Criteria abstracted from The Users' Guide to Medical Literature, from the Health Information Research Unit and Clinical Epidemiology and Biostatistics, McMaster University

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Article Reviewed:

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Noninvasive positive-pressure ventilation in children with lower airway obstruction.

Thill PJ, McGuire JK, Baden HP, Green TP, Checchia PA.

Pediatr Crit Care Med. 2004 Jul;5(4):337-342. [abstract]

Reviewed by Sami Rishmawi MD, Advocate Hope ChildrenÕs Hospital, Oak Lawn, IL

Review posted October 23, 2004

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I. What is being studied?:

The study objective:

To determine whether NPPV improve respiratory function in children with asthma and obstructive lower airways diseases

The study design:

A Prospective, unblinded, randomized crossover study.

The patients included:

Sixteen patients (age 2 mo to 14 years, median 48 months) during a 6 month period with lower airway obstruction characterized by increased work breathing, wheezing, dyspnea and a Clinical Asthma Score (CAS) > 3 were evaluated in the study.

The patients excluded:

Tracheostomy tube, absence of airway protective reflexes, need for emergent intubation as determined by the attending physician, facial or airway anomaly or injury precluding the use of a tight-fitting mask, a Clinical Asthma Score (CAS)> 8 or the discretion of attending. Twenty seven patients met eligibility criteria. Five patients were excluded at the discretion of the attending and two were not enrolled due to intermittent apnea. Twenty patients were randomized.

The interventions compared:

Patients were alternately randomized to one of two groups: group 1 received 2 hrs of NPPV, followed by crossover to 2 hrs of conventional therapy alone; group 2 received 2 hours of conventional therapy, followed by 2 hrs of NPPV.

The outcomes evaluated:

The primary end points for determining the efficacy of NPPV were change in respiratory rate, CAS, and assessment of gas exchange at the end of each two hour interval.

II. Are the results of the study valid?

Primary questions:

1. Was the assignment of patients to treatments randomized?

Yes. However the randomization process was not specified.

2. Were all patients who entered the trial properly accounted for and attributed at its conclusion?

Was followup complete?

Yes. Sixteen patients randomized, 8 in each group, completed the study endpoint which was 4 hours after enrollment. Four patients were withdrawn after randomization because of intubation (1) or discomfort with NPPV (3). These 4 patients could be somewhat significant because of the nature of their withdrawal from the study.

Were patients analyzed in the groups to which they were randomized?

Yes, but also no because they pooled data. Each group had total of 8 patients and both groups were analyzed at the end of each therapy period. They presumably created two groups to see if it mattered whether applying NPPV first or second made a difference, but then they do not report any results comparing the two groups and pooled the data for final analysis.

Secondary questions:

3. Were patients, health workers, and study personnel "blind" to treatment?

No. This study used an unblinded design, but interrater reliability between two presumably independent scorers (Kappa analysis) had been used to compare the more subjective CAS assessments.

4. Were the groups similar at the start of the trial?

Yes. There were no significant differences found between group 1 and group 2 for any of the variables, including age, respiratory rate, heart rate, FiO2, SaO2 or transcutaneous CO2 at the time of entry into the study.

5. Aside from the experimental intervention, were the groups treated equally?

The study didn't specify that both groups were treated equally. Both groups continued "conventional therapy" at the attending's discretion, but there is no comparison of these therapies. However, since they pooled the data from both groups anyway, and they stated that no changes in other therapies were undertaken during the 4 hours of the study, it probably is safe to assume the groups were treated equally.

III. What were the results?

1. How large was the treatment effect?

A decrease in respiratory rate (49.5 ± 13.9 vs. 32.0 ± 6.2 breaths/min, p < 0.0001) for all patients after 2 hrs of NIPPV compared with baseline. A lower total CAS (5.4 ± 1.2 vs. 2.1 ± 1.0, p < 0.0001) and lower scores for each individual component (accessory muscle use, wheeze, and dyspnea; all p < 0.01) was also seen after NPPV.

Also discontinuation of NPPV after 2 hours in Group 1 was associated with an increased in both respiratory rate and total CAS.

2. How precise was the estimate of the treatment effect?

The 95% confidence intervals for changes in CAS are not provided in this study, so we cannot comment on the precision of the treatment effect.

IV. Will the results help me in caring for my patients?

1. Can the results be applied to my patient care?

The patients in the study seem typical of patients with asthma admitted to most PICU's in this country.

2. Were all clinically important outcomes considered?

Although this study shows the physiological efficacy of NPPV - respiratory rate, CAS, and assessment of gas exchange - no data on other clinical outcomes, e.g., intubation, reducing length of stay, improving patient/parent satisfaction are available. These are the kind of meaningful clinical outcomes we demand today.

3. Are the likely treatment benefits worth the potential harms and costs?

There were no apparent adverse events associated with the use of NPPV, e.g. gastric air insufflation, emesis, or nasal pressure sores. The author stated that no assessment for potential benefits in length of ICU stay, cost savings, and differences in other medical therapy used were analyzed.

Although the study provides promising good transient symptomatic improvement for patients with status asthmaticus without need for invasive therapy, considering NPPV therapy as a first line therapy cannot be considered at this time without longer follow up. The need for larger randomized study could answer many of questions related to meaningful and durable clinical outcomes for these patients

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