Abstract
BACKGROUND: The O2 Flow Regulator (Dima, Bologna, Italy) is a new automated oxygen regulator that titrates the oxygen flow based on a pulse-oximetry signal to maintain a target SpO2. We tested the device's safety and efficacy.
METHODS: We enrolled 18 subjects with chronic lung disease, exercise-induced desaturation, and on long-term oxygen therapy, in a randomized crossover study with 2 constant-work-load 15-min cycling exercise tests, starting with the patient's previously prescribed usual oxygen flow. In one test the oxygen flow was titrated manually by the respiratory therapist, and in the other test the oxygen flow was titrated by the O2 Flow Regulator, to maintain an SpO2 of 94%. We measured SpO2 throughout each test, the time spent by the respiratory therapist to set the device or to manually regulate the oxygen flow, and the total number of respiratory-therapist titration interventions during the trial.
RESULTS: There were no differences in symptoms or heart rate between the exercise tests. Compared to the respiratory-therapist-controlled tests, during the O2 Flow Regulator tests SpO2 was significantly higher (95 ± 2% vs 93 ± 3%, P = .04), significantly less time was spent below the target SpO2 (171 ± 187 s vs 340 ± 220 s, P < .001), and the O2 Flow Regulator tests required significantly less respiratory therapist time (5.6 ± 3.7 min vs 2.0 ± 0.1 min, P = .005).
CONCLUSIONS: The O2 Flow Regulator may be a safe and effective alternative to manual oxygen titration during exercise in hypoxic patients. It provided stable SpO2 and avoided desaturations in our subjects.
Introduction
Long-term oxygen therapy (LTOT) has been a standard treatment for patients with COPD and chronic respiratory failure since the 1970s, when it was found that LTOT can improve survival.1,2 Indications for LTOT are accepted worldwide, and international guidelines recommend LTOT if the patient's resting PaO2 is < 55 mm Hg, or 55–59 mm Hg if there is evidence of right-atrial enlargement, congestive heart failure, and high hematocrit (> 55%).3–5 There is overall agreement that a PaO2 > 60 mm Hg is the goal of LTOT, to enhance peripheral oxygenation.6,7 The indications for LTOT in patients with exercise-induced desaturation are still controversial. Some studies have found an SpO2 drop despite supplemental oxygen during mild exercise, sleep, and usual activities of daily living.8–10
Recent guidelines on pulmonary rehabilitation emphasize the importance of COPD patients, including those with chronic respiratory failure, maintaining an active life, and an exercise program for the muscles of ambulation is recommended as a main component of pulmonary rehabilitation.11
Different types of exercise produce different levels of desaturation,12–14 so the commonly prescribed fixed oxygen flow, which is usually titrated at rest, may not meet every patient's need. It would be preferable, therefore, to regulate the oxygen flow according to the patient's actual, changing need. A new automatic O2 flow-regulator device, the O2 Flow Regulator (Dima, Bologna, Italy, distributed by Vivisol, Monza, Italy) was recently released (Fig. 1). Its primary function is to titrate the oxygen flow rate based on a pulse-oximetry signal, to maintain a target SpO2.
O2 Flow Regulator, Dima, Bologna, Italy, which is currently only available in Italy.
We conducted a pilot randomized crossover study to evaluate the safety and efficacy of the O2 Flow Regulator, compared to usual manual oxygen flow titration.
Methods
Patients
We recruited 18 consecutive clinically stable COPD patients on LTOT from the patients attending a pulmonary rehabilitation program. The inclusion criteria were hypoxia at rest (PaO2 < 55 mm Hg on room air) and exercise-induced desaturation when using their usual prescribed oxygen flow. The usual oxygen flow is prescribed based on a mean SpO2 ≤ 88% during a 6-min walk test, and reassessment the next day during a 15-min constant-exercise cycle-ergometer test, at the same oxygen flow. We excluded patients who had chronic heart failure or any other cardiopathy, atrial fibrillation, neurological disease, or difficulty in cycling; who needed an O2 flow of > 6 L/min at rest; whose carboxyhemoglobin was > 4%; or whose methemoglobin was > 1%. This study was approved by the Comitato Etico Centrale of Fondazione Salvatore Maugeri, and we obtained written informed consent from each subject.
Study Design
The study was a randomized controlled crossover trial. In each subject, during 2 standardized 15-min cycling tests, we measured SpO2, respiratory therapist (RT) time (to set or adjust the devices), and the total number of RT interventions. On 2 consecutive days, each subject performed, in random order, and using the same oxygen source (portable liquid oxygen cylinder, filled and calibrated before every test, with a maximum flow rate of 6 L/min), the exercise test with an individualized stable work load that was selected on the basis of 2 previous exercise tests that determined the maximum exercise load the patient could sustain without needing to pause, while using their prescribed oxygen flow. During the tests the patients were monitored continuously with a 3-lead electrocardiogram and pulse oximetry (Pulsox-3iA, Konica Minolta Sensing, Ramsey, New Jersey) with a finger probe. A priori we chose a target SpO2 of 94%.15 The randomization order was decided with opaque sealed envelopes.
O2 Flow Regulator
The O2 Flow Regulator was developed to automatically titrate the O2 flow to maintain a constant SpO2 (Fig. 2). It is placed in line between an oxygen source and the user. Once the clinician sets the target SpO2, the device should be able to maintain it, increasing or decreasing the flow for any SpO2 variation above or below the target. A microprocessor continuously reads the SpO2 signal; if SpO2 is lower than the target, it rapidly opens the flow valve (2 L change over 30 s) to increase oxygen delivery. If SpO2 exceeds the target, the valve slowly closes (0.5 L change over 30 s) to reduce the flow.
O2 Flow Regulator response to SpO2 variation. At point 1, SpO2 is below the target SpO2, and the O2 Flow Regulator valve rapidly opens and increases the oxygen flow. At point 2 SpO2 is above the target SpO2 and the O2 Flow Regulator valve slowly closes and decreases the oxygen flow. At point 3 the SpO2 is at the target, so the O2 Flow Regulator maintains the current oxygen flow.
Protocol
Each subject performed 2 exercise tests: one in which the RT manually titrated the oxygen flow (the RT-controlled test), and one in which the O2 Flow Regulator titrated the oxygen flow (the O2 Flow Regulator test) under the supervision of the same RT. During the RT-controlled test, to simulate the behavior of the O2 Flow Regulator, the RT titrated the oxygen flow rate every one minute, as necessary to achieve the target SpO2, with the same flow-change rates as the O2 Flow Regulator.
We measured dyspnea and leg fatigue with the modified Borg scale, every minute. The oximeter calculated the mean SpO2 during the test and the time spent with SpO2 < 94%.
We counted the number of RT interventions (titrations) during the RT-controlled test. An observer naïve to the protocol used a stopwatch to measure the RT time during the RT-controlled test, and, during the O2 Flow Regulator test, to measure the RT time to set the O2 Flow Regulator (ie, set the target SpO2 and alarms, and check the battery and memory card).
Statistical Analysis
We used a paired t test to compare the data from the exercise tests. Data are presented as mean ± SD. A P < .05 was considered statistically significant.
Results
Table 1 shows the cohort's mean age, PaO2, PaCO2, pH, baseline SpO2, and nadir SpO2 during exercise. All the patients tolerated well the experimental procedures and completed both tests. There was no statistical differences in dyspnea, leg fatigue, heart rate, or oxygen saturation at rest between the RT-controlled tests and O2 Flow Regulator tests (Table 2). Dyspnea, leg fatigue, and heart rate increased similarly. Mean SpO2 was significantly higher during the O2 Flow Regulator tests (95 ± 2% vs 93 ± 3%, P = .04).
Age and Arterial Blood Values Before the Exercise Tests*
Symptoms, Mean SpO2, and Heart Rate, at Rest and During Exercise
Figure 3 shows typical SpO2 traces from a representative patient during both the RT-controlled test and the O2 Flow Regulator test. Figure 4 shows the amount of time the subjects spent below the target SpO2. Overall, the O2 Flow Regulator tests had significantly less time below the target SpO2 (171 ± 187 s vs 341 ± 220 s, P < .001). During the O2 Flow Regulator tests only 2 of the 18 subjects had SpO2 decrease to < 90%, and those desaturation periods were < 30 s.
Typical SpO2 traces from a representative patient during exercise tests in which the supplemental oxygen flow was manually titrated by the respiratory therapist (RT) or automatically titrated by the O2 Flow Regulator.
Time spent below the target SpO2 during exercise tests (in 18 subjects) in which the supplemental oxygen flow was manually titrated by the respiratory therapist (RT) or automatically titrated by the O2 Flow Regulator.
Figure 5 illustrates the number of manual titrations during the RT-controlled tests. The mean RT time was significantly greater in the RT-controlled tests (5.6 ± 3.7 min vs 2.0 ± 0.1 min, P = .005).
Number of manual oxygen-flow titrations during exercise tests (in 18 subjects) in which the oxygen flow was manually titrated by the respiratory therapist to maintain the target SpO2.
Discussion
The major international guidelines and position papers on prescription of LTOT are based either on resting or exertional SpO2, usually assessed during the 6-min walk test.3–16 However, at home some LTOT patients have severe desaturations during sleep or activities of daily living, that are not necessarily revealed during the 6-min walk test.17 This suggests that the oxygen flow should be constantly titrated. We found the O2 Flow Regulator safe and effective in meeting the target SpO2. The O2 Flow Regulator tests had significantly less time below the target SpO2. We chose our target SpO2 on the basis of a study that found that an SpO2 of ≥ 93% should be the objective during exercise in patients who desaturate during exercise.15
There are several reasons an in-line oxygen flow regulator may be useful in LTOT patients. First, studies have found that, when reevaluating patients' LTOT requirement after the initial prescription, many patients no longer meet the LTOT eligibility criteria or that they need to have the oxygen flow reduced, mostly because they were recovering from an exacerbation.18 The O2 Flow Regulator can decrease the oxygen flow to zero if the target SpO2 is being met without oxygen flow, which is particularly important in patients with hypercapnia, because increasing PaO2 in a patient with hypercapnic respiratory failure causes deleterious changes to alveolar ventilation and gas exchange, which worsens acidosis, and increases morbidity and mortality.19
Second, it has been suggested that long-term rehabilitation programs may be useful in COPD patients, with or without chronic respiratory failure.11 Among the various rehabilitation activities, high-intensity training is more effective in improving exercise capacity, and supplemental oxygen increases exercise ability, allowing higher exercise intensity, in COPD patients without resting hypoxemia who desaturate during exercise.20 This highlights the importance of oxygen flow titration for these patients during rehabilitation at home, especially considering that their clinical status may deteriorate.
Third, few studies have recorded SpO2 over a 24-hour period in COPD patients, either receiving LTOT or not, and both groups manifest severe desaturations during sleep and activities of daily living.8–10 Walking is usually associated with the lowest mean SpO2 and with the highest number of desaturations, which are particularly severe in some individuals. However, eating, washing, house-work, dressing, and even watching television are activities of daily living that are associated with frequent desaturations, in certain cases even worse than during walking. Some patients may spend > 30% of the day with SpO2 below 90%.8–10 These desaturation episodes are dangerous, because they may transiently increase the mean pulmonary arterial pressure, which may be one of the main causes of chronic pulmonary hypertension in COPD patients (ie, out of proportion) with otherwise moderate but not severe air-flow obstruction.21 Therefore, continuous oxygen flow titration is needed to avoid desaturations that cannot be predicted on the basis of a simple exercise test in the hospital.
Fourth, development or worsening of hypoxemia during sleep is well documented in COPD patients and is associated with cardiac arrhythmia and, eventually, pulmonary hypertension.22 Nocturnal desaturation also occurs in approximately a quarter of COPD patients with diurnal PaO2 > 60 mm Hg, and is not necessarily evaluated with nocturnal oximetry.23
Indeed, even in the case of this evaluation, the first step is to perform the examination without oxygen, and then to repeat it with oxygen. With the O2 Flow Regulator, both tests could be performed in one night, because if SpO2 remains above the target 90%, the O2 Flow Regulator will not deliver any oxygen, which could be eventually added in case of desaturation, as established by the algorithm. In this case important information will be available for the clinician to set the appropriate oxygen flow.
Last, as clearly illustrated in the present study, the O2 Flow Regulator may save RT time when an exercise program should be set for a COPD patient, and at the same time make the appropriate adjustments in the case a clinician is not present.
Limitations
Our selection of a 15-min constant-work-rate test may be criticized, but compared to the incremental maximal, symptom-limited testing induces more severe hypoxemia and therefore would have resulted in substantially fewer patients qualifying for LTOT.14 Cutaneous oxygen saturation measurement (ie, pulse oximetry) has several advantages in the estimation of arterial oxyhemoglobin, but also some disadvantages: it is less accurate than direct measurement of arterial blood, particularly in patients with carboxyhemoglobin > 4% or methemoglobin > 1%. However, we excluded such individuals.3 Also, the target SpO2 we chose (94%)15 may be considered too high in usual clinical practice, and a lower SpO2 may also be acceptable.
Conclusions
The O2 Flow Regulator safely and effectively titrated oxygen flow during a constant-work-load exercise test, and may save RT time during pulmonary rehabilitation exercise. We see potential for the O2 Flow Regulator in many daily life situations where the oxygen flow should be reduced or augmented. Safety and patient satisfaction with the O2 Flow Regulator need to be examined in a larger prospective study.
Footnotes
- Correspondence: Stefano Nava MD, Pneumologia e Terapia Intensiva Respiratoria, Policlinico Sant Orsola-Malpighi, via Massarenti n.9, Bologna 40138 Italy. E-mail: stefano.nava{at}aosp.bo.it.
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Ms Cirio has disclosed a relationship with Vivisol. Dr Nava has disclosed no conflicts of interest.
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See the Related Editorial on Page 536
- Copyright © 2011 by Daedalus Enterprises Inc.
References
