Combined Pressure Control/High Frequency Ventilation in Adult Respiratory Distress Syndrome and Sickle Cell Anemia: Discussion
The goal of such a strategy is to incorporate the advantages of HFV (improved oxygenation by elevation of the MAP with subsequent sustained alveolar recruitment and diminution of the volutrauma associated with tidal breathing) with those of conventional ventilation (facilitation of carbon dioxide removal using low background rates and long expiratory times to facilitate ventilation in lung units with long time constants).
Inadvertent PEEP (also known as “auto-PEEP”), which may be produced by incomplete exhalation after a ventilator breath, is commonly invoked as a contributing factor in the development of air leaks in patients with ARDS. The PVDV may help avoid that problem, particularly if lower background respiratory rates are used. To the extent that combined mode ventilation is associated with cyclic changes in lung volumes and possible reflex changes in capacitance vessel tone, there may be less impedance to venous return and improved cardiac output compared with HFOV alone ventolin inhaler.
Potential disadvantages of this therapy include those associated with conventional ventilation (cyclic stretching of the airways may contribute to volutrauma) as well as problems associated with HFV (possible hypoventilation and increased carbon dioxide retention, particularly when resistance to expiratory flow is high; also a possible deleterious impact on pulmonary blood flow). In addition, there may be disadvantages peculiar to combined mode ventilation: Smith and colleagues described a dissociation of MAP and lung volume with subsequent gas trapping in cats ventilated with a system that provided both HFOV and IMV.
Use of the PVDV was effective in our patient: oxygenation and ventilation improved within 1 h, and we were able to significantly lower the MAP over several hours, presumably due to improved alveolar recruitment (Fig 5). We also noted dramatic resolution of extrapulmonary air leaks and improvement in pulmonary hyperinflation.
Figure 5. A timeline of clinical pulmonary events. Transcutaneous oxygen saturation and oxygen saturation determined by arterial blood gas analysis were similar and maintained at greater than 90 percent throughout the period of mechanical ventilation. Peak sustained values of airway pressure and FI02 were chosen for each time period.
Category: Respiratory Symptoms
Tags: barotrauma, high frequency ventilation, sickle cell anemia