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- cystic fibrosis
- chronic obstructive pulmonary disease
- pulmonary rehabilitation
- British Thoracic Society
Sharma and colleagues report the survival of 584 patients with cystic fibrosis (CF) attending the Royal Brompton Hospital between 1985 and 1996.1 They report that body wasting, as represented by % ideal weight, was a significant predictor of survival before and after correction for age, sex, % predicted FEV1, Pao2, and Paco2.
In 1997 Hayllar and colleagues reported the survival of 503 patients with CF attending the Royal Brompton Hospital between 1969 and 1993.2 They found that low blood haemoglobin concentration (Hb), low plasma albumin concentration, and short stature were significant predictors of survival although, of these, only height was included in their final predictive model. Other recent reports have shown both weight and height to be significant predictors of survival in CF.3,4
We recently reported the survival of 181 children with CF referred to the paediatric lung transplantation programme at Great Ormond Street Hospital for Children (GOSH).5 Following Hayllar's report, we opted to study a wide range of variables including Hb, albumin, and % ideal weight as markers of nutritional status. All three variables were correlated in our population, but Hb and albumin were clearly better predictors of survival than % ideal weight, both before and after correction for age, sex, resting (age corrected) heart rate, and markers of lung function and exercise tolerance. Hayllar and colleagues speculated that failure of statural growth probably reflects a degree of malnutrition. This may explain our findings, as stunting of growth could result in % ideal weight giving an underestimate of malnutrition.
Given the previous report from their centre, it is regrettable that Sharma and colleagues did not include albumin, Hb, and height in their prognostic modelling as they may have discovered a more complex picture. They conclude that % ideal weight should be considered an independent risk factor for prognosis in CF. We welcome and support their conclusion, but suggest that poor nutritional status in general should be considered a risk factor, and that a patient with anaemia, hypoalbuminaemia, and/or growth failure should be considered at risk, even if they are not wasted.
On a separate point, we were unable to include Pao2 and Paco2 in our survival analyses. In common with many paediatric centres, GOSH does not routinely perform arterial blood gas analysis in children, even in those referred for transplantation assessment. Although the value of these measures is accepted in adult patients, data from children are scanty and paediatricians are reluctant to subject children to arterial blood sampling unless the results are clearly of value. Sharma and colleagues appear to have studied these data in a large number of children, and we ask that they present the paediatric data as a subset. In particular, in how many children were arterial blood gas analyses performed, what were the Pao2 and Paco2 values obtained, and did these results provide predictive information that was additive to that obtained less invasively? We encourage the authors to publish these data as they could change practice in other centres.
The extensive literature in this area indicates that numerous variables can be considered predictors of survival in CF. We suggest that any assessment of prognosis should include spirometric measurements, blood gas analysis in adults, and assessments of nutritional status, exercise tolerance, rate of decline, and possibly some measurement of resting energy expenditure or metabolic rate. Furthermore, in children at least, it appears that young age and female sex result in a poorer prognosis. Basing prognosis upon FEV1 and % ideal weight alone is unlikely to be sufficient.
We welcome the response of Drs Aurora and Wade to our article on the prognostic value of wasting in patients with cystic fibrosis (CF).1 They suggest that poor nutritional status in general should be considered a risk factor for mortality with particular emphasis on anaemia and hypoalbuminaemia. While we accept that nutritional status is likely to relate strongly to mortality in CF, we disagree that haemoglobin and albumin should be considered more accurate markers of prognosis than % ideal weight. There have been relatively few studies evaluating the prognostic value of haemoglobin and albumin in CF, none of which have shown these variables to be independent predictors of mortality.2,3 Furthermore, we note that in the study by Aurora and colleagues on 181 children with severe CF, neither haemoglobin nor albumin were found to be significant prognostic markers in multivariate survival analysis (table 3).2
In our paper we demonstrate that, in a stable outpatient CF population, % ideal weight represents an accurate predictor of survival which is independent of other established prognostic markers such as lung function and arterial blood gas tensions. The addition of % predicted FEV1 to % ideal weight provides an even stronger model with which to predict survival. We do not propose that these two variables should be the only ones considered when evaluating patients, but that they represent simple and accurate prognostic parameters which can be easily assessed in the outpatient clinic.
With regard to blood gas analysis, in our study this was performed in 58 children (age <18 years). We found the arterial oxygen tension but not carbon dioxide tension to be a significant predictor of survival in this age group (unpublished data). Furthermore, % ideal weight continued to be a strong and independent predictor of survival in children as well as in adults with CF.
RS is supported by the Robert Luff Foundation. SDA has been supported by the Ernst- and Bertha Grimmke Stiftung, Düsseldorf, Germany. SDA is holding a postgraduate fellowship of the Max-Delbrück-Centrum for Molecular Medicine, Germany.