Anesthesiology, Article

Oxygen inhalation using an oxygen concentrator in a low-pressure environment outside of a hospital

Original Contribution

Oxygen inhalation using an oxygen concentrator in a low-pressure environment outside of a hospitalB

Hirokazu Sakaue MD, Takashi Suto MD, Masafumi Kimura MD, Sou Narahara MD, Tomonobu Sato MD, Masaru Tobe MD, Chizu Aso MD, Toshie Kakinuma BA, Makiko Hardy-Yamada MD, Shigeru Saito MD?

Department of Anesthesiology, Gunma University Graduate School of Medicine, Maebashi 371-8511, Japan

Received 22 October 2007; revised 6 December 2007; accepted 8 December 2007

Abstract Supplementation with oxygen is fundamental in rescue and emergency medicine. However, transportation of oxygen cylinders or a rigid Hyperbaric chamber requires large work forces. Also, oxygen in a cylinder may be completely consumed during a rescue action. The oxygen concentrators, which enrich the oxygen percentage of ambient air, may free rescuers from carrying heavy oxygen cylinders. In the present study, 2 types of oxygen concentrators were tested in a mountain hut located at an altitude of 3776 m. Oxygen concentration of the generated gas was 28.6% +- 0.8% with the first machine, which was powered by an internal battery. arterial oxygen saturation of the volunteers inhaling through the machine increased from the original 79% +- 6% to 82% +- 6%. When the machine was used with a semi-closed circuit, the value increased further to 90% +- 3%. The second concentrator, which was powered by an external electric generator, outputted 90% +- 2% oxygen. Arterial oxygen saturation of the volunteers increased to 95% +- 1%. It is concluded that both types of oxygen concentrators were efficient at High altitude.

(C) 2008

Introduction

Because of advances in transport technology, many travelers are now able to visit highlands or moderate altitude

? This work was supported by a grant-in-aid from the Japanese Ministry of Education and Science and by a research grant from Dentsu, Inc. The results of this study were partly presented in 2 local meetings (the 26th Annual Meeting of the Japan Society for Clinical Anesthesia and the 25th Annual Meeting of the Japanese Society of Mountain Medicine). The authors appreciate Mr Kazuhiro Sasaki (Teijin, Inc) and Mr Shaphan Hardy Yamada (English editor) for their contribution to this study.

* Corresponding author. Department of Anesthesiology, Gunma Uni-

versity Graduate School of Medicine, Maebashi 371-8511, Japan. Tel.: +81 027 220 8454; fax: +81 027 220 8473.

E-mail address: [email protected] (S. Saito).

areas without having had any special training or acclimatiza- tion. This trend has had a significant impact on the trends in alpine accidents. Recently, the Japanese National Police Agency announced that alpine accidents induced by bad physical status (neither by poor climbing techniques nor by natural disaster) were increasing year by year [1]. This phenomenon may be common in many developed countries, where trekkers include many older people and people with medical problems. Our previous study demonstrated that most trekkers in a nonchallenging middle-altitude mountain were older than 50 years and that almost half of the trekkers had some kind of preexisting medical problems [2]. In this Social environment, rescuers and doctors working in emergency medicine have more patients at high altitudes, that is, in hypobaric hypoxic circumstances.

0735-6757/$ – see front matter (C) 2008 doi:10.1016/j.ajem.2007.12.009

Fig. 1 A, Semi-closed respiratory circuit using the first oxygen concentrator. B, Assembled semi-closed circuit attached to a transportable oxygen concentrator.

oxygen supplementation is one of the fundamental treatments for victims of high-altitude accidents and sufferers of high-altitude disorders. However, transportation of oxygen cylinders or a rigid hyperbaric chamber requires large work forces. Also, oxygen in a cylinder may be completely consumed during a rescue action. Oxygen concentrators increase the oxygen percentage when the supplied gas goes through the machines. Use of oxygen

concentrators has expanded recently among patients with chronic Respiratory disorders [3]. As the source of concen- trated oxygen is ambient air, it cannot be emptied even after long use. Because of an expanding market, manufacturers have been refining the mechanics each year. The purpose of this study was to examine the performance of 2 conventional oxygen concentrators, one of which works with an internal battery, under hypobaric Hypoxic conditions. There has been no report yet regarding the use of transportable oxygen concentrators at high altitudes. We also examined the effect of a semi-closed respiratory circuit that enables operators to reuse expired gas that contains a relatively high concentra- tion of oxygen. Because the oxygen enriching performance of the transportable machine is still limited, this assessment was considered to be necessary.

Methods

Approval of the local human ethics committee and informed consent of the experimental subjects were obtained before this study.

Two transportable oxygen concentrators were tested in this study. The first machine (MS-X100, Matsushita, Kadoma, Osaka, Japan) was designed to concentrate oxygen in ambient air to 30%, and the output flow was set at 3 L/min at sea level. The weight of the machine was 3.8 kg, and it required 47 W of electric power. In this study, the machine was run on an internal battery (Fig. 1). The second oxygen concentrator (TO-90-3N, Teijin, Inc, Chiyoda, Tokyo, Japan) was designed to concentrate oxygen in ambient air to 90%, and the output flow was set at 3 L/min at sea level (Fig. 2). The weight of the machine was 33.0 kg, and it required 240 W of electric power. To deliver the power, the machine was connected to an external electric generator. In both cases, the concentration of the oxygen was measured at the outlet of each machine.

Fig. 2 High-performance oxygen concentrator powered by an electric power generator in a mountain hut.

For the assessment of the clinical efficiency of the 2 machines, 10 volunteers (5 men and 5 women; mean age, 38 +- 11 years; range, 28-55 years) used each machine at a high altitude site. When they used the first machine, they breathed with a simple facemask, which was attached by the manufacturer, or with a semi-closed respiration circuit composed of a tight facemask, soda lime chamber, 1-way valve, and reservoir bag (Fig. 1). When the volunteers assessed the second high-performance machine, they inhaled the oxygen-enriched gas with a regular nontight facemask, which was not connected to any respiratory circuit. In both cases, simple tube diameter adjustment devices were used for the connection. The interval between the use of each machine was set at 60 minutes for each subject.

All of the subjects were office workers with no habitual physical exercise regimen and none of the subjects had been exposed to an altitude higher than 2000 m within a year before the study. However, all of them had already experienced the same altitude several times more than 1 year ago, and they did not experience any difficulty in the trekkings. None of the subjects had any medical complica- tions, such as cardiovascular or pulmonary diseases. The subjects reached an altitude of 2100 m by car and ascended another 1356 m on foot, trekking for 4 hours without any weight load. The total time required for the ascent from sea level (1013 hPa) to 3750 m (647 hPa) was approximately 6 hours. All of the measurements were performed in wind- sealed constructions, and the temperature was maintained at 15?C. After arrival at the site, the subjects were permitted 2 hours of resting time before any experimental measure- ments. Before the measurement, the physical fitness of the subjects was evaluated using Acute mountain sickness score (no symptom, 0; extreme symptom, 23) in accordance with the Lake Louise agreement [4], and all were confirmed to be without symptoms.

Arterial blood oxygen was monitored using a portable life monitor (ProPack II, Protocol Systems, Inc, Beaverton, Ore). An SpO2 probe was set on the right index finger. During the measurement, the subjects were resting quietly in a sitting position and were advised to breathe normally. Values were obtained immediately before the use of the oxygen concentrator and at 10 minutes after starting to breathe oxygen with each system.

Results

When the first machine was used, the oxygen concentra- tion of the generated gas was 28.6% +- 0.8%. When the second high-performance oxygen concentrator was used, the oxygen concentration of the generated gas was 90% +- 2%. The manufacturers designed the output oxygen concentra- tions at sea level as approximately 30% and 92% +- 3 %, respectively. Both oxygen concentrators could output oxygen at 3 L/min in high-altitude conditions as designed

by their manufacturers. The performance did not change throughout the study period.

Arterial oxygen saturation before the use of the first oxygen concentrator was 79% +- 6% among the volunteers. The value during the use of the oxygen concentrator with a conventional facemask was 82% +- 6%; during the use of the machine with a semi-closed circuit it was 90% +- 3%, respectively. Arterial oxygen saturation before the use of the second oxygen concentrator was 78% +- 6% among the volunteers. The value during the use of the oxygen concentrator with a conventional facemask was 95% +- 1%.

Discussion

Regardless of the site of an accident, oxygen is essential for emergency treatment including resuscitation [5]. The gas is normally supplied in cylinders, which are both heavy and bulky to transport. This is an extremely serious problem when emergency action is necessary at high altitudes or in very remote areas that are difficult to access by motor vehicles. A portable oxygen concentrator that extracts O2 from the ambient atmosphere seems to be effective in such circumstances.

In many developed countries, the population of aged people is expanding and the number of patients who have lung disease is increasing yearly. Oxygen concentrators are now widely used among patients with chronic respiratory disease who need oxygen supplementation for daily life. Because of market expansion, the technology of oxygen concentrating systems has also been refined, making the units more reliable and compact [3].

The original method of onsite O2 concentration from ambient air became possible nearly 30 years ago, using either an oxygen enriching membrane or zeolite molecular sieve technology. Although its efficacy is rapidly improving, the membrane type can produce 40% O2, whereas the molecular sieve can produce up to 95% O2 depending on compression power. Synthetic zeolite consists of a rigid framework of silica and aluminum. The lifespan of the zeolite crystal is reported to be at least 20000 hours, and the unit requires relatively simple maintenance. Despite its relatively low performance, a membrane concentrator is light and requires little energy for activation. The machine that we used in the first study is really transportable and can be powered by its internal battery for 30 minutes.

In the previous report, Litch and Bishop [6] reported the use of an oxygen concentrator in a high-altitude area. Shrestha et al [7] reported the use of a machine in a remote hospital in Nepal. They also mentioned that altitude has no effect on the concentration of O2 produced. Although both of them used relatively classic machines that required a regular electric power supply, they concluded that the use of the oxygen concentrator had been reliable and satisfactory. This report further confirmed that molecular sieving with zeolite

or with oxygen enrichment membrane is not affected by ambient pressure where the machine is used. Probably, the size of the sieve solely affects the concentration of oxygen at the outlet.

In the present study, we first reported the use of a compact oxygen concentrator at high altitude. Although previous concentrators are also transportable, all of them require external electrical power supply and they are heavier than 30 kg. The weight of the machine used in the first study is only 3.8 kg and it requires no external energy sources. As the oxygen concentrating performance of the machine was relatively low, we also used a semi-closed respiratory circuit with soda lime in the system. With a semi-closed circuit, oxygen contained in the expired gas can be efficiently reused, and expired carbon dioxide can be absorbed via the soda-lime canister [8].

In our preliminary study at sea level, the machine outputted 30% oxygen at 3 L/min as designed by the manufacturer and the inspiratory oxygen concentration in the semi-closed circuit measured by a gas monitor set at an inspiratory port ahead of the face mask was 22% to 26% (average +- SD, 24.7 +- 1.5%; 4 male and 2 female volunteers’ age, height, and weight were 35 +- 6 years, 165 +- 6 cm, and 61 +- 12 kg, respectively). Because of this approximately 5% increase in the inhaling oxygen, the subject at high altitude showed higher arterial oxygen saturation during the use of the system. The users felt breathing difficulty when using the circuit. Maybe the difficulty was due to valve resistance and expiratory auto-PEEP effect, and/or inspiratory resistance because of an air leak in the circuit. When this system is applied for some diseased patients, this breathing difficulty might be a serious concern. Further improvement of the circuit, such as a sophisticated 1-way valve, will make the system more effective and comfortable for the users. Also, improvement of the oxygen enrichment membrane and compressor will make the system more potent and applicable for clinical uses.

By using the high-performance oxygen concentrator, subjects could inhale almost 90% oxygen at 3 L/min. This oxygen supply was enough for the subjects at 3700 m, and the arterial oxygen saturation among the subjects was 95% +-

1% without further devices. As the subjects could breath using a conventional facemask, they did not experience any resistance during breathing. As of now, where electrical energy supply is available, and where the weight, 33 kg, is not a concern, this high-performance system seems to be most suitable for medical treatment.

Measurement of SpO2 was not the primary purpose of this study. We measured the value to assess the biological efficiency of 2 machines. As SpO2 value can be affected by multiple factors of the users, other than the oxygen concentration of the inhaling gas, the value did not directly reflect the mechanical performance of oxygen concentrators. Also, as our volunteers used several systems sequentially, interval between the testing may not be enough to cancel a takeover effect of the earlier trial. However, the results of the present study suggested that oxygen concentrators used in this study might be efficient as sources of oxygen in some clinical settings.

References

  1. National Police Agency. Alpine accidents in 2000. Tokyo, Japan: Yama-to-Keikoku Press; 2001. p. 154.
  2. Saito S, Tobe K, Harada N, et al. Physical condition among middle altitude trekkers in an aging society. Am J Emerg Med 2002;20:291-4.
  3. Gould GA, Scott W, Hayhurst MD, Flenley DC. Technical and clinical assessment of oxygen concentrators. Thorax 1985;40:811-6.
  4. Roach RC, Bartsch P, Hackett PH, Oelz O. The Lake Louise acute mountain sickness scoring system. In: Sutton JR, Houston CS, Coates G, editors. Hypoxia and mountain medicine. Burlington (Vt): Queen City Printers; 1993. p. 272-4.
  5. Maroko PR, Radvany P, Braunwald E, Hale SL. Reduction of infarct size by oxygen inhalation following acute coronary occlusion. Circulation 1975;52:360-8.
  6. Litch JA, Bishop RA. Oxygen concentrators for the delivery of supplemental oxygen in remote high-altitude areas. Wilderness Environ Med 2000;11:189-91.
  7. Shrestha BM, Singh BB, Gautam MP, CHand MB. The oxygen concentrator is a suitable alternative to oxygen cylinders in Nepal. Can J Anaesth 2002;49:8-12.
  8. Saito S, Shimada H, Yamamori K. A transportable hyperbaric chamber with Soda Lime for the treatment of high altitude disorders. J Wild Med 1994;5:295-301.

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