Latest Pulse Oximeters can Improve ICU Process of Care

Abstract & Commentary

Synopsis: A new-generation pulse oximeter with improved signal-extraction technology had less malfunctioning time than a conventional pulse oximeter placed on the same hand in postoperative cardiac surgery patients and was associated with fewer arterial blood gases and faster FIO2 reduction.

Source: Durbin CG Jr, et al. More reliable oximetry reduces the frequency of arterial blood gas analysis and hastens oxygen weaning after cardiac surgery. Crit Care Med. 2002;30(8):1735-1740.

Durbin and Rostow at the University of Virginia sought to determine whether a latest-generation pulse oximeter (Masimo SET) could improve the process of care in weaning postcardiac surgery patients from ventilatory support, in comparison with a state-of-the-art, previous-generation pulse oximeter (Ohmeda 3740). They recorded data from both oximeters simultaneously in each patient with both sensors applied to the same hand, but randomly withheld the data from 1 device from those taking care of the patient, who were unaware of the true purpose of the study. Outcomes studied were device nonfunctional monitoring time (the percentage of total monitoring time when the monitor was producing unreliable or unusable data according to predetermined criteria), time to extubation, number of ventilator changes, time to an FIO2 of 0.40, and number of arterial blood gas specimens obtained.

During a 13-month period, Durbin and colleagues entered 86 patients into the study, which was powered to detect a 20% reduction in weaning time with 90% confidence. Data from 4 patients were excluded. Data from the new-generation oximeter were available to clinicians in 43 patients and from the conventional oximeter in 39 patients. Time to extubation was the same in the 2 patient groups, although patients managed according to data from the latest-generation oximeter were weaned to an FIO2 of 0.40 an average of more than an hour faster than patients managed with the conventional oximeter (means, 176 vs 348 min, P = 0.0125) and required fewer blood gases during this time (means, 2.7 vs 4.1 measurements, P = 0.000015). There were no differences in the number of ventilator changes during weaning in the 2 patient groups. Durbin et al conclude that use of the new-generation oximeter enables clinicians to manage postoperative cardiac surgery patients in a more efficient and cost-effective manner with respect to oxygen weaning and the use of arterial blood gas measurements.

Comment by David J. Pierson, MD

Although data showing benefits in terms of patient-relevant outcomes have been lacking, routine monitoring of postoperative patients with pulse oximetry has become the standard of ICU care. Specially designed efficacy studies have demonstrated that it is possible to reduce the number of arterial blood gas measurements through the use of continuous pulse oximetry monitoring, but whether similar reductions occur in everyday practice remains to be seen. By detecting brief episodes of clinically unimportant desaturation that would otherwise have gone unnoticed, continuous pulse oximetry can actually increase the number of blood gas measurements, ventilator adjustments, and other interventions if bedside caregivers do not exercise clinical judgment every time the alarm sounds.

Be that as it may, the new generation of pulse oximeters, exemplified in the present study by the Masimo device, appears to offer a genuine advance in terms of avoiding artifact and providing accurate readings in the presence of hypoperfusion or patient movement. Other studies have demonstrated this improved reliability under laboratory conditions using volunteer subjects, but the Durbin study is the first to my knowledge to show measurable benefit in clinical use.

For example, Gehring and colleagues1 in Germany connected healthy volunteers to 3 new-generation oximeters and 1 device representing the previous generation and then induced hypoxemia. They generated motion artifacts using a standardized protocol and also reduced finger perfusion by means of an inflatable balloon applied over the brachial artery. Under the conditions of this model designed to mimic clinical situations in which standard oximeters frequently fail to produce reliable readings, the new-generation devices consistently outperformed their predecessor.

In another recent study, Barker2 evaluated the performance of 20 different pulse oximeter models during standardized hand motion under both normoxic and hypoxic conditions in healthy volunteers. The Masimo SET pulse oximeter exhibited the best overall performance, with the SpO2 reading remaining within 7% of reference (control) values 94% of the time. Comparable results with the Agilent Viridia 24C were 84%, with the Agilent CMS at 80%, the Datex-Ohmeda 3740 at 80%, and the Nellcor N-395 at 69%. The Criticare 5040, used by Barker as a representative of an older generation of oximeter, had an indicated SpO2 within 7% of the control value only 28% of the time.

Continuous monitoring of arterial oxygenation in ICU patients using pulse oximetry can provide early warning of clinical deterioration. It can also detect clinically insignificant physiological fluctuations in saturation, potentially leading to unnecessary interventions. Discriminating between these monitoring outputs remains an important challenge for clinicians at the bedside, both to safeguard patients and to avoid unwarranted expense and discomfort. However, it appears that the new generation of pulse oximeters can help reduce artifact and provide reliable data more of the time in the management of critically ill patients.

Dr. Pierson is Professor of Medicine University of Michigan, Medical Director Respiratory Care Harborview Medical Center, Seattle.

References

1. Gehring H, et al. The effects of motion artifact and low perfusion on the performance of a new generation of pulse oximeters in volunteers undergoing hypoxemia. Respir Care. 2002;47(1):48-60.

2. Barker SJ. "Motion-resistant" pulse oximetry: A comparison of new and old models. Anesth Analg. 2002;95: 967-972.