High frequency ventilation

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Operator panel of a high frequency ventilator

In the high-frequency ventilation (English High Frequency Ventilation , HFV ), in modern form, usually as High Frequency Oscillation Ventilation ( HFOV ), a high continuous alveolar Distentionsdruck (similar to the CPAP ) using a high-frequency gas flow in the ventilation system (not the patient) built up. The mechanism of gas transport to the patient is fundamentally different from other forms of ventilation .

Technical structure and mode of operation of the HFOV

Different forms of high frequency ventilation (HFV) were and are available: HFPPV (high frequency positive pressure ventilation), HFJV (high frequency jet ventilation), HFP (high frequency pulsation), HFJO (high frequency jet oscillation), FDV (forced diffusion ventilation) ) or HFO (high frequency oscillation).

With HFOV, an oscillator (loudspeaker or piston) integrated into the system sets the gas flow in oscillating vibrations with a frequency of typically 5–15 Hertz (up to 900 "breaths" per minute). There is always a positive pressure in the ventilation system, similar to CPAP ventilation (Continuous Positive Airway Pressure), the diffusion surface of the lungs increases; the alveoli (air sacs) are minimally inflated. Every single (very small) pressure fluctuation moves only a minimal volume of gas, which is many times less than the anatomical dead space volume . In the HFOV method, ventilation is not based on the movement of gas volumes through the airways, but rather on the continuous mixing of the breathing gases at every level in the airway system. Various physical effects are likely to come into play:

  • Turbulence in the large airways leads to mixing with fresh gas.
  • Proximal (close to the major airways) alveoli are ventilated directly.
  • Asymmetrical profile of the transmitted pressure wave: During "inhalation" the air flows faster on one side in the bronchus than on the other, while the profile on exhalation is quite symmetrical. In the course of many pressure cycles, a fresh air front migrates down the airways.
  • Diffusion: In distal alveoli (located towards the end of the branches of the air-conducting system) the pressure wave probably no longer plays a major role, here oxygen diffuses primarily along the difference in concentration.

Practical use

Prior recruitment (opening of the alveoli) of the lungs is a prerequisite for optimal use of the HFOV.

Two parameters influence the gas transport:

  • The mean airway pressure
  • The shape, height, and frequency of the oscillation

The level of the mean airway pressure determines the extent of the "flatulence" and opening of the alveoli and thus the supply of oxygen (oxygenation). Low mean airway pressures lead to little opening and thus to a small gas exchange area. High mean airway pressures lead to overinflation and compression of the pulmonary vessels with subsequent right heart failure. It is therefore important to find the "right" pressure and to ventilate in this safe window.

The shape of the amplitude is determined from its height and the relative duration of the positive and negative phase, as well as from the rise and fall of the wave. Often a rectangular wave with 1/3 positive duration is used. Adjusting the amplitude, frequency and waveform primarily affects the removal of carbon dioxide.

Clinical Applications and Evidence

HFOV was first in children and neonates for the treatment of respiratory distress syndrome of the newborn applied (IRDS, Infant respiratory distress syndrome), where it leads compared to CPAP in improved gas exchange, but not to reduced long-term effects or reduced mortality.

In adults, HFOV is occasionally used for acute lung failure ( ARDS ). Here, too, there is an early improvement in oxygen saturation compared to standard therapy, but no significant reduction in overall mortality. This was also confirmed by the British OSCAR study, in which high-frequency ventilation did not bring any benefit. The Canadian OSCILLATE study with a planned 1200 patients had to be discontinued after 548 patients due to an increased mortality with high-frequency ventilation. In contrast to newborns, there seems to be no advantage for adults, perhaps even a disadvantage, from high-frequency ventilation.

However, today's HFOV protocols use slightly different settings (lower tidal volume) that may be more effective. There are no current studies on this. HFOV remains an experimental therapy in clinical practice for ARDS patients who do not take in sufficient oxygen despite optimal conventional treatment.

See also

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  1. ↑ N. Mutz, M. Baum: High frequency ventilation. In: J. Kilian, H. Benzer, FW Ahnefeld (ed.): Basic principles of ventilation. Springer, Berlin a. a. 1991, ISBN 3-540-53078-9 , 2nd, unchanged edition, ibid. 1994, ISBN 3-540-57904-4 , pp. 395-403.
  2. ↑ AS Slutsky, JM Drazen: Ventilation with small tidal volumes. In: N Engl J Med. 347, 2002, p. 631. Abstract
  3. ↑ T. Müller, S. Budweiser et al.: High frequency oscillation ventilation in acute lung failure in adults. In: Dtsch Arztebl. 101, 2004, pp. 928-934. (Full text)
  4. ↑ DJ Henderson-Smart, T. Bhuta et al .: Elective high frequency oscillatory ventilation versus conventional ventilation for acute pulmonary dysfunction in preterm infants. In: Cochrane Database Syst Rev. 2003, p. CD000104
  5. ↑ S. Derdak, S. Mehta et al .: High-frequency oscillatory ventilation for acute respiratory distress syndrome in adults: a randomized, controlled trial. In: Am J Respir Crit Care Med. 166, 2002, p. 801. (full text)
  6. ↑ D. Young, S. Lamb, S. Shah, I. MacKenzie, W. Tunnicliffe, R. Lall, K. Rowan, BH Cuthbertson: High-Frequency Oscillation for Acute Respiratory Distress Syndrome. doi: 10.1056 / NEJMoa1215716 .
  7. ^ ND Ferguson, DJ Cook, GH Guyatt, S. Mehta, L. Hand, P. Austin, Q. Zhou, A. Matte, SD Walter, F. Lamontagne, JT Granton, YM Arabi, AC Arroliga, TE Stewart, AS Slutsky, MO Meade: High-Frequency Oscillation in Early Acute Respiratory Distress Syndrome. doi: 10.1056 / NEJMoa1215554 .