Pneumothorax & Mechanical Ventilation
Mechanical ventilation is the use of life-support to perform the work of breathing for patients who are unable to breathe on their own or are critically ill. The First Mechanical Ventilation machine was used in 1938 called the "Iron Lung " which used negative pressure. Positive Mechanical ventilators began to be used in anesthesia and intensive care during the 1950s. The development was confirmed by the need to treat polio patients and the increasing use of muscle relaxation, during anesthesia. Modern ventilators today are classified by the method of cycling from inspiratory phase to the expiatory phase.
Today we use positive ventilation over negative, negative is not as invasive but mimics normal breathing but is uncomfortable, today it is not commonly used. Positive-pressure ventilation means that pressure is applied at the patient's lungs through an ETT or tracheotomy tube. The positive pressure causes the gas to flow into the lungs until the ventilator breath has ended. As the airway pressure drops back to zero, elastic recoil of the chest accomplishes passive exhalation by pushing the tidal volume out. Every patient is treated differently depending on the reason to intubate, until we can extubate we have to fix the underlying problem. Prolonged mechanical ventilation can lead to nosocomial pneumonia, cardiac morbidity, and death. However, extubating a patient too soon may result in having to reintubate which can result in the same illnesses as prolonged intubation. “Respiratory therapists start testing for the opportunity to reduce support very soon after intubation and reduces support at every opportunity” (Cook 2000).
Most common mode of ventilation is AC-VC it provides a consistent breath-to-breath tidal volume, making the tidal volume and rate preset and guaranteed. The patient can attribute to the frequency and timing of the breaths. If the patient makes an inspiratory effort, the ventilator senses a decrease in the circuit pressure and delivers the preset tidal volume. This way the patient can determine a comfortable respiratory pattern and trigger additional breaths above the set rate. If the patient does not initiate a breath, the ventilator automatically delivers the preset rate and volume, ensuring minimum Ve. Assist-control is better than controlled ventilation because the patient can trigger the ventilator to deliver a breath and, adjust their Ve. In controlled ventilation, the patient receives only breaths initiated by the ventilator at the preset rate, making it difficult and uncomfortable to have spontaneous breaths. If a patient needs controlled ventilation they should be sedated. Vc is best used in patients with normal lungs.
Pressure control is increasing in popularity in the setting of acute lung injury, or patients with severe adult respiratory distress syndrome (ARDS). There is no evidence that pressure control is better than volume control. Nonetheless the ability to easily control inspiratory time, allows a more effective management of MAP. Pressure ventilation also shows better gas distribution, but you can achieve this in volume control by altering flow rates and inspiratory pause. When a patient is placed on pressure-ventilation, the clinician (RT) sets the rate, inspiratory time, positive end expiatory pressure (PEEP), and most importantly, the peak airway pressure limit. When utilizing pressure-control mode the patient can receive as much inspiratory flow as needed. By limiting the delivered peak airway pressure, the RT helps limiting the risk of barotraumas delivered to the lung.
Pressure support is a method of assisting spontaneous breathing in a ventilated patient. The patient controls all parts of the breath except the pressure limit. The patient triggers the ventilator, the ventilator delivers a flow up to a preset pressure limit depending on the desired minute volume, the patient continues the breath, and flow cycles off...
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