To the Editor,

Figure
figure 1

Transesophageal echocardiography probe positioning and securement on the chest. A) Probe secured with Tegaderm over the left parasternal intercostal space; B) PSAX view at the level of the aortic valve; C) PLAX view; D) View of probe placement during EGD and PEG tube placement in an intubated patient; E) View of probe placement in prone patient; F) Skin condition after probe removal from patient in image E.

AoV = aortic valve; EGD = vesophagogastroduodenoscopy; LA = left atrium; LV = left ventricle; LVOT= left ventricular outflow track; PEG = percutaneous endoscopic gastrostomy; PLAX = parasternal long axis; PSAX = parasternal short axis; RA = right atrium; RV = right ventricle; TEE = transesophageal echocardiography

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Historically, the precordial stethoscope was the universal standard for continuous cardiorespiratory monitoring during pediatric anesthesia.1,2 Today, transesophageal echocardiography (TEE) is preferred whenever advanced hemodynamic monitoring is required for neonates, infants, or children.3 Nevertheless, up to 3% of patients may experience a complication with insertion of the TEE probe,4 and advanced training and specialty certification are generally recommended for comprehensive application of TEE monitoring. Moreover, certain anatomic and clinical conditions may preclude its utilization. By contrast, surface ultrasound (transthoracic echocardiography, or TTE) has gained attention in recent years within anesthesiology because of its lower cost, wide availability, ease of use, and safety as a non-invasive technique.5 Nevertheless, traditional TTE monitoring in the operating room is limited by the acquisition of adequate ultrasound images while access to the patient’s chest is often restricted, and the use of a relatively bulky, handheld transthoracic probe—potentially interrupting surgery.

Therefore, we utilized the concept of the low-profile precordial stethoscope for continuous non-invasive cardiovascular monitoring by replacing the stethoscope with a low-profile TEE ultrasound probe applied to the surface of the chest. Here, we report our initial pilot tests during pediatric anesthesia.

We provided care to three patients (45 weeks post-conceptual age, nine months, and four years) who required advanced intraoperative hemodynamic monitoring where we elected to interrogate cardiac function with a TEE probe secured to the chest wall during surgery. Written consent for publication was obtained from the patients’ parents.

The echocardiographic exams were performed with the S7-3t pediatric TEE probe and a Philips CX 50 ultrasound machine (Philips Ultrasound, Bothell, WA, USA). The probe was placed over the left parasternal third or fourth intercostal space and the parasternal long axis and short axis views were obtained by adjusting the transducer angle (Figure, panels A, B, and C). The probe was secured with a transparent dressing (TegadermTM I.V. Advanced 1683, 3M, St. Paul, MN, USA; Figure, panel A). The TEE probe was also successfully used during a procedure in the prone position (Figure, panel E). The shaft was padded along the contact with the skin, and the contact between the probe and the chest was checked manually for pressure every 15 min. This technique safely secured the probe while maintaining easy access for simple TEE adjustments to provide virtually continuous cardiac monitoring. Thus, certain procedures in which esophageal insertion of a TEE probe is not feasible can be managed with this approach.

We found that a TEE probe secured in a transthoracic position in children provides echocardiographic assessment of intraoperative circulatory volume, fluid responsiveness, left and right ventricular function, and basic valvular integrity. In addition, left ventricular ejection fraction can be calculated and colour-flow Doppler utilized to assess the direction and turbulence of blood flow. Lastly, the need for and the efficacy of inotropic therapy can be guided by this method.

The transthoracic use of the TEE probe requires specific considerations. Careful padding of the probe and regular inspection of any pressure points are essential. Continuous monitoring of the ultrasound may need to be interrupted to prevent thermal injury of the skin under an active TEE transducer (which may generate significant heat up to 42°C).4 None of our patients exhibited any detectable skin issues even after a five hour long procedure (Figure, panel F).

We acknowledge that TEE probes are expensive, and this application is outside its traditional application. Nevertheless, if a TEE probe is readily available, transthoracic utilization of the TEE probe may be considered for intraoperative cardiac monitoring by pediatric anesthesiologists. Indeed, one may consider this modality the precordial stethoscope of the 21st century.