Spontaneous breathing during high-frequency oscillation revealed by diaphragm electrical activity

High-frequency oscillatory (HFO) ventilation can be used in severe respiratory failure.1Froese A.B. Kinsella J.P. High-frequency oscillatory ventilation: lessons from the neonatal/pediatric experience.Crit Care Med. 2005; 33: S115-S121Crossref PubMed Scopus (60) Google Scholar Though sedatives are prescribed to suppress the respiratory efforts in adults and children, spontaneous breathing has been tolerated using HFO in neonates.2van Heerde M. van Genderingen H.R. Leenhoven T. Roubik K. Plötz F.B. Markhorst D.G. Imposed work of breathing during high-frequency oscillatory ventilation: a bench study.Crit Care. 2006; 10: R23Crossref PubMed Scopus (23) Google Scholar However, little is known about spontaneous breathing and whether it occurs during HFO. The electrical activity of the diaphragm (Edi) signal can be used to detect and quantify respiratory effort. The Edi was originally developed for the neurally adjusted ventilatory assist mode of ventilation. It represents the final output of the respiratory centers after receiving multiple afferent inputs about lung stretch, diaphragm force, and arterial blood gases.3Sinderby C. Navalesi P. Beck J. Skrobik Y. Comtois N. Friberg S. et al.Neural control of mechanical ventilation in respiratory failure.Nat Med. 1999; 5: 1433-1436Crossref PubMed Scopus (427) Google Scholar Herein, we describe two Japanese neonates ventilated with HFO where the Edi signal was measured to determine whether spontaneous breathing was present. The neonates’ gestational age and birth weight were 25+0 weeks and 728 g in case 1 and 25+2 weeks and 533 g in case 2. Both neonates were intubated after birth, started on mechanical ventilation, and maintained with the HFO mode (Dräger Babylog® VN500). Before switching the ventilator mode from HFO to NAVA, a 6Fr Edi catheter was inserted orally. Then, the electrode array was positioned and confirmed at the gastroesophageal junction, and Edi was measured with the SERVO-i ventilator (MAQUET, Solna, Sweden). We recorded the Edi information every minute for 160 min on days 37 and 69 in cases 1 and 2 to monitor spontaneous breathing. The figure shows raw signals from the four Edi leads and the processed Edi waveform in patient 1 on HFO. Although the baseline waveforms were noticeably “shaky” because of HFO, Edi signals were processed satisfactorily (Fig. 1, left panel) . A total of 317 breaths were analyzed: 155 breaths in case 1 and 162 breaths in case 2. Edi signals were present and successfully recorded: the value of the Edi peak was 6.3 ± 3.4 μV, and Edi minimum was 1.9 ± 1.6 μV (mean ± standard deviation), and the correlation between the Edi peak and Edi minimum was significant (r = 0.746, p < 0.0001). We also evaluated the Edi peak and Edi minimum values on HFO by observing the video-recorded data in case 1. There were 80 breaths in 3 min (26.7 breaths/minute) with regular phasic breathing without tonic activity, and the Edi peak was 3.5 ± 3.4 μV, and Edi minimum was 0.5 ± 0.3 μV (Fig. 1, right panel). In neonates, HFO with spontaneous breathing can often be maintained. Therefore, sedation use is decreased, and muscle relaxants are avoided. To our knowledge, this is the first report to describe reliable and standardized measurements of Edi in preterm infants ventilated on HFO. The Edi peak and minimum measured in neonates ventilated with HFO might easily be manipulated based on the ventilatory support provided. Over-ventilation can suppress the Edi, and under-ventilation can enhance it. This preliminary report only aims to report the proof-of-concept without drawing any conclusions concerning outcomes because of the small number of patients. Therefore, a prospective, controlled, and randomized clinical trial is needed in the future. Daijiro Takahashi and Jennifer Beck was involved in the conception and design of this study. Daijiro Takahashi and Kei Goto analyzed the data. Daijiro Takahashi drafted initial versions of the manuscript, which were revised critically for important intellectual content by the other authors Keii Goto, Jennifer Beck and Christer Sinderby. All authors approved the final version of the manuscript. Dr. Takahashi and Dr. Goto have no conflict of interest in this study. Drs. Beck and Sinderby have made inventions related to neural control of mechanical ventilation that are patented. The patents are assigned to the academic institution(s) where inventions were made. The license for these patents belongs to Maquet Critical Care. Future commercial uses of this technology may provide financial benefit to Dr. Beck and Dr. Sinderby through royalties. Dr. Beck and Dr. Sinderby each own 50% of Neurovent Research Inc (NVR). NVR is a research and development company that builds the equipment and catheters for research studies. NVR has a consulting agreement with Maquet Critical Care.