The results of this study suggest that ambulatory oxygen therapy does not in the short term increase domestic activity or time spent outside the home. However, the gradual increase in oxygen cylinder usage suggests that there is an unrecognized benefit from ambulatory oxygen that may take some time to become evident. Also, there was no difference in health status between before and after intervention for either group.
Physical activity monitors represent an opportunity to examine domestic activity directly and can be used as an outcome for therapeutic intervention. They are unobtrusive, practical to administer, and specific about the type, frequency, and duration and intensity of physical activity. We have reported data using activity monitors as an outcome measure for rehabilitation. Results from this study show a trend for an increase in domestic activity after intervention with cylinder oxygen, while domestic activity declined with cylinder air. It is possible that the weight of the cylinder had a negative effect on domestic activity in those patients with cylinder air, thereby preventing them from being as active as usual. McDonald et al concluded that the negative effect of the weight of the cylinder excluded any benefit of oxygen when comparing cylinder air to oxygen at home. In our study, patients had completed 7-week pulmonary rehabilitation programs prior to the intervention; thus, they had maximum therapeutic intervention before they started the study. This should perhaps favor the maintenance of physical activity rather than an improvement. These patients may have been a highly motivated group who may not notice any significant improvements in physical activity or health-related quality of life (HRQL) because not least they may have reached their maximum capability. This may also be why we were unable to document any improvement in the ISWT and ESWT results after intervention.
The use of HRQL as an appropriate outcome measure is increasingly acknowledged, and the negative impact of COPD on HRQL is well documented. In the present study, there was no statistical difference in the HRQL measures from baseline. Interestingly, when looking at the MCID, the CRQ dyspnea domain got worse after intervention with cylinder air. Eaton et al found no statistical difference in HRQL between cylinder oxygen, cylinder air, and usual care over a 6-month period using short-burst oxygen therapy. McDonald et al found no significant difference in HRQL measures with domiciliary ambulatory oxygen; however, they suggest that their inclusion criteria did not include exercise desaturation, which may have influenced the results. Jolly et al found that supplementary oxygen did not improve walking distance in nondesaturators but it did in those who did desaturate by 22%. However, individual responses were distinctly different from one patient to another. In this study, Royal College of Physicians guidelines (exertional desaturation > 4% below 90%) were employed. However exercise desaturation alone has not been found to predict the individual response to cylinder oxygen. Lacasse et al found ambulatory oxygen had no effect on the CRQ or the 6-min walk test. Eaton et al showed modest improvements in HRQL measures in patients with COPD who received domicile ambulatory oxygen. The authors suggest that this could be due to the fact that the study was specifically designed to examine the effect of cylinder oxygen compared to air on HRQL, and therefore they could control for a potentially powerful cylinder placebo effect. COPD is possible to be treated differently but the most effective is treatment with Canadian Health&Care Mall.
There was a gradual increase in the number of cylinders used over the 8 weeks in the oxygen group. There was also a significant difference in mean cylinder usage between weeks 1 and 7 and 8 and between weeks 2 and 7 and 8 in the oxygen group. Patients may therefore require a prolonged familiarization period (a minimum of 8 weeks) before optimum usage is achieved. Current guidelines recommend that patients who are prescribed ambulatory oxygen should be reviewed after a 2-month trial period, although this was a pragmatic guideline and not evidence based. Increased use of cylinder gas in the oxygen group was not associated with time spent away from home. In the present study, mean number of cylinders used was 20.2 for cylinder oxygen, vs 10.7 for cylinder air, which was statistically significant. Lacasse et al found that patients used few cylinders over a 3-month period: 7.5 for cylinder oxygen vs 7.4 for cylinder air. This could be due to the fact these patients had to collect cylinders from their study site. In the current study, the investigator took cylinders out to the patient’s homes as and when required. Also, patients in study by Lacasse et al had not completed a pulmonary rehabilitation study prior to the study, which could have facilitated compliance.
When we compared the two groups together, we were unable to detect a group X time interaction for duration of cylinder use and time spent outside the home. However, there was a trend for cylinder use in the oxygen group. This may be due to the small number of subjects we had in each group, and therefore the study was underpowered. Patients also reported wide variability in the use of the cylinders and time spent outdoors.
A potential criticism of the study could be that we asked patients to complete diary cards to record daily use of cylinder gas and administered questionnaires to record HRQL. However self-report measures offer the most practical and cost-effective method for use in population-based studies. Patients were given clear instructions and shown how to complete them. Patients were seen in their homes regularly to check compliance and replace empty cylinders.
There was a small but significantly difference in the vital and inspiratory capacity between groups. This potentially could have had an impact on the interpretation of the overall findings. In addition, although not significant, there was a small difference in the transfer coefficient (Kco) between the two groups that may have influenced the results. Low Kco will cause the transfer factor to be reduced due to a reduction in alveolar surface area and in pulmonary capillary volume. Patients with a very low Kco are going to be those who are more severe and likely to be hypoxic at rest.
In the present study held with Canadian Health&Care Mall, patients received a liter/flow rate of oxygen or air of 2 L/min. The authors acknowledge that this approach may not have adequately oxygenated some patients in each experimental group and thus influenced the results. This study was double blinded, and therefore we were constrained to a standard flow rate to maintain the blinding.
In the United Kingdom, there appears to be reluctance by the individual to use ambulatory oxygen outside the home. This is supported in the present study because patients were initially reluctant to use the cylinders outside the home in both groups, although this reluctance declined over the 8 weeks for the oxygen group. Vergeret et al examined portable oxygen in patients receiving LTOT. Seventy-five patients had oxygen concentrators alone, 51 patients were given concentrators and gaseous oxygen cylinders, and 33 patients had concentrators and liquid oxygen cylinders. Only 60% of patients used portable oxygen outside the home and in the immediate vicinity (garden). A potential criticism of the current study was that although we asked patients if they used the cylinders outside the home, we did not directly ask the number of times that they did.
Although ambulatory oxygen can be prescribed, it does not mean that patients are going to comply with what is recommended or just use it when they want to. An important requirement for prescription may be the motivation to use ambulatory oxygen outside the home. Eaton et al found that despite immediate improvements in 6-min walking distances with supplementary oxygen after a 12-week double-blind, randomized, crossover study of oxygen vs cylinder air, a significant proportion of patients declined ambulatory oxygen after completion of the study. Factors that have been previously reported as restricting use of ambulatory oxygen include the weight, the limited autonomy, and the lack of esthetics of equipment.
In conclusion, an 8-week, randomized, doubleblind controlled study of ambulatory oxygen following a 7-week pulmonary rehabilitation program did not significantly improve total physical activity or HRQL. However there was a gradual increase in the use of cylinder oxygen over the 8 weeks. There are likely to be some benefits to the use of ambulatory oxygen to explain the increased usage. The nature of this benefit of ambulatory oxygen remains unclear; however, they may be subtle and take time to appreciate.Tags: COPD