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However buy terramycin 250 mg otc bacteria that live on the ocean floor are sustained by, there are some of the airway buy cheap terramycin 250mg on-line bacteria vs virus, which may increase accidentally purchase terramycin 250mg amex antibiotic knee spacer surgery, for basic principles that remain the same discount terramycin 250mg on-line antibiotic zinnat. High-powered ventilator with bellows compressed by a mechanical arm attached to an electric motor C. Components of these systems include V1, inspiratory valve; V2, expiratory valve; V3, non-return valve; F, fow restrictor; S, overpressure relief valve. These pressures may be insuffcient to over- come the increase in airways resistance and/or the reduc- Respirable gas with suffcient pressure to ventilate a tion in lung compliance that are seen in diseased lungs. Either expired minute volume or a compressed gas from a cylinder or pipeline supply capnography can be used to check that ventilation remains (Fig. With the advent of modern electronics, many ventilators that ft this classifcation exclusively have become obsolete Classifcation of ventilators in the developed world. Some older ventilators and some A number of attempts have been made to classify ventila- of those designed for the developing world are so con- tors according to their power, effciency and modes of structed that they can only deliver modest pressures (by cycling between inspiration and expiration. Such machines are simple Power to operate, reduce the potential incidence of barotrauma to lungs and, more pertinently, do not require an electrical Low-powered ventilators power supply and are essentially user serviceable. Low-powered ventilators generate only the modest gas However, many current electronic high-powered ventila- pressures required to deliver reasonable tidal volumes to tors have a pressure-controlled mode that allows operative lungs with normal and near-normal compliances and characteristics similar to low-powered ventilators. When 232 Automatic ventilators Chapter | 9 | used in this mode and the inspiratory pressure is limited taken up in compressing the gas. If the bellows travel is to 15–25 cm H2O via the machine’s electronics, the ven- calibrated for volume, it becomes apparent that the tidal tilator may be considered as low powered. The greater the pressure required to High-powered ventilators ventilate a patient’s lungs, the greater will be the amount In order to prevent a reduction in ventilator performance of gas lost in compression. This type of ventilator is in the presence of deteriorating lung conditions, a ventila- regarded as relatively ineffcient, as the discrepancy tor needs to be powerful enough to overcome the increases between anticipated and delivered tidal volumes may be in airways resistance and reduction in compliance with as great as 25% in patients with signifcant pathological little alteration in desired gas fow. Ineffcient ventilators (which include safety valve is always included in the gas pathway to the most anaesthetic ventilators that supply circle systems) patient to release any build-up of potentially dangerous may well require validation of the delivered tidal volume, pressures that might damage the lungs. The more sophisticated measurement of fow and electronic pressure-relief valve (S) can either be pre-set (usually at feedback to the ventilator, the compliance of this type of 4. Higher-pressure relief settings, however, More effcient ventilators utilize respiratory gas already equate to increased risk of barotrauma. This reduces the fow to the patient and prevents too rapid a build-up of pressure in lnspiratory characteristics the lung. Those ventilators that by their resistance to fow that the gas meets during delivery of design produce a pressure suffcient only to ventilate the intended tidal volume. Those ventilators that Low-powered ventilators develop pressures suffciently high enough to deliver a Low-powered ventilators deliver gas at modest pressure. However, as most other electromechanical produce an inspiratory fow rate of gas that is greatest devices in common usage are described in terms of power, in early inspiration, when the pressure differential the author prefers the frst classifcation. This may be defned as the ratio of the intended tidal High-powered ventilators volume (as determined by the settings on the ventilator) over the actual delivered tidal volume. For example, when High-powered ventilators function by delivering a suff- a ventilator acts on a bellows containing patient gas at ciently high driving gas pressure to overcome most abnor- atmospheric pressure, the gas undergoes a degree of com- mal resistance without signifcantly altering the fow from pression in order to raise the pressure suffciently to the ventilator, which remains largely unaltered from the provide an inspiratory fow. Inspiratory time Inspiratory time A Inspiratory characteristics will depend on a number of factors. The high driving pressure from a pipeline source or heavy weighted/spring-loaded storage bellows requires some form of fow restriction to prevent too rapid a rise or an excessive pressure transmitted to the patient’s P5 lungs that could produce barotrauma. Here the fow will be con- stant (pipeline supply or weighted bellows) or gradually P3 decreasing (spring loaded bellows) as the tension in the spring reduces with emptying of the bellows (Fig. P 3 However, practically in the case of the latter the reduction is insignifcant and fow is virtually constant. Inspiratory time Inspiratory time In more sophisticated ventilators, the inspiratory fow B valve acts as a variable fow restrictor (Fig. Constant high-pressure generation (P1) Ventilators may be designed to force their bellows to be well in excess of that required to ventilate abnormal compressed either mechanically, via a linkage from a suit- lungs (heavy weight or pipeline gas supply) with able power source, or pneumatically, by placing the fxed-performance fow restrictor. High-pressure generation bellows in a gas-tight container into which a pressurized produced by a bellows compressed by powerful springs gas source is fed (bag-in-bottle arrangement). The bellows provides a gradually declining pressure as the bellows in this type of ventilator normally flls with gas at near empties (P2 above). However, this is insuffcient to affect atmospheric pressures, so that when it is compressed, the the performance of the ventilator, which develops pressure developed rises as it overcomes the resistive prop- pressures and fows as if it were constant high-pressure erties of the lungs. Flow patterns generated by P1 and P2 are forms are dependent on the type of mechanical linkage hence similar in a given lung scenario. More sophisti- Classifcation of ventilators cated ventilators will provide an alarm signal if this occurs. There may also be a change in the pattern to identify a selected airways pressure at the of (d) fow (inspiratory waveform) at some stage in inspira- end of exhalation that would trigger the next tion. However, the ventilator can allow only one of these inspiratory phase variables (a–d) to terminate the inspiratory phase when • an expiratory fow-cycled ventilator would switch to its predetermined value is reached. As all four variables are the inspiratory phase when the desired fow rate at present in every inspiratory phase, it is sometimes diffcult the end of exhalation was reached, or to decide which one is the principal determinant of inspir- • an expiratory time-cycled ventilator that terminates atory cycling. This is the most versatile type as its phase may extend Volume cycling beyond the end of patient exhalation, unlike the A ventilator designed to use this method of inspiratory others. It is, therefore, the most popular method of cycling recognizes the point at which a pre-determined expiratory cycling and is achieved by using electronic volume of gas has left the ventilator and switches its or pneumatic timers within the ventilator to switch internal mechanism to allow exhalation to occur. Ventilators may use one of the methods described above However, volume remains the primary determinant of for inspiratory cycling and another for expiratory cycling, inspiratory cycling. Mechanical, pneumatic or electronic timers may be used to control the operation of the inspiratory and expiratory valves that govern the cycling of the ventilator which can, Cycling mechanisms in ventilators therefore, function independently of the delivered tidal volume. Gas fow to and from the patient from a ventilator (cycling) For example, not only can widely differing volumes be is usually controlled by a series of one-way valves that are delivered in a given time frame, but it may also allow a operated and synchronized either: tidal volume to be delivered early in the inspiratory cycle, • mechanically followed by a pause to allow better distribution of the gas • electronically, or prior to the start of the expiratory phase. Examples of these will be described where appropriate Pressure cycling in the section on individual ventilators. Pressure-cycled ventilators sense a predetermined airway pressure in order to terminate the inspiratory phase. Ventilation modes However, if the airway resistance increases and/or if com- pliance of a patient deteriorates a pressure-cycled ventila- The terminology used to describe the way in which a tor will deliver a reduced tidal volume at the pre-set cycling ventilator combines its power capability and cycling to pressure. The performance of these ventilators is thus very deliver a tidal volume has previously been almost self- variable. Flow cycling Originally, ventilators were used to ventilate apnoeic/ Recognition of fow pattern changes has been used to paralyzed patients. However, this method is rarely employed was delivered by a high-powered ventilator, this was usually nowadays. A, patient connection; B, expiratory valve; C, defated pneumatic valve; D, gas supply tube to pneumatic valve, which is now infated.

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Emphysema is associated with a Pulse oximetry when combined with clinical small heart buy discount terramycin 250 mg on-line virus 43215, hyperinflation purchase 250mg terramycin mastercard antibiotics used for urinary tract infections, flat hemidiaphragms discount 250 mg terramycin fast delivery antibiotics for acne bad, observation can be a very useful non-invasive test order terramycin 250 mg visa antibiotics oral thrush. Long-term oxygen therapy is the quit” single most effective treatment to improve the Fig. However, regular treatment with there is no step down its always step up (Table inhaled steroid is appropriate for symptomatic 8. Inhaled glucocorticoid combined with long-term decline in lung function that is the long-acting B2 agonist is more effective than hallmark of this disease. Long acting inhaled bronchodilators are population average of about 30 ml/year in more effective and convenient, but more expensive. Combining bronchodilators (β2-agonist, anti- cholinergic, and/or theophylline) may improve the Using spirometry to assess lung age (Fig. Patient should be encouraged to Disadvantage of smoking (pleasure) • Decide a quit date. Even a brief 3 minute period of counseling to urge a smoker to quit can be effective, and at the very least it should done for every smoker at every visit. The provision of smoking cessation support should follow the principles of the ‘five A’ (Ask, Advise, Assess, Assist, Arrange). If a significant portion of the night’s data indicates oxygen saturations below 88%, patients) should be added to counseling if not supplemental nocturnal oxygen can be provided. Compared with months if hypoxia developed during an acute the cost-effectiveness of other medical services for exacerbation. Rechecks should be performed example, breast cancer screening costs up to $26,800 annually if hypoxia is discovered in an outpatient per year of life gained. It can also have with pure sleep apnea tend to resaturate to normal beneficial impact on hemodynamics, exercise between apneas. Arterial prone to the complication like cor pulmonale and blood gas measurement is recommended for polycythemia. Titrate liter-flow to goal at rest breathlessness can provoke anxiety, which can be and add 1 L/min during exercise or sleep or titrate manifest as breathlessness and increased respiratory during exercise to goal of SaO2 greater than 89%. Peripheral muscle conditioning improves patterns through techniques such as guided imagery exercise tolerance. However, before their dried peas and beans (legumes), whole-grain foods, routine use can be recommended, the results of bran, cereals, pasta, rice and fresh fruit should be ongoing trials have to be carefully evaluated. Patients should be asked decrease in severity of exacerbations, but these to take following precautions while having meals: results have not been duplicated. Thus regular use 6 small meals each day, instead of 3 large meals to of this therapy cannot be recommended. By removing a large bulla that does not contribute to gas exchange, the adjacent Mood disorders (depression and anxiety) spell lung parenchyma is decompressed. Most report improvement in signs of respiratory distress is achie- conclude that epidural or spinal anesthesia have ved, or side effects of tachycardia and/or tremor lower risk than general anasthesia, although the develop. Otherwise, the patients before side effects develop, ipratropium bromide should undergo preoperative physiotherapy and should be added to produce additive bronchodila- optimum treatment in order to reduce the risk of tion and allow the use of lower doses of sabutamol, postoperative pulmonary complication. There is no • Moderate to severe dyspnea with use of accessory need to discontinue inhaled steroids while the muscles and paradoxic abdominal motion patient is taking oral prednisone. In fact, the inhaled • Respiratory rate of more than 25 breaths/min steroid may serve as a “systemic-steroid-sparing- • Moderate to severe acidosis (pH of 7. The choice of • Life- threatening hypoxemia (PaO2 < 40mm of Hg or PaO2/FiO2 < 200 mm of Hg antibiotic is controversial, and needs to be tailored • Respiratory arrest to the individual situation. If these fail or failure) the incidence of resistant organisms is high in the • Other complications (metabolic abnormality, sepsis, community or, the use of a “second-line agent” may pneumonia, pulmonary embolism, barotrauma, massive be preferable. Consensus and limited data respiratory failure and the need for noninvasive support the discharge criteria listed in (Table 8. The patient should be followed up after 4 to 6 weeks Ventilatory support includes noninvasive or for assessment given in Table 8. These studies have shown positive results, physiologic impairment (obstructive ventilatory with success rates of 80% to 85%. If the patient does not airway dimensions including luminal area and 238 Textbook of Pulmonary Medicine Table 8. International consensus conferences in intensive care medicine; noninvasive Table 8. Antibiotic benefits therapy in exacerbations of chronic obstructive • Explain about diet, prevention of infections, rehabilitation pulmo-nary disease. Chronic obstructive pulmonary groups, emphysema-dominant and airway disease- disease: prevention, early detection, and aggressive dominant patients, and treat them separately. The word bronchiectasis is derived from the Greek The frequency is estimated to be higher in the roots, Bronchion = Windpipe and Ektasis = stretch- developing world including India where measles, ing out. Bronchiectasis is present when one or more pneumonia, tuberculosis and human immueno- bronchi are abnormally and permanently dilated. First described by Laennec in 1819 and later detailed Cystic fibrosis was thought to be extremely rare in by Sir. However published reports, reviews and undergone significant changes in regard to preva- comments indicate that cystic fibrosis is probably far lence, etiology, presentation and treatment. The precise of children with obstructive pulmonary disease incidence of cystic fibrosis among Indians is being relatively uncommon in developed countries. In one study, the mean With the advent of vaccination and extended age at injury was found to be 20 years, the mean spectrum antibiotics, the prevalence of bronchiectasis age at onset of symptoms was 39 years, and the age has decreased in developed countries. In 1953,the range with the highest frequency of bronchiectasis prevalence of the disease was 1. S, Norman Clark a significant pulmonary insult in their history before estimated an incidence of 06: 10000 in his series the onset of symptoms. Elaine Field closely studied vaccinations and antibiotics the age of presentation children with bronchiectasis in London. Bronchiectasis is an abnormal dilatation of proximal, Therefore a marked fall in the prevalence is seen medium sized bronchi (> 2 mm in diameter) caused in the developed countries, which may be due to by destruction of the muscular and elastic compo- due to more effective treatment of childhood respi- nents of bronchial walls, which can be either congenital or acquired. In 1950, Reid characterized ratory infections (including pneumonia), effective vaccination programs for whooping cough and bronchiectasis as cylindrical, cystic or varicose in measles, decline in prevalence of pulmonary nature. Severe inflammation can lead to necrosis of bronchiectasis has ulceration with bronchial the bronchi focally as in mycobacterium tuberculosis neovascularization and a resultant ballooned or mycobacterium avium-intracellulare pneumonia. Varicose Diffuse damage can occur in inflammatory condi- bronchiectasis has a bulbous appearance and a tions such as cystic fibrosis and allergic broncho- dilated bronchus and interspersed sites of relative pulmonary aspergillosis. The unrelieved, leads to accumulation of mucus, latter subsequently may result in postobstructive distension of the peripheral airways and infection. Other childhood respiratory tract infections like measles may contribute to permanent airway damage. The presence of staphylococcus aureus is associated with cystic fibrosis or allergic bronchopulmonary aspergillosis.

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Unilateral swelling is most likely the result of trauma buy cheap terramycin 250mg on line antibiotic resistance japan, gout generic 250mg terramycin free shipping virus 792012, pseudogout 250 mg terramycin sale antibiotics for uti emedicine, torn meniscus order terramycin 250mg online bacteria del estomago helicobacter pylori, or septic arthritis, whereas bilateral swelling is seen more commonly in rheumatoid arthritis, osteoarthritis, lupus erythematosus, and Reiter disease. Knee swelling in a young individual would most likely be due to rheumatoid arthritis, rheumatic fever, gonorrhea, or lupus erythematosus, whereas knee swelling in elderly persons is more likely to be due to osteoarthritis, gout, or pseudogout. If it can be determined that the swelling is due to synovial fluid, arthrocentesis should be done and the fluid analyzed for crystals, mucin clot, leukocyte count, and microorganism by smear and culture. I—Inflammation brings to mind tuberculosis and ankylosing spondylitis, and idiopathic prompts the recall of Paget disease (osteitis deformans) and osteoarthritis. T—Trauma allows the recall of crush fractures of the vertebral bodies, especially in osteoporosis and osteomalacia. This mnemonic fails to facilitate the recall of emphysema, which produces kyphosis also. Approach to the Diagnosis The clinical picture will help establish the diagnosis in many cases. The large skull and bowing of the legs in Paget disease, the generalized abnormalities of the skeleton in mucopolysaccharidosis, and the barrel chest and shortness of breath seen in emphysema assure the identification of the cause. X-ray of the thoracolumbar spine will be diagnostic in Paget disease, menopausal osteoporosis, rickets fractures, and Scheuermann disease. If menopause is suspected, a serum follicle-stimulating hormone, luteinizing hormone, and estradiol will confirm the diagnosis. A human 554 leukocyte antigen B27 antigen test should be ordered if ankylosing spondylitis is suspected. A bone scan will be useful in diagnosing ankylosing spondylitis, osteomyelitis, and metastatic carcinoma. Before that, however, one should determine if the pain is actually originating from the hip or if it is the result of knee joint disease. Beginning with the skin, consider herpes zoster and various dermatologic conditions. In the subcutaneous tissue, one encounters cellulitis and occasionally filariasis, which may produce a similar picture. There may be hematomas of the muscle, trichinosis or cysticercosis, nonarticular rheumatism, or fibromyositis. Muscle cramping from low sodium or other electrolyte disturbances must be considered. The superficial and deep veins are the site of thrombophlebitis, a prominent cause of leg pain. The arteries may be involved by emboli (from auricular fibrillation, acute myocardial infarction, and subacute bacterial endocarditis), thrombosis (especially in Buerger disease and blood dyscrasias), and vasculitis (from arteriosclerosis and collagen diseases). As usual, when one moves centrally along the arterial pathways additional causes of pain come to mind. When superficial or deep infections of the leg spread to the lymphatics, lymphangitis is important in the differential. Neuromas may occasionally cause focal pain in the distribution of the nerve involved. Probably herniated discs of the lumbar spine account for most of these cases, but Pott disease, lumbar spondylosis (osteoarthritis? Pelvic tumors, endometriosis, and sciatic neuritis are, in a sense, “central” causes of leg pain, and all patients deserve a rectal and pelvic 556 examination when the diagnosis is obscure. Pelvic inflammatory disease and obturator hernias may rarely involve the obturator nerve. Meralgia paresthetica from diabetes mellitus and other causes must be considered in thigh pain and in causalgia. Finally, the thalamic syndrome and diseases of the cervical spine must be considered. Dissecting the limb layer by layer, we finally reach the bone, which suggests osteomyelitis, bone tumors, Osgood–Schlatter disease, tuberculous osteomyelitis, and Paget disease. Systemic diseases that may involve the nerves causing pain in the legs include tabes dorsalis, periarteritis nodosa, diabetes mellitus, metabolic and nutritional neuropathies, and blood dyscrasias. Approach to the Diagnosis The approach to the diagnosis of leg pain involves numerous ancillary examinations that one may not routinely do. Leg pain that is sudden in onset should be considered osteomyelitis until proven otherwise. Thus, a femoral 1 stretch test is done and when positive suggests a herniated disk at L2–3 or L3–4. Patients with pain in the hip should always be examined for greater trochanter bursitis, a common condition (page 226). Edema associated with phlebitis or atrophy associated with a herniated disc can be detected only with careful measurement of the calf and thigh. Deep vein thrombophlebitis can be diagnosed by ultrasonography or impedance plethysmography. Venography and arteriography may be necessary if plain x-ray films are unremarkable. One should almost always x-ray the spine, hips, knee joints, and, in difficult cases, the entire legs. Pain that is precipitated by walking suggests peripheral arteriosclerosis, but spinal stenosis is also possible. Case Presentation #62 A 36-year-old white female cashier developed acute pain in her right calf 2 hours before admission. V—Vascular would call to mind myocardial infarction, pulmonary infarction, cerebral vascular accident, and thrombophlebitis. I—Inflammation should bring to mind bacterial infections anywhere in the body, but especially septicemia. Viral infections are not usually associated with leukocytosis but there are notable exceptions, such as infectious mononucleosis. N—Neoplasm would of course prompt the recall of acute and chronic leukemias and agnogenic myeloid metaplasia. I—Intoxication would bring to mind various drugs that are associated with a leukocytosis, such as lithium, corticosteroids, and lead. A—Allergic and Autoimmune would prompt the recall of anaphylactic shock, asthma, and other diffuse hypersensitivity reactions as well as polyarteritis nodosa and dermatomyositis. T—Trauma reminds us that burns, fractures, massive hemorrhage, or contusions of various parts of the body cause a leukocytosis. E—Endocrine causes Cushing syndrome, and exogenous corticosteroids cause leukocytosis. Pregnancy thyroid storm and diabetic ketoacidosis are also associated with leukocytosis. Approach to the Diagnosis Because infection is the most common and often the most life-threatening cause, the history and physical examination are of most importance in locating a source. Urinalysis, urine culture, blood cultures, and spinal fluid cultures are just a few. If the count is very high, a pathologist or hematologist should be called in without delay. If there is massive splenomegaly consider chronic myelogenous leukemia or myeloid metaplasia.

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The following three basic principles are applied to achieve the above goals while designing experimental studies buy terramycin 250 mg otc antimicrobial and antibacterial. The principle of replication underlines the importance of repeating the experiment trusted 250 mg terramycin infection japanese horror movie, or readings of the experiment more than once discount terramycin 250 mg otc antibiotics given for ear infections, in order to avoid/neutralize experimental errors and maximize the reliability of the data terramycin 250mg cheap virus 1980 imdb. It means that each treatment is applied in many experimental units, or each phenomenon should be studied in different locations/centers (multi-centered studies). The principle of randomization provides protection, when we conduct an observational study or experimental study, against the effects of extraneous factors and bias. Eliminating bias, which is mainly caused due to human beings involved in the study (observer bias, selection bias, information bias, assessment bias, recall bias, response bias, healthy entrant effect) is the basic aim of a research design. In other words, this principle of randomization indicates that we should design or plan the study/experiment in such a way that the variations caused by extraneous factors can all be combined under the general heading of “chance”. The principle of randomization is achieved through selecting the sample units of a study/experiment randomly. In observational studies, it is achieved by following probability-sampling techniques (simple random sampling stratified random sampling, systematic random sampling, multi- stage/phase random sampling, etc). In clinical trials, randomization is achieved through single/double blind trials, cross-over trials, etc. The principle of local control also helps us to eliminate the variability due to extraneous factors. It is often possible to group observational subjects/experimental units that share similar characteristics into a homogeneous block or stratum (e. The variation between units in a block is less than that between units in different blocks. The individuals within each block are randomly assigned to treatments; we compare treatments within each block rather than making an overall comparison between the individuals in different blocks. We can, therefore, assess the effects of treatment more precisely than if there was no blocking. Study Design Options in Medical and Health Research 61 Diagram of an Experimental Study important Experimental Designs Experimental design refers to the framework of an experiment. Informal experimental designs are those designs that normally use a less sophisticated form of analysis based on differences in magnitudes, whereas formal experimental designs offer relatively more control and use precise statistical procedures for analysis. Before-and-after without control design (Pretest–post-test design): In this design only one experimental group of patients is selected and the dependent/outcome variable is measured before and after the treatment. The effect of the treatment is measured as the difference in the dependent/outcome variable before and after the treatment. Experimental Level of phenomenon Treatment Level of group before treatment (X) introduced phenomenon Treatment Effect = (y) – (x) after treatment (Y) ii. The dependent variable is then measured in both the groups of patients at the same time. The impact of the treatment is measured from 62 Research Methodology for Health Professionals the difference in the dependent variable between the experimental and control group of patients. Experimental Treatment introduced Level of phenomenon after control treatment (Y) Treatment Effect =(y)–(Z) Level of phenomenon without treatment (Z) iii. Before and after with control design: In this design two groups of patients are selected (experimental and control) and the dependent variable is measured in both the groups for an identical time-period before the treatment. The treatment is then introduced in experimental group of patients only, and the dependent variable is measured in both for an identical time period after the introduction of the treatment. The treatment effect is determined by subtracting the change in the dependent variable in the control group from the change in the dependent variable in the experimental group. The essential characteristic of this design is that the subjects are randomly assigned to experimental treatments (or vice-versa), using either single blind or double blind trial. The two-group simple randomized design can be further classified as: - Parallel trials, and - Cross-over trials. The two-group simple randomized design can be further classified as (i) Parallel trials and (ii) Cross-over trials. It is the classic way to evaluate efficacy or effectiveness of drugs (or exercise, diet, counseling) and patients are followed over time (prospective). Steps in Conducting the rct • Appropriate protocol development • Selecting reference and experimental populations • Randomization • Intervention/Manipulation • Follow-up • Assessment 64 Research Methodology for Health Professionals Appropriate protocol Development Protocol is blue print of the research study to be done which includes aims and objectives, research questions, selection criteria, sample size, procedures up to the evaluation of outcome. Preliminary test runs are to be conducted to find out feasibility or operational efficiency of the research. Selecting reference and Experimental populations • Reference or target population: Population to which the findings of the trial, if found successful, are expected to be applicable, e. Study participants must fulfill the following criteria: – Must give informed consent – Should be representative of the population – Should be qualified or eligible for the trial – Should be available to follow up as far as possible. Both groups (study and control) should be alike with regards to certain variables that might affect the outcome of the experiment. Randomization tends to produce study groups comparable with respect to known as well as unknown risk factors, removes investigator bias in the allocation of subjects and guarantees that statistical tests will have valid significance levels. It means that some of the subjects may leave the study or the place of residence or refuse to participate at a later stage or die during the study, etc. Study Design Options in Medical and Health Research 65 Assessment It may produce a positive results or negative results. Preventive Trials: Preventive trial is related to assessing the efficacy of primary preventive measures, e. Analysis of preventive trials should result in clear statement about benefits to community, risk involved and cost to health system. Risk Factor Trials: Here investigator intervenes to interrupt the usual sequence in the development of disease for those individuals who have risk factor for developing the disease, e. Cessation Experiment: An attempt is made to evaluate the termination of a habit which is considered to be causally related to disease, e. Trials of Etiological agents: It is to confirm or refute an etiological hypothesis. If a new treatment proves effective in a study, it may become a new standard treatment that can help many patients. Also, if the new treatment proves more effective than the standard treatment, study patients who receive it, may be among the first to benefit. Clinical trials of experimental drug, treatment, device or behavioral intervention may proceed through four phases: Phase I Clinical Trial: Phase I clinical trials are done to test a new biomedical or behavioral intervention in a small group of people (e. These studies are designed to monitor effectiveness of the approved intervention in the general population and to collect information about any adverse effects associated with widespread use. In this design, sample subjects are first divided into groups (blocks/strata), such that within each group the subjects are relatively homogeneous in respect to some selected variable. The number of sample subjects in a given block would be equal to the number of treatments and one subject in each block would be randomly assigned to each treatment. For example, as discussed, the two-group pretest-posttest design might result in an undetectable interaction effect between pretest and the independent variable, such that post-test differences, if found, could not be confidently attributed to the independent variable. The Solomon four-group design, which may also be viewed as a factorial design, was able to control for this potential interaction. The primary advantage of factorial designs is that they enable us to empirically examine the effects of more than one independent variable, both individually and in combination, on the dependent variable.

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