ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

Effective Date: 2014 Version #1

Chapter 17

Principle or Purpose In healthy individuals the partial pressure of arterial oxygen (Pa O 2 , if measured by pulse oximetry) remain mostly unchanged or increase during exercise. In individuals with substantial pulmonary disease, the Pa O 2 and Sa O 2 (Sp O 2 ) fall with exercise, indicating oxygen (O 2 ) desaturation. This desatura- tion can be defined as a decrease in Sa O 2 (as measured from arterial blood samples by CO-Oximetry) of at least 2% compared to rest, an Sa O 2 of less than 88% during exercise, and/or a Pa O 2 of less than or equal to 55 mm Hg during exercise (1, 2). It is generally accepted that a 3 to 4% fall in Sp O 2 is considered significant when using a pulse oxim- eter. Oxyhemoglobin desaturation with exercise implies that diffusion cannot be increased to accommodate for a shorter pulmonary capillary transit time. The exercise test used to determine if desaturation occurs can be performed as a component of a maximal cardiopul- monary exercise test (CPET), or as a less sophisticated test using a submaximal exercise test on a treadmill, cycle ergome- ter, or simply by having the patient climb stairs or walk in a hall corridor.The process of elucidating exercise desaturation during a maximal CPET is not addressed in this chapter. Exercise duration can vary from institution to institution, but is commonly less than 10 minutes. However, it is recommended that steady-state exercise be of at least 3 minutes duration. Shorter-duration exercisemay lead to both false-positive and false-negative results.The treadmill, cycle, or stair unit have the advantage of providing an environment for better monitoring, and require less space than hallway corridor walking. Walking in the hallway or using a stair unit with railing allows the patient to adjust the pace easily, pause to rest if neces- sary, and have fewer concerns about falling (3). The major disadvantage of these informal treadmill, stairs, or corridor walks (i.e., without sophisticated physiologic measuring and monitoring instrumentation) is the lack of information about the subtle physiologic changes during exercise, or about the relationship of work rate to desaturation (1). Procedure Name: Exercise Test for the Assessment of Desaturation ) and arterial oxygen saturation (Sa O 2 ; Sp O 2

Oxygen (O 2

) Titration

O 2 titration refers to the process of determining the appropriate level of supplemental O 2 prevent or attenuate desaturation. The goal usually is to determine the lowest level of supplemental O 2

required by the patient to

the patient

needs to maintain Sa O 2

or Sp O 2

at an acceptable level at rest and during exertion.

During exercise, there are two approaches to determine the lowest O 2 flow rate required to keep a patient’s Sa O 2 above a specific threshold (e.g., 90%): ( 1 ) adjusting while the patient continues to exercise; and ( 2 ) stopping the exercise, adjusting flow rate, and then restarting the exercise after equilibration. The first method is quicker and simpler. It only requires the technologist to increase the O 2 flow rate after desatura- tion is observedwhile the patient continues exercising.The disadvantage of this approach is that theO 2 flow rate needed to keep the patient adequately oxygenated during exercise, starting from rest, may not be accurately determined.

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