LITERATURE MONITOR:
A REVIEW OF RECENTLY PUBLISHED CLINICAL ARTICLES

AEROBIC FITNESS AND ASTHMA SEVERITY UNRELATED

Is physical fitness related to asthma severity in children? Pianosi and Davis studied children at an asthma camp during two separate summers and found that measurements of airway obstruction and hyperresponsiveness were not related to either aerobic capacity or body mass index (BMI). However, their findings suggested that children with severe asthma may subconsciously restrict their activity levels, thus predisposing them to overweight or obesity.

Fifty-eight children with clinically stable asthma were included in the study. Height, weight, forced vital capacity (FVC), and forced expiratory volume (FEV1) were measured, and all children underwent a histamine challenge. They also underwent a bicycle exercise test to measure peak oxygen consumption (Vo2). Questionnaires were used to determine levels of habitual activity, physical activity limitations due to asthma, perceived competence in physical activity, and attitudes towards physical activity.

Asthma was mild in 34 children, moderate in 20, and severe in four. Peak Vo2 did not correlate with asthma severity in any of the groups, nor did reported level of physical activity. However, children’s attitudes toward physical activity were linked strongly with Vo2. Interestingly, there were no differences in physical activity participation according to asthma severity.

Twenty-nine children had normal BMI, 11 were overweight, and 17 were obese. Although peak Vo2 was inversely correlated with BMI, forced expiratory volume and forced vital capacity were not. Obese children reported more limitations in their favorite activities than did normal weight children.

The authors noted that children with higher BMI may experience greater perceived effort and/or dyspnea on exertion. This could be misconstrued as asthma-related impairment and treated with more medication than necessary.

Pianosi PT, Davis HS. Determinants of physical fitness in children with asthma. Pediatrics. 2004; 113:e225-e229. [epub ahead of print]

HOME TREATMENT FOR CF PATIENTS NOT THE BEST

Are there advantages to treating patients who have cystic fibrosis (CF) and respiratory infections at home rather than in the hospital? A recent one-year study by Thornton et al found that in 116 adults with CF, home treatment, in comparison with hospitalization, was associated with a decline in lung function parameters.

This retrospective analysis included CF patients age 16 and older with respiratory infections who had received intravenous antibiotics either at home or in the hospital. They were assigned to one of three groups (home, hospital, or both) depending on where they had been given the majority of their care. Best and average values for FEV1, FVC, and body weight were calculated before the study’s start and compared with final values from measurements taken at the end of the study.

Forty-seven patients were in the home group, 51 were in the hospital group, and 18 were assigned to the both group. There were no significant differences in baseline characteristics among the groups. At one year, FEV1, FVC, and body weight had declined in the home group but had risen in the hospital group. The site of treatment was the only variable that affected change in FEV1.

The authors observed that CF patients often prefer home treatment because it interferes less with their work and normal activities. However, this study implies that patients may not be resting sufficiently at home and therefore may not be receiving optimal treatment.

Thornton J, Elliot R, Tully MP, et al. Long term clinical outcome of home and hospital intravenous antibiotic treatment in adults with cystic fibrosis. Thorax. 2004;59:242-246.

BMI NOT RELATED TO MORTALITY IN MECHANICALLY VENTILATED ICU PATIENTS

Historically, it has been thought that obese patients are at increased risk for morbidity and mortality in the ICU. However, O’Brien and colleagues recently performed a secondary analysis of results from the multicenter randomized trials conducted by the Acute Respiratory Distress Syndrome Network (ARDSNet). They found that among the patients in these trials, BMI had no effect on ICU outcomes.

Eight hundred seven patients were included in the secondary analysis. Of these, 27% were obese and 31% were overweight. The obese and overweight patients were more likely to have an indirect cause of lung injury, had higher airway pressures, and had higher set tidal volumes.

All BMI groups benefited from the lower tidal volume of 6 mL/kg. BMI was not associated with an increased risk of death by 28 or 180 days, nor was it linked to weaning difficulties. Even severe obesity (BMI of 40 kg/m2 or higher) was not associated with a higher incidence of death. Factors that did appear to increase the risk of death were older age, high APACHE III score, assignment to the12-mL/kg tidal volume group, a lower Pao2:Fio2 baseline ratio, and higher baseline airway pressure.

A limitation of this analysis is that the ARDSNet trials did exclude profoundly obese patients—those whose weight (in kilograms) equaled or exceeded their height (in centimeters). Furthermore, the fact that the tidal volumes delivered in these trials were standardized by body weight may have influenced the results. Nevertheless, O’Brien and colleagues concluded that although obese patients may have weight-related physiologic abnormalities and comorbidities, these do not necessarily lead to differences in mortality.

O’Brien Jr., JM, Welsh CH, Fish RH, et al. Excess body weight is not independently associated with outcome in mechanically ventilated patients with acute lung injury. Ann Intern Med. 2004;140:338-345.

SOCIOECONOMIC BACKGROUND MAY AFFECT RISK FOR MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) increases morbidity and mortality in cardiovascular surgery patients, according to a recent study. Although many risk factors for postoperative MRSA infection have been identified, two new ones have just been detected. Bagger et al followed patients admitted to their hospital for coronary artery bypass grafting during a five-year period. They found that socioeconomic background and duration of surgery were both associated with MRSA.

To gauge socioeconomic background, the authors divided patients into tertiles based on such variables as employment status, extent of household overcrowding, and vehicle ownership. They also recorded the duration of each patient’s operation, the length of hospital stay, and 30-day mortality.

Of the 1,739 patients studied, 23 developed MRSA infections. There was a significant positive correlation between the incidence of MRSA infections and socioeconomic status. Thirteen of the MRSA patients were in the tertile with the greatest evidence of deprivation, while only two were in the least deprived group.

The duration of surgery was 97 minutes in the MRSA patients versus 80 minutes in the patients who did not develop such infections. The MRSA patients also had a longer mean postoperative hospital stay (17.9 days compared to 8.5 days in the patients without the infection). There was no interaction between socioeconomic deprivation and length of surgery, nor was there any correlation between ethnicity and MRSA risk.

The reason for the preponderance of MRSA infection in persons of low socioeconomic status is unknown. The authors speculated that more MRSA carriers may live in socioeconomically deprived areas, or that people from these areas may be more susceptible to hospital infections. Twelve of the 23 patients with MRSA infections had been transferred from another hospital or department or had been admitted to the hospital in the six months before surgery.

The identification of a group at increased risk for postoperative MRSA could allow more careful monitoring and treatment to prevent complications in these patients.

Bagger JP, Zindrou D, Taylor KM. Postoperative infection with methicillin-resistant Staphylococcus aureus and socioeconomic background. Lancet. 2004; 363:706-708.

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