Patient-Ventilator Dysynchrony

Dysynchrony is a term which describes a patient fighting the ventilator (1-3) . If we assume that this is not because the patient is undersedated and is rebelling against the endotracheal tube, in the majority of cases failure to synchronize is due to inadequate flow delivery from the ventilator. If the flow of gas is inadequate, the patient attempts to suck gas out of the ventilator – which is extremely unpleasant. This only occurs in volume control modes. In pressure control, flow is unlimited – the reason is that flow is related to the pressure gradient between the upper and lower airway – a deeper attempted inspiration makes the pressure in the alveoli more negative in relation to the upper airway (this is true also in normal individuals, how else would you take a deep breath!), and the pressure gradient is larger – and the flow greater. In volume limited ventilation, this flexibility (which is physiological) does not exist. Of course, as with most problems in critical care, a number of technological solutions have been developed. the first was pressure augmentation (click here). Recently Dräger have been promoting Autoflow which brings to volume controlled ventilation the flexibility of spontaneous breathing using the same dynamic valve as in BiLevel ventilation (click here).

Patient-ventilator dysynchrony, the peak flow is too low and the trigger sensitivity too high

References

   (1)    Leung P, Jubran A, Tobin MJ. Comparison of assisted ventilator modes on triggering, patient effort, and dyspnea. Am J Respir Crit Care Med 1997; 155(6):1940-1948.

   (2)    Munoz J, Guerrero JE, Escalante JL, Palomino R, De La CB. Pressure-controlled ventilation versus controlled mechanical ventilation with decelerating inspiratory flow. Crit Care Med 1993; 21(8):1143-1148.

   (3)    Tobin MJ, Jubran A, Laghi F. Patient-ventilator interaction. Am J Respir Crit Care Med 2001; 163(5):1059-1063.

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