key: cord-0995284-rpyejwk5
authors: Whittle, Jessica S.; Dungan, George C.; DeBellis, Ronald J.
title: Response
date: 2020-10-05
journal: Chest
DOI: 10.1016/j.chest.2020.06.039
sha: 1d193df7c31536598399f1557034a9ea60ae74ea
doc_id: 995284
cord_uid: rpyejwk5

nan

To the Editor:

The coronavirus 2 pandemic has created an unprecedented rapid production of new information in the scientific literature. Translating experimental data into clinical practice remains a challenge that requires care and thoughtful validation. We greatly appreciate the commentary from Madney et al and agree with their primary conclusion that a more comprehensive study is needed to test the impact of implementation. Ultimately, careful monitoring of nosocomial transmission, especially to clinical staff, must be reported and that information considered in the risk-benefit calculation of any management paradigm. Madney et al ask a very reasonable question regarding the model-the selection of a peak flow of 40 L/min for the simulation. The communication is a short format, and the mechanistic considerations of the therapy tested could not be fully articulated.

The therapy simulated in our paper 1 evaluates a therapy classified as high-velocity nasal insufflation (HVNI). HVNI is mechanistically different from highflow nasal cannula (HFNC) therapy, while sharing some important characteristics. Both provide supraphysiological flow of conditioned, oxygen-rich gas to the patient using an open interface. 2 HVNI is in a separate Food and Drug Administration classification because it imparts higher velocities to the high flows of gas to facilitate the rapid clearance of the extrathoracic dead space. This provides the ability to manage respiratory distress in spontaneously breathing patients at volumetric flow rates typically well below 40 L/min. The clinical impact of this compared with other forms of HFNC has not yet been fully defined. In a trial of 204 adult patients presenting in the ED with undifferentiated respiratory failure requiring noninvasive ventilatory support, Doshi et al 3 demonstrated noninferiority to noninvasive positive pressure therapy with initial flow rates of 35 L/min and final titrated flow rates of 30 AE 6 L/min. Higher flow rates are commonly seen when using conventional HFNC therapy, 4 and such higher mass flow of gas leaving the nose and mouth may impact the overall particle dispersal and subsequent transmission. However, experimental evidence from Hui et al 5 suggests that a surgical mask over conventional forms of high-flow therapies likely reduce the risk of aerosol dispersion from them as well. All experimental evidence to date, although limited, suggests these therapies are safe and have limited risk for nosocomial or health-care provider infection when mitigated by use of a surgical mask on the patient.

The higher mass flow quantities generated with conventional HFNC were not evaluated in this report, and as such, the impact on the ventilatory effect of dead space washout for such therapy was not determined in this study and may be an interesting topic for future study. The current analysis demonstrated that the washout of the accessible extrathoracic dead space modeled in this simulation, with the virtual mask in place, still provided significant elimination of rebreathed CO 2 , and that reduction was amenable to adjustment in the flow rate of the high velocity gas entrained into the nose of the patient.

We greatly appreciate these suggestions for addition in our ongoing evaluation of mitigation methods being considered for patient management.

To the Editor:

I'd like to augment the persuasive viewpoints advanced by Drs Mannino and Thomashow 1 with additional caveats: spirometry flow rates above the cutoff threshold may falsely reassure the screened subject that he can continue to smoke with impunity. Both true-and false-positive reports of abnormality have adverse consequences. True positives impart a stigma that may compromise employment opportunities, and health and life insurability. False-positive reports, which are likely to be produced by inadequately trained assessors, can generate unjustified anxiety and depression. Two examples of harm from screening: (1) a lung cancer screenee became despondent when apprised that her CT scan demonstrated "emphysema," which she considered a lethal disorder. Spirometry, which demonstrated trivial obstruction, in combination with an explanation of the limited extent of her emphysema, served to reassure her; and (2) an electrician, who traveled interstate for employment, was declined a contract because of a screening ECG in which misplacement of precordial leads generated an algorithm interpretation of a possible anteroseptal myocardial infarction.

It is difficult to improve on an asymptomatic individual. Immunizations achieve this objective. Screening has an underappreciated potential for harm. In the setting of symptomatic disease, one is obligated to intervene. Conversely, in justifying screening, one is ethically compelled to be certain both of its efficacy and its freedom from offsetting harm. ) and demonstrated that the risk of pneumothorax varied considerably between these most common FLCN mutations. Other factors that they noted were that female patients presented with first spontaneous pneumothorax at a younger age and patients who had only a single spontaneous pneumothorax were significantly older at the time of initial event. The authors acknowledged certain limitations in their study, namely smoking history and number of pulmonary cysts; in particular, they posed the question of whether genotype-phenotype correlations would be applicable to patients with Birt-Hogg-Dube syndrome of different ethnic and regional origin. Indeed, the phenotypic variations may also exist within mutations, regardless of penetrance; we present a single large family to highlight this point.

In this single family, at least 12 members are affected by Birt-Hogg-Dube syndrome; five family members had germline FLCN testing, which showed a c.17_21delCTCTC (p.[Ala6VALfs*29]) mutation, and the seven other affected family members are considered obligate carriers (Fig 1) . Ten of 12 affected members (six female, four male) had a history of spontaneous pneumothorax, of which seven were single occurrences; three patients had recurrent episodes, and all patients had

The "helmet bundle" in COVID-19 patients undergoing noninvasive ventilation

Preliminary findings on control of dispersion of aerosols and droplets during highvelocity nasal insufflation therapy using a simple surgical mask: implications for the high-flow nasal cannula

Computational fluid dynamics modeling of extrathoracic airway flush: evaluation of high flow nasal cannula design elements

High-velocity nasal insufflation in the treatment of respiratory failure: a randomized clinical trial

High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure

Exhaled air dispersion during highflow nasal cannula therapy versus CPAP via different masks