Resp Care
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Patient-ventilator interaction can be described as the relationship between 2 respiratory pumps: (1) the patient's pulmonary system, which is controlled by the neuromuscular system and influenced by the mechanical characteristics of the lungs and thorax, and (2) the ventilator, which is controlled by the ventilator settings and the function of the flow valve. When the 2 pumps function in synchrony, every phase of the breath is perfectly matched. Anything that upsets the harmony between the 2 pumps results in asynchrony and causes patient discomfort and unnecessarily increases work of breathing. ⋯ During pressure-controlled or pressure-support ventilation we can adjust variables that affect when the inspiration terminates (eg, inspiratory time, expiratory sensitivity). (4) Expiratory phase. Patients with obstructive lung disease are particularly prone to developing intrinsic positive end-expiratory pressure (auto-PEEP) and therefore have difficulty triggering the ventilator. Bedside evaluation for the presence of auto-PEEP should be routinely performed and corrective adjustments made when appropriate.
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The interaction of a mechanical ventilator and the human cardiovascular system is complex. One of the most important effects of positive-pressure ventilation (PPV) is that it can decrease venous return. PPV also alters right- and left-ventricular ejection. ⋯ Understanding and managing these complex and often opposing interactions in critically ill patients is facilitated by analysis of hemodynamic and ventilator waveforms at the bedside. The relationship of PPV to changes in the arterial pressure waveform gives important information regarding appropriate fluid and vasopressor treatment. This article focuses on effects of respiratory pressures on hemodynamics and considers how cardiac pressures can be transmitted to the airway and cause ventilator malfunction.
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Ventilator management of the patient recovering from acute respiratory failure must balance competing objectives. On the one hand, aggressive efforts to promptly discontinue support and remove the artificial airway reduce the risk of ventilator-induced lung injury, nosocomial pneumonia, airway trauma from the endotracheal tube, and unnecessary sedation. On the other hand, overly aggressive, premature discontinuation of ventilatory support or removal of the artificial airway can precipitate ventilatory muscle fatigue, gas-exchange failure, and loss of airway protection. ⋯ Third, ventilatory support strategies should be aimed at maximizing patient comfort and unloading the respiratory muscles. Fourth, patients who require prolonged ventilatory support beyond the intensive care unit should go to specialized facilities that can provide gradual reduction of support. Fifth, many of these management objectives can be effectively carried out with protocols executed by nonphysicians.
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Dual-control ventilation modes were introduced with the goal of combining the advantages of volume-control ventilation (constant minute ventilation) and pressure-control ventilation (rapid, variable flow). Dual-control ventilation modes have gained popularity despite little evidence to support routine use. ⋯ Inspecting the waveforms will lead clinicians to the realization that dual-control does not guarantee a set tidal volume and that variability in delivered tidal volume is greater with dual-control than with pressure control. These realizations have important implications for low-tidal volume strategies.
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Graphical waveforms have become ubiquitous in clinical care. Using and understanding pictures and symbols is a daily activity. Humans are neurologically equipped to understand symbolic information and have done so for millennia. ⋯ Didactic study, frequent viewing, and understanding of the background of the artist (artistic context) are needed to fully appreciate art. Using waveforms to care for patients requires understanding of the clinical context under which they are obtained, factors that affect their creation, and artifacts that interfere with interpretation. This article summarizes the presentation and discussions at this Journal Conference on ventilator waveforms in relation to lung and chest wall compliance, resistance, carbon dioxide kinetics, hemodynamics, specific modes of ventilation, specific lung diseases, and ventilator-weaning.