ASSESSMENT OF VENTILATION DURING HFOV

NeoNotes Journal Club
Andrew B. Kairalla MD, Editor
Thomas M. Berger MD Guest Editor

ASSESSMENT OF VENTILATION DURING HFOV

Sturtz WJ, Touch SM, Locke RG, et al. Assessment of neonatal ventilation during high-frequency oscillatory ventilation. Pediatr Crit Care Med 2008;9:101-104 [Fulltext] | [PDF (190 K)]

Objectives. To determine alterations in high frequency oscillatory ventilation (HFOV) performance during clinical ventilator management.

Setting and Patients: Two level III intensive care nurseries in Wilmington, Delaware, and Philadelphia, Pennsylvania. Thirty infants 1.49 ± 1.01 kg with respiratory distress receiving HFOV.

Methods: Due to the demonstrated bench top load sensitivity of the HFOV (SensorMedics 3100), we hypothesized that measured tidal volume (VT/kg) and high-frequency minute ventilation (HFMV) would vary inversely with respiratory rate adjustments and that ventilator performance will be affected with endotracheal tube (ETT) suctioning. Both VT/kg and HFMV were recorded using a novel hot-wire anemometry technique at the time of ETT suctioning or changes in ventilator settings.

Results. During HFOV it was found that VT/kg = 2.52 ± 0.68 mL/kg and HFMV = 69 ± 45 ([mL/kg]² x Hz); effective ventilation was observed in the range of HFMV = 29–113 ([mL/kg]² x Hz). HFMV decreased with an increase in breathing frequency. Although there was a significant increase in the mean VT/kg after suctioning events, there was no difference in VT/kg or HFMV after disconnection of the ETT alone. There were significant alterations in HFOV performance as a result of clinical adjustments in respiratory rate and suctioning. In addition, we found that measured VT during clinically effective HFOV is at least equivalent to expected deadspace.

Conclusions. Measurement of tidal volume and HFMV may be clinically important in optimizing HFOV performance both during ETT suctioning and adjustments to breathing frequency.

Comments. This study suggests that - contrary to what has been written and taught for many years - tidal volume (VT) during HFOV is approximately 2.5 ml/kg (range 1.7-5.1 ml/kg) and thus frequently not below deadspace. On the other hand, the authors did confirm that a decrease in frequency leads to an increase high frequency minute ventilation (HFMV). It would be interesting to see if this monitoring technology would enable clinicians to readily recognize lung under- and/or overdistension by displaying decreases of VT due to shifting of the compliance curve. This would perhaps allow clinicians to reduce the number of chest X-rays currently taken in patients on HFOV to assess lung expansion. TMB

Additional Comments:

Date: 05 May 2008
Time: 01:34:23

I think it is amazing that after all this years we are not yet clear on how the CO2 wash out happens so quickly in HFOV. According to my understanding it has not much to do with the very small tidal volumes, but is the consequence of the asymmetrical velocity profile, which results in an almost linear airflow inwards centrally and outwards at the side of the airways. It is not hard to understand that this increases with decreasing frequency or increasing delta P. Changes in VT are related to delta P and frequency as well but may be at best only indirectly related to a better ventilation (?).

UserName: Hans Van Rostenberghe
Institution: Universiti Sains Malaysia
telephone: ++ 60 9 7663000
email: hansvr@kb.usm.my

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