Hemodynamic and Oxygen Transport Characteristics of Common Ventilatory Modes: Conclusion
The information comparing SIMV and ACV modes are conflicting. Opposite effects of SIMV on cardiac function’ and oxygen consumption have been reported. The SIMV can influence oxygen consumption as the result of increasing the oxygen cost of breathing by the respiratory muscles during spontaneous breathing activity. This, in turn, could be reflected in the frequency of spontaneous breaths while on SIMV and possibly in the respiratory muscle mass that has to be moved to achieve spontaneous breaths. Analyzing the data in each individual patient on SIMV vs ACV modes, we could not detect any parallel correlation between the change in V02I and parameters such as spontaneous breathing frequency, Ve, or body mass index. In all patients, except one, however, the direction of change in V02I from ACV to SIMV was parallel to the change in TO2I. Canadian family pharmacy Link This linear correlation between V02I and TO2I in our patient population may reflect the pathologic dependency between these two parameters which is a well-recognized phenomenon in various disease states.” Alternatively, this correlation could be the result of the mathematical coupling of variables determining V02I and TO2I, or it could be related to the increased metabolic demands while on SIMV mode.
Several studies have reported the effects of various levels of pressure support under different clinical conditions on a variety of ventilatory, hemodynamic, and oxygenation parameters. Differences in the design of these studies make any comparison among those, and particularly between those and ours, difficult. We are not aware of any study, such as ours, in which ACV, SIMV, and PSV modes were compared among the same patients by adjusting the level of PSV to achieve similar Vt as on ACV mode, and by standardizing the rate of SIMV to 75 percent of the respiratory rate on ACV. The closest study to ours is that by Maclntrye in which the initial level of PSV was set to result in a Vt that approximated the Vt achieved on SIMV-delivered mandatory breaths. The level of PSV, however, was then reduced stepwise to a level which resulted in the slowest regular respiratory rate. Only the data obtained after 10 to 15 min at this level of PSV were reported. It showed a lower Vt and peak airway pressure, but a higher mean airway pressure compared with SIMV, with no difference in Ve between the two modes. No explanation was given regarding similar Ve despite lower Vt and f on PSV. Tokioka and associates applied 0, 5, and 10 cm H2O PSV for 30 min to surgical patients requiring respiratory support. Compared with PSV level of O, as the level of pressure support increased, f fell, Vt and Ve rose, and РаСОг and the inspiratory work added by the ventilator decreased.