By X. Avogadro. Strayer University.
It involves washing with a solvent (usually water equipment will be for ‘single use’ or ‘single patient use’ and detergent) order generic priligy online, which may be heated (e order priligy 30 mg with visa. This process does not necessarily the item to be used once only on an individual patient destroy infectious agents purchase priligy with american express. The packaging will be labelled either disinfection or sterilization to remove bioburden. The ultrasound causes the ‘Single patient use’ indicates that the manufacturer water to vibrate at high frequencies so that it literally advises that the item may be used more than once on the 7 ‘shakes’ off organic matter. Examples of ‘single patient use’ items in larly useful for equipment where conventional cleaning anaesthesia include ventilator tubing and bacterial/viral methods might not reach some aspects of the device, or flters used in critical care units. Consequently, decon- Disinfection tamination by sterilization or disinfection is required. Low-level disinfection kills most vegeta- lead clinician and the relevant manufacturer’s guidance. High-level disinfection kills veg- will depend on a number of factors, including the nature etative bacteria (but not endospores), mycobacteria, fungi of the contamination, the time required for processing, the and viruses. Sterilant This is a liquid chemical agent, which can kill bacteria, fungi, viruses and bacterial spores (e. Dry saturated steam This involves saturated steam that contains no water par- ticles in suspension (Fig. Disinfection by washer-disinfectors careful thought needs to be given to where disposable (Fig. To avoid compromising envi- employed, since autoclaving (with dry saturated steam) ronmental cleaning standards, good communication is may damage anaesthetic equipment that is repeatedly required between theatre and supply managers. They are produced by a number of manufacturers to reprocess heat-sensitive fbre-optic endoscopes to the satisfaction of the innumerable advisory and regulatory Figure 21. Intrinsic to most of these systems is the integration of some form of instrument tracking (see below). When preparing an infection control action plan, it should Endoscopes frst need manual cleaning before being be agreed at the outset with all relevant parties, that repro- attached into the machines. Their use necessitates instrument cleaning (the most external wrapping of the fbrescope which would other- important component of the decontamination process) wise allow ingress of the caustic fuids and also pose an within the theatre complex. The working channel(s) of the endoscope quality control measures required for the safe use of auto- is connected into the washers so that it receives the same claves cannot be guaranteed outside non-specialist areas. Their in stagnant fuid in endoscope channels, has resulted in decontamination should be undertaken in designated recommendations requiring that endoscopes are processed endoscopy units with appropriately trained personnel. Change between patients if visibly contaminated or used for highly infectious cases, e. A second autoclave indicator is present inside the pack to confrm that adequate sterilization has taken place. Filters and cabinet are irradiated with ultraviolet patient in the event of a ‘clinical incident’; for example, light, which is bacteriostatic at adequate exposure levels. Single-use equipment overcomes the need of medical equipment, the one exception being the pre- for tracking systems to be in place. The consistent application of effective hand hygiene is Damage caused by the cornerstone of good infection control practice and will the decontamination process minimize the risk of bacterial contamination of the oper- ating theatre environment by anaesthetists (e. Use 435 Ward’s Anaesthetic Equipment of washer-disinfectors operating at lower temperatures prion protein has also been detected in the appendix, may then be the preferred option. Some light sources for ard washing techniques do reduce the concentration of metal laryngoscope blades lose luminance with repeated prions in an exponential fashion, but 10–20 cycles are high-temperature autoclaving. Although their Working Group and the National Institute for Health and role in the prevention of nosocomial pneumonia is 12,17 15 Clinical Excellence. Similarly, prion disease can be reduced by the strict adherence to implementation of a local policy on the reuse of breathing standard universal infection control precautions and the systems in line with manufacturers’ instructions is recom- employment of single-use instruments when they are con- mended. Some breathing systems are marketed with sidered to be as reliable and safe as reuseable alternatives. However, to ensure consistent application of intubation aids should not be reused. For procedures involving high- or remain on surgical instruments after standard decontami- medium-risk tissues (i. There has been no evi- olfactory epithelium), instruments should be dence of droplet-transmission. However, for procedures highest concentration of prion protein occurs in the brain, on low-risk tissues, normal reprocessing guidance spinal cord and posterior eye. Control 134°C on light intensity laryngoscope as a potential source of Substances Hazardous to Health provided by fbrelight Macintosh of cross-infection. Sterilisation, Anaesthetists’ role in computer Pathogens and the Transmissible disinfection and cleaning of medical keyboard contamination in an Spongiform Encephalopathy equipment: guidance on operating room. Transmissible decontamination from the Medical Hospital Infection 2008;70: spongiform encephalopathy agents: Advisory Committee to Department of 148–53. This must be Record keeping 439 viewed in the context of the time when records were all Other information and communication paper based, and the majority of information systems did systems 445 not communicate with each other. Anaesthetists perform the majority of their clinical work in the operating theatre: the anaesthetic machine there- Functions of the anaesthetic record fore, acts as their desk and offce as well as a device for delivering anaesthesia. It is essential that it is equipped In addition to the legal imperative for keeping an with the tools to provide care, record activity, provide anaesthetic record there are many practical reasons for information and enable communication. This chapter will consider not only how information technology can assist in maintaining a record of the anaes- Clinical communication thetic, but also its wider use in the theatre environment. Most clinicians in the developed world work in a system that is based on corporate responsibility. The earliest anaesthetic records date from 1894, although Therefore, it is important that all information about the over 80 years later 3. It is now investigations, the intraoperative record and postoperative a legal requirement that an anaesthetic record is kept. The report of the National Confdential information about anaesthetic and surgical care. This Enquiry for Perioperative Deaths for 2000 showed that1 can help to improve patient care and can assist in the 5% of case notes were lost, and in 3% of those present management of the surgical process. There is no evidence vided for national and local use including information that these fgures have changed signifcantly since then. Clinical correspondence with coding Electronic prescribing Medicolegal The record should be accurate, complete and legible, as its quality may be seen as a refection of the quality of care given. It may also protect from litigation where the onus the introduction of a computerized record. A modern computerised anaesthetic record system should also have comprehensive links to other clinical information systems to ensure that up-to-date information Computerized anaesthetic records is available, and to avoid duplicate entry of pre-existing Computerized anaesthetic record systems have been avail- information (e. Now it is anticipated that One of the diffculties in providing a business case is the ‘Clinical Five’6 (see Box 22.
The disadvantages are some tests can be near-maximal or maximal for some individuals order 30 mg priligy otc, particularly in individuals with low aerobic fitness discount 90 mg priligy amex, and potentially be unmonitored for test termination criteria (Box 4 generic 30 mg priligy otc. Therefore, these tests may be inappropriate for sedentary individuals or individuals at increased risk for cardiovascular and/or musculoskeletal complications. An individual’s level of motivation and pacing ability also can have a profound impact on test results. Motor-driven treadmills can be used for submaximal and maximal testing and are often employed for diagnostic testing in the United States. They provide a familiar form of exercise to many and, if the correct protocol is chosen (i. Nevertheless, a practice session might be necessary in some cases to permit habituation and reduce anxiety. On the other hand, treadmills usually are expensive, not easily transportable, and potentially make some measurements (e. Treadmills must be calibrated periodically to ensure the accuracy of the test when O is not directly2 measured (82). In addition, holding on to the support rail(s) should be discouraged to ensure accuracy of metabolic work output, particularly when O is estimated as opposed to directly measured. Cycle ergometers also provide a non–weight-bearing test modality in which work rates are easily adjusted in small increments. The main disadvantage is cycling may be a less familiar mode of exercise to some individuals, often resulting in limiting localized muscle fatigue and an underestimation of O2max. Electronic cycle ergometers can deliver the same work rate across a range of pedal rates (i. Step tests require little or no equipment, steps are easily transportable, stepping skill requires little practice, the test usually is of short duration, and stepping is advantageous for mass testing (110). Special precautions may be needed for those who have balance problems or are extremely deconditioned. Therefore, the protocol chosen must be appropriate for the physical fitness level of the client. In addition, inadequate compliance to the step cadence and excessive fatigue in the lead limb may diminish the value of a step test. The objective of the Cooper 12- min test is to cover the greatest distance in the allotted time period and for the 1. O2max is estimated using the following regression equation (61): −1 −1 O 2max (mL · kg · min ) = 132. The American Thoracic Society has published guidelines on 6-min walk test procedures and interpretation (6). Even though the test is considered submaximal, it may result in near-maximal performance for those with low physical fitness levels or disease (52). Clients and patients completing less than 300 m (~984 ft) during the 6-min walk demonstrate a poorer short-term survival compared to those surpassing this threshold (14). Several multivariate equations are available to predict O2peak from the 6-min walk; however, the following equation requires minimal clinical information (14): O2peak = O2 mL · kg−1 · min−1 = (0. These variables must be controlled to have a valid estimate that can be used as a reference point in an individual’s fitness program. See Chapter 5 for a list of incremental treadmill protocols that may be used to assess submaximal exercise responses. Cycle Ergometer Tests The Astrand-Ryhming cycle ergometer test is a single-stage test lasting 6 min (5). This equation is valid to estimate O at submaximal steady state workloads (from 300 to 1,2002 −1 kg · m · min ) (50–200 W); therefore, caution must be used if extrapolating to workloads outside this range. Treadmill Tests The primary exercise modality for submaximal exercise testing traditionally has been the cycle ergometer, although treadmills are used in many settings. Astrand and Ryhming (5) used a single-step height of 33 cm (13 in) for women and 40 cm (15. Because of this, step tests are not a good choice of modality for less fit or diseased clients. The Canadian Home Fitness Test has demonstrated that such testing can be performed on a large scale and at low cost (106). The Queens College Step Test (also called the McArdle Step Test) requires −1 −1 participants to step at a rate of 24 steps · min for men and 22 steps · min for women for 3 min. O2max is calculated using the formulas below (76): For men: −1 −1 O2max (mL · kg · min ) = 111. Although submaximal exercise testing is not as precise as maximal exercise testing, it provides a general reflection of an individual’s physical fitness at a lower cost, potentially reduced risk for adverse events, and requires less time and effort on the part of the subject. Despite differences in test accuracy and methodology, virtually all evaluations can establish a baseline and be used to track relative progress during exercise training. These equations produce a single expected aerobic capacity value for comparison to a measured response as opposed to percentiles. Muscular strength refers to the muscle’s ability to exert a maximal force on one occasion, muscular endurance is the muscle’s ability to continue to perform successive exertions or repetitions against a submaximal load, and muscular power is the muscle’s ability to exert force per unit of time (i. Traditionally, tests allowing few (≤3) repetitions of a task prior to reaching muscular fatigue have been considered strength measures, whereas those in which numerous repetitions (>12) are performed prior to muscular fatigue were considered measures of muscular endurance. Rationale Physical fitness tests of muscular strength and muscular endurance before commencing exercise training or as part of a health/fitness screening evaluation can provide valuable information on a client’s baseline physical fitness level. For example, muscular fitness test results can be compared to established standards and can be helpful in identifying weaknesses in certain muscle groups or muscle imbalances that could be targeted in exercise training programs. The information obtained during baseline muscular fitness assessments can also serve as a basis for designing individualized exercise training programs. An equally useful application of physical fitness testing is to show a client’s progressive improvements over time as a result of the training program and thus provide feedback that is often beneficial in promoting long-term exercise adherence. Results of any one test are specific to the procedures used, and no single test exists for evaluating total body muscular endurance or strength. Moreover, a warm-up consisting of 5–10 min of light intensity aerobic exercise (i. These warm-up activities increase muscle temperature and localized blood flow and promote appropriate cardiovascular responses for exercise. In both cases, caution must be used in the interpretation of the scores because the norms may not include a representative sample of the individual being measured, a standardized protocol may be absent, or the exact test being used (e. In addition, the biomechanics for a given resistance exercise may differ significantly when using equipment from different manufacturers, further impacting generalizability. Muscular Strength Although muscular strength refers to the external force (properly expressed in newtons, although kilograms and pounds are commonly used as well) that can be generated by a specific muscle or muscle group, it is commonly expressed in terms of resistance met or overcome. Static or isometric strength can be measured conveniently using a variety of devices including cable tensiometers and handgrip dynamometers. Measures of static strength are specific to the muscle group and joint angle involved in testing and thus may be limited in describing overall muscular strength. Despite this limitation, simple measurements such as handgrip strength have predicted mortality and functional status in older individuals (99,109). Adjust the grip bar so the second joint of the fingers fits snugly under the handle and takes the weight of the instrument. The subject holds the handgrip dynamometer in line with the forearm at the level of the thigh, away from the body.
Cord conditions like syringomyelia and brain stem involvement of the thalamus by embolism or thrombosis may occasionally cause pain in the hand best buy priligy, but in the latter condition order priligy line, there is usually an accompanying leg pain purchase priligy in india. In the deepest penetration of our dissection of the hand, we encounter the most common structures that cause hand pain, the bones and joints. The bones may be fractured, dislocated, or contused or the joints may be sprained, but if the joints are painful, arthritis is the most likely cause. More rarely, it is 409 associated with psoriatic arthritis, lupus erythematosus, and other systemic diseases. Approach to the Diagnosis In diagnosis, most of these conditions will be obvious on inspection. Pain over the radial aspect of the wrist which is aggravated by flexing the thumb and applying ulnar deviation is most likely de Quervain tenosynovitis. Therapeutic trial of a steroid and Xylocaine injection (carpal tunnel syndrome) 410 Case Presentation #38 A 33-year-old Filipino female secretary complained of pain, numbness, and tingling in both hands for several months. Neurologic examination revealed diminished sensation to touch and pain in the thumb and index fingers bilaterally and a positive Tinel sign at the wrists. Moving by layers from the skin to the center of the brain is the local application of the anatomic process. Thus, sunstroke is a cause of headache originating in the sunburnt skin, as is herpes zoster. Moving to the muscles, one encounters the most common cause of headache, muscle traction headache, which may be secondary to other conditions (e. The next most common type of headache, migraine, originates from the superficial arteries. It usually involves the superficial temporal arteries, but it can also involve the internal carotid arteries (Horton cephalalgia or cluster headaches), the occipital artery, and the intracranial arteries (e. Temporal arteritis and hypertension are two other important causes of headache originating from the extracranial arteries. The adjacent superficial nerves are a less common but important cause of headache. Occipital neuralgia may result from inflammation or compression of either the minor or major occipital nerve, and is often involved secondarily in muscle contraction headaches. Several common causes of headache come to mind when considering the organs of the head. Thus, the eyes are affected by refractive errors, astigmatism, and glaucoma, all etiologies of headache. The ear is affected by otitis media, mastoiditis, acoustic neuromas, and cholesteatomas. The nose is affected by infectious rhinitis, allergic rhinitis, Wegener granulomatosis, nicotine toxicity, fractures, and deviated septum, all causes of headache. Sinusitis (both the purulent and the vacuum type), sinus polyps, and tumors make checking the nasal sinuses important in analyzing the cause of headaches. Finally, the teeth should be investigated for caries, abscesses, and fillings that may be too close to the nerve root. The meninges are the site of subarachnoid hemorrhages, subdural and epidural hematomas, meningitis, and hydrocephalus. The cerebral arteries are the site of cerebral hemorrhages, thrombosis, and emboli, as well as aneurysms and arteriovenous anomalies. The cerebral veins, especially the venous sinuses, may become inflamed and thrombosed, producing a headache. The cranial nerves are the site of trigeminal neuralgia mentioned above and glossopharyngeal neuralgia. Although the brain itself is not tender, lesions of the brain cause increased intracranial pressure or traction on other painful structures, such as the intracranial arteries, venous sinuses, or nerves. Concussions, pituitary tumors, toxic encephalopathy from alcohol, bromides, and other substances are important causes, in addition to the cerebral hemorrhage, thrombosis, and emboli already mentioned. The various systemic diseases shown in Table 33 are too numerous to mention here, but fever of any etiology is an important cause and must not be forgotten, although this symptom is usually obvious. If one approaches the challenge simply on the basis of what is common, the patient most likely has migraine or muscle traction headache. Shouldn’t we look for serious conditions such as brain tumor, meningitis, or subarachnoid hemorrhage to avoid a serious mistake and a malpractice suit? First, check for nuchal rigidity to rule out meningitis and subarachnoid hemorrhage. Next, do a careful neurologic examination to rule out a brain tumor or other space-occupying lesion. These steps are particularly important in a patient who is experiencing his or her first serious headache. If there is nuchal rigidity or focal neurologic signs, it is wise to immediately refer the patient to a neurologist or neurosurgeon for further workup and possible hospitalization. One other condition that must be considered in acute headache (particularly in elderly persons) is temporal arteritis. A sedimentation rate will usually be positive, but a neurology consult is axiomatic so that steroids can be started immediately. In the patient with chronic or recurring headaches and no neurologic findings, it is wise to see the patient during the attack. Migraine and histamine headaches can be diagnosed by the response to sumatriptan by mouth or injection. If the headaches are due to chronic allergic or infectious rhinitis, relief can be had by spraying the turbinates with phenylephrine. Muscle traction headaches will often be relieved by occipital nerve blocks supporting the diagnosis. Compression of the superficial temporal artery will often relieve migraine temporarily supporting that diagnosis. Compression of the jugular veins will often give relief to patients with postspinal tap headaches. If the patient is seen between headaches, certain prophylactic measures may help establish the diagnosis. For migraine, β-blockers may be prescribed; if the headaches are prevented, there is good support for the diagnosis. A course of corticosteroids may be initiated in patients with histamine (cluster) headaches to help establish the diagnosis. Muscle relaxants and/or tricyclic drugs may be given to help diagnose muscle contraction headaches. She was seen in the emergency room the night before and was diagnosed with migraine, given a shot, and sent home. On examination, the patient was found to have nuchal rigidity but no focal neurologic signs. I—Infection recalls syphilis in which the head assumes the shape of a hot cross bun. N—Neurologic disease includes microcephaly (small underdeveloped brain) and hydrocephaly (due to several causes); the most important diseases from a treatable standpoint are subdural hematomas, brain abscesses, and neoplasms.
The power setting (sometimes referred to as delta P) increases 270 Ventilation in the intensive care unit Chapter | 10 | A B Figure 10 generic priligy 60mg free shipping. The white shuttle of a pneumatically operated valve termed the ‘impedence valve’ is visible: this isolates the diaphragm from the respiratory circuit when the ventilator is used in conventional mode order cheap priligy on line. Carbon accompanying wide bore non-kink catheters inserted into dioxide elimination from the patient is achieved by a the femoral vein and artery best priligy 30 mg. Safe anti-kink bindings of the patient circuit are embedded and easy-to-use machines are important for clinical prac- throughout with a heating wire. Low compliance 15 mm tice with the ability to ventilate while not restricting the diameter tubing is used. Giuliani R, Mascia L, Recchia F, – reported classifcations and their Intensive Care Med 1995;21:159–68. Autotriggering caused by support prevents diaphragmatic Continuous calculation of cardiogenic oscillation during fatigue during weaning from intratracheal pressure in tracheal fow-triggered mechanical mechanical ventilation. Fort P, Farmer C, Westerman J, The effects of pressure control alveolar rupture during positive Johannigman J, Beninati W, Dolan versus volume control assisted pressure ventilation. Am J Respir Crit Care Med device to treat hypoxaemia and Principles and practice of mechanical 2000;161:1450–8. Respir Care Clin N Am Buchner S, Jeron A, Karagiannidis Conti G, Mancebo J, Rekik N, 2001;7:341–62, vii. This allows the delivery Filtration is the removal of particles from either a gas or of various gas mixtures and/or vapours, and any necessary a liquid suspension. In addition, a tracheostomy may from gasses delivered to patients, to prevent microbes be carried out on some patients to bypass the upper from patients cross-infecting other patients and staff, and airways, either temporarily or for the longer term, whilst to reduce the contamination of equipment. These sputum expectorated by a patient and condensation in devices bypass the normal physiological functions of the breathing systems may harbour pathogens, and flters can nasopharynx. During normal breathing, the nasopharynx warms, humidifes and, particularly during nasal breathing, flters Mechanisms of fltration of inspired gasses. When the patient’s nasopharynx is bypassed, gas-borne particles these functions are lost. The trachea has a continuous stream of mucus, called the mucociliary elevator; this Filter material generally consists of fbres formed into a moves towards the pharynx, trapping and removing any non-woven wad or sheet. The mucociliary elevator by which the flter material removes particles from a fow relies on optimum levels of temperature, and particularly of gas (Fig. Interception very dry to reduce the risk of corrosion, condensation and Particles will tend to follow streamlines in a fow of gas. Gasses deliv- However, if a particle in the gas stream comes within one ered to the patient’s trachea, therefore, need to be artif- particle radius of the surface of a fbre, the particle will cially warmed, humidifed and fltered to prevent damage to adhere to the fbre. The particles may, therefore, strike the fbre, even Most penetrating particle size though the gas streamline is more than one particle radius The relative effciencies of the fve mechanisms of fltration from the fbre. Large particles in slow-moving air do not follow gas This size is known as the most penetrating particle size. Diffusion Small particles do not remain on particular streamlines in the gas but undergo Brownian motion due to interactions Types of flter with gas molecules. This effectively increases their cross- sectional area and so increases the probability of them There are two main types of flter material used in breath- striking a fbre. Electrostatic attraction Glass fbre flters Some flter material (see below) is electrostatically charged during manufacture to enhance its ability to This flter material consists of a sheet of resin-bonded glass capture particles. A sitely charged fbres; neutral particles are attracted to a sheet with a large surface area is used to reduce the resist- charged fbre as the electric feld on the fbre induces a ance to gas fow to an acceptable level. The sheet is then dipole in the particles (positive and negative charges on pleated to minimize the required volume, and hence dead opposite sides of the particles); and charged particles space, for the housing. This type of flter material is hydro- are attracted to neutral fbres by inducing image forces on phobic and under normal clinical conditions, does not the fbres. Electrostatic flters Measuring the performance of There are two main types of electrostatic flter material. In breathing system flters both types, the fbre density is lower than in glass fbre The fltration effciency of a flter is determined by measur- flters and hence the resistance to gas fow is lower per unit ing the number of particles passing through the flter as a area. The fltration performance is enhanced by using elec- percentage of the number of particles in an aerosol chal- trostatically charged material, which attracts and binds lenge to the flter. This percentage is the penetration value with any particles passing through the flter material. Although challenges of microbes can be Therefore, this type of flter material does not need to be 6 used, the standard for breathing system flters specifes pleated, and a fat layer is generally used in breathing that the challenge should consist of a particular quantity system flters. Tribocharged flters flter is challenged at a fow of 15 or 30 L min−1 for flters An electrostatic charge can be induced on two dissimilar intended for use with paediatric or adult patients, respec- fbres by rubbing them together during the manufacturing tively. Typical penetration values for flters are shown in process, so that one type becomes positively charged and Fig. Fibrillated coronal-charged flters Humidity An electrostatic charge can be applied to a sheet of poly- Humidity is used to describe the amount of water vapour propylene by using a point electrode emitting ions (corona in air or gas. This type of material is often called an elec- humidity that gas can contain is limited by temperature tret. At the maximum humidity for a particular strength of the molecular bonds is enhanced in the direc- temperature, the gas is said to be saturated with water tion of the stretching, but reduced in a direction perpen- vapour, and the level of humidity is the humidity at satura- dicular to it. The difference between the two (−34 g m−3) is the humid- ity defcit: humidity must be added by the airways to reduce this defcit to 0 g m−3. If the room air is warmed from 22 to 37°C without any humidifcation, the relative humidity will fall to 100 × (10 ÷ 44) = 23%. To saturate inspired gasses, which have a low level of humidity, a considerable proportion of the body’s heat A production must be used (up to one-third for a neonate). This can then lead to a fall in the patient’s core tempera- ture of more than 1°C. Humidifcation requirements The level of humidity acceptable in gasses delivered to patients whose upper airways have been bypassed depends on the length of time of the bypass. Active systems, such as heated humidifers, add water vapour to a fow of gas inde- pendently of the patient. If the exhaled gas is at 34°C and the surface of different types of flter material. These devices generally consist of a transparent plastic housing so that any obstructions and secretions in the Room air at 22°C typically has an absolute humidity device can be seen readily. The humidity at satura- either foam or paper that is commonly coated with a tion of air at 22°C is approximately 20 g m−3, so that the hygroscopic salt such as calcium chloride. If the salt absorbs water vapour, hence reducing the relative air cools to an even lower temperature, condensation will humidity of the gas to below saturation level, although 278 Breathing flters, humidifers and nebulizers Chapter | 11 | 100 10 N95 N99 1 0. Filters were tested at fows of 15 l min−1 (paediatric) or 30 l min−1 (adult), respectively. An ideal flter would have low values for penetration, pressure drop and internal volume (a small ‘bubble’ in the lower left hand side of the fgure). However, flters with low penetration (high fltration effciency) and low-pressure drop tend to be large flters; smaller flters tend to have higher pressure drops and higher penetration values (low fltration performance). Heat and moisture exchangers and breathing system flters: their use in anaesthesia and intensive care.