Hemodynamic effects of high frequency jet ventilation during acute hypovolemia.

The hemodynamic effects of high frequency jet ventilation (HFJV) at three different rates (60, 100, 200/min) and at rate 200/min combined with jet sighs 12/min (HFJV-200 + 12S) during two degrees of hemorrhagic hypovolemia were investigated in dogs. Also, the results were compared with those of intermittent positive pressure ventilation (IPPV). Two degrees of hypovolemia were produced by bleeding dogs until mean arterial pressure was 25% or 50% lower than basic value respectively. At both periods of hypovolemia, HFJV at rate 60 or 100 were found to have better hemodynamic effects than IPPV due to their lower airway pressures. However, HFJV at rate 200 or HFJV-200 + 12S did not demonstrate the same superiority because of their higher airway pressure, the latter even represented a tendency of worse hemodynamic effect than IPPV. The best cardiovascular effect was seen during HFJV at rate 100. Our study indicated that the hemodynamic effect of HFJV better than that of IPPV during acute hypovolemia can be seen only when proper ventilatory settings are chosen. Jet sighs at 12/min added to usual HFJV are not beneficial to circulatory function. It is recommended that HFJV at a rate below 200/min without jet sighs be used in patients who need respiratory support during acute hypovolemia or shock.

Clinical studies on high frequency two-way jet ventilation.

A new mode of jet ventilation, high frequency two-way jet ventilation (HFTJV) was devised and introduced to increase carbon dioxide elimination during jet ventilation. Its ventilatory efficiency and features were investigated and compared with those of high frequency jet ventilation (HFJV) in 10 patients with normal cardiopulmonary function. Random sample selection and randomized cross-over trial were used for comparison between HFTJV and HFJV at the same ventilatory settings of driving pressure 1 kg/cm2 (14.22 Psi), respiratory rate 100/min and I/E ratio 1:2. Peak inspiratory pressure (PIP), end-expiratory pressure (EEP) and main variables of air blood gas analysis (PaO2, PaCO2, pH) were measured and recorded during the use of HFJV and HFTJV. PIP and EEP were significantly lower than with HFTJV than with HFJV. EEP of HFTJV showed a slightly negative pressure (-0.17 +/- 0.03 kPa). PaCO2 with HFTJV was significantly lower than that with HFJV, but PaO2 and pH with HFTJV were significantly higher than those with HFJV. HFTJV was shown to have a ventilatory feature of decreasing airway pressure and simultaneously increasing carbon dioxide elimination, as compared with HFJV. Whether this ventilatory feature of HFTJV can be utilized for various respiratory support in patients with abnormal cardiopulmonary function needs to be further studied.