This small case series showed improvement in spirometry but not exercise capacity in a group of children with CF undertaking home IV antibiotic therapy. This is the first time that the effect of home IV antibiotic therapy on spirometry and exercise capacity has been reported in children. In contrast, a number of studies evaluating hospital-based IV antibiotic therapy in CF patients with varying disease severity have shown improvements in exercise capacity as measured by cycle ergometry,16
2-minute walking distance,17
3-minute step test performance,18
and the MST.15
In the current case series, the percentage improvement in MST distance was correlated with the percentage improvement in FEV1. However, it was not possible to predict the precise magnitude of improvement of the MST by the increase in FEV1 for an individual child. This could indicate that exercise capacity and spirometry, while related, are not dependent upon one another.
With only half of the children presented in this study showing improvement in MST distance, we would speculate that factors such as fatigue or reluctance of parents to allow children to participate in their normal physical activity for fear of disrupting the route of IV access may contribute to the exercise capacity outcomes seen. When receiving home IV therapy, fatigue associated with a full day at school, in addition to the demands of therapy in the home, may have contributed to a lack of improvement in mean exercise capacity. An additional consideration may be parental fatigue when accounting for work, daily family activities, and the responsibility of providing IV therapy, thus limiting available time to encourage and instigate physical activity participation.
It is difficult to determine how active the children were during the home-based treatment. Eight of the 10 children reported participation in some physical activity, such as school sport or outside games during home IV therapy; however, the intensity and duration of these activities was not recorded. Another consideration in participating in physical activity whilst undertaking home IV therapy is time of year, and thus ambient weather conditions. Inclement weather would naturally limit activity participation, and this may have coincided with the treatment period for some of our subjects. In contrast, in the studies of hospital based IV antibiotic treatment where exercise capacity was shown to increase, supervised inpatient exercise training was provided,16,20, 21
which may have contributed to the improvement. Any in-hospital training would occur in a temperature controlled environment. In future studies, activity monitors may be useful in assessing the impact of home IV antibiotic therapy on physical activity, and direct supervision of exercise may be required in order to optimize improvements in exercise capacity and control for factors in the home environment that may have led to a decline in performance in 4 of 10 children in this study.
In summary, this case series of 10 children with CF showed a significant improvement in spirometry, but inconsistent changes in exercise capacity, in response to a 14-day course of home IV antibiotic therapy. This would suggest factors in addition to lung health influence exercise capacity. Further studies are needed, with greater numbers of participants, to investigate the effect of home IV antibiotic therapy on exercise capacity. A randomized trial comparing home-based to hospital-based IV therapy in terms of exercise response, in addition to respiratory function, ideally controlled for exercise training during the IV period, would provide the best information to determine whether hospital-based and home-based treatment of CF exacerbations produce equivalent improvements in respiratory function and exercise capacity. The information presented in this case series may be of interest to therapists when preparing patients to undertake home IV therapy.