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Correspondence |

Body Mass Index in COPD Mortality Response: Is It All in the Water? FREE TO VIEW

Sai Praveen Haranath, MBBS; Byung S. Park, PhD; Molly Osborne, MD, PhD, FCCP
Author and Funding Information

Affiliations: Oregon Health & Science University, Portland, OR,  Center for Pneumology, Donaustauf Hospital, Donaustauf, Germany,  Institute and Outpatient Clinic for Occupational, Social and Environmental Medicine, Ludwig-Maximilians-University, Munich, Germany

Correspondence to: Sai Praveen Haranath, MBBS, Fellow, Pulmonary and Critical Care Medicine, Division of Pulmonary and Critical Care Medicine, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, UHN-67, Portland, OR 97239; e-mail: haranath@ohsu.edu



Chest. 2008;133(1):318-319. doi:10.1378/chest.07-2285
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Published online

The article in a recent issue of CHEST (June 2007) by Budweiser et al1addressed the ability of body mass index (BMI) to predict mortality. Indeed, in a related study2in a population of cirrhotic patients BMI was found to be a good predictor of malnutrition, although peripheral edema and removal of ascites did not affect the outcome. However, the authors did not address some factors that might account for the positive association of BMI and survival. First, it is possible that the cohort with a BMI > 25 kg/m2 might not have been at baseline weight (ie, they might have had volume overload), given that patients with advanced COPD often have volume retention.3 Thus, the results might reflect the benefit of diuresis. Indeed, 74% of patients were receiving therapy with diuretics at hospital admission. This hypothesis could be checked by recalculating the BMI on a daily basis or at hospital discharge.

Second, it is unclear why confidence intervals are given for specific survival rates under the heading “survival and prognostic value of baseline parameters” when exact values are given as follows: overall mortality rate, 44.7% (n = 84); 1-year survival rate, 84.0% (158 of 188 patients; 95% confidence interval [CI], 69.3 to 96.3%); 2-year survival rate, 65.3% (98 of 150 patients; 95% CI, 49.5 to 82.8%); 5-year survival rate, 26.4% (28 of 106 patients; 95% CI, 16.5 to 42.2%).

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

The authors have no conflicts of interest to disclose.

Budweiser, S, Jorres, RA, Riedl, T, et al (2007) Predictors of survival in COPD patients with chronic hypercapnic respiratory failure receiving noninvasive home ventilation.Chest131,1650-1658. [PubMed] [CrossRef]
 
Campillo, B, Richardet, JP, Bories, PN Validation of body mass index for the diagnosis of malnutrition in patients with liver cirrhosis.Gastroenterol Clin Biol2006;30,1137-1143. [PubMed]
 
de Leeuw, PW, Dees, A Fluid homeostasis in chronic obstructive lung disease.Eur Respir J Suppl2003;46,33s-40s. [PubMed]
 
To the Editor:

We would like to thank Dr. Haranath and colleagues for their helpful comments. Malnutrition, as quantified by body mass index (BMI), is accepted as an important predictor of long-term survival in advanced respiratory diseases,12 particularly COPD.3Consequently, BMI became part of a multidimensional scoring system that is in widespread use.4Our finding of an association between BMI and mortality in chronic hypercapnic respiratory failure5is fully in line with the literature, and malnutrition is especially prevalent in these patients.67 As correctly pointed out by Dr. Haranath and mentioned by us, functionally active fat-free mass might better reflect the nutritional state than BMI.89 We also agree that fluid retention could have influenced the predictive value of BMI, particularly on initial admission. There are, however, several arguments to be considered. First, with regard to therapy and/or signs for cor pulmonale, our population was fairly homogeneous (74% diuretics), and in the diuretics subgroup BMI was also predictive. Second, as suggested, we also have performed analyses of patients in a stable clinical state at routine clinical follow-up. This study10 demonstrated BMI as a predictor, similar to previous results.14 Third, patients with severe edema (and cor pulmonale) are likely to be at higher risk for death; we thus would have underestimated, not overestimated, the risk by using BMI. Therefore, the association of BMI with long-term mortality is a consistent finding, and BMI is certainly a good proxy for nutritional state in clinical routine.

Of course, survival rates were precise values derived from the absolute numbers given. To get a feeling for the reliability of these estimates inferred from a large but still limited sample of patients, we computed confidence intervals for proportions by the usual statistics. We are sorry if the limitations of space prevented us from providing more details on the reasons for this seemingly paradoxical presentation.

References
Cano, NJ, Pichard, C, Roth, H, et al C-reactive protein and body mass index predict outcome in end-stage respiratory failure.Chest2004;126,540-546. [PubMed] [CrossRef]
 
Chailleux, E, Fauroux, B, Binet, F, et al Predictors of survival in patients receiving domiciliary oxygen therapy or mechanical ventilation: a 10-year analysis of ANTADIR observatory.Chest1996;109,741-749. [PubMed]
 
Chailleux, E, Laaban, JP, Veale, D Prognostic value of nutritional depletion in patients with COPD treated by long-term oxygen therapy: data from the ANTADIR observatory.Chest2003;123,1460-1466. [PubMed]
 
Celli, BR, Cote, CG, Marin, JM, et al The body-mass index, airflow obstruction, dyspnea, and exercise capacity index in chronic obstructive pulmonary disease.N Engl J Med2004;350,1005-1012. [PubMed]
 
Budweiser, S, Jorres, RA, Riedl, T, et al Predictors of survival in COPD patients with chronic hypercapnic respiratory failure receiving noninvasive home ventilation.Chest2007;131,1650-1658. [PubMed]
 
Cano, NJ, Roth, H, Court-Ortune, I, et al Nutritional depletion in patients on long-term oxygen therapy and/or home mechanical ventilation.Eur Respir J2002;20,30-37. [PubMed]
 
Budweiser S, Meyer K, Jorres RA, et al. Nutritional depletion and its relationship to respiratory impairment in patients with chronic respiratory failure due to COPD or restrictive thoracic diseases. Eur J Clin Nutr 2008 (in press).
 
Schols, AM, Broekhuizen, R, Weling-Scheepers, CA, et al Body composition and mortality in chronic obstructive pulmonary disease.Am J Clin Nutr2005;82,53-59. [PubMed]
 
Vestbo, J, Prescott, E, Almdal, T, et al Body mass, fat-free body mass, and prognosis in patients with chronic obstructive pulmonary disease from a random population sample: findings from the Copenhagen City Heart Study.Am J Respir Crit Care Med2006;173,79-83. [PubMed]
 
Budweiser S, Heidtkamp F, Jorres RA, et al. Predictive significance of six-minute walk distance for long-term survival in chronic hypercapnic respiratory failure. Respiration 2008 (in press).
 

Figures

Tables

References

Budweiser, S, Jorres, RA, Riedl, T, et al (2007) Predictors of survival in COPD patients with chronic hypercapnic respiratory failure receiving noninvasive home ventilation.Chest131,1650-1658. [PubMed] [CrossRef]
 
Campillo, B, Richardet, JP, Bories, PN Validation of body mass index for the diagnosis of malnutrition in patients with liver cirrhosis.Gastroenterol Clin Biol2006;30,1137-1143. [PubMed]
 
de Leeuw, PW, Dees, A Fluid homeostasis in chronic obstructive lung disease.Eur Respir J Suppl2003;46,33s-40s. [PubMed]
 
Cano, NJ, Pichard, C, Roth, H, et al C-reactive protein and body mass index predict outcome in end-stage respiratory failure.Chest2004;126,540-546. [PubMed] [CrossRef]
 
Chailleux, E, Fauroux, B, Binet, F, et al Predictors of survival in patients receiving domiciliary oxygen therapy or mechanical ventilation: a 10-year analysis of ANTADIR observatory.Chest1996;109,741-749. [PubMed]
 
Chailleux, E, Laaban, JP, Veale, D Prognostic value of nutritional depletion in patients with COPD treated by long-term oxygen therapy: data from the ANTADIR observatory.Chest2003;123,1460-1466. [PubMed]
 
Celli, BR, Cote, CG, Marin, JM, et al The body-mass index, airflow obstruction, dyspnea, and exercise capacity index in chronic obstructive pulmonary disease.N Engl J Med2004;350,1005-1012. [PubMed]
 
Budweiser, S, Jorres, RA, Riedl, T, et al Predictors of survival in COPD patients with chronic hypercapnic respiratory failure receiving noninvasive home ventilation.Chest2007;131,1650-1658. [PubMed]
 
Cano, NJ, Roth, H, Court-Ortune, I, et al Nutritional depletion in patients on long-term oxygen therapy and/or home mechanical ventilation.Eur Respir J2002;20,30-37. [PubMed]
 
Budweiser S, Meyer K, Jorres RA, et al. Nutritional depletion and its relationship to respiratory impairment in patients with chronic respiratory failure due to COPD or restrictive thoracic diseases. Eur J Clin Nutr 2008 (in press).
 
Schols, AM, Broekhuizen, R, Weling-Scheepers, CA, et al Body composition and mortality in chronic obstructive pulmonary disease.Am J Clin Nutr2005;82,53-59. [PubMed]
 
Vestbo, J, Prescott, E, Almdal, T, et al Body mass, fat-free body mass, and prognosis in patients with chronic obstructive pulmonary disease from a random population sample: findings from the Copenhagen City Heart Study.Am J Respir Crit Care Med2006;173,79-83. [PubMed]
 
Budweiser S, Heidtkamp F, Jorres RA, et al. Predictive significance of six-minute walk distance for long-term survival in chronic hypercapnic respiratory failure. Respiration 2008 (in press).
 
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