Improved oxygenation with superimposed high frequency jet ventilation at resonant frequency

Introduction

Superimposed high-frequency jet-ventilation (SHFJV) is a new form of a combined high frequency (HF) jet ventilation technique in treatment of ARDS. Since the HF jet-stream improves oxygenation partially due to enhancement of the intra-pulmonary gas mixture [1] the question arises which frequency would be the most effective. Animal models and in vitro experiments demonstrate that the best results may be achieved with frequencies close to the resonant frequency (RF) of the lungs [1,2]. In this study we tried to find RF using SHFJV.

Materials and methods

SHFJV is a combination of a pressure controlled low-frequent and a pressure controlled HF jet-ventilation. The RF was studied in two patients groups with SHFJV. Group 1 included pulmonary healthy patients (n = 11) and group 2 included patients with ARDS (n = 13). The individual RF was determined in each patient analysing the ventilation-pressure waves which were recorded at 0.5 Hz intervals starting with 5 Hz up to 16.5 Hz. The amplitudes of the recorded pressure waves were analyzed and the average calculated at each examined frequency. The frequency with the maximum pressure amplitude represented the RF [3]. After RF was determined the patients were ventilated for 30 min using SHFJV at a frequency different than the RF followed by 30 min of SHFJV at RF. FiO₂ levels and airway pressure did not change in the study period. Blood gas analysis was performed in intervals of 5 min throughout the study.

Results

In contrast to non-resonant frequency in group 1 PaO₂increased from 113 mmHg to 122 mmHg with SHFJV at RF. In group 2 PaO₂ increased from 89 mmHg to 101 mmHg with SHFJV at RF.

Discussion

Our results demonstrate an improvement of PaO₂ when applying HF ventilation at the individual RF compared to non-resonant frequencies. Although the effects of SHFJV, as with other HF jet ventilation techniques, are not fully understood, studying RF with its improvement of oxygenation may be another step towards explaining the beneficial effects of HF ventilation techniques observed.