Continuous Flow Vs on Demand Oxygen

Continuous vs. Pulse Dose Point & Counterpoint

Pulse Dose

Bob Messenger is the Clinical Respiratory Education Specialist for Invacare Corp. His 30-year respiratory career includes acute care, as well as operational and ownership experiences in both homecare and sleep diagnostics, and he has served on the respiratory care program faculty at Cuyahoga Community College in Cleveland. Prior to joining Invacare, he was a clinical specialist and supervisor of clinical education at university-affiliated MetroHealth Medical Center in Cleveland. His research has been published in trade and professional journals and he lectures on a variety of respiratory-and sleep-related topics.

Continuous Flow

Patrick Dunne is president of HealthCare Productions Inc., a respiratory care training and development enterprise in Fullerton, Calif. Patrick is a veteran respiratory therapist and has been practicing in the home care setting since 1985. He is a past-president of the American Association for Respiratory Care (AARC) and a former chair of the AARC's Home Care Specialty Section. He presently serves the AARC as a governor and executive committee member on the International Council for Respiratory Care (ICRC). Dunne has a clinical consulting relationship with SeQual Technologies Inc.

The Moderators

Robert Chatburn, RRT-NPS, FAARC, is a clinical research manager in the Cleveland Clinic's respiratory therapy section, associate professor of medicine at Case Western Reserve University's Lerner College of Medicine in Cleveland, and vice president of research and clinical services for Strategic Dynamics Inc.

Tom Williams is managing director of Strategic Dynamics, Inc., Scottsdale, Ariz. Williams assists clients in strategy formulation, market research, sales training and clinical and benchmark studies. He can be reached via e-mail: at TWilliams@StrategicDynamicsFirm.com.

Topic 1: Clinical Differences Between Continuous and Pulse Dose Devices

How do these devices function differently? What are the advantages and drawbacks of each? Are some patients more suitable for each type of device?

Messenger: The controversy of continuous flow vs. conserving technology for long-term home oxygen delivery is a debate of flawed systems. By their nature, each is a low-flow system, and each falls victim to the variations in oxygen concentration that result from changes in respiratory rate, tidal volume, inspiratory flow rate and other factors.^1-5 Despite all of these variables, clinicians use low-flow systems because they are practical — they offer the advantages of patient comfort and convenience. It is within these practical aspects that the advantages and limitations of each system need to be evaluated. Oxygen-conserving technology is essential to reducing the size and weight of portable oxygen systems without sacrificing duration. In a study of the effect that the weight of a portable oxygen system has on exercise capacity, Leggett and Flenley⁶ demonstrated that when the system weighs more than 10 pounds, all of the endurance benefit of the oxygen is consumed in the process of carrying the system. Indeed, the Fifth Oxygen Consensus Conference⁷ recognized the benefits of meeting the practical needs of ambulatory COPD patients. That conference established three criteria for portable oxygen systems: the system must weigh less than or be equal to 10 pounds, it must be able to be carried by most patients, and it needs to provide an equivalent of 2 liters per minute for a minimum of fourhours. All of the self-sustaining systems that meet these criteria utilize oxygen conserving technology.

Dunne: A continuous flow device administers oxygen in liters per minute (L/min), whereas a pulse dose device intermittently administers a volume (or bolus) of oxygen in milliliters per breath (mL/breath). Continuous flow delivery — the traditional method for oxygen therapy — is considered by many to be the "gold standard." However, the introduction of pulse dose delivery in the 1980s to conserve oxygen contents during ambulation, proved to be as effective in maintaining adequate oxygenation when properly applied to a patient by a respiratory therapist (RT) using pulse oximetry. Hence, both approaches to oxygen therapy can be considered efficacious. However, the introduction of portable oxygen concentrators (POCs) capable of only delivering oxygen in the pulse dose mode raises an important clinical question: Can pulse dose oxygen delivery be used on a 24/7 basis to maintain adequate oxygenation? Unfortunately, the answer is not so clear-cut since there are two important factors that impact oxygen delivery with a POC: (1) the maximum bolus size a particular POC is capable of producing; and (2) the time it takes to actually deliver the bolus. Both of these performance characteristics vary widely between POCs. Other factors include: the patient's systemic oxygen requirement (especially during exercise and sleep), as well as the ability of a particular POC to produce sufficient concentrated oxygen with increased respiratory rates.

Moderators: A continuous flow device provides oxygen in liters per minute (L/min) usually in the therapeutic range of 1-3 L/min. A pulse dose device intermittently administers a volume or bolus of oxygen in milliliters per breath. Settings on pulse dose devices are arbitrary and are not an absolute equivalent to continuous flow. As of this writing, there are two manufacturers that provide continuous flow delivery (CFD) and pulse dose oxygen delivery (PDOD) within the same device, with a third manufacturer slated to enter the market within the next few months. There are six different manufacturers that offer a PDOD POC. Another difference in the two technologies is their size and weight. To provide continuous flow, pulse dose oxygen delivery (PDOD) requires a larger pump/motor assembly, additional electronics and a more molecular sieve. All of this must then be placed within a larger case. This is what increases the device's size and weight (approximately 18-20 lbs). PDOD POCs weigh less than 10 lbs. The market niche for PDOD/CFD POCs versus PDOD POCs is hotly debated for many reasons. A prominent reason is that some clinicians believe that CFD is required for all oxygen-dependent patients during sleep. Others believe that if a patient does not desaturate during sleep, as proven by an overnight oximetry test, then a PDOD POC is fine to use. The issue is not whether a person desaturates at night but why they desaturate. If desaturation is due to sleep apnea, then neither continuous flow nor pulse dose systems will be effective. On the other hand, if patients desaturate because they have shallow breathing and are not triggering a pulse dose system, then continuous flow may offer an advantage. In practice, nobody is really motivated to fund the sleep studies required to answer these kinds of questions. Therefore, at a minimum, we believe a patient should be evaluated for desaturation at night using an appropriate level of continuous flow (perhaps a higher flow than required for normal awake rest). If the patient desaturates, then the issue of sleep apnea should be addressed. If not, then at least we know one effective therapy mode. If there is sufficient motivation to use a PDOD POC then a second study can be done using a specific device. Regarding the issue of whether continuous flow should be considered a "gold standard," the fact is that, as Mr. Messenger pointed out, the Fifth Oxygen Consensus Conference established a definition for portable oxygen systems that includes a criterion that the system must provide an equivalent of 2 l/m for a minimum of four-hours. By default, then, a constant flow of 2 L/min becomes the standard. However, the fallacy of this definition is that the term "equivalent of 2 L/min" has no definite meaning. If you require a flow meter manufacturer to produce an instrument that outputs 2 L/min plus or minus an acceptable tolerance, then you have created a genuine standard that can be checked by anyone. But referring to oxygen delivery to a patient using a nasal cannula as being equivalent to anything is like requiring a broken clock to read the correct time, which it indeed can do only for an instant twice a day. This ambiguity in the Consensus definition allows the wide variety of performance from commercial POCs and perhaps, more importantly, reinforces the practice of physicians writing prescriptions in terms of flow settings as if they were actual drug dosages. Aside from the issue of ambiguous dosing with a nasal cannula, there are at least two other factors that invalidate any assumption of "equivalence" between continuous flow and pulsed dose devices. First, the FiO₂ delivered by a continuous flow device must decrease as the patient's minute ventilation increases. At least in theory, pulsed dose systems can avoid or mitigate this problem by maintaining a constant pulse volume per breath. Second, the standard "rule of thumb" for estimating the FiO₂/flow relationship relies heavily on the assumption of an "anatomic reservoir" that is filled by a continuous flow device between breaths. Our lab has data to show that patients with COPD may have end expiratory flow in excess of the cannula flow setting, thus eliminating the reservoir effect and lowering the FiO₂. Again, pulse devices may avoid this effect because they do not require a reservoir effect in the first place. The bottom line is that portable devices have widely varying performance characteristics and probably always will. The only rational way to deal with this variability is by titrating each patient to a specific device for the expected usage conditions including rest, activity and sleep.

This article originally appeared in the Respiratory Management September 2009 issue of HME Business.

thomasestand.blogspot.com

Source: https://hme-business.com/Articles/2009/09/01/Continuous-Flow-vs-Pulse-Dose.aspx