Volume 74, February 2023, 103344Author links open overlay panelAbstractObjective

To assess the different effect of filters’ application during helmet-CPAP delivered with three different flow generators on the delivered fresh gas flow, FiO2, and the noise level inside and outside the helmet.

Methods

In a bench study, three flow generators (air-oxygen blender, turbine ventilator and Venturi system) were used to generate two different gas flows (60 L/min and 80 L/min), with a fixed FiO2 at 0.6, to perform a helmet-CPAP on a manikin. Three different fixed PEEP valves (7.5, 10, and 12.5 cmH2O) were applied at the expiratory port. Gas flow, FiO2 and noise were recorded for each Flow-generator/Flow/PEEP combination, first without filter interposition and then after positioning a heat and moister exchanger filter (HMEF) at the helmet inlet port.

Results

The application of the HMEF lead to a significant difference in the flow variation among the three flow generators (p < 0.001). Compared to baseline, the highest flow reduction was observed with the VENTURI (−13.4 ± 1.2 %, p < 0.001), a slight increase with the BLENDER (1.2 ± 0.5 %, p < 0.001), whereas no difference was recorded with the TURBINE (0.1 ± 0.6 %, p = 0.12). After HMEF was interposed, a significant FiO2 variation was observed only with VENTURI (11.3 ± 1.8 %, p < 0.001). As for the noise, the TURBINE was the least noisy system, both with and without the filter interposition.

Conclusions

Flow generators used to deliver helmet-CPAP have different characteristics and responses to HMEF interposition. Users should be aware of the effects on FiO2 and flow of the different devices in order to make a precise setup of the circuit.

Section snippetsBackground

The effectiveness of continuous positive airway pressure (CPAP) in reducing endotracheal intubation and mortality in acute respiratory failure (ARF) due to cardiogenic pulmonary edema is well established (Bellone et al., 2005, Collins et al., 2006; Di Marco et al., 2008; Weng et al., 2010, Vital and Atallah, 2013, Rochwerg et al., 2017). In the last decade, it has been increasingly used to treat hypoxemic respiratory failure due to pneumonia, showing a good efficacy in improving patients’

Methods

The present bench study was performed at the ASST Grande Ospedale Metropolitano Niguarda, Milan, Italy. The study setup was prepared using a certified, small-sized helmet CPAP (Harol S.r.L. San Donato Milanese, Milan, Italy) sealed with standard armpit straps on a half-body manikin (size medium) (Fig. 1). A 150 cm respiratory circuit for adults characterized by a smooth inner surface was used (285/5063, DAR™, Covidien, Mansfield, MA, USA) to link the flow generator to the inlet port of the

Experimental setup

Three different flow generators were tested: a Venturi system, labeled “VENTURI” (EasyFlow, Dimar, Mirandola, Italy); a gas blender (Air/O2) flow generator, labeled “BLENDER” (RM/145-2, Flow-Meter S.p.A., Levate, Italy) and a turbine ventilator, labeled “TURBINE” (Monnal T75, Air Liquide Medical Systems, Paris, France) (Fig. 1). The flow generators underwent testing and calibration according to the manufacturers’ specifications. To generate a high gas output flow, the VENTURI requires a single

Measurements

Before the beginning of the experiments, environmental noise was measured using the sound meter placed one meter away from the flow generator. The highest noise level inside and outside the helmet was recorded. The fresh gas flow was recorded fivefold for each tested setting. The average value of 5 measurements performed 15 s apart was used for analysis. Lastly, the FiO2 was acquired after the measured values were stable for 30 s.

Results

For each flow generator tested, the interposition of HMEF had similar effects on flow reduction regardless of the applied flow (60 or 80 L/min) and PEEP level (7.5, 10, 12 cmH2O). Consequently, data of each flow generator were pooled together.

The application of the HMEF on the different flow generators lead to different flow variations (Fig. 2). A remarkable flow reduction was observed with the VENTURI system (−13.4 ± 1.2 %, p < 0.001 as compared to BASELINE), while a significant increase in

Discussion

We have described the bench performance of H-CPAP delivered using three different flow generators and the effects of the interposition of an HMEF within the respiratory circuit. The application of an HMEF at the inlet port of the helmet when H-CPAP is delivered, is a common maneuver in clinics to muffle the internal noise and improve patient’s comfort and compliance (Lucchini et al., 2020c, Privitera et al., 2022c).

A previous bench study showed that the interposition of an HMEF reduces the

Limitations

Our bench study allowed us to assess and compare precisely-three different flow generators and the effects of the interposition of filter on several variables during H-CPAP delivery. However, given the nature of the study, we could not evaluate the potential impact on flow and delivered FiO2 of patient’s characteristics (e.g., inspiratory effort, minute ventilation).

In addition, only one type of HMEF was used. The variability of the resistances generated by the different types of filters could

Conclusion

Flow generators used for H-CPAP performance have different characteristics and response to the HMEF interposition. The TURBINE is the least noisy system, does not require HMEF interposition, but requires an oxygen source and power supply. The Venturi is the simplest system, requiring only an oxygen source. It is louder and the HMEF interposition is useful to reduce the noise within the helmet. The effects on delivered flow and FiO2 should, however, be taken into account. The interposition of an

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (36)G. Bellani et al.Noninvasive ventilatory support of patients with covid-19 outside the intensive care units (ward-covid)

Ann. Am. Thoracic Soc.

(2021)

A. Bellone et al.Noninvasive pressure support ventilation vs. continuous positive airway pressure in acute hypercapnic pulmonary edema

Intensive Care Med.

(2005)

B. Berglund et al.New who guidelines for community noise

Noise Vibr. Worldwide

(2000)

A.M. Brambilla et al.Helmet CPAP vs. oxygen therapy in severe hypoxemic respiratory failure due to pneumonia

Intensive Care Med.

(2014)

C. Brusasco et al.CPAP devices for emergency prehospital use: a bench study

Respiratory Care

(2015)

F. Cavaliere et al.Noise exposure during noninvasive ventilation with a helmet, a nasal mask, and a facial mask

Intensive Care Med.

(2004)

F. Cavaliere et al.Exposure to noise during continuous positive airway pressure: Influence of interfaces and delivery systems

Acta Anaesthesiol. Scand.

(2008)

A. Coppadoro et al.Helmet CPAP to treat hypoxic pneumonia outside the ICU: an observational study during the COVID-19 outbreak

Crit. Care

(2021)

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