Physiologic evaluation of the HFPPV pneumatic valve principle and PEEP. An experimental study

High frequency venturi jet ventilation. Adult respiratory distress syndrome--a case report

A Penlon Nuffield Series 200 Ventilator, adapted for use as a high frequency jet ventilator, was used to treat a patient with adult respiratory distress syndrome. Adequate alveolar ventilation with this method was achieved with lower mean intrapulmonary pressure (5.4 cmH2O) than with conventional intermittent positive pressure ventilation (IPPV) (6 cmH2O). An improved cardiac output was also apparent, as judged by a better systemic blood pressure [105/50 mmHg for high frequency jet ventilation (HFJV) compared to 90/40 mmHg for IPPV] and a lower central venous pressure 6 cmH2O for HFJV as compared to 9.5 cmH2O with conventional IPPV. During HFJV, the patient's need for sedatives and narcotics was reduced. This allowed an assessment to be made of any potential neurological damage caused by the cervical fracture. An assessment had not been possible during conventional ventilation due to the heavy narcotic and sedative regime required to settle the patient. This case report provides further evidence that HFJV is a useful adjunct in the management of patients requiring mechanical ventilation and also that the Penlon Nuffield Series 200 Ventilator is capable of high frequency jet ventilation.

New parachute cuff and positive end-expiratory pressure to minimize tracheal injury and prevent aspiration

A new parachute cuff has been tested in combination with a positive end-expiratory pressure (PEEP) on mongrel dogs. During positive-pressure ventilation the intracuff and intratracheal pressures showed synchronous, identical pressure variations, and therefore theoretically with this type of cuff the pressure against the tracheal wall would be minimal. The cuff provided a seal against gas leakage from the lungs throughout the entire test period, i.e., for up to 7 h. To avoid aspiration of mouth contents during the passive exhalation phase, different amounts of PEEP were tested. A PEEP of 4.0--8.0 cm H2O always produced a seal against a column of fluid in the mouth exerting a hydrostatic pressure of 5.4--8.8 cm H2O against the cuff. This seal was maintained during the whole test period. No difference in sealing capacity was found when the cuff was used with a normal respiratory frequency (20/min) and with high-frequency positive-pressure ventilation (60/min). When the PEEP is eliminated, e.g., when the respirator is disconnected for suction of the endotracheal tube, the sealing effect will be abolished. As the cuff extends up into the larynx there will be no pooling of fluid above the cuff. The risk of aspiration can therefore be diminished by suction of oral cavity before disconnecting the respirator. With the use of the pneumatic valve principle together with high-frequency positive-pressure ventilation, an open respirator system can produce a continuous PEEP, thereby preventing aspiration even during suctioning of the tracheal tube.

High-frequency positive-pressure ventilation (HFPPV) in neonates and infants during neuroleptal analgesia and routine plastic surgery, and in postoperative management

The low pulmonary compliance, the high airway resistance and the "rapid" breathing pattern of neonatal and paediatric patients make it necessary to design special ventilators to match the pulmonary physiology of infants. A ventilator system which also in small children has a negligible compression volume was evaluated in a lung model and during repair of cleft lip and palate in 16 patients under general anaesthesia and in two other infants during other operations. High-frequency positive-pressure ventilation (HFPPV) was given with an insufflation frequency (f) of 60 per min and a relative insufflation time (t%) of 32%. In addition, two neonates treated postoperatively with HFPPV are reported. Despite the "open" character of the ventilator system both intra- and postoperative ventilation were uneventful in all patients. The arterial oxygenation was good in all cases, as judged from clinical signs or blood gas analyses. Postoperative ventilation required conventional clinical observation and intermittent analyses of blood. HFPPV has been shown to depress, or abolish, spontaneous respiration via reflex mechanisms. In all patients in this investigation respiratory movements were absent at normo- or slight hyperventilation during HFPPV.