Hypoxemia in Pulmonary Rehabilitation

A patient walks into rehab . and so begins the journey for both patient and practitioner through treatment in pulmonary rehabilitation. Many of the patients that walk through our doors suffer not only from chronic lung disease but from hypoxemia as well. Defined as a lower than normal level of oxygen in the blood,1 hypoxemia can result from a variety of causes, including: ventilation perfusion mismatch, right to left shunt and alveolar hypoventilation.

Depending upon the particular lung disease and the etiology of the resulting hypoxemia, adequate treatment with supplemental oxygen can consist of a vast range of delivery methods, flow rates and oxygen modalities. In order to appropriately treat an individual patient, the practitioner in a pulmonary rehabilitation setting must be skilled in the art of oxygen assessment and titration, while also being well-versed in the delivery methods and modalities available. These skills have been added to the recently updated AACVPR Clinical Competency Guidelines for Pulmonary Rehabilitation Professionals as core competencies.2

As practitioners in pulmonary rehabilitation, we consider it our mission to restore as much physical function to our patients as possible, which is quite impossible to do without treating hypoxemia.

Oxygen has been shown to improve the effectiveness of exercise training in pulmonary rehabilitation by reducing dyspnea, hypoxic ventilatory drive and hyperinflation. Appropriate ambulatory oxygen equipment can increase mobility, compliance, exercise tolerance and autonomy in hypoxemic patients.3 A thorough assessment that concludes with an oxygen system and setting that adequately treats a patient’s hypoxemia is of upmost importance in maximizing physical function.

hypoxiaThe Problem
To date there is neither a universal standard for oxygen assessment, nor clinical guideline to guide the treatment of hypoxemia in patients with chronic lung disease. This means that oxygen assessment and titration is performed differently in clinics across the country, resulting in very different outcomes and prescriptions for treatment.

In 2011, the University of California San Diego (UCSD) Pulmonary Rehabilitation Program collected retrospective data on the oxygen systems used by their patients as well as whether the oxygen prescription that they had when entering rehabilitation proved to be adequate in maintaining oxygen saturation. They found that approximately 40% of the patients entering rehabilitation required changes in their oxygen prescriptions during rehabilitation, all to higher flows of oxygen and some to different oxygen devices altogether.4 (Figure 1) All of these patients had been assessed and prescribed oxygen prior to entering pulmonary rehabilitation, begging the question “how do we get it right?”

First Steps
Returning to the patient walking into a pulmonary rehabilitation clinic, the first step in assessment is a thorough medical history. This will reveal more about the patient’s type of lung disease and level of physical function prior to becoming symptomatic, when diagnosed with lung disease, and after diagnosis to the present time. This information is key in determining the goals of pulmonary rehabilitation as a whole, and more specifically to what level of physical function an oxygen assessment will need to be performed.

Herein lies the discrepancy between the outcomes of oxygen assessments performed by different providers. If a patient is not assessed at the level of physical function at which he lives, we cannot hope to arrive at an oxygen prescription that will maintain adequate saturation. Better understanding of physical activity level will give the practitioner an idea as to what type of oxygen system might be appropriate for an individual patient.

For an active patient, an e-cylinder may not be the ideal system as it is cumbersome and does not allow for prolonged or rigorous physical activity; for a patient with severe orthopedic limitations a small cylinder with a backpack may be impossible to manage. Obviously system decisions must ultimately be determined by oxygen flow requirements.

Following a thorough medical history, an initial physical test may be helpful in determining whether a patient is hypoxemic at rest or with exertion, and if already on supplemental oxygen, may reveal the adequacy of the flow setting and system. The six minute walk and shuttle walk tests are commonly used in pulmonary rehabilitation settings as brief, easily performed exericse tests which give insight into a patient’s oxygen requirements as well as changes in heart rate response and self-reported symptoms of dyspnea and fatigue.

A pulse oximeter is ideally used throughout the duration of the test to monitor saturation and heart rate, and the modified BORG or visual analog scale to measure dyspnea and fatigue. If a patient is currently prescribed supplemental oxygen for exertion, the test should ideally be performed using their own system on the setting prescribed.

changes in delivery mechanism and oxygen flow rate
There are a few possible outcomes of this testing in a hypoxemic patient:

  1. the patient already prescribed oxygen remains well saturated on their own system.
  2. the patient desaturates using the system and setting they are prescribed.
  3. the untreated patient desaturates on room air.

In scenario one, the patient remains well saturated on their prescribed system and setting, and further observation and monitoring is important during the course of rehabilitation to ensure that as the patient (hopefully) improves with respect to duration and intensity of exercise, and they remain adequately saturated on their prescribed system and setting. In scenarios two and three, assessment and titration are needed accompanied by clinical judgement. Now it gets complicated.

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Assessment and Titration
As there is no clinical guideline as to how to perform this assessment and titration in a standardized fashion, clinical experience and judgement combined with information gathered during the medical history and exercise testing may be used to determine how to assess and titrate the individual patient.

For example, the clinician must interpret the results of the exercise testing . was maximal effort given? Was the patient walking at a pace indicative of their “normal walking pace” or a pace at which they perform daily activities? This interpretation, combined with the patient’s reported level of physical activity and function can give the clinician insight as to an appropriate activity level for titration.

Though there are many variables influenced by the individual patient and by clinical judgement, there is a framework for assessment required by Medicare that may serve as a guideline in creating a more standardized testing procedure. As seen in figure 2, a patient must be evaluated in 3 phases within the same test to demonstrate the need for oxygen.5 Again, the variable that remains even when using this framework is what level of exertion to use in assessment.

Medicare Guidelines for Oxygen Testing

The Right System
Once a flowrate is determined for exertion, the remaining consideration is the type of oxygen system appropriate and available to the individual patient. In many areas of the country, competitive bidding has changed the DME landscape and greatly diminished the variety of oxygen equipment available. There may be very little selection from which to choose depending on the DME companies in your area, as well as the patient’s medical insurance and DME coverage guidelines.

A further consideration, as mentioned earlier, is the patient’s physical abilities and functional level. Whatever the product desired, it is absolutely necessary to test the individual patient on the specific device. Two liters per minute is not the same as a “#2” setting on an oxygen conservation device (OCD), and a “#2” setting on one conservation device does not equal a “#2” setting on another. Due to this variability, illustrated in Figure 3, each device must be tested on the patient to ensure adequacy.6

Many a patient has walked into a pulmonary rehabilitation clinic with a brand new portable oxygen concentrator (POC), very small and portable, purchased independently, only to find that it does not meet their oxygen needs at all. This can be a very expensive lesson. Similarly, with OCDs it may be tempting to a patient to be able to conserve oxygen and carry a smaller tank, but it is only feasible if the device can provide adequate oxygen to saturate the patient.

Following these steps and considerations can be helpful in accomplishing the goal of appropriate treatment and assessment of the hypoxemic patient in a pulmonary rehabilitation setting. However, a more standardized, evidence based clinical practice guideline is needed to improve practice across the country.

Arianna Villa, BS, RRT, is the case manager and study coordinator for the UCSD Pulmonary Rehabilitation Program.

Oxygen Dose Per Setting

References

  1. Mayo Clinic. http://www.mayoclinic.org/symptoms/hypoxemia/basics/definition/SYM-20050930.
  2. Collins E, et al. Clinical Competency Guidelines for Pulmonary Rehabilitation Professionals. Journal of Cardiopulmonary Rehabilitation and Prevention. 2014;1-12.
  3. Garvey C, et. al. Severe Exercise-Induced Hypoxemia. Respiratory Care. July 2012;1154-1160.
  4. Villa A. et al. Pulmonary Rehabilitation Corrects Oxygen Prescriptions in Chronic Lung Disease Patients. Respiratory Care. October 2011;1692.
  5. Centers for Medicare and Medicaid Services. Oxygen therapy supplies: Complying with documentation and coverage requirements. December 2011. http://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNProducts/downloads/OxgnThrpy_DocCvg_FactSheet_ICN904883.pdf.
  6. Bliss PL, et al. Characteristics of Demand Oxygen Delivery Systems:
  7. Maximum Output and Setting Recommendations. Respiratory Care. 2004;49(2):160-165.

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