Chest
Volume 122, Issue 6, December 2002, Pages 2105-2114
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Clinical Investigations in Critical Care
Comparison of Five Bilevel Pressure Ventilators in Patients with Chronic Ventilatory Failure: A Physiologic Study

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Objective

To compare patient-ventilator interaction and comfort in patients with chronic ventilatory failure (CVF) who are undergoing noninvasive positive-pressure ventilation with five different commercial bilevel pressure home ventilators. Also, we wanted to evaluate the short-term effects of the five ventilators on physiologic variables, namely, breathing patterns and inspiratory muscles.

Design

Randomized, controlled physiologic study.

Setting

Pulmonary division of a rehabilitation institution.

Patients

Twenty-eight patients with CVF due to COPD (17 patients) and restrictive chest wall diseases (11 patients).

Measurements

Sensation of comfort, breathing patterns and minute ventilation (V˙e), respiratory muscles and mechanics, and patient-ventilator interaction during both unassisted and assisted ventilation with the five ventilators applied randomly.

Results

The five ventilators showed different flow and pressure waveforms. The level of comfort was somehow different among the studied ventilators. When compared to unassisted ventilation, all ventilators induced a significant increase in V˙e (p < 0.01) without any significant difference among ventilators. Use of the five ventilators resulted in significant differences in peak airway opening pressure (Pao, peak) but not in mean airway opening pressure computed over a period of 1 min (PTPao, min), and in a duty cycle. Ineffective efforts (IEs) were similar among the studied ventilators. In comparison with unassisted ventilation, all ventilators induced significant reductions in inspiratory muscle effort (p < 0.001). No significant relationship was found between level of comfort and PTPao, min, Pao, peak, or the number of IEs.

Conclusions

In stable, awake patients with CVF, all of the studied ventilators were well-tolerated, although with a great intersubject variability in comfort, and performed well in terms of improvement in V˙e and inspiratory muscle unloading, thus fulfilling the aims of mechanical ventilation. This effect was obtained with similar levels of PTPao, min, despite the fact that Pao, peak was different among some ventilators. The number of IEs was similar among the studied ventilators.

Section snippets

Materials and Methods

The investigative protocol was approved by the institutional ethics committee (S. Maugeri Foundation, Gussago, Italy) and was conducted according to the declaration of Helsinki. Informed consent was obtained from all the patients before their enrollment into the study.

Patients

Thirty-one patients were enrolled in the study. All but three patients (COPD, two patients; RCWD, one patient) completed the study and tolerated the experimental procedure well. Two of the patients who dropped out did not tolerate the mask, and the other one withdrew his consent. The individual characteristics of the 28 patients completing the study are shown in Table 1.

Breathing Pattern and V˙e

Figure 3shows a polygraphic tracing from a representative patient (patient 7) during the application of the studied

Discussion

This study shows that in stable, awake patients with CVF, all of the studied ventilators were tolerated quite well, although with a great intersubject variability in comfort. All ventilators performed well in terms of improvement in V˙e and inspiratory muscle unloading, thus fulfilling the aims of mechanical ventilation.25 IEs were similar among the studied ventilators. Among the ventilators, there was no significant difference in PTPao, min levels, whereas some ventilators differed in Pao,

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