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Non-invasive ventilation in hypercapnic acute respiratory failure in COPD vs. non-COPD conditions

Citation/s: Phuna J, et al. Noninvasive ventilation in hypercapnic acute respiratory failure due to chronic obstructive pulmonary disease vs. other conditions: effectiveness and predictors of failure. Intensive Care Medicine (2005) 31:533-539

Lead author's name and email: T K Lim, mdclimtk@nus.edu.sg

Three-part Clinical Question: How effective is non-invasive ventilation (NIV) in hypercapnic acute respiratory failure (ARF) due to chronic obstructive pulmonary disease (COPD) vs. other conditions? Secondary question: What are the risk factors for failure of NIV?
Search Terms: Non-invasive ventilation - hypercapnic acute respiratory failure - chronic obstructive pulmonary disease – pneumonia

The Study: Prospective Cohort Study.

The Study Patients: Medical ICU. Hypercapnic ARF was defined as - respiratory rate >25bpm, arterial pH <7.35, PaCO₂ >45mmHg, and 1st episode of NIV. Excluded: patients with severe haemodynamic instability, peri-arrest, upper GI bleed, pneumothorax, facial trauma and patients for whom active treatment including intubation were deemed inappropriate.

COPD patients: diagnosed based on previous medical records, PFT's, or compatible history, examination and CXR. Exacerbations diagnosed if: increased dyspnoea, sputum production, without CXR changes. All were treated with systemic steroids, 3 nebulisers of salbutamol plus atrovent, and repeat ABG following. NIV applied only if continued hypercapnic ARF.

Non-COPD group: sub classified into - pneumonia, neuromuscular disorders, pulmonary oedema, bronchiectasis, sepsis and asthma. Pneumonia diagnosed by CXR together with acute signs of SOB, temp >38C, cough with sputum.

Exposure of Interest: Non-invasive ventilation (BiPAP, initially 18 over 4)in COPD vs. non-COPD patients
The Outcome: Primary outcome: Success or failure (progression to intubation) of NIV. Some criteria subjective, and one was stated as systolic BP >70mm Hg (sic). Secondary endpoints: length of ICU/hospital stay, hospital mortality rates
 

The Evidence:

Secondary endpoints were:

1.      Independent predictors of failure of NIV:  high APACHE II score in both COPD and. non-COPD groups: no patient with APACHE II <23 required intubation. In non-COPD group pneumonia, increased HR, increased PaCO2 1hour post NIV.

2.      Predictors of in-hospital mortality: NIV failure, increased respiratory rate 1hour post NIV.

EBM Comments:

 

1.      Do the methods allow accurate testing of the hypothesis? No. “The aim of this study was to compare the effectiveness of NIV in hypecapnic ARF due to COPD vs. non-COPD conditions and to alucidate the risk factors for NIV failure in these two groups”. 32% of the non-COPD patients had COPD. Although their inclusion in this group was justified on the grounds that the primary cause of their ARF was pneumonia this throws serious doubt on the ability of this study to differential between the two groups of patients set out in the aims. Different definition of ARF - no mention made of PaO2 levels as in other studies.

2.      Do the statistical tests correctly test the results to allow differentiation of statistically significant results? Yes, but note 1. Study had small numbers.

3.      Are the conclusions valid in light of the results? They suggested that NIV is statistically more effective in patients with hypercapnic ARF due to COPD than other conditions. This is not a trial of the effectiveness of NIV in either group.  see note 1 + 2.

4.      Did results get omitted, and why? No

5.      Did they suggest areas of further research? No

6.      Did they make recommendations based on the results and were they appropriate? To evaluate the patient's overall condition rather than focus on isolated variables when considering NIV in COPD patients (based on result that high APACHE score is a good predictor on NIV failure) Hopefully we all already do this!

7.      Is the study relevant to my clinical practice? Yes, but does not provide any information that can be used to change practice...

8.      What level of evidence does this study represent? 2^-. Cohort study with high risk of confounding, bias or chance, based on dubious methods and small study numbers.

9.      What grade of recommendation can I make on this result alone? N/A

10.  What grade of evidence can I make when this study is considered along with other available evidence? N/A.

11.  Should I change my practice because of these results? No. We already know of the effectiveness of BiPAP in patients with exacerbations of COPD. This study does not tell us about its effectiveness, or otherwise, in other patients.

12.  Should I audit my current practice because of these results? It will help to gain further evidence on this subject. It is also good clinical practice to evaluate current hospital practice, and to look towards areas for improvement.

Appraised by: Alice Murray37/4 London Street Edinburgh EH3 6LX; 05 June 2005

Email: alicefmurray@hotmail.com

Edited by CC & SJM.

Kill or update by: 1st January 2010

Citation: EBM Critical Appraisals. Scottish Intensive Care Society EBM Group. Murray A. 2005: Phuna J, et al. Noninvasive ventilation in hypercapnic acute respiratory failure due to chronic obstructive pulmonary disease vs. other conditions: effectiveness and predictors of failure. Intensive Care Medicine (2005) 31:533-539.

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