All children for whom data are presented in this series had previously performed the MST as a measure of exercise capacity and were proficient in performing spirometry. Only results of those children who completed testing procedures (MST and spirometry) at the clinic within 48 hours of commencement and cessation of IV antibiotic therapy are presented in this report.

Antibiotic therapy most often consisted of two antibiotics that were prescribed based on the sensitivity patterns of bacteria obtained from sputum cultures. All children in the study sample isolated pseudomonas aeruginosa. Intravenous antibiotics were planned as a 14-day course, and airway clearance techniques were reviewed by a physiotherapist prior to commencement.

Five of the children demonstrated improvement in MST distance over the 14-day period. In these children, all had an increase in FEV₁ %predicted. Of the 5 children who had a decline in MST distance, one of these was by only 10m (or one shuttle) and as such could be considered an equivalent performance to their baseline effort. Interestingly, this child also showed no change in FEV₁ %predicted over the course of the treatment period. Of the 4 remaining children who had a decline in MST distance, only one of these children achieved an improvement in their FEV₁ %predicted, with the remaining 3 recording an FEV₁ either unchanged or within 3%predicted of their baseline measure.

The SRM for FEV₁ %predicted was 0.96 and for MST distance was 0.24. Guidelines for interpreting SRM¹⁴ indicate that values 0.80, 0.50, and 0.20 are considered highly, moderately, and slightly sensitive, respectively. Being standardized scores, the SRM for MST distance can be directly compared to the SRM for %predicted FEV₁. The SRM values showed FEV₁ %predicted to be highly responsive to home IV antibiotic therapy, while the SRM for MST distance showed only a small response to home IV antibiotic therapy.

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.