Reliable tidal volume estimates at the airway opening with an infant monitor during high-frequency oscillatory ventilation

Crit Care Med. 2001 Oct;29(10):1925-30. doi: 10.1097/00003246-200110000-00013.


Objective: To assess the suitability of a hot-wire anemometer infant monitoring system (Florian, Acutronic Medical Systems AG, Hirzel, Switzerland) for measuring flow and tidal volume (Vt) proximal to the endotracheal tube during high-frequency oscillatory ventilation.

Design: In vitro model study.

Setting: Respiratory research laboratory.

Subject: In vitro lung model simulating moderate to severe respiratory distress.

Intervention: The lung model was ventilated with a SensorMedics 3100A ventilator. Vt was recorded from the monitor display (Vt-disp) and compared with the gold standard (Vt-adiab), which was calculated using the adiabatic gas equation from pressure changes inside the model.

Measurements and main results: A range of Vt (1-10 mL), frequencies (5-15 Hz), pressure amplitudes (10-90 cm H2O), inspiratory times (30% to 50%), and Fio2 (0.21-1.0) was used. Accuracy was determined by using modified Bland-Altman plots (95% limits of agreement). An exponential decrease in Vt was observed with increasing oscillatory frequency. Mean DeltaVt-disp was 0.6 mL (limits of agreement, -1.0 to 2.1) with a linear frequency dependence. Mean DeltaVt-disp was -0.2 mL (limits of agreement, -0.5 to 0.1) with increasing pressure amplitude and -0.2 mL (limits of agreement, -0.3 to -0.1) with increasing inspiratory time. Humidity and heating did not affect error, whereas increasing Fio2 from 0.21 to 1.0 increased mean error by 6.3% (+/-2.5%).

Conclusions: The Florian infant hot-wire flowmeter and monitoring system provides reliable measurements of Vt at the airway opening during high-frequency oscillatory ventilation when employed at frequencies of 8-13 Hz. The bedside application could improve monitoring of patients receiving high-frequency oscillatory ventilation, favor a better understanding of the physiologic consequences of different high-frequency oscillatory ventilation strategies, and therefore optimize treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Airway Resistance / physiology
  • Equipment Design
  • Equipment Safety
  • High-Frequency Ventilation / instrumentation*
  • High-Frequency Ventilation / methods
  • Humans
  • Infant, Newborn
  • Models, Biological
  • Predictive Value of Tests
  • Sensitivity and Specificity
  • Tidal Volume
  • Ventilators, Mechanical*