Circulation 37,100 • Volume 19, No. 2 • Summer 2004   Issue PDF

Pulse-OX Tone Conveys Vital Information

Julian M. Goldman, MD; Frederick A. Robertson, MD

The value of audible clinical alarm signals is widely recognized.1 As of January 1, 2004, all Joint Commission on Accreditation of Healthcare Organizations (JCAHO) health care facilities are required to comply with a set of 7 National Patient Safety Goals.2 Goal #6 is to “improve the effectiveness of clinical alarm systems” and requires that alarms are “activated” and “are sufficiently audible.” Integral to the ongoing national analysis of the JCAHO requirements is a question regarding the applicability of goal #6 when an “operator” (clinician) is present—such as in the OR.3,4 Similarly, there is a long-standing debate among anesthesiologists about the utility of audible clinical alarm signals in the operating room.

The argument supporting the use of audible alarm signals is straightforward: Audible alarm signals can enhance vigilance by directing the clinician’s attention to out-of-bounds parameters. Undoubtedly, we have all experienced the benefits of timely and effective audible clinical alarm signals in the OR.The argument against the mandated use of audible clinical alarm signals in the OR is based on a subjective risk-benefit analysis of the alarms. Yes, alarms might be useful, the argument goes, but the cacophony of alarm signals during critical periods of anesthetic management may distract and overwhelm the clinician.5 As a result of cognitive overload, vigilance may be diminished, not enhanced.6 These perceptions of the performance of extant clinical alarm systems appear to be universally held. Thus, many anesthesiologists silence physiologic alarms.7 Unfortunately, unlike machines, we are not eternally vigilant,8,9 and the silencing of intraoperative physiologic alarm signals has resulted in clinical disasters.

To be clear, the debate about the usage of audible clinical alarms applies primarily to physiologic alarm conditions (e.g., ECG rhythm, blood pressure) and not to some of the “equipment” technical alarm conditions that are integral to medical devices. For example, the US national safety and performance standard for anesthesia workstations requires an audible alarm signal to indicate failure of the oxygen supply and the presence of sub-atmospheric breathing system pressure, among other conditions.10

The complexity of deploying effective clinical alarm systems that have adequate sensitivity and specificity for the detection of clinically significant events is becoming widely recognized.11 Various “intelligent” alarm systems have been considered for years.12-14 In fact, the newly published international alarm system standard has a section (201.2) dedicated to intelligent alarm systems.15 However, the intelligence of alarm systems is hampered by their inability to be “aware” of the context of clinical management.16 For example, absence of contextual awareness may prevent an “intelligent” alarm system from correctly displaying the alarm message generated by a hypotensive non-pulsatile arterial blood pressure tracing. For this situation, is the appropriate alarm urgency “high priority” to direct our attention to unexpected cardiac arrest; “medium priority” for a partially occluded arterial catheter; or is no alarm necessary since the changes are due to the initiation of cardiopulmonary bypass?

Despite the limitations of current clinical alarm systems, anesthesiologists have enthusiastically embraced one clinical alarm sound that isn’t strictly an alarm: it is an information signal. The audible “pulse tone,” “saturation tone,” or “beep tone” of the pulse oximeters has become indispensable for modern anesthetic practice. According to the requirements of the US national standard for pulse oximeters, the variable pitch tone (if present) must parallel the SpO2 reading.17 Thus, the pulse tone conveys pulse rate, pulse regularity, and changes in SpO2. The matching of changes in pulse tone to changes in SpO2 seems to be based on an intuitive relationship that appeals to “clinical sense.” And, by virtue of conveying this information, the pulse oximeter fulfills the definition of an alarm, which is “communicating information that requires a response or awareness by the operator.”18 The pulse oximeter’s values can be affected by a variety of physiological changes, so the high-level information conveyed by the instrument must be interpreted with other data to provide a diagnosis and guide corrective action. Nevertheless, it is precisely the real-time, high-level assessment of general cardio- pulmonary performance that underlies the instrument’s value. Consequently, as anesthesia providers, we are not the only clinicians in the OR to respond to the pulse tone. Surgeons routinely use the tone to guide interventions.

With due respect to the long-standing debate about the “limited proven clinical value” of pulse oximetry for intraoperative management, the jury of clinicians has spoken: pulse oximetry has become the de-facto standard of care for intraoperative monitoring of oxygenation, and the pulse tone is the one monitor that is always heard in almost every operating room. Isn’t it time that we mandate the use of the pulse oximeter pulse tone for the monitoring of all patients undergoing general anesthesia and incorporate this requirement in the ASA Standards for Basic Anesthetic Monitoring?19 If so, we must explore related issues, such as the necessity of standardizing the pulse oximeter’s pitch-saturation values.

Dr. Goldman is an Instructor at the Harvard Medical School (Departments of Anesthesia and Biomedical Engineering, Massachusetts General Hospital) and is an Adjoint Associate Professor of Anesthesiology at the University of Colorado School of Medicine.

Dr. Robertson is an Assistant Professor of Anesthesiology at the Medical College of Wisconsin.


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