
Masimo Announces Clinical Review of Forehead Sensors
Studies suggest forehead oximetry appropriate in limited applications
PARIS, France - April 20, 2004 - Today, at the 13th World Congress of Anesthesia Meeting in Paris, France, Masimo announced the latest study on forehead oximetry and the results of its clinical review investigating the use and clinical viability of forehead pulse oximetry monitoring. Published clinical studies, beginning in 1988, consistently demonstrate a lack of reliability in forehead sensor monitoring. Masimo markets its own pulse oximetry forehead sensor, the TF-I TransFlectance™ sensor, primarily for use as a potential adjunct to traditional sensors, for those patients on whom the digits or ears are not accessible, or in niche applications such as exercise physiology for oxygenation monitoring. Masimo has never marketed its forehead sensor for general-purpose monitoring, and cautions against such use.
In the late 1980s, forehead sensors were introduced with the hope of becoming the general-purpose sensor for oxygenation monitoring. Their application to the forehead promised faster response times in subjects with low peripheral perfusion and a convenient location for anesthesiologists in the operating room. However, clinical studies began showing a fundamental flaw in pulse oximetry measurements on the forehead.
A 1988 study by Eugene Cheng, MD, et al., Department of Anesthesiology, Medical College of Wisconsin, compared the performance of a Criticare Systems' forehead sensor to a digit sensor from the same company. The researchers concluded that the forehead sensor worked well on healthy, well-oxygenated volunteers, but was unreliable when applied to critically ill patients.1
In 1991, Steven J. Barker, PhD, MD, then a professor at University of California, Irvine, reported failure rates for forehead sensors as high as 59% on patients undergoing surgery in a study presented at the Society for Technology in Anesthesia. The same study reported failure rates for finger sensors placed on the same patients at no greater than 1.36%.2
The problems associated with forehead sensors relate primarily to physiology, not technology. When a patient is in the supine or Trendelenberg positions - both very common in the clinical setting - venous blood tends to pool in the head. As the venous system becomes engorged, it pulsates at the same frequency as the arterial blood supply. The pulse oximeter therefore receives a mixed arterial and venous pulsating signal and reports a lower number than the true arterial oxygen saturation. Since the venous pulsation is at the same frequency as the arterial pulsation, even next generation pulse oximeters cannot eliminate it. Conventional pulse oximeters are even worse off with forehead sensors. Not only do conventional pulse oximeters suffer from the venous pulsation problem inherent to all forehead sensors, but also they are more susceptible to gross errors caused by motion since they produce less signal compared to noise.
Beginning in 2002, Tyco-Nellcor reintroduced the forehead sensor and made it their flagship sensor for the new Oximax sensor line, marketing it to clinicians as a general-purpose sensor. The timing of this re-introduction of forehead sensors is close in proximity to the expiration of certain Nellcor sensor patents during 2003. Notably, Nellcor built their latest pulse oximeters, e.g. N595 & N550, to be incompatible with their non-Oximax sensors, and they in turn made their Oximax Max-Fast forehead sensors incompatible with their legacy oximeters, e.g. N200. In attempting to convert the market to their new proprietary Oximax encrypted sensors, Nellcor marketed the Max-Fast forehead sensor as an improvement over traditional pulse oximetry sensors, such as the digit adhesive sensor. Nellcor promoted a 2003 study that suggested that forehead oximetry had improved and warranted Nellcor's marketing of the Max-Fast forehead sensor for general-purpose use. Richard Branson, BA, RRT, FAARC, Associate Professor of Surgery at the University of Cincinnati, et al. compared the performance of Nellcor's Max-Fast forehead sensor to a digit sensor on 20 postoperative patients at risk of hypotension and/or hypothermia. Branson reported that the forehead sensor performed 98% of the time over the 26 hours of monitoring.3
On the other hand, the data found in another study by Mr. Branson et al. suggested that forehead oximetry had not clinically improved after all. A study was done on 20 trauma patients monitored with both the Nellcor Max-Fast reflectance sensor and the Nellcor Max-A digit sensor with the Nellcor N595 OxiMax pulse oximeter. A total of 73 arterial blood gas-oximeter data pair samples were obtained. Analysis of the study reveals the Max-Fast forehead sensor failed to give reliable readings on 5 of the 20, or 25%, of the patients in the test due to various reasons.4
As new research on forehead oximetry increased, the historic problems continued to resurface and clinical studies discrediting forehead oximetry vastly outnumbered those finding forehead oximetry now useful as a general-purpose oximetry solution.
In an operating room study (see Table 1), Dr. Barker showed that the Nellcor Max-Fast forehead sensor had a percentage error time of almost 28% on 18 patients undergoing surgery. A Masimo SET device with an LNOP TC-I ear sensor demonstrated a percentage error time of 2.5%.5
Table 1
| Nellcor N-595 MAX-FAST Forehead Sensor | Masimo SET TC-I Ear Sensor |
Bias (%) |
-3.91 % |
-0.47 % |
Precision (%) |
3.25 % |
1.03 % |
Percentage of time errors were greater than 7% |
27.7% |
2.5% |
Aman Mahajan, MD, et al., of the Department of Anesthesiology at UCLA School of Medicine, reported poor performance with the Max-Fast sensor in the adult population. Of the 42 adult surgical patients monitored with the Max-Fast sensor connected to the N-595, 17 (or 40%) showed significant error. In these patients, the Max-Fast sensor displayed a greater than 7% difference in SpO2 than the values of the control pulse oximeters for more than 20% of the surgical case. Dr. Mahajan concluded, "The results of this study suggest that the Max-Fast sensor attached to the N-595 oximeter might not be accurate or reliable enough for use in surgical patients."6
Kirk Shelley, MD, et al., of the Department of Anesthesiology at Yale University, found that the Max-Fast forehead sensor produced corrupt plethysmographic waveforms when used on patients in the supine position. The researchers suggest the presence of an underlying venous waveform is the root cause of this error.7
Daniel Redford, MD, et al., Department of Anesthesiology, University of Arizona in Tucson, reported a performance index of just 71% for the Nellcor N-595 Max-Fast forehead sensor on patients undergoing surgery. Dr. Redford's team also showed significant performance and reliability differences between the Masimo TF-I forehead sensor and the Nellcor N-595 Max-Fast forehead sensor in the Operating Room. The Masimo forehead reflectance sensor performed significantly better than the Nellcor forehead sensor (see Table 2).8
Table 2
| Nellcor N595 MAX-FAST Forehead Sensor | Masimo SET TF-I Forehead Sensor |
Bias (%) |
-5.1 + 8.0 |
0.3 + 1.0 |
Precision |
3.9 + 5.7 |
0.8 + 0.7 |
Percentage of time errors were greater than 7% |
22.2 + 37.99 |
1.5 + 3.0 |
Performance Index |
71.2 |
98.2 |
Dr. Redford, the lead author of the study on forehead sensors, stated, "The Nellcor monitor demonstrated an unacceptable use in the surgical patient. The Masimo LNOP TF-I forehead sensor, in contrast, performed with a small bias and precision which was essentially the same as our control finger sensors." Dr. Redford added, "The increased response time of a more centrally located oximeter is welcome and I've seen research demonstrating a successful ear and forehead sensor from Masimo, but anesthesiologists dealing with patients in the clinical environment have better things to do with their time than spend it ruling out falsely low saturations."
In a forehead oximetry study presented this week at the WCA, Dr. Mahajan tested the Max-Fast forehead sensor on a pediatric population and found that poor bias and precision, along with high rates of error, render Max-Fast unacceptable for clinical use. On over half the patients, the Max-Fast erred by greater than 5% for more than 20% of the total operative time. The authors concluded, "…the Max-Fast forehead sensor and the N-595 oximeter is not accurate nor reliable enough for clinical use in pediatric surgical patients." 9
In a second study presented at the WCA conference in Paris this week, Dr. Redford compared the Masimo LNOP TF-I forehead sensors to the TC-I earlobe sensor and showed that the TC-I earlobe sensor worked better than Masimo's own TF-I forehead sensor.10 These results are consistent with Masimo's formal recommendations for earlobe oximetry as the most reliable alternative to traditional sensor sites, such as the digit.
Maribeth Sayre, MD, Director of Medical Affairs of Masimo stated, "Tyco-Nellcor's latest marketing campaign has touted their new forehead sensor as the next big development in pulse oximetry. While quick response time is important to clinicians, the lack of reliability of forehead sensors has been very difficult for manufacturers to overcome. Even though Masimo's LNOP TF-I sensors perform better than Nellcor Max-Fast sensors, we still believe that fingers on adults and the hand, foot, or toe on babies and children provide the most reliable monitoring locations."
Dr. Sayre continued, "There are clear physiological challenges with forehead monitoring, and we strongly suggest their use as an adjunct to the normal sensors or for applications where the patient is upright, such as with exercise physiology. Based on the latest clinical studies, we also believe that, when clinicians want to use the forehead as a monitoring site, they will find greater reliability with the Masimo Transflectance TF-I forehead sensor. We continue to be grateful for researchers testing the marketing claims of devices so directly linked to patient outcomes."
Joe E. Kiani, CEO of Masimo, said, "Masimo understands that this release may not be an exhaustive review of the available clinical literature on forehead oximetry. Until we have such a review, however, we hope this will add to the discussion on alternative monitoring sites. In the interest of patient care, we believe it is imperative that clinicians survey the range of available literature on forehead oximetry and do thorough evaluations of their own before using it routinely in their practice."
