Respiratory care clinics of North America最新文献

This article begins with a brief look at the epidemiology of SARS in Canada and then discusses barrier use and potential containment strategies that could be applied to the respiratory equipment and supportive procedures that have been implicated in the spread of SARS or other respiratory infections. The article ends with a discussion of how practice and regulations have changed in Canada since SARS and some suggestions on how practice or regulations could further improve.

The use of breathing system filters may be particularly beneficial in small infants, compared with older children and adults, because of their greater need for warming and humidification of inspired gases as well as their increased susceptibility to lower respiratory tract contamination. The only evidence available regarding the safety and efficacy of breathing system filters in small infants comes from a few small studies conducted on intensive care patients, however. These studies have suggested that the use of HME filters may be effective in preserving body temperature and airway humidity while decreasing fluid build-up in the breathing system and therefore reducing breathing system contamination. Nonetheless, the use of filters has not been shown to decrease the incidence of VAP in small infants. In contrast,their use in adult intensive care patients, particularly those requiring prolonged ventilation, has been associated with a decrease in the infection rate. The use of breathing system filters is not associated with a statistically significant increase in the rate of complications, despite the potentially greater hazards associated with their use in small infants compared with older children and adults. In practice the use of breathing system filters, even in small infants, rarely causes any major clinical problems that cannot be prevented with a high degree of vigilance and appropriate monitoring. This vigilance is particularly important to prevent the serious morbidity and even mortality that may result from filter occlusion; when subjected to excessive loading, smaller filters are more prone to obstruction than are their larger counterparts. The increased resistance provided by smaller filters should not translate into a clinically significant increase in the work of breathing during general anesthesia, because it is common practice to ventilate small infants for all but the shortest of surgical procedures. An increase in the work of breathing may, however, become more significant when spontaneous ventilation is established at the end of a surgical case. It remains unclear whether the use of filters allows the safe reuse of breathing systems in small infants. None of the breathing system filters tested by the MHRA had a zero-percent penetrance to sodium chloride particles, and pediatric filters generally had a higher penetrance than their adult counterparts. This finding suggests that there is a potential, albeit small, risk of cross-contamination. The exact risk depends on the type of filter used and on the particular patient undergoing anesthesia or ventilation in the ICU. Although no evidence has been published showing cross-infection occurring when any filter has been used in the anesthesia breathing system for adults or small infants, the level of filtration performance required to allow the safe reuse of anesthesia breathing systems in small infants remains unanswered. Because the incidence of lower respiratory tract coloniza

Humidification of inspired gases during mechanical ventilation remains a standard of care. Optimal humidity is an elusive target and is not clearly defined in the literature. The choice of a humidification device cannot be made solely on the basis of moisture output, however. The clinician must consider the effects of the device on gas exchange and spontaneous breath-ing. The author's group has used the data reviewed here to modify their previous algorithm for choosing a humidification device (see Fig. 2). Humidification requirements for noninvasive ventilation need further study.

The cheap manufacture of plastics compared with the relatively expensive labor-intensive cost of decontaminating medical equipment encourages the use of disposable single-use equipment. Although the manufacture and disposal of single-use equipment superficially would seem to have more environmental impact than reusable equipment, the processes of cleaning and decontaminating reusable items may impose an even greater cost on the environment. In a recent study at two United States hospitals, anesthetic tubing accounted for less than 10% of medical waste, about half the amount of the plastic waste generated by the cafeterias at the same two hospitals [34]. There may be a higher cost to the organization by using single-use breathing systems. One United States institution has estimated that changing from single-use to re-usable breathing systems, with a new filter for each patient, resulted in savings in initial cost and waste disposal of more than Dollars 100,000 per year [20]. In the light of current knowledge concerning infective agents, reusing breathing systems for up to 1 week with a new appropriate filter for each new patient seems to be safe practice, provided the manufacturer of the breathing system recommends such use, and the breathing system is carefully checked before each new patient.

Breathing systems used with heated humidifiers are associated with a rapid and high level of bacterial colonization. This colonization is considerably reduced with the use of HMEs. Breathing systems do not need to be changed during the entire ventilation period of a given patient unless they are visibly soiled or mechanically malfunctioning. The incidence of VAP is not influenced by the type of humidification device (heated humidifier or HME). The incidence of VAP is not affected by the duration of use of HMEs or the type of HME, but prolonging the use of a HME further reduces the risk of cross-contamination and results in considerable cost savings.

Respiratory mucosal and lung structures and functions may be severely impaired in mechanically ventilated patients when delivered gases are not adequately conditioned. Although under- and over-humidification of respiratory gases have not been defined clearly, a safe range of temperature and humidity may be suggested. During mechanical ventilation, gas entering the trachea should reach at least physiologic conditions (32 degrees C-34 degrees C and 100%relative humidity) to keep the ISB at its normal location. Clinicians must keep in mind that relative humidity is more important than absolute humidity: the warmer the gas, the higher the risk of tracheal mucosa dehydration and proximal airway obstruction. Practical assessment of the adequacy of the humidification system in use is not easy. The consistency (thin, moderate, or thick) of the patient's sputum should be evaluated regularly [47]. Full saturation of inspiratory gases is likely when water condensation is observed in the flex tube [91,92]. Nevertheless, no clinical parameter is accurate enough to detect all the effects of inadequate conditioning [45]. When mechanical ventilation is extended beyond several days, adequate conditioning of respiratory gases becomes increasingly crucial to prevent retention of secretions and to maximize mucociliary function; a requirement that respiratory gases reach at least physiologic conditions is appropriate.

This synopsis of the background to the standardization of medical devices allows a comparison of the functional operation of two regulatory authorities, the FDA and the European Commission. It can be seen that with time they have developed many common features. However, there remains a significant difference with the older style of regulation imposed by the FDA, in particular the obligation to comply with USA Federal Law and Federal Codes of Regulation. Further, the FDA expects manufacturers, when submitting medical devices for approval, to provide their own supportive evidence by showing compliance with ISO and IEC good manufacturing practice and safety standards. Finally, it is only pragmatic to accept that marketing permission for all devices is ultimately overseen, inspected and enforced solely by the FDA. By comparison, within Europe it is the more modern Medical Device Directives of the European Commission that are the statutory legislation. In order to market a medical device, the only fundamental responsibility of the manufacturer is that it must have a CE marking, which is achieved by showing compliance with the Essential Requirements. One means of accomplishing this is to conform with the provisions of relevant harmonized standards. Such concurrence may be verified if needed, by one of the international pool of independent Notified Bodies, who are ultimately overseen by the Competent Authorities of the individual States of the Community. The preparation of standards for medical devices is a slow process, involving the cooperation of the multiple stakeholders with an interest in the device. They are expected to produce a final document that is fair, consistent and practical for all the parties involved, from the initial designer to the final patient to whom the device is attached. Analysis of the three standards applicable to humidifiers, HME and BSF demonstrates some of the difficulties encountered in meeting these obligations. It is to be hoped that the solutions which were found achieve the ultimate goal of all medical device standards-specifically that the equipment should not cause a hazard to either the patient or user. But it is interesting to wonder whether it can be shown that any BSF meets one of the prime requirements of the FDA, to wit that all medical devices must be able to demonstrate efficacy. There is a dearth of clinical trials supporting the allegation of BSF manufacturers that the routine use of these devices improves patient care, which can only be taken to mean that to date such claims are difficult to vindicate. This paralogism must be countered by the indisputable fact that BSF can significantly increase the work of breath-ing, enlarge the deadspace and even, as has been shown recently, result ina complete blockage of the breathing system. Whatever standards are in place with reference to any particular medical device, it must never be forgotten that it is only the clinician who will finally be accountable f

Which temperature and humidity is optimal and can be recommended to the clinician? Some authors advocate the delivery of gas at body temperature and 100% relative humidity, which is equivalent to a water content of 44 mg/L [5,88,89]. They argue that energy neutrality is the best indicator of optimum humidity and that the intubated airway cannot be equated with the natural airway. Water loss as well as temperature and humidity gradients along the airway are necessary for mucociliary clearance and maintenance of the liquid layer of the airway epithelium, however [3]. Theoretical considerations and long-lasting experience in clinical practice support a setting that mirrors physiologic conditions even in the intubated airway. Thus, saturated gas at a temperature of 330 degrees to 35 degrees C should be delivered to the airway threshold of ventilated neonates and infants. Heated humidifiers and some HMEs can comply with these conditions. With active humidification (primarily the condensation of water) over humidification or possible malfunctions must be kept in mind. The neonatologist must consider increase in deadspace, water-retention capability, leak around the tracheal tube, and the slight increase in airway resistance when using HMEs. HMEs should not be used during weaning from ventilatory support in babies who have a body weight less than 2500 g.

The mucociliary elevator is a highly evolved organ that humidifies inspired gases and protects the lungs from particulate, chemical, and microbiologic matter. Studies of disorders mucus and ciliary function have improved the understanding of this forgotten organ. The clinical implications of this understanding have yet to be explored.