Case Reports of Inversed Ratio Ventilation

The prolongation of inspiratory time from an I : E ratio of 1:2 to a ratio of 4:1 significantly improved arterial oxygenation in 7 patients with acute respiratory failure due to pulmonary disease or cardiogenic lung edema when positive end-expiratory presure had failed. The reduction in the respiratory index (y) (y=-2.02x+9.392,r=-0.5732,p<0.05) and the pulmonary shunt ratio (y) (y=-5.502x+41.329, r=-0.5561, p<0.05) were in proportion to the prolongation of inspiratory time (x). A reduction in cardiac output and a concomitant reduction oxygen delivery were observed with the I : E ratio of 4 : 1 but not with an I : E ratio of 3 : 2 or 2.6 : 1 in patienta with pulmonary disease. However, two of three patients with cardiac diserse had a reduction in cardiac output and oxygen delivery with an I : E ratio of 1.2 : 1. The results suggest that the improvement of arterial oxygenation proportional to the prolongation of inspiratory time is due to the increase in the endexpiratory lung volume with a short exhalation time. Although this ventilatory pattern may be indicated when the effect of positive end-expiratory pressure on artrerial oxygenation has failed, an unduly long prolongation of inspiratory time is not suitable for patients with cardiac disease.

Respiration

IRV

I

E ratio

Mechanical ventilation

Respiratory failure Oxygenation

oxygenation transport