Physiologic implications of high frequency jet ventilation techniques
Two experiments were performed in 35 mongrel dogs, weighing 18-21 kg, to define hemodynamic and respiratory consequences of different mechanical conditions using high frequency ventilation. In the 1st experiment, 6 dogs were used as controls; respiratory failure was induced in 9 with oleic acid iv and HCl intratracheally. The dogs were anesthetized, paralyzed, and ventilated on either volume-cycled ventilation (VCV) with a minute ventilation of 300 ml/kg, or high frequency jet ventilation (HFJV) with a minute ventilation of 600 ml/kg. Respiratory rate (100 and 150 breath/min), injector cannula diameter (1.06 and 1.62 mm) and PEEP (0 and 15 cm H2O) were the independent variables on HFJV. PEEP was 0 and 15 cm H2O on VCV. Ten experimental conditions were alternated at random in each dog. Hemodynamic and respiratory variables were measured. In the 2nd experiment, 10 dogs served as controls; in the other 10, respiratory failure was induced. PEEP was 10 cm H2O and FIO2 0.50 in all conditions; respiratory rate was 15 breath/min on VCV and 100 breath/min on HFJV. Injector cannula diameter was 1.62 mm. Minute ventilation was 200, 300, and 400 ml/kg on VCV; 600, 900, and 1200 ml/kg on HFJV. Inspiratory time was 20, 30, and 40% on HFJV. Twelve different experimental conditions were alternated in random order. The experiment indicated that a minute ventilation of 600 ml/kg cannot maintain a normal alveolar ventilation in most conditions tested. Ventilation and oxygenation deteriorated with higher respiratory rate and injector cannula of smaller diameter. Ventilation deteriorated with higher PEEP. In the 2nd experiment, oxygenation and ventilation were within normal limits in most experimental conditions. The end-expiratory pressure generated by HFJV, albeit small (3-5 mm Hg), impaired cardiac function in normal dogs. Otherwise, there was no significant difference in hemodynamic function between the 2 types of ventilation. The major differences between HFJV and VCV were the tidal volume required to maintain a normal alveolar ventilation, which was half as large on HFJV than on VCV, and the peak inspiratory pressure, which was considerably lower on HFJV. The best physiologic results were obtained on HFJV with a respiratory rate of 100 breath/min, an injector cannula diameter of 1.62 mm, and a tidal volume of 9 ml/kg. This investigation indicates that HFJV is a safe and predictable method of mechanical ventilation in animals with normal and abnormal pulmonary physiology.