In this study conducted with 83 critically ill adults with a recommendation for enteral nutrition, the BUS, using a single epigastric window, was capable to confirm the EC position in 97.6% of the cases. The median time for the confirmation of the EC position by ultrasound was only two minutes. Performing this exam was not associated with any adverse events.
Studies on the use of BUS to confirm the positioning of the EC are scarce in the literature, included a low number of patients in most cases, and only a few tested protocols using a single exam window. For example, Takaaki et al., in a study with 12 pediatric patients, combining the esophageal and epigastric windows, were capable to identify the positioning of the EC in all of the patients [10]. In 114 adult patients, Zatelli and Vezzali demonstrated a sensitivity of 100% when using four windows (esophageal, esophagogastric, epigastric: antrum and gastric fundus) [5]. In a systemic review including 10 studies, Tsujimoto et al. observed a sensitivity of 91% − 98% and a specificity of 56% − 100%. It should be stressed that, despite the favorable results observed in these studies, the use of protocols with multiple ultrasound windows to verify the positioning of the EC can increase the technical demand to perform this exam, as well as prolong the time for its execution [2].
Few experiences using a single window have been published. In one recent study with 41 patients undergoing invasive mechanical ventilation, conducted by Nedel et al., the authors confirmed the EC positioning in all of the patients, using only the epigastric window [6]. Testing similar protocol, again in mechanically ventilated patients, Gok et al showed that the ultrasound was effective in 92.8% of the cases; however, there was a need to use additional patient sedation in order to perform the exam [9].
The time needed to confirm the positioning of the EC with the BUS was quite short in the present study, more exactly, 100 times shorter than the time spent between the plain radiography request and its release in the imaging system. This result regarding the BUS is possibly due to the expertise of the examiners responsible for the exams, in addition to the use of a single ultrasound window. Vigneau et al., using only the epigastric window, spent, on average, 5 min to confirm the positioning of the EC in 35 patients hospitalized in ICUs. In their study, the ultrasound was effective in 34 of the 35 procedures (sensitivity 97%), when compared to the X-ray [11]. A similar time was spent in another recent study conducted with 30 critically ill patients, which also evaluated only the epigastric window [12].
Even in studies that used two or more ultrasound windows, the time to perform the exam was shorter than the interval required for the X-ray confirmation. For example, in one study published in 2017, which evaluated the precision of BUS to verify the correct positioning of the EC, using four windows (longitudinal and cross-sectional scan of the esophagus, gastroesophageal junction, antrum, and gastric fundus) the average time required to perform the exam was 10 minutes [5]. The time recorded between the request for the X-ray and the release of the digital image for the assistant physicians’ appointment – approximately 225 minutes – in the present study may have been longer than the average observed in other institutions, due local to logistic aspects of the main institution of this study. Nevertheless, prior studies conducted in other institutions, have also observed that the X-ray can impose an excessive delay for the beginning of enteral nutrition - time spent to perform the exam varying from 162 to 180 min - and can represent an excessive use of healthcare resources[6, 11].
In two patients of the present study, it was not possible to confirm the positioning of the EC. The two patients had a BMI of above 32 and presented abdominal distension with a major interference caused by gases. Furthermore, in one of these patients, the epigastric auscultation proved to be negative. Similar difficulties were reported in previous studies [5, 12]. The distribution of BMI values observed in the present study was similar to that found by other authors [6, 12].
Critically ill patients, such as those included in this study, have a greater potential to benefit from the use of effective tools that are easy to execute and that can minimize the mobility of unstable patients. This is also valid for the context of the pandemic, considering that nearly half of the patients included in this study had confirmed COVID-19 [13, 14]. In addition to these benefits, the BUS avoids exposuring patients and the medical care team to ionizing radiation. As regards the costs, there is no true definition of the real cost of the ultrasound exam to verify the positioning of the EC. However, since many ICUs currently have ultrasound devices easily available to perform other evaluations and routine procedures, the use of theseequipments to verify the EC positioning would add only minimal costs to the healthcare system. Furthermore, the training necessary to perform the BUS is simple, especially if the protocol calls for the use of a single epigastric window, which can involve medical and nursing professionals [5].
This study has a number of limitations. First, the BUS technique commonly depends on the operator and the quality of the equipment, requiring a certain learning curve and a standardization of the technique used in order to obtain an appropriate image. However, the same protocol was used in all of the exams, which were performed by two professionals who were homogeneously trained in epigastric ultrasound exams geared toward the localization of EC. Second, this study was conducted in a single center and the sample size was relatively small, limiting the external validity of our findings.