Four methods of measuring tidal volume during high-frequency oscillatory ventilation

Abstract

Tidal volume can be measured during high-frequency oscillatory ventilation using a variety of techniques. Frequency-specific calibration improves the accuracy and precision of tidal volume measurements. Hot wire anemometry exhibits stable performance characteristics across the range of temperature, humidity, Fio2, and inspiratory/expiratory ratios encountered clinically, has a small deadspace, is unaffected by mean airway pressure, and is therefore suitable for clinical applications.

Tidal volume delivery during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome*

“…Furthermore, due to rigid enrollment criteria that prohibited the study of patients requiring vasopressors or those in whom PAW was Ͼ35 cm H 2 O, our patients tended to be those who were recovering and approaching transition back to conventional mechanical ventilation. Last, placement of the HW between the ETT and Y-connector of the 3100B reduces delivered VT by approximately 13% across all settings (10). The VTs we have reported therefore underestimate by a small amount what would actually be delivered.…”

“…Volume measurements were corrected in real-time using frequency, I:E ratio, and ETT internal diameter-specific calibrations. In a previous study, we demonstrated that these calibrations improve the accuracy of this device (mean error of Ϫ1.1%; 95% confidence interval, Ϫ5.5% to 3.3%) across a wide range of 3100B settings (f, 3-12 Hz; ⌬P, 30 -90 cm H 2 O) when compared with a plethysmograph (10). In the present study, reported VTs are the average of ten cycles of inspired and expired volumes, which are distinguished by zero crossings of the flow signal.…”

“…Tidal volumes were initially measured for each of 25 frequencies (4,6,8,10 (20,30, and 40 L/min), and I:E ratio (1:2 and 1:1) on the magnitude of delivered VT (Table 1). Comparisons are reported as proportional changes in the magnitude of VT. Resistance of the test lung was held constant at 5 cm H 2 O/L/sec for all measurements.…”

“…Tidal volumes were measured using a previously validated adult hot wire (HW) anemometer designed for VT measurement during high-frequency ventilation (CE 0124, Acutronics Medical Systems, Barr, Switzerland) (10). Using a computer data acquisition system (LabView 7.0, National Instruments, Austin, TX), the HW's analog flow signal was sampled at 1000 Hz and digitally integrated to determine inspiratory and expiratory phase volumes.…”

“…Frequency, ⌬P, and inspiratory/expiratory (I:E) ratio are important ventilator-based variables that alter the magnitude of VTs delivered by the 3100B (9,10). However, the effects on delivered VTs of other ventilator settings, such as mean airway pressure (Paw) and bias flow, and load conditions, such as respiratory system compliance and endotracheal tube (ETT) internal diameter, have not been described.…”