Pulse Oximeter Performance, Racial Inequity, and the Work Ahead.

It has long been known that many pulse oximeters function less accurately in patients with darker skin. Reasons for this observation are incompletely characterized and potentially enabled by limitations in existing regulatory oversight. Based on decades of experience and unpublished data, we believe it is feasible to fully characterize, in the public domain, the factors that contribute to missing clinically important hypoxemia in patients with darkly pigmented skin. Here we propose 5 priority areas of inquiry for the research community and actionable changes to current regulations that will help improve oximeter accuracy. We propose that leading regulatory agencies should immediately modify standards for measuring accuracy and precision of oximeter performance, analyzing and reporting performance outliers, diversifying study subject pools, thoughtfully defining skin pigmentation, reporting data transparently, and accounting for performance during low-perfusion states. These changes will help reduce bias in pulse oximeter performance and improve access to safe oximeters.

Validation of a conical cuff on the forearm for estimating radial artery blood pressure.

INTRODUCTION: There has been a growing need for and interest in measuring noninvasive blood pressure (NIBP) in obese patients. In many situations, available rectangular upper arm blood pressure cuffs do not fit properly, closing in a crisscross manner or overlapping the elbow. To address this issue, GE Healthcare has designed a conically shaped cuff for use on the forearm to estimate radial arterial blood pressure. This study evaluated using this forearm cuff with an oscillometric NIBP algorithm compared with an invasive radial arterial blood pressure reference. PATIENTS AND METHODS: Thirty-four patients were enrolled in the study with an aim to acquire a minimum of 150 paired measurements. Blood pressure was measured and recorded invasively from the radial artery of each patient, while noninvasive oscillometric measurements were acquired from the same limb using a conically shaped cuff placed on the patient's forearm. ANALYSIS: NIBP values were compared with the invasive blood pressure values acquired in the combined 30-s period preceding cuff inflation and the 30-s period following cuff deflation. The acceptance criteria for measurement accuracy were defined in accordance with the ANSI/AAMI/ISO 81060-2:2009 standard, which requires an absolute average error of 5 mmHg or less, with an SD of 8 mmHg or less. RESULTS: The systolic mean error (-0.82 mmHg) and SD (6.08 mmHg) and the diastolic mean error (1.53 mmHg) and SD (3.83 mmHg) were within the 81060-2 acceptance criteria. CONCLUSION: The statistical results show that oscillometric NIBP measurements taken with the conically shaped cuff placed on the forearm give an accurate estimation of radial arterial blood pressure.

Maximizing the laboratory setting for testing devices and understanding statistical output in pulse oximetry.

Maximizing the laboratory setting for testing baseline pulse oximetry accuracy in an arterial desaturation study requires a study design that considers management of several aspects in the physiology of the test subject, special attention to the device under test, and great care in the preanalytical (sample handling) and analytical (Co-oximeter) phases. Statistics used to describe the resulting SpO2 performance include Precision (size of the data cloud), Bias (offset of the data cloud), and A(rms) (accuracy root mean square), which combines the size and offset of the data cloud in one number. The A(rms) is the primary statistic required by regulatory organizations to describe general performance over the entire saturation range. It does not describe any one point, but is a compilation of all points over the range tested. Most pulse oximeters in use today specify an A(rms) of 2%. To meet this specification, two-thirds of the readings will be within 2% of the Co-oximeter reference; however, some individual readings can be as inaccurate as 6% or more. The A(rms) statistic does not have the capacity to represent all pulse oximeter behavior. Saturation pop-ups, drop-downs, frozen readings, and periods of no reading are not portrayed by the A(rms). The next steps in the advancement of regulatory validation testing would be to develop standards that include an expanded analysis of pulse oximeter performance by assessment of pop-ups, dropouts, frozen readings, and periods of no reading through assessment of sensitivity/specificity and possibly a "Performance Index" similar to the approach taken by Barker.

Effects of tissue outside of arterial blood vessels in pulse oximetry: a model of two-dimensional pulsation.

We describe a new model of pulse oximetry that addresses the disagreement between theoretical calibration curves based on Beer-Lambert's Law and test results based on human test subjects. Sources of this discrepancy include variability among human subjects, experimental conditions and the effect of optical radiation propagating in tissue surrounding arteries. Unlike the conventional model, our model considers the change in the relative proportion of light that does or does not pass through blood in pulsating vessels in addition to the change in the path length of optical radiation through the blood. Theoretical calibration curves based on this model agree with human test results and help to explain the variability between in vitro and in vivo test conditions.

A characterization of motion affecting pulse oximetry in 350 patients.

As part of an oximetry research effort in which plethysmographic data were collected from moving patients, a wide variety of patient motion affecting pulse oximetry was observed and characterized by the clinical incidence, type, severity and duration of patient motion. 350 patients were observed for movement in clinical settings, including ICU, SICU, MICU, PICU, NICU, OR and PACU, at 4 hospitals and on an ambulance. 20% (70) of the patients exhibited motion. Half (35) of the moving patients were instrumented to record oximetric, plethysmographic and/or acceleration information. 31% of NICU infants moved compared to only 7% of adults in ICUs. The most common noisy oximetry signals were caused by motion characterized by extending/flexing (/kicking in infants) and by clenching/pressing/rubbing. In infants, these motion types accounted for 53% and 11% of motion, respectively. Less common infant motion types were patient cares, shifting body position and cough/cry. The most common adult motions were equally divided among extend/flex, clench/press/rub, twitch/shake and transport motion types. Extend/flex motions typically demonstrated high plethysmographic waveform modulation (71.5% maximum) and high acceleration. Clench/press/rub motions typically also had high modulations, but low G-force. With one high-G exception, twitch/shake motions had little or no effect on oximetry readings. Less common adult motion types affecting pulse oximetry included cough/cry, strain/posture, tremors and tap/bump. Most recorded motions were aperiodic and short-lived, 62% lasting less than 10 seconds, only 5% lasting over 1 minute. NICU patients made the longest lasting continuous series of motions, while adults made 86% of the motions lasting a second or less.