can take during pregnancy, 1991 purchase flutamide mastercard symptoms of ms, pp 674-679, 1991. In Gylstorff “Tauben-Paramyxovirus” sowie Über- dystrophy and necrosis in cockatoos. J Am Jagdfalken - Klinik, pathomorpholo- Stuttgart, Eugen Ulmer, 1987, pp schiedener Newcastle-Disease- Vet Med Assoc 189:999-1005, 1986. Ames, Iowa State I, Grimm F: Vogelkrankheiten, Magen/Darmbereich bei Großpa- fection in white-masked lovebirds University Press, 1991, pp 471-484. Stuttgart, Verlag Eugen Ulmer, 1987, pageien (wasting macaw complex, in- (Agapornis personata). Prakt Tier- Stuttgart, Verlag Eugen Ulmer, 1987, ton, Kluwer Academic Publ, 1988, pp arzt 61:952-954, 1980. Mustaffa-Babjee A, et al: Acute enteri- Impfung gegen die Paramyxovirose aetiology. Mustaffa-Babjee A, et al: A patho- Langzeitversüches unter Laborbedin- ated outbreaks in domestic poultry in 264. Logemann K, et al: Comparative stud- noviruses and reoviruses from avian fection in normal and antibody defi- Oklahoma (reservoir of a virus that ies for the characterization of avian species other than domestic fowl. Kraft V, et al: Nachweis eines Pocken- Stuttgart, Gustav Fischer Verlag Poultry 9th ed. Ames, Iowa State Uni- logical characterization of influenza virus bei Zwergpapageien (Agapornis Jena, 1992, pp 695-770. McOrist S, et al: Psittacine beak and undulatus): Clinical and aetiological feather dystrophy in wild sulphur- al: Krankheiten des Wirtschaftsge- studies. Landowska-Plazewska E, et al: Aus- anemia virus associated with Plasmo- Pathol 20:531-539, 1991. Exp Parasitol 31:29- Discordance between neutralizing an- Pinguinen im Warschauer Zoo. Proc Assoc four cockatoos with psittacine beak egg drop syndrome 1976 virus in do- Comp Pathol 93:127-134, 1983. Malkinson M: An outbreak of an acterization of rotavirus from feral pi- puffinus). In: Francki cons (as vectors of the disease to poul- West Poult Dis Conf, 1982, p 110. Ottis K, et al: Isolation and charac- the bursa of Fabricius of herring cies of fowl and waterfowl. Study of terization of ortho- and paramyxovir- gulls (Larus argentatus pontoppidan) immunity afforded by Reovirus vac- In Heider, et al: Krankheiten des us from feral birds in Europe. Müller H, et al: A polyoma-like virus associated with acute disease of fledg- 302. Proc Assoc Wellensittiche, eines aviaren guineafowl: Characterization on two Proc 34th West Poult Dis Conf, 1985, Avian Vet, 1988, pp 27-30. Avian Pathol 16:623-633, myelosis in conures, the “hemor- Charakterisierung von aviären Vet Pract 15:55-60, 1985. Proc Intl Conf Avian tischen und detuschen Haustauben of psittacine beak and feather dis- tis in a tawny frogmouth (Podargus Med, 1984, pp 213-228. J Gen Virol 50:410- nologic relationship of quail and my- Newcastle disease in Egypt. Schemera B et al: A paramyxovirus of tralian cockatoos Cacatua galerita beim Geflügel. Sironi G: Concurrent papavirus-like Cockatoo, Cacatua roseicapilla geese in Saskatchewan. Am J Vet fication of a papovavirus in a Moluc- beak disease: A cluster of cases in a article 2:329 (No 329), 1975. Pfister R: Zur Verträglichkeit und tion inhibition for detection of anti- Probleme der Influenzavirusinfek- waterfowl of Michigan (Possible Wirksamkeit einiger Adjuvantien in bodies against the virus. J As- Virusinfektion bei Prachtfinken bei Enten, Gänsen und Graureihern: 513, 1989. Assoc Avian Vet Today 1:152- pesvirus der Hepatosplenitis infec- avian species for neutralizing anti- versity Press, 1991, pp 621-627. Aust Eulen (Sträges) mit Ausnahme der birds in the spread of influenza vi- Vet J 63:337-338, 1986. Woods L: Case report: Papova-like vi- subgenus within the polyomavirus ge- cockatiels. Vindevogel H, et al: Comparaison de Krankheiten des Wirtschaftsge- feather disease/French molt. Winteroll G, et al: Schwere durch Her- characteristics of an agent inducing 18:133-139, 1982. Waddell G, et al: Genetic variability des Respirationsapparates bei Ama- 385, 1979. J Am Vet Med Assoc 50:1466- akuten Form der Nephro-Enteritis Zbl Vet Med B 13:215-218, 1966. Proc Assoc Avian hemorrhagic syndrome and a chronic versity Press, 1991, pp 439-456. Tumova B, et al: A further member of Conf Zool & Avian Med, 1984, pp 15- schiedener Desinfektionsmittel and the Yucaipa group isolated from the 19. Avian bacteriology is further complicated by the fact that bacteria that are as yet taxonomically undescribed can be isolated from a variety of avian species. Some of these bacterial strains have been erroneously classified as taxons (eg, Pasteurella haemolytica, Alcaligenes faecalis). In general, bacte- 33 rial adaption to an avian host minimizes cross-spe- cies transmission from birds to mammals. Non-host- adapted transmission usually requires large numbers of organisms, repeated exposures, specific susceptibility or immunosuppression. Some host- adapted strains may form biovars that are specific to one avian species (or a few closely related species) as compared to the dominant species. After becoming established, many Helga Gerlach secondary invaders are able to maintain a disease process independent of other infectious agents or predisposing conditions. Laboratory examinations (biochemical or serologic) are rarely of any help in differentiating primary from secondary invaders. The companion bird clinician must determine the importance of bacterial isolation for a specific bird species and a specific disease process. Analogous con- clusions drawn from poultry literature may not be valid, and experimental infections are frequently not possible. Some specific points may guide the clinician in interpreting bacterial culture results (Table 33. Because whole blood has bacteriostatic and bacteri- Isolation of an organism in an almost pure culture (approxi- cidal properties, blood culture samples must be mately 80% of the colonies present) may indicate that the transferred immediately after collection to attenuant bacteria is a component in the disease process. Isolating a bacteria that is part of the autochthonous flora may indicate that it is functioning as an opportunistic (secondary) pathogen.
In many cases cheap flutamide 250mg overnight delivery symptoms of strep throat, dermatologic lesions are mone is important in initiating a molt; however order generic flutamide treatment atrial fibrillation, secondarily infected with bacterial or fungal agents discount flutamide 250mg line medicine grace potter, other studies indicate that progesterone and pro- and the identification of microbial agents from cul- lactin can induce a molt without a change in circulat- tures of the skin does not necessarily implicate these ing levels of thyroid hormone. In a study of King Penguins, it was found that thy- Using a dermatology examination form is a concise roxine levels rose significantly (five times resting way to consistently evaluate and record integumen- levels) during the molting period, and corticosterone tary lesions. In other5 is an effective method of recording the precise loca- studies, it has been demonstrated that thyroid activity tion and the effects of therapy on skin lesions. By (as measured by thyroidal uptake of radioactive iodine) using a standardized form and evaluation system, did not differ appreciably between molting and non- avian veterinarians and dermatologists can more ef- molting hens. These apparent conflicts in experimental fectively quantify and compare their findings, which findings may suggest that research protocols, no mat- will ultimately lead to improved clinical description, ter how effectively conceived, may not accurately re- diagnosis and treatment of skin and feather diseases. The predilection to develop certain types of integu- Feather formation is prevented by circulating estro- mentary diseases may vary among species (Table gens. The diagnostic evaluation used for avian der- follicles that are already replacing a feather but will matologic diseases is similar regardless of the etiol- not stimulate feather development. The evaluation of feather and skin gish and prolonged in fowl exposed to 12 to 14 hours lesions, particularly in small birds, can be facilitated of light. Inflammation of the companion birds that originate from widely varying skin can occur as a result of trauma, chemical irrita- geographic regions is undetermined. Molting activity can be induced by high doses of medroxyprogesterone, de- Cytology, culture and biopsy are indicated in cases of creased exposure to light or administration of thyrox- dermatitis. Birds that are stressed by handling during Protozoal Irradiation a molt may lose more feathers than birds that are in Metazoal (parasitic) Neoplastic a relaxed atmosphere. Some birds are able to release Immune-mediated Behavioral feathers when being restrained (fear or stress molt). These general therapeutic considera- “Bumblefoot” syndrome tions include: “Wet feather” Vesicular dermatitis and photosensitization Correcting any nutritional deficiencies by admin- Leech infestation istering parenteral multivitamins, minerals (trace Raptors minerals) and placing the bird on a formulated diet Malnutrition supplemented with some fruits and vegetables. Poxvirus “Bumblefoot” syndrome Removing the bird from all exposure to aerosolized Gangrene of wing toxins that may accumulate on the feathers and Tuberculosis “Blain” (bursitis of carpus) skin and cause irritation (eg, cigarette smoke, Damaged nails and beak kerosene fumes, cooking oils). Neoplasia including melanomas Identifying and correcting any behavioral abnor- Ratites Poxvirus malities that are causing over-grooming (feather Malnutrition picking). Skin lesions should be kept clean, and creams, lotions any scabs, moistening the culturette in the sterile or solutions can be used to moisturize and sooth dry, transport media and rolling the tip over the lesion. Moistened swabs will yield better results than dry Any medications placed on a wound should either kill ones, and it is important that the swab be plated as specific target microorganisms or protect healing tis- soon as possible after collection. Ointments and oily compounds interfere with sive diagnostic technique in practice is to apply a normal feather function and should be avoided (Color microscope slide to the affected area and to examine 24. Skin biopsies are iodine compounds for example, are effective in con- most diagnostic if collected from the center and the trolling bacteria, but may also impair healing by periphery of the lesion. A mixture gars and occasionally in large Psittaciformes (see of Penetran and aloe vera may relieve severe pruri- Chapter 32). This therapy should be discontinued or the solution should be “French moult” is a descriptive term used to describe diluted further if a bird becomes depressed or lethar- feather dystrophy in young psittacine birds, primar- ily budgerigars. If a bird does not improve within 48 hours of initiating therapy, the preparation should be consid- premature molting of the wing and tail feathers and ered ineffective and discontinued. Affected young birds are termed “runners” be- If an infectious agent is identified, specific antimicro- cause they are usually incapable of flying. It should be noted that any factor (infectious or however, surgery should not be considered until all noninfectious) that damages the epidermal collar can other therapeutic modalities have failed to resolve result in a gross lesion resembling that induced by the lesions over a six-month treatment period. Techniques that are discussed in the lay literature, including dietary additives and careful selection of Lesions should be evaluated regularly (generally on breeding stock, are probably futile. Good hygiene is a weekly basis) to determine if prescribed therapy is advisable, and birds should be purchased from effective. Poxvirus can cause skin lesions in most avian species and may retard wound healing. Uncomplicated le- sions are characterized by the formation of nodules on the unfeathered skin. Skin lesions should be kept clean and dry to prevent secondary bacterial or fun- Specific Etiologies of gal infections (see Chapter 32). Generalized Dermatopathies Cutaneous papillomas may occur on the head, neck, beak commissure, feet or uropygial glands. Some of these lesions have been associated with papil- Viral Diseases lomavirus or herpesvirus while others are of undeter- mined etiology. Dermatologic lesions may oc- “feather dusters,” and adenoviral folliculitis has been cur with poxvirus, papillomavirus and herpesvirus reported in lovebirds (see Chapter 32). The ally attack birds causing characteristic hyperemic disease progression can be acute or chronic depending swellings (Color 24. The likelihood of a bird being stung can be reduced by removing uneaten soft foods (particularly fruits) from the enclosure and destroying wasp nests found near the aviary. Flies, mosquitoes and gnats can cause severe derma- titis on the face, feet and legs, particularly in birds raised in warm coastal areas (see Color 26). Lesions are most common in Amazon parrots and macaws, but can occur in any species. The flies that commonly parasitize cattle and deer can induce small bleeding ulcers on the unfeathered areas of the body (Color 24. Topical application of antibiotic and steroid lotions or creams Bacterial and Fungal Diseases can be used to reduce swollen or hyperemic lesions. There have been remarkably few studies on the bac- Ant bites also may cause localized necrosis that re- terial flora of the avian skin other than in poultry sults in defects in the webs of the feet in waterfowl 39 and birds of prey. Some helminths and mites can cause more attention, and several surveys on the fungal dermatitis (see Chapter 36). In one A sarcoptid mite infection was described in a Grey- study, 6000 fungi were recovered from the feathers, cheeked Parakeet with feather loss and flaking skin nests, pellets, droppings and organs of 92 species of free-ranging birds. Severe pyogranulomatous dermatitis was associated with a sarcoptic mite in- were potential pathogens and a number were kerat- fection in a Green-winged Macaw. Control of ectoparasites, genic bacteria or may provide appropriate nutrients for competitive autochthonous flora. Only those parasiticidal agents that are fungal infections of facial skin are usually secondary licensed or recommended for use in birds should be to trauma or possibly a contact dermatitis. Avian applied, and such therapy must be accompanied by skin abscesses are rare but can be found following other measures to exclude the parasites. In subtropical and tropical areas, the sticktight flea (Echidnophaga gallinacea) can be a problem on Although frequently discussed, documented cases of many species of birds. The pulp can be large numbers may attach to the skin of the head, examined for the presence of bacteria by making especially around the eyes, and cause anemia (see impression smears or by culturing the pulp cavity Color 8). Bacterial pathogens that have been topical application of a pyrethrin-based product. The birds in these cases responded favorably to fungicidal therapy, suggest- ing that the fungus was involved in the feather pick- ing behavior. Malnutrition, particularly hypovitaminosis A, is suggested by the smoothing of the normally papil- lary surface of the plantar surface of the feet (see Color 8). The pulp cavity of birds with thistype of presentation should the sheath on the developing feather is retained, always be examined cytologically, and cultures should be submit- resulting in a bird that appears to have an excess ted for bacterial and fungal isolation. The precise effects that mal- nutrition and organopathy (particularly hepatopa- thy) have on the quality and pigmentation of feathers cus spp.
A distended bladder in patients suffering from lower urinary tract obstruction can be palpated cheap 250 mg flutamide mastercard treatment anemia. Often discount 250mg flutamide with visa treatment hepatitis c, urinary bladder catheterisation is all that is required purchase flutamide 250 mg online symptoms for hiv, although in certain cases, one must resort to suprapubic bladder drainage. Obstruction leads to proximal dilatation of urinary pathways, which may be documented by ultrasound, computed tomography and antegrade or retrograde ureteropyelography. Antegrade ureteropyelography is performed by inserting a catheter into the renal pelvis, whereas retrograde ureteropyelography is performed by inserting a catheter into the bladder cystoscopically and injecting contrast into the ureteral ori¿ces. A detailed medical history must be taken and special attention paid to Àuid losses, such as vomiting, diarrhoea, sweat- ing, bleeding, through a nasogastric tube, biliary ¿stula, etc. The clinical examination may reveal dehydration, dry mucosal membranes, tachycardia, orthostatic hypotension and poor ¿lling of jugular veins in a recumbent position. Invasive monitoring may reveal a central venous pressure lower than the expected 8–12 cm water (H2O) (0. The intravascular volume should be supplemented by isotonic Àuid, with the exception of bleeding, when volume should be replaced by packed red blood cells. Fluid loss may be precipitated by vomiting, diarrhoea, sweating and through various ¿stulae. This empha- sises the fact that volume replenishment must be supplemented by various electrolytes and additives, depending upon the aetiology of Àuid loss. The daily net Àuid de¿cit is about 400 ml and is the result of endogenous water formation in the amount of 400 ml and insensible Àuid losses in the amount of approximately 800 ml. This daily net Àuid de¿cit must be incorporated into calculations regarding daily Àuid supplementation. Hyperkalaemia may be urgently treated by 10–30 ml of 20% solution of cal- cium gluconate due to the rapidity of is action. Calcium antagonises the effects of hyper- kalaemia on cardiac myocyte polarisation. One of these strategies is to infuse 200–500 ml of 10–20% glucose solution with 1 U of insulin per 3 g of glucose. The modern management dogma no longer includes protein restriction, as the increased rate of catabolism may lead to deg- radation of enzymatic proteins that are critical to cell function. In patients who are unable to meet their needs by oral intake or by a feeding nasogastric tube, parenteral nutrition must be instituted. It has to meet the patient’s calorie requirements, which are increased due to the aforementioned catabolism. In- stead of restricting Àuid intake and awaiting the development of uremic symptoms, one should commence dialysis early and provide simultaneous hyperalimentation. Dialysis is necessary if more conservative methods of treating hyperkalaemia, hypervolaemia or metabolic acidosis fail. Once serum creatinine reaches 400 mol/L or the potassium con- centration exceeds 6 mmol/L in a patient with oliguric renal failure, haemodialysis should be promptly instituted to prevent the development of uraemic syndrome with its associated complications. Dialysis may be performed inter- mittently for several hours on a daily basis or continuously over a 24-h period. The dosing of haemo¿ltration is inÀuenced by choosing the volume of ¿ltration and its simultaneous replacement. Procedures characterised by high ef¿cacy (with large volumes of ¿ltration) improve patient outcomes. In the event of substantial catabolism coupled with inadequate management of small molecules (potassium, urea, creatinine) 28 V. Gornik with haemo¿ltration alone, the procedure may be expanded to include a dialysate Àow. The ensuing diffusion (haemodialysis) will improve the elimination of small molecules. It is important to ensure that dialysis duration is adequate for both metabolic and volume control. There is no conclusive evidence supporting the bene¿t of continuous methods of dialysis over inter- mittent ones. It has been substituted by extracorporeal dialysis procedures due to their ef¿cacy and reduced complications. The outcome is greatly inÀuenced by the underlying condition that led to renal fail- ure. In the majority of survivors, renal function will recover, but in as many as 50% of those survivors, a subclinical impairment will persist. Sometimes, temporary im- provement in renal function is seen only to be followed by progressive deterioration. Despite the ad- vances in medical management, it is still associated with a high mortality rate. The cost of care and duration of treatment make it a substantial burden on healthcare resources. This should be complemented by the evaluation of serum elec- trolyte concentrations as well as the acid-base status. Oxford University Press, New York pp 1435–1644 Hilton R (2006) Acute renal injury. B Med J 333(7572):786 Lamiere N, Van Biesen W, Vanholder R (2005) Acute renal injury. At end expiration, the alveolar pressure is equal to atmospheric pressure, and during inspiration, the alveolar pressure must be less than atmospheric pressure. As the movements of the lungs are entirely passive, forces must be applied in order to expand the lungs, and as a consequence, alveolar pressure is decreased from its resting pressure at the end of expiration. In the case of spontaneous breathing, the respiratory muscles provide the external forces, whereas arti¿cial ventilation moves the relaxed respiratory system . During inspiration, the external forces must overcome the impedance of the lung and chest wall, the two components of the respi- ratory system. This impedance stems mainly from the force to overcome elastic recoil, the frictional resistance during the movement of the tissues of the lungs and thorax, and the force to overcome the frictional resistance to airÀow through the tracheobronchial tree. The inertial component of gas and tissue is usually negligible during conventional ventilation . At end inspiration, the potential energy accumulated in the elastic tissues of the lungs and thorax throughout inspiration is used to generate the pressure gradient that will favour exhala- tion. During spontaneous ventilation, the beginning of expiration is determined by the pro- gressive and gradual inactivation of the inspiratory muscles . On the other hand, a release exhalation valve avoids expiration during arti¿cial ventilation. If non-elastic tissue and airway resistances are negligible, the elastic recoil causes the lung and thorax to return very rapidly to the resting expiratory level in a completely passive expiration. If expiratory resistances op- posing elastic recoil are abnormally large, active contraction is necessary unless the expiratory time increases. In this chapter, we present the pressures and resistances that determine the continuous Àow of gas in and out of the lungs. For this purpose, we consider basic aspects of respira- tory system mechanics, its utility in the clinical scenario and the most recent techniques applied at the bedside for patient monitoring and, most often, for optimising ventilatory support. Over a certain range of volumes and pressures, lung and chest-wall structures obey Hooke’s law.