In just over 80 years, pulse oximetry has gone from theory to (probably) overutilization. But just because a test or therapy is used frequently does not necessarily mean that it is useful. This review will briefly discuss the origins of pulse oximetry and the four major benefits of pulse oximetry in the emergency department (ED).

Pulse oximetry, first theorized in the 1930s, became a clinically useful tool for monitoring patients in the mid 1970s. Due to the size and expense of the equipment, however, its use was initially limited to pulmonary clinics, the operating room, and postoperative services. It took approximately a decade before these initial limitations could be resolved to make its use widespread in the field of emergency medicine and a few years longer still before it became the “standard of care” in the ED.1 Shortly thereafter, its use in the prehospital setting was established and validated and it likewise became the standard of care for use by emergency medical services (EMS).2

Prior to the introduction of pulse oximetry, the only way to accurately measure a patient’s oxygenation status was through arterial blood gas (ABG) sampling, which, in addition to having several potential serious complications, is also a technically difficult and painful procedure.3 When additional testing confirmed the precision and accuracy of pulse oximetry, it soon became known as the “fifth vital sign.”4-6

The utility of pulse oximetry measuring for the management of patients in acute situations is now focused in four main areas: 1) improving triage classification; 2) decreasing the use of ABG sampling; 3) improving management and monitoring of acutely ill patients; and 4) decreasing the length of stay in the ED.

Improving Triage Classification

PO can result in patients being classified to a lower acute category.

The first and most important aspect of properly managing an acutely ill patient is to recognize that a medical emergency exists. While this would seem to be obvious, in the setting of a busy emergency department with multiple complex patients, often inadequate historians, and space and time limitations, it often is not obvious. The question many were asking was “Will the addition of pulse oximetry measurement at ED triage ‘catch’ more potential medical emergencies?”

Most emergency personnel thought they knew the answer, and, as it turns out, they did. The routine use of pulse oximetry measurement at ED triage does improve the acuity classification of patients.7 Summers et al found that the ultimate triage classification of patients presenting to the ED was changed 2.8% of the time. The vast majority of these patients were moved from a less acute triage category to a more acute category with a small but significant number moved to the most acute triage category based solely on the pulse oximetry measurement.

While 2.8% is certainly not a large number, given the noninvasive nature of measuring and the low cost (effectively no cost) of routine triage measurement of oxygen saturation, it possesses a very good benefit to cost ratio. It is difficult to determine the additional cost incurred to save one additional life, but it is certainly very small.

Much of the focus at triage has been on not “missing” any medical emergencies. But what about the opposite: Can routine use of pulse oximetry allow some patients to be triaged into a lower acuity category? Again, the answer seems to be that it does. While on the surface this question may not seem as important as the last, given ever increasing numbers of patients presenting to the ED as well as physical and fiscal constraints, the unjustified “up-triage” of patients does hinder overall patient care provided by the ED.

Decreasing the Use of ABG Sampling

As mentioned earlier, ABG sampling is not a risk-free procedure; and, in addition to the risks, it is labor intensive, painful, and time-consuming. The logical question to ask of pulse oximetry this time is “Can pulse oximetry decrease the number of ABG samples ordered?”

It very soon became clear that it does decrease the number of ABG samples ordered.8 Everyone who has ever had their radial artery punctured knows this is probably good news, but a question remains, “Does pulse oximetry decrease ABG samples ordered overall, or does it just decrease the number of ‘unnecessary’ samples?” After all, the goal is not to just decrease the use of a certain test, but rather to refine the use of that test. Additional studies showed that indeed the use of a pulse oximeter only decreased the number of unnecessary ABG measurements.9

Both studies demonstrated that ABG sampling decreased by over one-third with the introduction of routine pulse oximetry use. Extrapolating this data to the entire ED patient population leads to truly impressive conclusions. If the data hold, it would imply that well over 1 million ABG samples are not ordered every year because of the availability of pulse oximeters. This significantly improves the function and efficiency of the ED as a whole and of nursing and respiratory therapists specifically. Additionally, it allowed a tremendous cost savings to hospitals nationwide. It is one of the few examples of health care technology that actually decreases the overall cost of health care as opposed to increasing it.

Improving Management and Monitoring of Acutely Ill Patients

Improving triage classification and eliminating unnecessary tests are clearly beneficial to both the ED and the patients in the ED, but the real question that is asked of any new test or therapy is: “Does this test actually improve patient care?” Or more critically, does it improve outcomes?

Mower et al demonstrated that knowledge of a patient’s oxygen saturation via pulse oximetry does in fact change the further management of the patient.10 In their study, the investigators examined what additional tests or treatments were ordered on patients with oxygen saturation less than 95% once the pulse oximetry information was available. The most common additional test ordered was, not surprisingly, a repeat oxygen saturation measurement via pulse oximetry. Other tests ordered included chest radiography, complete blood counts, ABG sampling, spirometry, and ventilation-perfusion scans. The most common additional therapy ordered was, again not a surprise, supplemental oxygen. Other therapies included antibiotics and ß-agonists. This information combined to change the diagnosis of more than 6% of patients and to increase admissions by 3%.

Mallory et al examined a similar question with respect to the pediatric population, specifically in regard to the admission rate of children with bronchiolitis.11 They observed that with the advent of routine pulse oximetry use, the admission rate for children with bronchiolitis increased. The obvious question, which is unfortunately still unanswered, is: “Did these children need to be admitted?” Mallory and colleagues surmise that many of these patients did not need admission, and the increased admission rate was another example of doctors “treating the test result and not the patient.”

The preceding information raises a few interesting points. First, as discussed earlier, it had previously been shown that routine use of pulse oximetry decreased the overall number of ABG orders. This study showed that an ABG sample was ordered on 2.9% of patients who would not have otherwise received the test. Do these studies contradict each other? Not necessarily. The initial studies cited measured the overall number of ABG samples ordered, which decreased. This study measured the number of ABG samples ordered on hypoxic patients. Combining these two, it implies that ABG samples were now being done on patients who actually needed them (patients with hypoxia) as opposed to patients simply with suspected hypoxia.

We now know that pulse oximetry changes patient care, but does it improve patient care? Both studies showed an increased admission rate, but neither measured the ultimate patient outcome. So we’re left with something along the lines of: The routine use of pulse oximetry does change patient care, and it might even improve patient care.

Decreasing the Length of Stay in the ED

The overall length of stay for ED patients in the United States is increasing. Additionally, it has been shown that increased length of stay has a negative impact on patient outcome.12,13 Therefore, there is tremendous interest in any new tests or therapies that can demonstrably decrease the ED length of stay, which, according to Choi et al, routine triage pulse oximetry accomplishes.14 They specifically studied the effects of routine triage pulse oximetry use on a pediatric population with bronchiolitis. For the patients who received a triage pulse oximetry measurement, the overall time spent in the ED was reduced by nearly 17% compared to the control group who did not receive a triage pulse oximetry measurement.

While this certainly qualifies as a special population, it is likely that the results can be extrapolated to the general ED patient population. Clinically, pediatric patients with bronchiolitis present the same diagnostic and treatment dilemmas as adult patients with asthma or chronic obstructive pulmonary disease exacerbations, ie, they are in respiratory distress. These are the exact types of patients that a triage pulse oximetry measurement would be expected to benefit. Likely, if all ED patients received triage pulse oximetry measurement, the overall impact on length of stay would not be nearly as dramatic as the 17% shown by the Choi et al study (as it would be difficult to see how a pulse oximetry measurement on a patient with a sprained ankle would change or expedite care).

While the study did not have the goal of showing improved outcome, it does follow logically that shortening the length of stay could improve patient outcomes. So while proof may be lacking, the results are certainly encouraging.

Conclusions

Pulse oximetry is now routinely used in most, if not all, EDs in the United States. The combination of low cost, ease of use, and high accuracy provided the initial impetus for this implementation. Subsequently, multiple studies have examined if and how this increased use benefits ED patients.

Pulse oximetry has been shown to benefit patient care in the four categories discussed. While each study cited examined only a specific use and measured a specific outcome, taken together they demonstrate the incredible utility of routine pulse oximetry measurements. This technology has allowed better classification of patients at triage, reduced the rate of ABG sampling, improved the management of patients in the ED, and shortened ED patient length of stay. Very few medical technologies have demonstrated such diverse and profound effects on patient care. Additionally, and nearly as important, is the low cost of pulse oximetry. All things considered, it has been one of the most useful ED implementations of the last 20 years.


Jonathan S. Jones, MD, is assistant professor, and Richard L. Summers, MD, is professor, Department of Emergency Medicine, University of Mississippi Medical Center, Jackson. For further information, contact [email protected]

References

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