Inverse ratio ventilation

IRV Inverse ratio ventilation ventilator mode in which inspiratory time is prolonged in comparison to expiration time. Used to decrease plateau pressure and improve oxygenation. 

Prolonging inspiratory time may recruit more slowly recruitable alveoli (24) and improve V/Q matching (24,25). The development of intrinsic PEEP from the short expiratory times can have similar effects to that of applied PEEP. Since long inspiratory times increase the total intrathoracic pressures, cardiac output may be affected. Finally, inspiratory-to-expiratory time ratio (I/E) > 1 1— known as inverse ratio ventilation—is uncomfortable, in the absence of airway pressure release ventilation (26,27). 

Inverse ratio ventilation (I/E >1 1) can increase PEEP and improve V/Q in severe respiratory failure (24—27). This setting is applied as airway pressure release ventilation (APRV) (Table 1), which, although appealing, lacks good outcome studies supporting its use. 

Armstrong BW, MacIntyre NR. Pressure controlled inverse ratio ventilation that avoids air trapping in ARDS. Crit Care Med 1995 23 279-285. 

Cole AGH, Weller SF, Sykes MD. Inverse ratio ventilation compared with PEEP in adult respiratory failure. Intensive Care Med 1984 10 227-232. 

If the situation is dire, consider inverse-ratio ventilation... 

Morris, A.H. et al. 1994. Randomized clinical trial of pressure-controUed inverse ratio ventilation and extracorporeal COj removal for adult respiratory distress syndrome. Am J Respir Crit Care Med 149 295-305. 

The data available on the molecular diffusion coefficient of organic vapors in air are meager, but they indicate (in accordance with approximate theory) an inverse proportionality to the square root of molecular weight. The rate of mass transfer by molecular diffusion will be proportional to the diffusion coefficient and to the SVC, itself proportional to vapor pressure times molecular weight (M). We should expect, therefore, under standard conditions of ventilation, that the rate of loss will be proportional to vapor pressure X The ratio of observed rate to... 

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