Abstract
BACKGROUND: Most patients on long-term oxygen therapy use stationary oxygen delivery systems. It is not uncommon for guidelines to instruct patients to use tubing lengths no longer than 19.68 ft (6 m) when using an oxygen concentrator and 49.21 ft (15 m) when using cylinders. However, these concepts are not based on sufficient evidence. Thus, our objective was to evaluate whether a 98.42-ft (30-m) tubing length affects oxygen flow and FIO2 delivery from 1 cylinder and 2 oxygen concentrators.
METHODS: The 3 oxygen delivery systems were randomly selected, and 1, 3, and 5 L/min flows and FIO2 were measured 5 times at each flow at the proximal and distal outlets of the tubing by a gas-flow analyzer. Paired Student t test was used to analyze the difference between flows and FIO2 at proximal and distal outlets of tubing length.
RESULTS: A total of 45 flows were measured between proximal and distal outlets of the 98.42-ft (30-m) tubing. Flows were similar for 1 and 3 L/min, but distal flow was higher than proximal flow at 5 L/min (5.57 × 5.14 L/min, P < .001). FIO2 was lower at distal than proximal outlet tubing at flows 1, 3, and 5 L/min, but the mean difference between measurements was less than 1%.
CONCLUSIONS: Tubing length of 98.42 ft (30 m) may be used by patients for home delivery oxygen with flows up to 5 L/min, as there were no important changes in flows or FIO2.
Introduction
Long-term oxygen therapy (LTOT) plays an important role in management of hypoxemic patients1,2 due to its benefits related to lung function,3 survival,4 pulmonary hypertension, and exercise.5 However, the effect of LTOT on quality of life remains controversial.6 Some studies have shown a reduced quality of life in patients under LTOT5,6 due to the excessive noise produced by the oxygen concentrators (OCs) and/or limitation of patient's mobility.7–9
Usually, the majority of patients on LTOT use stationary oxygen delivery systems (ODS) such as cylinders and OCs. It is not uncommon for oxygen providers and guidelines to instruct patients to use tubing lengths no longer than 19.68 ft (6 m) when using an OC and 49.21 ft (15 m) when using cylinders.10 This is the usual recommendation for tubing lengths in the literature.8,11
Despite the idea that longer tubing would cause reduction in flow and/or FIO2, we believe that health professionals, oxygen suppliers, and guidelines are establishing their concepts on insufficient evidence. As far as we are aware, only one study investigated the oxygen tubing length and output flows.11 The authors showed significant reduction in flow at 2 L/min for tubing length greater than 100 ft when using cylinders as an oxygen source and additional flow loss at greater tubing lengths (100–200 ft) with 3–5 L/min from an OC.11 However, FIO2 was not assessed in this study.
Further investigation would provide more evidence for adequate instructions to the patients. Thus, our objective was to evaluate whether 98.42-ft (30-m) tubing affects oxygen flow and FIO2 delivery from stationary cylinders and OCs.
QUICK LOOK
Current knowledge
Long-term oxygen therapy (LTOT) plays an important role in management of hypoxemic patients due to its benefits related to lung function, survival, pulmonary hypertension, and exercise. Quality of life may be reduced in patients under LTOT due to the excessive noise produced by the oxygen concentrators (OCs) and/or limitation of patient's mobility from stationary oxygen systems.
What this paper contributes to our knowledge
Tubing length of 98.42 ft (30 m) may be used by patients with home OCs and flows up to 5 L/min. Despite commonly held beliefs, longer tubing lengths had no clinically important changes in flows or oxygen purity.
Methods
This was an experimental study conducted at the Pulmonary Rehabilitation Center at Escola Paulista de Medicina, Federal University of São Paulo, São Paulo, Brazil with ODS. Three ODS were randomly selected to assess flows and oxygen concentration: 2 OCs (one by Respironics Millennium [Respironics, Murrysville, Pennsylvania] and the other by Invacare Platinum XL [Invacare, Elyria, Ohio]) and a 6 m3 stationary oxygen cylinder (White Martins, Danbury, Connecticut). One OC of each brand available in our division was randomly chosen; just 1 oxygen cylinder was evaluated, as there was only one brand available in our division at the period of the study.
Flow and FIO2 were measured at 1, 3, and 5 L/min by a gas flow analyzer (VT Plus, Fluke Biomedical, Everett, Washington) previously calibrated at zero flow and at FIO2 0.21 connected to the oxygen cylinder or the oxygen concentration (proximal flow and FIO2). Measurement was recorded after a 2-min period once flow stability was reached (Fig. 1A).
Scheme of flows and FIO2 measurements at proximal outlet (A) and distal outlet (B).
Then, a 98.42-ft (30-m) tubing length was connected to the oxygen cylinder or concentrator, and the same gas analyzer was now connected to the distal end of the tubing. In the same way, 2 min elapsed for stabilization of the flow, after which FIO2 and flow were recorded (distal FIO2 and flow; see Fig. 1B). Stability of the flows and FIO2 was defined as when these 2 parameters had reached steadiness for 20 s at the tubing outlet as read on the gas-flow analyzer graph. Reproducibility was tested at each flow 5 times in a random sequence.
Statistical Analysis
Measurements of oxygen flows and concentration were expressed as mean and standard deviation. Paired Student t test was used to analyze the difference between flow and FIO2 at proximal end and at 98.42 ft (30 m) tubing length (distal flow). The level of significance was set at P ≤ .05.
Results
A total of 45 flow measurements were performed: 15 measurements from each ODS. Flows measured were similar between proximal and distal outlets of the 98.42-ft (30-m) tubing at 1 and 3 L/m; distal flow was higher than proximal flow at 5 L/min (5.57 × 5.14 L/min, P < .001) (Fig. 2). When the ODS flows were individually evaluated, only the 5 L/min flow from the cylinder was significantly different, with distal flow higher than proximal flow (Table 1).
Mean values of proximal and distal tubing length flows. White bars represent proximal measured flows, and black bars represent distal tubing length measured flows. *P < .05.
Flows Values at 1, 3, and 5 L/min Measured at Proximal and Distal Tubing Length According to 3 Different Devices
A total of 45 FIO2 measurements were performed: 15 measurements from each ODS. The FIO2 at 1 and 5 L/min flows were significantly lower at the distal than proximal outlet tubing (Fig. 3). When the ODS FIO2 measurements were individually evaluated, the distal FIO2 was usually lower than the proximal outlet, but with a very small difference that may not have any clinical influence (Table 2).
Mean values of proximal and distal tubing length FIO2. White bars represent proximal measured FIO2, and black bars represent distal tubing length measured FIO2. *P < .05.
FIO2 Values at 1, 3, and 5 L/min Measured at Proximal and Distal Tubing Length Flow According to 3 Different Devices
Discussion
Inadequate instructions regarding length of oxygen tubing can greatly affect patients in their daily activities, LTOT compliance, and quality of life. A review highlighted factors influencing the compliance of patients using LTOT and emphasized novel strategies and interventions that may prove to be of significant benefit. The authors suggested that the use of a stationary OC or liquid oxygen with incorporated tubing up to 50 ft (15.24 m) in length, in conjunction with an additional small M-6 cylinder (2 kg, 4 h/use) or a small portable liquid reservoir (∼2 kg, 5 h/use) could be an ideal and complete home oxygen system.12 In our study, we observed that long tubing (30 m) should be safe for patient use, as no important difference was observed between proximal and distal measured flows, except at 5 L/min. In addition, the difference in FIO2 between proximal and distal outlets was less than 1% in all 3 ODS.
Most LTOT system providers and healthcare professionals rely on deficient data when managing oxygen-dependent patients. Moreover, there has been a historical belief that the length of the tubing could affect the oxygen flow in different ODS. Most guidelines still indicate that tubing up to 19.68 ft (6 m) should be used with OCs and 49.21 ft (15 m) with cylinders.10
Cullen and Koss11 recommended tubing lengths up to 200 ft (60.96 m) for flow up to 3 L/min or 100 ft (30.48 m) for 4–5 L/min for Invacare and similar OCs. The authors observed that the cylinder regulator/flow meter system suffered the greatest flow loss, with significant reductions in flow at 2 L/min for tubing lengths greater than 100 ft (30.48 m). The authors attributed the changes in flow to the individual oxygen system operational mechanism.
In the analysis of flow using 3 randomly selected ODS, we observed that there was no change in flow for 1 and 3 L/min and only a slight increase for 5 L/min flow comparing proximal and 30-m output flows. This is not expected, but there are 2 possible explanations. First, the flow analyzer has some variability (approximately 2% according to the manufacturer′s instructions manual); second, as we have observed previously,12 there is a normal flow variation in flow meters. For flow reading at the tubing distal end, the flow analyzer had to be disconnected from the proximal end and connected to the distal end and another 2 min elapsed, which may have introduced some flow variation. It is possible that the difference in flow seen may be accounted for by these 2 sources of variation. However, these differences in flow do not seem to have clinical importance, as the mean difference in FIO2 was less than 1%. Moreover, no difference in flow was seen when the tested flow was 1 L/min; a small difference of 0.03 L/min was seen at 3 L/min and approximately 0.4 L/min at 5 L/min. These variations are in keeping with our previous observation of flow meter variation as flow is increased12
Furthermore, Cullen and Koss11 consider as clinically important flow reductions ≥ 20%. Our results showed < 10% change in flow measurements, and are therefore considered not clinically important if we use the same criteria.11 It is important to point out that the ODS used in this study were verified by the manufacturer and considered adequate for the study.
To our knowledge, no other study has verified the FIO2 output in tubing length up to 98.42 ft (30 m). Despite the statistical difference observed between proximal and distal FIO2 measurements in all 3 ODS, the maximal difference between them was less than 1%, which may not influence the clinical treatment. This is also an important finding, considering the historical belief that the length of the tubing may also affect the FIO2.
Finally, we chose to analyze 98.42-ft (30-m) tubing, because this seems to be a length that could fit most of the patient's homes on LTOT with the studied ODS. This length should be enough to provide them with more freedom of movement within the home. In conclusion, tubing length at 98.42 ft (30 m) may be used by patients for home delivery oxygen with no important changes in flow or FIO2. Further studies, especially clinical ones, should be done to support these findings.
Footnotes
- Correspondence: Josy Davidson PT PhD, Rua Botucatu, 740, 3° andar, Pneumologia (Respiratory Division), Departament of Medicine, Escola Paulista de Medicina, Federal University of São Paulo, São Paulo 04039-002, Brazil. E-mail: josydavidson{at}yahoo.com.br.
The authors have disclosed no conflicts of interest.
- Copyright © 2015 by Daedalus Enterprises
