Which mode is better, A/C or SIMV?

Which mode is better, A/C or SIMV?


Marino, Paul L. ICU Book, 3rd Edition,2007,p.478.

" In summary, IMV provides few benefits over assist-control ventilation. The principal benefit of IMV is for the patient who is breathing rapidly because volume-cycled (assist-control) ventilation for these patients creates a risk for hyperinflation, auto-PEEP, and volutrauma. The risk of ventilator-induced lung injury may be lower with IMV than assist-control because less time is devoted to volume-cycled ventilation with IMV. This, however, is unproven. Finally, IMV should be avoided in patients with respiratory muscle weakness or left-ventricular dysfunction."

JESSE B. HALL, GREGORY A. SCHMIDT, LAWRENCE D.H. WOOD,PRINCIPLES OF CRITICAL CARE, 2005. P486:

"Typically, the patient performs inspiratory work during an assist-control breath.. This may not be obvious despite careful examination of the patient unless measures of intrathoracic pressure (esophageal pressure and central venous pressure) are available, or the inspiratory pressure waveform is examined carefully (Chap 32). Effort at the end of the breath will affect the Ppk and Pplat, making determination of respiratory system mechanics unreliable. When the patient is assisting every breath, the work of breathing can be increased by increasing the magnitude of the trigger or by lowering Vt (which increases the rate of assisting; see Table 36-2). Decreasing f at the same Vt generally has no effect on the work of breathing (in contrast to SIMV, discussed below) when the patient is initiating all breaths.

The SIMV mode is often used to gradually augment the patient’s work of breathing by lowering the mandatory breath f (or Vt ), thereby driving the patient to breathe more rapidly to maintain adequate ventilation, but this approach appears to prolong “weaning’’. (seeTable 36-2). Although this mode continues to be used widely,
there is little rationale for it and SIMV is falling out of favor."


Patrick Neligan says:

"Consequently, a pressure controlled SIMV mode has been developed for partially weaned patient. Most authorities agree that SIMV volume control is a poor weaning technique, and the patient is better off fully established on pressure support or assist-control (pressure or volume) if requiring ongoing ventilation. However, for most post operative patients, heavily sedated patients and those with little lung injury, the mode used is probably irrelevant, and it is much easier to wean a patient from SIMV than from VAC.
Further, a high percentage of intensive care units worldwide use SIMV + pressure support as their prime method of ventilation, and there is little evidence that this “mixed” mode is of any harm to the patient. My recommendation is that once a patient begins to breath spontaneously, there is no indication for mandatory breaths, and the patient should be switched over to pressure support ventilation alone: gradual weaning of IMV breaths in these circumstances is unnecessary."

Link: http://www.ccmtutorials.com/rs/mv/page12.htm

In my country the general sequence of MV is to start ptn on A/C then SIMV+PS then PS alone then T piece then extubation !!!! no need for this long chin , when your ptn need MV, start him on A/C whatever the case was, if he is improving and become weanable shift him to PS ( or T piece directly in some case)…no need to go through SIMV




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