Resp Care
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Comparative Study Clinical Trial
Accuracy of physiologic dead space measurements in patients with acute respiratory distress syndrome using volumetric capnography: comparison with the metabolic monitor method.
Volumetric capnography is an alternative method of measuring expired carbon dioxide partial pressure (P(eCO2)) and physiologic dead-space-to-tidal-volume ratio (V(D)/V(T)) during mechanical ventilation. In this method, P(eCO2) is measured at the Y-adapter of the ventilator circuit, thus eliminating the effects of compression volume contamination and the need to apply a correction factor. We investigated the accuracy of volumetric capnography in measuring V(D)/V(T), compared to both uncorrected and corrected measurements, using a metabolic monitor in patients with acute respiratory distress syndrome (ARDS). ⋯ Volumetric capnography measurements of V(D)/V(T) in mechanically-ventilated patients with ARDS are as accurate as those obtained by metabolic monitor technique. .
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No hypothesis relating to respiratory care in the intensive care unit has proved more difficult to study in an objective fashion than the commonly held belief that tracheostomy hastens weaning from ventilatory support. Tracheostomy might facilitate weaning by reducing dead space and decreasing airway resistance, by improving secretion clearance, by reducing the need for sedation, and by decreasing the risk of aspiration. Available evidence indicates that dead space and airway resistance are in fact reduced, although whether the magnitude of these reductions explains the clinical observation of more rapid weaning after tracheotomy is less certain. ⋯ The most recent clinical trial found that percutaneous dilational tracheotomy performed in the first 2 days in patients projected to need > 14 days of ventilatory support greatly reduced ventilator and intensive care unit days, and decreased both the incidence of pneumonia and overall mortality, in comparison with tracheostomy done after day 14. Conducting such trials is difficult because of investigator and clinician bias, the inability to predict which patients will actually require prolonged mechanical ventilation, and several other factors discussed in this article. Tracheotomy probably does aid in liberating some patients from ventilatory support, but this may be as much from its effect on clinician behavior as from any physiologic impact.
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Tracheostomy tubes are used to administer positive-pressure ventilation, to provide a patent airway, to provide protection from aspiration, and to provide access to the lower respiratory tract for airway clearance. They are available in a variety of sizes and styles, from several manufacturers. The dimensions of tracheostomy tubes are given by their inner diameter, outer diameter, length, and curvature. ⋯ Others are designed with a port above the cuff that allows for subglottic aspiration of secretions. The tracheostomy button is used for stoma maintenance. It is important for clinicians caring for patients with a tracheostomy tube to understand the nuances of various tracheostomy tube designs and to select a tube that appropriately fits the patient.
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An increasing number of technology-dependent patients are sent home for long-term home-management of stable chronic illness. With a patient who is going to undergo tracheotomy, patient-education (for the patient and his/her caregivers) should begin early (before the tracheostomy, if possible), should be individualized to the patient, and should include basic airway anatomy, medical justification for the tracheostomy, tube description and operation, signs and symptoms of respiratory and upper-airway distress, signs and symptoms of aspiration, suctioning technique, tracheostomy tube-cleaning and maintenance, stoma-site assessment and cleaning, cardiopulmonary resuscitation, emergency decannulation and reinsertion procedures, tube-change procedure, equipment-and-supply use and ordering procedures, and financial issues. There should be a scheduled follow-up plan with the attending physician. A combination of process-validation, through additional research, and expert consensus may be needed to standardize the long-term care of patients who undergo tracheostomy.