Pulse Oximetry in the New Millennium
Pulse oximetry has been widely used for about 15 years. Its use is so widespread that it has been called the “fifth vital sign.” Currently the pulse oximeter provides data concerning pulse rate, oxygen saturation, and the presence of perfusion. Results are obtained noninvasively with varying degrees of accuracy depending on the status of multiple factors.
The accuracy of pulse oximetry is very patient-dependent. There are three basic conditions to be met for it to be useful. First, the area under the sensor must have pulsate perfusion. Second, hemoglobin species capable of binding with oxygen must be present in large enough volume to provide a saturation of at least 60%. Third, enough oxygen must be present to also fulfill the condition of the preceding condition.
In addition to the above conditions, add ambient light effects—issues of skin tone, tattoos, and nail polish—as well as low peripheral perfusion due to trauma, wearing a sock, and hypothermia. Furthermore, the effects of probe site, tightness, and motion artifact all predicate that proper training is required for sufficient oximetry practice. Shivering, fine muscle tremors, and seizures can result in false or no pulse oximeter readings.
Because we depend on peripheral perfusion to detect SpO2, we need to be aware of the factors that can reduce the flow of blood to the sensor site. Temperature is an important factor. Low digital temperature resulting from shunt, hypothermia, or shock can lead to pulse oximetry error. A pulse oximetry sensor that detects site (usually a finger) temperature is often useful.
A third group of issues affects the reliability of pulse oximetry data and that is related to the chemical and physical properties of the hemoglobin molecule. The presence of varying amounts of sulfhemoglobin, methemoglobin, and carboxyhemoglobin affects the accuracy of the pulse oximeter. These species of hemoglobin may be seen by the oximeter as hemoglobin that is saturated with oxygen. This will lead to an overstatement of the patient’s SpO2 and perhaps result in the alteration of the patient’s orders and treatment.
Where do we go from here? Pulse oximetry has the potential to improve its reliability and expand its menu of analysis options. Currently we are seeing pulse oximeters that minimize the effects of motion artifact by means of rapid-sampling signal-averaging techniques. These methods increase the number of sampling periods per second and then process the captured data utilizing a signal-averaging technique. This results in output signals that minimize the effect of motion on the data. In a similar fashion, “c-lock” devices synchronize the oximeter’s signal-capture period with the cardiac cycle to increase the probability that sampling takes place during pulsate flow situations.
Research into new or improved sensor technology has already spurred the development of oximeter-like devices to measure blood glucose levels. It would seem that by varying the light spectrum emission of the emitter and receiver in the oximeter probe, other important physiologic variables may be detected and measured. Just as newer models of blood gas analyzers, both point-of-care and laboratory-based, now have the capacity to provide accurate analysis of arterial blood gases and electrolytes, perhaps future pulse oximeters will have similar capabilities. Additionally, perhaps the ability to detect varying species of hemoglobin (as we do with cooximetry) could be incorporated into the pulse oximeter.
If nothing else is clear about the future of pulse oximetry, one thing is certain—change will occur. Our task as manufacturers, distributors, and clinicians using these instruments is to assure that the changes are well thought out and well tested, and, in the final analysis, provide added value to patient monitoring.
Paul Mathews, PhD, RRT, FCCM, FCCP, is associate professor at the University of Kansas Medical Center, Kansas City. He is also on RT Magazine’s editorial advisory board.
Datex-Ohmeda, Louisville, Colo, announces the newly patented features on the 3800 pulse oximeter that ensure reliability of information for clinical decision-making. The PerfTrak™ waveform display indicates both the quality and strength of the pulsatile signal in a single display. The 3800’s TruTrak™ data sampling system calculates digital SpO2 1,800 times per minute instead of once per pulse. Since the calculation rate does not vary with the patient’s pulse rate, readings are stable and reliable even in situations where there is motion or low perfusion. The 3800 features the largest LEDs of any stand-alone oximeter for exceptional display visibility. (800) 345-2700; www.datex-ohmeda.com.
Nonin Medical Inc, Plymouth, Minn, offers the 9840 Series Pulse Oximeter and CO2 Detector. The 9840 Series combines pulse oximetry technology with CO2 detection to eliminate the need for two devices. In addition to pulse rate and oxygen saturation, the 9840 Series provides an indication of approximate changes in the level of exhaled CO2 for verification of endotracheal tube placement. This handheld monitor’s functions can be used simultaneously or independently and are compatible with Nonin’s full line of pulse oximeter sensors and proprietary mainstream CO2 sensor. Designed specifically for short-term monitoring, the 9840 Series is ideal for patient transport and emergency applications. Three models of the device are available, with optional audible and visual alarms. In addition to the above products, the complete product line includes handheld and bedside monitors, with a wide array of sensor options and accessories. (800) 356-8874; www.nonin.com.
SIMS BCI Inc, Waukesha, Wis, introduces the MiniCorr Hand-Held Pulse Oximeter, which provides SpO2 and pulse rate monitoring on patients from neonates to adults. The device is battery or AC powered, and has adjustable alarm limits, as well as visible and audible alarm signals. It incorporates the patented Serial Autocorrelation (SAC) technology used in the SIMS BCI Autocorr™ Pulse Oximeter. This technology enhances the ability of the device to detect pulse readings in all environments, including high motion and poor perfusion. The MiniCorr is adaptable to home, sleep, and clinical environments, providing reliable monitoring of the most challenging patients. (800) 558-2345; www.sims-bci.com.
Mallinckrodt Inc, St Louis, introduces the Nellcor® N-395 Pulse Oximeter with Oxismart XL Advanced Signal Processing and SatSeconds™ Revolutionary Alarm Management technology, which received FDA clearance in August 1999. With the introduction of the N-395, designed for use with all patient populations in all clinical and intrahospital transport environments, Mallinckrodt continues to address the challenge of precisely finding and consistently tracking patient blood oxygen saturation and pulse rate, especially in the presence of motion. The N-395 is cleared by the FDA to produce accurate pulse rate and saturation values on adults and neonates during motion and low perfusion. In addition, the N-395 with SatSeconds can significantly reduce nuisance alarms. (800) 635-5267; www.mallinckrodt.com.
Nonin Medical Inc, Plymouth, Minn, offers the Onyx® finger pulse oximeter. The Onyx incorporates the sensor, batteries, electronics, and bright LED display in a rugged housing, and weighs only 2 oz including batteries. The Onyx is ideal for spot-checking or attended-care monitoring of adult or pediatric patients. To determine the estimated financial savings of using the Onyx, Nonin offers the “Onyx Cost Justification” at www2.nonin.com/savings.html. This interactive program provides cost analysis of pulse oximetry based on data input. In addition to the above products, the complete product line includes handheld and bedside monitors, with a wide array of sensor options and accessories. (800) 356-8874; www.nonin.com.
MSA, Pittsburgh, offers its MiniOX oxygen products, featuring the new portable MiniOX® 3000 oxygen monitor, which replaces its long-running MiniOx III monitor. The MiniOX 3000 monitor with a large display features automatic calibration, a battery-strength indicator, alarm verification ability, and a sensor/cable-disconnect alarm. MSA also has available a full range of oxygen sensors for most applications. (800) 851-4500; www.msanet.com/instruments/ps/medical/index.htm.
Medtronic Physio-Control Corp, Redmond, Wash, introduces the LIFECAP PLUS handheld capnograph and pulse oximeter. This device provides continuous measurement of end tidal carbon dioxide (EtCO2), SpO2, respiratory rate, and pulse rate. Microstream CO2 technology with Nellcor pulse oximetry provides clinicians with a versatile respiratory monitor for use on all patients from neonates to adults. (800) 442-1142; www.physiocontrol.com.
Spacelabs Burdick, Deerfield, Wis, introduces the Model 100 Pulse Oximeter, which provides simple, noninvasive blood oxygen level testing. The Model 100 offers the following features:
• accurate SpO2, pulse rate, and pulse strength measurements;
• easy-to-read LED display;
• comfortable, nonthreatening sensors;
• compact, durable, and easy to use;
• neonate to adult use; and
• battery operation and optional printer.
(800) 777-1777; www.burdick.com
Masimo, Irvine, Calif, has a new pulse oximeter, Radical, which offers the ideal pulse oximetry solution for virtually every site. Radical provides three pulse oximeters in one: a stand alone device for bedside monitoring, a detachable handheld unit for easy portable monitoring, and a monitor interface to upgrade existing multi-parameter patient monitors to Masimo SET technology. Radical not only delivers the unsurpassed accuracy and reliability of the breakthrough Masimo SET technology, but with multi-functionality, ease of use, and true sensor standardization. (877) 4-MASIMO; www.masimo.com
Criticare Systems, Milwaukee, offers the 503DX miniSpO2T Handheld Pulse Oximeter. This compact, low-cost device features the company’s DOX™ Digital Oximetry technology, which ensures high-performance readings during low perfusion, motion artifact, or ambient noise. The product is available with a 4-year replacement warranty. (800) 458-4615; www.csiusa.com.
Respironics, Pittsburgh, introduces the 920P Oximeter. This pocket-sized and powerful device delivers on-the-spot continuous readings. The attachable printer allows the user to print real time data collected with Respironics 920/920M oximeters when and where it is needed. Powered only by the oximeter batteries, the 920P is perfect for documenting spot checks. (800) 345-6443; www.respironics.com.
Epic Medical Equipment Services Inc, Plano, Tex, is introducing its patented STAT-SHELL™ disposable oximetry sensor—Epic’s first entry into the $300+ million disposable oximetry sensor market. The STAT-SHELL is designed for five uses on a single patient before disposing, making it more cost-effective for hospitals. (800) 327-3742; www.epicmedical.com.