Page 40 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 2
Diagnostic applications
A – Airway
First-attempt success rates of prehospital rapid sequence intubations vary between 46% and 85%.27 An attempt fails when the endotracheal tube (ETT) cannot be placed between the vocal cords in the trachea or is inadvertently placed in the esophagus. It is of paramount importance to acknowledge esophageal intubation as soon as possible.
The use of tracheal and cricothyroid ultrasound can be very useful to confirm correct ETT placement. This was first described in neonates by Slovis in 1986.28 Fourteen years later, Dreschler was the first to also visualize the esophagus and to detect esophageal intubation in five out of five cadaver models.29 A recent review showed a pooled sensitivity and specificity of respectively 98% and 94% of transtracheal US in emergency intubations.30 Therefore, the confirmation of correct ETT position by PoCUS in the prehospital setting is likely to be beneficial.12,31,32 Although capnography is considered the gold standard to confirm a correct tube position, it doesn’t discriminate between endotracheal or endobronchial intubation.33 Furthermore, in a prehospital setting, chest radiography is impossible, and auscultation is not always feasible. Therefore, PHUS might be a valuable tool to assess the airway.34
Zadel et al. confirmed endotracheal tube position by the detection of bilateral lung sliding and bilateral diaphragmatic excursion in 124 out-of-hospital patients.32 Esophageal intuba- tion occurred in 13 patients (10.5%) of which only 30% was detected visually or by auscultation before waveform capnography was recorded. Both sensitivity and specificity of PHUS for a correct tube position was 100%. The performance of PHUS took a median of 30 s (SD = 8–120 s). A prospective study in pediatrics preferred the assessment of bilateral diaphragmatic excursions to confirm proper ETT placement.35 Therefore, the assessment of lung sliding and diaphragmatic excursions is of value in the absence of chest radiography or capnography.
B – Chest, pulmonary
The cause of acute dyspnea is not immediately apparent, especially in the prehospital setting. Caregivers must differentiate between a cardiac or a pulmonary cause. In an emergency de- partment (ED)-study, Kajimoto proposed a quick method to integrate (1) lung ultrasound, (2) cardiac ultrasound, and (3) measurements of the inferior vena cava (LCI).36 Lung ultra- sound is performed in eight chest areas (four anterior and four lateral). Cardiac ultrasound estimates the global left ventricular function and mitral or tricuspid valve regurgitation. Subsequently, collapsibility of the inferior vena cava is determined. The LCI integrated ex-