Pressure support ventilation

For the spontaneously breathing patient, pressure support ventilation (PSV) has been advocated to limit barotrauma and to decrease the work of breathing. Pressure support differs from A/C and IMV in that a level of support pressure is set to assist every spontaneous effort. Airway pressure support is maintained until the patient's inspiratory flow falls below a certain cutoff (eg, 25% of peak flow). The patient determines the tidal volume, respiratory rate, and flow rate.With some mechanical ventilators, there is the ability to set a back-up IMV rate should spontaneous respirations cease.

PSV is frequently the mode of choice in patients whose respiratory failure is not severe and who have an adequate respiratory drive. It can result in improved patient comfort, reduced cardiovascular effects, reduced risk of barotrauma, and improved distribution of gas.

Noninvasive ventilation

The application of mechanical ventilatory support through a mask in place of endotracheal intubation is becoming increasingly accepted and used in the emergency department. Considering this modality for patients with mild-to-moderate respiratory failure is appropriate. The patient must be mentally alert enough to follow commands. Clinical situations in which it has proven useful include acute exacerbation of chronic obstructive pulmonary disease (COPD) or asthma, decompensated congestive heart failure (CHF) with mild-to-moderate pulmonary edema, and pulmonary edema from hypervolemia. It is most commonly applied as continuous positive airway pressure (CPAP) and biphasic positive airway pressure (BiPAP). BiPAP is commonly misunderstood to be a form of pressure support ventilation triggered by patient breaths; in actuality, BiPAP is a form of CPAP that alternates between high and low positive airway pressures, permitting inspiration (and expiration) throughout.

Reviews of the literature have shown noninvasive positive-pressure ventilation (NPPV) to be beneficial for COPD, reducing the rate of tracheal intubations and the length of stay.Recently developed clinical guidelines recommend that NPPV be considered as an adjunct to standard medical therapy in patients with severe COPD exacerbations (pH < 7.35 and relative hypercarbia), as well as in patients with cardiogenic pulmonary edema and respiratory failure without shock or acute coronary syndrome requiring urgent percutaneous coronary intervention.

The use of NPPV has been less well studied in asthma, though a recent meta-analysis found that NPPV improved secondary outcomes such as number of hospital admissions, length of ICU stay, and length of hospital stay, as well as had a favorable effects on certain lung function parameters such as peak expiratory flow, forced vital capacity, and FEV1. However, the study did not demonstrate a definite benefit ofNPPV for mortality or intubation rates.