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Accurate Oxygen Saturation Values Between 50 and 60 Torr as Determined by a Computer Spreadsheet FREE TO VIEW

Robert Demers; Wayne Wallace
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Education and Research, Kaiser Permanente Southern California, Pasadena, CA

Chest. 2014;146(4_MeetingAbstracts):32A. doi:10.1378/chest.1962825
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SESSION TITLE: COPD Diagnosis and Evaluation Posters II

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 29, 2014 at 01:30 PM - 02:30 PM

PURPOSE: The Centers for Medicare & Medicaid Services (CMS) require that a patient’s saturation value read ≤ 88% before that patient can be reimbursed for home oxygen. It is commonly assumed that: 1) a saturation of 88% coincides with an arterial oxygen tension (paO2) value of about 60 torr; and 2) pulse oximeters are highly accurate/precise.

METHODS: A computer spreadsheet (Numbers®; Apple, Inc., Cupertino, CA) incorporating a polynomial expression for oxygen saturation1 was used to calculate the actual saturation of a blood sample as a function of paO2. Spreadsheet functionality allows users to generate plots of numerical parameters incorporated within any tables which it creates. The software was employed to generate the plot (shown below) of percent saturation (ordinate) versus oxygen tension (abscissa) for adult hemoglobin for paO2 values ranging between 50 and 60 torr. In addition, the specification sheet2 for a typical pulse oximeter (Radical-7®; Masimo, Irvine, CA) was consulted in order to determine the typical accuracy of that type of device.

RESULTS: The plot of hemoglobin saturation versus arterial oxygen tension revealed that the saturation corresponding to oxygen tensions of 50 and 60 torr were 85% and 91%, respectively. The specifications for the pulse oximeter revealed that the tolerance of that category of device, under ideal circumstances (no motion), and when applied to an adult patient/subject, was ± 2%. It is entirely possible, then, that a pulse oximeter might furnish a readout of 88% when, in fact, the patient’s actual saturation were 86%. That saturation level corresponds to an arterial oxygen tension of only 51 torr.

CONCLUSIONS: Hypoxemia-induced dyspnea, triggered by activation of the hypoxic ventilatory drive, elicits severe discomfort and anxiety when the prevailing paO2 falls into the 50-to-60-torr range3. Clinicians would be well advised to administer oxygen to their patients such that the observed oximeter reading is at least 93%. In that instance, even if the oximeter reading were falsely high (by 2%), the patient’s paO2 would still be 60 torr.

CLINICAL IMPLICATIONS: ​The current threshold value which CMS sets for reimbursement for home oxygen is far too low.

DISCLOSURE: The following authors have nothing to disclose: Robert Demers, Wayne Wallace

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