Chest
Volume 128, Issue 4, October 2005, Pages 2984-2990
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Laboratory and Animal Investigations
Physiologic Evaluation of Different Levels of Assistance During Noninvasive Ventilation Delivered Through a Helmet

https://doi.org/10.1378/chest.128.4.2984Get rights and content

Objective

To evaluate the effects of various levels of pressure support (PS) during noninvasive ventilation delivered through a helmet on breathing pattern, inspiratory effort, CO2 rebreathing, and comfort.

Design

Physiologic study.

Setting

University-affiliated hospital.

Patients and participants

Eight healthy volunteers.

Interventions

Volunteers received ventilation through a helmet with four different PS/positive end-expiratory pressure combinations (5/5 cm H2 O, 10/5 cm H2 O, 15/5 cm H2 O, and 10/10 cm H2 O) applied in random order.

Measurements and results

The ventilatory respiratory rate, esophageal respiratory rate (RRpes), airway pressure, esophageal pressure tracings, esophageal swing, and pressure-time product (PTP) [PTP per breath, PTP per minute, and PTP per liter] were evaluated. We also measured the partial pressure of inspired CO2 (Pico2) at the airway opening, mean partial pressure of expired CO2 (Peco2), CO2 production ( V˙ co2), minute ventilation ( V˙ e) delivered to the helmet ( V˙ eh), and the true inspired V˙ e. By subtracting V˙ e from V˙ eh, we obtained the V˙ e washing the helmet ( V˙ ewh). A visual analog scale (from 0 to 10) was used to evaluate comfort. Compared to spontaneous breathing, different levels of PS progressively increased tidal volume (Vt) and decreased RRpes, reducing inspiratory effort. The increased levels of assistance did not produce significant changes in Pico2, end-tidal CO2, and V˙ co2. Peco2 had a slight decrease when increasing the level of PS from 5 to 10 cm H2 O (p < 0.05). Despite the presence of constant values of V˙ e, the increase of PS produced an increase in V˙ ewh, without significant differences comparing 10 cm H2 O and 15 cm H2 O of PS. The subjects had a slight but not significant increase in discomfort by augmenting the level of assistance. At the highest level of PS (15 cm H2 O), the discomfort was significantly higher (p < 0.001) than at the other levels of assistance.

Conclusion

In volunteers, the helmet is efficient in ventilation, allowing a Vt increase and RRpes reduction. A significant discomfort was present only at the highest level of assistance; however, it did not affect patient/ventilator interaction.

Section snippets

Materials and Methods

The protocol was approved by our institutional review board, and written informed consent was obtained from each subject. NIV was delivered through a helmet equipped with an soft inner inflatable cushion for dead space reduction (CaStar Starmed; Starmed; Mirandola, Italy) [Fig 1]using an ICU ventilator (EVITA 4; Dräger Medical; Lübeck, Germany) set in PS ventilation (PSV) mode. The fraction of inspired oxygen was set at 0.21, and the inspiratory trigger threshold was set at 2 L/min, checking

Results

All the subjects completed the study protocol. In comparison to spontaneous breathing, during helmet NIV, RRpes was reduced by 7% during PS/PEEP at 5/5 cm H2 O (p = 0.086), by 13.1% during PS/PEEP at 10/5 cm H2 O (both with and without an inflated cushion) [p = 0.023 and p = 0.015, respectively], by 28% during PS/PEEP at 15/5 cm H2 O (p = 0.000003),and by 5.2% during PS/PEEP at 10/10 cm H2 O (p = 0.12) [Table 1].

No significant differences were found between RRvent and RRpes, which were similar

Discussion

The main finding of the present study is that increasing levels of assistance in healthy volunteers receiving PS ventilation through a helmet significantly reduced RRpes, with a significant increase in Vt. Increasing levels of assistance produced a significant reduction in tidal excursions of Pes only during PS/PEEP at 10/5 cm H2 O with the cushion inflated and PS/PEEP at 10/10 cm H2 O, while, compared to spontaneous breathing, ventilatory support produced a significant decrease of PTP per

ACKNOWLEDGMENT

The authors thank Dr. Melanie Lindsey for her helpful review of the manuscript.

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    Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

    Presented in part as abstract at the Sixteenth Annual ESICM Congress, Amsterdam, October 2003.

    Funded by a research grant from Università Cattolica del Sacro Cuore, No. D1-PT 0004162.

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