PEAK EXPIRATORY FLOW A POOR PREDICTOR OF SMALL AIRWAYS FUNCTION

Although peak expiratory flow (PEF) measurements are recommended as follow-up for patients with asthma, a recent study has determined that such measurements are not effective in predicting small airways obstruction in asthmatic children. The study compared this measurement with forced expiratory flow at 50% of vital capacity (FEF50).

Goldberg and coworkers put 111 asthmatic children into one of three categories, depending on whether their forced expiratory volume in one second (FEV1) was within normal range, mildly reduced, or moderately to severely reduced. All patients underwent lung function testing after refraining from bronchodilator use for at least six hours.

The researchers found an overall correlation between FEF50 and PEF, but in 42% of the patients there was a difference of more than 20% between actual FEF50 and that calculated through PEF measurements.

Surprisingly, PEF was best able to predict FEF50 in the patients with moderate to severe asthma. Among the patients with normal FEV1, the correlation between PEF and FEF50 had only borderline significance, and there was no correlation between the two variables among those with mild disease.

The variability in PEF’s accuracy in predicting FEF50 was sufficiently great that the researchers ruled out PEF as a reliable indicator of small airways obstruction. Thus, they recommend that home PEF monitoring be augmented by regular spirometric analysis.

The researchers acknowledge that to date no association has been established between FEF50 and the clinical status of asthma patients. Nevertheless, they believe that accurate assessment of small airways function will prove to have an important role in asthma management.

Goldberg S, Springer C, Avital A, et al. Can peak expiratory flow measurements estimate small airway function in asthmatic children? Chest. 2001;120:482-488.

ANTI-INFLAMMATORIES UNDERUSED BY INNER-CITY KIDS WITH ASTHMA

Because asthma is a major cause of morbidity in inner-city children, Warman et al attempted to determine how sociodemographics influenced asthma treatment in this population. They found that only about one third of inner-city children with asthma were receiving daily anti-inflammatory agents.

The study’s subjects were 219 children (ages 2 to 12 years) who had been hospitalized with asthma between January 1995 and September 1996. The researchers determined the subjects’ asthma severity by asking their caregivers about the frequency of nocturnal and daily symptoms during the preceding four weeks. The children were then classified according to 1997 National Asthma Education and Prevention Program (NAEPP) guidelines.

Overall, only 35% of the children were given anti-inflammatory agents on a regular basis. Even more alarming, the researchers found that although 83% of the children met NAEPP criteria for persistent asthma, just 39% of those with persistent asthma received anti-inflammatory therapy on a daily basis. Even among the children with moderate to severe asthma, anti-inflammatory treatment was often inadequate: Only 42% of them received these agents daily.

No sociodemographic factors were found to influence whether a child would receive anti-inflammatory medications. However, families with a primary care provider and those who knew how to reach their child’s physician were twice as likely as were other caregivers to report that their children were using daily anti-inflammatories.

Warman KL, Silver EJ, Stein REK. Asthma symptoms, morbidity, and antiinflammatory use in inner-city children. Pediatrics. 2001;108:277-282.

CPAP PLACEBO DEMONSTRATES THE TREATMENT’S EFFECTIVENESS

Continuous positive airway pressure (CPAP) is believed to be the best treatment for sleep apnea/hypopnea syndrome (SAHS), but until recently its efficacy had never been clearly proved. The development of a sham CPAP treatment as placebo allowed a randomized trial to demonstrate CPAP’s effectiveness in improving daytime function and SAHS-related symptoms.

Montserrat et al stratified 48 patients with moderate to severe SAHS into four groups according to the severity of their disease. These groups were then randomized to receive either optimal or sham CPAP for six weeks. The Epworth Sleepiness Scale (ESS), Functional Outcomes Sleep Questionnaire (FOSQ), and Short Form Health Survey were completed by all patients at inclusion and again by the 45 patients who completed follow-up. Ten days of washout followed, and the placebo group was reassessed before and after follow-up treatment with optimal CPAP.

The researchers found that FOSQ measures of vigilance, general productivity, relief of sleepiness, and other SAHS-related symptoms were better in the group receiving optimal CPAP than in the placebo cohort. Furthermore, the patients in the placebo group experienced improvement in ESS scores after subsequently being treated with optimal CPAP. The researchers concluded that CPAP was shown in this study to be effective in treating moderate to severe SAHS.

Montserrat JM, Ferrer M, Hernandez L, et al. Effectiveness of CPAP treatment in daytime function in sleep apnea syndrome. Am J Respir Crit Care Med. 2001;164:608-613.

S AUREUS OFTEN INFECTS CARDIAC DEVICES

Cardiac device infections caused by Staphylococcus aureus bacteremia (SAB) are surprisingly common, a recent study has shown. Chamis et al have also found that physical examination and echocardiography cannot be relied upon to rule out cardiac device infections.

Thirty-three patients with SAB and implanted cardiac devices were evaluated prospectively for a six-year period. SAB was considered to be clinically significant when more than one blood culture was positive for S aureus or if a single blood culture showed S aureus in a patient with clinical signs of infection.

The SAB cases were defined as early if they occurred less than one year after device implantation or its last alteration, or late if they occurred more than one year after those procedures.

The total incidence of cardiac device infections was 45.4%; no specific type of device appeared to be more commonly associated with infection. Confirmed cases of infection occurred more commonly in patients with early SAB than in those with late SAB (75% vs 28.5%, respectively).

The incidence of cardiac device infections hematogenously seeded from a distant or unknown primary infection site was 27.3%. Local signs of generator pocket infection were absent in 60% (9 of 15) of the patients with confirmed cardiac device infections, but generator pocket cultures found S aureus in five of these instances.

The researchers said that SAB posed great risks for patients with permanent pacemakers or implantable cardioverter-defibrillators, and that it should be suspected in all patients with SAB during the first year after implantation. They added that further studies were needed to identify other clinical characteristics that could be used to determine which bacteremic patients had infected cardiac devices.

Chamis AL, Peterson GE, Cabell CH, et al. Staphylococcus aureus bacteremia in patients with permanent pacemakers or implantable cardioverter-defibrillators. Circulation. 2001;104:1029-1033.

LOW VT EFFICACY DOES NOT CHANGE WITH RISK FACTORS

Low tidal volume (VT) ventilation—when compared with traditional mechanical ventilation—has been shown to reduce mortality by 22% in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Eisner et al found that the efficacy of a tidal volume of 6 mL/kg does not appear to be affected by clinical risk factors for ALI/ARDS.

The researchers evaluated the relative efficacy of low VT ventilation in 902 patients, all of whom had been drawn from ARDS Network randomized controlled trials and had different risk factors for ALI/ARDS. Of these, 473 had been treated with a low VT strategy; the other 429 patients had been given traditional ventilation.

The researchers found that clinical risk factors had a profound influence on the risk of death before discharge home; for example, this risk was 43% for patients with sepsis, 36% for patients with pneumonia, 37% for patients experiencing aspiration, and 11% for those with trauma. However, there was no evidence that the efficacy of low VT ventilation varied in any of these subgroups.

Nor was there any evidence of a difference in the efficacy of low VT ventilation among subgroups when the authors examined other study outcomes, such as the proportion of patients achieving unassisted breathing, the number of ventilator-free days, or the development of non-pulmonary organ failure.

Furthermore, reclassification of predisposing clinical risk factors as pulmonary versus non-pulmonary, or as infection-related versus non–infection-related had no appreciable effect on the results. Neither did controlling for demographic and clinical covariates.

This, the researchers concluded, provided ample evidence for implementation of low VT strategies in patients with ALI/ARDS.

Eisner MD, Thompson T, Hudson LD. Efficacy of low tidal volume ventilation in patients with different clinical risk factors for acute lung injury and the acute respiratory distress syndrome. Am J Respir Crit Care Med. 2001;164:231-236.

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