Curious Case of the Pretracheal Stethoscope

If you could bring only 1 anesthesia monitor to provide deep sedation/general anesthesia while marooned on a desert island, which would you choose? This idea arose during a recent captivating presentation by a physician anesthesiologist on airway management updates for obese pediatric patients. As the lecture segued through various respiratory monitors used in and outside of the operating room (OR), 1 modality was noticeably absent—the pretracheal stethoscope. This prompted your editor to not only press the presenter for comment but also informally poll the audience, comprised primarily of dentist anesthesiologists, for a show of hands indicating routine pretracheal stethoscopy (PTS) use. Although substantial, audience affirmation was far from unanimous, which was particularly enlightening as I expected a more robust response.

The presenter acknowledged that although pretracheal or precordial stethoscopy was common historically, it has not been used regularly in his hospital for quite some time. He further questioned its utility in the OR for intubated cases despite agreeing that it had potential elsewhere. Of note, he also indicated a lack of familiarity with any advancements in stethoscopy technology. This anecdote is intended not to serve as an indictment of the outstanding presenter but rather to bring increased attention to the pretracheal stethoscope, an often forgotten yet profoundly useful anesthesia monitor.

Stethoscopy for assessing heart and lung sounds intraoperatively is nothing new; the earliest reports of its use date back to 1896.¹ Anesthesiologists heavily relied on stethoscopes as primary cardiac and respiratory monitors throughout the mid-to late-1900s. Prior to electronic devices capable of real-time assessments, a weighted metal stethoscope bell affixed to the precordial or pretracheal skin and connected via flexible tubing to an adjustable foam or custom-molded plastic earpiece was considered the most reliable method for cardiac and pulmonary monitoring during anesthesia. Other designs included esophageal stethoscopes that also incorporated probes for monitoring temperature. Unfortunately, sound quality was often poor due to the “analog” nature inherent with PTS devices of this style, particularly when deployed in settings with ample ambient noise (ie, a busy OR), not to mention the added drawback of being physically tethered to the patient.

Regardless of these shortcomings, “analog” PTS constituted the standard of care at the time, and virtually all anesthesia providers were trained in its use. However, the pretracheal stethoscope was essentially relegated to history's dustbin with little opposition following the arrival of pulse oximetry and capnography. As many considered it obsolete, exposure to PTS during anesthesia training waned along with its worldwide use as documented by several contemporary studies.^2,3

Despite its rapid decline in use, PTS remained as an optional ventilatory monitor within most anesthesia guidelines, particularly those covering sedation. Those same guidelines received substantial attention starting in 2011 when the American Society of Anesthesiology added capnography as a standard monitor for moderate and deep sedation. The American Dental Association and other dental organizations with sedation and/or anesthesia practice guidelines quickly followed suit.

As many were quick to note, capnography for sedation and nonintubated general anesthetics was often less than ideal, particularly for dental cases where the airway is shared. Capnography for nonintubated cases is often subject to a host of potential issues, including mouth breathing, dilution, and poor sampling, leading to occasions when it simply fails to work well. It is likely these innate flaws of capnography inadvertently contributed to the unexpected resurgence of a monitor many unceremoniously buried.

PTS has reemerged as a useful ventilatory monitor, propelled by drastic improvements in electronic microphones along with Bluetooth technology. Exponentially improved audio quality with amplified sounds delivered directly into a Bluetooth earpiece or speaker allow real-time monitoring of airway sounds without being physically tethered to a patient. Potential ventilatory issues (eg, fluid pooling in the airway, obstruction, apnea, etc) can be appreciated without delay, and airway patency assessed continuously with ease.

Although useful for secured airway cases, PTS really shines when combined with capnography during sedations and nonintubated general anesthetics, which are common to dentistry. This “belt and suspenders” approach provides built-in redundancy ensuring effective continuous ventilatory monitoring and countering factors that may preclude use of capnography alone. Pulse oximeter tones along with the audible presence of flowing oxygen and clear breath sounds provide feedback on the patient's respiratory status without needing to look at a screen. Lastly, modern pretracheal stethoscope devices require minimal disposables beyond double-sided adhesive discs and are easily disinfected, economically feasible, and environmentally friendly if rechargeable batteries are used. The benefits of PTS are numerous and abundantly clear.

It has been my experience that PTS comes with a fairly unique learning curve. New users commonly complain about the added noise and distraction. But they quickly adapt and overcome any initial reservations, typically growing so accustomed to PTS feedback that they become unsettled if it is unavailable during a case. Interestingly, new users usually are unaware of their dependence on PTS until it is highlighted.

Modernization of the pretracheal stethoscope has breathed new life into a monitoring relic most anesthesiologists left for dead. Many already incorporate PTS as part of standard anesthetic monitoring. Yet, as indicated by the previously mentioned informal poll results, numerous providers remain who have not yet seen the light. Inadequate oxygenation and ventilation continue as the leading causes of significant morbidity and mortality related to non-OR anesthesia. PTS is an effective adjunct that can help providers prevent being caught with their pants down if other ventilatory monitors fail to work effectively. To those who have never used PTS and to those who have long since passed it off as outdated and useless, I cannot encourage you enough to give it another try, even if operating exclusively within an OR. In fact, PTS might just be my preferred monitor if unexpectedly tasked with providing anesthesia while isolated on an island.