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Acute effects of supplemental oxygen therapy using different nasal cannulas on walking capacity in patients with idiopathic pulmonary fibrosis: a randomised crossover trial

Patients with idiopathic pulmonary fibrosis (IPF) and concurrent hypoxaemia should be treated with oxygen therapy [1]. Oxygen therapy is commonly given by conventional nasal cannulas (CNC), but can also be delivered by other less conventional cannulas such as the Oxymizer. The Oxymizer is a nasal cannula with an internal pendant reservoir incorporated in the lumen at the patient end which has the potential to provide increased oxygenation while using the same oxygen setting as one would with CNC [2].

The primary outcome was the change of endurance walking capacity measured by the ESWT. Secondary outcomes were S pO 2 , P tcCO 2 , heart rate (all measured via an ear lobe sensor; SenTec Switzerland; the monitor was carried in a bag by the investigator with the display not visible by participants), time to desaturation, breathing frequency (measured via pressure signal to a NoxT3; Nox Medical USA) and sensation of dyspnoea (10-point Borg-scale).
Each participant completed a short questionnaire with the investigator at the end of each ESWT. Participants were asked two questions to rate perceived comfort and suitability for use in the daily life of the nasal cannula on a standardised Likert scale. After all tests, participants were asked which nasal cannula they preferred. All questions are provided in table 1.
Data were analysed for outliers and for normality. A crossover design was used to analyse continuously distributed data to test for significant differences, possible period or carry-over effects. 95% confidence intervals were computed for means for treatment effects, i.e. difference of means. For the crossover, period and carry-over effect, the α-level was set to 5%. All statistical analyses in this report were performed by use of NCSS (NCSS 10, NCSS, LLC, Kaysville, UT).  At isotime (end of the shortest ESWT), S pO 2 was significantly higher, while heart rate and breathing rate were significantly lower when using the Oxymizer compared to CNC. Time until S pO 2 <90% and S pO 2 <80% were significantly shorter with CNC (table 1).
Overall, a significantly smaller number of participants desaturated (S pO 2 <90% and S pO 2 <80%) with the Oxymizer in comparison to CNC (table 1).
No statistical differences were seen for P tcCO 2 and dyspnoea levels between the Oxymizer and CNC.
A higher number of participants did not agree that the delivery of SOT by an Oxymizer was comfortable in comparison to a CNC. Further, more participants could not imagine wearing the Oxymizer during daily life (table 1). After all study-related measurements, 63.6% (n=14) of the participants prefer SOT with a CNC over the Oxymizer.
This study shows that in people with IPF using oxygen during exercise, the simple change from CNC to a nasal cannula incorporating an internal reservoir leads to a significantly improved walking capacity, higher oxygen saturation and is associated with a lower heart rate and breathing frequency.
Of the participants who walked longest with the Oxymizer, 56% (n=9) walked beyond the minimal important difference (MID) of 65 s for an ESWT [4]. With CNC, only one reached this MID. Previously published studies of the Oxymizer used cycling exercise and did not reach clinical significance [3,5]. In the Edvardsen study [3], participant pathologies were diverse and not specific to IPF. Further, in the Edvardsen [3] and the Gloeckl [5] study, cycle exercise was used which is not as demanding on oxygenation as walking and therefore could have limited improvements in exercise performance.
In line with these studies, the difference in oxygen saturation at ESWT isotime was significantly in favour of the Oxymizer (Δ=3.1%, 95% CI [1.4-4.9], p=0.001) preventing a decline in saturation in the range of that presented as a meaningful drop of 2-5% [6]. Additionally, a significantly smaller number of participants showed severe desaturations. In those participants who did desaturate during ESWTs while using the Oxymizer, time until S pO 2 dropped below 90% and below 85% was increased by 112% and 48%, respectively. This can be interpreted as an Oxymizer-related significant and potentially clinically relevant increase in oxygenation.
Even with longer walking duration and better oxygenation, however, only 36% of participants would prefer the Oxymizermainly due to the stiff, inflexible material of the cannula being uncomfortable, a fact that was already described in prior research [7][8][9].
There are some limitations to the current study: 1) it was not possible to blind the participants nor the investigator for the nasal cannulas; however, the statistician was blinded. 2) Due to a lack of data, a sample size estimation was performed based on previous studies using the Oxymizer. However, these studies were not in walking IPF patients. Ultimately, the primary endpoint effect was proven to be statistically significant and the risk of a false decision only limited by the significance level of 5%.
This study revealed that something simple like using better oxygen cannulas can result in significant and clinically relevant benefits like improving walking duration and oxygen saturation in patients with IPF. However, only a minority would prefer to use the Oxymizer due to the cannula being uncomfortable. This shows an unmet need of combining superior technical aspects with an adequate level of comfort for the optimal nasal cannula. Attention should be brought to oxygen providers that besides the traditional requirements like how to store, transport or generate medical gases, the interface between oxygen supply and patients is of great importance.