High Frequency Positive Pressure Ventilation During Anaesthesia and Routine Surgery in Man

Abstract

The respiratory and circulatory conditions in high frequency positive pressure ventilation (HFPPV) in the dog have been investigated previously. By means of expiratory resistance a positive intratracheal pressure was maintained throughout the respiratory cycle. Adequate ventilation was achieved at low intratracheal and transpulmonary pressures.A clinical test of this form of ventilation was conducted in connection with routine surgery in 15 patients; in 11 patients neuroleptic analgesia and in four patients thiopental sodium anaesthesia and pethidine analgesia was combined with oxygen-nitrous oxide ventilation (30 % 0, in N 2 0 ) . Muscle relaxants were given to all patients except one.The patients were ventilated, with the same gas mixtures, either manually (anaesthetic apparatus), with the Engstrom Respirator (ER-300) or by HFPPV. HFPPV was studied at different frequencies and different relative insufflation times ( 15-35 % of the period time). Expiratory minute volumes, intratracheal pressures (HFPPV) and tubing pressures (ER-300), arterial pH, Pco;?, Po2, base excess and standard bicarbonate were determined.During HFPPV there was a positive intratracheal pressure throughout the respiratory cycle. I n all patients adequate alveolar ventilation was obtained with HFPPV. The changes both in the blood gases and acid-base status, and in the intratracheal pressures and expiratory volumes, in relation to frequency and insufflation time, agreed in principle with those observed in the previous animal experiments.During HFPPV, i. e. with low intratracheal pressures, the patients maintained an adequate arterial Po2 and to judge from the pH and Pcoe this did not necessitate hyperventilation.

In what respect does high frequency positive pressure ventilation differ from conventional ventilation?

“…In 197 1, this HFPPV technique was therefore investigated in 15 patients scheduled for routine surgery under general anesthesia (2). Adequate oxygenation and ventilation were achieved with HFPPV at rates of 60-1 10 bpm and insumation times of 15-30y0.…”

High frequency ventilation.

“…Subsequent studies showed that the technique could also be used in anaesthetised patients. 3 Further developments led to the use of this technique for bronchoscopy, laryngoscopy, paediatric anaesthesia, and neonatal respiratory care.45 A trial in 12 patients with adult respiratory distress syndrome, however, showed no convincing benefit over conventional mechanical ventilation. 6 There have been few detailed studies of gas exchange during HFPPV, since many of the systems do not permit complete separation of inspired and expired gas.…”

“…33 These studies showed that after a deep breath arterial Po2 was better maintained and the mortality rate less in the group of rabbits treated with HFO, while histological examination showed minimal lung damage in the HFO group, but appreciable hyaline membrane formation in the group submitted to conventional mechanical ventilation. It was suggested that the rabbits in the HFO group were maintained on the descending limb of the P-V curve, so that lung volumes were higher for a given transpulmonary pressure, and that the small tidal volumes resulted in fewer intraregional stresses than in the conventional mechanical ventilation group (3) convective transport of gases resulting from the asymmetry between the inspiratory and the expiratory flow profiles; (4) longitudinal dispersion from interaction between the axial stream and radial dispersion due to turbulence; (5) molecular diffusion in the alveolar capillary membrane region.…”

“…The technique was first used experimentally in the late 1960s' to minimise fluctuations in intraarterial pressure associated with mechanical ventilation and has now been used for respiratory support in patients with normal and abnormal lungs. The range of frequencies used is 1-40 Hz (60-2400 bpm), the lower range (1)(2)(3)(4)(5) being used predominantly with high frequency positive pressure ventilation (HFPPV), or high frequency jet ventilation (HFJV), and the higher range (5-40 Hz) with high frequency oscillation (HFO). Although this rather crude categorisation ignores many of the subtle differences in the design of the ventilator and gas delivery systems which may affect their performance, it highlights the essential differences between the three techniques.…”

“…With the latter inspiration is produced by the opening of a solenoid operated valve connected to a high pressure gas source (usually 200-400 kPa (2-4 atmospheres)). The opening time of the valve may be adjusted from 40 to 500 msec, thus providing a Ti/ Ttot of 20-50% at frequencies of [1][2][3][4][5] Hz. The driving gas is delivered to the patient through a jet (usually 1.0-1.8 mm in internal diameter), the inspiratory flow rate being determined by the driving pressure, the resistance of the solenoid valve and connecting tubing, and the resistance of the jet.…”