Mechanical and Noninvasive Ventilation

Chapter 9 Mechanical and Noninvasive Ventilation



Manuel Pardo, Jr. , MD




1 What are the primary indications for mechanical ventilation?


The primary indications for mechanical ventilation are inadequate oxygenation, inadequate ventilation, and elevated work of breathing.



2 What is the difference between conventional and noninvasive ventilation?




image The conventional approach to mechanical ventilation involves use of an airway device inserted directly into a patient’s trachea.


image Noninvasive ventilation is mechanical ventilation without the use of an endotracheal tube or tracheotomy. See Figure 9-1.


image

Figure 9-1 A demonstration of noninvasive positive-pressure ventilation with a nasal mask. A, The respiratory therapist is adjusting the inspiratory pressure support level and checking for proper mask fit. B, The mask must be fitted properly to minimize air leak but avoid excessive pressure on the skin.



3 What are the main types of mechanical ventilation?


The two main types are positive-pressure and negative-pressure ventilation. With positive-pressure ventilation, positive pressure is applied to the airway to inflate the lungs directly. This can be accomplished with an artificial airway (e.g., endotracheal tube) or with a nasal or face mask (noninvasive ventilation). With negative-pressure ventilation, negative pressure is applied to the abdomen and thorax to draw air into the lungs through the upper airway. This form of ventilation is typified by the iron lung negative pressure ventilators used after the polio epidemics in the first half of the 20th century. For the remainder of this chapter, noninvasive ventilation will refer to noninvasive positive-pressure ventilation.



4 What are the advantages of noninvasive ventilation compared with conventional mechanical ventilation with an endotracheal tube?


In most studies of noninvasive ventilation in the intensive care unit (ICU) setting, the main outcome measure has been reduced need for tracheal intubation. For those patients who avoid intubation, the main advantage is the avoidance of artificial airway complications. Several studies document a lower infection rate (e.g., nosocomial pneumonia and sinusitis) with noninvasive ventilation, which may be related to the maintenance of the protective glottic barrier. Other advantages include reduced need for sedative medications. Some noninvasive ventilation trials have demonstrated reductions in ICU length of stay, ICU mortality, or in-hospital mortality.



5 What are the disadvantages and contraindications of noninvasive ventilation?


Patient selection is crucial to ensuring success with noninvasive ventilation. Patients who are uncooperative, need immediate intubation, have upper airway pathologic conditions, are hemodynamically unstable, or have excessive secretions are not likely to have successful ventilation. Noninvasive ventilation should be contraindicated in these patients. In practical terms, noninvasive ventilation can initially require significant attention by the respiratory therapist and/or ICU nurse.



6 Which patients with acute respiratory failure are most likely to benefit from noninvasive ventilation?


Patients with acute exacerbations of chronic obstructive pulmonary disease are most likely to benefit, in terms of reduction in need for tracheal intubation and decreased mortality. Other populations likely to have a decreased intubation rate with noninvasive ventilation include patients with immune compromise from solid organ transplants or hematologic malignancies, cardiogenic pulmonary edema, respiratory failure after lung resection, and respiratory failure immediately after elective abdominal surgery. If noninvasive ventilation is used for patients that do not fit in these categories, consider limiting the time to 2 hours unless clear improvement is evident.



7 What are the most commonly used modes of mechanical ventilation?


For noninvasive ventilation, the most common mode is pressure support ventilation. For conventional ventilation, the three most commonly used modes are assist control ventilation, synchronized intermittent mandatory ventilation (SIMV), and pressure support ventilation.



8 How does pressure support ventilation work?


Pressure support ventilation requires the patient to trigger each breath. When a patient inhales and generates inspiratory gas flow, the ventilator rapidly delivers a preset inspiratory pressure, typically 5 to 20 cm H2O. The ventilator’s inspiratory flow stops when a certain threshold flow has been reached, typically 25% of the peak flow rate. During the expiratory phase of the respiratory cycle, positive end-expiratory pressure (PEEP) is often applied, typically between 5 and 10 cm H2O. The patient’s work of breathing is reduced, proportional to the amount of inspiratory pressure that is set. This is usually judged by the patient’s tidal volume, which can vary with each breath on the basis of patient effort and lung mechanics. Because minute ventilation is not guaranteed during pressure support ventilation, the patient may have hypoventilation if the pulmonary process is severe enough or if respiratory depressant sedatives are administered.

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Jul 6, 2016 | Posted by in CRITICAL CARE | Comments Off on Mechanical and Noninvasive Ventilation

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