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Canadian Journal of Anesthesia 49:297-301 (2002)
© Canadian Anesthesiologists' Society, 2002
Cardiothoracic Anesthesia, Respiration and Airway

The OxyArmTM – a new minimal contact oxygen delivery system for mouth or nose breathing

[Le nouveau système de distribution d'oxygène à contact minimal OxyArmTM pour la respiration buccale ou nasale]

Elizabeth Ling, BSc MD MSc Frcpc*, Lee McDonald, RN{dagger}, Tim R.J. Dinesen, PhD MBA{ddagger} and Donald DuVall, MD FRCPC§

* From the Departments of Anesthesia, McMaster University, Hamilton, Southmedic Inc.,
{dagger} Barrie, Dinesen Research Group,
{ddagger} Toronto, and the Royal Victoria Hospital,
§ Barrie, Ontario, Canada.

Dr. Elizabeth Ling, Assistant Clinical Professor, McMaster University, Department of Anesthesia, Hamilton Health Sciences, Hamilton General Site, 237 Barton Street East, Hamilton, Ontario L8L 2X2, Canada. Phone: 905-527-0271, ext. 46698; Fax: 905-577-8023; E-mail: linge{at}mcmaster.ca


   Abstract
TOP
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
Purpose: To describe the development and performance of a new minimal contact oxygen (O2) delivery system for both nasal and oral breathing, with capnographic capabilities.

Methods: The development and design challenges of the OxyArmTM (OA) prototype are described. The innovative design utilizes a headset with a semi-rigid boom and an O2 diffuser. The OA was compared to the Venturi mask in eight healthy adults after informed consent. Inspired O2 fractions were measured in the hypopharynx using continuous gas sampling at low to high O2 flow rates. Mean data were compared using two-tailed paired t tests with significance set at 0.05.

Results: The measured inspired O2 concentration was higher in the OA at 2 (26.3 ± 2.5 vs 23.3 ± 0.5, P <0.01) and 6 L•min–1 (33.5 ± 3.3 vs 28.8 ± 1.2, P <0.01) flow rates. At 12 L•min–1, the O2 concentration was less in the OA (39.2 ± 6.3 vs 46.0 ± 2.7, P <0.02). All subjects found both systems comfortable for the short duration of the study.

Conclusions: The OA delivered predictable concentrations of O2 over low to medium flow rates. This system is comfortable, easy to use, non-obtrusive, odorless, and latex-free. The ability to monitor capnography makes this device ideal for monitored anesthesia care or in other settings (intensive care) where monitoring of respiration is warranted. This device does not contact the face and thus may be ideal for pediatric patients and those on long-term home O2 therapy. Further clinical trials in these areas are warranted.


   Introduction
TOP
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
TREATMENT of respiratory insufficiency and postoperative hypoxemia most often necessitates supplemental oxygen (O2).1,2 O2 is most commonly administered to patients using a variety of different face masks and nasal cannulae. The performance of such devices is somewhat variable, particularly in terms of the inspired O2 concentration delivered to the patient. The standard O2 mask ensures supplementation of inspired air with O2 for mouth and nose breathing. However, some patients find these masks uncomfortable, claustrophobic and their speech is hindered. In those with borderline hypoventilation, dead space is increased.3 Routine mouth care, postoperative nausea and vomiting, and restlessness all lead to mask removal or displacement, resulting in no O2 delivery at all.4

Nasal cannula delivery systems lie in close proximity with mucous membranes. With dry O2 flow, this may lead to local irritation, infection and bleeding.3,5 Air embolism is a rare but described complication.6 Mouth breathing presents another underestimated problem with these devices, since O2 is not inhaled.7,8 This occurs when talking and while snoring during sleep.9 Nasal cannulae are less likely to be removed than face masks, although they are frequently dislodged.10

The OxyArmTM (OA) (Southmedic Inc., Barrie, Ontario, Canada), a new minimal contact open O2 delivery system, has been designed to overcome the problems of face masks and nasal cannulae. Capnography monitoring has also been incorporated into this novel device. We describe the development of this system and results of preliminary clinical studies.


   Materials and methods
TOP
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
The concept of an open O2 delivery system came from anecdotal evidence of open tubes fixed in proximity to the face.11 The headset design originated from adapting the headsets used in hands-free telecommunications device. Subsequent modification of the commercial headset allowed delivery of O2 through an open-ended tube. The first prototype of the OA included a tension band that traversed the top of the head (headset), O2 supply and carbon dioxide (CO2) sampling lines attached to an adjustable boom, and a diffuser consisting of both a "cup" and "pin" to deliver a premixed O2 plume and sample end-tidal CO2. The patented cup and pin consists of a plastic molded ‘pin’ centrally located in the diffuser cup (Figure 1Go).



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  		FIGURE 1 Cross-sectional drawing illustrating shape of the cup that houses the pin diffuser unique to the OxyArmTM.

 
Several design challenges led to the further development of the prototype. The headset went through various transformations after studying available headsets in the marketplace. Modifications were incorporated so the headset could rest either behind or on top of the head to allow for various patient positions. The final headset prototype fits around the back or the top of the patient's head, with arms resting on top of the ears (Figure 2Go). Positional stability of the headset and boom became an issue due to the weight of the O2 supply tubing. The design of the boom had to be flexible enough to allow for adjustments, but sufficiently rigid to stay in place. This was achieved by inserting a length of stainless steel wire through the lumen of the boom. This semi-rigid boom was designed to be either left-or-right-sided and also made adjustable so it could be shortened or lengthened to fit. The shape of the boom follows the contour of the cheek and rests out of the line of sight.



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  		FIGURE 2 Final prototype of the OxyArmTM in situ.

 
The requirements that impacted the design of the diffuser were the need to incorporate O2 delivery and CO2 sampling, without the patient feeling the O2 supply stream. Initial testing revealed that an open O2 hose continually blowing in the face was not well tolerated and also not effective at delivering O2. O2 needed to be focused and directed at the mouth and nose area. Various shapes of diffuser prototypes were initially constructed using dental molds, and their subsequent airflow properties studied. A variety of cup and pin configurations were tested for both O2 delivery efficacy and reproducibility of end-tidal CO2 waveforms. Utilizing computer simulated wind tunnel modeling, it was possible to understand and illustrate the open O2 flow dynamics from the diffuser. Thus computerized fluid dynamics were studied on the O2 plume at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario (Dr. H. Hangan, London, Ontario, Canada).

The three-dimensional geometry of the OA was reproduced in a computer simulation, based on an AutoCAD (computer-aided design) generated drawing. The geometry was meshed with a finite volume grid consisting of many independent cells. The momentum (Navier-Stokes), continuity and a passive scalar equation were solved for every cell in the domain. The result of this process was the calculation of velocities, pressures and O2 concentrations at every point in space inside and around the device. A standard -epsilon turbulence model was employed in the context of steady state simulations. Figure 3Go shows the O2 concentration profile at passive conditions, as calculated through the computer simulation. O2 diffuses out from the inlet and pin in the shape of a mushroom. During inspiration, the shape of the diffuser causes complex velocity vortexes to form, which forces O2 into a flame-like shape towards the face (Figure 4Go). This dynamic property of the diffuser is unique to the OA, concentrating O2 delivery during inspiration, and allowing sampling of CO2 during expiration.



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  		FIGURE 3 Oxygen (O2) mass fraction gradient of the OxyArmTM at 4 L•min–1 from computer simulated wind tunnel testing. O2 diffuses from the inlet region out from the pin like a mushroom cloud towards the face in passive conditions (no inspiration). The recuperator region is the concave area of the diffuser cup.

 


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  		FIGURE 4 Oxygen (O2) mass fraction gradient of the OxyArmTM at 4 L•min–1 with inspiration from computer simulated wind tunnel testing. The shape of the diffuser (recuperator region) causes velocity vortexes to develop which concentrate the flow of O2 from the pin into a flame-like shape towards the face.

 
Initial clinical testing compared inspired O2 concentrations in the hypopharynx with varying O2 flows between the OA prototype and the Venturi mask (AirlifeTM, Percento2 Mask, Allegiance) in healthy adults.

Oxygen concentrations in the hypopharynx
Eight healthy adults (ages 26–59 yr, ASA I) were studied after giving informed consent. Subjects were seated at rest under normal respiratory conditions. No instructions were given on breathing pattern. Subjects were shown how to use the OA once and no further feedback was provided. A sampling catheter was attached to a pediatric suction catheter (Baxter T64C, Chicago, Illinois, USA) and inserted nasally by an anesthesiologist to lie between 8–10 cm in the hypopharynx. The sampling catheter was connected to a multigas analyzer and recorder (Datex-Ohmeda AS/3) calibrated according to manufacturer's guidelines. Medical grade pure O2 was supplied to each subject at flow rates of 2, 4, 6, 8, 10, and 12 L•min–1 using the OA and the Venturi mask, in no predetermined order. In addition, the corresponding diluter jets were attached to the Venturi mask at the appropriate flow rate to provide O2 concentrations of 24, 28, 31, 35, 40, and 50%. Flow rates were determined by an O2 regulator needle valve (Western Medica XA-2831). At each stage, the concentration of inspired O2 was measured in the hypopharynx at least ten times over 90-sec intervals, after steady state inspired O2 and end-tidal CO2 concentrations had been reached.

Mean data and standard deviations were compared for the two delivery systems using two-tailed paired t tests with significance set at 0.05.


   Results
TOP
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
Oxygen concentration in the hypopharynx
The mean O2 concentrations and 95% confidence interval measured in the hypopharynx for each flow rate are presented in the Table. Both the OA and Venturi mask delivered acceptable O2 concentrations for clinical administration at low to medium flow rates. The measured O2 concentration in the hypopharynx using the OA was higher than with the Venturi mask at flow rates of two (26.3 ± 2.5 vs 23.3 ± 0.5, P=0.01) and 6 L•min–1 (33.5 ± 3.3 vs 28.8 ± 1.2, P=0.01). At a flow rate of 12 L•min–1, the OA delivered lower O2 concentrations as compared to the Venturi mask (39.2 ± 6.3 vs 46 ± 2.7, P=0.02). At all other flow rates, there was no difference between the two O2 delivery systems. All subjects found both systems comfortable for the short duration of the study period. Noise levels from the OA were perceived to be low and consistent at all flow rates.


   Discussion
TOP
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
Postanesthetic care units handle large volumes of patients each year, the majority requiring higher concentrations of inspired O2 to prevent postoperative hypoxemia. Evaluation of O2 delivery systems should be based on adequacy of O2 delivery, simplicity and ease of use, patient acceptability and compliance, and cost effectiveness. Traditional O2 masks and nasal cannulae are most commonly used, but both have disadvantages.3–10 The OA was designed primarily as a means of offering some advantages over the O2 mask and nasal cannula, while also incorporating end-tidal CO2 monitoring capabilities.

Compared to the Venturi mask, the OA delivered the same or a greater fraction of inspired O2 concentrations at flow rates from 2–10 L•min–1. At the highest flow rate of 12 L•min–1, the fraction of measured inspired O2 in the hypopharynx was less using the OA. However, delivery of O2 at this flow rate lies outside that of the conventional mask and one would likely consider using a rebreathing mask. It should be stated that this study was of a very preliminary nature with a small number of subjects. Nevertheless, the OA was well tolerated without any side effects, easy to adjust and simple to use.

The OA is a novel, minimal contact, open O2 delivery system and is well suited for either oral or nasal O2 delivery. The unique headset design with the baffled cup diffuser offers controlled delivery of variable concentrations of O2 in an unencumbered and comfortable way. It is simple to modulate the O2 concentration with the OA by adjusting the supply flow rate. To achieve this with the Venturi mask, matching combinations of diluter jets and flow rates must be changed.

The minimal contact design allows patients to talk comfortably, and routine nursing tasks may be accomplished without disturbing O2 delivery. Patient anxiety and claustrophobia may be reduced due to the lack of facial contact and unhindered line of sight. The entire system is odorless and latex-free. The OA received Food and Drug Administration approval in Canada in May 2000 and is currently pending a worldwide patent. It is currently available in 57 countries.

In further studies, use of the OA for long-term O2 therapy may prove beneficial. Compliance in these patients may be improved due to improved comfort, minimal contact, and the global acceptability of headsets giving it a non-medical appearance. Talking, eating and drinking may be permitted with uninterrupted O2 delivery. It may also prove to be an important alternative in the postoperative pediatric population, as some are intolerant of traditional O2 delivery systems. The ability of the OA to incorporate capnography may prove useful in the operating room during monitored anesthesia care. Future clinical trials are ongoing and will further define the clinical utility of the OA in these various settings.


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  		TABLE Oxygen concentrations measured in the hypopharynx using the OxyArmTM and the Venturi mask at incremental flow rates
 

   Acknowledgments
 
The authors wish to thank Dr. James Paul for statistical assistance and Dr. Sandy McDonald for his support in this project.


   Footnotes
 
Developmental work was carried out at Southmedic Inc., and clinical work at Dr. S. McDonald's office in Barrie, Ontario. Supported by a grant from Southmedic, Inc. of Barrie, Ontario, Canada.

Revision received November 16, 2001. Accepted for publication September 5, 2001.


   References
TOP
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 Stewart BN, Hood CI, Block AJ. Long-term results of continuous oxygen therapy at sea level. Chest 1975; 68: 486–92.[Abstract/Free Full Text]

2 Craig DB. Postoperative recovery of pulmonary function. Anesth Analg 1981; 60: 46–52.[Free Full Text]

3 Miller WF. Oxygen therapy, catheter, mask, hood and tent. Anesthesiology 1962; 23: 445–51.

4 Nolan KM, Baxter MK, Winyard JA, Roulson CJ, Goldhill DR. Video surveillance of oxygen administration by mask in postoperative patients. Br J Anaesth 1992; 69: 194–6.[Abstract/Free Full Text]

5 Hoffman LA, Dauber JH, Ferson PF, Openbrier DR, Zullo TG. Patient response to transtracheal oxygen delivery. Am Rev Respir Dis 1987; 135: 153–6.[Medline]

6 Merino-Angulo J, Perez de Diego I, Casas JM. Subcutaneous emphysema as a complication of oxygen therapy using nasal cannulas (Letter). N Engl J Med 1987; 316: 756.[Medline]

7 Camner P, Bakke B. Nose or mouth breathing? Environ Res 1980; 21: 394–8.[Medline]

8 Canet J, Sanchis J. Performance of a low flow O2 Venturi mask: diluting effects of the breathing pattern. Eur J Respir Dis 1984; 65: 68–73.[Medline]

9 Kauffmann F, Annesi I, Neukirch F, Oryszczyn MP, Alpérovitch A. The relation between snoring and smoking, body mass index, age, alcohol consumption and respiratory symptoms. Euro Respir J 1989; 2: 599–603.[Abstract]

10 Nolan KM, Winyard JA, Goldhill DR. Comparison of nasal cannulae with face mask for oxygen administration to postoperative patients. Br J Anaesth 1993; 70: 440–2.[Abstract/Free Full Text]

11 Kumar RM, Kabra SK, Singh M. Efficacy and acceptability of different modes of oxygen administration in children: implications for a community hospital. J Trop Pediatr 1997; 43: 47–9.[Abstract/Free Full Text]




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