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Communications to the Editor |

Limitations to Study on Noninvasive Ventilation FREE TO VIEW

George Ntoumenopoulos, PhD
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Physiotherapy Department Royal Melbourne Hospital Parkville, Australia



Chest. 1999;115(1):303. doi:10.1378/chest.115.1.303
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Published online

To the Editor:

The recent publication by Wood and colleagues1 evaluated whether noninvasive positive pressure ventilation in the emergency department reduced the need for intubation and mechanical ventilation. The authors propose that noninvasive ventilation may be detrimental and increase mortality in a selected group of patients. This investigation has specific design problems limiting the conclusions made by these authors.

The study is described as a randomized, controlled clinical trial; however, unequal numbers of patients were enrolled in each group, which was not adequately explained by the authors. Pertinent comorbid factors that may have influenced outcome, including smoking history, were either not recorded or not reported in this study. The initiation and titration of noninvasive positive pressure ventilation therapy was based on ventilatory and gas exchange parameters. The levels of inspiratory and expiratory airway pressure used up until the major endpoints were reached (ie, intubation, death) were not reported. These details would have allowed greater insight into the appropriateness of the inspiratory and expiratory airway pressure settings used during the patients transition from the emergency department to the ICU setting. The limited reporting of vital signs and gas exchange data precluded a more detailed adequate examination of these appropriate variables. The documentation of the daily changes (up to 5 days) in gas exchange, vital signs, and noninvasive ventilation settings would have enabled an improved evaluation of the therapy used in this study.

The admission characteristics of the study patients were documented as being similar between the two groups; however, the trend in the data indicates differences, with increased APACHE II score, risk of death, and incidence of community-acquired pneumonia in the noninvasive positive pressure ventilation group. Statistically significant differences in these variables may not have been demonstrated merely because of the small sample size, as correctly pointed out by the authors.

The authors alluded that noninvasive ventilation caused increased multiple system organ failure and death, because of the delayed time for oral intubation and mechanical ventilation. It is difficult to come to such a conclusion when the average length of hospital stay for the noninvasive ventilation group demonstrated larger standard deviation when compared with the control group. The noninvasive ventilation group may have included a number of patients with increased severity of illness, which contributed to the increased length of stay and mortality.

As current research2 has demonstrated that noninvasive ventilation both reduces work of breathing and improves gas exchange in a variety of patient groups and settings, it is perplexing that Wood and colleagues propose increased patient mortality associated with this therapy. The increased mortality in the noninvasive ventilation group1 occurred with improvements in the measures of therapy effectiveness, namely arterial pH, Pao2, respiratory rate, and heart rate not lending support to the authors conclusions. This study,1 may have been comparing two different patient groups in regard to severity and type of illness.

Alternatively, the poor outcome for the noninvasive ventilation group may have resulted through the use of a single profession (respiratory care practitioners) to institute and monitor the therapy. The Australian and European Health Care Systems, in contrast, deliver noninvasive ventilation through multidisciplinary teams including physiotherapy, nursing, and medical staff, with significant skill overlap in the service delivery, to ensure the safe and continuous monitoring of this therapy. The intermittent supervision (1 to 2 h per day as described by the authors1) of the noninvasive ventilation by the respiratory care practitioners may have been inadequate. The multiskilled application and greater monitoring (as in 1:1 nursing in the ICU setting) of this therapy (including nursing and medical staff) may have improved outcome. Wood and colleagues in fact alluded to the logistical problem of adequately monitoring patients with noninvasive ventilation.

Correspondence to: George Ntoumenopoulos, PhD, Physiotherapy Department, Royal Melbourne Hospital, Grattan Street, Parkville 3050, Australia

Wood, KA, Lewis, L, Von Harz, B, et al (1998) The use of noninvasive positive pressure ventilation in the emergency department.Chest113,1339-1346. [PubMed] [CrossRef]
 
Jasmer, RM, Luce, JM, Mathay, MA Noninvasive positive pressure ventilation for acute respiratory failure: underutilized or overrated?Chest1997;111,1672-1678. [PubMed]
 

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References

Wood, KA, Lewis, L, Von Harz, B, et al (1998) The use of noninvasive positive pressure ventilation in the emergency department.Chest113,1339-1346. [PubMed] [CrossRef]
 
Jasmer, RM, Luce, JM, Mathay, MA Noninvasive positive pressure ventilation for acute respiratory failure: underutilized or overrated?Chest1997;111,1672-1678. [PubMed]
 
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