Marc Wysocki

Adaptive support ventilation: an appropriate mechanical ventilation strategy for acute respiratory distress syndrome?

Background:Adaptive support ventilation (ASV) allows the clinician to set a maximum plateau pressure (PP) and automatically adjusts tidal volume to keep PP below the set maximum. Methods:ASV was compared to a fixed tidal volume of 6 ml/kg. ASV determined the respiratory rate and tidal volume based on its algorithms. Maximum airway pressure limit was 28 cm H2O in ASV. Six sets of lung mechanics were simulated for two ideal body weights: 60 kg, Group I; 80 kg, Group II. Positive end expiratory pressure was 8, 12, and 16 cm H2O, and target minute volume 120%, 150%, and 200% of predicted minute volume. Results:ASV “sacrificed” tidal volume and minute ventilation to maintain PP in 9 (17%) of 54 scenarios in Group I and 20 (37%) of 54 scenarios in Group II. In Group I, the number of scenarios with PP of 28 cm H2O or more was 14 for ASV (26%) and 19 for 6 ml/kg (35%). In these scenarios, mean PP were ASV 28.8 ± 0.86 cm H2O (min 28, max 30.3) and 6 ml/kg 33.01 ± 3.48 cm H2O (min 28, max 37.8) (P = 0.000). In group II, the number of scenarios PP of 28 cm H2O or more was 10 for ASV (19%) and 21 for 6 ml/kg (39%). In these cases, mean PP values were ASV 28.78 ± 0.54 cm H2O (min 28, max 29.6) and 6 ml/kg 32.66 ± 3.37 cm H2O (min 28.2, max 38.2) (P = 0.000). Conclusion:In a lung model with varying mechanics, ASV is better able to prevent the potential damaging effects of excessive PP (greater than 28 cm H2O) than a fixed tidal volume of 6 ml/kg by automatically adjusting airway pressure, resulting in a decreased tidal volume.

Ventilator software version markedly affects time to trigger and time delay.

In the July 2011 issue of Respiratory Care we read with great consideration the paper from Marchese et al,[1][1] reporting the performance of 6 intensive-care ventilators currently available on the market. The present letter has no intention to contest the data reported in that paper;[1][1] instead

Response to Dr. Tehrani

Sir: We would like to answer the letter from Ms Tehrani, regarding the paper we recently published in the present journal [1]. Ms Tehrani argued on the fact that ASV is a patented mode of ventilation, that she is the inventor and that authors deliberately do not refer to her patent and related publications. Adaptive support ventilation (ASV) was developed by a team of medical doctors together with Hamilton Medical and was introduced in a commercially available device in 1997. A couple of years later, Ms Tehrani brought a patent infringement suit against Hamilton Medical alleging that ASV would infringe on her patent issued in 1991. First, a District Court found Hamilton Medical guilty of infringement but later, the Court of Appeals finding numerous errors in the District Court’s claim construction, was ‘‘unable to agree with the district court... therefore vacate the summary judgment and remand for further proceedings’’ [2]. To avoid the high litigation cost, Hamilton Medical decided to enter into negotiations with Ms Tehrani to find a settlement out of court. Such settlement was achieved to end the dispute between Hamilton Medical and Ms Tehrani. It does not say and imply that ASV is based on Ms Tehrani’s patent. While it is correct that ASV and the patent both describe methods to automate certain aspects of ventilation, they have little in common. The reader is referred to the Court deliberation [2] and the literature [3] to decide independently. Having said that and for a less mercantile point of view, the letter from Ms Tehrani open the possibility to make the reader better informed on ASV. First and as mentioned by Ms Tehrani, without the works done by Otis et al. [4], ASV and the concept of optimal breath pattern minimizing the work of breathing, would not have been possible. We believe also worth mentioning the works done by Mitamura et al. more than 30 years ago testing in dogs an optimally controlled respirator [5, 6] designed to adapt minute volume according to the end-tidal CO2 with an optimal rate to minimize the work of breathing according to Otis concept [4]. ASV would also not be possible without further investigations on finding an doable solution in estimating the respiratory mechanics during mechanical ventilation [7]. Therefore, we must admit that ASV as implemented in Hamilton Medical ventilators today is resulting from a continuum of humble and symbiotic contributions from hard working and qualified scientists. Ms Tehrani was advocating that in order to preserve the integrity of scientific publications, inventors and patents should be cited. Actually, this is not part of author’s recommendation for publication in major scientific journals [8]. In the opposite, patents have been clearly reported as a source of conflict (science vs. business), when authors of a scientific publication are involved (inventor) with a patent [9]. In this situation, it is worth mentioning that the authors have a patent in relation with the publication which may bias the scientific integrity of the publication. Finally, we would like to say that in scientific publications reporting original findings (as it is the case for the Arnal’s paper [1]), the references should be cautiously and adequately selected, i.e. the number of references are limited. That is also, why the paper from Laubscher et al. [10] has not been mentioned. In review articles, where more references are possible, Ms Tehrani’s works are eventually cited [11]. In addition, we do not believe that a scientific publication is the right platform to mention who is the inventor of what; otherwise we will have to mention the inventors of all the techniques cited in Arnal et al. article [1]...such as PEEP or Pressure Support! In summary, the letter from Ms Tehrani offers the possibility to further inform the readers on ASV. We do believe that ASV does not belong to one person but to many ‘‘fathers’’ who previously gave a contribution to make it available today at the bedside.