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

Peak intratracheal pressure during controlled ventilation in infants and children. A computer study of the Servo 900C ventilator

The mathematical relationship between peak ventilator breathing system pressure displayed on the digital meter of the Siemens SV900C ventilator, and peak intratracheal pressure measured at the distal end of the tracheal tube, was defined and incorporated into a computer program. The mean difference between peak airway pressure calculated by the computer and directly measured peak intratracheal pressure was 0.02 kPa (SD 0.10) in 18 infants and children. The mean difference between ventilator breathing system pressure and intratracheal pressure in the same group was 0.82 kPa (SD 0.91). Bench tests established that the decrease in peak pressure displayed by the ventilator (from 1.36 to 0.38 kPa) while inspiratory time was increased from 20 to 80% of the respiratory period, concealed an increase (from 0.2 to 0.38 kPa) in intratracheal pressure which occurs during this process; and that the large increase in pressure displayed by the ventilator (from 0.3 to 6 kPa) while respiratory frequency was increased from 20 to 120 breaths/minute, concealed a small increase in peak intratracheal pressure (0.2-0.3 kPa) which occurs during this process. These changes were accurately predicted by the computer program. The increase in intratracheal pressure associated with prolonged inspiratory times explains the high incidence of barotrauma which has recently been associated with this procedure in infants.

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

In experiments in dogs the ventilatory and circulatory conditions prevailing with the ventilatory pattern in high-frequency positive-pressure ventilation (HFPPV) were investigated with use of a pneumatic valve principle and a ventilator system of an "open" character. Keeping the gas input constant the importance of insufflation frequency and insufflation time and the reactions to various levels of positive end-expiratory pressure (PEEP) were investigated in terms of changes in arterial pH, Pco2 and Po2. With the volumes of delivered gas kept constant, an increasing insufflation frequency from 60 to 100 per min gave a parallel decrease in tidal volume accompanied by lower maximum intratracheal pressures and a significant decrease in alveolar ventilation. Also taking into account the possibilities of inducing a suppression of the spontaneous respiration, higher ventilatory frequencies than 60 per min do now seem to introduce any further advantages. Including the associated effects on cardiac output and venous admixture, the cardio-pulmonary and circulatory parameters studied did not show any substantial changes with PEEP levels below 7.5--10 cm H2O. Thus the level of PEEP, which often is part of the ventilatory pattern in HFPPV, does not seem to have any untoward influence on the circulation (stroke volume, cardiac output, total peripheral vascular resistance) and oxygen transport (arterial oxygen content and oxygen flux) in normovolaemic dogs.