Chest

Chest

Volume 126, Issue 3, September 2004, Pages 851-859
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Clinical Investigations in Critical Care
Assessment of Physiologic Variables and Subjective Comfort Under Different Levels of Pressure Support Ventilation

https://doi.org/10.1378/chest.126.3.851Get rights and content

Study objectives:

To evaluate the effects of 12 ventilator settings (pressure support ventilation [PSV] plus positive end-expiratory pressure [PEEP], 30 + 0 cm H2O; 25 + 5 cm H2O; 25 + 0 cm H2O; 20 + 5 cm H2O; 20 + 0 cm H2O; 15 + 5 cm H2O; 15 + 0 cm H2O; 10 + 5 cm H2O; 10 + 0 cm H2O; 5 + 5 cm H2O; 5 + 0 cm H2O; and 0 + 5 cm H2O) on physiologic variables; the percentage of ineffective efforts; patient comfort; and whether the diagnosis of COPD may influence results.

Design:

Prospective, randomized, physiologic study.

Setting:

Three weaning centers.

Patients:

Thirty-six consecutive patients (20 patients with COPD).

Intervention:

Patients were randomly submitted to the 12 settings.

Measurements and results:

Breathing pattern, respiratory drive (p0.1), arterial oxygen saturation (Sato2), heart rate, percentage of ineffective efforts per minute, patient comfort measured by means of a visual analogue scale (VAS), and BORG scale were recorded under each setting. Under different levels of assistance, breathing pattern, Sato2, and p0.1 significantly and linearly changed (p < 0.0001) while VAS and BORG scale presented a significant (p = 0.027) U-shaped trend; high or low assistance caused the most discomfort. Under high levels of assistance, a higher (analysis of variance, p = 0.023) frequency of ineffective effort percentage was observed in the subgroup of 26 patients who presented this phenomenon. Breathing pattern significantly (p = 0.013) changed when compared to PSV alone (PSV plus zero end-expiratory pressure [ZEEP]) at the same total inspiratory pressure assistance (PSV plus PEEP). A huge variability among patients in breathing pattern and comfort was found under the setting rated as the most comfortable by patients. The diagnosis of COPD did not influence the overall results.

Conclusions:

The following conclusions are made: (1) physiologic variables followed a linear trend, while comfort followed a U-shaped trend under different levels of PSV (irrespective of COPD diagnosis); (2) high assistance caused an increase in ineffective efforts; (3) only the breathing pattern significantly changed when total assistance was given as PSV plus PEEP when compared to PSV alone (PSV plus ZEEP); and (4) the extreme levels of PSV are not associated with the best comfort.

Section snippets

Materials and Methods

The study was conducted according to the Declaration of Helsinki and with approval of the protocol by the ethics committee of each hospital. Patients gave their informed consent to the study.

Results

Anthropometric and clinical characteristics of all patients enrolled in the study classified according to underlying disease are shown in Table 1. All patients included in the study completed the protocol. Among the 16 non-COPD patients, 8 patients (50%) had neuromuscular diseases (amyotrophic lateral sclerosis, three patients; Duchenne muscular dystrophy, three patients; myasthenia gravis, two patients), while 8 patients (50%) were recovering from cardiovascular (six patients), thoracic (one

Discussion

This study, carried out on a miscellaneous group of patients with prolonged/difficult weaning, showed that different levels of PSV are associated with significant changes in breathing pattern, oxygenation, and p0.1, as well as ineffective efforts and changes in patient comfort. Extreme high or low levels of PSV are not associated with the best comfort. Breathing pattern significantly changed when total assistance was given as PSV plus PEEP when compared to PSV alone (PSV plus ZEEP). The

Participating Centers and Investigators

Lung Function and Respiratory Intermediate Intensive Care Unit, S. Maugeri Foundation IRCCS, Gussago (Brescia, Italy): M. Vitacca, M. Zigliani, L. Bianchi, L. Barbano, and R. Porta; Lung Function and Respiratory Intermediate Intensive Care Unit, S. Maugeri Foundation IRCCS, Montescano (Pavia, Italy): E. Zanotti; Department of Pulmonary Rehabilitation and Respiratory Intermediate Intensive Care Unit, Fondazione ONLUS Villa Pineta Gaiato (Modena, Italy) and University of Modena Reggio-Emilia

ACKNOWLEDGMENT

The authors thank Mrs. Donna D'Agostino for English editing, and Giovanni Bader, MD, for statistical assistance.

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    †

    A list of participating centers and investigators is given in the Appendix.

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    Copyright © 2004 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.