Oxygen conserving devices and methodologies

Transcription

1 Chronic Respiratory Disease 2008; 5: REVIEW ARTICLE B Tiep 1,2,3 and R Carter 4,5 1 Respiratory Disease Management Institute, Monrovia, California, USA; 2 Director of Pulmonary Rehabilitation, City of Hope National Cancer Center, Duarte, California, USA; 3 Associate Professor Medicine, Western University of Health Sciences, Pomona, California, USA; 4 HESS Exercise Sciences Center, Texas Tech University, Lubbock, Texas, USA; and 5 Adjunct Professor, Physiology Texas Tech Health Sciences Center, Lubbock, Texas, USA Collective experience with pulmonary rehabilitation and disease management has shown that patients with lung diseases including COPD and restrictive lung diseases live a longer and more productive quality of life if they can remain active. Patients who require oxygen supplementation but can otherwise be active should have the most portable and non-encumbering systems possible. Oxygen conserving devices have made a high level of portability possible. Small gas, liquid and even some concentrators have replaced the 20 pound E cylinder with 4 and 5 pound systems. In a parallel physiological development, exercise plus oxygen increases the physiological benefits of exercise and thereby enhances the patient s ability to function in life. This paper examines available options and their mechanical and physiological foundations. Chronic Respiratory Disease 2008; 5: Key words: oxygen conserving devices; exercise; nocturnal; therapeutic oxygen; transtracheal; reservoir cannula; long term oxygen; demand oxygen delivery devices; chronic obstructive pulmonary disease Patients with chronic obstructive pulmonary disease and restrictive lung disease endure a slowly progressive illness that eventually impedes their ability to gather sufficient oxygen to support their metabolic processes. Typically, the earliest indication of inadequate gas exchange is dyspnea and oxygen desaturation during exertion. At this point, the patient is usually capable of returning to an active life-style if provided supplementary oxygen and pulmonary rehabilitation. However, it is difficult to be active if they are weighed down by a 20-plus pound E-cylinder oxygen system. Activity, particularly endurance building exercise, and oxygen are mutually therapeutic in improving quality and length of life and for patients with chronic lung disease. Oxygen is essential for cellular metabolism and exercise maximizes oxygen transport to the cells. Oxygen therapy for patients with hypoxemia improves survival 1,2 and reduces the frequency of exacerbations. Exercise, particularly in pulmonary rehabilitation, enables an active life-style, reduces dyspnea, and decreases the frequency of exacerbations. Because exacerbations Correspondence to: Brian L Tiep, Respiratory Disease Management Institute, Monrovia, California, USA. btiep@respiratory-institute.com often lead to disease progression and disability, exercise may alter the trajectory to disability. Both oxygen therapy and exercise, individually and in concert, minimize pulmonary hyperinflation a major limitation to exercise and maintenance of an active life-style. Conceptually, oxygen is more than replacement/supplementation, it is a therapeutic enabler for active living. Creating an active life-style is the standard of care for lung disease patients, 3 and for those who are hypoxemic, their oxygen systems must be lightweight and very portable. In the 1980s, oxygen conserving devices were introduced to improve the efficiency of oxygen delivery several-fold so that lighter systems became practical. 4 With the advent of portable oxygen concentrators and concentrators that refill portable systems, patients have a wide variety of options for both supplemental oxygen and oxygen as a therapeutic adjunct to exercise training. Continuous flow oxygen delivery Continuous flow dual prong nasal cannulas are common and effective means for delivering oxygen to most chronic lung disease patients both in the hospital and in the home setting. They predate the SAGE Publications 2008 Los Angeles, London, New Delhi and Singapore /

2 110 Figure 1 FiO 2 achievable by various continuous flow settings. oxygen conserving devices and served as the standard of comparison for the development of more efficient delivery devices. They are small and comfortable and are well tolerated by most patients. It is important to remember that oxygen being delivered via the nasal cannula consists of a low flow of pure oxygen in a much higher inspiratory flow of atmospheric air (20.9% oxygen). Each 1 L/min increase in oxygen delivery raises the oxygen concentration approximately 3.5%. Thus, 1 L/min increases the FiO 2 to 24%; 2 L/min increases it to 28% and so forth 4 (Figure 1). This relationship varies depending on anatomical diversity, breathing patterns, and nasal dominance. The greatest drawback of continuous flow delivery is that it is highly inefficient. Upon examining the volume/time cycle of respiration, it becomes clear that effective oxygen delivery occurs only during a short time window of opportunity. In a 450-ml inspiration and an I:E ratio of 1:2, the last 2/3 of the cycle is exhalation. Of the 1/3 cycle devoted to inhalation, the last 1/2 of that period is devoted to dead space inhalation (last 150 ml = dead space requiring about 1/2 inspiratory time) and will not reach the alveoli to participate in gas exchange. Considering the fact that there may be some dwell time between breaths, the window of opportunity to effectively deliver oxygen to the alveoli is as little as the first 1/6 to 1/7 of the ventilatory cycle. In order to maximize the efficiency of oxygen delivery for the most effective arterial oxygen, the device must focus oxygen delivery at the beginning of inhalation. That is the aim of the oxygen conserving devices that follow. In a previous study, Tiep, et al. 5 found that a delivery delay of 164 ms resulted in a lower oxygen saturation. By progressively shortening the delay, arterial oxygen saturation was significantly improved (Figure 2). Efficacy of various devices The efficacy of oxygen conserving systems is expressed as the ratio of oxygen flow required by continuous flow delivery to the flow required by the conserver to achieve equivalent oxygen saturation (Figure 3). Figure 2 Effect of earlier oxygen pulse deliveries after the beginning of inhalation. Figure 3 Longevity of oxygen cylinders when coupled with oxygen conserving devices of various efficiencies. Chronic Respiratory Disease

3 111 Efficiency ¼ ½O 2ðmL=minÞ required via continuous flowš ½O 2 ðml=minþ required via conserving deviceš Oxygen conserving devices Oxygen conserving devices are designed to improve the efficiency of oxygen therapy by synchronizing delivery to the patient s initiation of inhalation. There are three major categories of oxygen conserving devices: Reservoir cannulas. Demand pulse devices. Transtracheal oxygen catheters. Although it is possible to combine the benefits of two or more of these systems, it is useful to consider each category of devices separately for clarity. Reservoir cannulas Reservoir cannulas were the first devices to become available and utilized on a widespread basis. While the use of these devices in the home setting has given way to demand pulse devices, they are important as they provide another option for effectively and efficiently delivering oxygen to ambulatory patients particularly those with higher flow requirements. Reservoir cannulas store oxygen during exhalation making available a bolus of concentrated oxygen for delivery during the early portion of the following inhalation. 6,7 They are available in two configurations: mustache (Oxymizer ) and pendant (Oxymizer Pendant ). Their structure is different and they function via different mechanisms. The mustache cannula utilizes a storage mechanism under the nose. The patient inhales and exhales through the cannula, while oxygen is flowing into the cannula. The mustache cannula is a reservoir cannula with a pliable membrane separating each side. When the patient exhales the membrane pushes forward, creating a chamber that accommodates ml of enriched oxygen. Upon the ensuing inhalation, the patient inhales oxygenated air from the chamber in addition to the continuously supplied flow. As a result the oxygen setting may be lowered to 1/2 to 1/4 the original continuous flow setting while achieving equivalent arterial oxygenation. The Pendant involves fluidic technology. It is constructed of a reservoir that rests against the anterior chest wall of the patient. It has a storage chamber. The oxygen enters the chamber as a jet that either directs to the cannula tubing and on to the patient or the back pressure of the tubing deflects the oxygen flow into the chamber. It functions as a no-moving-parts switch that stores oxygen during exhalation, which is then delivered during the following inhalation in addition to the ongoing oxygen supply flow. Again, the oxygen flow may be lowered to 1/2 to 1/4 the continuous flow counterpart, while achieving equivalent arterial oxygenation. Both reservoir cannulas are simple, reliable, inexpensive, and disposable. They operate in response to the patient s nasal airflow. While the efficacy of both cannulas is similar, there are differences in design that affect patient preference: The Oxymizer tends to be more comfortable than the Pendant and, in some cases, the standard nasal cannula. However, it is noticeable on the face, causing some patients to refuse to wear it. The Pendant is less noticeable. Previous Pendant configurations utilized ear loops and wide tubing that some found to be uncomfortable. The present fluidically controlled configuration has thinner tubing and no ear loops. A major advantage of the reservoir cannula is that it can be utilized for patients with high flow oxygen requirements. Few studies are available on this use but experience in the field, as well as, personal experience indicates that nasal oxygen via the Oxymizer is at times more effective in maintaining oxygenation than a face mask. 8 Additionally, patients can be active and eat meals while receiving oxygen. Demand pulse devices Demand devices deliver a pulse of oxygen to the patient only during the first part of inhalation. 9 The system consists of an inspiratory pressure sensor and valve interposed between the pressurized oxygen source and the nasal cannula. These devices function by sensing the beginning of inhalation through the cannula and immediately delivering a pulse of oxygen. Some devices are simply switches that enable oxygen to flow at their specific settings during the opportune window, while other devices deliver a quick pulse of high-flow oxygen during a short time window. Some devices are high precision electronic modules that sense and deliver a rapid early-inspiratory oxygen pulse. Other devices are pneumatically triggered and do not involve electronics. Though the pneumatic devices are not as

4 112 efficient, they are less expensive and tend to weigh less because they do not require a battery. However, oxygen cylinders will not last as long between refills. Some of the pneumatic devices require a specialized oxygen cannula that senses inspiration through one port and delivers oxygen through the other port. These cannulas tend to be a little more expensive. Other pneumatic devices are able to accomplish both sensing and delivery through a single port. Electronic and pneumatic demand devices vary in efficiency between devices. Some respond slowly and thereby fail to meet patient oxygenation requirements during exertion where conditions for oxygenation are less lenient. 10 These devices utilize different protocols and programming formats depending on the intent of the designer. Settings for oxygen delivery are adjusted on some devices by varying the length of the oxygen pulse. Other devices deliver an early pulse each time they discharge, thus avoiding lengthening of the pulse into the dead space portion of inhalation. This leads to higher efficiency, but a sharper sounding pulse for the higher settings. Demand conservers vary in efficacy gain from twofold to sevenfold compared with continuous flow delivery (Figure 2). Their batteries may last from 3 h to 3 weeks, depending on the delivery protocol. Some devices have a feature which automatically reverts to continuous flow if they fail to detect a breath in s, but this feature uses more battery current. The demand devices can be very efficient but are mechanically complex, therefore device failure is possible. Pulsing devices can be coupled with transtracheal catheters to combine the advantages of highly efficient inspiratory oxygen delivery and cosmetic acceptability with high efficacy. 5 One potential problem with some pulsing devices is their inability to adequately oxygenate some patients during exertion or high demand states. Modifying the device to deliver a larger pulse during the earliest part of inhalation or use of a higher oxygen delivery setting can prevent this limitation. 11 It is always advisable to test each patient during rest and exertion to assure adequate saturation while using the device prescribed. Adaptive demand systems One of the more recent developments in pulse demand delivery are devices that therapeutically adapt to the patient s activity requirements. One such device incorporates an activity sensor that automatically adjusts to the exercise setting and remains at that setting for 50 s following the discontinuation of activity. 12 Such devices not only conserve oxygen, but also respond to meet the higher energy requirements during exertion. These devices strive to eliminate periodic desaturations brought on by increased demands of movement. Consequently, these devices may be therapeutic beyond simple oxygen supplementation by minimizing desaturation responses. Pulsing devices are available as stand alone modules or integrated into a liquid oxygen system, compressed gas system, or coupled to portable oxygen concentrators. By integrating the delivery device with the oxygen source, it is possible to maximize the advantages of both devices. Liquid oxygen offers highly efficient oxygen storage. For example, 1 L liquid oxygen provides nearly 1000 L gas oxygen. Thus, high storage and minimization of delivery will extend the life of oxygen delivery and make it possible for patients to remain away from their transfilling for longer periods of time. A portable oxygen concentrator runs on battery, or can be used with a DC (cars, boats, motor homes, etc.) or an AC source. Portable concentrators that can operate at lower flow settings will extend battery life and by coupling conserving devices to the portable concentrator patients realize improved portability with optimization of oxygen delivery. 13 Transtracheal catheters Transtracheal catheters were first introduced by Dr. Henry Heimlich to improve both the efficiency and cosmetic acceptability of oxygen therapy. 14 The transtracheal catheter is inserted directly into the trachea through a small puncture in the anterior neck. The catheter is directed towards the carina. Oxygen flowing into the lower trachea bypasses considerable dead space of the nose, pharynx, and upper trachea during inhalation. Because the oxygen flows continuously during the respiratory cycle, oxygen is stored in the patient s anatomic air space at the end of exhalation. Upon the ensuing inhalation, the stored oxygen is available for immediate delivery to the alveoli. Consequently, transtracheal oxygen storage in the upper airways functions similarly to a reservoir cannula and with a reduced dead space for ventilation. The improvement in efficiency is 3:1 over continuous flow, which is again similar to a reservoir cannula. 15 Transtracheal catheters have been studied under a variety of conditions and are effective during rest, exercise, and sleep. 16 Furthermore, they are effective in patients Chronic Respiratory Disease

5 113 with obstructive and restrictive lung diseases and differ with respect to the rate and depth of respiration for each disease process. The major cosmetic advantage of transtracheal delivery is its removal of tubing from the face. Consistently, many patients find transtracheal delivery to be more comfortable than nasal cannula delivery, because it avoids chafing on the ears and nose and can also be concealed from view. Higher flow transtracheal oxygen delivery reduces minute ventilation and work of breathing. The effect of reducing the work of breathing is slower respiratory rate and less hyperinflation for the same activity level. Christopher, et al reported the successful reversal of refractory hypoxemia in eight patients requiring >40% oxygen via transtracheal L/min. There are studies that address the possibility that high flow transtracheal insufflation can be utilized in patients with obstructive sleep apnea. Moreover, transtracheal augmentation is being investigated as an alternative to noninvasive ventilation. 18 Transtracheal catheters must be introduced surgically and complications, although rare, are possible. Transtracheal catheter insertion is a relatively minor surgical procedure and should only be performed by those clinicians trained and experienced in the technique. A more complicated surgical procedure enables the epithelialization of the stoma for ease of placement and care. The earliest transtracheal catheter was the Heimlich Microtrach while the SCOOP catheter (a system of catheters) became available and utilized on a more widespread basis. The SCOOP system provided training for both the patient and clinician via personal instruction and a series of videotapes. Thus, the educational system advanced an understanding of the placement and care of the catheter and assisted the patient and other care-givers with routine care. Some studies 19 demonstrate a reduction in hospitalization utilizing transtracheal oxygen therapy. Moreover, patient compliance or adherence to oxygen appears greater with transtracheal delivery. The most common complication of transtracheal oxygen delivery is the formation of mucous balls at the tip of the catheter. These are generally easily managed, however, an occasional serious mucous plug has occurred. As with all oxygen therapy, the patient and family should be trained in the use of the equipment and be vigilant for problems that may arise. This is especially true for patients receiving their oxygen via transtracheal catheters. Patients must be taught to clean the site at least twice daily to maintain patency and to prevent infection. Oxygen supply Oxygen is supplied as compressed gas, liquid oxygen, or concentrator. Each oxygen source has its advantages and disadvantages. Compressed gas is available in cylinders pressured typically to psi. Oxygen cylinders are relatively inexpensive, come in a wide variety of sizes, are constructed using several different materials of varying weights, and may be stored easily. They do not have any power requirements and lend to a portable cylinder oxygen conserving device configuration can weigh as little as 4.5 lb. Liquid oxygen is supercooled to nearly absolute zero to maintain oxygen in its liquid state. Its greatest advantages are its ability to be stored in large volumes of oxygen in small lightweight containers as well as its ability to transfill from large stationary reservoirs to the portable system. Some portable liquid systems are constructed to include an integrated oxygen conserving device; these systems weigh as little as 3.5 lb. Liquid oxygen is more expensive than compressed gas, requires venting to room air to avoid vessel rupture, and if not used, the stored oxygen will eventually vent off into the atmosphere. Oxygen concentrators are electrically powered devices that extract oxygen directly from the atmosphere and thus provide an endless source of enriched oxygen. These concentrators provide the least expensive source of stationary oxygen. Specialized oxygen concentrators have become available that refill portable gas cylinders, and thus provide the best of both systems. The most recent development in oxygen therapy is the battery powered portable oxygen concentrator. It is much lighter and more compact than the stationary plug-in console. However, it is heavier and more expensive than other portable options. Its greatest advantage is for travel; some airlines allow portable concentrators on board. Thus, patients can travel by car, rail, boat, or air with their portable concentrator, and the utility of the concentrator is maximized with a DC or AC converter. Choosing the right oxygen conserving device When choosing the most appropriate oxygen conserving device or even whether to prescribe one, it is first important to consider the individual needs of

6 114 each patient. Each oxygen conserving device has advantages and drawbacks inherent to its design criteria and philosophy. 3 Otherwise stated, oxygen therapeutic devices encompass a series of tradeoffs and the choice of one device over another often represents a compromise. Reservoir cannulas are simple, inexpensive and reliable, but they are often considered obtrusive. Pulse demand devices are potentially most efficient and widely manufactured, but they may trigger late or even fail to trigger release of oxygen. Transtracheal catheters improve on cosmetics and comfort, but require a minor surgical procedure and substantial patient training and care to ensure ongoing patency of the cannula and prevention of complications. The future Our hopes and dreams for a better quality of life for our patients, along with a more thorough understanding of cardio-respiratory physiology, will guide future developments for oxygen delivery devices. Oxygen containers and storage devices are becoming smaller and lighter while demand pulsing devices are evolving into more efficient and lighter configurations. Motion sensing systems that adjust to the patient s varying activity levels are able to minimize the patient s desaturation responses to exertion. This is a first step to truly adaptive oxygen delivery systems. Portable oxygen concentrators will likely become even smaller, lighter and their battery life will continue to lengthen due to better battery designs and increased operational efficiency. In a noteworthy parallel development, oxygen and exercise are known to be adjunctive partners in optimizing exercise physiology. It is possible and even likely that specific exercise and breathing retraining programs will soon be developed that will enable patients to improve ventilation, oxygen delivery, and even obviate the need for supplemental oxygen in some patients. Pursed lips breathing already serves part of this function. Our efforts for the long term should be focused on circumventing the entire problem by creating a smoke free society and ridding the world of this lethal addiction. Presently, we will maximize technologies and interventional strategies for those already afflicted. References 1 Report of the Medical Research Council Working Party. Longterm domiciliary oxygen therapy in chronic hypoxic cor pulmonale complicating chronic bronchitis and emphysema. Lancet 1981; 1: Kvale, PA, Cuggell, DW, Anthonisen, NR, Timms, RM, Petty, TL, Boylen, CT. Nocturnal Oxygen Therapy Trial Group. Continuous or nocturnal oxygen therapy in hypoxemic chronic obstructive lung disease. Ann Intern Med 1980; 93: American Thoracic Society/European Respiratory Society Task Force. Standards for the Diagnosis and Management of Patients with COPD [Internet]. Version 1.2. New York: American Thoracic Society; [updated ]. 4 Tiep, BL. Continuous flow oxygen therapy and basis for improving the efficiency of oxygen delivery. In: Tiep, BL, (ed), Portable oxygen therapy: including oxygen conserving methodology. Mt Kisco, New York: Futura Publishing; Tiep, BL, Christopher, KL, Spofford, BT, Goodman, JR, Worley, PD, Macy, SL. Pulsed nasal and transtracheal oxygen delivery. Chest 1990; 97: Soffer, M, Tashkin, DP, Shapiro, BJ, Littner, M, Harvey, E, Farr, S. Conservation of oxygen supply using a reservoir nasal cannula in hypoxemic patients at rest and during exercise. Chest 1985; 88: Gonzales, S, Huntington, D, Remo, R, Light, R. Efficacy of the Oxymizer Pendant in reducing oxygen requirements of hypoxemic patients. Respir Care 1986; 31: Sheehan, JC, O Donohue, WJ. Use of a reservoir nasal cannula in hospitalized patients with refractory hypoxemia. Chest 1996; 110: s1. 9 Tiep, BL, Nicotra, B, Carter, R, Phillips, R, Otsap, B. Lowconcentration oxygen therapy via a demand oxygen delivery system. Chest 1985; 87: McCoy, R. Oxygen-conserving techniques and devices. Respir Care 2000; 45: Tiep, BL, Barnett, J, Schiffman, G, Sanchez, O, Carter, R. Maintaining oxygenation via demand oxygen delivery during rest and exercise. Respir Care 2002; 47: Tiep, BL, Murray, R, Barnett, M, Carter, R Auto-adjusting demand oxygen delivery system that minimizes SaO2 swings between rest and exertion. Chest 2004 [Abstract] chestjournal.org/ cgi/reprint/126/4/763s. 13 Keller, RR. Long-term oxygen therapy: advances and perspectives in technical devices. Monaldi Arch Chest Dis 1999; 54: Heimlich, HJ. Respiratory rehabilitation with transtracheal oxygen system. Ann Otol Rhinol Laryngol 1982; 91: Hoffman, LA, Wesmiller, SW, Sciurba, FC, et al. Nasal cannula and transtracheal oxygen delivery: comparison of patient response after six months use of each technique. Am Rev Respir Dis 1992; 145: Benditt, J, Pollock, M, Roa, J, Celli, B. Transtracheal delivery of gas decreases the oxygen cost of breathing. Am Rev Respir Dis 1993; 147: Christopher, KL, Spofford, BT, Brannin, PK, et al. Transtracheal oxygen therapy for refractive hypoxemia. JAMA 1986; 256: Schaten, MA, Christopher, KL, Goodman, S, et al. High-flow transtracheal oxygen: a promising technique for the management of hypercarbic respiratory failure. Chest 1990; 98: 22S. 19 Bloom, BS, Daniel, JM, Wiseman, M, Knorr, RS, Cebul, R, Kissick, WL. Transtracheal oxygen delivery and patients with chronic obstructive pulmonary disease. Respir Med 1989; 83: Chronic Respiratory Disease